Transition metal-free C-3 functionalization of quinoxalin-2(1H)-ones: recent advances and sanguine future

Abstract

Transition metal-free C-3 functionalization of quinoxalin-2(1H)-ones has recently emerged as a modern sustainable protocol, as C-3 functionalized quinoxalin-2(1H)-ones offer robust applications in the medicinal, pharmaceutical and agriculture industry. In recent times, various sustainable protocols for the construction of C–C, C–N, C–P, C–S, and C–O bonds via the C–H functionalization of quinoxalin-2(1H)-ones were developed. A gradual shift from metal-catalyzed to metal-free methodologies has been observed in last few years, as the latter provide an environmentally benign synthetic route in organic chemistry. The present review offers an extensive discussion on recent advances in transition metal-free C–H functionalization of quinoxalin-2(1H)-ones. The review has been decoratively categorized based on C–C, C–O/C–S and C–N/C–P bond formation using metal-free, visible light and electrochemically catalyzed strategies. In addition, mechanistic features of chemical transformation of quinoxalin-2(1H)-ones have been highlighted.