Ring-opening reactions of functionalized bicyclo[2.2.0]hexanes

Abstract

On hydrolysis, the bicyclohexanes 1a,b give the cyclobutanes 2a,b and/or the cyclobutenes 3a,b. On bromination they lead to the bromocyclobutanes 5a,b and the dibromocyclobutane 6a or the bromocyclobutene 7b, respectively. The ease of the electrophilic ring-opening of compounds 1a,b can be explained by assuming that the presence of the methoxycarbonyl and gem-dimethoxy groups at C-1 and C-2 favours the formation of well-stabilized ionic intermediates or polar transition states. However, the brominations may involve radical pathways, even to a minor extent, and these would lead to the same products.