The reduction of nitriles to aldehydes

The three title reductant systems have significant advantages in generating aldehydes fromnitriles. These include: the utilization of convenient hydrogen sources, namely, sodium hypophosphite monohydrate and formic acid, respectively, and of the relatively inexpensive Raney nickel and Raney (Ni/Al) alloy; the convenience of conducting the reaction(s) in aqueous media at ambient temperatures and pressures, and avoiding the use of trapping agents (except when transforming glycosyl nitriles (vide infra)) and of hydrogen cylinders. Numerous examples of the utilization of the title systems are presented (mostly from the more recent literature) that demonstrate the utility of the respective methods in transforming a solo cyano group, or when accompanied by other chemosensitive functions in a structure, to the corresponding aldehyde. Such substrates include benzonitriles, glycosyl nitriles, O-, N- and S-containing heterocyclic nitriles, aliphatic-aromatic situations, and more complex fused heterocyclic and carbocyclic scaffolds. The review reports modifications of the title methods and several notable steric effects.