Hydrodimerization enones

Reductive dimerization of enones to form a new carbon-carbon bond at the p-position, known as hydrodimerization or electrohydrodimerization, has considerable synthetic utility.For example, high yields of cyclic products are achieved when cyclization is kinetically favorable, leading to three- to six-membered rings from the corresponding unsaturated diesters (Scheme 19). ... 

Some fundamental studies were made earlier. It was found that the hydrodimerization of an O, j6-unsaturated ketone (enone) was at least partially stereospecific, with the d, I dimer formed from the /ranj-enone and mainly the meso dimer formed from the cw-enone. Kanetsuna and Nonaka [50] also examined both the stereoselectivity and stereospecificity of the hydrodimerization in detail. It was indicated that either the reaction mechanism or the stereochemical course is changed by the nature (protic or aprotic) of the reaction media. Particularly, the latter is greatly influenced by the manner of adsorption of an anion radical intermediate on the cathode. It was also postulated to explain the experimental results that the radical anion is adsorbed at the )6-position, where the radical p electron is delocalized and the adsorption is affected by the nature of the media. 

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