Study on the Cyclization Methods of 3-[1-(Phenyl-hydrazono)ethyl]-chromen-2-ones.

Abstract Some new methods, such as air oxidation, catalytic oxidation, and solvent-free synthesis, are developed for the synthesis of 3-methyl-1-phenylchromeno[4,3-c]pyrazol-4(1H)-ones(2) from the cyclization of 3-[1-(phenyl-hydrazono)ethyl]-chromen-2-ones(1). Compared with air oxidation, catalytic oxidation can increase the rate of the cyclization of compound 1, and the solvent-free synthesis showed advantages of no organic solvent pollution, elevated reaction rate, and higher selectivity.