Overcrowded molecules. Part X. Photoreactions of photochromic (α-phenylethylidene)(substituted methylene)succinic anhydrides

Abstract

The photochemical, electrocyclic reactions and E–Z isomerisation of benzylidene-, diphenylmethylene-, and isopropylidene-(α-phenylethylidene)succinic anhydrides and of bis-(α-phenylethylidene)succinic anhydrides are reported. Cyclisation reactions are believed to occur by n→π* excitation of one of the two largely independent chromophores in the molecule, and the dependence of product composition on temperature is attributed to competing thermal processes (disrotatory ring opening and 1,5-hydrogen shifts) from the 1,8a-dihydronaphthalene intermediates. Structural assignments of the products, 1,2-dihydronaphthalene-2,3-dicarboxylic anhydrides, are based on n.m.r. studies.