Synthetic approaches toward hexaprismane and heptaprismane (synthesis of bishomohexaprismanedione): Synthesis and structural properties of two biscyclopropenes

Synthesis of bishomohexaprismanedione 136, the D$\rm\sb{2h}$ dimer of norbornadienone and a potential precursor to hexaprismane, is reported. The synthesis starts with known (11$\alpha,\ 14\beta$)-5, 5, 16, 16-tetramethoxy-heptacyclo ($7.6.1.0\sp{2,8} .0\sp{3,7}.0\sp{4,13}.0\sp{6,12}.0\sp{10,15}$) hexadecane-11, 14-dione (47) and includes a Grob fragmentation to give 5, 5, 16, 16-tetramethoxy-heptacyclo (7.6.1.0$\sp{2,8}.0\sp{3,7}.0\sp {4,13}.0\sp{6,12}$) hexadeca-10, 14-diene (78). Diene 78 was converted to a highly water soluble tetraol in quantitative crude yield using catalytic OsO$\sb4$. Treatment of crude tetraol with periodic acid leads to the formation of (10$\alpha,\ 13\beta$)-10, 13-dihydroxy-5, 5, 14, 14-tetramethoxy-hexacyclo (7.4.1.0$\sp{2,8}.0\sp{3,7}.0 \sp{4,12}0\sp{6,11}$) tetradecane-1, 11-dicarbaldehyde (94), the doubly ring contracted product, in 58% yield from diene 78. The alcohols are protected and the aldehydes are oxidized to acids and then converted to bromides under Hunsdiecker conditions to yield (10$\alpha,\ 13\beta$)-10, 13-diacetoxy-1, 11-dibromo-5, 5, 14,14-tetramethoxy-hexacyclo(7.4,1.0$\sp{2,8}.0\sp {3,7}.0\sp{4,12}.0\sp{6,11}$) tetradecane (131). Treatment of 131 with a lithium dispersion in t-BuOH/THF solution resulted in reductive debromination and also reductive fragmentation to form 13, 13, 14, 14-tetramethoxy-pentacyclo (8.2.1.1$\sp{4,7}.0\sp{5,12}.0\sp{6,11}$) tetradeca-2, 8-diene (56) in 24% overall yield. Hydrolysis of 56 produced a dienedione which underwent photochemical ring closure to the highly sought-after heptacyclo(9.3.0.0.$\sp{2,5}.0\sp{3,13}.0\sp {4,8}.0\sp{6,10}.0\sp{9,12}$) tetradecane-7, 14-dione (136). The structure of bishomohexaprimanedione 136 was determined from single crystal x-ray analysis. Further reactivity of diene 78 was explored. Diene 78 was selectively deprotected to yield a dienone and then photolyzed through Pyrex with loss of CO to give 9, 9-dimethoxytetracyclo(8.5.0.0$\sp{2,8}.0\sp{7,11}$) pentadeca-3, 5, 12, 14,-tetraene (81). Photolysis of the tetraene 81 through a Vycor filter gave a 4+4 photocycloaddition to yield 9, 9-dimethoxytetracyclo (8.5.0.0$\sp{2,8}.0\sp{3,15} .0\sp{6,12}.0\sp{7,11}$) pentadeca-4,13-diene (82). Tetraene 81 was also reacted with maleic anhydride to give a tandem Diels-Alder product. Oxidative decarboxylation of this product followed by deprotection gave hexacyclo(8.5.1.1$\sp{4,7}.0\sp{6,12}.0\sp{5,14}.0\sp{11 ,15}.0\sp{16,17}$) heptadeca-2, 8-diene-13-one (195). The synthesis of two biscyclopropenes, dispiro(2.2.2.2) deca-1,7-diene (231) and dispiropentacyclo(5.4.0.0$\sp{2,6}.0\sp{3,10} .0\sp{5,9}$) undecane-8:1$\sp\prime$-(cyclopropene)-11:1$\sp{\prime\prime}$-(cyclopropene) (232), is described. Compounds 231 and 232 are obtained from the corresponding dienes via standard procedures that include a reaction with dibromocarbene. Both compounds are moderately sensitive to oxygen and Lewis acids. The conformational properties of 231 were examined by dynamic $\sp1$H NMR spectroscopy. The structure of 232 was determined by low temperature x-ray crystallography. Ab initio calculations successfully reproduce the structure for 232 and the conformational properties of 231