Asymmetric Oxidative Lactonization of Enynyl Boronates

Abstract

Oxidation of CÀ B bonds is extensively used in organic synthesis, materials science, and chemically biology. However, these oxidations are usually limited to the oxidation of C(sp 3 )À B and C(sp 2 )À B bonds. The C(sp)À B bond oxidation is rarely developed. Herein we present a novel strategy for the preparation of γ-lactones via the oxidation of enynyl boronates. This process successively involves the C(sp)À B bond oxidation, the epoxidation of CÀ C double bond and the lactonization. This protocol provided various γ-lactones and unsaturated butenolides efficiently that are prevalent in numerous nature products and bioactive molecules. Most importantly, asymmetric oxidative lactonization of enynyl boronates was also achieved, providing chiral γlactones in high enantioselectivities and diastereoselectivities. The versatile transformations and ubiquity of γlactones shed light on the importance of this strategy in the construction and late-stage functionalization of complex molecules.