Regio- and enantio-selective enolisations of cyclic ketones using chiral lithium amide bases

Abstract

Enolisations of 3-methylcyclohexanone 16, and of a trans-fused perhydroisoquinolone derivative 8, using several chiral lithium amide bases have been examined. In reactions involving a single enantiomer of the ketone 8, the use of a chiral base can result in enhancement or reversal of the normal regioselectivity of enolisation to give the enol silane derivatives 9 and 10, depending on the configuration of the base used. Similar matched and mismatched results are observed when (R)-3-methylcyclohexanone, (R)-16, is treated with either enantiomer of the chiral base 3. A new type of kinetic resolution, termed regiodivergent resolution, is observed when enolisation of the racemic ketones 8 or 16 is carried out using the chiral base 3.