Copper II -Mediated Radical Reactions

Finally, the pioneering work of Snider et al. demonstrated that copper(II)-mediated radical reactions can be applied for an elegant tandem strategy [19]. Thus, oxidation of silyl enol ether 40 by copper(II) triflate generates electrophilic radicals 41, which undergo a 5-exo-trig cyclization to the intermediate 42. Oxidation to a 

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Compared to iron(III), copper(ll), and especially manganese(III) and cerium(IV) other metals have found less application for the oxidative generation of radicals [1]. An exception is cobalt(III)-mediated radical reactions, based on the pioneering work of Iqbal et ah, which was recently reviewed [20] (see also Volume 1, Chapter 1.8). Some examples of oxidative couplings of silyl enol ethers 44 in the presence of silver(I) oxide were developed [21]. However, there is no advantage over copper(II)-mediated radical reactions, since the reagent is more expensive and the 1,4-diketones 45 are isolated in only moderate yield (Scheme 15). 

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