Asymmetric Enamine Catalysis

Abstract

The catalysis by primary and secondary amines of electrophilic substitution reactions in the α-position of carbonyl compounds and related reactions via enamine intermediates is called enamine catalysis. To a large degree this chemistry can be considered the catalytic variant of the classical preformed enamine chemistry (Scheme 1) pioneered by Stork. In such transformations an enamine (III) is generated by reacting a carbonyl compound (I) with an amine (II) under dehydration conditions. Reaction of the enamine (III) can proceed via an addition (route A) or substitution (route B) route depending on the nature of the reaction partner (electrophile). In either case, iminium ions (IV) are usually formed, which are then hydrolyzed to afford the products (V). A vast array of transformations has been achieved via preformed enamine chemistry. Therefore, a catalytic version of this chemistry was highly desirable.