Photochemical reactions of [5,6: 7,8]dibenzo-2-silabicyclo[2.2.2]octanes

Abstract

The photochemical reactions of 2-R-2-phenyl[5,6: 7,8]dibenzo-2-silabicyclo[2.2.2]octanes (R = Ph, 1, R = Me, 5) in cyclohexane have been studied in the presence or absence of trapping agents such as methanol and methoxytrimethylsilane. The photolysis of 1 in the presence of methanol gave 9-(1,1-diphenylmethoxysilyl-3,3-dimethylbutyl)-9,10-dihydroanthracene as the major product and the methanol adduct of 1,1-diphenyl-2-neopentylsilene as the minor product. When trimethylmethyoxysilane was used as the trap, the silene adduct was only isolated in small quantity and no 9,10-disubstituted anthracene product was obtained. The photolysis of pure Z-5 or E-5 in the absence of trapping agent gave Z - E photoisomerization products and polymeric products. During the photolysis a constant ratio of Z-5 and E-5 was never observed because the formation of high molecular weight products was faster than isomerization. The major product of photolysis of pure E-5 or Z-5 in the presence of methanol or deuterated methanol was SS(RR), 6, and RS(SR), 6′, respectively, at early stages of the reaction but the other diastereomer was produced also as the photolysis proceeded. Photoisomerization of the diastereomers 6 and 6′ also occurred. The 1,6-biradical intermediates formed from Z- and E-5 retain their asymmetry at the silicon atom prior to the abstraction of methoxy group from methanol, but not at carbon. ？ 1991.