Electrocyclic reactions. Part X. Photochemical cyclisation of trans,trans-dibenzylideneacetone

Abstract

Photolysis of trans,trans-dibenzylideneacetone (1,5-diphenylpenta-1,4-dien-3-one) in benzene solution at ca. 300 nm gave, as the major product by head-to-head staggered [_π2_s+_π2_s] cycloaddition, the truxinic-type dimer (IV), whose structure has been established by both chemical and physical methods. As minor products, four stereoisomeric trimers have been isolated; these appear to be derivatives of tri(cyclobuta)[a,d,g]nonane-3,6,9-trione (XII), and their structures and modes of formation are discussed.