3,6-DIMETHOXYBENZOCYCLOBUTENONE: A REAGENT FOR QUINONE SYNTHESIS

Article abstract of DOI:10.1016/S0040-4020(01)81452-6

3,6-Dimethoxybenzocyclobutenone 4 is prepared in four efficient steps from 2,5-dimethoxybenzoic acid 8.The derived benzocyclobutenol 13 undergoes electrocyclic ring opening at 110-115 deg C to give the hydroxy-o-quinone dimethide 21, which reacts with dienophiles to give 5,8-dimethoxy-1,2,3,4-tetrahydro-1-naphthol derivatives stereoselectively.Since the ketone 4 can be functionalised at C-5 using electrophiles and at C-2 via homolytic bromation, the ring opening and cycloaddition sequence offers a flexible route to linear fused hydroquinone and quinone derivatives.In model studies, the benzocyclobutenol derivative 48 underwent thermal electrocyclic ring opening and intramolecular cycloaddition to give 49, while the analogous reaction with 52 failed due to adverse steric effects during the cycloaddition step.In photochemical experiments, attempts to generate the silyl ether 57 by in situ silylation of the dienol 55 and to prepare the benzocyclobutenol 62 via irradiation of the o-phthalaldehyde monoacetal 60 were unsuccessful.