A Simple Hückel Model-Driven Synthetic Strategy to Overcome Electronic Barriers to Retro-Brook Silylation Relevant to Aryne and Bisaryne Precursor Synthesis

Electronic Supplementary Material (ESI) for ChemComm. This journal is © The Royal Society of Chemistry 2021

Electronic Supporting Information Volume 1

Edward A. Neal,*,† A. Yannic R. Werling† and Christopher R. Jones*

School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London, E1 4NS, UK

Email: [email protected], [email protected]

S. E Electronic Supplementary Information

Table of Contents Volume 1 S1. General Experimental Information ...... S-3 S2. Molecular Modelling Data...... S-4 S3. 3,6-Dimethoxybenzyne Precursor: Synthetic Experimental Procedures ...... S-113 S4. 9,10-Phenanthryne Precursor: Synthetic Experimental Procedures...... S-114 S5. 9,10-Phenanthryne Precursor: Test Reactions ...... S-117 S6. Bisbenzyne Precursor: Preliminary Synthetic Experimental Procedures ...... S-120 S7. Bisbenzyne Precursor: Unsuccessful Adaptations of Other Methods ...... S-121 S8. Bisbenzyne Precursor: Synthetic Mechanistic Test...... S-122 S9. Bisbenzyne Precursor: Mechanistic Discussion/Analysis...... S-124 S10. Bisbenzyne Precursor: Mechanistic Retro-Brook Validation Test on 2,5-dibromo-3,6- di(trimethylsilyloxy)xylene 13v ...... S-128 S11. Bisbenzyne Precursor: Isolation Tests of Key Intermediates ...... S-129 S12. Bisbenzyne Precursor: Optimized Synthesis of Precursor and Diels-Alder Test...... S-130 Volume 2 S13. NMR Spectra: Characterisation ...... S-131 S14. NMR Spectra: Mechanistic Tests...... S-162 S15. IR Spectra...... S-165 S16. GC/MS Analyses: 9,10-Phenanthryne Series ...... S-167 S17. GC/MS Analyses: Bisbenzyne Series...... S-172 S18. GC/MS Analyses: Bisbenzyne Mechanistic Tests ...... S-175 S19. References ...... S-191

S-2 Electronic Supplementary Information

S1. General Experimental Information Materials and Purification. All reagents were purchased from commercial sources and used without further purification except for phenanthrene, which was recrystallised from ethanol. All reactions were carried out under an atmosphere of N2 using anhydrous solvents unless otherwise stated. Anhydrous Et2O was obtained by passing through an activated alumina column on an MBRAUN MB SPS-800 solvent purification system. Anhydrous THF was purchased from Acros.

Anhydrous CHCl3 was dried over CaCl2 and distilled, then stored over 4 Å molecular sieves under nitrogen. All other solvents were purchased from commercial sources and used without further purification. Petrol refers to the fraction of petroleum ether boiling in the range 40-60 °C. Flash column chromatography was performed using a Biotage Isolera One automated chromatography systems, employing Biotage ZIP or SNAP cartridges with KP-SIL silica (normal phase).

Author Contributions. EAN devised the study, wrote the paper, ran the MM2/Hückel models, performed initial phenanthryne precursor synthetic tests, phenanthryne precursor optimization, synthesis of initial compounds towards the bisbenzyne precursor, the bisbenzyne precursor aliquot experiment and validation experiments thereof. AYRW validated the results of EAN, developed the synthesis of the dimethoxybenzyne precursor 13z, optimized the synthesis of H and performed key aryne Diels-Alder experiments (S3, 20 in S5, S12). CRJ co-wrote the paper and guided the study.

Analytical. Melting Point Determination: Melting points were determined using a Sanyo Gallenkamp apparatus and are uncorrected. Nuclear Magnetic Resonance Spectroscopy: Analytical NMR spectra were recorded on Bruker Avance III 400, AvanceHD 400 or AV 600 NEO instruments, at a constant temperature of 300 K, by the NMR service at Queen Mary, University of London. 13C NMR were typically recorded as DEPTQ-135 experiments (phased spectrum including quaternary carbons). Chemical shifts (δ) are reported in parts per million (ppm) from low to high field and referenced to residual solvent (usually CDCl3). Coupling constants (J) are reported in Hertz (Hz). Standard abbreviations indicating multiplicity were used as follows: m = multiplet, quint. = quintet, q = quartet, t = triplet, d = doublet, s = singlet, br. = broad, app. = apparent. Infrared Spectroscopy: IR spectra were recorded on a Perkin Elmer Spectrum 65 FT-IR instrument fitted with an Attenuated

Total Reflectance (ATR) accessory. Wavenumbers of maximum absorbances (νmax) are reported in cm-1 with abbreviations indicating intensity as follows: s = strong, m = medium, w = weak, br. = broad. Mass Spectrometry: Low resolution MS was carried out by the Mass Spectrometry Laboratory at Queen Mary, University of London using an Agilent 6890N Network Gas Chromatography system with an Agilent 5973 Network Mass Selective Detector: the column was heated linearly from 40-300 °C over 19 min except for the phenanthrol series from 40-280 °C over 13 min. High resolution MS was carried out by the Mass Spectrometry Laboratory at Queen Mary, University of London using a Waters Synapt G2Si HDMS, or the National Mass Spectrometry Facility at Swansea University using either a Waters Xevo G2-S instrument with an Atmospheric Solids Analysis Probe and Time of Flight detector or Waters GCT Premier GC/MS with Electron Ionisation and orthogonal acceleration Time of Flight detector.

Computational. Data Reprocessing: Data sets were reprocessed using MestReNova (NMR, Mestrelab Research, S.L), SpectraGryph (IR, Dr Friedrich Menges)1 or OpenChrom (GC/MS, Lablicate GmbH)2 unless shown raw. GC/MS peaks were detected by first derivatives over an auto-detected smoothed TIC baseline and integrated with the Max Integration setting. Molecular Models: Structures were drawn in ChemDraw (PerkinElmer Informatics)3, imported into Chem3D and energy minimised using the implementation of MM2 provided therein. Hückel aromatic charges were calculated from the energy-minimised structures using the algorithm provided.

S-3 Electronic Supplementary Information

S2. Molecular Modelling Data 2-(Trimethylsiloxy)bromobenzene (2) O Si Br

+0.056 2

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -1.606 -0.496 -0.173 C Alkene -0.0689378 C(2) -1.413 -1.251 0.916 C Alkene -0.071531 C(3) -2.456 -1.891 1.465 C Alkene -0.0829333 C(4) -3.683 -1.767 0.932 C Alkene 0.0563544 C(5) -3.908 -0.999 -0.157 C Alkene 0.236971 C(6) -2.836 -0.382 -0.695 C Alkene -0.105141 O(7) -5.146 -0.855 -0.726 O Enol -0.496145 Br(8) -5.098 -2.717 1.773 Br 0.0360265 Si(9) -5.970 0.500 -0.334 Si Silane 1.38379 C(10) -7.762 0.011 -0.021 C Alkane -0.500458 C(11) -5.273 1.336 1.199 C Alkane -0.497413 C(12) -5.890 1.689 -1.791 C Alkane -0.498013 H(13) -0.755 0.029 -0.639 H 0.0203526 H(14) -0.405 -1.352 1.352 H 0.0204261 H(15) -2.280 -2.515 2.357 H 0.020468 H(16) -2.968 0.241 -1.595 H 0.024893 H(17) -8.340 0.932 0.212 H 0.0583881 H(18) -8.157 -0.478 -0.939 H 0.057357 H(19) -7.789 -0.694 0.839 H 0.0577003 H(20) -5.895 2.233 1.413 H 0.0582185 H(21) -4.222 1.641 1.002 H 0.0576443 H(22) -5.323 0.625 2.052 H 0.0579544 H(23) -6.304 1.176 -2.687 H 0.0575073 H(24) -6.497 2.587 -1.541 H 0.058454 H(25) -4.828 1.974 -1.959 H 0.0580635

S-4 Electronic Supplementary Information

MM2 Constant Value Quality Cubic stretch constant-2.000 4 Quartic stretch constant2.333 4 X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4 X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4 X-Si,P-Y Stretch-Bend force constant0.200 4 Sextic bending constant (* 10**8)7.000 4 Dielectric constant for dipoles1.500 4 Cutoff distance for charge/charge interactions35.000 4 Cutoff distance for charge/dipole interactions25.000 4 Cutoff distance for dipole/dipole interactions18.000 4 Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality 2 1.940 0.044 12.000 0.000 0 4 6 1.740 0.050 15.995 0.000 2 4 13 2.180 0.320 78.918 0.000 0 4 19 2.250 0.140 27.977 0.000 0 4 1 1.900 0.044 12.000 0.000 0 4 5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality 2-2 9.600 1.337 0.000 4 2-5 4.600 1.100 0.000 4 2-13 2.500 1.881 1.560 3 2-6 6.000 1.355 0.000 4 6-19 5.500 1.626 -0.400 3 1-19 2.970 1.880 -0.600 4 1-5 4.600 1.113 0.000 4

Angle KB XR2 XRH XH2 Quality 2-2-5 0.360 120.0 120.5 0.0 4

S-5 Electronic Supplementary Information

2-2-2 0.430 120.0 0.0 0.0 4 2-2-13 0.450 118.1 0.0 0.0 3 2-2-6 0.700 124.3 0.0 0.0 4 1-19-1 0.480 110.8 110.4 108.5 3 1-19-6 0.350 108.5 0.0 0.0 3 5-1-5 0.320 109.4 109.0 109.5 4 5-1-19 0.320 108.6 110.8 107.0 3

Atoms Force Constant Quality 2-2 0.050 4 2-5 0.050 4 2-13 0.050 3 2-6 0.050 4

Torsional V1 V2 V3 Quality 5-2-2-5 0.000 15.000 0.000 4 2-2-2-5 0.000 9.000 -1.060 4 2-2-2-2 -0.930 8.000 0.000 4 5-2-2-13 0.000 15.000 0.000 3 2-2-2-13 0.000 15.000 0.000 3 6-2-2-13 0.000 15.500 0.000 3 2-2-2-6 0.000 16.250 0.000 4 5-2-2-6 0.000 16.250 0.000 4 0-0-0-0 0.000 0.000 0.000 1 1-19-1-5 0.000 0.000 0.200 3 5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality 2 1 -11.160 11.134 4

PiBond DForce DLength Quality 2-2 4.600 0.166 4

S-6 Electronic Supplementary Information

VDW Interaction Radius Eps Quality 1-5 3.340 0.046 4

S-7 Electronic Supplementary Information

5-Bromo-6-(trimethylsiloxy)-benzo[d][1,3]dioxole (13a) O O Si O Br

-0.029 13a

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -2.247 0.106 -0.069 C Alkene 0.170877 C(2) -2.358 1.436 -0.066 C Alkene 0.168091 C(3) -1.361 2.200 0.395 C Alkene -0.221618 C(4) -0.248 1.592 0.849 C Alkene -0.0289238 C(5) -0.104 0.245 0.845 C Alkene 0.156252 C(6) -1.139 -0.492 0.385 C Alkene -0.242767 O(7) 1.023 -0.380 1.309 O Enol -0.51863 Br(8) 1.136 2.721 1.503 Br 0.00869137 Si(9) 2.104 -0.860 0.180 Si Silane 1.38345 C(10) 1.963 -2.725 -0.024 C Alkane -0.498174 C(11) 1.810 -0.021 -1.477 C Alkane -0.497874 C(12) 3.824 -0.423 0.808 C Alkane -0.500687 O(13) -3.258 -0.425 -0.521 O Furan -0.180971 C(14) -4.168 0.619 -0.873 C Alkane 0.404133 O(15) -3.442 1.797 -0.517 O Furan -0.183884 H(16) -1.477 3.296 0.394 H 0.0235452 H(17) -1.080 -1.592 0.376 H 0.0280867 H(18) 2.736 -3.055 -0.753 H 0.0584662 H(19) 2.135 -3.201 0.967 H 0.057529 H(20) 0.946 -2.966 -0.402 H 0.0580497 H(21) 2.591 -0.377 -2.184 H 0.0581561 H(22) 1.889 1.080 -1.343 H 0.0579233 H(23) 0.801 -0.300 -1.853 H 0.0575739 H(24) 3.979 -0.928 1.787 H 0.0573789 H(25) 4.569 -0.780 0.063 H 0.0584259 H(26) 3.888 0.681 0.924 H 0.0577112 H(27) -4.386 0.604 -1.966 H 0.00459166 H(28) -5.110 0.540 -0.282 H 0.0046024

S-8 Electronic Supplementary Information

Bond KS Bond Length Dipole Quality 2-2 9.600 1.337 0.000 4 2-41 10.000 1.225 0.950 3 2-5 4.600 1.100 0.000 4 2-13 2.500 1.881 1.560 3 2-6 6.000 1.355 0.000 4 6-19 5.500 1.626 -0.400 3 1-19 2.970 1.880 -0.600 4 1-5 4.600 1.113 0.000 4 1-41 5.360 1.414 0.220 3

S-9 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality 2-2-41 0.600 120.0 118.1 0.0 3 2-2-2 0.430 120.0 0.0 0.0 4 2-2-5 0.360 120.0 120.5 0.0 4 2-2-13 0.450 118.1 0.0 0.0 3 2-2-6 0.700 124.3 0.0 0.0 4 1-19-1 0.480 110.8 110.4 108.5 3 1-19-6 0.350 108.5 0.0 0.0 3 5-1-5 0.320 109.4 109.0 109.5 4 5-1-19 0.320 108.6 110.8 107.0 3 1-41-2 0.770 113.6 0.0 0.0 3 5-1-41 0.540 106.7 0.0 0.0 3

Atoms Force Constant Quality 2-2 0.050 4 2-41 0.050 3 2-5 0.050 4 2-13 0.050 3 2-6 0.050 4 1-41 0.050 3

Torsional V1 V2 V3 Quality 41-2-2-41 -2.000 15.000 0.000 3 2-2-2-41 0.000 15.000 0.000 3 2-2-2-2 -0.930 8.000 0.000 4 5-2-2-41 0.000 15.000 0.000 3 2-2-2-5 0.000 9.000 -1.060 4 1-41-2-2 0.000 9.200 0.000 3 5-2-2-13 0.000 15.000 0.000 3 2-2-2-13 0.000 15.000 0.000 3 6-2-2-13 0.000 15.500 0.000 3

S-10 Electronic Supplementary Information

2-2-2-6 0.000 16.250 0.000 4 5-2-2-6 0.000 16.250 0.000 4 0-0-0-0 0.000 0.000 0.000 1 1-19-1-5 0.000 0.000 0.200 3 5-1-19-6 0.000 0.000 0.210 3 2-41-1-5 0.000 0.000 0.350 3

PiAtom Electron Ionization Repulsion Quality 2 1 -11.160 11.134 4 41 2 -17.600 19.342 4

PiBond DForce DLength Quality 2-2 4.600 0.166 4 2-41 5.440 0.196 3

VDW Interaction Radius Eps Quality 1-5 3.340 0.046 4

S-11 Electronic Supplementary Information

2-Bromo-1-(diethoxymethyl)-3-(trimethylsiloxy)benzene (13b) O Si Br EtO OEt +0.041 13b

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) 1.814 1.617 0.302 C Alkene -0.0698419 C(2) 1.763 0.281 0.359 C Alkene -0.0796344 C(3) 0.695 -0.398 -0.097 C Alkene -0.0350648 C(4) -0.335 0.309 -0.612 C Alkene 0.0411445 C(5) -0.323 1.662 -0.668 C Alkene 0.236365 C(6) 0.778 2.290 -0.212 C Alkene -0.112888 O(7) -1.353 2.405 -1.186 O Enol -0.498035 Br(8) -1.867 -0.593 -1.303 Br 0.0339146 Si(9) -2.388 3.062 -0.105 Si Silane 1.38357 C(10) -4.130 2.875 -0.796 C Alkane -0.50095 C(11) -2.286 2.219 1.573 C Alkane -0.497565 C(12) -1.983 4.890 0.083 C Alkane -0.498176 C(13) 0.747 -1.921 0.017 C Alkane 0.397744 O(14) 1.822 -2.457 -0.746 O Ether -0.362217 O(15) 1.048 -2.290 1.361 O Ether -0.355305 C(16) 0.707 -3.619 1.675 C Alkane 0.158582 C(17) 1.530 -2.522 -2.119 C Alkane 0.160792 H(18) 2.701 2.157 0.672 H 0.0203943 H(19) 2.626 -0.259 0.784 H 0.0179168 H(20) 0.837 3.390 -0.258 H 0.0246071 H(21) -4.841 3.351 -0.085 H 0.0583884 H(22) -4.171 3.380 -1.786 H 0.0573556 H(23) -4.353 1.790 -0.901 H 0.0576514 H(24) -3.029 2.703 2.245 H 0.0582397 H(25) -1.261 2.347 1.984 H 0.0576421 H(26) -2.529 1.140 1.451 H 0.057956 H(27) -2.035 5.367 -0.921 H 0.0575522 H(28) -2.731 5.344 0.769 H 0.0585084 H(29) -0.960 4.987 0.509 H 0.0581 H(30) -0.198 -2.425 -0.267 H -0.00638665 H(31) -0.397 -3.749 1.590 H 0.0132534 H(32) 1.218 -4.319 0.975 H 0.0127659 C(33) 1.148 -3.909 3.107 C Alkane -0.140216 H(34) 0.660 -3.200 -2.283 H 0.0128276 H(35) 1.283 -1.503 -2.497 H 0.0136834 C(36) 2.751 -3.064 -2.855 C Alkane -0.140543 H(37) 0.889 -4.953 3.400 H 0.0426404 H(38) 2.249 -3.787 3.220 H 0.0406271 H(39) 0.650 -3.220 3.827 H 0.0406145 H(40) 2.559 -3.131 -3.951 H 0.0427058 H(41) 3.635 -2.402 -2.705 H 0.0406384

S-12 Electronic Supplementary Information

H(42) 3.019 -4.083 -2.492 H 0.0406387

Bond KS Bond Length Dipole Quality 2-2 9.600 1.337 0.000 4 2-5 4.600 1.100 0.000 4 1-2 4.400 1.497 0.300 4 2-13 2.500 1.881 1.560 3 2-6 6.000 1.355 0.000 4 6-19 5.500 1.626 -0.400 3 1-19 2.970 1.880 -0.600 4 1-5 4.600 1.113 0.000 4

S-13 Electronic Supplementary Information

1-6 5.360 1.402 0.440 4 1-1 4.400 1.523 0.000 4

Angle KB XR2 XRH XH2 Quality 2-2-5 0.360 120.0 120.5 0.0 4 2-2-2 0.430 120.0 0.0 0.0 4 1-2-2 0.550 121.4 122.0 120.0 4 2-2-13 0.450 118.1 0.0 0.0 3 2-2-6 0.700 124.3 0.0 0.0 4 1-19-1 0.480 110.8 110.4 108.5 3 1-19-6 0.350 108.5 0.0 0.0 3 5-1-5 0.320 109.4 109.0 109.5 4 5-1-19 0.320 108.6 110.8 107.0 3 5-1-6 0.540 106.7 106.7 106.7 4 6-1-6 0.460 99.9 97.0 102.2 4 2-1-5 0.360 109.4 109.4 110.0 4 2-1-6 0.700 109.5 0.0 0.0 4 1-6-1 0.770 106.8 0.0 0.0 4 1-1-5 0.360 109.4 109.4 110.0 4 1-1-6 0.700 107.5 107.7 107.4 4

Atoms Force Constant Quality 2-2 0.050 4 2-5 0.050 4 1-2 0.050 4 2-13 0.050 3 2-6 0.050 4

Torsional V1 V2 V3 Quality 5-2-2-5 0.000 15.000 0.000 4 2-2-2-5 0.000 9.000 -1.060 4 2-2-2-2 -0.930 8.000 0.000 4

S-14 Electronic Supplementary Information

1-2-2-5 0.000 12.500 0.000 4 1-2-2-2 -0.270 10.000 0.000 4 0-0-0-0 0.000 10.000 0.000 1 2-2-2-13 0.000 15.000 0.000 3 2-2-1-5 0.000 0.000 -0.240 4 2-2-1-6 0.000 0.000 0.000 3 6-2-2-13 0.000 15.500 0.000 3 2-2-2-6 0.000 16.250 0.000 4 5-2-2-6 0.000 16.250 0.000 4 1-19-1-5 0.000 0.000 0.200 3 5-1-19-6 0.000 0.000 0.210 3 1-6-1-5 0.000 0.000 0.530 4 1-6-1-6 -0.170 -1.200 0.000 4 1-6-1-2 0.000 0.000 0.400 3 1-1-6-1 0.400 0.520 0.467 4 5-1-1-5 0.000 0.000 0.237 4 5-1-1-6 0.000 0.000 0.180 4

PiAtom Electron Ionization Repulsion Quality 2 1 -11.160 11.134 4

PiBond DForce DLength Quality 2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality 1-5 3.340 0.046 4

Atoms DLength Quality 5-1-6 -0.002 4 1-1-6 -0.009 4

S-15 Electronic Supplementary Information

3,6-Difluoro-2-(trimethylsiloxy)bromobenzene (13c) F O Si Br F

-0.034 13c

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) 2.782 -0.426 1.116 C Alkene -0.158272 C(2) 2.522 -0.447 2.429 C Alkene -0.160977 C(3) 1.275 -0.693 2.856 C Alkene 0.27571 C(4) 0.294 -0.909 1.957 C Alkene -0.033864 C(5) 0.530 -0.877 0.625 C Alkene 0.153228 C(6) 1.800 -0.644 0.229 C Alkene 0.258481 O(7) -0.453 -1.103 -0.306 O Enol -0.503783 Br(8) -1.459 -1.268 2.614 Br 0.0239809 Si(9) -1.152 0.211 -0.982 Si Silane 1.38037 C(10) -3.020 -0.001 -0.871 C Alkane -0.501741 C(11) -0.651 1.799 -0.110 C Alkane -0.497063 C(12) -0.657 0.300 -2.796 C Alkane -0.499181 F(13) 1.043 -0.715 4.161 F -0.15381 F(14) 2.096 -0.613 -1.062 F -0.15219 H(15) 3.809 -0.228 0.764 H 0.0241801 H(16) 3.332 -0.268 3.155 H 0.0239769 H(17) -3.500 0.864 -1.380 H 0.0583771 H(18) -3.297 -0.953 -1.376 H 0.057377 H(19) -3.313 -0.029 0.202 H 0.0576805 H(20) -1.182 2.643 -0.603 H 0.0581086 H(21) 0.449 1.935 -0.204 H 0.0576202 H(22) -0.949 1.732 0.959 H 0.0578054 H(23) -0.946 -0.656 -3.287 H 0.0575645 H(24) -1.195 1.155 -3.262 H 0.0585014 H(25) 0.442 0.455 -2.861 H 0.0579188

