Organophosphorus-Catalyzed Reductive Functionalization of Nitrocompounds via P(III)/P(V) Redox Couple

Abstract

Nitro compounds are widely available synthetic building blocks which present a strategical opportunity to serve as direct precursors for the construction of nitrogen-containing molecules with increasing complexity and value. With the utilization of geometric-distorted organophosphetanes as catalysts and hydrosilanes as terminal reductants, nitro compounds (nitroarenes, nitromethane and nitroalkanes) undergo reductive O-atom transfer reactions involving the conversion of P(III)/P(V)=O. With that, boronic acids were employed as coupling partners to intercept the nitrene reactivity of nitro compounds derived oxazaphosphorane intermediates for direct reductive C–N coupling. This organophosphorus-catalyzed nitro deoxygenative platform was further developed to a tandem C–N coupling/cyclization sequence, yielding a variety N-functionalized azaheterocycles (oxindoles, indoles, quinoxalinediones, and benzimidazoles). Besides boronic acids, anilines were also introduced as an exogenous coupling partner for novel cross-selective intermolecular N–N bond forming reactivity in the formation of various hydrazines with excellent chemoselectivities and functional group tolerance. These works herein not only expand the reactivity of low-cost and environment-benign organophosphorus compounds as platforms for catalytic reductive O-atom transfer, but also details the P(III)/P(V)=O redox couple catalyzed reaction mechanism, providing further precedents for the catalytic potential of organophosphorus compounds in reaction classes heretofore dominated by transition-metal catalysis and suggesting potential opportunities for organophosphorus catalyst optimization.