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An Expedient Four-Component Domino Protocol for the Regioselective Synthesis of Highly Functionalized Pyranopyrazoles and Chromenopyrazoles via Nitroketene-N,S-acetal Chemistry under Solvent-Free Condition. -A simple one-pot protocol for the condensation/Knoevenagel reaction/Michael addition/annulation sequence of aldehydes (I) with hydrazines, ethyl acetoacetate, and nitroketene--N,S-acetal (IV) to give pyranopyrazoles. The use of salicylaldehydes (VII) results in the formation of chromenopyrazoles under similar conditions. -(JAYABAL, K.; PARAMASIVAN*, T. P.; Tetrahedron Lett. 55 (