Sodium triacetoxyborohydride is presented as a general reducing agent for the reductive amination of aldehydes and ketones. Procedures for using this mild and selective reagent have been developed for a wide variety of substrates. The scope of the reaction includes aliphatic acyclic and cyclic ketones, aliphatic and aromatic aldehydes, and primary and secondary amines including a variety of weakly basic and nonbasic amines. Limitations include reactions with aromatic and unsaturated ketones and some sterically hindered ketones and amines. 1,2-Dichloroethane (DCE) is the preferred reaction solvent, but reactions can also be carried out in tetrahydrofuran (THF) and occasionally in acetonitrile. Acetic acid may be used as catalyst with ketone reactions, but it is generally not needed with aldehydes. The procedure is carried out effectively in the presence of acid sensitive functional groups such as acetals and ketals; it can also be carried out in the presence of reducible functional groups such as C-C multiple bonds and cyano and nitro groups. Reactions are generally faster in DCE than in THF, and in both solvents, reactions are faster in the presence of AcOH. In comparison with other reductive amination procedures such as NaBH(3)CN/MeOH, borane-pyridine, and catalytic hydrogenation, NaBH(OAc)(3) gave consistently higher yields and fewer side products. In the reductive amination of some aldehydes with primary amines where dialkylation is a problem we adopted a stepwise procedure involving imine formation in MeOH followed by reduction with NaBH(4).
Reductive Amination of Aldehydes and Ketones with Sodium Triacetoxyborohydride.Studies on Direct and Indirect Reductive Amination Procedures.-NaBH(O-Ac) is found to be a synthetically useful reagent for reductive amination of aldehydes and ketones. With aliphatic acyclic and cyclic ketones, aliphatic and aromatic aldehydes, and primary and secondary amines including weakly basic and nonbasic amines the reaction proceeds effectively. In some cases of reductive amination of aldehydes with primary amines considerable amounts of dialkylated or other side products are obtained. A stepwise (indirect) procedure involving imine formation followed by NaBH4-mediated reduction is a convenient alternative for such cases. -(ABDEL-MAGID, A. F.; CARSON, K. G.; HARRIS, B. D.; MARYANOFF, C. A.; SHAH, R. D.; J.
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