PtI2-catalyzed cyclization of 3-acyloxy-1,5-enynes with the elimination of HOAc and a benzyl shift: synthesis of unsymmetrical m-terphenyls.

Abstract

A novel cyclization of 3-acyloxy-1,5-enynes is developed in the presence of PtI2 for the synthesis of substituted unsymmetrical m-terphenyls in good to excellent yields. Two unique steps are involved in this transformation, which includes the elimination of HOAc and benzyl group migration. DFT calculations indicated that the rate-determining step is the migration of the benzylic carbocation to form a zwitterionic intermediate followed by the elimination of HOAc. The subsequent cyclopropanation of the zwitterionic intermediate is the regioselectivity-determining step.