The acid-catalysed rearrangement of a 1,2-Diphenyl-2a,8b-dihydrocyclobuta-[a]naphthalene. A new synthesis of triarylethylenes

Abstract

Treatment of 4,8b-dimethyl-1,2-diphenyl-2a,8b-dihydrocyclobuta[a]naphthalene (4) with trifluoroacetic acid gives the stereoisomeric 2-(1,4-dimethylnaphthyl)-stilbenes (5) and (6), the structures of which have been proved by an independent synthesis. One of these stilbenes rearranges irreversibly under the influence of trifluoroacetic acid to its stereoisomer; stereomodels suggest that the less stable isomer has the structure (5). Mechanisms are proposed for the rearrangement of (4) to (5) and for the direct conversion of (4) into (6).