A surprising mechanistic 'switch' in Lewis acid activation: a bifunctional, asymmetric approach to [alpha]-hydroxy acid derivatives

An unusual bifunctional, sequential hetero-Diels-Alder/ring-opening reaction in which chiral, metal complexed ketene enolated have reacted with o-quinones to produce highly enantioenriched, [alpha]-hydroxylated carbonyl derivatives in excellent yield, is studied. The studies have shown a fundamental mechanistic 'switch', namely the formation of a tandem Lewis base/Lewis acid activated metal enolate in preference to a metal-coordinated quinone species.