Asymmetric chlorination of 4-substituted pyrazolones catalyzed by natural cinchona alkaloid

A natural quinidine-catalyzed asymmetric chlorination of 4-substituted pyrazolones is developed, affording products with a quaternary chiral chlorine-attached carbon centre in high yield with excellent enantioselectivity. The low catalyst loading (1 mol%), broad substrate scope, and facile and valuable transformation of the product highlight the practical utility of this process.