A Powerful <i>o</i>-Quinone Dimethide Strategy for Intermolecular Diels−Alder Cycloadditions

Abstract

Conrotatory thermal fragmentation of trans-1,2-disilyloxybenzocyclobutenes generates o-quinone dimethides at remarkably low temperatures. Smooth stereoselective Diels−Alder cycloaddition with a range of dienophiles provides hydronaphthalene derivatives in excellent yield. Direct oxidative desilylation of the adducts affords the corresponding naphthoquinones. Substitution of the benzene nucleus with an electron-releasing methoxyl group directs the cycloaddition to give good control of regioselectivity in the expected direction. A short synthesis of the aglycon of the anticancer antibiotic idarubicin is presented.