MuchMuch AdoAdo AboutAbout Nothing:Nothing: TheThe PlatonicPlatonic SolidsSolids andand HydrocarbonHydrocarbon ChemistryChemistry

Chris Galliford

20th January 2004 IntroductionIntroduction -- TheThe PlatonicPlatonic SolidsSolids

•According to Plato, the matter surrounding us and out of which we are made is composed of four elements: fire, earth, water and air. •A fifth element also exists, not part of the physical world, but provides the basis for the construction of the ”heavenly matter”, or ”ether”, and is responsible for the ”beautiful order” of the universe.

•These five elements are assigned characteristic regular polyhedra - the tetrahedron (fire), the cube (earth), the octahedron (water), the icosahedron (air) and the pentagonal dodecahedron (ether). •These platonic solids are both pleasing aesthetically, and when considered as a hydrocarbon framework, provide interesting synthetic challenges.

www.sbu.ac.uk/water/ platonic.html TetrahedraneTetrahedrane

•Tetrahedrane is the only platonic hydrocarbon which has not yet been prepared in unsubstituted form. •126-140 kcal/mol calculated strain energy, kinetically and thermodynamically highly unstable. Tetra-Tetra-terttert-Butyl-Butyl TetrahedraneTetrahedrane

t-Bu SiR3

t-Bu t-Bu t-Bu t-Bu

t-Bu t-Bu

•The stability of tetra-tert-butyltetrahedrane compared to tetrahedrane is attributed to the ”corset effect”. •Intramolecular repulsion between the four tert-butyl groups is at a minimum when their mutual distance is at a maximum. This condition is satisfied by the symmetry of a tetrahedron

G. Maier & S. Pfriem Angew. Chem. Int. Ed. Engl. (1978), 17, 520 CubaneCubane

Cubane, C8H8 was first synthesized by Eaton and Cole in 1964.

Octa- and other polynitrocubane derivatives Have attracted considerable military interest, The non-shock sensitive ONC is reported to be 30% more explosive than it’s nearest non- nuclear alternative!

P.E. Eaton & T.W. Cole J. Am. Chem. Soc., (1964), 86, 962-964. P.E. Eaton & T.W. Cole ibid., (1964), 86, 3157-3158. P.E. Eaton et al.Propellants, Explosives and Pyrotechnics, (2002), 27, 1-6. P.E. Eaton et al. Angew. Chemie. Int. Ed. Engl.,(2000), 39, 401-404. CubaneCubane -- FirstFirst SynthesisSynthesis byby EatonEaton andand ColeCole

O O O Br O + O 1. (CH2OH)2/H Br hν 2. HCl(aq) (95%) O Br (85% combined) Br Br Br O O

10% KOH(aq) (95%)

O O O 1. SOCl2 o O O O cumene 152 C 2. t-BuO3H (95% combined) Br (55%) Br Br t-BuO3C HO2C

75% H2SO4(aq) (30%)

1. SOCl2 O 2. t-BuO3H 25% KOH(aq) CO2H (95% combined) Br (55%) 3. diisopropylbenzene 100 oC (30%) CubaneCubane -- AnAn AlternativeAlternative SynthesisSynthesis byby PettitPettit

O Br O Br O Br Ce(IV) hν Fe(CO)3 80% 90% Br Br O Br O O

aq. KOH 90%

CO2H

SOCl2 followed by t-BuOOH, then Δ CO2H

R. Pettit, L. Watts & J. C. J. Am. Chem. Soc., (1966), 88, 1328-1329. DodecahedraneDodecahedrane

•The first dodecahedrane ever prepared was 1,16- dimethyl dodecahedrane in 19 steps in 1982 by Paquette and co-workers.

•Paquette reported the synthesis of the parent hydrocarbon by a similar route shortly afterwards.

