Carbonyl groups electroreduction

The radical or anion species generated by electroreduction of halides are able to add to unsaturated systems such as aromatic ring and carbonyl group. The intramolecular addition of a radical species formed by electroreduction of an aromatic iodide to an aromatic ring has been applied to the synthesis of aporphines as it is shown in the following scheme 32). 

These tosic principles will hopefully clarify some data presented in the following review that covers the literature from 1979 until the present, dealing with the electroreduction of a carbonyl group to an alcohol, and of an imino group to the corresponding amine. Earlier literature on this topic has been reviewed elsewhere. ... 

The reduction potential of an unactivated carbonyl group in aprotic media lies so close to the reduction potential of the supporting electrolyte that the latter is often reduced first. Kariv-Miller and coworkers recently exploited this seemingly undesirable effect in the development of extremely powerful electroreductions,They showed that the tetraalkylammonium cation can act as a mediator, which accepts an... 

Kariv-Miller and coworkers have developed indirect electroreductive cyclizations with the dimethyl-pyrrolidinium ion (DMP") as a mediator. Preparative electrolysis of 6-hepten-2-one (9) at a graphite cathode afforded cu-dimethylcyclopentanol (10) in 90% yield (equation 5). The reduction is believed to occur via the ketyl radical anion, which cyclizes onto the alkenic bond. In the absence of DMP simple reduction to 6-hepten-2-ol takes place.Very recently it was shown that instead of DMP several aromatic hydrocarbons can be used as mediators to initiate the cyclization reaction. The carbonyl group can also be cyclized onto an alkynic bond and even an aromatic ring. - ... 

When an alkenic bond is conjugated with the carbonyl group, the carbonyl carbon and the p-carbon become the two reactive centers and a variety of products can be obtained depending on the medium. Presence of water in the reduction of 4-methyl-2-cyclohexenones results in a mixture of products. However, when the p-position is substituted such as in retinal (11), pinacolization takes place to form the pinacol (12) in 89% yield, provided that the electroreduction is carried out in an aprotic medium in the presence of a mild proton donor, such as diethyl malonate (equation 6). ... 

The electroreduction of the carbonyl group in aqueous or partially aqueous electrolytes primarily yields the corresponding alcohol and alkane, metal alkyl compounds, and a 1,2-diol ... 

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