Reductive Amination of Aldehydes Using Aminoboranes as Iminium Ion Generators

Abstract

2-Dialkylamino-4H-1,3,2-benzodioxaborins, salicyl alcohol derived aminoboranes, serve as efficient and mild iminium ion generators in the reductive amination of aldehydes with NaBH₄. Using a diisopropylamino derivative, a variety of amines including secondary and primary amines, and ammonia can participate to the reductive amination in aprotic organic solvents without the use of acidic promoters.

Key words

reductions - aminations - boron - chemoselectivity - aldehydes

References and Notes

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7

Although the addition of 2-piperidinone is not crucial to attain the reductive amination product, it moderately accelerates the reaction and improves the yield to some extent.

9

Typical Procedure for Reductive Amination Using 1b.
To a solution of 2-piperidinone (0.048 mmol) in 1,2-dichloroethane (0.5 mL) were added 1b (57 mg, 0.24 mmol), amines (0.24-0.48 mmol), aldehyde (0.24 mmol) and NaBH₄ (11 mg, 0.29 mmol) at r.t. After stirring for 0.5-3 h, MeOH (0.5 mL) was added and the mixture was subjected directly to column chromatography on silica gel pretreated with 5% Et₃N in hexane.