Intramolecular Reactions of Metal Carbenoids with Allylic Ethers: Is a Free Ylide Involved in Every Case?

摘要

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 a-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]-sigma- tropic rearrangement products. In the case of the iridium-catalyzed reaction of a-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-C bond.