title: Cu-promoted sydnone cycloadditions of alkynes: scope and mechanism studies.
abstract: Cu salts have been found to promote the cycloaddition reaction of sydnones and terminal alkynes, providing significant reduction in reaction times. Specifically, the use of Cu(OTf)2 is found to provide 1,3-disubstituted pyrazoles, whereas simply switching the promoter system to Cu(OAc)2 allows the corresponding 1,4-isomers to be produced. The mechanism of the Cu-effect in each case has been investigated by experimental and theoretical studies, and they suggest that Cu(OTf)2 functions by Lewis acid activation of the sydnone, whereas Cu(OAc)2 promotes formation of reactive Cu(I) acetylides.
authors.affiliation: Department of Chemistry, The University of Sheffield, Brook Hill, Sheffield, S3 7HF (UK).
authors.forename: Júlia
authors.initials: J
authors.lastname: Comas-Barceló
authors.forename: Robert S
authors.initials: RS
authors.lastname: Foster
authors.forename: Béla
authors.initials: B
authors.lastname: Fiser
authors.forename: Enrique
authors.initials: E
authors.lastname: Gomez-Bengoa
authors.forename: Joseph P A
authors.initials: JP
authors.lastname: Harrity
keywords: cycloadditions; density functional calculations; pyrazole; regioselective reactions; sydnones