S-16 Electronic Supplementary Information

Bond KS Bond Length Dipole Quality 2-2 9.600 1.337 0.000 4 2-5 4.600 1.100 0.000 4 2-11 5.400 1.320 1.480 3 2-13 2.500 1.881 1.560 3 2-6 6.000 1.355 0.000 4 6-19 5.500 1.626 -0.400 3 1-19 2.970 1.880 -0.600 4 1-5 4.600 1.113 0.000 4

S-17 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality 2-2-5 0.360 120.0 120.5 0.0 4 2-2-2 0.430 120.0 0.0 0.0 4 2-2-11 0.650 121.0 0.0 0.0 3 2-2-13 0.450 118.1 0.0 0.0 3 2-2-6 0.700 124.3 0.0 0.0 4 1-19-1 0.480 110.8 110.4 108.5 3 1-19-6 0.350 108.5 0.0 0.0 3 5-1-5 0.320 109.4 109.0 109.5 4 5-1-19 0.320 108.6 110.8 107.0 3

Atoms Force Constant Quality 2-2 0.050 4 2-5 0.050 4 2-11 0.050 3 2-13 0.050 3 2-6 0.050 4

Torsional V1 V2 V3 Quality 5-2-2-5 0.000 15.000 0.000 4 2-2-2-5 0.000 9.000 -1.060 4 2-2-2-2 -0.930 8.000 0.000 4 5-2-2-11 0.000 15.000 0.000 3 2-2-2-11 0.000 15.000 0.000 3 0-0-0-0 0.000 10.000 0.000 1 2-2-2-13 0.000 15.000 0.000 3 6-2-2-13 0.000 15.500 0.000 3 2-2-2-6 0.000 16.250 0.000 4 1-19-1-5 0.000 0.000 0.200 3 5-1-19-6 0.000 0.000 0.210 3

S-18 Electronic Supplementary Information

PiAtom Electron Ionization Repulsion Quality 2 1 -11.160 11.134 4

PiBond DForce DLength Quality 2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality 1-5 3.340 0.046 4

S-19 Electronic Supplementary Information

5-Bromo-6-(trimethylsiloxy)indane (13d) O Si Br

+0.037 13d

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -15.753 -0.889 -0.367 C Alkene 0.0164626 C(2) -15.702 -1.515 0.812 C Alkene 0.0145158 C(3) -16.389 -1.038 1.857 C Alkene -0.115799 C(4) -17.133 0.071 1.693 C Alkene 0.0374395 C(5) -17.214 0.716 0.506 C Alkene 0.21882 C(6) -16.492 0.215 -0.519 C Alkene -0.138223 Br(7) -18.079 0.700 3.216 Br 0.0286588 C(8) -14.901 -1.571 -1.402 C Alkane -0.0854533 C(9) -13.998 -2.450 -0.511 C Alkane -0.0449074 C(10) -14.810 -2.725 0.773 C Alkane -0.0859203 O(11) -17.965 1.847 0.326 O Enol -0.502566 Si(12) -19.429 1.637 -0.369 Si Silane 1.38433 C(13) -19.329 2.212 -2.158 C Alkane -0.498064 C(14) -19.987 -0.158 -0.316 C Alkane -0.497609 C(15) -20.666 2.706 0.565 C Alkane -0.500628 H(16) -16.323 -1.567 2.821 H 0.0201091 H(17) -16.506 0.711 -1.503 H 0.0246332 H(18) -14.320 -0.853 -2.023 H 0.0314388 H(19) -15.554 -2.196 -2.054 H 0.0420408 H(20) -13.654 -3.380 -1.018 H 0.0243017 H(21) -13.091 -1.858 -0.234 H 0.0318727 H(22) -14.165 -2.815 1.676 H 0.0313578 H(23) -15.441 -3.638 0.662 H 0.0419339 H(24) -20.341 2.119 -2.611 H 0.0584631 H(25) -18.993 3.272 -2.169 H 0.0575121 H(26) -18.602 1.566 -2.699 H 0.0580666 H(27) -20.995 -0.217 -0.784 H 0.0581939 H(28) -20.039 -0.488 0.745 H 0.0579481 H(29) -19.265 -0.782 -0.887 H 0.0576107 H(30) -20.711 2.353 1.619 H 0.0577033 H(31) -20.321 3.762 0.521 H 0.0573588 H(32) -21.660 2.598 0.077 H 0.0584002

S-20 Electronic Supplementary Information

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

1-2 4.400 1.497 0.300 4

2-5 4.600 1.100 0.000 4

2-13 2.500 1.881 1.560 3

2-6 6.000 1.355 0.000 4

1-1 4.400 1.523 0.000 4

1-5 4.600 1.113 0.000 4

6-19 5.500 1.626 -0.400 3

S-21 Electronic Supplementary Information

1-19 2.970 1.880 -0.600 4

Angle KB XR2 XRH XH2 Quality

1-2-2 0.550 121.4 122.0 120.0 4

2-2-2 0.430 120.0 0.0 0.0 4

2-2-5 0.360 120.0 120.5 0.0 4

2-2-13 0.450 118.1 0.0 0.0 3

2-2-6 0.700 124.3 0.0 0.0 4

5-1-5 0.320 109.4 109.0 109.5 4

1-1-5 0.360 109.4 109.4 110.0 4

2-1-5 0.360 109.4 109.4 110.0 4

1-1-2 0.450 109.5 109.5 109.5 4

1-1-1 0.450 109.5 109.5 109.5 4

1-19-1 0.480 110.8 110.4 108.5 3

1-19-6 0.350 108.5 0.0 0.0 3

5-1-19 0.320 108.6 110.8 107.0 3

Atoms Force Constant Quality

2-2 0.050 4

1-2 0.050 4

2-5 0.050 4

2-13 0.050 3

2-6 0.050 4

Torsional V1 V2 V3 Quality

1-2-2-1 -0.100 10.000 0.000 4

1-2-2-2 -0.270 10.000 0.000 4

2-2-2-2 -0.930 8.000 0.000 4

1-2-2-5 0.000 12.500 0.000 4

2-2-2-5 0.000 9.000 -1.060 4

S-22 Electronic Supplementary Information

2-2-1-5 0.000 0.000 -0.240 4

1-1-2-2 -0.440 0.240 0.060 4

5-2-2-13 0.000 15.000 0.000 3

2-2-2-13 0.000 15.000 0.000 3

6-2-2-13 0.000 15.500 0.000 3

2-2-2-6 0.000 16.250 0.000 4

5-2-2-6 0.000 16.250 0.000 4

0-0-0-0 0.000 0.000 0.000 1

5-1-1-5 0.000 0.000 0.237 4

2-1-1-5 0.000 0.000 0.500 4

1-1-1-5 0.000 0.000 0.267 4

1-1-1-2 0.170 0.270 0.093 4

1-19-1-5 0.000 0.000 0.200 3

5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality

2 1 -11.160 11.134 4

PiBond DForce DLength Quality

2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

S-23 Electronic Supplementary Information

2-(Trimethylsiloxy)-4,5-difluoro-bromobenzene (13e) F O Si F Br

+0.005 13e

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -1.588 -0.483 -0.173 C Alkene 0.25915 C(2) -1.392 -1.249 0.914 C Alkene 0.255319 C(3) -2.439 -1.890 1.456 C Alkene -0.174655 C(4) -3.669 -1.768 0.928 C Alkene 0.00458303 C(5) -3.895 -0.994 -0.155 C Alkene 0.186697 C(6) -2.823 -0.373 -0.686 C Alkene -0.196536 Br(7) -5.082 -2.726 1.766 Br 0.0164614 O(8) -5.133 -0.848 -0.723 O Enol -0.511545 Si(9) -5.962 0.503 -0.326 Si Silane 1.38332 C(10) -7.749 0.007 -0.004 C Alkane -0.500481 C(11) -5.257 1.337 1.205 C Alkane -0.497661 C(12) -5.891 1.694 -1.782 C Alkane -0.498031 F(13) -0.577 0.159 -0.740 F -0.150202 F(14) -0.186 -1.379 1.447 F -0.15108 H(15) -2.263 -2.520 2.344 H 0.0245132 H(16) -2.959 0.256 -1.582 H 0.02886 H(17) -8.330 0.926 0.231 H 0.0584211 H(18) -8.148 -0.483 -0.919 H 0.0573831 H(19) -7.770 -0.697 0.857 H 0.0577239 H(20) -5.881 2.231 1.426 H 0.0581921 H(21) -4.208 1.647 1.001 H 0.0575961 H(22) -5.297 0.623 2.056 H 0.0579319 H(23) -6.306 1.180 -2.677 H 0.0575239 H(24) -6.501 2.589 -1.529 H 0.0584627 H(25) -4.831 1.983 -1.953 H 0.0580547

S-24 Electronic Supplementary Information

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

11 1.650 0.078 18.998 0.000 0 4

5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

2-11 5.400 1.320 1.480 3

2-5 4.600 1.100 0.000 4

2-13 2.500 1.881 1.560 3

2-6 6.000 1.355 0.000 4

6-19 5.500 1.626 -0.400 3

1-19 2.970 1.880 -0.600 4

S-25 Electronic Supplementary Information

1-5 4.600 1.113 0.000 4

Angle KB XR2 XRH XH2 Quality

2-2-11 0.650 121.0 0.0 0.0 3

2-2-2 0.430 120.0 0.0 0.0 4

2-2-5 0.360 120.0 120.5 0.0 4

2-2-13 0.450 118.1 0.0 0.0 3

2-2-6 0.700 124.3 0.0 0.0 4

1-19-1 0.480 110.8 110.4 108.5 3

1-19-6 0.350 108.5 0.0 0.0 3

5-1-5 0.320 109.4 109.0 109.5 4

5-1-19 0.320 108.6 110.8 107.0 3

Atoms Force Constant Quality

2-2 0.050 4

2-11 0.050 3

2-5 0.050 4

2-13 0.050 3

2-6 0.050 4

Torsional V1 V2 V3 Quality

11-2-2-11 -2.300 15.500 0.000 3

2-2-2-11 0.000 15.000 0.000 3

2-2-2-2 -0.930 8.000 0.000 4

5-2-2-11 0.000 15.000 0.000 3

2-2-2-5 0.000 9.000 -1.060 4

5-2-2-13 0.000 15.000 0.000 3

2-2-2-13 0.000 15.000 0.000 3

6-2-2-13 0.000 15.500 0.000 3

2-2-2-6 0.000 16.250 0.000 4

S-26 Electronic Supplementary Information

5-2-2-6 0.000 16.250 0.000 4

0-0-0-0 0.000 0.000 0.000 1

1-19-1-5 0.000 0.000 0.200 3

5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality

2 1 -11.160 11.134 4

PiBond DForce DLength Quality

2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

S-27 Electronic Supplementary Information

2-(Trimethylsiloxy)-4,5-dimethyl-bromobenzene (13f) O Si Br

+0.039 13f

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -1.610 -0.294 -0.311 C Alkene 0.0104489 C(2) -1.357 -1.124 0.721 C Alkene 0.00778963 C(3) -2.374 -1.838 1.233 C Alkene -0.108865 C(4) -3.622 -1.733 0.748 C Alkene 0.0389078 C(5) -3.904 -0.898 -0.272 C Alkene 0.219742 C(6) -2.867 -0.205 -0.781 C Alkene -0.130868 Br(7) -4.975 -2.798 1.551 Br 0.0297202 O(8) -5.160 -0.759 -0.801 O Enol -0.501526 Si(9) -6.018 0.535 -0.291 Si Silane 1.3844 C(10) -7.780 -0.038 0.041 C Alkane -0.500526 C(11) -5.300 1.290 1.274 C Alkane -0.497537 C(12) -6.025 1.823 -1.664 C Alkane -0.498077 C(13) -0.512 0.537 -0.939 C Alkane -0.144923 C(14) 0.035 -1.272 1.294 C Alkane -0.145009 H(15) -2.169 -2.523 2.072 H 0.0186126 H(16) -3.066 0.472 -1.628 H 0.0229036 H(17) -8.382 0.844 0.353 H 0.0584091 H(18) -8.189 -0.478 -0.895 H 0.0573564 H(19) -7.756 -0.799 0.852 H 0.0577164 H(20) -5.947 2.146 1.569 H 0.0581998 H(21) -4.268 1.648 1.066 H 0.0576099 H(22) -5.296 0.521 2.077 H 0.0579402 H(23) -6.448 1.357 -2.581 H 0.057503 H(24) -6.655 2.679 -1.336 H 0.058464 H(25) -4.980 2.158 -1.843 H 0.0580542 H(26) 0.211 -0.118 -1.476 H 0.0514483 H(27) -0.898 1.274 -1.679 H 0.037797 H(28) 0.036 1.124 -0.168 H 0.0476221 H(29) 0.345 -0.333 1.807 H 0.0513633 H(30) 0.108 -2.093 2.041 H 0.0377397 H(31) 0.774 -1.507 0.495 H 0.0475862

S-28 Electronic Supplementary Information

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

1-2 4.400 1.497 0.300 4

2-5 4.600 1.100 0.000 4

2-13 2.500 1.881 1.560 3

2-6 6.000 1.355 0.000 4

6-19 5.500 1.626 -0.400 3

1-19 2.970 1.880 -0.600 4

1-5 4.600 1.113 0.000 4

S-29 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality

1-2-2 0.550 121.4 122.0 120.0 4

2-2-2 0.430 120.0 0.0 0.0 4

2-2-5 0.360 120.0 120.5 0.0 4

2-2-13 0.450 118.1 0.0 0.0 3

2-2-6 0.700 124.3 0.0 0.0 4

1-19-1 0.480 110.8 110.4 108.5 3

1-19-6 0.350 108.5 0.0 0.0 3

5-1-5 0.320 109.4 109.0 109.5 4

5-1-19 0.320 108.6 110.8 107.0 3

2-1-5 0.360 109.4 109.4 110.0 4

Atoms Force Constant Quality

2-2 0.050 4

1-2 0.050 4

2-5 0.050 4

2-13 0.050 3

2-6 0.050 4

Torsional V1 V2 V3 Quality

1-2-2-1 -0.100 10.000 0.000 4

1-2-2-2 -0.270 10.000 0.000 4

2-2-2-2 -0.930 8.000 0.000 4

1-2-2-5 0.000 12.500 0.000 4

2-2-2-5 0.000 9.000 -1.060 4

2-2-1-5 0.000 0.000 -0.240 4

5-2-2-13 0.000 15.000 0.000 3

2-2-2-13 0.000 15.000 0.000 3

6-2-2-13 0.000 15.500 0.000 3

S-30 Electronic Supplementary Information

2-2-2-6 0.000 16.250 0.000 4

5-2-2-6 0.000 16.250 0.000 4

0-0-0-0 0.000 0.000 0.000 1

1-19-1-5 0.000 0.000 0.200 3

5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality

2 1 -11.160 11.134 4

PiBond DForce DLength Quality

2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

S-31 Electronic Supplementary Information

2-(Trimethylsiloxy)-3-methoxy-bromobenzene (13g) OMe O Si Br

+0.047 13g

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -1.725 -0.511 0.531 C(1) -0.148404 C(2) -1.620 -1.519 1.408 C(2) -0.0672115 C(3) -2.656 -2.346 1.584 C(3) -0.123433 C(4) -3.784 -2.143 0.886 C(4) 0.0465268 C(5) -3.907 -1.120 0.012 C(5) 0.173738 C(6) -2.846 -0.296 -0.186 C(6) 0.175306 Br(7) -5.202 -3.371 1.196 Br(7) 0.0313928 O(8) -5.065 -0.919 -0.699 O(8) -0.501328 Si(9) -6.116 0.189 -0.116 Si(9) 1.37888 C(10) -7.799 -0.633 0.085 C(10) -0.501567 C(11) -5.562 0.885 1.541 C(11) -0.496589 C(12) -6.281 1.588 -1.367 C(12) -0.499333 O(13) -2.987 0.731 -1.091 O(13) -0.210676 C(14) -1.958 1.684 -1.225 C(14) 0.0763848 H(15) -0.841 0.136 0.421 H(15) 0.0285372 H(16) -0.687 -1.670 1.976 H(16) 0.0197263 H(17) -2.557 -3.177 2.302 H(17) 0.0199465 H(18) -8.529 0.144 0.405 H(18) 0.0584291 H(19) -8.097 -1.067 -0.895 H(19) 0.0573848 H(20) -7.722 -1.427 0.858 H(20) 0.0577657 H(21) -6.336 1.606 1.886 H(21) 0.0580843 H(22) -4.589 1.407 1.409 H(22) 0.0576785 H(23) -5.465 0.050 2.268 H(23) 0.057808 H(24) -6.589 1.151 -2.342 H(24) 0.0575463 H(25) -7.055 2.295 -0.996 H(25) 0.0584982 H(26) -5.303 2.107 -1.464 H(26) 0.0576201 H(27) -2.294 2.441 -1.969 H(27) 0.0282763 H(28) -1.785 2.204 -0.256 H(28) 0.0243443 H(29) -1.033 1.205 -1.615 H(29) 0.0246653

S-32 Electronic Supplementary Information

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

2-5 4.600 1.100 0.000 4

2-13 2.500 1.881 1.560 3

2-6 6.000 1.355 0.000 4

6-19 5.500 1.626 -0.400 3

1-19 2.970 1.880 -0.600 4

1-5 4.600 1.113 0.000 4

1-6 5.360 1.402 0.440 4

S-33 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality

2-2-5 0.360 120.0 120.5 0.0 4

2-2-2 0.430 120.0 0.0 0.0 4

2-2-13 0.450 118.1 0.0 0.0 3

2-2-6 0.700 124.3 0.0 0.0 4

1-19-1 0.480 110.8 110.4 108.5 3

1-19-6 0.350 108.5 0.0 0.0 3

5-1-5 0.320 109.4 109.0 109.5 4

5-1-19 0.320 108.6 110.8 107.0 3

1-6-2 0.770 110.8 0.0 0.0 4

5-1-6 0.540 106.7 106.7 106.7 4

Atoms Force Constant Quality

2-2 0.050 4

2-5 0.050 4

2-13 0.050 3

2-6 0.050 4

Torsional V1 V2 V3 Quality

5-2-2-5 0.000 15.000 0.000 4

2-2-2-5 0.000 9.000 -1.060 4

2-2-2-2 -0.930 8.000 0.000 4

5-2-2-6 0.000 16.250 0.000 4

2-2-2-6 0.000 16.250 0.000 4

5-2-2-13 0.000 15.000 0.000 3

2-2-2-13 0.000 15.000 0.000 3

6-2-2-13 0.000 15.500 0.000 3

6-2-2-6 -2.000 16.250 0.000 4

0-0-0-0 0.000 0.000 0.000 1

S-34 Electronic Supplementary Information

1-6-2-2 3.530 2.300 -3.530 4

1-19-1-5 0.000 0.000 0.200 3

5-1-19-6 0.000 0.000 0.210 3

2-6-1-5 0.000 0.000 0.530 4

PiAtom Electron Ionization Repulsion Quality

2 1 -11.160 11.134 4

PiBond DForce DLength Quality

2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

Atoms DLength Quality

5-1-6 -0.002 4

S-35 Electronic Supplementary Information

2-(Trimethylsiloxy)-3-methyl-bromobenzene (13h)

O Si Br

+0.054 13h

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -1.507 -0.462 0.558 C Alkene -0.0931032 C(2) -1.352 -1.624 1.205 C Alkene -0.0711736 C(3) -2.322 -2.543 1.128 C Alkene -0.0977022 C(4) -3.434 -2.284 0.422 C Alkene 0.0539298 C(5) -3.624 -1.106 -0.217 C Alkene 0.209308 C(6) -2.619 -0.199 -0.151 C Alkene 0.000772175 Br(7) -4.733 -3.671 0.368 Br 0.0356562 O(8) -4.764 -0.847 -0.937 O Enol -0.495922 Si(9) -5.982 -0.077 -0.164 Si Silane 1.38074 C(10) -7.541 -1.130 -0.276 C Alkane -0.501667 C(11) -5.581 0.254 1.642 C Alkane -0.496484 C(12) -6.324 1.553 -1.046 C Alkane -0.501808 C(13) -2.697 1.129 -0.877 C Alkane -0.140752 H(14) -0.696 0.283 0.614 H 0.018186 H(15) -0.434 -1.826 1.782 H 0.0204064 H(16) -2.179 -3.504 1.652 H 0.0199621 H(17) -7.734 -1.359 -1.348 H 0.0574065 H(18) -7.392 -2.065 0.304 H 0.0577948 H(19) -8.384 -0.545 0.153 H 0.0585112 H(20) -6.455 0.770 2.098 H 0.0581644 H(21) -4.681 0.904 1.703 H 0.0578962 H(22) -5.400 -0.716 2.156 H 0.0578787 H(23) -6.528 1.335 -2.118 H 0.0575359 H(24) -7.213 2.023 -0.570 H 0.0584668 H(25) -5.441 2.219 -0.943 H 0.0581661 H(26) -3.256 1.061 -1.835 H 0.042213 H(27) -3.181 1.890 -0.224 H 0.0546491 H(28) -1.688 1.514 -1.147 H 0.0409667

S-36 Electronic Supplementary Information

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

2-5 4.600 1.100 0.000 4

2-13 2.500 1.881 1.560 3

2-6 6.000 1.355 0.000 4

1-2 4.400 1.497 0.300 4

6-19 5.500 1.626 -0.400 3

1-19 2.970 1.880 -0.600 4

1-5 4.600 1.113 0.000 4

S-37 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality

2-2-5 0.360 120.0 120.5 0.0 4

2-2-2 0.430 120.0 0.0 0.0 4

2-2-13 0.450 118.1 0.0 0.0 3

2-2-6 0.700 124.3 0.0 0.0 4

1-2-2 0.550 121.4 122.0 120.0 4

1-19-1 0.480 110.8 110.4 108.5 3

1-19-6 0.350 108.5 0.0 0.0 3

5-1-5 0.320 109.4 109.0 109.5 4

5-1-19 0.320 108.6 110.8 107.0 3

2-1-5 0.360 109.4 109.4 110.0 4

Atoms Force Constant Quality

2-2 0.050 4

2-5 0.050 4

2-13 0.050 3

2-6 0.050 4

1-2 0.050 4

Torsional V1 V2 V3 Quality

5-2-2-5 0.000 15.000 0.000 4

2-2-2-5 0.000 9.000 -1.060 4

2-2-2-2 -0.930 8.000 0.000 4

1-2-2-5 0.000 12.500 0.000 4

1-2-2-2 -0.270 10.000 0.000 4

5-2-2-13 0.000 15.000 0.000 3

2-2-2-13 0.000 15.000 0.000 3

6-2-2-13 0.000 15.500 0.000 3

2-2-2-6 0.000 16.250 0.000 4

S-38 Electronic Supplementary Information

1-2-2-6 -1.200 16.250 0.000 4

0-0-0-0 0.000 0.000 0.000 1

2-2-1-5 0.000 0.000 -0.240 4

1-19-1-5 0.000 0.000 0.200 3

5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality

2 1 -11.160 11.134 4

PiBond DForce DLength Quality

2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

S-39 Electronic Supplementary Information

2-(Trimethylsiloxy)-3-nitro-bromobenzene (13i)

