I was reading an excellent article in the Journal of the American Chemical Society (JACS) this week from the MacMillan group at Princeton (J. Am. Chem. Soc, 2013, 13S, 16074—16077), which describes the α-amination of ketones, esters, and aldehydes via a copper bromide-catalyzed process in the presence of air or, preferably, oxygen. This seems a really valuable reaction for process chemists since not only does it accomplish the transformation in one step instead of the usual two (bromination to the α-bromoketone followed by displacement), but it also avoids having to handle lachrymatory α-bromoketone intermediates and possibly bromine, too. It is possibly more environmentally friendly since there is less brominated waste, the only negative from an environmental viewpoint being the use of DMSO as solvent. OK, one does not have to use DMSO as solvent, but the paper studied several solvents, and DMSO gave by far the best yields. This was attributed to stabilization of the transient copper enolate species, but I wondered, since any HBr could react with DMSO to give traces of bromine (and smelly dimethyl sulfide) which would brominate the ketone and release HBr again, continuing the cycle, whether the solvent also had a beneficial "catalytic" effect.
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