reaction of substituted pyrazolin-5-ones with het-arylidene-malononitriles

3-Methyl-L-phenylpyrazolin-5-one 1a reacts with the heterocyclic arylidenes 2a,b to afford the pyrano[2,3-c] pyrazole derivatives 3a,b and/or the acyclic adducts 4a,b depending on the reaction conditions. l,3-Diphenylpyrazolin-5-one 1b reacts with 2a,b to afford the oxinobispyrazole derivatives 5a,b along with pyrano[2,3-c] pyrazole derivatives 6a,b when the reaction was catalyzed by piperidine, while the pyrano[2,3-c]pyrazole derivatives 6a,b were only obtained when the reaction was catalyzed by sodium ethoxide. 3-Methyl and 3-phenylpyrazolin-5-ones 1c,d react with 2a,b to afford solely the pyrano [2,3-c] pyrazole derivatives 9a-d. A plausible mechanism is presented to account for these results