Photocyclisation of some 1,6-diarylhexa-1,3,5-trienes

Abstract

On irradiation in benzene solution in the presence of air or iodine, 1,6-dimethyl-1,6-dimethyl-1,6-diphenylhexa-1,3,5-triene is converted into 6,12-dimethylchrysene. Under the same conditions 3-methyl-1,6-diphenylhexatriene gives chrysene, by ejection of the methyl group, but 1,3,6-triphenylhexatriene unexpectedly cyclises to 1,2,4-triphenylbenzene.

Wittig condensation of cinnamylidenetriphenylphosphorane with benzylideneacetone takes an unusual course, affording 2-methyl-1,4-diphenylbenzene as one product. An example of double-bond isomerisation during a Wittig reaction is reported.