Progress in (Thio)urea- and Squaramide-Based Brønsted Base Catalysts with Multiple H-Bond Donors

Abstract

Thiourea- and squaramide-based bifunctional base catalysts represent nowadays a powerful tool in the field of asymmetric catalysis and have demonstrated very efficient for promoting a wide variety of transformations enantioselectively. New versions that incorporate one or various additional H-bond donor site(s) in the catalyst structure have been developed recently which led to more active (reduced catalyst loadings) and selective catalysts. This review highlights the pioneering ideas and the most recent contributions to the area with the material organized according to the nature of the additional H-bond donor functionality. The advantages, current limitations and perspectives of these new multifunctional catalysts are discussed.