Radical trap cerium

Using ammonium cerium(IV) nitrate (CAN) as the oxidant for the azide anion, the azido radicals are trapped by alkenes, to form, ultimately, /i-azido nitrates84 cerium azide species may be considered as intermediates. Alkenes conjugated with carbonyl groups are recovered intact. The stereochemistry of the adducts from acenaphthylene and indene was trans, as shown by H-NMR studies (/AX < 2 Hz for the acenaphthylene adduct), but with (-Eyi-phenyl-l-propene both syn and anti additions were formed. 

More recently, cerium(IV)-mediated radical reactions were extended to additions to alkenes [3]. One of the many examples from the pioneering work of Nair et al. is the addition of dimedone Ic to the cyclohexene derivative 8 [7]. In the first step, adduct radicals 9 are formed, which are rapidly oxidized to the cation 10 by CAN. Intramolecular trapping of this intermediate by the carbonyl group affords after deprotonation the dihydrofuran 11 in excellent yield (Scheme 3). 

Very recently, cerium(IV)-mediated C-C bond formations were applied for the first time in carbohydrate chemistry [9]. Again, radicals are generated from malo-nates la at low temperatures, and even sensitive glycals 16 are stable under such conditions. The regioselectivity of the additions is controlled by favorable orbital interactions and the adduct radicals are oxidized to cations, which are trapped by the solvent or CAN to afford the carbohydrate C-analogs 17 in good yields (Scheme... 

As an example, this apply to enols or tautomeric enols such as maleic acid derivatives. While with a chemical reagent (cerium ammonium nitrate) the only process occurring is oxidative dimerization, when aromatic nitriles are used as the photochemical oxidant, selective trapping of the radicals by an electrophilic alkenes or by the nitrile itself occurs. Under these conditions, both the alkylation of alkenes and the oxidative alkylation/dimerization of dienes have been smoothly obtained (see Scheme 8) and side processes such as double alkylation or polymerization often occurring with other methods have been avoided. A three-component (Nucleophile-Olefin Combination, Aromatic Substitution) process is also possible. ... 

The intermediacy of azido-radicals in the cerium (iv) oxidation of metallic azides to molecular nitrogen has been demonstrated by olefin trapping a-azido-jS-nitratoalkanes are formed (Scheme 153), with a regioselectivity consistent with initial addition of the azido-radical. 

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