An oxidative carbon&ndash;carbon bond-forming reaction proceeds via an isolable iminium ion

Tsang, Althea S.-K.; Jensen, Paul; Hook, James M.; Hashmi, A. Stephen K.; Todd, Matthew H.

doi:10.1351/PAC-CON-11-01-01

Pure Appl. Chem., 2011, Vol. 83, No. 3, pp. 655-665

http://dx.doi.org/10.1351/PAC-CON-11-01-01

Published online 2011-02-07

An oxidative carbon–carbon bond-forming reaction proceeds via an isolable iminium ion

Althea S.-K. Tsang¹, Paul Jensen¹, James M. Hook², A. Stephen K. Hashmi³ and Matthew H. Todd¹*

¹ School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia
² NMR Facility, Analytical Centre, University of New South Wales, Sydney, NSW 2052, Australia
³ Organisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany

Abstract: The mechanism of our previously reported DDQ-mediated oxidative C–C bond-forming reaction is investigated. We are able to trap and characterize an iminium ion intermediate with X-ray crystallography, elemental analysis, and solid-state NMR spectroscopy; to our knowledge this is the first time this putative intermediate ion has been directly observed in such cross-dehydrogenative couplings (CDCs). The intermediate can be reacted with a range of nucleo-philes, including a malonate that is not amenable to a one-pot reaction protocol.