Reductive Amination of Aldehydes and Ketones with Sodium Triacetoxyborohydride. Studies on Direct and Indirect Reductive Amination Procedures¹

Abstract

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).

Fluoxetine and Norfluoxetine Revisited: New Insights into the Electrochemical and Spectroscopic Properties

“…20, 21 The structural elucidation of the compounds was performed by FT-IR, NMR, and EM and is presented in the Experimental Methods.…”

Amination of Aliphatic Alcohols and Diols with an Iridium Pincer Catalyst

“…Another useful approach in the synthesis of amines is the reductive amination of aldehydes and ketones. [7] However, this method requires the use of strong reducing reagents or dangerous hydrogen gas and is not always selective for monoalkylation of primary amines. [8] Catalytic amination of alcohols is an alternative method for the preparation of amines (Scheme 1) and it is attractive from several points of view.…”

Syntheses of diazadithiacrown ethers containing two 8-hydroxyquinoline side arms

“…18 In the present case, 8-hydroxyquinoline-2-carbaldehyde and the appropriate ligand (16-18 or 20) were treated with NaBH(OAc) 3 to form the bis(8-hydroxyquinolin-2-ylmethyl)-substituted ligands 33-36 in yields of 46% -66% (Scheme 3). It is important to note that the hydroxy group of HQ did not have to be protected for this reaction as previously reported.…”