Photochemical reactions. Part IV. Thermal generation of photoenols and their derivatives from disubstituted 1,2-dihydrobenzocyclobutenes

Abstract

Various disubstituted 1,2-dihydrobenzocyclobutenes bearing at least one oxygen substituent have been prepared and their thermal conversion into substituted o-quinonedimethides studied by appropriate trapping reactions. In all cases the oxygen substituent adopts the E-configuration. Benzocyclobuten-1(2H)-one ethylene acetal and cis-1,2-dimethoxy-1,2-dihydrobenzocyclobutene did not open to give a quinone dimethide. Vinylic or phenyl substituents aid the valence isomerisation to the ring opened form. The thermal reactions of the photoenol derived from either 2-methylbenzophenone or 1-phenyl-1,2-dihydrobenzocyclobuten-1-ol have been studied.