Chiral Benzothiophene Synthesis via Enantiospecific Coupling of Benzothiophene S‐Oxides with Boronic Esters

Abstract

AbstractBenzothiophenes are valuable heterocycles that are widely used in medicines, agrochemicals, and materials science. Herein, we report a general method for the synthesis of enantioenriched 2,3‐disubstituted benzothiophenes via a transition‐metal‐free C2‐alkylation of benzothiophenes with boronic esters. The reactions utilize benzothiophene S‐oxides in lithiation‐borylations to generate intermediate arylboronate complexes, and subsequent Tf2O‐promoted S−O bond cleavage to trigger a Pummerer‐type 1,2‐metalate shift, which gives the coupled products with complete enantiospecificity. Primary, secondary and tertiary alkyl boronic esters and aryl boronic esters are successfully coupled with a range of C3‐substituted benzothiophenes. Importantly, this transformation does not require the use of C3 directing groups, therefore it overcomes a major limitation of previously developed transition‐metal‐mediated C2 alkylations of benzothiophenes.