Highly enantioselective alkyne additions to aldehydes in the presence of 1,1′-bi-2-naphthol and hexamethylphosphoramide

It is found that the addition of hexamethylphosphoramide to the solution of an alkyne, Et2Zn, and (S)-1,1'-bi-2-naphthol in methylene chloride allows the generation of an alkynylzinc at room temperature and shows highly enantioselective additions to aldehydes. The mild condition for the formation of the alkynylzinc reagent enables the use of functional alkynes in this asymmetric reaction with excellent enantioselectivity. It avoids the reflux of the toluene solutions of the alkynes and Et2Zn as previously reported.