Lewis Base Assisted Brønsted Base: Phosphine Oxides and La-Aryloxides

Significance

Combined acid and base catalysis is a well-established concept which has led to the development of highly reactive systems. However, utilization of a Lewis base to activate a Brønsted base in a catalytic system is genuinely rare. The authors report that addition of a bidentate phosphine oxide Lewis base to a lanthanum aryl oxide produces a highly reactive catalyst for the anti-­selective Mannich-type reaction. In control experiments, with the absence of Lewis base, La(OAr)₃ gives both poor reactivity and diastereoselectivity.