Iron(III)-Catalyzed Ring-Opening Annulation of 2-Arylindoles with 1,2-Diaminoarenes and -Butyl Nitrite (TBN) to Prepare 2-Aminoaryl Quinoxalines.

A variety of 2-aminoaryl quinoxaline derivatives were prepared in moderate to excellent yields through the iron(III)-catalyzed ring-opening of 2-substituted indoles and sequential annulation with 1,2-diaminoarenes in the presence of -butyl nitrite (TBN) as the oxidant. Experimental results revealed that the reaction might undergo TBN-mediated nitrosation, tautomerization, iron(III)-catalyzed condensation, intramolecular cyclization, and aromatization via selective C-N bond cleavage in one pot. More importantly, a paracyclophane-derived 2-aminoaryl quinoxaline could be synthesized in 38% total yield over three steps from paracyclophane. The present method features broad substrate scope, good functional group tolerance, N1-C2 bond cleavage of indoles, and C3-position formal umpolung of indoles.