Thermal and photochemical isomerization of exocyclic 1,3-dienes: 1,1-diphenyl-3,4-bis(trimethylsilylmethylene)-1-silacyclopentane s-cis(E,E)

This paper describes the photochemical and the thermal isomerization of s-cis(E,E)1, 1-diphenyl-3,4-bis(trimethylsilylmethylene)-1-silacyclopentane (1a). Under thermal conditions a 1,3-sigma-tropic of the methylene hydrogen occurs, yielding the s-trans isomer (1b). The photochemical irradation of (1a) at 300 nm for 1 h gives the corresponding s-cis(E,Z) isomer (1c) and then the s-cis(Z,Z) isomer (1d) after prolonged irradiation (3 h).