NO2 O Si Br

+0.057 13i

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -1.612 -0.549 0.535 C Alkene -0.0202827 C(2) -1.617 -1.672 1.261 C Alkene -0.0676525 C(3) -2.711 -2.438 1.243 C Alkene -0.0392004 C(4) -3.778 -2.059 0.521 C Alkene 0.0566907 C(5) -3.813 -0.914 -0.200 C Alkene 0.285179 C(6) -2.677 -0.163 -0.198 C Alkene 0.0304244 Br(7) -5.224 -3.295 0.613 Br 0.0337317 O(8) -4.963 -0.612 -0.898 O Enol -0.437957 Si(9) -6.011 0.504 -0.320 Si Silane 1.37035 C(10) -7.508 -0.415 0.380 C Alkane -0.511559 C(11) -5.298 1.538 1.080 C Alkane -0.496167 C(12) -6.657 1.598 -1.710 C Alkane -0.499312 N(13) -2.552 0.902 -0.857 N Nitro 1.27691 O(14) -1.474 1.654 -0.861 O Nitro -0.801017 O(15) -3.494 1.375 -1.624 O Nitro -0.755351 H(16) -0.675 0.034 0.572 H 0.0174316 H(17) -0.733 -1.971 1.849 H 0.0198601 H(18) -2.698 -3.372 1.831 H 0.0186383 H(19) -8.279 0.338 0.653 H 0.0576035 H(20) -7.898 -1.104 -0.402 H 0.0564844 H(21) -7.192 -0.978 1.285 H 0.0573074 H(22) -6.115 2.179 1.480 H 0.0583046 H(23) -4.475 2.178 0.696 H 0.0577553 H(24) -4.927 0.854 1.875 H 0.0581153 H(25) -7.077 0.941 -2.504 H 0.057911 H(26) -7.452 2.254 -1.292 H 0.0585773 H(27) -5.830 2.218 -2.117 H 0.0572237

S-40 Electronic Supplementary Information

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for charges1.500 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

46 1.820 0.055 14.003 0.000 0 3

47 1.740 0.066 15.995 0.000 0 3

5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

2-5 4.600 1.100 0.000 4

2-13 2.500 1.881 1.560 3

2-6 6.000 1.355 0.000 4

2-46 11.090 1.248 1.500 1

S-41 Electronic Supplementary Information

6-19 5.500 1.626 -0.400 3

1-19 2.970 1.880 -0.600 4

1-5 4.600 1.113 0.000 4

46-47 6.000 1.310 2.000 1

Angle KB XR2 XRH XH2 Quality

2-2-5 0.360 120.0 120.5 0.0 4

2-2-2 0.430 120.0 0.0 0.0 4

2-2-13 0.450 118.1 0.0 0.0 3

2-2-6 0.700 124.3 0.0 0.0 4

2-2-46 0.430 120.0 0.0 0.0 1

1-19-1 0.480 110.8 110.4 108.5 3

1-19-6 0.350 108.5 0.0 0.0 3

5-1-5 0.320 109.4 109.0 109.5 4

5-1-19 0.320 108.6 110.8 107.0 3

47-46-47 0.400 120.0 0.0 0.0 1

2-46-47 0.400 120.0 0.0 0.0 1

Atoms Force Constant Quality

2-2 0.050 4

2-5 0.050 4

2-13 0.050 3

2-6 0.050 4

2-46 0.050 1

46-47 0.100 1

Torsional V1 V2 V3 Quality

5-2-2-5 0.000 15.000 0.000 4

2-2-2-5 0.000 9.000 -1.060 4

2-2-2-2 -0.930 8.000 0.000 4

S-42 Electronic Supplementary Information

5-2-2-46 0.000 15.000 0.000 2

2-2-2-46 0.000 15.000 0.000 2

5-2-2-13 0.000 15.000 0.000 3

2-2-2-13 0.000 15.000 0.000 3

6-2-2-13 0.000 15.500 0.000 3

2-2-2-6 0.000 16.250 0.000 4

0-0-0-0 0.000 10.000 0.000 1

2-2-46-47 0.000 10.000 0.000 1

1-19-1-5 0.000 0.000 0.200 3

5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality

2 1 -11.160 11.134 4

46 1 -13.145 17.210 1

47 1 -17.210 14.520 1

PiBond DForce DLength Quality

2-2 4.600 0.166 4

2-46 10.880 0.196 1

46-47 4.600 0.105 1

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

S-43 Electronic Supplementary Information

2-(Trimethylsiloxy)-3-chloro-bromobenzene (13j) Cl O Si Br

+0.053 13j

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -1.509 -0.483 0.125 C Alkene -0.140138 C(2) -1.466 -1.353 1.142 C Alkene -0.0657515 C(3) -2.578 -2.021 1.475 C Alkene -0.13604 C(4) -3.722 -1.806 0.804 C Alkene 0.0526227 C(5) -3.805 -0.914 -0.210 C Alkene 0.163131 C(6) -2.658 -0.277 -0.540 C Alkene 0.1063 Br(7) -5.222 -2.834 1.360 Br 0.0337682 O(8) -4.976 -0.697 -0.896 O Enol -0.500551 Si(9) -5.948 0.511 -0.376 Si Silane 1.37638 C(10) -7.650 -0.196 0.017 C Alkane -0.502898 C(11) -5.256 1.362 1.151 C Alkane -0.496796 C(12) -6.158 1.774 -1.760 C Alkane -0.502902 Cl(13) -2.607 0.853 -1.851 Cl 0.0322615 H(14) -0.584 0.051 -0.154 H 0.0192876 H(15) -0.524 -1.527 1.688 H 0.0200223 H(16) -2.522 -2.746 2.305 H 0.0199792 H(17) -8.328 0.652 0.261 H 0.0584632 H(18) -8.019 -0.742 -0.879 H 0.0574455 H(19) -7.569 -0.880 0.888 H 0.0577967 H(20) -5.968 2.162 1.450 H 0.0581013 H(21) -4.267 1.806 0.902 H 0.0577599 H(22) -5.157 0.614 1.968 H 0.0577708 H(23) -6.517 1.242 -2.669 H 0.0574879 H(24) -6.908 2.526 -1.430 H 0.05848 H(25) -5.183 2.269 -1.955 H 0.0580169

S-44 Electronic Supplementary Information

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

12 2.030 0.240 34.969 0.000 0 4

5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

2-5 4.600 1.100 0.000 4

2-13 2.500 1.881 1.560 3

2-6 6.000 1.355 0.000 4

2-12 3.400 1.719 1.580 3

6-19 5.500 1.626 -0.400 3

1-19 2.970 1.880 -0.600 4

S-45 Electronic Supplementary Information

1-5 4.600 1.113 0.000 4

Angle KB XR2 XRH XH2 Quality

2-2-5 0.360 120.0 120.5 0.0 4

2-2-2 0.430 120.0 0.0 0.0 4

2-2-13 0.450 118.1 0.0 0.0 3

2-2-6 0.700 124.3 0.0 0.0 4

2-2-12 0.550 118.8 0.0 0.0 3

1-19-1 0.480 110.8 110.4 108.5 3

1-19-6 0.350 108.5 0.0 0.0 3

5-1-5 0.320 109.4 109.0 109.5 4

5-1-19 0.320 108.6 110.8 107.0 3

Atoms Force Constant Quality

2-2 0.050 4

2-5 0.050 4

2-13 0.050 3

2-6 0.050 4

2-12 0.050 3

Torsional V1 V2 V3 Quality

5-2-2-5 0.000 15.000 0.000 4

2-2-2-5 0.000 9.000 -1.060 4

2-2-2-2 -0.930 8.000 0.000 4

5-2-2-12 0.000 15.000 0.000 3

2-2-2-12 0.000 15.000 0.000 3

5-2-2-13 0.000 15.000 0.000 3

2-2-2-13 0.000 15.000 0.000 3

6-2-2-13 0.000 15.500 0.000 3

2-2-2-6 0.000 16.250 0.000 4

S-46 Electronic Supplementary Information

6-2-2-12 -0.500 15.500 0.000 3

0-0-0-0 0.000 0.000 0.000 1

1-19-1-5 0.000 0.000 0.200 3

5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality

2 1 -11.160 11.134 4

PiBond DForce DLength Quality

2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

S-47 Electronic Supplementary Information

2-(Trimethylsiloxy)-3-bromo-allylbenzene (13k)

O Si Br

+0.055 13k

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -1.649 -1.032 0.443 C Alkene -0.0976055 C(2) -1.635 -2.046 1.316 C Alkene -0.0703495 C(3) -2.748 -2.769 1.482 C Alkene -0.101211 C(4) -3.856 -2.455 0.791 C Alkene 0.0545005 C(5) -3.904 -1.411 -0.070 C Alkene 0.203661 C(6) -2.756 -0.710 -0.251 C Alkene 0.00867552 Br(7) -5.357 -3.583 1.093 Br 0.0368525 O(8) -5.044 -1.107 -0.770 O Enol -0.494492 Si(9) -6.095 -0.048 -0.099 Si Silane 1.37833 C(10) -7.759 -0.888 0.187 C Alkane -0.501867 C(11) -5.465 0.647 1.529 C Alkane -0.496735 C(12) -6.394 1.352 -1.324 C Alkane -0.505712 C(13) -2.635 0.438 -1.239 C Alkane -0.0669988 C(14) -2.515 1.773 -0.546 C Alkene 0.0647873 C(15) -2.926 2.930 -1.082 C Alkene -0.191786 H(16) -0.717 -0.460 0.294 H 0.0185049 H(17) -0.716 -2.295 1.873 H 0.0203616 H(18) -2.722 -3.618 2.186 H 0.0197978 H(19) -8.493 -0.105 0.478 H 0.0585441 H(20) -8.073 -1.380 -0.760 H 0.0573416 H(21) -7.661 -1.633 1.005 H 0.0578335 H(22) -6.230 1.354 1.918 H 0.0582577 H(23) -4.508 1.182 1.351 H 0.058833 H(24) -5.319 -0.191 2.246 H 0.0580206 H(25) -6.758 0.912 -2.279 H 0.0574306 H(26) -7.159 2.035 -0.893 H 0.0582385 H(27) -5.443 1.899 -1.486 H 0.0599713 H(28) -1.702 0.287 -1.833 H 0.061073 H(29) -3.453 0.452 -1.991 H 0.0350544 H(30) -2.009 1.801 0.434 H 0.0276457 H(31) -2.790 3.884 -0.549 H 0.0362555 H(32) -3.401 2.966 -2.074 H 0.0367847

S-48 Electronic Supplementary Information

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

2-5 4.600 1.100 0.000 4

2-13 2.500 1.881 1.560 3

2-6 6.000 1.355 0.000 4

1-2 4.400 1.497 0.300 4

6-19 5.500 1.626 -0.400 3

1-19 2.970 1.880 -0.600 4

1-5 4.600 1.113 0.000 4

S-49 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality

2-2-5 0.360 120.0 120.5 0.0 4

2-2-2 0.430 120.0 0.0 0.0 4

2-2-13 0.450 118.1 0.0 0.0 3

2-2-6 0.700 124.3 0.0 0.0 4

1-2-2 0.550 121.4 122.0 120.0 4

1-19-1 0.480 110.8 110.4 108.5 3

1-19-6 0.350 108.5 0.0 0.0 3

5-1-5 0.320 109.4 109.0 109.5 4

5-1-19 0.320 108.6 110.8 107.0 3

2-1-5 0.360 109.4 109.4 110.0 4

2-1-2 0.450 109.5 109.5 109.5 4

1-2-5 0.360 118.2 0.0 0.0 4

5-2-5 0.320 119.0 0.0 0.0 4

Atoms Force Constant Quality

2-2 0.050 4

2-5 0.050 4

2-13 0.050 3

2-6 0.050 4

1-2 0.050 4

Torsional V1 V2 V3 Quality

5-2-2-5 0.000 15.000 0.000 4

2-2-2-5 0.000 9.000 -1.060 4

2-2-2-2 -0.930 8.000 0.000 4

1-2-2-5 0.000 12.500 0.000 4

1-2-2-2 -0.270 10.000 0.000 4

5-2-2-13 0.000 15.000 0.000 3

S-50 Electronic Supplementary Information

2-2-2-13 0.000 15.000 0.000 3

6-2-2-13 0.000 15.500 0.000 3

2-2-2-6 0.000 16.250 0.000 4

1-2-2-6 -1.200 16.250 0.000 4

0-0-0-0 0.000 0.000 0.000 1

2-2-1-5 0.000 0.000 -0.240 4

2-1-2-2 0.100 0.000 0.500 4

1-19-1-5 0.000 0.000 0.200 3

5-1-19-6 0.000 0.000 0.210 3

5-1-2-5 0.000 0.000 0.520 4

2-1-2-5 0.000 0.000 0.600 4

PiAtom Electron Ionization Repulsion Quality

2 1 -11.160 11.134 4

PiBond DForce DLength Quality

2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

S-51 Electronic Supplementary Information

2-(Trimethylsiloxy)-3-bromo-(1,1-dimethylpropyl)benzene (13l)

O Si Br

+0.051 13l

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -2.045 -1.244 -0.299 C Alkene -0.0987373 C(2) -1.862 -2.488 0.154 C Alkene -0.0734196 C(3) -2.739 -2.981 1.031 C Alkene -0.0958068 C(4) -3.802 -2.237 1.371 C Alkene 0.0511939 C(5) -4.039 -1.001 0.863 C Alkene 0.20499 C(6) -3.078 -0.452 0.064 C Alkene -0.0181205 Br(7) -4.947 -3.079 2.639 Br 0.0389128 O(8) -5.183 -0.331 1.226 O Enol -0.48976 Si(9) -6.566 -0.673 0.414 Si Silane 1.37737 C(10) -7.905 -1.215 1.630 C Alkane -0.504634 C(11) -7.274 0.861 -0.429 C Alkane -0.500618 C(12) -6.319 -2.010 -0.886 C Alkane -0.497041 C(13) -3.063 1.006 -0.492 C Alkane 0.0688912 C(14) -1.602 1.569 -0.511 C Alkane -0.0585719 C(15) -3.889 2.028 0.321 C Alkane -0.156005 C(16) -1.389 3.071 -0.773 C Alkane -0.131948 C(17) -3.596 0.955 -1.939 C Alkane -0.12556 H(18) -1.271 -0.902 -1.000 H 0.0244805 H(19) -0.991 -3.086 -0.162 H 0.0195083 H(20) -2.566 -3.992 1.438 H 0.0190301 H(21) -8.870 -1.258 1.078 H 0.0583012 H(22) -7.670 -2.219 2.038 H 0.057465 H(23) -7.962 -0.461 2.446 H 0.0574594 H(24) -6.605 1.193 -1.250 H 0.0580373 H(25) -7.398 1.660 0.335 H 0.0574958 H(26) -8.265 0.587 -0.853 H 0.0584732 H(27) -6.026 -2.960 -0.389 H 0.0577186 H(28) -7.285 -2.147 -1.422 H 0.0581657 H(29) -5.531 -1.685 -1.600 H 0.0584067 H(30) -1.002 1.071 -1.308 H 0.0334524 H(31) -1.120 1.337 0.470 H 0.0295266 H(32) -4.981 1.885 0.249 H 0.0467411 H(33) -3.793 3.064 -0.067 H 0.0434865 H(34) -3.589 2.033 1.393 H 0.0363096 H(35) -1.700 3.704 0.088 H 0.0399125 H(36) -0.307 3.293 -0.929 H 0.0404506 H(37) -1.923 3.415 -1.687 H 0.0400859 H(38) -2.952 0.330 -2.597 H 0.0364528 H(39) -4.615 0.517 -1.980 H 0.0403061

S-52 Electronic Supplementary Information

H(40) -3.655 1.968 -2.396 H 0.0376031

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

2-5 4.600 1.100 0.000 4

2-13 2.500 1.881 1.560 3

2-6 6.000 1.355 0.000 4

1-2 4.400 1.497 0.300 4

6-19 5.500 1.626 -0.400 3

1-19 2.970 1.880 -0.600 4

S-53 Electronic Supplementary Information

1-5 4.600 1.113 0.000 4

1-1 4.400 1.523 0.000 4

Angle KB XR2 XRH XH2 Quality

2-2-5 0.360 120.0 120.5 0.0 4

2-2-2 0.430 120.0 0.0 0.0 4

2-2-13 0.450 118.1 0.0 0.0 3

2-2-6 0.700 124.3 0.0 0.0 4

1-2-2 0.550 121.4 122.0 120.0 4

1-19-1 0.480 110.8 110.4 108.5 3

1-19-6 0.350 108.5 0.0 0.0 3

5-1-5 0.320 109.4 109.0 109.5 4

5-1-19 0.320 108.6 110.8 107.0 3

1-1-1 0.450 109.5 109.5 109.5 4

1-1-2 0.450 109.5 109.5 109.5 4

1-1-5 0.360 109.4 109.4 110.0 4

Atoms Force Constant Quality

2-2 0.050 4

2-5 0.050 4

2-13 0.050 3

2-6 0.050 4

1-2 0.050 4

Torsional V1 V2 V3 Quality

5-2-2-5 0.000 15.000 0.000 4

2-2-2-5 0.000 9.000 -1.060 4

2-2-2-2 -0.930 8.000 0.000 4

1-2-2-5 0.000 12.500 0.000 4

1-2-2-2 -0.270 10.000 0.000 4

S-54 Electronic Supplementary Information

5-2-2-13 0.000 15.000 0.000 3

2-2-2-13 0.000 15.000 0.000 3

6-2-2-13 0.000 15.500 0.000 3

2-2-2-6 0.000 16.250 0.000 4

1-2-2-6 -1.200 16.250 0.000 4

0-0-0-0 0.000 0.000 0.000 1

1-1-2-2 -0.440 0.240 0.060 4

1-19-1-5 0.000 0.000 0.200 3

5-1-19-6 0.000 0.000 0.210 3

1-1-1-5 0.000 0.000 0.267 4

1-1-1-1 0.200 0.270 0.093 4

2-1-1-5 0.000 0.000 0.500 4

1-1-1-2 0.170 0.270 0.093 4

5-1-1-5 0.000 0.000 0.237 4

PiAtom Electron Ionization Repulsion Quality

2 1 -11.160 11.134 4

PiBond DForce DLength Quality

2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

S-55 Electronic Supplementary Information

2-(Trimethylsiloxy)-1-bromobiphenyl (13m) Ph O Si Br

+0.049 13m

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -2.316 -1.100 0.025 C Alkene -0.0821417 C(2) -1.276 -0.313 -0.281 C Alkene -0.072879 C(3) -1.495 0.827 -0.941 C Alkene -0.0910557 C(4) -2.755 1.169 -1.246 C Alkene 0.0488881 C(5) -3.821 0.400 -0.915 C Alkene 0.225407 C(6) -3.592 -0.794 -0.299 C Alkene -0.00865232 Br(7) -2.946 2.825 -2.171 Br 0.0341744 O(8) -5.087 0.858 -1.192 O Enol -0.493606 Si(9) -5.831 1.698 0.000 Si Silane 1.38598 C(10) -7.192 0.638 0.759 C Alkane -0.501065 C(11) -4.645 2.217 1.364 C Alkane -0.497964 C(12) -6.624 3.225 -0.768 C Alkane -0.501642 C(13) -4.561 -1.702 -0.006 C Alkene 0.0735513 C(14) -4.464 -2.541 1.050 C Alkene -0.0491812 C(15) -5.410 -3.445 1.353 C Alkene -0.02871 C(16) -6.503 -3.561 0.588 C Alkene -0.0464684 C(17) -6.622 -2.766 -0.483 C Alkene -0.0294064 C(18) -5.667 -1.866 -0.766 C Alkene -0.0462472 H(19) -2.035 -2.053 0.501 H 0.0197503 H(20) -0.246 -0.615 -0.027 H 0.0198561 H(21) -0.633 1.460 -1.211 H 0.01947 H(22) -7.767 1.272 1.470 H 0.0583815 H(23) -7.854 0.272 -0.057 H 0.0573603 H(24) -6.725 -0.211 1.303 H 0.0585754 H(25) -5.230 2.769 2.132 H 0.0582139 H(26) -3.861 2.879 0.937 H 0.0577526 H(27) -4.190 1.307 1.814 H 0.0577531 H(28) -7.319 2.892 -1.570 H 0.0574704 H(29) -7.180 3.765 0.030 H 0.0584071 H(30) -5.825 3.873 -1.187 H 0.0576219 H(31) -3.624 -2.493 1.761 H 0.0200952 H(32) -5.298 -4.090 2.241 H 0.0202323 H(33) -7.282 -4.303 0.827 H 0.0202834 H(34) -7.499 -2.871 -1.143 H 0.0201592 H(35) -5.819 -1.314 -1.706 H 0.0196317

