The effect of added salts on enantioselective transformations of cyclic ketones by chiral lithium amide bases

Abstract

The asymmetric transformation of certain cyclic ketones, using enantiomerically pure chiral lithium amide bases, has been carried out using several reaction protocols. In general, the enantioselectivity observed in the conversion of ketones into non-racemic enol silanes is optimal under in situ quench (ISQ) conditions, with products of lower enantiomeric excess being obtained using the external quench (EQ) protocol. However, substantial improvements in the enantiomeric excess of products obtained from EQ reactions can be achieved if either LiCl or ZnCl₂ is included in the reaction mixture.