Enantioselective reaction of alpha-lithiated dithioacetals using chiral bis(oxazoline)s: new chiral formyl anion equivalents

The enantioselective reaction of various alpha-lithiated dithioacetals with aldehydes or a ketone in the presence of bis(oxazoline)s was examined. Among them, unsymmetrical dithioacetals were found to be the best choice for attaining high enantioselectivity. The reaction of lithiated tert-butylthio(2-pyridylthio)methane with aldehydes proceeded with good diastereoselectivity as well as with good enantioselectivity. The enantioselective reaction was shown to proceed through dynamic thermodynamic resolution. Mercury(II) chloride effected hydrolysis of the dithioacetal moiety of the products to 2-hydroxyaldehydes, which were directly reduced to give the optically active 1,2-diols.