Metal- and Additive-Free Intramolecular Direct Amidation of Ester Functionality within a Nitroarene Framework: Facile Access to Azaheterocycles

A novel intramolecular direct amidation of unactivated esters with nitroarenes under a mild, practical, and scalable synthetic protocol is the subject of this present investigation. The method uses a green, environmentally friendly, inexpensive, and readily available single-electron reductant, sodium dithionite (Na2S2O4), as the sole reagent under metal-free, additive-free, mild reaction conditions. Various nitroarenes containing ortho-ester functionalities are subjected to tandem chemoselective reductive cyclization/amidation to deliver high-value azaheterocycles in excellent yields. Notably, the present method enables the rapid construction of pharmaceutically relevant azaheterocycles from readily accessible ortho-functionalized nitroarenes. Furthermore, gram-scale synthesis of several key starting materials and pharmaceuticals demonstrates the practical utility of the developed protocol.