Oximes electroreduction

Most of the current preparative methods of oximes from nitroalkenes are not versatile. Reduction of nitroalkenes by CrCl2 or NaH2P02 in the presence of palladium was reported to afford the corresponding oximes, but the yields are not satisfactory. Zn-acetic acid and Na2Sn02 reductions are limited to the preparation of ketoximes only. Electroreduction of alkenes was reported to yield mixmres of ketones and ketoximes, or oximes and acetals (or ketones) depending on the strucmre of nitroalkanes. 

Sera and coworkers, during their investigation on electroreduction of nitroalkenes, found that plates of powder or metalhc lead can reduce nitroalkene 20 to give oxime 21 in acetic acid-DMF solution without electricity (Scheme 18). The reduction of 1-nitro-1-alkenes afforded the corresponding aldoximes or ketoximes in excellent yield. 

On the other hand, since oxime ethers were electrochemically more inert than ketones under the electroreduction conditions, the electroreductive intra- and inter-molecular coupling of ketones with oxime ethers proceeded via anion radicals in good yields (equations 5 and 6) °4i. Moreover, cobaloxime-mediated intramolecular radical addition onto oxime functions in the electrolysis media proceeded to afford the cyclized aminoethers (equation 7). ... 

Another method for reductive amination of carbonyl compounds is based on the electroreduction of oximes in aqueous media. Thus, sugar oximes were reduced to their corresponding glycamines in good yields (Hg, KCl, acetate buffer). Similar reductions of oximes derived from furfural, salicylaldehyde, benzophenone and cyclohexanone have also been described, " but reports of preparative electrolyses in strictly aprotic media seem to be absent in the literature. 

When electroreduction was used, it was even possible to obtain cross-products, by coupling a ketone to an O-methyl oxime O-Methyl oxime ethers are coupled... 

In the same way, various Co macrocycles were chemically bonded to the glassy carbon electrodes by the same method . A 4-aminopyridine was the bridging molecule, the attached macrocycles were Co(n) naphthalocyanine, Co(II) phthalocyanine,dibromo (1 l-hydroxyimino-4,10-dipropyl-5,9-diazatri-deca-5,9-dien-3one oximate) Co(III), (denoted as CoDO), two kinds of hydrophobic Bi2 vitamins (heptamethyl cobyrinate perchlorate and heptapropyl cobyrinate perchlorate), Co(n) tetraphenyl porphyrin and Co(II) 5,10,15,20-tetrakis-(4-methoxyphenyl) porphyrin. Not all of the macrocycles were active toward the electroreduction of CO2. In fact, Co naphthalocyanine and Co phthalo-cyanine (CoPc) produce larger amounts of H2 even CoPc was the macrocycle with the most positive potential to give H2. CoDO was unable to produce CO at... 

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