Brønsted acid-mediated mono- and di-substitution of quinoxalines with indoles: a pathway to indolocarbazole-quinoxaline scaffolds

Abstract

A versatile and efficient protocol for the mono- and di-substitution of quinoxalines with indoles has been developed, offering a direct pathway to indolocarbazole-quinoxaline scaffolds. By optimizing the reaction conditions, selective coupling at the C-2 and C-3 positions of quinoxalines with diverse indole derivatives was achieved under transition metal-free conditions. Substrate scope evaluation revealed broad functional group tolerance and the synthetic utility was demonstrated by gram-scale synthesis and subsequent cyclization into novel indolocarbazole-quinoxalines. Mechanistic studies suggest an ionic pathway, highlighting the potential of this method for constructing biologically relevant heterocyclic architectures.