Brønsted acid-catalyzed metal-free one-pot synthesis of benzimidazoles via [4+1] heteroannulation of ortho-phenylenediamines with β-oxodithioesters

Abstract

An operationally simple and user-friendly one-pot domino protocol for the synthesis of 2-aryl/hetaryl benzimidazoles has been devised from easily available and inexpensive 1,2-phenylenediamines and β-oxodithioesters. The strategic [4+1] heteroannulation initiated by Bronsted acid PTSA relies on remarkable domino sequence of condensation, cyclization, and elimination. The current approach enables N-H/N-H functionalization under solventless and metal-free conditions leading to diverse benzimidazoles. The reactions proceeded smoothly affording the desired products in good to excellent yields, exhibiting gram-scale ability and broad functional groups tolerance. Notably, the approach is highly chemo- and regioselective.