Na₂S₂O₄: A Versatile Reagent for the One-Pot Synthesis of 2-Aryl-1H-imidazo[4,5-c]pyridines from 4-Amino-3-nitropyridine and Aldehydes via Reductive Cyclization

Abstract

A highly efficient and versatile method for the synthesis of 2-aryl-1H-imidazo[4,5-c]pyridines 3 was achieved in one step via reductive cyclization of 4-amino-3-nitro-pyridines 4 with aromatic aldehydes in the presence of Na₂S₂O₄. Treatment of 3 with benzyl chloride in nonaqueous media under phase-transfer conditions to afford N-benzylated derivatives 10. Compounds 3 and 10 could also be prepared by other routes: dehydrogenative cyclization of monoanil 4-amino-3-arylideneaminopyridine 11 with different oxidizing reagents resulted in the formation of 3, and reduction of 11 with NaBH₄, followed by cyclization with aromatic acids using POCl₃, gave the N-benzyl-2-aryl-imidazo[4,5-c]pyridines 10. Compound 11 could be synthesized from 3,4-diamino pyridine 1. The structures of all the compounds obtained in the present work are supported by spectral and analytical data.

Keywords:

• 4-Amino-3-nitro-pyridine
• aromatic aldehydes
• benzyl chloride
• Na₂S₂O₄
• one-pot
• reductive cyclization

ACKNOWLEDGMENTS

We thank Azakem Laboratories Pvt. Ltd. management for encouragement and the staff of the analytical laboratories of our research center for spectral analyses.