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New Reactions with Allyl- and Allenylboron Reagents !" # $ %&'( '&)&& * +, -" +" #".'/) #" 0 # ) # # + " " " ) # 123123 " " 4 ) # 05 " + # # )6 0 # + " # 0 # ) " " # 4 ) 0 4 " + # ) + # # 4 #0 " ) 0 0 # #) # ) # # # 7# 0 " ) 8 + 9# 0 ) 0 0 # " ) : # 9# # + # ## # + # # 9# 9# ) %&'( ;<<#) ) < " =#>#;; ;#;"'?$@/A 8BA$(A'$$A$2@&A 8BA$(A'$$A$2@'/ !" +'&/A' NEW REACTIONS WITH ALLYL- AND ALLENYLBORON REAGENTS Dong Wang New Reactions with Allyl- and Allenylboron Reagents Transition-Metal-Catalyzed and Transition-Metal-Free Carbon-Carbon Bond Formation Processes Dong Wang ©Dong Wang, Stockholm University 2018 ISBN print 978-91-7797-340-9 ISBN PDF 978-91-7797-341-6 Cover picture: "Hiking on Kungsleden" by Dong Wang Printed in Sweden by Universitetsservice US-AB, Stockholm 2018 Distributor: Department of Organic Chemistry, Stockholm University To my parents Abstract Organoboron compounds have been widely used in carbon-carbon bond formation reactions in organic synthesis and catalysis. This thesis is focused on cross-coupling reactions of allyl-, allenylboronic acids and their ester derivatives via transition metal catalysis or transition-metal-free pro- cesses. The first part of the thesis describes Cu-catalyzed C(sp3)-C(sp3) for- mation reactions involving allylboronic acids and D-diazoketones. This coupling process shows high J-regioselectivity, resulting in branched al- lylic products. When stereodefined cyclic allylboronic acids were employed as the substrate, the relative facial configuration was retained in the reaction product. The second part involves Pd-catalyzed cross-coupling of allylboronic acid and D-diazoketones. The reaction proceeds with high D-regioselectiv- ity, affording linear allylic products. Accordingly, the palladium- and copper-catalyzed cross-coupling of allylboronic acid and D-diazoketones occurs with opposite regioselectivity. The third part concerns a new transition-metal-free carbon-carbon bond formation between allenylboronic acids and in situ generated diazo com- pounds. The diazo compounds are generated from tosylhydrazones in the presence of base. The reaction is suitable for synthesis of densely substi- tuted conjugated dienes with high Z-selectivity. In the final part, the allylation of quinones with allylboronates is presented. The reaction was performed without any catalyst or additive. Various quinones can be employed as substrates, including unsubstituted, monosubstituted benzoquinones and naphthoquinones. vii List of publications This thesis is based on the following publications, referred to in the text by their Roman numerals I-V. Reprints were made with the kind permission of the publisher (Appendix A). I. Copper-Catalyzed Cross-Coupling of Allylboronic Acids with α- Diazoketones Das, A.; Wang, D.; Belhomme, M.-C.; Szabó, K. J. Org. Lett. 2015, 17, 4754-4757. II. Copper-Catalyzed Stereoselective Cross-Coupling of Cyclic Allylboronic Acids with D-Diazoketones Wang, D.; Szabó, K. J. Org. Lett. 2017, 19, 1622-1625. III. Formation of C(sp3)–C(sp3) Bonds by Palladium-Catalyzed Cross- Coupling of α-Diazoketones and Allylboronic Acids Belhomme, M.-C.; Wang, D.; Szabó, K. J. Org. Lett. 2016, 18, 2503-2506. IV. Synthesis of Densely Substituted Conjugated Dienes by Transition- metal-free Reductive Coupling of Allenylboronic Acids and Tosylhydrazones Wang, D.; de Wit, M. J. M.; Szabó, K. J. J. Org. Chem. 2018, ASAP, DOI: 10.1021/acs.joc.8b01104. V. Direct Allylation of Quinones with Allylboronates Deng, H.-P.; Wang, D.; Szabó, K. J., J. Org. Chem. 2015, 80, 3343-3348. viii Contents Abstract........................................................................................................vii List of publications.................................................................................... viii Abbreviations ...............................................................................................xi 1. Introduction...............................................................................................1 1.1 Transition-metal-catalyzed cross-couping reactions ............................1 1.1.1 Reactions of allylboron compounds with C(sp2) electrophiles.....2 1.1.2 Reactions of allylboron compounds with C(sp3) electrophiles.....5 1.1.3 Reactions of allenylboronates.......................................................7 1.1.4 Diazo compounds as cross-coupling partners...............................8 1.2 Transition-metal-free cross-coupling with organoboron reagents.....10 1.3 The objectives of this thesis ...............................................................11 