The Michael-type Addition of 1-Cyanoacetyl-3,5-dimethylpyrazole to Arylmethylenecyanoacetamides

The Et3N-promoted reaction of (E)-3-aryl-2-cyanoacrylamides (arylmethylenecyanoacetamides) with 1-cyanoacetyl-3,5-dimethylpyrazole was thoroughly studied. It was found that either triethylammonium 4-aryl-3,5-dicyano-6-oxo-1,4,5,6-tetrahydropyridine-2-olates 1 (salts of Guareschi imides) or their oxidation products – triethylammonium 4-aryl-3,5-dicyano-6-oxo-1,6-dihydropyridine-2-olates 2 were formed, depending on the nature of substituents in the 3-aryl fragment of starting acrylamides. Thus, when Ar = ortho-, meta-substituted phenyl or hetaryl such as 2-furyl, 3-thienyl etc., only Guareschi imides salts 1 were obtained in good to excellent yields. In the case of para-substituted or unsubstituted phenyl, pyridine-2-olates 2 were isolated as major products due to fast oxidation of Guareschi intermediates. The influence of reaction conditions and the nature of the base on the structure of final products is discussed.