Asymmetric Synthesis of Chiral 1,4‐Enynes through Organocatalytic Alkenylation of Propargyl Alcohols with Trialkenylboroxines

A highly enantioselective synthesis of 1,4‐enynes is described that proceeds through an organocatalytic reaction between propargyl alcohols and trialkenylboroxines. Our strategy relies on acid‐mediated generation of the carbocationic intermediate from propargyl alcohols followed by enantioselective alkenylation with trialkenylboroxines. A range of chiral 1,4‐enynes were obtained in moderate to good yields with high levels of enantioselectivity. Use of a highly acidic chiral N‐triflyl phosphoramide catalyst, which has two distant Lewis basic oxygen atoms, was found to be crucial for both high reactivity and selectivity in the present reaction.