S-56 Electronic Supplementary Information

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

2-5 4.600 1.100 0.000 4

2-13 2.500 1.881 1.560 3

2-6 6.000 1.355 0.000 4

6-19 5.500 1.626 -0.400 3

1-19 2.970 1.880 -0.600 4

1-5 4.600 1.113 0.000 4

S-57 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality

2-2-5 0.360 120.0 120.5 0.0 4

2-2-2 0.430 120.0 0.0 0.0 4

2-2-13 0.450 118.1 0.0 0.0 3

2-2-6 0.700 124.3 0.0 0.0 4

1-19-1 0.480 110.8 110.4 108.5 3

1-19-6 0.350 108.5 0.0 0.0 3

5-1-5 0.320 109.4 109.0 109.5 4

5-1-19 0.320 108.6 110.8 107.0 3

Atoms Force Constant Quality

2-2 0.050 4

2-5 0.050 4

2-13 0.050 3

2-6 0.050 4

Torsional V1 V2 V3 Quality

5-2-2-5 0.000 15.000 0.000 4

2-2-2-5 0.000 9.000 -1.060 4

2-2-2-2 -0.930 8.000 0.000 4

5-2-2-13 0.000 15.000 0.000 3

2-2-2-13 0.000 15.000 0.000 3

6-2-2-13 0.000 15.500 0.000 3

2-2-2-6 0.000 16.250 0.000 4

0-0-0-0 0.000 0.000 0.000 1

1-19-1-5 0.000 0.000 0.200 3

5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality

2 1 -11.160 11.134 4

S-58 Electronic Supplementary Information

PiBond DForce DLength Quality

2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

S-59 Electronic Supplementary Information

2-(Trimethylsiloxy)-3,6-dimethoxy-bromobenzene (13n) O O Si Br O

-0.011 13n

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -1.768 -0.089 0.049 C Alkene -0.144103 C(2) -1.665 -1.154 0.852 C Alkene -0.132471 C(3) -2.693 -1.998 1.040 C Alkene 0.180002 C(4) -3.861 -1.649 0.460 C Alkene -0.0110508 C(5) -3.996 -0.566 -0.342 C Alkene 0.174624 C(6) -2.915 0.216 -0.584 C Alkene 0.143734 Br(7) -5.373 -2.773 0.772 Br 0.0254146 O(8) -5.193 -0.254 -0.942 O Enol -0.502332 Si(9) -6.122 0.881 -0.219 Si Silane 1.37811 C(10) -7.831 0.152 0.094 C Alkane -0.501818 C(11) -5.386 1.464 1.410 C Alkane -0.496589 C(12) -6.311 2.346 -1.389 C Alkane -0.499769 O(13) -3.066 1.307 -1.410 O Enol -0.221786 O(14) -2.555 -3.058 1.904 O Enol -0.281844 C(15) -1.972 -4.200 1.319 C Alkane 0.089709 C(16) -2.031 2.256 -1.499 C Alkane 0.0766014 H(17) -0.866 0.533 -0.066 H 0.0280895 H(18) -0.707 -1.350 1.363 H 0.0237832 H(19) -8.483 0.958 0.498 H 0.0584578 H(20) -8.234 -0.227 -0.871 H 0.0573897 H(21) -7.741 -0.674 0.833 H 0.0577711 H(22) -6.086 2.205 1.856 H 0.0580888 H(23) -4.401 1.941 1.215 H 0.0576753 H(24) -5.273 0.588 2.087 H 0.0578232 H(25) -6.728 1.974 -2.351 H 0.0575479 H(26) -7.007 3.075 -0.920 H 0.0584866 H(27) -5.316 2.815 -1.550 H 0.0575588 H(28) -1.936 -5.003 2.089 H 0.0283237 H(29) -2.587 -4.547 0.459 H 0.0228061 H(30) -0.936 -3.972 0.983 H 0.0228582 H(31) -2.383 3.078 -2.162 H 0.0282905 H(32) -1.816 2.688 -0.496 H 0.0240918 H(33) -1.126 1.804 -1.962 H 0.02453

S-60 Electronic Supplementary Information

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

2-5 4.600 1.100 0.000 4

2-6 6.000 1.355 0.000 4

2-13 2.500 1.881 1.560 3

6-19 5.500 1.626 -0.400 3

1-19 2.970 1.880 -0.600 4

1-5 4.600 1.113 0.000 4

1-6 5.360 1.402 0.440 4

S-61 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality

2-2-5 0.360 120.0 120.5 0.0 4

2-2-2 0.430 120.0 0.0 0.0 4

2-2-6 0.700 124.3 0.0 0.0 4

2-2-13 0.450 118.1 0.0 0.0 3

1-19-1 0.480 110.8 110.4 108.5 3

1-19-6 0.350 108.5 0.0 0.0 3

5-1-5 0.320 109.4 109.0 109.5 4

5-1-19 0.320 108.6 110.8 107.0 3

1-6-2 0.770 110.8 0.0 0.0 4

5-1-6 0.540 106.7 106.7 106.7 4

Atoms Force Constant Quality

2-2 0.050 4

2-5 0.050 4

2-6 0.050 4

2-13 0.050 3

Torsional V1 V2 V3 Quality

5-2-2-5 0.000 15.000 0.000 4

2-2-2-5 0.000 9.000 -1.060 4

2-2-2-2 -0.930 8.000 0.000 4

5-2-2-6 0.000 16.250 0.000 4

2-2-2-6 0.000 16.250 0.000 4

6-2-2-13 0.000 15.500 0.000 3

2-2-2-13 0.000 15.000 0.000 3

1-6-2-2 3.530 2.300 -3.530 4

6-2-2-6 -2.000 16.250 0.000 4

0-0-0-0 0.000 0.000 0.000 1

S-62 Electronic Supplementary Information

1-19-1-5 0.000 0.000 0.200 3

5-1-19-6 0.000 0.000 0.210 3

2-6-1-5 0.000 0.000 0.530 4

PiAtom Electron Ionization Repulsion Quality

2 1 -11.160 11.134 4

PiBond DForce DLength Quality

2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

Atoms DLength Quality

5-1-6 -0.002 4

S-63 Electronic Supplementary Information

2-(Trimethylsiloxy)bromonaphthalene (13o) O Si Br

+0.076 13o

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -2.260 -0.230 0.997 C Alkene 0.0341948 C(2) -2.723 -0.112 2.256 C Alkene 0.0327922 C(3) -4.013 -0.397 2.503 C Alkene -0.121268 C(4) -4.834 -0.786 1.514 C Alkene 0.0757378 C(5) -4.400 -0.897 0.241 C Alkene 0.2531 C(6) -3.099 -0.622 0.023 C Alkene -0.144585 Br(7) -6.639 -1.171 1.971 Br 0.0514322 O(8) -5.208 -1.292 -0.792 O Enol -0.488118 Si(9) -5.812 -0.100 -1.732 Si Silane 1.38451 C(10) -7.624 -0.491 -2.062 C Alkane -0.50043 C(11) -5.675 1.587 -0.912 C Alkane -0.497669 C(12) -4.866 -0.088 -3.359 C Alkane -0.498011 C(13) -0.969 0.046 0.737 C Alkene -0.0519074 C(14) -0.142 0.438 1.719 C Alkene -0.0538385 C(15) -0.604 0.556 2.972 C Alkene -0.0533023 C(16) -1.890 0.281 3.238 C Alkene -0.0520012 H(17) -4.398 -0.309 3.533 H 0.0156713 H(18) -2.718 -0.725 -1.008 H 0.0197913 H(19) -8.035 0.297 -2.732 H 0.0584183 H(20) -7.686 -1.489 -2.549 H 0.0573647 H(21) -8.166 -0.496 -1.090 H 0.0577182 H(22) -6.123 2.338 -1.599 H 0.0582293 H(23) -4.602 1.822 -0.739 H 0.0576159 H(24) -6.233 1.567 0.049 H 0.0579564 H(25) -4.955 -1.094 -3.825 H 0.0575111 H(26) -5.316 0.688 -4.017 H 0.0584759 H(27) -3.801 0.153 -3.149 H 0.0580602 H(28) -0.565 -0.043 -0.286 H 0.0160314 H(29) 0.914 0.663 1.497 H 0.0202521 H(30) 0.072 0.877 3.782 H 0.0202476 H(31) -2.247 0.383 4.277 H 0.016019

S-64 Electronic Supplementary Information

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

2-5 4.600 1.100 0.000 4

2-13 2.500 1.881 1.560 3

2-6 6.000 1.355 0.000 4

6-19 5.500 1.626 -0.400 3

1-19 2.970 1.880 -0.600 4

1-5 4.600 1.113 0.000 4

S-65 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality

2-2-2 0.430 120.0 0.0 0.0 4

2-2-5 0.360 120.0 120.5 0.0 4

2-2-13 0.450 118.1 0.0 0.0 3

2-2-6 0.700 124.3 0.0 0.0 4

1-19-1 0.480 110.8 110.4 108.5 3

1-19-6 0.350 108.5 0.0 0.0 3

5-1-5 0.320 109.4 109.0 109.5 4

5-1-19 0.320 108.6 110.8 107.0 3

Atoms Force Constant Quality

2-2 0.050 4

2-5 0.050 4

2-13 0.050 3

2-6 0.050 4

Torsional V1 V2 V3 Quality

2-2-2-2 -0.930 8.000 0.000 4

2-2-2-5 0.000 9.000 -1.060 4

5-2-2-13 0.000 15.000 0.000 3

2-2-2-13 0.000 15.000 0.000 3

6-2-2-13 0.000 15.500 0.000 3

2-2-2-6 0.000 16.250 0.000 4

5-2-2-6 0.000 16.250 0.000 4

0-0-0-0 0.000 0.000 0.000 1

1-19-1-5 0.000 0.000 0.200 3

5-1-19-6 0.000 0.000 0.210 3

5-2-2-5 0.000 15.000 0.000 4

PiAtom Electron Ionization Repulsion Quality

S-66 Electronic Supplementary Information

2 1 -11.160 11.134 4

PiBond DForce DLength Quality

2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

S-67 Electronic Supplementary Information

Ortho-(trimethylsiloxy)bromo[5]Helicene (13p)

O Si Br

+0.003 13p

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -1.041 0.425 -0.409 C Alkene 0.0114838 C(2) -0.903 -0.926 -0.420 C Alkene 0.0151843 C(3) -1.867 -1.659 -1.024 C Alkene 0.0131878 C(4) -3.060 -1.092 -1.304 C Alkene 0.00308595 C(5) -3.334 0.184 -0.952 C Alkene 0.206059 C(6) -2.284 0.941 -0.557 C Alkene -0.00153432 Br(7) -4.479 -2.109 -2.105 Br 0.0325423 O(8) -4.592 0.721 -1.113 O Enol -0.497997 Si(9) -5.595 0.620 0.178 Si Silane 1.38324 C(10) -5.851 2.324 0.938 C Alkane -0.49952 C(11) -7.268 -0.006 -0.422 C Alkane -0.502233 C(12) -4.926 -0.536 1.503 C Alkane -0.497517 C(13) -2.472 2.256 -0.335 C Alkene -0.0462832 C(14) -1.463 3.079 -0.034 C Alkene -0.0601527 C(15) -0.207 2.615 -0.089 C Alkene 0.0423193 C(16) -0.002 1.302 -0.330 C Alkene 0.0423847 C(17) 0.116 -1.599 0.182 C Alkene 0.0447277 C(18) 0.354 -2.899 -0.092 C Alkene 0.0394976 C(19) -0.489 -3.557 -0.900 C Alkene -0.0548303 C(20) -1.612 -2.953 -1.301 C Alkene -0.0562625 C(21) 0.879 -1.065 1.162 C Alkene -0.0323695 C(22) 1.906 -1.718 1.727 C Alkene -0.0559316 C(23) 2.189 -2.969 1.348 C Alkene -0.0471143 C(24) 1.393 -3.563 0.449 C Alkene -0.0480154 C(25) 0.811 3.484 0.051 C Alkene -0.0492822 C(26) 2.078 3.088 -0.123 C Alkene -0.0459266 C(27) 2.306 1.820 -0.484 C Alkene -0.0566022 C(28) 1.279 0.964 -0.600 C Alkene -0.0334663 H(29) -6.662 2.244 1.695 H 0.058624 H(30) -4.909 2.648 1.432 H 0.0579012 H(31) -6.143 3.032 0.132 H 0.0573819 H(32) -7.968 -0.009 0.443 H 0.0583713 H(33) -7.150 -1.036 -0.822 H 0.057536 H(34) -7.635 0.682 -1.216 H 0.0574962 H(35) -3.941 -0.154 1.852 H 0.0576909 H(36) -5.652 -0.545 2.346 H 0.0580688 H(37) -4.823 -1.559 1.081 H 0.057538 H(38) -3.457 2.741 -0.415 H 0.020876 H(39) -1.675 4.149 0.135 H 0.0147165 H(40) -0.336 -4.623 -1.144 H 0.0146475

S-68 Electronic Supplementary Information

H(41) -2.310 -3.604 -1.848 H 0.0219409 H(42) 0.673 -0.065 1.577 H 0.0230489 H(43) 2.506 -1.235 2.517 H 0.0201165 H(44) 3.024 -3.520 1.812 H 0.0201379 H(45) 1.591 -4.619 0.198 H 0.0155555 H(46) 0.628 4.550 0.271 H 0.0154859 H(47) 2.911 3.805 -0.034 H 0.0201301 H(48) 3.335 1.491 -0.706 H 0.0200301 H(49) 1.551 -0.037 -0.971 H 0.0240324

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

2-13 2.500 1.881 1.560 3

S-69 Electronic Supplementary Information

2-6 6.000 1.355 0.000 4

6-19 5.500 1.626 -0.400 3

1-19 2.970 1.880 -0.600 4

1-5 4.600 1.113 0.000 4

2-5 4.600 1.100 0.000 4

Angle KB XR2 XRH XH2 Quality

2-2-2 0.430 120.0 0.0 0.0 4

2-2-13 0.450 118.1 0.0 0.0 3

2-2-6 0.700 124.3 0.0 0.0 4

1-19-1 0.480 110.8 110.4 108.5 3

1-19-6 0.350 108.5 0.0 0.0 3

5-1-5 0.320 109.4 109.0 109.5 4

5-1-19 0.320 108.6 110.8 107.0 3

2-2-5 0.360 120.0 120.5 0.0 4

Atoms Force Constant Quality

2-2 0.050 4

2-13 0.050 3

2-6 0.050 4

2-5 0.050 4

Torsional V1 V2 V3 Quality

2-2-2-2 -0.930 8.000 0.000 4

2-2-2-13 0.000 15.000 0.000 3

2-2-2-5 0.000 9.000 -1.060 4

6-2-2-13 0.000 15.500 0.000 3

2-2-2-6 0.000 16.250 0.000 4

0-0-0-0 0.000 0.000 0.000 1

1-19-1-5 0.000 0.000 0.200 3

S-70 Electronic Supplementary Information

5-1-19-6 0.000 0.000 0.210 3

5-2-2-5 0.000 15.000 0.000 4

PiAtom Electron Ionization Repulsion Quality

2 1 -11.160 11.134 4

PiBond DForce DLength Quality

2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

S-71 Electronic Supplementary Information

9-Bromo-10-(trimethylsiloxy)phenanthrene (13q)

O Si Br

+0.001 13q

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -3.149 -1.854 -0.154 C Alkene 0.0235867 C(2) -4.452 -2.228 -0.164 C Alkene 0.022591 C(3) -5.391 -1.396 0.347 C Alkene 0.0221747 C(4) -5.016 -0.193 0.833 C Alkene 0.000685875 C(5) -3.730 0.227 0.810 C Alkene 0.204909 C(6) -2.802 -0.644 0.344 C Alkene 0.0109031 O(7) -3.371 1.471 1.282 O Enol -0.494836 Br(8) -6.312 1.007 1.592 Br 0.0310147 Si(9) -3.325 2.692 0.190 Si Silane 1.38175 C(10) -1.544 3.229 -0.115 C Alkane -0.500193 C(11) -4.096 2.202 -1.454 C Alkane -0.497462 C(12) -4.251 4.169 0.909 C Alkane -0.502853 C(13) -1.496 -0.305 0.388 C Alkene -0.0494321 C(14) -0.525 -1.103 -0.074 C Alkene -0.0403474 C(15) -0.863 -2.287 -0.591 C Alkene -0.0507331 C(16) -2.155 -2.643 -0.619 C Alkene -0.0495085 C(17) -4.867 -3.418 -0.654 C Alkene -0.0470898 C(18) -6.151 -3.802 -0.650 C Alkene -0.0542275 C(19) -7.072 -2.982 -0.138 C Alkene -0.0356916 C(20) -6.681 -1.798 0.350 C Alkene -0.0619855 H(21) -1.567 4.167 -0.712 H 0.0586068 H(22) -1.054 3.407 0.867 H 0.0573697 H(23) -1.015 2.436 -0.687 H 0.0578188 H(24) -4.021 3.075 -2.140 H 0.0580918 H(25) -5.163 1.935 -1.295 H 0.0575828 H(26) -3.533 1.339 -1.873 H 0.057756 H(27) -3.794 4.425 1.890 H 0.0575026 H(28) -4.149 5.020 0.199 H 0.0583838 H(29) -5.323 3.904 1.033 H 0.0575364 H(30) -1.143 0.643 0.821 H 0.0207901 H(31) 0.533 -0.798 -0.024 H 0.0194347 H(32) -0.080 -2.963 -0.976 H 0.0189134 H(33) -2.319 -3.641 -1.049 H 0.023492 H(34) -4.193 -4.166 -1.093 H 0.0234705 H(35) -6.451 -4.782 -1.059 H 0.018912 H(36) -8.134 -3.280 -0.124 H 0.0191727 H(37) -7.505 -1.186 0.746 H 0.02191

S-72 Electronic Supplementary Information

Bond KS Bond Length Dipole Quality 2-2 9.600 1.337 0.000 4 2-13 2.500 1.881 1.560 3 2-6 6.000 1.355 0.000 4 6-19 5.500 1.626 -0.400 3 1-19 2.970 1.880 -0.600 4 1-5 4.600 1.113 0.000 4 2-5 4.600 1.100 0.000 4

Angle KB XR2 XRH XH2 Quality 2-2-2 0.430 120.0 0.0 0.0 4

S-73 Electronic Supplementary Information

2-2-13 0.450 118.1 0.0 0.0 3 2-2-6 0.700 124.3 0.0 0.0 4 1-19-1 0.480 110.8 110.4 108.5 3 1-19-6 0.350 108.5 0.0 0.0 3 5-1-5 0.320 109.4 109.0 109.5 4 5-1-19 0.320 108.6 110.8 107.0 3 2-2-5 0.360 120.0 120.5 0.0 4

Atoms Force Constant Quality 2-2 0.050 4 2-13 0.050 3 2-6 0.050 4 2-5 0.050 4

Torsional V1 V2 V3 Quality 2-2-2-2 -0.930 8.000 0.000 4 2-2-2-5 0.000 9.000 -1.060 4 2-2-2-13 0.000 15.000 0.000 3 6-2-2-13 0.000 15.500 0.000 3 2-2-2-6 0.000 16.250 0.000 4 0-0-0-0 0.000 0.000 0.000 1 1-19-1-5 0.000 0.000 0.200 3 5-1-19-6 0.000 0.000 0.210 3 5-2-2-5 0.000 15.000 0.000 4

PiAtom Electron Ionization Repulsion Quality 2 1 -11.160 11.134 4

PiBond DForce DLength Quality 2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

S-74 Electronic Supplementary Information

1-5 3.340 0.046 4

S-75 Electronic Supplementary Information

2,5-Dibromo-4-(trimethylsiloxy)phenol (13r) +0.024

Br O Si HO Br 13r +0.017

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) 2.460 0.131 -1.256 C Alkene 0.0243153 C(2) 2.766 -1.175 -1.349 C Alkene 0.170515 C(3) 1.752 -2.049 -1.245 C Alkene -0.158885 C(4) 0.485 -1.649 -1.049 C Alkene 0.0174543 C(5) 0.171 -0.341 -0.938 C Alkene 0.194391 C(6) 1.193 0.530 -1.061 C Alkene -0.161839 O(7) -1.107 0.108 -0.740 O Enol -0.50917 Br(8) -0.852 -2.994 -0.926 Br 0.022143 Si(9) -1.506 0.502 0.795 Si Silane 1.384 C(10) -3.222 -0.190 1.138 C Alkane -0.500488 C(11) -0.286 -0.200 2.042 C Alkane -0.497735 C(12) -1.543 2.378 0.938 C Alkane -0.497963 O(13) 4.036 -1.625 -1.547 O Enol -0.281927 Br(14) 3.815 1.451 -1.399 Br 0.0198682 H(15) 1.991 -3.123 -1.327 H 0.0239816 H(16) 0.965 1.607 -0.993 H 0.0249828 H(17) -3.518 0.103 2.169 H 0.0584244 H(18) -3.929 0.237 0.393 H 0.0573785 H(19) -3.180 -1.298 1.046 H 0.0577277 H(20) -0.633 0.088 3.059 H 0.0581834 H(21) 0.721 0.230 1.848 H 0.0575907 H(22) -0.267 -1.307 1.944 H 0.0579128 H(23) -2.265 2.774 0.190 H 0.0575215 H(24) -1.866 2.643 1.969 H 0.0584755 H(25) -0.521 2.770 0.740 H 0.0580559 H(26) 4.034 -2.594 -1.595 H Enol 0.205082

S-76 Electronic Supplementary Information

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4 X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4 X-Si,P-Y Stretch-Bend force constant0.200 4 Sextic bending constant (* 10**8)7.000 4 Dielectric constant for dipoles1.500 4 Cutoff distance for charge/charge interactions35.000 4 Cutoff distance for charge/dipole interactions25.000 4 Cutoff distance for dipole/dipole interactions18.000 4 Cutoff distance for van der Waals interactions10.000 4

Bond KS Bond Length Dipole Quality 2-2 9.600 1.337 0.000 4 2-13 2.500 1.881 1.560 3 2-6 6.000 1.355 0.000 4 2-5 4.600 1.100 0.000 4 6-19 5.500 1.626 -0.400 3 1-19 2.970 1.880 -0.600 4 1-5 4.600 1.113 0.000 4 6-28 7.200 0.972 -0.700 3

Angle KB XR2 XRH XH2 Quality 2-2-13 0.450 118.1 0.0 0.0 3 2-2-2 0.430 120.0 0.0 0.0 4

S-77 Electronic Supplementary Information

2-2-6 0.700 124.3 0.0 0.0 4 2-2-5 0.360 120.0 120.5 0.0 4 1-19-1 0.480 110.8 110.4 108.5 3 1-19-6 0.350 108.5 0.0 0.0 3 5-1-5 0.320 109.4 109.0 109.5 4 5-1-19 0.320 108.6 110.8 107.0 3 2-6-28 0.350 108.0 0.0 0.0 4

Atoms Force Constant Quality 2-2 0.050 4 2-13 0.050 3 2-6 0.050 4 2-5 0.050 4

Torsional V1 V2 V3 Quality 6-2-2-13 0.000 15.500 0.000 3 2-2-2-13 0.000 15.000 0.000 3 2-2-2-6 0.000 16.250 0.000 4 2-2-2-2 -0.930 8.000 0.000 4 5-2-2-13 0.000 15.000 0.000 3 2-2-2-5 0.000 9.000 -1.060 4 5-2-2-6 0.000 16.250 0.000 4 2-2-6-28 2.000 1.700 -2.000 4 0-0-0-0 0.000 0.000 0.000 1 1-19-1-5 0.000 0.000 0.200 3 5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality 2 1 -11.160 11.134 4

PiBond DForce DLength Quality 2-2 4.600 0.166 4

S-78 Electronic Supplementary Information

VDW Interaction Radius Eps Quality 2-28 2.340 1.000 3 6-28 2.140 2.400 4 13-28 2.580 0.400 3 1-5 3.340 0.046 4

