Cu–N‐heterocyclic carbene‐catalysed synthesis of 2‐aryl‐3‐(arylethynyl)quinoxalines from one‐pot tandem coupling of<i>o</i>‐phenylenediamines and terminal alkynes

Abstract

A series of new benzimidazolium chlorides bearing N , N ′‐benzyl, 2,4,6‐trimethylbenzyl and 2,4,6‐triisopropylbenzyl substituents have been designed and synthesized from various o ‐phenylenediamines. Subsequently, corresponding Cu‐based N ‐heterocyclic carbenes (NHCs) were generated in situ in the reaction medium which represents a new application of NHCs exploiting distinct catalytic property towards intermolecular cyclization reaction cascade for the synthesis of 2‐aryl‐3‐(arylethynyl)quinoxalines from o ‐phenylenediamines and terminal alkynes. The outcome of the cyclization reaction product depends upon the N , N ′‐substituents present on the benzimidazolium chlorides.