Non-Classical C-H•••X Hydrogen Bonding and Its Role in Asymmetric Organocatalysis

Non-classical hydrogen bonds (NCHBs) have attracted significant interest in the past decade particularly because of their important role in asymmetric catalytic systems. These weak interactions (< 4 kcal/mol) offer much flexibility in the preorganization of molecular entities required to achieve high enantioselectivity. Herein, we review some recent important organocatalytic asymmetric reactions where a NCHB serves as a critical factor in determining the stereoselectivity. 1 Introduction 2 Hydrogen Bonds (HBs) and Non-Classical Hydrogen Bonds (NCHBs) 3 Early Developments in NCHBs 4 Selected Examples of NCHBs in Organic Transformations 5 Recent Examples of NCHBs in Enantioselective Reactions 6 Conclusions and Outlook