Nitroalkene reduction in deep eutectic solvents promoted by BH₃NH₃

Abstract

Deep eutectic solvents (DESs) have gained attention as green and safe as well as economically and environmentally sustainable alternative to the traditional organic solvents. Here, we report the combination of an atom-economic, very convenient and inexpensive reagent, such as BH3NH3, with bio-based eutectic mixtures as biorenewable solvents in the synthesis of nitroalkanes, valuable precursors of amines. A variety of nitrostyrenes and alkyl-substituted nitroalkenes, including α- and β-substituted nitroolefins, were chemoselectively reduced to the nitroalkanes, with an atom economy-oriented, simple and convenient experimental procedure. A reliable and easily reproducible protocol to isolate the product without the use of any organic solvent was established, and the recyclability of the DES mixture was successfully investigated.

Towards Green Reductions in Bio‐Derived Solvents

“…The best reaction medium was the eutectic mixture composed by betaine/glycolic acid (1 : 2 mol/mol); this mixture allowed the shortening of the reaction time up to 6 h, a good improvement if compared with the 18 h reaction time required in ChCl/gly (1 : 2 mol/mol) mixture and in pure glycerol. [23] The amino group is a central functionality in synthetic chemistry, due to its presence in natural products, pharmaceutical, and many biologically active molecules, as well as in keyintermediates for the synthesis of fine chemicals and dyes. [27] The direct reductive amination of carbonyl compounds still remains one of the most powerful tools for the preparation of molecules that contain such a pivotal functional group.…”

“…Deep Eutectic Solvents showed to be good solvents also to perform the reduction of nitroalkanes with BH 3 NH 3 (ammonia borane, AB) as the reducing agent, Scheme 6. [23] AB is receiving increasing attention as relatively inexpensive and useful reducing reagent for developing new green synthetic transformations [24,25] because it generates much less waste compared to other reducing agents, such as the bioinspired Hantzsch ester. [26] The reduction of nitroolefins (17) using BH 3 NH 3 (1.0 equiv.)…”

“…Electron‐rich substrates such as methoxy‐4‐(2‐nitrovinyl)benzene or methyl‐4‐(2‐nitrovinyl)benzene reacted much faster than electron‐poor ones which needed 2 equivalents of AB to achieve good yields. The best reaction medium was the eutectic mixture composed by betaine/glycolic acid (1 : 2 mol/mol); this mixture allowed the shortening of the reaction time up to 6 h, a good improvement if compared with the 18 h reaction time required in ChCl/gly (1 : 2 mol/mol) mixture and in pure glycerol [23] …”

Research Progress on Reactions Involving β-Nitrostyrene

“…41). 同年, Benaglia 课题组 [81] 与王泉明课题组 [82] 分别介 绍了由氨硼烷和铜氢化物促进的 β-硝基苯乙烯还原反 应, 以良好的产率获得相应的硝基烷烃, 为研究创新 的、可持续的和立体选择性的还原方法提供了新思路.…”