La(OTf)3 catalyzed reaction of salicylaldehyde phenylhydrazones with β-ketoesters and activated alkynes: facile approach for the preparation of chromenopyrazolones

Abstract

A facile approach has been developed for the preparation of chromenopyrazolones (5a–o, 7a–k) by the reaction of salicylaldehyde phenylhydrazones (3a–o) with β-ketoesters (4a, 4f–g) and activated alkynes (6a–e) in the presence of La(OTf)₃ with good yields. However, the reaction of salicylaldehyde phenylhydrazones (3a, 3c, 3j–k, 3n) with ethyl 4-chloro-3-oxobutanoate (4e) underwent cyclization with reductive dechlorination and provided the methyl chromenopyrazolones instead of chloromethyl chromenopyrazolones. The present solvent free protocol provided the novel heterocyclic compounds.