title: Intramolecular reactions of metal carbenoids with allylic ethers: is a free ylide involved in every case?
abstract: Rhodium-, copper- and iridium-catalyzed reactions of the (13)C-labelled diazo carbonyl substrates 18* and 19* were performed. Results obtained from copper- and iridium-catalyzed reactions of the (13)C-labelled α-diazo β-keto ester 19* indicate that either or both of these reactions do not proceed via a free oxonium ylide but instead follow a competing non-ylide route that delivers apparent [2,3]-sigmatropic rearrangement products. In the case of the iridium-catalyzed reaction of α-diazo β-keto ester 19*, results obtained from crossover experiments indicate that the initially formed metal-bound ylide dissociates to give an iridium enolate and an allyl cation, which recombine to form the -C bond.
authors.affiliation: WestCHEM, School of Chemistry, Joseph Black Building, University of Glasgow, University Avenue, Glasgow G12 8QQ (UK), Fax: (+44) 141-330-6867. stephen.clark@glasgow.ac.uk.
authors.forename: J Stephen
authors.initials: JS
authors.lastname: Clark
authors.forename: K Emelie
authors.initials: KE
authors.lastname: Hansen
keywords: carbenoids; cyclization; isotopic labeling; rearrangement; ylides