Photochemical reactions of silacyclic compounds

Abstract

Reaction of tert-butyllithium with chlorodivinylphenylsilane or dichloropyenylvinylsilane in hydrocarbon solvents at room temperature or below generated E and Z isomers of silene which were trapped by dienes to give [4+2] cycloadducts. Photolysis of pure trans-or cis-1,1,3,3-tetraphenyl-2,4-dineopentyl-1,3-disilacyclobutane, 4, caused a rapid rearrangement to give a 70/30 equilibrium mixture of the isomers and less rapid formation of ringopened alkenylsilane isomers. In the presence of MeOH, $MeOSiMe_3$, or $(EtO)_3$ SiH as traps, the expected adducts of 1,1-diphenyl-2-neopentylsilene were also observed. The results were consistent with the initial formation of a ringopened 1,4-biradical which reclosed rapidly to give the starting material and observed products. The photolysis of 2,2-diphenyl-3-neopentyl[5,6:7,8] dibenzo-2-silabicyclo[2.2.2] octane, 22, in the presence of methanol gave 9-(1-diphenyl-methoxysilyl-3,3-dimethylbutyl)-9,10-dihydroanthracene, 23, as the major product and the methanol adduct of 1,1-diphenyl-2-neopentylsilene as the minor product. The photolysis of the pure 2-methyl-3-neopentyl-2-phenyl[5,6:7,8] dibenzo-2-silacyclo [2.2.2] octane, Z-24 or E-24, in the absence of trapping agent gave Z-E photoisomerization products and polymeric products. The major product of photolysis of pure E-24 or Z-24 in the presence of methanol or deuterated methanol was 9-(1-methylphenylmethoxysilyl-3,3-dimethylbutyl)-9,10-dihydroanthracenes, (S,S), (R,R) 26a, and (R,S), (S,R) 26b, respectively. The photoisomerization of the diastereomers, 26a and 26b, also occurred. The 1,6-biradical intermediates formed from Z-and E-24 retained their asymmetry at the silicon atom prior to the abstraction of methoxy group from methanol, but not at carbon. Photolysis of 3-neopentyl-2-phenyl-2-vinyl [5,6:7,8] dibenzo-2-silabicyclo[2.2.2] octane, 8, in the presence of methanol and methanol-OD gave products, opening products, 27a and 27b, arising from trapping a silaallylic 1,6-bir...