Catalyst‐Free Propargylboration of Ketones with Allenyl‐Bpins: Highly Stereoselective Synthesis of tert‐Homopropargyl Alcohols Bearing Vicinal Stereocenters

Abstract

A practical and efficient propargylboration of ketones is presented using general allenylboronic acid pinacol esters (allenyl‐Bpins) without a catalyst. This reaction is triggered by in‐situ activation of stable allenyl‐Bpins through the sequential addition of 1.25 equiv. of nBuLi and the prerequisite 2.0 equiv. of TFAA. Under the optimized reaction conditions, the versatile trisubstituted allenyl‐Bpins react with various ketones smoothly to afford a wide range of tert‐homopropargyl alcohols bearing vicinal stereocenters in high yields with good to excellent diastereoselectivities. Furthermore, propargylboration of ketones with chiral trisubstituted allenyl‐Bpins allows for the asymmetric synthesis of chiral tert‐homopropargyl alcohols with a full chirality transfer.