S-79 Electronic Supplementary Information

2,5-Dibromo-1.4-di(trimethylsilyloxy)benzene (13s) +0.017

Br O Si Si O Br 13s +0.017

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) 1.240 0.939 1.001 C Alkene 0.0171419 C(2) 1.194 -0.349 1.399 C Alkene 0.197339 C(3) -0.032 -0.857 1.627 C Alkene -0.161327 C(4) -1.156 -0.148 1.436 C Alkene 0.0171629 C(5) -1.112 1.127 0.999 C Alkene 0.197338 C(6) 0.116 1.648 0.809 C Alkene -0.161284 O(7) -2.232 1.883 0.775 O Enol -0.511237 Br(8) -2.813 -1.011 1.786 Br 0.0220107 Si(9) -2.715 1.981 -0.784 Si Silane 1.38625 C(10) -4.582 1.742 -0.828 C Alkane -0.500072 C(11) -2.282 3.695 -1.430 C Alkane -0.498071 C(12) -1.888 0.678 -1.860 C Alkane -0.498 O(13) 2.313 -1.114 1.592 O Enol -0.511221 Br(14) 2.897 1.810 0.675 Br 0.0219841 Si(15) 2.700 -2.118 0.362 Si Silane 1.38623 C(16) 4.557 -1.995 0.076 C Alkane -0.500106 C(17) 2.255 -3.875 0.869 C Alkane -0.498046 C(18) 1.789 -1.673 -1.223 C Alkane -0.498001 H(19) -0.098 -1.901 1.977 H 0.0246919 H(20) 0.182 2.698 0.475 H 0.0246766 H(21) -4.922 1.846 -1.882 H 0.0584897 H(22) -4.816 0.725 -0.443 H 0.0577915 H(23) -5.051 2.521 -0.187 H 0.0574363 H(24) -2.655 3.777 -2.475 H 0.0584671 H(25) -1.177 3.816 -1.402 H 0.0580411 H(26) -2.775 4.451 -0.780 H 0.0575057 H(27) -2.139 -0.330 -1.465 H 0.0578421 H(28) -2.280 0.790 -2.895 H 0.0581417 H(29) -0.788 0.839 -1.852 H 0.0575499 H(30) 4.833 -2.704 -0.734 H 0.0584842 H(31) 4.799 -0.951 -0.221 H 0.0577839 H(32) 5.076 -2.262 1.023 H 0.0574401 H(33) 2.564 -4.563 0.051 H 0.0584741 H(34) 1.155 -3.931 1.027 H 0.0580475 H(35) 2.798 -4.119 1.809 H 0.0575063 H(36) 2.049 -0.631 -1.510 H 0.0578392 H(37) 2.118 -2.380 -2.016 H 0.0581466 H(38) 0.694 -1.772 -1.057 H 0.0575586

S-80 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality 2-2-13 0.450 118.1 0.0 0.0 3

S-81 Electronic Supplementary Information

2-2-2 0.430 120.0 0.0 0.0 4 2-2-6 0.700 124.3 0.0 0.0 4 2-2-5 0.360 120.0 120.5 0.0 4 1-19-1 0.480 110.8 110.4 108.5 3 1-19-6 0.350 108.5 0.0 0.0 3 5-1-5 0.320 109.4 109.0 109.5 4 5-1-19 0.320 108.6 110.8 107.0 3

Atoms Force Constant Quality 2-2 0.050 4 2-13 0.050 3 2-6 0.050 4 2-5 0.050 4

Torsional V1 V2 V3 Quality 6-2-2-13 0.000 15.500 0.000 3 2-2-2-13 0.000 15.000 0.000 3 2-2-2-6 0.000 16.250 0.000 4 2-2-2-2 -0.930 8.000 0.000 4 5-2-2-13 0.000 15.000 0.000 3 2-2-2-5 0.000 9.000 -1.060 4 5-2-2-6 0.000 16.250 0.000 4 0-0-0-0 0.000 0.000 0.000 1 1-19-1-5 0.000 0.000 0.200 3 5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality 2 1 -11.160 11.134 4

PiBond DForce DLength Quality 2-2 4.600 0.166 4

S-82 Electronic Supplementary Information

VDW Interaction Radius Eps Quality 1-5 3.340 0.046 4

S-83 Electronic Supplementary Information

2-Bromo-3-(trimethylsilyloxy)-1,4-xylene (13t)

O Si Br 13t +0.026

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) 0.633 -0.020 0.033 C Alkene -0.0926852 C(2) 0.755 -1.098 0.816 C Alkene -0.0932408 C(3) -0.276 -1.944 0.976 C Alkene 0.00239827 C(4) -1.431 -1.659 0.340 C Alkene 0.0256666 C(5) -1.592 -0.559 -0.434 C Alkene 0.209297 C(6) -0.521 0.254 -0.596 C Alkene -0.0151061 O(7) -2.776 -0.281 -1.074 O Enol -0.497135 Br(8) -2.887 -2.876 0.541 Br 0.0336689 Si(9) -3.832 0.705 -0.307 Si Silane 1.38033 C(10) -5.486 -0.182 -0.127 C Alkane -0.501961 C(11) -3.215 1.223 1.391 C Alkane -0.496494 C(12) -4.121 2.233 -1.372 C Alkane -0.50213 C(13) -0.566 1.477 -1.489 C Alkane -0.14127 C(14) -0.086 -3.159 1.864 C Alkane -0.142415 H(15) 1.503 0.646 -0.090 H 0.018181 H(16) 1.719 -1.286 1.316 H 0.0182115 H(17) -6.223 0.542 0.283 H 0.0585047 H(18) -5.806 -0.536 -1.132 H 0.0574108 H(19) -5.367 -1.039 0.571 H 0.0577582 H(20) -3.987 1.880 1.850 H 0.0581517 H(21) -2.260 1.781 1.277 H 0.0578876 H(22) -3.068 0.314 2.014 H 0.0578766 H(23) -3.180 2.819 -1.439 H 0.05815 H(24) -4.446 1.900 -2.382 H 0.0575652 H(25) -4.916 2.844 -0.890 H 0.0584613 H(26) -0.905 2.361 -0.904 H 0.053938 H(27) 0.435 1.719 -1.911 H 0.0409516 H(28) -1.234 1.342 -2.368 H 0.0419691 H(29) 0.930 -3.207 2.315 H 0.0374098 H(30) -0.803 -3.147 2.716 H 0.0491519 H(31) -0.213 -4.101 1.283 H 0.0495006

S-84 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality

S-85 Electronic Supplementary Information

2-2-5 0.360 120.0 120.5 0.0 4 2-2-2 0.430 120.0 0.0 0.0 4 1-2-2 0.550 121.4 122.0 120.0 4 2-2-13 0.450 118.1 0.0 0.0 3 2-2-6 0.700 124.3 0.0 0.0 4 1-19-1 0.480 110.8 110.4 108.5 3 1-19-6 0.350 108.5 0.0 0.0 3 5-1-5 0.320 109.4 109.0 109.5 4 5-1-19 0.320 108.6 110.8 107.0 3 2-1-5 0.360 109.4 109.4 110.0 4

Atoms Force Constant Quality 2-2 0.050 4 2-5 0.050 4 1-2 0.050 4 2-13 0.050 3 2-6 0.050 4

Torsional V1 V2 V3 Quality 5-2-2-5 0.000 15.000 0.000 4 2-2-2-5 0.000 9.000 -1.060 4 2-2-2-2 -0.930 8.000 0.000 4 1-2-2-5 0.000 12.500 0.000 4 1-2-2-2 -0.270 10.000 0.000 4 0-0-0-0 0.000 10.000 0.000 1 2-2-2-13 0.000 15.000 0.000 3 2-2-1-5 0.000 0.000 -0.240 4 6-2-2-13 0.000 15.500 0.000 3 2-2-2-6 0.000 16.250 0.000 4 1-2-2-6 -1.200 16.250 0.000 4 1-19-1-5 0.000 0.000 0.200 3 5-1-19-6 0.000 0.000 0.210 3

S-86 Electronic Supplementary Information

PiAtom Electron Ionization Repulsion Quality 2 1 -11.160 11.134 4

PiBond DForce DLength Quality 2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality 1-5 3.340 0.046 4

S-87 Electronic Supplementary Information

2,5-Dibromo-6-hydroxy-3-(trimethylsilyloxy)xylene (13u) -0.002

Br O Si HO Br 13u -0.008

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -1.623 0.089 -0.266 C Alkene -0.0022381 C(2) -1.326 -1.214 -0.432 C Alkene 0.152304 C(3) -2.275 -2.131 -0.152 C Alkene -0.0703834 C(4) -3.490 -1.709 0.257 C Alkene -0.00787573 C(5) -3.810 -0.400 0.389 C Alkene 0.173595 C(6) -2.836 0.508 0.147 C Alkene -0.071444 O(7) -5.062 -0.001 0.793 O Enol -0.511556 Br(8) -4.813 -3.019 0.700 Br 0.0207348 Si(9) -6.152 0.324 -0.385 Si Silane 1.38223 C(10) -7.727 -0.653 -0.038 C Alkane -0.502578 C(11) -6.596 2.155 -0.352 C Alkane -0.501636 C(12) -5.498 -0.122 -2.091 C Alkane -0.4973 C(13) -3.102 1.991 0.360 C Alkane -0.14518 C(14) -1.979 -3.612 -0.334 C Alkane -0.139971 O(15) -0.081 -1.596 -0.839 O Enol -0.299652 Br(16) -0.244 1.352 -0.662 Br 0.0136441 H(17) -8.492 -0.351 -0.787 H 0.0584571 H(18) -7.512 -1.739 -0.129 H 0.0576602 H(19) -8.072 -0.406 0.990 H 0.0574937 H(20) -6.892 2.428 0.685 H 0.057491 H(21) -7.446 2.315 -1.052 H 0.0585589 H(22) -5.719 2.751 -0.684 H 0.0581474 H(23) -6.288 0.122 -2.835 H 0.0580574 H(24) -4.584 0.478 -2.295 H 0.0577572 H(25) -5.270 -1.209 -2.121 H 0.0576715 H(26) -3.998 2.211 0.977 H 0.0413673 H(27) -3.226 2.507 -0.619 H 0.0497315 H(28) -2.285 2.483 0.932 H 0.0465696 H(29) -1.921 -4.122 0.654 H 0.0488466 H(30) -2.750 -4.108 -0.965 H 0.0474225 H(31) -1.029 -3.835 -0.861 H 0.0456129 H(32) 0.043 -2.552 -0.758 H Enol 0.206458

S-88 Electronic Supplementary Information

Bond KS Bond Length Dipole Quality 2-2 9.600 1.337 0.000 4 2-13 2.500 1.881 1.560 3 2-6 6.000 1.355 0.000 4 1-2 4.400 1.497 0.300 4 6-19 5.500 1.626 -0.400 3 1-19 2.970 1.880 -0.600 4 1-5 4.600 1.113 0.000 4 6-28 7.200 0.972 -0.700 3

S-89 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality 2-2-13 0.450 118.1 0.0 0.0 3 2-2-2 0.430 120.0 0.0 0.0 4 2-2-6 0.700 124.3 0.0 0.0 4 1-2-2 0.550 121.4 122.0 120.0 4 1-19-1 0.480 110.8 110.4 108.5 3 1-19-6 0.350 108.5 0.0 0.0 3 5-1-5 0.320 109.4 109.0 109.5 4 5-1-19 0.320 108.6 110.8 107.0 3 2-1-5 0.360 109.4 109.4 110.0 4 2-6-28 0.350 108.0 0.0 0.0 4

Atoms Force Constant Quality 2-2 0.050 4 2-13 0.050 3 2-6 0.050 4 1-2 0.050 4

Torsional V1 V2 V3 Quality 6-2-2-13 0.000 15.500 0.000 3 2-2-2-13 0.000 15.000 0.000 3 2-2-2-6 0.000 16.250 0.000 4 2-2-2-2 -0.930 8.000 0.000 4 0-0-0-0 0.000 10.000 0.000 1 1-2-2-2 -0.270 10.000 0.000 4 1-2-2-6 -1.200 16.250 0.000 4 2-2-6-28 2.000 1.700 -2.000 4 2-2-1-5 0.000 0.000 -0.240 4 1-19-1-5 0.000 0.000 0.200 3 5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality

S-90 Electronic Supplementary Information

2 1 -11.160 11.134 4

PiBond DForce DLength Quality 2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality 2-28 2.340 1.000 3 6-28 2.140 2.400 4 13-28 2.580 0.400 3 1-5 3.340 0.046 4

S-91 Electronic Supplementary Information

2,5-Dibromo-3,6-di(trimethylsilyloxy)xylene (13v) -0.009

Br O Si Si O Br 13v -0.009

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) 0.575 0.692 -0.868 C Alkene -0.00920691 C(2) 0.866 -0.574 -0.492 C Alkene 0.177934 C(3) -0.173 -1.424 -0.321 C Alkene -0.07212 C(4) -1.437 -0.965 -0.427 C Alkene -0.00933159 C(5) -1.728 0.322 -0.720 C Alkene 0.177665 C(6) -0.690 1.144 -0.997 C Alkene -0.0721923 O(7) -3.025 0.773 -0.783 O Enol -0.51347 Br(8) -2.888 -2.174 -0.115 Br 0.0206089 Si(9) -3.623 1.441 0.588 Si Silane 1.3844 C(10) -5.244 0.586 1.030 C Alkane -0.50221 C(11) -2.418 1.289 2.024 C Alkane -0.497583 C(12) -4.002 3.263 0.290 C Alkane -0.501738 C(13) -0.956 2.573 -1.449 C Alkane -0.145337 C(14) 0.094 -2.893 -0.024 C Alkane -0.145268 O(15) 2.163 -1.001 -0.335 O Enol -0.513715 Br(16) 2.027 1.890 -1.213 Br 0.0204104 Si(17) 2.772 -0.910 1.183 Si Silane 1.38463 C(18) 4.393 0.051 1.137 C Alkane -0.502156 C(19) 1.575 -0.071 2.368 C Alkane -0.497591 C(20) 3.153 -2.644 1.814 C Alkane -0.501701 H(21) -5.689 1.119 1.899 H 0.0585306 H(22) -5.922 0.643 0.150 H 0.0575385 H(23) -5.038 -0.472 1.299 H 0.0577297 H(24) -2.889 1.755 2.917 H 0.0580229 H(25) -1.477 1.824 1.768 H 0.0577346 H(26) -2.215 0.213 2.219 H 0.0576335 H(27) -4.544 3.652 1.180 H 0.0585627 H(28) -3.050 3.819 0.157 H 0.0581316 H(29) -4.639 3.346 -0.618 H 0.0575198 H(30) -1.997 2.764 -1.782 H 0.0412325 H(31) -0.727 3.291 -0.628 H 0.0493471 H(32) -0.363 2.842 -2.351 H 0.0470406 H(33) 1.133 -3.224 -0.232 H 0.0411734 H(34) -0.125 -3.120 1.044 H 0.0494088 H(35) -0.507 -3.566 -0.675 H 0.0469608 H(36) 4.845 0.013 2.153 H 0.0585351 H(37) 5.065 -0.431 0.394 H 0.0575311 H(38) 4.185 1.105 0.853 H 0.0577393 H(39) 2.054 -0.039 3.372 H 0.0580171

S-92 Electronic Supplementary Information

H(40) 0.634 -0.662 2.414 H 0.0577205 H(41) 1.372 0.962 2.011 H 0.0576323 H(42) 3.699 -2.547 2.778 H 0.0585642 H(43) 2.201 -3.194 1.975 H 0.0581427 H(44) 3.786 -3.162 1.061 H 0.0575188

S-93 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality 2-2-13 0.450 118.1 0.0 0.0 3

S-94 Electronic Supplementary Information

2-2-2 0.430 120.0 0.0 0.0 4 2-2-6 0.700 124.3 0.0 0.0 4 1-2-2 0.550 121.4 122.0 120.0 4 1-19-1 0.480 110.8 110.4 108.5 3 1-19-6 0.350 108.5 0.0 0.0 3 5-1-5 0.320 109.4 109.0 109.5 4 5-1-19 0.320 108.6 110.8 107.0 3 2-1-5 0.360 109.4 109.4 110.0 4

Atoms Force Constant Quality 2-2 0.050 4 2-13 0.050 3 2-6 0.050 4 1-2 0.050 4

Torsional V1 V2 V3 Quality 6-2-2-13 0.000 15.500 0.000 3 2-2-2-13 0.000 15.000 0.000 3 2-2-2-6 0.000 16.250 0.000 4 2-2-2-2 -0.930 8.000 0.000 4 0-0-0-0 0.000 10.000 0.000 1 1-2-2-2 -0.270 10.000 0.000 4 1-2-2-6 -1.200 16.250 0.000 4 2-2-1-5 0.000 0.000 -0.240 4 1-19-1-5 0.000 0.000 0.200 3 5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality 2 1 -11.160 11.134 4

PiBond DForce DLength Quality 2-2 4.600 0.166 4

S-95 Electronic Supplementary Information

VDW Interaction Radius Eps Quality 1-5 3.340 0.046 4

S-96 Electronic Supplementary Information

2-Bromo-6-hydroxy-5-trimethylsilyl-3-(trimethylsilyloxy)xylene (13w) +0.032

Br OH Si O Si

13w

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -0.988 2.013 -0.728 C Alkene 0.0319099 C(2) -0.714 0.697 -0.859 C Alkene 0.162215 C(3) -1.721 -0.180 -0.629 C Alkene -0.0130022 C(4) -2.936 0.242 -0.209 C Alkene -0.423754 C(5) -3.170 1.565 -0.074 C Alkene 0.205607 C(6) -2.197 2.461 -0.340 C Alkene -0.0809108 O(7) -4.405 2.015 0.277 O Enol -0.300721 Si(8) -4.359 -0.963 0.186 Si Silane 1.25737 C(9) -2.470 3.950 -0.180 C Alkane -0.141022 C(10) -1.456 -1.654 -0.885 C Alkane -0.159006 O(11) 0.531 0.264 -1.254 O Enol -0.512239 Br(12) 0.379 3.283 -1.142 Br 0.0326688 C(13) -3.762 -2.523 1.074 C Alkane -0.494333 C(14) -5.658 -0.265 1.372 C Alkane -0.495532 C(15) -5.234 -1.420 -1.420 C Alkane -0.477542 Si(16) 1.589 -0.137 -0.071 Si Silane 1.38207 C(17) 3.157 0.890 -0.265 C Alkane -0.502239 C(18) 0.869 0.143 1.643 C Alkane -0.496919 C(19) 2.071 -1.949 -0.262 C Alkane -0.502316 H(20) -4.503 2.958 0.085 H Enol 0.208121 H(21) -3.389 4.194 0.393 H 0.0462391 H(22) -1.672 4.459 0.405 H 0.0472523 H(23) -2.566 4.436 -1.178 H 0.0490649 H(24) -0.650 -1.847 -1.623 H 0.042753 H(25) -1.183 -2.174 0.060 H 0.0533547 H(26) -2.320 -2.159 -1.365 H 0.0490776 H(27) -4.644 -3.000 1.556 H 0.0566939 H(28) -3.328 -3.246 0.353 H 0.0569184 H(29) -3.023 -2.226 1.850 H 0.0573157 H(30) -6.305 -1.108 1.703 H 0.0563648 H(31) -6.295 0.480 0.848 H 0.0555696 H(32) -5.142 0.180 2.251 H 0.0563261 H(33) -5.633 -0.486 -1.874 H 0.0573444 H(34) -4.510 -1.906 -2.109 H 0.0568117 H(35) -6.064 -2.119 -1.175 H 0.0570186 H(36) 3.908 0.513 0.463 H 0.0585215 H(37) 3.531 0.768 -1.306 H 0.0574388 H(38) 2.926 1.956 -0.053 H 0.0577894 H(39) 1.644 -0.137 2.390 H 0.058059 H(40) -0.031 -0.497 1.770 H 0.0577954

S-97 Electronic Supplementary Information

H(41) 0.605 1.218 1.753 H 0.0577767 H(42) 1.188 -2.591 -0.054 H 0.0580305 H(43) 2.435 -2.107 -1.301 H 0.0575588 H(44) 2.879 -2.169 0.470 H 0.0584949

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality 2 1.940 0.044 12.000 0.000 0 4 6 1.740 0.050 15.995 0.000 2 4 19 2.250 0.140 27.977 0.000 0 4 1 1.900 0.044 12.000 0.000 0 4 13 2.180 0.320 78.918 0.000 0 4 28 0.900 0.015 1.008 0.000 0 4 5 1.500 0.047 1.008 0.915 0 4

Bond KS Bond Length Dipole Quality 2-2 9.600 1.337 0.000 4 2-13 2.500 1.881 1.560 3 2-6 6.000 1.355 0.000 4 1-2 4.400 1.497 0.300 4 2-19 3.500 1.865 -0.650 4

S-98 Electronic Supplementary Information

6-28 7.200 0.972 -0.700 3 1-19 2.970 1.880 -0.600 4 1-5 4.600 1.113 0.000 4 6-19 5.500 1.626 -0.400 3

Angle KB XR2 XRH XH2 Quality 2-2-13 0.450 118.1 0.0 0.0 3 2-2-2 0.430 120.0 0.0 0.0 4 2-2-6 0.700 124.3 0.0 0.0 4 1-2-2 0.550 121.4 122.0 120.0 4 2-2-19 0.400 122.5 120.5 0.0 3 2-6-28 0.350 108.0 0.0 0.0 4 1-19-1 0.480 110.8 110.4 108.5 3 1-19-2 0.400 110.2 0.0 0.0 3 5-1-5 0.320 109.4 109.0 109.5 4 2-1-5 0.360 109.4 109.4 110.0 4 5-1-19 0.320 108.6 110.8 107.0 3 1-19-6 0.350 108.5 0.0 0.0 3

Atoms Force Constant Quality 2-2 0.050 4 2-13 0.050 3 2-6 0.050 4 1-2 0.050 4 2-19 0.050 4

Torsional V1 V2 V3 Quality 6-2-2-13 0.000 15.500 0.000 3 2-2-2-13 0.000 15.000 0.000 3 2-2-2-6 0.000 16.250 0.000 4 2-2-2-2 -0.930 8.000 0.000 4 0-0-0-0 0.000 10.000 0.000 1

S-99 Electronic Supplementary Information

1-2-2-2 -0.270 10.000 0.000 4 1-2-2-6 -1.200 16.250 0.000 4 1-2-2-19 0.000 15.000 0.000 3 2-2-2-19 0.000 15.000 0.000 3 2-2-1-5 0.000 0.000 -0.240 4 1-19-2-2 -0.440 -0.240 0.060 3 2-2-6-28 2.000 1.700 -2.000 4 1-19-1-5 0.000 0.000 0.200 3 2-19-1-5 0.000 0.000 0.117 3 5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality 2 1 -11.160 11.134 4

