One-pot regioselective synthesis of substituted pyrazoles and isoxazoles in PEG-400/water medium by Cu-free nano-Pd catalyzed sequential acyl Sonogashira coupling–intramolecular cyclization

Abstract

Catalyst efficacy of in situ generated Pd-nanoparticles in the regioselective one-pot synthesis of substituted pyrazoles and isoxazoles via sequential coupling-cyclization methodology in environmentally benign medium is described.

Heterocycles by Consecutive Multicomponent Syntheses via Catalytically Generated Alkynoyl Intermediates

“…Without losing significant catalytic efficiency the PdNPs were reused in five successive cycles. In this process, 14 examples of isoxazoles 54 were obtained in good-to-excellent yields (Scheme 28) [92]. In addition, 19 examples of 1,3,5-substituted pyrazoles were obtained in 75-92% yield by adding (phenyl)hydrazine to the in situ generated ynones underlining the versatility of the one-pot sequence.…”

A decennary update on applications of metal nanoparticles (MNPs) in the synthesis of nitrogen- and oxygen-containing heterocyclic scaffolds

“…In situ-formed PdNP-catalyzed copper-free acyl Sonogashira coupling followed by intramolecular 5-endo-dig cyclization was reported for the one-pot synthesis of substituted pyrazoles (92i) and isoxazoles (274, Scheme 163) in PEG-water. 298 The treatment of PdCl 2 with PEG-400 resulted in the formation of Pd(0) NPs, which in turn reacted with 228 and 270 in the presence of TBAB (tetrabutyl ammonium bromide) as a phase transfer catalyst or stabilizer and pyrrolidine as a base to form a ynone intermediate (273). In the same pot, the addition of substituted hydrazine (64d) or hydroxylamine hydrochloride (275) led to the regioselective synthesis of 92i or 274, respectively, via palladation with regenerated Pd(0)NPs.…”

Recent advances in metal catalyzed or mediated cyclization/functionalization of alkynes to construct isoxazoles

“…35 For example, Vadde and Jonnalagadda and co-workers developed a one-pot Cu-free nano-Pd catalyzed sequential acyl Sonogashira coupling-intramolecular cyclization for the synthesis of various substituted isoxazoles (34) in an environmentally benign PEG-400/water system (Scheme 16). 36 The Pd-NHC catalyst precursors can be synthesized from Pd(OAc) 2 and NHC ligands (33) in the presence of DBU in THF. It is worth mentioning that an in situ generation of catalytic palladium nanoparticles from Pd-NHC afforded significantly better results than the direct use of commercially available palladium catalysts such as PdCl 2 , and Pd(OAc) 2 .…”