title: Anomalous intramolecular C-H insertion reactions of rhodium carbenoids: factors influencing the reaction course and mechanistic implications.
abstract: The intramolecular insertion of rhodium carbenoids into the alpha-C-H bonds of allylic ethers to give 3(2H)-furanones has been explored. Cyclopropanation is favored irrespective of the complex used for carbenoid generation or the substitution pattern of the allylic ether, unless a substituent is placed on the tether connecting the ether to the alpha-diazo ketone. Unusual acetal products resulting from an anomalous C-H insertion process are obtained in addition to the expected 3(2H)-furanones formed by conventional carbenoid C-H insertion. These acetals are the favored C-H insertion products in certain circumstances and particularly in cases where carbenoid generation is effected using an electron-deficient rhodium complex. Experiments with simple deuterium labeled substrates reveal that anomalous C-H insertion products arise by a mechanism that is distinct from that leading to the formation of conventional C-H insertion products. The formation of acetal products and the outcome of reactions performed using deuterium-labeled substrates suggest that a mechanism involving hydride migration to the rhodium center of the carbenoid is operative.
authors.affiliation: School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK. j.s.clark@nottingham.ac.uk
authors.forename: J Stephen
authors.initials: JS
authors.lastname: Clark
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Dossetter
authors.forename: Yung-Sing
authors.initials: YS
authors.lastname: Wong
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Townsend
authors.forename: William G
authors.initials: WG
authors.lastname: Whittingham
authors.forename: C Adam
authors.initials: CA
authors.lastname: Russell