Steric aspects of the photochemistry of conjugated dienes and trienes

Abstract

The photochemical transformation of the 1,3-cyclohexadiene chromophore can lead via orbital symmetry allowed pathways either to a bicyclo[2.2.0]hex-2-ene derivative or to a 1,3,5-hexatriene derivative. It was established that the ground state conformation of the starting 1,3-cyclohexadiene controls the primary photochemical reaction. The photoproducts composition can be changed by variation of the wavelength or of the temperature. The mechanisms of these processes are discussed. The photochemical transformation of a 1,3,5-hexatriene derivative to a bicyclo[3.1.0]hex-2-ene has been shown to proceed from an s-trans,s-cis conformation. The mechanism of the rearrangement has been shown to be an extension of the rearrangement of a 1,3-butadiene to a bicyclo[1.1.0]butane. © 1973, Walter de Gruyter. All rights reserved.