Rhodium(III)-catalyzed [4+1] annulation of aromatic and vinylic carboxylic acids with allenes: An efficient method towards vinyl-substituted phthalides and 2-furanones

Abstract

A highly regio- and stereoselective synthesis of 3,3-disubstituted phthalides from aryl carboxylic acids and allenes using a rhodium(III) catalyst has been demonstrated. The reaction features broad functional group tolerance and provides a simple and straightforward route to the synthesis of various 3-vinyl-substituted phthalides. Furthermore, the catalytic reaction can also be applied to the synthesis of biologically active 5-vinyl-substituted 2-furanones from α,β-unsaturated carboxylic acids and allenes. The reactions proceed through a carboxylate-assisted ortho-C-H activation and [4+1] annulation. The preliminary mechanistic studies suggest that a C-H cleavage is the rate-determining step. An efficient synthesis of highly substituted phthalides and 2-furanones from aryl and vinyl carboxylic acids with allenes by using a Rh III catalyst is demonstrated (see scheme). The reactions proceed through a carboxylate-assisted ortho-C-H activation and [4+1] annulation.