2. Copper-catalyzed cross-coupling of D-diazoketones with allylboronic acids (Paper I-II) ....................................................................................13 2.1 Formation of branched allylic products with copper catalysis...........13 2.2 Scope of the reaction..........................................................................15 2.3 Stereochemistry of the Cu-catalyzed allylation of diazoketones........17 2.3.1 Using disubstituted D-diazoketones as substrates.......................17 2.3.2 Using stereodefined allylboronic acids as substrates..................18 2.3.3 Experimental mechanistic studies...............................................23 2.4 Proposed mechanism of the Cu-catalyzed cross-coupling .................24 2.5 Summary of the Cu-catalyzed cross-coupling reaction......................25 3. Palladium-catalyzed cross-coupling of D-diazoketones and allylboronic acids (Paper III)......................................................................................26 3.1 Development of the Pd-catalyzed cross-coupling reaction and its regioselectivity.....................................................................................26 3.2 Mechanism of the Pd-catalyzed cross-coupling affording linear allylic products ...............................................................................................30 ix 3.3 Summary of the Pd-catalyzed cross-coupling reaction ......................32 4. Transition-metal-free coupling of allenylboronic acids with in situ generated diazo compounds (Paper IV) ...............................................33 4.1 Development of the reductive coupling reactions involving allenylboronic acids.............................................................................33 4.1.1 Optimization of the reaction conditions......................................34 4.1.2 Assignment of the double bond geometry of the major product 35 4.1.3 Reaction with allenylboronic pinacol ester (allenyl-Bpin) .........36 4.1.4 Scope of the coupling of allenylboronic acids............................37 4.1.5 One-pot approach .......................................................................40 4.1.6 Deuterium labeling experiment ..................................................41 4.2 Proposed mechanism..........................................................................41 4.3 Summary ............................................................................................42 5. Allylation of quinones with allylboronates (Paper V)..........................43 5.1 Scope of the allylation of quinones ....................................................43 5.2 Reactivity of allylboronic acids..........................................................48 5.3 Proposed mechanism for the allylation of quinones...........................48 5.4 Synthesis of hemi-tectol .....................................................................50 5.5 Summary of the allylation of quinones ..............................................50 6. Closing remarks ......................................................................................51 7. Summary in Swedish ..............................................................................52 Appendix A: Reprint permissions .............................................................53 Acknowledgement.......................................................................................54 References....................................................................................................56 x Abbreviations Abbreviations are used in agreement with the standards of the subject.# Only non-standard and unconventional abbreviations are listed here. Boc tert-butyloxycarbonyl Bpin pinacolato boron B2pin2 bis(pinacolato)diboron BQ benzoquinone Cp* 1,2,3,4,5-pentamethyl-cyclopentadienyl CuTC copper(I)-thiophene-2-carboxylate dba dibenzylideneacetone D-t-BPF 1,1’-bis(di-tert-butylphosphino) ferrocene d.r. diastereomeric ratio er enantiomeric ratio HSQC heteronuclear single quantum correlation L ligand NOEDIFF NOE difference PEPPSI pyridine-enhanced precatalyst preparation stabiliza- tion and initiation rt room temperature RuPhos 2-dicyclohexylphosphino-2’,6’-diisopropoxybiphenyl SE2 bimolecular electrophilic substitution Xphos 2-dicyclohexylphosphino-2’,4’,6’-triisopropylbi- phenyl #The ACS Style Guide, 3rd ed.; Oxford University Press: New York, 2006. xi xii 1. Introduction Organoboron compounds are widely used in organic synthesis, catalysis, drug development, and material science.1 Application of organoboron reagents is a fundamental
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