The exploratory far-UV photochemistry of 1-methyl-1-silabicyclo[2.2.1]hept-2-ene and 2-trimethylsilylbicyclo[2.2.1]hept-2-ene

Article abstract of DOI:10.1016/0022-328X(95)06087-D

1-Methyl-1-silabicyclo[2.2.1]hept-2-ene was synthesized in 27% yield by chloramine-T oxidation of a mixture of C-2/C-3 phenylselenide derivatives of 1-methyl-1-silabicyclo[2.2.1]heptane. The phenylselenides in turn were produced in 8% yield by Gif^III oxidation of 1-methyl-1-silabicyclo[2.2.1]heptane. The 214 nm photolysis of the rigid 1-silanorbornene in MeOH or (CH₃)₃COH resulted in [1,3-C] migration to afford 3-alkoxy-3-methyl-3-silabicyclo[4.1.0]heptanes with quantum yields of 0.053 (methoxy derivative) and 0.062 (tert-butoxy derivative). The efficiency for photoprotonation was estimated to be Φ < 0.01 for methanol and negligible for tert-butyl alcohol. [1,3-C] photorearrangement was also observed upon 214 nm irradiation of 2-trimethylsilylbicyclo[2.2.1]hept-2-ene in pentane and (CH₃)₃COH, but the major photoprocess appeared to be reversible [1,2-Si] migration to give a carbene intermediate, which underwent CH insertion to form 3-trimethylsilylnortricyclene. Competing [1,2-C] shift of the carbene accounted for the formation of trimethylsilylmethylenebicyclo[2.1.1]hexane. In pentane the respective quantum yields of the two carbene-derived products were 0.0062 and 0.0019. In CH₃OH(D) as the solvent, photoprotonation was a minor photoprocess that produced 2-trimethylsilylnorbomane via hydride transfer. Photoprotonation assumed greater importance in CF₃CH₂OH and resulted in desilylation to norbornene (Φ = 0.0091) and alcohol addition to give a mixture of three alcohol addition products (Φ = 0.0053); the formation of carbene-derived products was relatively less efficient (Φ = 0.0095).