Carbon−Carbon Bond Formation by Electrochemical Catalysis in Conductive Microemulsions

Bicontinuous microemulsions made from oil, water, and surfactants were examined as substitutes for organic solvents in carbon−carbon bond-forming reactions. Conjugated additions of primary alkyl iodides 3a − c to 2-cyclohexen-1-one ( 4 ) to give 3-alkyl cyclohexanones 5a − c and cyclization of 2-(4-bromobutyl)-2-cyclohexen-1-one ( 9 ) to 1-decalone ( 10 ) were mediated by the Co(I)L complex vitamin B 12s generated at carbon cloth electrodes under mild conditions. Reaction of the Co(I)L nucleophile with the alkyl halides gives a Co−alkyl complex. Cleavage of the Co−alkyl complexes by using an electrode potential of −0.85 V (all vs SCE) and irradiation with visible light, or a potential of −1.45 V in the dark, were compared. Addition of the resulting alkyl radicals to the activated double bonds gave comparable yields of 3-alkylcyclohexanone 5a − c (70−80% using −0.85 V + light) and 1-decalone (90%, both cleavage modes) 10 in microemulsions and in DMF. Microemulsions containing hexadecyltrimethylammonium bromide (CTAB) gave remarkable stereoselectivity for the trans isomer of 10, while homogeneous DMF and a sodium dodecylsulfate (SDS) microemulsion gave little stereoselectivity.