Efficient regioselective five-component synthesis of novel thiazolo[3,2-a]pyridine carbohydrazides and oxazolo[3,2-a]pyridine carbohydrazides
- PMID: 35587848
- DOI: 10.1007/s11030-022-10446-0
Efficient regioselective five-component synthesis of novel thiazolo[3,2-a]pyridine carbohydrazides and oxazolo[3,2-a]pyridine carbohydrazides
Abstract
Two new categories of fused pyridines include 2H-thiazolo[3,2-a]pyridine-6-carbohydrazides and 2H-oxazolo[3,2-a]pyridine-6-carbohydrazides have been successfully synthesized via five-component cascade reactions using 9-fluorenone, cyanoacetohydrazide, 1,1-bis(methylthio)-2-nitroethene, aromatic aldehydes and cysteamine hydrochloride or ethanol amine as starting materials. This new approach involves a subsequence of key steps: N,S-acetal or N,O-acetal formation, Knoevenagel condensation, Michael addition, tautomerization and N-cyclization. It also has some advantages, such as convenience of operation, tolerance of a wide diversity of functional groups, use of green solvent and ease of purification by washing the crude products with ethanol.
Keywords: Cyanoacetohydrazide; Nitroketene acetal; One-pot reaction; Oxazolopyridine; Thiazolopyridine.
© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.
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