Copper-catalyzed radical transnitrilation of arylborons with dimethylmalononitrile and mechanistic insights

Abstract

Aromatic nitriles hold a prominent position in organic synthesis due to the unique importance of the cyanide moiety and also the diverse transformations of such groups to various functionalities. Traditional preparative routes are mainly based on Sandmeyer and Rosenmund–von Braun reactions, using toxic CuCN as a reagent. Organoborons are convenient building blocks for new chemical bond construction, and thus developing transition-metal catalytic systems for the cyanation of arylborons would provide attractive synthetic routes. Herein, we first establish the development of a mild and oxidant-free copper catalytic system for the transnitrilation of arylborons with dimethylmalononitrile (DMMN). The present system features broad scope, high functionality tolerance, scalability and practicality. Moreover, the system can be applied for the late-stage functionalization of various complex molecules. Distinct from the reported transnitrilation systems via polar mechanisms, the current copper system occurred via an unprecedent radical pathway with a Cu⁰/Cu^I catalytic cycle. The radical trapping, EPR and XPS experiments all supported the radical reaction mechanism.