Novel Intramolecular Cyclopropanation Reaction of Unsaturated β-Keto Esters.

Abstract

Fused cyclopropane β-keto esters are versatile intermediates for the synthesis of many biologically active natural products. Here we report a new intramolecular cyclopropanation reaction of unsaturated β-keto esters. In the presence of I2, Et3N, and Lewis acids such as Mg(ClO4)2 and Yb(OTf)3, β-keto esters 1 bearing various olefin substituents were transformed to fused cyclopropanes 2 in a highly stereospecific manner with moderate to good yields. The mechanism of the reaction was also investigated.