Asymmetric Cyanation Reactions

The asymmetric cyanation across C C, C O, and C N bonds ranks among the most important and well-studied reactions in asymmetric catalysis to achieve useful chiral building blocks for pharmaceuticals, agrochemicals, and specialty materials. The asymmetric cyanation reaction demands careful selection of a chiral catalyst and a cyanide source. A number of efficient and successful synthetic strategies have been developed that include asymmetric cyanation-utilizing enzyme, organocatalyst, and metal complexes as catalysts. As for the concern of the source of cyanide, inorganic cyanides, for example, NaCN and KCN; and organic cyanides, for example, trimethylsilyl cyanide, alkyl cyanoformates, acetone cyanohydrin, acetyl cyanide, alkyl cyanophosphorylates, etc. have been employed, depending upon the targeted substrates. Since the subject is vast, this chapter discusses in detail chiral-metal-complex-based catalytic asymmetric synthesis of cyanohydrins using different cyanide sources. An attempt is made to discuss the reaction mechanism involved in enantioselective cyanation reactions.