Development of Bio-mimic Electrochemical Reaction by using Cobalt Complex and Its Application

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We developed a tin-free method for carbon radical generation by using cobaloxime, which was used as a mimic of metalloenzyme vitamine B_<12>. Regeneration of low valency cobalt catalyst was carried out by electroreduction with a sacrifical Zn anode in an undivided cell system. Development of a catalytic radical generation method is very meaningful in the synthesis of commonly useful compounds.1.We investigated the 1,2-acyl rearrangement of 2-(halomethyl)cyclopentane-1,3-diones, giving the corresponding cyclohexane-l,4- diones by the electrochemical radical generation method. This reaction was utilized for the synthesis of functionalized biaryls. The electroreduction of monoacetals of 2-(halomethyl)cyclopentane-1,3-diones in the presence of cobaloxime as a catalyst afforded the cyclohexane-1,4-dione monoacetals in good yields. The Bu_3SnH-reduction of 2-aryl-2-(halomethyl)cyclopentane- 1,3-diones under refluxing in benzene resulted in the rearrangement, affording the corresponding cyclohexane-1,4-diones, and 1,4- hydroquinones proceeded in moderate yields when heating was prolonged.2.We present here the radical cyclization reaction of O-alkyloximes by using cobalt complex-sacrificial electrode system, giving functionalized β-aminoacetals. The radicals generated from primary, secondary, and tertialy alkyl bromides added to the carbon- nitrogen double bonds without any difficulty and difference in their reactivity. This reaction seems to be slightly influenced by steric factor in the cyclization process.3.We investigated the three component combination reaction of bromoacetal with benzaldehyde, giving the corresponding cyclization product by the electrochemical radical generation method. The best result was obtained by using [Co^<III>(N_4)Cl_2]ClO_4 as a cobalt complex.