印度国立科学教育研究院Sharanappa Nembenna团队揭示了氢化锌催化异氰酸酯的化学选择性硼氢化反应机制——酰胺键的形成和C=O键的断裂。 相关研究成果发表在2021年2月26日出版的国际学术期刊《德国应用化学》。

该文报道了一种显著的共轭双胍盐（CBG）负载氢化锌，[{LZnH}2；L={（ArHN）（ArN）‐C=N‐C=（NAr）（NHAr）；Ar=2,6‐Et2‐C6H3}]（I）通过硼氢化催化的杂烯部分还原。在含有给电子/缺电子基团的大量的芳基/烷基异氰酸酯，能够通过还原反应选择性合成N-硼基甲酰胺，双硼基半酰胺，N-硼基胺。化合物I有效催化各种异氰酸酯的化学选择性还原，构建酰胺键。

异氰酸酯通过脱氧氢硼化反应，C=O键切断生成N-硼基甲胺，该方法兼容硝基、氰基、卤化物和烯烃官能团。

研究人员通过一系列动力学实验、控制实验、中间体结构表征等方法，揭示了反应中Zn-H物种在还原步骤、C=O键切断反应中起到关键作用。

附：英文原文

Title: Zinc Hydride Catalyzed Chemoselective Hydroboration of Isocyanates: Amide Bond Formation and C=O Bond Cleavage

Author: Sharanappa Nembenna, Rajata Kumar Sahoo, Nabin Sarkar

Issue&Volume: 2021-02-26

Abstract: Herein, a remarkable conjugated bis‐guanidinate (CBG) supported zinc hydride, [{LZnH}2; L = {(ArHN)(ArN)‐C=N‐C=(NAr)(NHAr); Ar = 2,6‐Et2‐C6H3}] (I) catalyzed partial reduction of heteroallenes via hydroboration is reported. A large number of aryl and alkyl isocyanates, including electron‐donating and withdrawing groups, undergo reduction to obtain selectively N‐boryl formamide, bis(boryl) hemiaminal and N‐boryl methyl amine products. The compound I effectively catalyzes the chemoselective reduction of various isocyanates, in which the construction of the amide bond occurs. Isocyanates undergo a deoxygenation hydroboration reaction, in which the C=O bond cleaves, leading to N‐boryl methyl amines. Several functionalities such as nitro, cyano, halide, and alkene groups are well‐tolerated. Furthermore, a series of kinetic, control experiments and structurally characterized intermediates suggest that the zinc hydride species are responsible for all reduction steps and breaking the C=O bond.

DOI: 10.1002/anie.202100375

Source: https://onlinelibrary.wiley.com/doi/10.1002/anie.202100375