Synthesis of highly functionalized thiazolo[3,2- a ]pyridine derivatives via a five-component cascade reaction based on nitroketene N , S -acetal.

A highly efficient and straightforward synthesis of N-fused heterocyclic compounds including 5-amino-7-(aryl)-8-nitro- N '-(1-(aryl)ethylidene)-3,7-dihydro-2 H -thiazolo[3,2- a ]pyridine-6-carbohydrazide derivatives is successfully achieved via a five-component cascade reaction utilizing cyanoacetohydrazide, various acetophenones, aromatic aldehydes, 1,1-bis(methylthio)-2-nitroethylene and cysteamine hydrochloride in ethanol at reflux conditions. The new approach involves domino N , S -acetal formation, Knoevenagel condensation, Michael reaction, imine-enamine tautomerization and N -cyclization sequences. The prominent advantages of this protocol include: facility of operation, available and economical starting materials, no need for toxic solvents, high yields and tolerance of a wide variety of functional groups.