Cyclic enamines radical reactions

Anodic regioselective acetamidosulfeny-lation of alkenes is similarly achieved by oxidation of diphenyldisulfide in acetonitrile [81]. Cyclic enamines, which are intermediates in the oxidation of cyclic N-methoxycarbonyl amines, react in aqueous acetonitrile that contains chloride ions to a-hydroxy- 8-chloro compounds via intermediate chloronium ions [82]. Enolethers undergo a regioselective azidomethoxyla-tion to yield acetals of a-azido carbonyl compounds upon electrolysis in methanol containing sodium azide [83]. The reaction proceeds possibly via addition of an anodicaUy generated azide radical. 

Cyclic enamines, ynamines and ureas, preparative methods 86MI12. Design of free radical reactions for the synthesis of heterocycles 88S417, 88S489. 

Guertler et al. (1996) described a wide range of cycloaddition reaction between 2-vinyl indoles acting as heterodienes and cyclic or acyclic enamines bearing acceptor groups in (3 positions. The reaction was induced by the formation of 2-vinylindole cation-radicals through anodic oxidation. The synthesis of 4a-carbomethoxy-6-cyano-5,7-dimethylindolo[l,2-a]-l,2,3,4,4a,12a-hexahydro-1,8-naphthyridine can serve as an example (Scheme 7.24). 

From an electrochemical reduction of some cyclic immonium salts of the type N-cyclohexylidenepyrrolidinium fluoborate in aprotic media, the enamine and the saturated tertiary amine were the major products [42]. It was suggested that the reaction was a one-electron transfer followed by a rate-determining radical-radical disporportionation involving hydrogen atom transfer. 

On the basis of the cyclic voltammetry (CV) results, DFT calculations, and control experiments, the reaction mechanism involving the cationic radical enamine was proposed. 

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