Synthesis of 5-amino- N '-(9 H -fluoren-9-ylidene)-8-nitro-7-aryl-1,2,3,7-tetrahydroimidazo[1,2- a ]pyridine-6-carbohydrazide derivatives based on heterocyclic ketene aminals.

A new class of tetrahydroimidazo[1,2- a ]pyridine derivatives has been successfully prepared via a five-component domino reaction using cyanoacetohydrazide, 9-fluorenone, aromatic aldehydes, 1,1-bis(methylthio)-2-nitroethene and ethylenediamine in ethanol at reflux. The new efficient cascade approach involves a sequence of N , N -acetal formation, Knoevenagel condensation, Michael addition, imine-enamine tautomerization and N -cyclization as key steps. The merit of this protocol is highlighted by its available and economical starting compounds, operational simplicity, clean reaction profile and tolerance of a wide diversity of functional groups.