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-fo rming reactions. Conjugated additions of primary alkyl iodides 3a-c to 2-cyclohexen-1-one (4) to give 3-alkyl cyclohexanones 5a-c and cycliz ation of 2-(4-bromobutyl)-2-cyclohexen-1-one (9) to 1-decalone (10) we re mediated by the Co(I)L complex vitamin B-12s generated at carbon cl oth electrodes under mild conditions. Reaction of the Co(I)L nucleophi le 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 SC E) and irradiation with visible light, or a potential of -1.45 V in th e 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 cleavag e modes) 10 in microemulsions and in DMF. Microemulsions containing he xadecyltrimethylammonium bromide (CTAB) gave remarkable stereoselectiv ity for the trans isomer of 10, while homogeneous DMF and a sodium dod ecylsulfate (SDS) microemulsion gave little stereoselectivity.