PiBond DForce DLength Quality 2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality 2-28 2.340 1.000 3 1-5 3.340 0.046 4 6-28 2.140 2.400 4 13-28 2.580 0.400 3

S-100 Electronic Supplementary Information

2-Bromo-5-trimethylsilyl-3,6-bis(trimethylsilyloxy)xylene (10) +0.031

Br O Si Si O Si

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) 1.809 1.045 -0.419 C(1) 0.0305559 C(2) 1.566 -0.114 -1.063 C(2) 0.163843 C(3) 0.399 -0.743 -0.792 C(3) -0.0132751 C(4) -0.474 -0.252 0.122 C(4) -0.429412 C(5) -0.239 0.950 0.706 C(5) 0.228733 C(6) 0.940 1.571 0.465 C(6) -0.0818701 O(7) -1.159 1.527 1.550 O(7) -0.508248 Si(8) -2.030 -1.247 0.609 Si(8) 1.25572 C(9) 1.302 2.846 1.212 C(9) -0.145976 C(10) 0.091 -2.008 -1.576 C(10) -0.159963 O(11) 2.464 -0.632 -1.969 O(11) -0.510261 Br(12) 3.425 1.989 -0.817 Br(12) 0.0326127 C(13) -1.671 -3.107 0.726 C(13) -0.497205 C(14) -2.613 -0.886 2.376 C(14) -0.500101 C(15) -3.427 -0.976 -0.620 C(15) -0.476258 Si(16) 3.548 -1.726 -1.414 Si(16) 1.38112 C(17) 5.297 -1.108 -1.751 C(17) -0.502408 C(18) 3.347 -2.048 0.428 C(18) -0.496789 C(19) 3.332 -3.339 -2.366 C(19) -0.50293 Si(20) -2.099 2.715 0.920 Si(20) 1.38735 H(21) 1.209 3.735 0.548 H(21) 0.0492034 H(22) 2.335 2.807 1.624 H(22) 0.0472243 H(23) 0.703 3.022 2.129 H(23) 0.0421901 H(24) -0.983 -2.097 -1.837 H(24) 0.0489485 H(25) 0.433 -2.911 -1.026 H(25) 0.0538241 H(26) 0.555 -2.030 -2.585 H(26) 0.0435086 H(27) -0.679 -3.247 1.211 H(27) 0.0567157 H(28) -1.709 -3.583 -0.276 H(28) 0.0561478 H(29) -2.463 -3.571 1.353 H(29) 0.0560176 H(30) -1.726 -0.890 3.047 H(30) 0.0570235 H(31) -3.152 0.079 2.434 H(31) 0.0587648 H(32) -3.317 -1.692 2.677 H(32) 0.0564665 H(33) -4.354 -1.419 -0.193 H(33) 0.0579182 H(34) -3.174 -1.477 -1.578 H(34) 0.0581281 H(35) -3.560 0.111 -0.793 H(35) 0.0598121 H(36) 6.005 -1.928 -1.502 H(36) 0.0585398 H(37) 5.374 -0.842 -2.828 H(37) 0.0574194 H(38) 5.505 -0.224 -1.111 H(38) 0.0577836 H(39) 4.120 -2.787 0.732 H(39) 0.0581081 H(40) 2.332 -2.458 0.620 H(40) 0.0578795

S-101 Electronic Supplementary Information

H(41) 3.494 -1.093 0.979 H(41) 0.0578576 H(42) 2.345 -3.786 -2.123 H(42) 0.0579547 H(43) 3.404 -3.115 -3.453 H(43) 0.057593 H(44) 4.147 -4.031 -2.058 H(44) 0.0584575 C(45) -1.880 2.866 -0.943 C(45) -0.498144 C(46) -1.709 4.379 1.721 C(46) -0.501251 C(47) -3.918 2.397 1.311 C(47) -0.502169 H(48) -4.508 3.245 0.899 H(48) 0.0584371 H(49) -4.250 1.449 0.841 H(49) 0.0587293 H(50) -4.037 2.354 2.416 H(50) 0.0578173 H(51) -2.519 5.089 1.439 H(51) 0.0584436 H(52) -0.739 4.766 1.346 H(52) 0.0576473 H(53) -1.686 4.243 2.825 H(53) 0.0575243 H(54) -0.834 3.174 -1.161 H(54) 0.0578692 H(55) -2.104 1.888 -1.419 H(55) 0.0583897 H(56) -2.587 3.642 -1.309 H(56) 0.0579871

MM2 Constant Value Quality

Cubic stretch constant-2.000 4

Quartic stretch constant2.333 4

X-B,C,N,O-Y Stretch-Bend interaction force constant0.120 4

X-B,C,N,O-H Stretch-Bend interaction force constant0.090 4

X-Si,P-Y Stretch-Bend force constant0.200 4

Sextic bending constant (* 10**8)7.000 4

Dielectric constant for dipoles1.500 4

Cutoff distance for charge/charge interactions35.000 4

Cutoff distance for charge/dipole interactions25.000 4

Cutoff distance for dipole/dipole interactions18.000 4

Cutoff distance for van der Waals interactions10.000 4

MM2 c3dAtomRadius Eps Weight Reduct Lone Pairs Quality

2 1.940 0.044 12.000 0.000 0 4

6 1.740 0.050 15.995 0.000 2 4

19 2.250 0.140 27.977 0.000 0 4

1 1.900 0.044 12.000 0.000 0 4

13 2.180 0.320 78.918 0.000 0 4

5 1.500 0.047 1.008 0.915 0 4

S-102 Electronic Supplementary Information

Bond KS Bond Length Dipole Quality

2-2 9.600 1.337 0.000 4

2-13 2.500 1.881 1.560 3

2-6 6.000 1.355 0.000 4

1-2 4.400 1.497 0.300 4

2-19 3.500 1.865 -0.650 4

6-19 5.500 1.626 -0.400 3

1-19 2.970 1.880 -0.600 4

1-5 4.600 1.113 0.000 4

Angle KB XR2 XRH XH2 Quality

2-2-13 0.450 118.1 0.0 0.0 3

2-2-2 0.430 120.0 0.0 0.0 4

2-2-6 0.700 124.3 0.0 0.0 4

1-2-2 0.550 121.4 122.0 120.0 4

2-2-19 0.400 122.5 120.5 0.0 3

1-19-1 0.480 110.8 110.4 108.5 3

1-19-2 0.400 110.2 0.0 0.0 3

5-1-5 0.320 109.4 109.0 109.5 4

2-1-5 0.360 109.4 109.4 110.0 4

5-1-19 0.320 108.6 110.8 107.0 3

1-19-6 0.350 108.5 0.0 0.0 3

Atoms Force Constant Quality

2-2 0.050 4

2-13 0.050 3

2-6 0.050 4

1-2 0.050 4

2-19 0.050 4

S-103 Electronic Supplementary Information

Torsional V1 V2 V3 Quality

6-2-2-13 0.000 15.500 0.000 3

2-2-2-13 0.000 15.000 0.000 3

2-2-2-6 0.000 16.250 0.000 4

2-2-2-2 -0.930 8.000 0.000 4

0-0-0-0 0.000 10.000 0.000 1

1-2-2-2 -0.270 10.000 0.000 4

1-2-2-6 -1.200 16.250 0.000 4

1-2-2-19 0.000 15.000 0.000 3

2-2-2-19 0.000 15.000 0.000 3

2-2-1-5 0.000 0.000 -0.240 4

1-19-2-2 -0.440 -0.240 0.060 3

1-19-1-5 0.000 0.000 0.200 3

2-19-1-5 0.000 0.000 0.117 3

5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality

2 1 -11.160 11.134 4

PiBond DForce DLength Quality

2-2 4.600 0.166 4

VDW Interaction Radius Eps Quality

1-5 3.340 0.046 4

S-104 Electronic Supplementary Information

2,4-Dibromo-1,3-bis(trimethylsilyloxy)benzene (13x) +0.015

Br O Si Br O Si 13x -0.019

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) 1.865 1.399 -0.118 C Alkene -0.118887 C(2) 1.594 0.716 1.000 C Alkene -0.143916 C(3) 0.545 -0.123 1.075 C Alkene 0.197692 C(4) -0.250 -0.208 -0.016 C Alkene -0.0194226 C(5) -0.036 0.490 -1.159 C Alkene 0.178621 C(6) 1.064 1.276 -1.186 C Alkene 0.0146112 O(7) -0.860 0.377 -2.255 O Enol -0.497786 Br(8) -1.745 -1.395 0.085 Br 0.0331403 Si(9) -2.119 1.416 -2.380 Si Silane 1.37345 C(10) -3.726 0.438 -2.514 C Alkane -0.503376 C(11) -2.213 2.580 -0.906 C Alkane -0.496602 C(12) -1.954 2.423 -3.965 C Alkane -0.503296 Br(13) 1.572 2.271 -2.723 Br 0.0225179 O(14) 0.322 -0.819 2.236 O Enol -0.509102 Si(15) 1.213 -2.170 2.457 Si Silane 1.3831 C(16) 0.081 -3.493 3.174 C Alkane -0.50102 C(17) 1.964 -2.791 0.849 C Alkane -0.497812 C(18) 2.586 -1.790 3.687 C Alkane -0.498463 H(19) 2.754 2.052 -0.133 H 0.0197031 H(20) 2.263 0.834 1.869 H 0.0243606 H(21) -3.926 -0.079 -1.552 H 0.0577135 H(22) -3.621 -0.297 -3.342 H 0.0574932 H(23) -4.547 1.155 -2.733 H 0.0584514 H(24) -2.348 1.981 0.021 H 0.0577495 H(25) -1.275 3.176 -0.856 H 0.0577665 H(26) -3.086 3.253 -1.056 H 0.0581018 H(27) -2.892 3.006 -4.100 H 0.058485 H(28) -1.810 1.720 -4.815 H 0.0574716 H(29) -1.091 3.116 -3.875 H 0.0578379 H(30) 0.687 -4.406 3.363 H 0.0584197 H(31) -0.352 -3.108 4.124 H 0.0573871 H(32) -0.724 -3.707 2.436 H 0.0576645 H(33) 2.536 -3.718 1.073 H 0.0582302 H(34) 2.646 -2.013 0.441 H 0.0576324 H(35) 1.145 -3.012 0.130 H 0.0579583 H(36) 2.123 -1.412 4.625 H 0.0575415 H(37) 3.148 -2.730 3.882 H 0.0585148 H(38) 3.258 -1.022 3.246 H 0.0580701

S-105 Electronic Supplementary Information

Bond KS Bond Length Dipole Quality 2-2 9.600 1.337 0.000 4 2-5 4.600 1.100 0.000 4 2-6 6.000 1.355 0.000 4 2-13 2.500 1.881 1.560 3 6-19 5.500 1.626 -0.400 3 1-19 2.970 1.880 -0.600 4 1-5 4.600 1.113 0.000 4

Angle KB XR2 XRH XH2 Quality 2-2-5 0.360 120.0 120.5 0.0 4

S-106 Electronic Supplementary Information

2-2-2 0.430 120.0 0.0 0.0 4 2-2-6 0.700 124.3 0.0 0.0 4 2-2-13 0.450 118.1 0.0 0.0 3 1-19-1 0.480 110.8 110.4 108.5 3 1-19-6 0.350 108.5 0.0 0.0 3 5-1-5 0.320 109.4 109.0 109.5 4 5-1-19 0.320 108.6 110.8 107.0 3

Atoms Force Constant Quality 2-2 0.050 4 2-5 0.050 4 2-6 0.050 4 2-13 0.050 3

Torsional V1 V2 V3 Quality 5-2-2-5 0.000 15.000 0.000 4 2-2-2-5 0.000 9.000 -1.060 4 2-2-2-2 -0.930 8.000 0.000 4 5-2-2-13 0.000 15.000 0.000 3 2-2-2-13 0.000 15.000 0.000 3 5-2-2-6 0.000 16.250 0.000 4 2-2-2-6 0.000 16.250 0.000 4 6-2-2-13 0.000 15.500 0.000 3 0-0-0-0 0.000 0.000 0.000 1 1-19-1-5 0.000 0.000 0.200 3 5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality 2 1 -11.160 11.134 4

PiBond DForce DLength Quality 2-2 4.600 0.166 4

S-107 Electronic Supplementary Information

VDW Interaction Radius Eps Quality 1-5 3.340 0.046 4

S-108 Electronic Supplementary Information

2-Bromo-1,3-bis(trimethylsilyloxy)benzene (13y) O Si Br O Si 13y -0.023

X (Å) Y (Å) Z (Å) Atom Type (MM2) Charge (Hückel) C(1) -4.737 1.881 -0.394 C Alkene -0.0872588 C(2) -4.455 0.569 -0.398 C Alkene 0.134416 C(3) -3.291 0.273 0.517 C Alkane -0.0956171 C(4) -3.249 1.535 1.398 C Alkane -0.0437528 C(5) -3.853 2.654 0.529 C Alkane -0.0791599 Br(6) -6.058 2.677 -1.454 Br 0.0484675 O(7) -5.035 -0.399 -1.156 O Enol -0.484214 Si(8) -6.229 -1.242 -0.430 Si Silane 1.38687 C(9) -5.575 -2.962 -0.033 C Alkane -0.498136 C(10) -6.832 -0.420 1.150 C Alkane -0.497495 C(11) -7.658 -1.375 -1.649 C Alkane -0.499444 H(12) -3.447 -0.646 1.125 H 0.0325568 H(13) -2.367 0.162 -0.097 H 0.038877 H(14) -2.230 1.773 1.777 H 0.0241608 H(15) -3.915 1.374 2.282 H 0.0318857 H(16) -4.414 3.398 1.138 H 0.0297605 H(17) -3.066 3.170 -0.068 H 0.037095 H(18) -6.400 -3.552 0.424 H 0.058371 H(19) -5.235 -3.436 -0.980 H 0.0574343 H(20) -4.727 -2.862 0.680 H 0.0580402 H(21) -7.651 -1.045 1.569 H 0.0581413 H(22) -7.214 0.595 0.907 H 0.0577788 H(23) -5.991 -0.361 1.874 H 0.0577804 H(24) -8.021 -0.349 -1.878 H 0.0577617 H(25) -7.287 -1.873 -2.573 H 0.0573102 H(26) -8.465 -1.979 -1.178 H 0.0583703

S-109 Electronic Supplementary Information

Angle KB XR2 XRH XH2 Quality 2-2-5 0.360 120.0 120.5 0.0 4

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Atoms Force Constant Quality 2-2 0.050 4 2-5 0.050 4 2-6 0.050 4 2-13 0.050 3

Torsional V1 V2 V3 Quality 5-2-2-5 0.000 15.000 0.000 4 2-2-2-5 0.000 9.000 -1.060 4 2-2-2-2 -0.930 8.000 0.000 4 5-2-2-6 0.000 16.250 0.000 4 2-2-2-6 0.000 16.250 0.000 4 6-2-2-13 0.000 15.500 0.000 3 2-2-2-13 0.000 15.000 0.000 3 0-0-0-0 0.000 0.000 0.000 1 1-19-1-5 0.000 0.000 0.200 3 5-1-19-6 0.000 0.000 0.210 3

PiAtom Electron Ionization Repulsion Quality 2 1 -11.160 11.134 4

PiBond DForce DLength Quality 2-2 4.600 0.166 4

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VDW Interaction Radius Eps Quality 1-5 3.340 0.046 4

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S3. 3,6-Dimethoxybenzyne Precursor: Synthetic Experimental Procedures 3,6-Dimethoxy-2-(trimethylsilyl)phenyl trifluoromethanesulfonate (13z) via 2- (trimethylsiloxy)-3,6-dimethoxy-bromobenzene 13n To a solution of 2-bromo-3,6-dimethoxyphenol (25.7 mg, 110 µmol) in anhydrous THF (550 µL) in a sealed tube was added hexamethyldisilazane (17.8 mg, 22.9 µL, 110 µmol) and the mixture refluxed for 2 h. The solvent was reduced in vacuo and anhydrous THF (550 µL) was added. The system was cooled to -78 °C, nBuLi (57.3 µL, 143 µmol, 2.5 M in hexanes) was injected, and stirred for 20 min at -

78 °C. Tf2O (40.4 mg, 24.1 µL, 143 µmol) was injected and the mixture stirred for 20 min.

The reaction mixture was quenched by the addition of saturated aqueous NaHCO3 (5 mL) and being allowed to warm up to room temperature gradually. The mixture was extracted with Et2O (3 x 5 mL).

The organic layers were washed with brine (5 mL), dried over MgSO4 and reduced in vacuo.

The crude product purified using flash column chromatography (n-hexane/EtOAc) to afford the title 1 compound as a colourless oil (27.4 mg, 76.5 µmol, 70%): H NMR (400 MHz, CDCl3) δ ppm 6.96 (1H, 13 d, J = 8.9), 6.78 (1H, d, J = 8.9), 3.80 (3H, s), 3.77 (3H, s), 0.38 (9H, s); C NMR (100 MHz, CDCl3) δ ppm 1 19 158.3, 145.3, 142.8, 124.1, 119.0 (q, JCF = 320), 114.3, 110.1, 56.2, 56.0, 0.9; F NMR (376 MHz, CDCl3) δ ppm -71.9. Consistent with literature.4

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S4. 9,10-Phenanthryne Precursor: Synthetic Experimental Procedures 9-Bromophenanthrene (17) 9-Bromophenanthrene 17 was prepared by a modification of an existing method,5 with updated characterisation provided. Phenanthrene 16 (8.91 g, 50.0 mmol) was dissolved in anhydrous CHCl3 (25.0 mL) and heated to reflux with stirring. Bromine (7.99 g, 2.60 mL, 50.0 mmol) was added dropwise over 1 h and the system refluxed O/N (16 h) with stirring under a drying tube filled with

Na2CO3 to absorb HBr.

The mixture was allowed to cool, diluted with CH2Cl2 (50 mL) and washed with water (50 mL). The aqueous layer was extracted with 50 mL CH2Cl2, the organic layers combined, dried over MgSO4, and reduced in vacuo affording the title compound as a brown solid (12.0 g, 93%) which was used 1 without further purification: m.p. 65-67 °C; H NMR (600 MHz, CDCl3) δ ppm 8.70-8.66 (1H, m), 8.64 (1H, d, J = 8.4), 8.40-8.35 (1H, m), 8.11 (1H, s, H10), 7.80 (1H, d, J = 8.4), 7.74-7.64 (3H, m), 7.63-7.58 13 (1H, m); C NMR (150 MHz, CDCl3) δ ppm 132.4 (C), 131.5 (C), 130.6 (CH), 130.5 (C), 129.9 (C), 128.2 (CH), 127.9 (CH), 127.6 (CH), 127.6 (CH), 127.4 (CH), 127.2 (CH), 123.0 (CH), 122.9 (CH), 121.9 (C); IR -1 (ATR) νmax/cm 3055 (m, Ar C-H), 3030 (m, Ar C-H), 1615 (m, Ar C=C), 1586 (s, Ar C=C), 1570 (m, Ar C=C), + + 1524 (w, Ar C=C), 1490 (s, Ar C=C); LRMS (GC/MS EI+) tr = 8.41 min, m/z 256 ([M] , 100 %), 176 ([M-Br] , 79 51); HRMS (ASAP+) m/z found 255.9887 (calc. for C14H9 Br = 255.9888).

9-Methoxyphenanthrene (18) 9-Methoxyphenanthrene 18 was prepared by a modification of an existing method,6 with updated characterisation provided. Sodium (1.38 g, 60.0 mmol) was added in small pieces to N2-degassed MeOH (25.0 mL, general laboratory grade) until dissolved. Pyridine (25 mL) was added, followed by vacuum-dried Copper(I) iodide (3.81 g, 20.0 mmol) to afford a green solution which was heated to 80 °C with stirring.

9-Bromophenanthrene 17 (5.14 g, 20.0 mmol) in pyridine (25 mL) was injected to the first solution dropwise over 10 min. The system was refluxed for 42 h.

The mixture was allowed to cool and poured into aqueous HCl (3 M, 250 mL) and stirred with EtOAc (75 mL) for 30 min. Solids were filtered off, the organic layer retained, and the aqueous layer extracted with EtOAc (3 x 75 mL). The organic layers were combined, washed with water (2 x 75 mL), dried over MgSO4 and reduced in vacuo to afford the title compound as an orange-brown oil which 1 solidified as a tan solid (4.09 g, 98%) upon drying: m.p. 89-93 °C; H NMR (600 MHz, CDCl3) δ ppm 8.66 (1H, d, J = 8.2), 8.59 (1H, d, J = 8.2), 8.37 (1H, dd, J = 8.2, 0.8), 7.78 (1H, dd, J = 7.7, 0.8), 7.68 (1H, ddd, J = 8.2, 7.1, 1.4), 7.62 (1H, ddd, J = 8.2, 7.0, 1.1), 7.54 (1H, ddd, J = 7.7, 7.1, 1.1), 7.50 (1H, ddd, J = 8.2, 10 13 7.0, 1.4), 6.99 (1H, s, H ), 4.10 (3H, s, OCH3); C NMR (150 MHz, CDCl3) δ ppm 153.7 (C), 133.1 (C), 131.4 (C), 127.5 (CH), 127.3 (CH), 127.0 (CH), 126.8 (C), 126.7 (C), 126.5 (CH), 124.4 (CH), 122.7 (CH), -1 3 122.7 (CH), 102.1 (CH), 55.6 (CH3); IR (ATR) νmax/cm 3058 (w, Ar C-H), 3008 (w, Ar C-H), 2964 (w, sp C-H), 2936 (w, sp3 C-H), 2837 (w, sp3 C-H), 1623 (s, Ar C=C), 1597 (s, Ar C=C), 1527 (w, Ar C=C), 1496 (m, 3 + Ar C=C), 1395 (s, sp C-H), 1199 (m, Ar C-O); LRMS (GC/MS EI+) tr = 8.23 min, m/z 208 ([M-H] , 95 %), + 165 ([M-CHOBr] ,100); HRMS (ASAP+) m/z found 209.0965 (calc. for C15H12O = 209.0966).

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9-Phenanthrol (19) 9-Phenanthrol 19 was prepared by a modification of an existing method,7 with updated characterisation provided. A solution of 9-methoxyphenanthrene 18 (14.4 mmol, 3.00 g) in acetic acid (200 mL) and aqueous HBr (47 %, 40 mL) was refluxed with stirring O/N (16 h). The mixture was allowed to cool and quenched with water (100 mL) to destroy any methyl bromide by-product, affording a yellow solution. The mixture was extracted with CH2Cl2 (3 x 100 mL). The combined organic layers were washed with brine (50 mL), dried over MgSO4 and reduced in vacuo to afford a purple-black solid.

