Asymmetric addition of alkynylzinc reagents to nitrones utilizing tartaric acid ester as a chiral auxiliary

The asymmetric addition of alkynylzinc reagents, prepared in situ from dialkylzinc and 1-alkynes, to nitrones was achieved by utilizing di(t-butyl) (R,R)-tartrate as a chiral auxiliary to afford the corresponding optically active (R)-alpha-substituted propargylic N-hydroxylamines. By the addition of product-like N-hydroxylamine, unprecedented enhancement of enantioselectivity was observed to afford the N-hydroxylamines up to 95% ee.