SILICON CARBON UNSATURATED-COMPOUNDS .33. REGIOCHEMISTRY IN THE PHOTOCHEMICAL FORMATION OF SILENES FROM 1,2,2,2-TETRAMETHYLPHENYLVINYLDISILANE, 1,1,2,2-TETRAMETHYLPHENYLVINYLDISILANE, AND 2-ETHYL-1,2,2-TRIMETHYLPHENYLVINYLDISILANE

The photolysis of phenylvinyldisilanes has been studied. Irradiation of 1,2,2,2-tetramethylphenyl-vinyldisilane (1) in the presence of acetone gave two products, 1-[(isopropenyloxy)methylphenylsilyl]-2-(trimethylsilyl)ethane and 1-(isopropoxymethylvinylsilyl)-2-(trimethylsilyl)benzene, which were produced from the reaction of two different silenes derived from a 1,3-silyl shift to the vinyl group and also to the phenyl group with acetone in 56 and 5% yield, respectively. Similar irradiation of 1 in the presence of 2,3-dimethylbutadiene afforded trans-1-[methyl(2,3-dimethyl-2-butenyl)phenylsilyl]-2-(trimethylsilyl)ethene, 1-[methyl(3-methyl-2-methylene-3-butenyl)phenylsilyl]-2-(trimethylsilyl)ethane, and 1-[methyl(2,3-dimethyl-3-butenyl)vinylsilyl]-2-(trimethylsilyl)benzene, in 9, 31, and 28% yields. The photolysis of 2-ethyl-1,2,2-trimethylphenylvinyldisilane (9) in the presence of methanol produced 2-(ethyldimethyl-silyl)-1-(methoxymethylphenylsilyl)ethane in 94% yield. Irradiation of 9 in the presence of acetone gave 2-(ethyldimethylsilyl)-1-[(isopropenyloxy)methylphenylsilyl]ethane in 67% yield, in addition to a small amount of 2-(ethyldimethylsilyl)-1-(isopropoxymethylvinylsilyl)benzene. Irradiation of 9 in the presence of 2,3-dimethylbutadiene gave trans-2-(ethyldimethylsilyl)-1-[methyl(2,3-dimethyl-2-butenyl)phenyl-silyl]ethene, 2-(ethyldimethylsilyl)-1-[methyl(3-methyl-2-methylene-3-butenyl)phenylsilyl]ethane, and (E)-2-[(ethyldimethylsilyl)methyl]-1,4,5-trimethyl-1-phenyl-1-silacyclo-4-hexene in 5, 57, and 20% yields. Irradiation of 1,1,2,2-tetramethylphenylvinyldisilane (16) in the presence of acetone produced 1-[(isopropenyloxy)dimethylsily]-2-(dimethylphenylsilyl)ethane, (isopropenyloxy)dimethylphenylsilane, and dimethylphenylsilane, while in the presence of 2,3-dimethylbutadiene 16 gave trans-1-[dimethyl(2,3-dimethyl-2-butenyl)silyl]-2-(dimethylphenylsilyl)ethene and 1-[dimethyl(3-methyl-2-methylene-3-butenyl)silyl]-2-(dimethylphenylsilyl)ethane in 20 and 42% yields.