Asymmetric Oxidative Lactonization of Enynyl Boronates

Oxidation of C−B bonds is extensively used in organic synthesis, materials science, and chemically biology. However, these oxidations are usually limited to the oxidation of C(sp3)−B and C(sp2)−B bonds. The C(sp)−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)−B bond oxidation, the epoxidation of C−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 γ‐lactones in high enantioselectivities and diastereoselectivities. The versatile transformations and ubiquity of γ‐lactones shed light on the importance of this strategy in the construction and late‐stage functionalization of complex molecules. We present herein the first oxidation of enynyl boronates for the synthesis of γ‐lactones, including spiro‐, and fused‐butanolides as well as butenolides that are prevalent in nature products and bioactive molecules. The asymmetric version of this oxidation was also achieved in the presence of chiral ketone and Oxone. This process successively involves the oxidation of C(sp)−B bond, the epoxidation of C−C double bond, and the lactonization.