Catalytic asymmetric dialkynylation reaction of α-dinitrone by utilizing tartaric acid ester as a chiral auxiliary

The asymmetric addition of alkynylzinc reagents, prepared in situ from dimethylzinc and 1-alkynes, to alpha-dinitrones derived from glyoxal and N-(4-isopropylbenzyl)hydroxylamine was investigated by utilizing dicyclohexyl (R,R)-tartrate as a chiral auxiliary. The addition reaction of methyl(2-phenylethynyl)zinc afforded the corresponding optically active C-2-symmetric (R,R)-bis(hydroxylamine) derivative with enantioselectivities of 90% and 81% ee by utilizing a stoichiometric and catalytic amount of the tartrate, respectively. Furthermore, the catalytic addition reaction of several alkynylzinc reagents also furnished the corresponding bis(hydroxylamine) with moderate to good enantioselectivities. (C) 2008 Elsevier Ltd. All rights reserved.