Synthesis of structurally diverse pyrazolo[1,2-a]pyrazolones based on the selective C–H bond alkenylation–annulation of 1-arylpyrazolidinones with allenyl acetates

Abstract

Presented herein is a concise synthesis of structurally diverse pyrazolo[1,2-a]pyrazolones based on condition-controlled divergent reactions of 1-arylpyrazolidinones with allenyl acetates. To be specific, mono C–H bond alkenylation–annulation or double C–H alkenylation–annulation could be realized selectively and effectively to furnish pyrazolo[1,2-a]pyrazolone scaffolds with distinct substitution patterns by simply regulating the reaction conditions. To our knowledge, such a controllable selective reaction pattern has not been disclosed previously. In addition, the products thus formed could be transformed into several value-added hybrid compounds through easy-to-run derivations by taking advantage of the rich chemistry of the functional groups introduced in situ. In general, these newly developed protocols feature simple substrates with a broad scope, structurally diverse products, easily modulated selectivity, concise synthetic procedures, excellent step-economy and ready scalability.