Sven Fuermeier et.al.: Chelation-Controlled Radical Chain Reactions Studied by Electrospray

Author(s): Sven Fuermeier, Jens Griep-Raming, Ahlke Hayen, Juergen O. Metzger

Title: Chelation-Controlled Radical Chain Reactions Studied by Electrospray

Date of Upload: 2005

Article: Chem. Eur. J. 2005, 11, 5545 – 5554, Institute of Pure and Applied Chemistry, Carl von Ossietzky University Oldenburg, Carl-von-Ossietzky-Strasse 9–11, 26111 Oldenburg (Germany)

Keywords: Mass spectrometry, Microreactor, Radical reactions, Reactive intermediate, ESI-MS, electrosprayionazation, mass spectrometry, reaction, solution, chelates, Lewis acids,

Abstract:
Abstract: Electrospray ionization mass spectrometry (ESI-MS) is a novel tool for the investigation of chemical reactions in solution and for the direct detection and identification of reactive intermediates. The tributyltin hydride mediated addition of tert-butyl iodide to dimethyl 2-cyclohexyl-4-methyleneglutarate (2) in the presence of Lewis acids was investigated by ESI-MS using a microreactor coupled on-line to an ESI mass spectrometer. For the first time we have been able to show that transient radicals in radical chain reactions can be detected unambiguously under steady-state conditions in the reaction solution and can be characterized by ESI-MS/MS and accurate mass determination. The detection of different heterodimer radical complexes by ESI-MS/MS has provided new insights into the mechanism of Lewis acid controlled radical chain reactions. Dimeric chelate complexes of glutarates, such as 2 and 3, and Lewis acids, like Sc- (OTf)3, MgBr2·OEt2 and LiClO4, were observed as well as higher aggregates with additional equivalents of Lewis acid. Evidence for a dynamic equilibrium of the complexes in solution was found by NMR spectroscopy. The ESIMS investigation of the chelation of glutarate 2 with various Lewis acids has led to the conclusion that the tendency for Lewis acids to form dimeric chelate complexes and higher aggregates has an important effect on the stereoselective outcome of the radical reactions.

URL: http://www.chemie.uni-oldenburg.de/oc/metzger/publikationen/pdf/106.pdf (application/pdf)

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