Mechanistic analysis of an asymmetric palladium-catalyzed conjugate addition of arylboronic acids to β-substituted cyclic enones
An asymmetric palladium-catalyzed conjugate addition reaction of arylboronic acids to enone substrates was investigated mechanistically. Desorption electrospray ionization coupled to mass spectrometry was used to identify intermediates of the catalytic cycle and delineate differences in substrate reactivity. Our findings provide evidence for the catalytic cycle proceeding through formation of an arylpalladium(II) cation, subsequent formation of an arylpalladium–enone complex, and, ultimately, formation of the new C–C bond. Reaction monitoring in both positive and negative ion modes revealed that 4-iodophenylboronic acid formed a relatively stable trimeric species under the reaction conditions.
Additional Information© 2015 The Royal Society of Chemistry. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. Received 30 Oct 2014, Accepted 13 Dec 2014, First published online 17 Dec 2014. We gratefully acknowledge funding from the National Science Foundation under the CCI Center for Selective C–H Functionalization (CHE-1205646). C.L.B. thanks The Center for Molecular Analysis and Design (CMAD) at Stanford University for a postdoctoral fellowship. The Zare lab gratefully acknowledges financial support from a subcontract with the University of Utah (Agreement # 10029173-S2) for which the Air Force Office of Scientific Research (Grant FA9550-12-1-0481) is the prime sponsor. The Stoltz lab is thankful to the Caltech, Amgen, and the American Chemical Society Division of Organic Chemistry (predoctoral fellowship to J.C.H.) for funding. B.L.H.T. gratefully acknowledges the National Institutes of Health for a postdoctoral fellowship (F32GM106596). Computational resources were provided by the UCLA Institute for Digital Research and Education (IDRE) and the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the NSF.
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