The crude product was triturated in 3 mL CH2Cl2 and the suspension* purified using flash column chromatography (linear: 60% CH2Cl2/Petrol; SNAP 100) to afford the title compound as a beige solid 1 (2.12 g, 76%): m.p. 156-159 °C; H NMR (600 MHz, CDCl3) δ ppm 8.68 (1H, d, J = 8.4), 8.60 (1H, d, J = 8.2), 8.32 (1H, d, J = 8.2), 7.74-7.68 (2H, m), 7.65 (1H, ddd, J = 8.2, 7.1, 1.1), 7.56-7.48 (2H, m), 7.03 (1H, 10 13 s, H ), 5.29 (1H, s, OH); C NMR (150 MHz, CDCl3) δ ppm 149.5 (C), 132.8 (C), 131.7 (C), 127.4 (CH), 127.1 (CH), 126.9 (CH), 126. 9 (C), 126.6 (CH), 125.7 (C), 124.5 (CH), 122.9 (CH), 122.7 (CH), 122.5 (CH), -1 106.3 (CH); IR (ATR) νmax/cm 3236 (br., O-H), 3064 (w, Ar C-H), 3025 (w, Ar C-H), 1631 (s, Ar C=C), 1604

(s, Ar C=C), 1571 (m, Ar C=C), 1526 (m, Ar C=C), 1512 (w, Ar C=C), 1222 (s, Ar C-O); LRMS (GC/MS EI+) tr = 8.44 min, m/z 194 ([M]+, 100 %), 165 ([M-CHOBr]+, 97); HRMS (ASAP+) m/z found 194.0728 (calc. for 8 C14H10O = 194.0732). Consistent with literature.

*Reproducibility tips. The poorly soluble material is a by-product but serves as an excellent matrix for column chromatography. Do not use automated purification cartridges designed for wet loading: this material can block the top and cause system overpressures. Wet load cartridges designed for dry loading with the insert removed to trap the insoluble parts, then top the area up with sand prior to elution.

10-Bromo-9-phenanthrol (14) 10-Bromo-9-phenanthrol 14 was prepared by a modification of an existing method.9 9-Phenanthrol i 19 (1.79 g, 9.20 mmol) was suspended in anhydrous CH2Cl2 (20 mL) and HN Pr2 (93.9 mg, 130 μL, 928

μmol) added with stirring. Further anhydrous CH2Cl2 (30 mL) was added to afford a near-saturated yellow solution. A solution of N-Bromosuccinimide (1.64 g, 9.20 mmol) in anhydrous CH2Cl2 (90 mL) was added dropwise via syringe over 30 min at rt and the mixture stirred for 60 min. The solution was added to water (160 mL) and acidified to pH 1 with dropwise addition of conc. H2SO4. The mixture was extracted with CH2Cl2 (3 x 60 mL), the organic layers dried over MgSO4 and reduced in vacuo to afford an off-brown solid.

The crude product was purified using flash column chromatography (linear: 12.5% EtOAc/Hexane (as 25% of 50% mixture); ZIP 45) to afford the title compound as an off-white solid (1.97 g, 76%): 1 m.p. 125-130 °C; H NMR (600 MHz, CDCl3) δ ppm 8.65 (1H, d, J = 8.3), 8.62 (1H, d, J = 8.2), 8.38 (1H, dd, J = 8.2, 1.2), 8.14 (1H, dd, J = 8.3, 1.0), 7.72 (1H, ddd, J = 8.3, 7.0, 1.2), 7.66 (2H, app. dddd, J = 8.2, † 13 7.0, 2.9 , 1.0), 7.57 (1H, ddd, J = 8.3, 7.0, 1.2), 6.30 (1H, s, OH); C NMR (150 MHz, CDCl3) δ ppm 147.2 (C), 130.6 (C), 130.5 (C), 128.0 (CH), 128.0 (2 x CH), 127.5 (C), 127.2 (CH), 126.4 (CH), 125.1 (CH), 125.0 -1 (C), 123.4 (CH), 122.9 (CH), 103.8 (C); IR (ATR) νmax/cm 3475 (s, O-H), 3077 (w, Ar C-H), 3031 (w, Ar C- H), 1613 (w, Ar C=C), 1596 (s, Ar C=C), 1571 (w, Ar C=C). 1524 (w, Ar C=C), 1492 (s, Ar C=C), 1208 (br. s, + + Ar C-O); LRMS (GC/MS EI+) tr = 8.89 min, m/z 272 ([M-H] , 100 %), 165 ([M-CHOBr] , 92); HRMS (ASAP+) 79 m/z found 272.9917 (calc. for C14H10 Br = 272.9915).

†This is not a true coupling but the separation between two overlapping ddd in Hz.

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Phenanthryne Precursor: 10-(Trimethylsilyl)-9-phenanthryl Trifluoromethanesulfonate (15) 10-(Trimethylsilyl)-9-phenanthryl trifluoromethanesulfonate 15 was prepared by a modification of a previous method.9 10-Bromo-9-phenanthrol 14 (1.09 g, 4.00 mmol) was dissolved in anhydrous THF (36 mL) and cooled to -78 °C (dry ice/acetone bath). nBuLi (3.80 mL, 6.00 mmol, 1.6 M in hexanes) was added dropwise and the solution stirred for 15 min to afford a yellow solution. Me3SiCl (695 mg, 812 μL, 6.40 mmol) was added and the solution stirred at rt for 10 min, whereupon the colour faded. The solution was cooled to -78 °C and further nBuLi injected dropwise (5.00 mL, 8.00 mmol, 1.6M in hexanes) and stirred for 15 min. Further Me3SiCl (1.39 g, 1.64 mL, 12.8 mmol) was injected and the green-yellow solution stirred at rt O/N (16 h), whereafter the solution paled.

The solvent was removed directly in vacuo*, the orange residue dried for 15 min in vacuo and anhydrous Et2O (40.0 mL) was added with stirring for 5 min. Stirring was stopped and the insoluble white lithium salts allowed to settle before the solution was transferred by syringe to a second sealed and dried flask with a stirrer bar under nitrogen.

The orange solution was cooled to 0 °C and nBuLi added dropwise via syringe (2.65 mL, 4.20 mmol, 1.6 M in hexanes). The solution was stirred at rt for 4 h, during which it paled again. The solution was cooled to 0 °C and Tf2O added (1.47 g, 873 μL, 5.20 mmol) and stirred for 40 min.

The reaction was quenched with water (36 mL), aqueous NaHCO3 (sat., 4.0 mL) and the mixture extracted with Et2O (2 x 80 mL). The organic layers were dried over MgSO4 and reduced in vacuo to afford a pale-yellow oil. The crude product was purified using flash column chromatography (linear: hexane, ZIP 30) to afford the title compound as a colourless, transparent oil which solidified upon 1 refrigeration to a white low-melting solid (1.00g, 63%): m.p. <20 °C; H NMR (600 MHz, CDCl3) δ ppm 8.69 (1H, d, J = 8.2), 8.67 (1H, d, J = 8.2), 8.28 (1H, dd, J = 8.2, 1.1), 8.13 (1H,br. d, J = 8.3), 7.75 (1H, ddd, J = 8.2, 7.1, 1.3), 7.69 (2H, app. dddd, J = 8.3, 7.1, 3.2†, 1.3), 7.64 (1H, ddd, J = 8.3, 7.1, 1.3), 0.62 13 (9H, s); C NMR (150 MHz, CDCl3) δ ppm 148.1 (C), 134.8 (C), 132.9 (C), 130.7 (C), 130.2 (CH), 129.9 (C), 128.5 (CH), 127.5 (CH), 127.3 (CH), 126.8 (CH), 126.0 (C), 123.5 (CH), 122.9 (CH), 122.4 (CH), 118.9 (q, 1 19 -1 JC-F = 321, CF3), 2.4 (CH3); F NMR (376 MHz, CDCl3) δ ppm -72.4 (SO2CF3); IR (ATR) νmax/cm 3079 (w, Ar C-H), 3072 (w, Ar C-H), 2972 (w, sp3 C-H), 2958 (w, sp3 C-H), 1575 (m, Ar C=C), 1487 (m, Ar C=C), 1443 3 + (w, Ar C=C), 1396 (s, sp C-H) 1009 (s, S=O); LRMS (GC/MS EI+) tr = 8.95 min, m/z 398 ([M] , 15 %), 383 + + ([M-CH3] , 50), 266 ([M-Tf] , 100); HRMS (GC/MS EI+) m/z found 398.0610 (calc. for C18H17O3SF3Si = 398.0620).

*Reproducibility tips. Take care not to disturb the vessel during solvent exchange to prevent bumping. A DrySyn block set to 30 °C helps prevent the vessel cooling. An RBF of double volume, combined with a vacuum line, long and short needles, makes an efficient cold trap to collect the solvent.

†This is not a true coupling but the separation between two overlapping ddd in Hz.

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S5. 9,10-Phenanthryne Precursor: Test Reactions Attempted Synthesis of 10-(Trimethylsilyl)-9-phenanthryl Trifluoromethanesulfonate (15) by the Hexamethyldisilazane Approach The following procedure was adapted from that towards 13d,10 itself taken from the general 2002 method.11 Note: specific temperature control and durations for the key retro-Brook step herein matched exactly to the 2002 method.

10-Bromo-9-phenanthrol 14 (273 mg, 1.00 mmol) was dissolved in anhydrous THF (4.0 mL) and hexamethyldisilazane (250 mg, 323 μL, 1.55 mmol) was added. The mixture was refluxed for 3 h and volatiles were removed in vacuo. The material was re-dissolved in anhydrous THF (4.0 mL) and n cooled to -100 °C (N2(l)/acetone bath) before the addition of BuLi (1.80 mL, 1.08 mmol, 1.6 M/hexanes), whereupon the solution browned. The mixture was stirred at -78 °C (dry ice/acetone bath) for 20 min. The system was then cooled to -100 °C before the injection of Tf2O (367 mg, 218 μL,

1.30 mmol) and the solution stirred for 20 min at -78 °C. The reaction was quenched with NaHCO3

(sat. aq, 10 mL). The mixture was extracted with Et2O (3 x 10 mL). The organic layers were washed with brine (2 x 5.0 mL), dried over MgSO4 and reduced in vacuo to afford a complex mixture of aromatics.

Spectroscopic analysis: The 1H NMR Stack plot on the next page (silyl region shown in the full spectrum in S11) shows the progress of this attempt. The first row shows the 10-bromo-9- phenanthrol precursor, with a clear 9-OH singlet just above 6.00 ppm. Although our HMDS reflux is longer than the original method, the crude aliquot (second row) shows that the O-silylation is successful: the 9-OH signal disappears, trimethylsilyl signals appear at around 0.40 ppm (ESI S11) and the aromatic signals shift slightly.

The third row shows a crude reaction mixture after the completion of the above reaction protocol, with the same durations and temperature control as used in the original work. A broad 9-OH signal at 6.33 ppm appears despite attempted triflation – an O-trimethylsilyl group must have blocked this position from triflation then been hydrolyzed, without transfer – along with some singlets around 7.00 ppm that are close to the 10-H position in 9-phenanthrol, although not identical. The aromatic signals appear larger in proportion to these two signals and the signal at 0.40 ppm remains in the middle of a more complicated silyl region in the spectrum (ESI S11). This suggests that the nBuLi may have successfully driven halogen-metal exchange, but a large amount of trimethylsilyl has not successfully undergone retro-Brook, hence the observed 10-H peak from subsequent protonation. Crucially, comparing this spectrum to the isolated product from the previous method (bottom row) shows that the target material is not present, with the silyl groups in that material being around 0.60 ppm rather than 0.40 ppm. The aromatic region is also more complicated, possibly suggesting that some materials with more than one phenanthrene ring form: indeed, other than 10-bromo-9- phenanthrene starting material, no signals match our precursory compounds.

To try to force the retro-Brook to occur, we repeated the method, allowing for a 4h stir at room temperature after the addition of nBuLi at -100 °C (fourth row). The aromatic region and especially the silyl region of the spectrum are again complicated. The 10-H signal has shifted and the 9-OH has sharpened. No target material is again observed but a purification attempt isolated an impure fraction of starting material (fifth row), suggesting that O-desilylation by nBuLi is competitive with halogen-metal exchange at room temperature, consuming the 1.08 equivalents. The previous work indeed states this as a reason for the temperature control and we also use such steps to follow their original method for the 9,10-phenanthryne precursor, drawing on this for the bisbenzyne

S-117 Electronic Supplementary Information mechanistic study (S7). We do not observe C-desilylation by nBuLi in our reactions and therefore, were the retro-Brook step to be successful, these products would be stable to these conditions.

Overall, we observe that HMDS silylates on oxygen as expected and that halogen-metal exchange is partially successful, but in the case of the 9,10-phenanthyne precursor these reactions proceed without successful retro-Brook transfer.

Commentary & discussion: The one-pot retro-Brook method published by Pérez and Guitián in 2002 works well for a range of oSAT derivatives, which we regularly use in our research; however we could not repeat it for 9,10-phenanthryne precursor 15.11 We believe the negligible aromatic character of these positions, in line with our model, explains this singular inconsistency.

As previously described, the 9,10-phenanthryne precursor 15 can be reliably made by our gram- scale modification of the approach originally reported by Pérez and Guitián in 2000.9 The 2000 paper contained NMR spectroscopic and HRMS data for 15 but no melting point or physical description was provided.9 Despite being listed in the original 2002 article,10 no spectroscopic data was provided therein for 15, only a melting point for a white solid (94 ˚C). Using our method (ESI S3), we obtained 15 as a liquid and provide full spectroscopic characterization: our finding is consistent with the physical properties reported by Idris et al. who repeated the 2000 method and also report the product as an oil.12

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It is worth noting that several studies using the 9,10-phenanthryne precursor that cite the 2002 paper in the main text, or for other aryne precursor syntheses, actually cite the 2000 method (sometimes the earlier 1999 method13) in the supporting information.14–18

In addition, an independent report from Ikawa and Akai also attempted a retro-Brook synthesis of 15 from 10-bromo-9-phenanthol 14 using triethylamine to deprotonate the phenolic position, O- silylation with chlorotrimethylsilane then nBuLi to drive halogen-metal transfer and a subsequent quench.19 Three different quenches were reported: (i) with ammonium chloride (to restore the phenol), (ii) with triflic anhydride (to triflate the oxygen) or (iii) with additional chlorotrimethylsilane (to resilylate the oxygen). For the synthesis of a 2-naphthyl precursor, all three quenches worked; however, for the 9,10-phenanthryne precursor, the first two quenches failed and only the chlorotrimethylsilane quench worked to give the doubly silylated product in 72% yield. Although the formation of the desired O,C-disilylated product from the final quench was attributed to a successful retro-Brook reaction in the paper, we believe this cannot be the case: C-silylation is not observed at all from the ammonium chloride or triflation experiments, when in the latter case at least these products should be stable to the work-up conditions employed.19 When the retro-Brook fails, the ortho-position is still lithiated and therefore the succesful formation of the doubly-silylated 9-phenanthrol-derived product can only be due to C-silylation at quench, rather than O-silylation after a successful retro-Brook transfer as reported. This is in line with our model and experimental findings.

1,4-Dihydro-1,4-epoxytriphenylene (20) To a solution of 10-(trimethylsilyl)phenanthren-9-yl trifluoromethanesulfonate (49.2 mg, 124 µmol) in anhydrous acetonitrile (824 µl) was added furan (42.0 mg, 618 µmol) and caesium fluoride (37.5 mg, 247 µmol). The mixture was stirred at 40 °C for 16 h. The solvent was removed in vacuo. The crude product was dissolved in Et2O (1.0 mL) and filtered over a silica plug, washed with Et2O (3 x 1.0 mL). The solvent was removed in vacuo to afford the title compound as a colourless solid (31.3 1 mg, 128 µmol, quant.): H NMR (400 MHz, CDCl3) δ ppm 8.77-8.71 (2H, m), 7.99-7.93 (2H, m), 7.69-7.62 (4H, m), 7. 30 (2H, s), 6.41 (2H, s).

1H NMR data are consistent with published data.20

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S6. Bisbenzyne Precursor: Preliminary Synthetic Experimental Procedures 2,5-Dibromo-3,6-dimethylhydroquinone (9)

To a solution of 2,5-dimethylbenzoquinone 21 (409 mg, 3.00 mmol) in anhydrous Et2O (15 mL) at 0 °C was added bromine (959 mg, 310 µL, 6.00 mmol) dropwise over 10 min. The solution was stirred at rt for 72 h, cooled to 0 °C and conc. H2SO4 added (589 mg, 320 µL, 6.00 mmol) to afford a black solution of the quinhydrone. H2O (10 mL) was added, followed by Na2S2O4 (4.27 g, 22.5 mmol) and the mixture stirred for 2 h to reduce the benzoquinone present. The organic layer was separated, reduced in vacuo and the residue extracted with CH2Cl2 (2 x 25 mL). The organic layers were washed with brine (25 mL), dried over MgSO4 and reduced in vacuo to afford the title compound as a white solid (820 mg, 92 %) which was stored in the refrigerator under nitrogen: m.p. oxidizes on heating; 1H 13 NMR (400 MHz, CDCl3) δ ppm 5.41 (s, 2H), 2.39 (s, 6H); C NMR (100 MHz, CDCl3) δ ppm 144.3 (C), -1 122.1 (C), 113.5 (C), 17.1 (CH3); IR (ATR) νmax/cm 3410 (w, ArO-H), 2922 (w, C-H), 1655 (m, Ar C=C), + + 1238 (m, Ar C-O); LRMS (GC/MS EI+) tr = 9.16 min, m/z 294 ([M] , 100 %), 266 ([M-CH2O] , 17), 215 ([M- Br]+, 37).

*Reproducibility tips. This preparation is operationally simple, but solutions of this compound are prone to oxidation to the 2,5-dibromo-3,6-dimethylbenzoquinone, so ensure the compound is dry and under nitrogen when stored in the refrigerator. Signals at 27.5 (CH2) and 39.2 (CH) ppm in the 13C NMR likely correspond to radical mono- and dibrominations on the methyl groups by this benzoquinone: the signals do not match known solvents and although no significant 1H proton signals match these signals – although minor singlets at 6.13 and 4.46 ppm are similar to α,α- dibromotoluene and benzyl bromide respectively – the intensity of the two extra signals in the 13C NMR suggests ongoing changes in the NMR tube.

2,5-Dibromo-3,6-dimethylbenzoquinone (22) The title compound can be formed from 2,5-dibromo-3,6-dimethylhydroquinone 9 by aerial oxidation, can be reduced by stirring in a mixture of Et2O and aqueous Na2S2O4, and can be separated in small amounts by flash column chromatography (5% EtOAc/Petrol). An analytical 1 13 sample was characterised: H NMR (400 MHz, CDCl3) δ ppm 2.30 (s, 6H); C NMR (100 MHz, CDCl3) δ -1 ppm 176.9 (C), 145.7 (C), 135.9 (C), 18.1 (CH3); IR (ATR) νmax/cm 1656 (s, C=O), 1603 (m, Ar C=C), 1260 + + + (s, C-H); LRMS (GC/MS EI+) tr = 8.77 min, m/z 292 ([M] , 82 %), 266 ([M-CO] , 100), 213 ([M-Br] , 38).

*Reproducibility tips. Although this compound is already the oxidised form, it appears unstable to itself. A minor signal at 4.12 ppm is observed in the 1H NMR, similar to commercial 2- bromomethylacrolein (structurally similar to half of the benzoquinone α-brominated). This further 13 suggests radical bromination is taking place on the methyl groups; the C NMR signal at 30.9 (CH2) ppm is also consistent with this.

2,5-Dibromo-3,6-di(trimethylsilyloxy)xylene (13v) The title compound was synthesised by an adaptation of a literature method for 1,4-dibromo-2,5- di(trimethylsilyl)benzene.21 To a solution of 2,5-dibromo-3,6-dimethylhydroquinone 9 (592 mg, 2.00 mmol) in anhydrous toluene (8 mL) in a sealed vial was added pyridine (660 µL) and chlorotrimethylsilane (1.304 g, 12.0 mmol, 1.52 mL). The solution was heated to reflux for 24 h and reduced in vacuo to 2 mL, whereupon precipitate of pyridine hydrochloride formed. The precipitate was removed by filtration and the filtrate reduced in vacuo to afford the target as off-white needles (789 mg, 90%) which were stored in the refrigerator under nitrogen and used without purification: 1 13 m.p. oxidizes on heating; H NMR (600 MHz, CDCl3) δ ppm 2.32 (s, 6H), 0.30 (s, 18H); C NMR (150 MHz,

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CDCl3) δ ppm 146.2 (C), 127.9 (C), 118.1 (C), 19.3 (CH3), 1.2 (CH3); LRMS (GC/MS EI+) tr = 10.89 min, + + + m/z 438 ([M] , 100 %), 425 ([M-CH3] , 28), 344 ([M-Br] , 95).

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S7. Bisbenzyne Precursor: Unsuccessful Adaptations of Other Methods Attempted Synthesis of 2,5-di(trimethylsilyl)-3,6-di(trimethylsilyloxy)xylene: Double Sodiation Approach from 2,5-dibromo-3,6-di(trimethylsilyloxy)xylene (13v) The following method is an adaptation of the method for 1,4-di(trimethylsilyl)-2,5- di(trimethylsilyloxy)benzene.21

To a solution of 2,5-dibromo-3,6-di(trimethylsilyl)xylene 13v (110 mg, 250 µmol) in anhydrous toluene (1.2 mL) in a sealed tube was added sodium metal (25.7 mg, 1.12 mmol) and the system heated to reflux, whereupon the system blackened. The solution was allowed to cool and chlorotrimethylsilane (57.1 mg, 70 µL, 0.525 mmol) was injected via syringe to afford a blue-black precipitate in a straw-coloured solution and the mixture stirred at reflux for 16 h thereafter. The supernatant was removed via syringe and reduced in vacuo to afford a tan solid insoluble in CDCl3 and therefore inconsistent with target product.

