A convenient 1,3-dipolar cycloaddition–reduction synthetic sequence from 2-allyloxy-5-nitro-salicylaldehyde to aminobenzopyran-annulated heterocycles

Abstract

A microwave-assisted, one-pot synthesis of some nitro benzopyran-annulated pyrroles as well as pyrrolo-fused isoquinolines via a 1,3-dipolar cycloaddition, which involves the in situ generation of azomethine ylide formed by reacting secondary amines with 2-allyloxy-5-nitro-salicylaldehyde, has been achieved in a solvent-free environment. Compared to methods of conventional and thermal heating, the present microwave-assisted method is rapid and highly efficient. In addition, amino analogous heterocycles were successfully accessed after treating the reaction mass further with iron in acidic medium, which also highlights a one-pot procedure for a new 1,3-dipolar cycloaddition–reduction synthetic sequence. All amino-products are new bioprofiles and anticipated to be effective drug-like candidates. All compounds were characterised based on their elemental analysis, mass, IR, and ¹H and ¹³C NMR spectroscopic data. The stereochemistry of the product was confirmed by 2D NMR COSY and NOESY experiments, which, on the basis of single crystal X-ray diffraction data analysis, was further confirmed and supported.