L.A. Paquette; D.W. Balogh & J.F. Blont J. Am. Chem. Soc., (1981), 103, 228-230. L.A. Paquette; G.G. Christophe; D.W. Balogh, D. Kountz, R. Usha Science (1981), 211, 575. L.A. Paquette; D.W. Balogh J. Am. Chem. Soc., (1982), 104, 774-783. L.A. Paquette; G.G. Christoph & D.W. Balogh, P.Engel, R. Usha ibid, (1982), 104, 784-7. DodecahedraneDodecahedrane -- FirstFirst SynthesisSynthesis byby PaquettePaquette

H 950 oC I , THF Ni 2 2 Na -78 oC H

H3CO2C CO2CH3 Δ

ε ε 20% optimized yield for whole sequence ε ε

CO2CH3

ε

ε ε ε CO2CH3 CompletingCompleting thethe CarbonCarbon FrameworkFramework

I I KOH(aq)/MeOH I NaOH/MeOH I then I NaHCO (quantitative) OH CO2CH3 2 3 O CO2CH3 (94%) O OH CO2CH3 O CO2CH3 O

+ 1. Na2Cr2O7/H (92%) 2. Zn/Cu, CH3OH (78%)

O CO CH 2 3 O O SPh2

CO2CH3 O (77%) O CO2CH3 CO2CH3 CO CH O 2 3 CO2CH3

H2O2, CH3OH (quantitiative)

O CO CH O 2 3 O O

CO2CH3 ClosureClosure ofof thethe DodecahedraneDodecahedrane CageCage

O O CO CH CO CH O CO2CH3 2 3 O 2 3

O P O , MeSO H H , Pd/C EtOAc O 4 10 3 2 O (83%) (quantitative) O CO CH CO2CH3 CO2CH3 2 3

NaBH4, MeOH (81%)

O Cl O CO2CH3 PhOH2C CO2CH3 1. Li, NH3 Cl 2. PhOCH Cl O O 2 HCl, MeOH (48% combined) (62%) O

CO2CH3 ClosureClosure ofof thethe DodecahedraneDodecahedrane CageCage

PhOH2C CO2CH3 PhOH2C CO2CH3 PhOH2C CHO 1. hν DIBAl-H O 2. TsOH 3. N2H2

1. hν 2. Li, NH3 + 3. H3O

O O HO CHO CH2OH KOH, EtOH PCC (37%)

1. hν 2. TsOH

H H

o N2H2 H2 Pd/C, 250 C (50%) DodecahedraneDodecahedrane CC20HH20 IsomersIsomers

There are many C20H20 isomers, including various multi- bridged cyclophanes, dimers of C10 structures (e.g. basketene dimer) and other saturated polycyclic systems.

Interconversion of these hydrocarbons by thermally or photochemically mediated isomerization reactions has been the basis for several attempted syntheses of hydrocarbon structures.

Prinzbach and co-workers were able to demonstrate an alternative route to dodecahedrane, via the thermodynamically controlled isomerization of another

C20H20 hydrocarbon, pagodane. PagodanePagodane

•ca. 40 kcal/mol higher heat of formation than dodecahedrane. •Readily isomerized to dodecahedrane by Pt/Re

on Al2O3.

W. D. Fessner; B. Murty; J. Worth; D. Hunkler; H. Fritz & H. Prinzbach Angew. Chem. Intl, Ed. Engl., (1987), 26, 452-454. BuildingBuilding thethe ReflectionReflection ofof aa PagodaPagoda

O O O hν O O Δ O

1. B2H6/THF, o quinoline 150 C Cu2O, bypyridyl, H O 2. NaOH, H2O2 2 O 3. CrO3 O O (91% combined) O O CompletionCompletion ofof thethe CarbonCarbon FrameworkFramework

1. HCO2CH3/NaH 2. p-TsN3/NEt3 rt N N O (82% combined) O O O N N

MeOH hν, rt (95%)

Na-K, THF, then t-BuOH Pb(OAc)4, I2, CCl4, hν (quantitative) (80%) I I H3CO2C CO2CH3