Attempted Synthesis of 1,4-(2,5-dimethyl-3,6-di(trimethylsilyl)phenylene) ditrifluoromethylsulfonate (12a): Hexamethyldisilazane Approach from 2,5-dibromo-3,6- dimethylhydroquinone (9) The following method is an adaptation of the method for 5-(trimethylsilyl)benzo[d][1,3]dioxol-6-yl trifluoromethanesulfonate 13a.10

To a solution of 2,5-dibromo-3,6-dimethylhydroquinone 9 (59.2 mg, 200 µmol) in anhydrous THF (1.0 mL) in a sealed tube was added hexamethyldisilazane (136 mg, 180 µL, 840 µmol) and the mixture refluxed for 3 h. The solvent was reduced in vacuo and anhydrous THF (1.0 mL) was added. n The system was cooled to -94 °C (N2(l)/acetone), BuLi (275 µL, 440 µmol, 1.6 M in hexanes) was injected, and stirred for 2 h at -78 °C thereafter. Tf2O (155 mg, 923 µL, 550 µmol) was injected and the mixture stirred for 20 min.

The reaction mixture was quenched by the addition of aqueous NaHCO3 (1.0 M, 1.0 mL) and being allowed to warm up to room temperature gradually. The mixture was extracted with Et2O (3 x 10 mL). The organic layers were washed with brine (2 x 10 mL), dried over MgSO4 and reduced in vacuo to afford a pale-yellow oil that darkened gradually upon exposure to air, in which the target material was not identified.

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S8. Bisbenzyne Precursor: Synthetic Mechanistic Test NB: This protocol, an adaptation of the phenanthryne precursor synthesis, in its approach and proportions, involves a series of temperature changes and injections of different volumes of the same reagent liquids/solutions.

First O-silylation. A solution of 2,5-dibromo-3,6-dimethylhydroquinone 9 (592 mg, 2.00 mmol) in anhydrous THF (18 mL) was cooled to -78 °C. nBuLi (1.20 mL, 3.00 mmol, 2.5 M in hexanes) was added dropwise over 10 min and the solution stirred for 15 min to afford a yellow solution. Chlorotrimethylsilane (3.48 mg, 410 μL, 3.20 mmol) was injected and solution stirred for 10 min at rt until the colour almost disappeared. An aliquot (100 μL) was taken at this point and quenched for analysis.

Second O-silylation. The system was cooled to -78 °C again and further nBuLi (1.20 mL, 3.00 mmol, 2.5 M in hexanes) was added dropwise over 10 min and the reaction stirred for 15 min to afford a deep-yellow solution. Transient precipitates were observed which re-dissolved within the stated time. Further chlorotrimethylsilane (3.48 mg, 410 μL, 3.20 mmol) was injected and the solution stirred for 10 min at rt until the colour faded again. An aliquot (100 μL) was taken at this point and quenched for analysis.

First metal-halogen exchange. The system was cooled to -78 °C for a third time and a larger portion of nBuLi (2.40 mL, 6.00 mmol, 2.5 M in hexanes) was added dropwise over 10 min and the reaction stirred for 15 min to afford a pale-brown solution. A larger portion of chlorotrimethylsilane (7.96 mg, 810 μL, 6.40 mmol) was injected and the solution stirred at rt over 20 h to afford a colourless solution on top of colourless precipitate. An aliquot (100 μL) was taken at this point and quenched for analysis.

Solvent exchange. Without removing the seal, the solvent was evaporated via a cannula and condensed into trap cooled to -78 °C. The system was flushed with nitrogen followed by three evacuation and flush cycles. Anhydrous Et2O (20 mL) was added to the beige residue with stirring to afford a suspension of white solids in an olive-green solution. The solution was transferred via syringe into a dried, nitrogen-flushed flask charged with a stirrer bar.

Second metal-halogen exchange. The solution was cooled to -78 °C and a larger portion of nBuLi (2.40 mL, 6.00 mmol, 2.5 M in hexanes) was added dropwise over 10 min and the reaction stirred for 30 min. An aliquot (100 μL) was taken at this point and quenched for analysis.

O-Desilylation, triflation and completion. To ensure total oxygen desilylation prior to triflation, a further portion of nBuLi (2.40 mL, 6.00 mmol, 2.5 M in hexanes) was added dropwise over 10 min, and the reaction stirred for 4 h at rt. Transient precipitates were again observed and the colour varies through browns and yellows. The solution was cooled to 0 °C and Tf2O (1.47 g, 880 μL, 5.20 mmol) was injected in one portion. The mixture was stirred for 40 min.

The mixture was quenched with aqueous NaHCO3 (0.1 M, 20 mL) and extracted with Et2O (2 x 40 mL).

The organic layers were dried over MgSO4 and reduced in vacuo to afford a reddish-waxy solid, from which an analytical crude sample was taken.

Analytical aliquots. All aliquots (100 μL) were shaken with 500 μL CDCl3 and 500 μL H2O, and the organic layer analysed directly by 1H-NMR, 19F-NMR (where appropriate) and GC/MS thereafter.

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Purification attempt. Purification was attempted by flash column chromatography (SiO2, 25%

CH2Cl2/hexane) to afford a red solution that gave a vivid red-waxy solid on drying. This was determined by the methyl signals in the 1H NMR to be 80 % oxidised to the benzoquinone with the loss of triflate groups and 20 % hydroquinone-like signals, including the target material (313 mg, 41% (benzoquinone)).

2,5-dimethyl-3,6-di(trimethylsilyl)benzoquinone (23)

1 H NMR (400 MHz, CDCl3) δ ppm 2.09 (s, 6H), 0.29 (s, 18H); LRMS (GC/MS EI+) tr = 8.86 min, m/z 280 + + + + ([M] , 14 %), 265 ([M-CH3] , 52), 250 ([M-(CH3)2] , 26), 191 ([M-Me3SiOH] , 34)

The presence of small amounts of the target 1,4-(2,5-dimethyl-3,6-di(trimethylsilyl)phenylene) ditrifluoromethylsulfonate 12a was determined by GC/MS: LRMS (GC/MS EI+) tr = 10.02 min, m/z 531 + + + ([M-CH3] , 21%), 381 ([M-Me3SiOTf] , 8 %), 263 ([M-Me3SiOTf-Me3Si+CH3] , 31%), 251 ([M-Me3SiOTf- + Me3Si] , 29%),

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S9. Bisbenzyne Precursor: Mechanistic Discussion/Analysis In order to synthesize 15 and garner further mechanistic insights, a synthetic route was proposed that drew from both our model and the previous synthesis of 9,10-phenanthryne n precursor 8. This involved the use of BuLi and SiMe3Cl in separate steps for each side of the molecule, followed by triflation (Supplementary Info S7). The method envisaged: two sets of O-deprotonation and O-silylation (‘1st O-silylation’/’2nd O-silylation’); a first halogen-lithium st exchange and trapping with SiMe3Cl to effect C-silylation (‘1 halogen-metal exchange’); solvent exchange, solution transfer then a second halogen-lithium exchange towards spontaneous retro-Brook C-silylation (‘2nd halogen-metal exchange’); and finally double O- desilylation, triflation and workup. To follow the transformation, an aliquot was taken after each of the steps and analysed by GC/MS (Figure 3, Supplementary Information S15) and 1H- NMR spectroscopy (Supplementary Information S11, shifted by reaction solvent). These steps maintained the reagent proportions used for each side to ensure a fair comparison with successful mono-benzyne oSAT syntheses, although due to the solvent exchange step, an internal standard would be unreliable and so was not used. The first aliquot shows that the O-silylations proceed in a straightforward manner, with the O,O’-disilylated material C (13v) predominating even after the first step, from the 1.5 equivalents of nBuLi present (Scheme 3). Starting material A (9) and mono-silylated B are also present. The second aliquot after the second O-silylation cycle shows some early halogen-metal exchange product D – with the lithium centres quenched at work-up – as a result of the extra nBuLi present at the start of this stage. However, unexpected O- desilylations are also observed for the singly C-lithiated (S and T, red) and even C,C’- dilithiated V (blue), even though SiMe3Cl, exceeding the amount of organolithium, is present. This is supported by a downfield-shifted broad phenolic signal, downfield shift of the aryl methyl signals and new silyl methyl signals next to those for mono- and di-silylated B and C in the 1H NMR. A quinone species AQ (22) from aerial oxidation of A, B or C is also observed, but this is likely to have occurred in the GC vial post work-up, given the absence of other oxidized species in most aliquots. n After a further injection of double BuLi and double SiMe3Cl with an overnight room temperature stir to maximize silylation at carbon, C-silylated products E (10, from D) and G (11) –unexpected C,C’-dilithiated species DD, which predominates – are observed, along with products U and W where a O-silyl group is missing. The persistence of DD suggests that the retro-Brook is not viable on the first side as predicted by our model, but that the presence G (11) shows that the retro-Brook proceeds on the second side. The failure of the first retro- Brook was confirmed by a separate test on pure 13v where a single C-silylation was observed under sufficient reagent to functionalize both sides, consistent with direct C-silylation rather than retro-Brook transfer (Supplementary Info S9). Observed W can only be formed from F (or possibly the C-silylation of U) but G (11) is formed in turn from F. F and G (11) have identical mass spectra as isomers, but the presence of two large phenolic signals in the 1H NMR means that C,C’,O-isomer G (11) must be present alongside U. The retro-Brook reaction on the second side is therefore successful, in line with our mechanistic model. Tetrasilylated H is also detected; whether the fourth silylation is on oxygen after a retro-Brook on or carbon before it can occur is unknown, but given the predominance of G (11) from a unimolecular

S-125 Electronic Supplementary Information process and this bimolecular process would be expected to be slower, it is likely to be the former case. n After exchanging the solvent from THF to Et2O and the addition of a further amount of BuLi – crucially with no further silane added thereafter – tetrasilylated product H predominates with F and G (11) also present. E from the third aliquot has undergone halogen-metal exchange to afford F but the retro-Brook to G has not completed in the 30 min reaction time, compared to the overnight step at room temperature before. It is possible, due to the O- desilylations observed earlier, that intermolecular silyl transfers also take place, which would also afford G (11) from H. Unfortunately, after work-up, a quinone species KQ (23) predominated, although O,O’- desilylated species I and later triflated species J and target K (12a) are observed. It is almost certain, that this quinone is the oxidation product from all three of these species with the loss of the triflate groups after work-up, although the C,C’-disilylation is therefore confirmed to be successful. Triflation products X, Y and Z are also present from unsuccessful silyl transfers to carbon, with the presence of many triflate positions confirmed by 19F NMR.

By selecting appropriately stabilising 1,4-substituents, in place of di-Me, this method should facilitate the synthesis of previously elusive functionalized bisaryne precursors.

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Scheme S1 – Putative mechanism of the formation of bisbenzyne precursor 12a (K) from dibromodimethylhydroquinone 9 (A).

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Figure S1 - Stack plot of GC/MS aliquots from the formation of bisxylyne precursor between 6.5 and 11.5 min. Letters correspond to the species in Scheme S1.

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S10. Bisbenzyne Precursor: Mechanistic Retro-Brook Validation Test on 2,5- dibromo-3,6-di(trimethylsilyloxy)xylene 13v To a solution of 2,5-dibromo-3,6-di(trimethylsilyl)xylene 13v (220 mg, 500 μmol) in anhydrous THF n (2.5 mL) in a sealed tube at -94 °C (N2(l)/acetone) was added BuLi (667 μL, 1.10 mmo;, 1.65 in hexanes) and the mixture stirred at -78 °C for 20 min. The mixture was cooled to -94 °C, Tf2O (353 mg, 210 μL, 1.25 mmol) was injected and the reaction stirred at -78 °C for 20 min.

The mixture was quenched with aqueous NaHCO3 (1.0 M, 2.5 mL) and being allowed to warm up to room temperature gradually. The mixture was extracted with Et2O (3 x 25 mL). The organic layers were washed with brine (2 x 25 mL), dried over MgSO4 and reduced in vacuo to afford a crude orange solid (480 mg).

Analysis of the crude by GC/MS revealed the predominance of the precursor 2,5-dibromo-3,6- dimethylhydroquinone (data as above) and singly C-silylated 2-bromo-3,6-dimethyl-5- + (trimethylsilyl)benzoquinone: LRMS (GC/MS EI+) tr = 8.98 min, m/z 271 ([M-CH3] , 100 %).

The eventual target bisbenzyne precursor 1,4-(2,5-dimethyl-3,6-di(trimethylsilyl)phenylene) ditrifluoromethylsulfonate was not observed at 10.02 min, nor its oxidation product 2,5-dimethyl-3,6- di(trimethylsilyl)benzoquinone at 8.87 min.

---

The predominance of O,O’-doubly desilylated starting material is consistent with the failure of the retro-Brook reaction in the position tested, as given how facile this reaction is in amenable substrates, singly C-silylated products would be expected to predominate. As such, intermolecular abstraction of O-trimethylsilyl groups likely results in the C-silylation observed, but the wide array of minor products suggest that other reactions compete.

Were the first C-silylation to take place via a retro-Brook reaction, the bisbenzyne precursor and the related benzoquinone oxidation product would be expected to predominate, as the second bromine position would undergo metal-halogen exchange and this second retro-Brook is even more favourable according to our models. As no C,C’-disilylated products are observed, desilylated starting material predominates and the first silylation appears incomplete under conditions previously used to drive a retro-Brook reaction, it is reasonable to conclude that silyl groups have only been abstracted from the oxygens or lost upon their oxidation, so that the retro-Brook reaction was therefore not successful.

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S11. Bisbenzyne Precursor: Isolation Tests of Key Intermediates 2,5-Di(trimethylsilyl)-3,6-di(trimethylsilyloxy)xylene (H) from 2,5-dibromo-3,6- di(trimethylsilyloxy)xylene (13v) A solution of 2,5-dibromo-3,6-di(trimethylsiloxy)xylene (13v) (329 mg, 747 μmol) in anhydrous THF (5 mL) was cooled to -78 °C. nBuLi (448 μl, 1.12 mmol, 2.5 M in hexanes) was added and the solution stirred for 15 min. Chlorotrimethylsilane (122 mg, 142 μl, 1.12 mmol) was then added and the solution allowed to warm to rt over 30 min. The solution was then cooled to -78 °C again and further nBuLi (898 μl, 2.24 mmol, 2.5 M in hexanes) was added, then the solution was stirred for 30 min. Further chlorotrimethylsilane (244 mg, 284 μl, 2.24 mmol) was added and the solution allowed to warm to rt over 30 min. The reaction mixture was quenched with diluted HCl (1 M, 5 ml) and the mixture then extracted with Et2O (3 x 10 ml). The combined organic extracts were dried over MgSO4 and reduced in vacuo.

The crude product was purified using flash column chromatography (n-hexane) to afford the title 1 compound as a colourless solid (181 mg, 57 %): m.p. 34-35 °C; H NMR (400 MHz, CDCl3) δ ppm 2.23 13 (s, 6H, ArCH3), 0.37 (s, 18H, ArOSiMe3), 0.20 (s, 18H, ArSiMe3); C NMR (100 MHz, CDCl3) δ ppm 153.4, -1 3 3 3 131.8, 131.7, 19.7, 3.0, 1.5; IR (ATR) νmax/cm 2977 (w, sp C-H), 2953 (w, sp C-H), 2904 (w, sp C-H), 3 1467 (w, Ar C=C), 1454 (w, Ar C=C), 1355 (s, sp C-H), 1254 (s, Ar C-O); LRMS (GC/MS EI+) tr = 10.82 min, m/z 426 ([M]+, 50 %).

2,5-Di(trimethylsilyl)-3,6-dimethylbenzoquinone (23) from 2,5-dibromo-3,6- di(trimethylsilyloxy)xylene (13v) A solution of 2,5-dibromo-3,6-di(trimethylsiloxy)xylene (275 mg, 625 μmol) in anhydrous THF (5.6 mL) was cooled to -78 °C. nBuLi (750 μl, 1.87 mmol, 2.5 M in hexanes) was added and the solution stirred for 25 min. Chlorotrimethylsilane (203 mg, 237 μl, 1.87 mmol) was then added and the solution allowed to warm to rt over 80 min. The solution was again cooled to -78 °C, further nBuLi (750 μl, 1.87 mmol, 2.5 M in hexanes) was added and the solution was stirred for 30 min. Further chlorotrimethylsilane (203 mg, 237 μl, 1.87 mmol) was added and the solution allowed to warm to rt. A third portion of nBuLi (750 μl, 1.87 mmol, 2.5 M in hexanes) was added and the reaction mixture was stirred at rt for 19 h.

The reaction mixture was quenched with diluted HCl (1 M, 5 ml), extracted with Et2O (3 x 10 ml), then combined organic extracts dried (MgSO4) and reduced in vacuo. The crude product was purified using flash column chromatography (n-hexane/ EtOAc) to yield the title compound as a red solid 1 (98.5 mg, 351 μmol, 56 %): m.p. 75-77 °C; H NMR (400 MHz, CDCl3) δ ppm 2.11 (s, 6H), 0.30 (s, 18H); 13 -1 3 C NMR (100 MHz, CDCl3) δ ppm 191.4, 154.3, 146.2, 15.8, 1.4; IR (ATR) νmax/cm 2955 (w, sp C-H), 3 3 3 2902 (w, sp C-H), 1634 (s, Ar C=O), 1580 (m, Ar C=C), 1372 (w, sp C-H),1250 (s, sp C-H); LRMS (GC/MS + + + + EI+) tr = 8.86 min, m/z 280 ([M] , 14 %), 265 ([M-CH3] , 52), 250 ([M-(CH3)2] , 26), 191 ([M-Me3SiOH] , 34) 2,5-Di(trimethylsilyl)-3,6-dimethylhydroquinone (I) from 2,5-di(trimethylsilyl)-3,6- dimethylbenzoquinone (23) A suspension of 2,5-di(trimethylsilyl)-3,6-dimethylbenzoquinone (23) (200 mg, 713 μmol) and 10%

Pd/C (20 mg) in anhydrous THF (3 mL) was stirred for 1 h at rt under an atmosphere of H2 (1 atm). Insolubles were then filtered from solution and the filtrate concentrated in vacuo to afford the title compound as a transparent, colourless and air-sensitive oil (201 mg, quant.): 1H NMR (400 MHz, 13 CDCl3) δ ppm 4.63 (s, 2H, ArOH), 2.26 (s, 6H, ArMe), 0.41 (s, 18H, ArSiMe3); C NMR (100 MHz, CDCl3) δ + + ppm 152.8, 126.6, 126.3. 16.3, 2.7; LRMS (GC/MS EI+) tr = 9.20 min, m/z 282 ([M] , 28 %), 267 ([M-CH3] , + 24), 266 ([M-H-CH3] , 47)

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S12. Bisbenzyne Precursor: Optimized Synthesis of Precursor and Diels-Alder Test Optimized synthesis of 2,5-Di(trimethylsilyl)-3,6-di(trimethylsilyloxy)xylene (H) from 2,5- dibromo-3,6-dimethylhydroquinone (9) A solution of 2,5-Dibromo-3,6-dibromohydroquinone (2.00 g, 6.76 mmol) and hexamethyldisilazane (2.18 g, 2.81 ml, 13.5 mmol) in THF (10 ml) was heated to reflux for 2 h. The solvent was removed in vacuo to afford 2,5-dibromo-3,6-bis(trimethylsilyloxy)xylene (13v) as a tan solid (2.98 g, 6.76 mmol, >99 %), matching the previous characterization.

A solution of 13v (2.98 g, 6.76 mmol) in anhydrous THF (45 ml) was cooled to -78 °C. nBuLi (4.06 ml, 10.1 mmol, 2.5 M in hexanes) and the solution was stirred for 10 min. Chlorotrimethylsilane (1.10 g, 1.29 ml, 10.1 mmol) was then added and the solution allowed to warm to rt over 10 min. The solution was then cooled to -78 °C and further nBuLi (8.11 ml, 20.3 mmol, 2.5 M in hexanes) was added, then the solution was stirred for 15 min. Further chlorotrimethylsilane (2.20 g, 2.57 ml, 20.3 mmol) was added and the solution allowed to warm to rt over 60 min. The reaction mixture was quenched with diluted HCl (1 M, 30 ml) and the mixture then extracted with Et2O (3 x 30 ml). The combined organic extracts were dried over MgSO4 and the solvent removed in vacuo. The crude product was purified using flash column chromatography (n-hexane) to yield the title compound as a colourless solid

(2.13 g, 4.99 mmol, 74 %), matching the previous characterization (Rf (2:1/ n-hexane:EtOAc) = 0.78). 9,10-Dimethyl-1,4,5,8-tetrahydro-1,4:5,8-diepoxyanthracene (24) from 2,5-di(trimethylsilyl)- 3,6-di(trimethylsilyloxy)xylene (H) and furan A Schlenk flask charged with CsF (290 mg, 1.91 mmol) was flame dried under vacuum and backfilled with argon, followed by two more vacuum and backfilling cycles. Anhydrous MeCN (2.13 ml, 0.1 M), NfF (193 mg, 115 μl, 639 μmol), furan (145 mg, 155 μl, 2.13 mmol) and 2,5-Di(trimethylsilyl)-3,6- di(trimethylsilyloxy)xylene (H)) (90.8 mg, 213 μmol) were added, and the reaction was stirred at rt for 6 d. The solvent was removed in vacuo and the crude product was purified using flash column chromatography (n-hexane/ EtOAc) to yield the title compound as a colourless solid as mixture of 1 syn- and anti-isomers (6.42 mg, 26.9 μmol, 13 %, 1:1): H NMR (400 MHz, CDCl3) δ ppm 7.03 (t, J 1.0, 4Hsyn), 7.02 (t, J 1.0, 4Hanti), 5.70 (t, J 1.0, 4H), 2.25 (s, 6Hanti), 2.25 (s, 6Hsyn). Consistent with literature.22

Recrystallisation by vapour diffusion of n-hexane into a CH2Cl2 solution yielded the title compound enriched in the anti-isomer as a colourless solid (14:1): m.p. 219-220 °C (dec.); 1H NMR (600 MHz, syn anti anti syn CDCl3) δ ppm 7.03 (s, J 1.0, 4H ), 7.02 (s, J 1.0, 4H ), 5.70 (s, J 1.0, 4H), 2.25 (s, 6H ), 2.25 (s, 6H ); 13 anti syn syn anti C NMR (150 MHz, CDCl3) δ ppm 146.6 (C ), 146.6 (C ) 143.5 (C ), 143.4 (C ), 81.3, 14.7; IR (ATR) -1 3 3 2 3 νmax/cm 3005 (w, sp C-H) , 2924 (w, sp C-H), 1739 (w, sp CAr-H ), 1488 (w, Ar C=C), 1385 (s, sp C-H), 1279 (s, Ar C-O).

Reproducibility tips: Although this can also be successfully performed with TBAT, the purification of the product is challenging, as is yield determination by NMR. It may be the case that other fluoride sources allow for greater yields, but the use of caesium fluoride here allows us the cleanest demonstration of a successful reaction. The development of other bisbenzynes and the screening of suitable fluoride sources for each would need specific conditions taking the substituent groups into effect in analysis and purification. As such, this will be investigated in future work.

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