Heterocyclization of Acetamidrazones. I. Synthesis of 1,2,4‐triazolo[4,3‐a]pyridines via ring closure of 6‐(2‐acylhydrazino)pyridine intermediates

Abstract

The reaction of N1‐acyl‐2‐ethoxycarbonylacetamidrazones with ethyl ethoxymethylenecyanoacetate (EMCA) has been examined. The acetamidrazone 1a reacts with EMCA in boiling dimethyl sulphoxide to give the 1,2,4‐triazolo[4,3‐a]pyridin‐3(2H)‐one 2 in excellent yield. Similarly from the amidrazones 1b‐h the 1,2,4‐triazolo[4,3‐a]pyridines 3b‐h were obtained. When the reaction between the amidrazones and EMCA was performed in ethanolic solution, the 6‐(2‐acylhydrazino)‐pyridines 4 were isolated. Ring closure of 4 afforded the 1,2,4‐triazolo[4,3‐a]pyridines.