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

Abstract

This paper describes the photochemical and the thermal isomerization of s-cis(E,E) 1,1-diphenly-3,4-bis(trimethylsilylmethylene)-1-silacyclopentane ( 1a). Under thermal conditions a 1,3-sigmatropic of the methylene hydrogen occurs, yielding the s-trans isomer ( 1b). The photochemical irradiation of ( 1a) at 300 nm for 1 h in deoxygenated benzene gives the corresponding s-cis( E, Z) isomer ( 1c) and then the s-cis( Z, Z) isomer ( 1d) after prolonged irradiation (3 h). There was no evidence for the formation of the corresponding cyclobutene resulting from the ring closure of the exocylic diene.