Microwave-assisted and Zn[l-proline]2 catalyzed tandem cyclization under solvent free conditions: Rapid synthesis of chromeno[4,3-c]pyrazol-4-ones

Present study and investigations reveals that, the hydrazones of 3-acetyl-4-hydroxycoumarin undergo ring cyclization to give, 3-methyl-1-substituted phenyl-1H-chromeno[4,3-c]pyrazol-4-ones (2a–m) under the influence of microwave irradiation and by using Zn[l-proline]2, a novel Lewis acid catalyst. The overall yields of the products were found to be 82–93%. Without use of the catalyst, no reaction progress was observed. No significant changes in the overall yields of the products were observed at high microwave power and at high temperatures. The reusability of the catalyst was also checked and found up to seven cycles.

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