Acylation-Type Reactions: Synthesis of Esters Via Selective Acyl Transfer

Abstract

Acyl transfer reactions are one of the most common transformations in organic synthesis as well as in nature. Though many methods (acidic catalysis, basic catalysis, and nucleophilic catalysis, e.g., 4-dimethylaminopyridine) for the acylation of alcohols have been known for centuries, asymmetric approaches were just realized in the last 25–30 years. Asymmetric acyl transfer onto alcohols presents a powerful tool for the synthesis of enantiopure substrates, which are important building blocks for the synthesis of natural products, pharmaceuticals, and chiral ligands. The introduction explains the differences between kinetic resolution, dynamic kinetic resolution, and desymmetrization and shows how the catalytic efficacy of a kinetic resolution is typically expressed (Kagan's equation). This article summarizes organocatalysts and metal-complexes capable of an enantioselective acyl transfer. Substrate scope, reaction conditions, selectivities, mechanism, and the accessibility of the catalysts are organized by type of catalyst. The performances of the catalysts are discussed and, if possible, comparisons toward efficiency are made. In the final part of the chapter, examples of the utilization of chiral acylation catalysts to achieve regioselective acylation in polyol-substrates are presented.