Reductions of aldehydes and ketones with a readily available N-heterocyclic carbene borane and acetic acid

Vladimir Lamm,Dennis P Curran,Tsuyoshi Taniguchi,Xiangcheng Pan

doi:10.3762/bjoc.9.76

Abstract

Acetic acid promotes the reduction of aldehydes and ketones by the readily available N-heterocyclic carbene borane, 1,3-dimethylimidazol-2-ylidene borane. Aldehydes are reduced over 1–24 h at room temperature with 1 equiv of acetic acid and 0.5 equiv of the NHC-borane. Ketone reductions are slower but can be accelerated by using 5 equiv of acetic acid. Aldehydes can be selectively reduced in the presence of ketones. On a small scale, products are isolated by evaporation of the reaction mixture and direct chromatography.

Highlights

Reduction of carbonyl compounds is a common, fundamental chemical transformation
DiMe-Imd-BH3 (1) does not react with silica gel, so it seems likely that silica gel serves as a weak acid to activate carbonyl groups toward reduction by 1
We decided to replace the silica gel with weak acids in order to extend the practicality of reductions with NHC-boranes

Summary

Introduction

Reduction of carbonyl compounds is a common, fundamental chemical transformation. Among the numerous hydride reagents available for such reductions, boron reductants are widely used in the field of synthetic chemistry due to their availability and favorable reaction profiles [1,2,3]. Scheme 1: Aldehydes and ketones are reduced by 1 when silica gel is added. We decided to replace the silica gel with weak acids in order to extend the practicality of reductions with NHC-boranes.

Results

Conclusion