Hydroboration Reaction and Mechanism of Carboxylic Acids using NaNH2(BH3)2, a Hydroboration Reagent with Reducing Capability between NaBH4 and LiAlH4

Jin Wang; Ming-Yue Ju; Xinghua Wang; Yan-Na Ma; Donghui Wei; Xuenian Chen

doi:10.1021/acs.joc.1c00302

Hydroboration Reaction and Mechanism of Carboxylic Acids using NaNH₂(BH₃)₂, a Hydroboration Reagent with Reducing Capability between NaBH₄ and LiAlH₄

J Org Chem. 2021 Apr 2;86(7):5305-5316. doi: 10.1021/acs.joc.1c00302. Epub 2021 Mar 17.

Authors

Jin Wang^{1

2}, Ming-Yue Ju¹, Xinghua Wang³, Yan-Na Ma^{1

3}, Donghui Wei³, Xuenian Chen^{1

3}

Affiliations

¹ School of Chemistry and Chemical Engineering, Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials, Henan Normal University, Xinxiang 453007, China.
² College of Chemistry and Chemical Engineering, Mudanjiang Normal University, Mudanjiang 157011, China.
³ Green Catalysis Center and College of Chemistry, Zhengzhou University, Zhengzhou 450001, China.

PMID: 33729800
DOI: 10.1021/acs.joc.1c00302

Abstract

Hydroboration reactions of carboxylic acids using sodium aminodiboranate (NaNH₂[BH₃]₂, NaADBH) to form primary alcohols were systematically investigated, and the reduction mechanism was elucidated experimentally and computationally. The transfer of hydride ions from B atoms to C atoms, the key step in the mechanism, was theoretically illustrated and supported by experimental results. The intermediates of NH₂B₂H₅, PhCH═CHCOOBH₂NH₂BH₃^-, PhCH═CHCH₂OBO, and the byproducts of BH₄^-, NH₂BH₂, and NH₂BH₃^- were identified and characterized by ¹¹B and ¹H NMR. The reducing capacity of NaADBH was found between that of NaBH₄ and LiAlH₄. We have thus found that NaADBH is a promising reducing agent for hydroboration because of its stability and easy handling. These reactions exhibit excellent yields and good selectivity, therefore providing alternative synthetic approaches for the conversion of carboxylic acids to primary alcohols with a wide range of functional group tolerance.