Cyanohydridoborate anion as a selective reducing agent

TLDR: The use of modified boron hydrides as selective reducing agents for organic functional g roups has been studied extensively as discussed by the authors, with a focus on reducing a wide variety of organic functional groups with remarkable selectivity.

Abstract: Sodium cyanohydridoborate (NaBH3CN) reduces a wide variety of organic functional groups with remarkable selectivity. The reduction of aldehydes and ketones is p H dependent, the reaction proceeding readily a t pH 3-4. Oximes a re smoothly reduced to alkylhydroxylamines and enamines are reduced to amines under acid catalysis. Reaction of a n aldehyde or ketone with ammonia, primary amine, or secondary amine a t p H -7 i n the presence of BHaCNleads t o primary, secondary, or tertiary amines, respectively, uia reductive amination of the carbonyl group. Reaction of substituted pyruvic acids with ammonia and BH3CNaffords an excellent method for the synthesis of amino acids; l5N labeling can be accomplished by using I5NH3. The hydrogens of BHICNcan be readily exchanged for either deuterium or tritium, thus permitting the synthesis of deuteriumor tritiumlabeled alcohols, amines, and amino acids. onsiderable attention has been devo ted t o t h e The earlier d iscovery o f the reduc ing p o w e r 4 and t h e acid stability5 of l i t h ium cyanohydr idobora t e encourstudy of modified boron hydrides as selective reducing agents for organic functional g roups . 2.3 2127 (1962); (c) R. Paul and N . Joseph, Bull. SOC. Chem. Fr., 550 (1952); (d) H. C. Brown and E. J. Mead, J . Amer. Chem. SOC., 75, 6263 (1953). (3) (a) H. Noth and H. Beyer, Chem. Ber., 93, 1078 (1960); (b) J. H. Billman and J. W. McDowell, J . Org. Chem., 26, 1437 (1961); (C) s. s. White, Jr., and H. C. Kelly, J . Amer. Chem. Soc., 92, 4203 (1970). and references therein. C (1) (a) Alfred P. Sloan Foundation Fellow; (b) National Institutes of Health Predoctoral Fellow, 1968-1970. Taken in part from the Ph.D. Thesis of H. D. D., University of Minnesota, 1970. (2) (a) H. C. Brown and B. C. Subba Rao, J . Amer. Chem. SOC., 78, 2582 (1956); (b) G. R. Pettit and D. M. Piatak, J . Org. Chem., 27, (4) R. F. Borch and H. D. Durst, ibid., 91, 3996 (1969). Borch, Bernstein, Durst Cyanohydridoborate Anion