Rhodium-catalyzed CC coupling reactions involving ring opening of strained molecules: II. Addition to olefins and aromatic substitution

Abstract

Rhodium-catalyzed CC coupling reactions, involving ring opening of strained molecules, have been studied using diphenylmethylenecyclopropanes as models. It has been established that, as rhodium takes control of the ring opening process, activated olefins can react to form open-chain unsaturated compounds. In the presence of acids, protonation of the substrate competes with olefin incorporation, and intramolecular aromatic electrophilic substitution, leading to indene derivatives, can be obtained. Aromatic substitution can also occur in a sequential process, involving ring opening, 3-butenoic acid addition, leading to linear and branched isomeric complexes, and selective formation of a benzocycloheptene derivative from the branched isomer. The regioselectivity of 3-butenoic acid insertion is contrasted with the non-regioselectivity observed with the same acid in reactions which probably involve metallacycle formation.