A series of modular amino thiol and amino alcohol ligands have been synthesized in enantiopure form from common enantiopure precursors. Their structures have been optimized for performance in the asymmetric alkynylzinc addition to aldehydes, and a direct comparison of the effect of the S and O coordinating atoms on the catalytic outcome of these ligands has been performed. Amino thiols have shown to be superior as ligands for this type of chemistry.