Enones electrochemical reduction

Stoichiometric Reactions. In 1974, Touboul reported amazing selectivity in the controlled potential electrochemical reduction of the enone (Scheme 36) (63). While the dimerization of the enantiomerically pure enone gives solely the cis,threo,cis diol, the racemic compound behaves similarly to produce the racemic dimer with the same relative configuration and no other possible diastereomers. A radical anion intermediate... 

Inokuchi, Kusumoto and Torii reported the electrochemical reduction of epoxyketone 29 at a carbon cathode (equation 16)62. In the absence of a proton source, two deoxygenated products (enone 30 and pinacol dimer 31) were produced in a combined yield of 37%. However, in the presence of a proton source (CH2(CC>2Et)2), ring-opened product 32 was produced in 65% overall yield. 

The irradiation of enone 20 in the presence of Et3N or DABCO as electron donors yields 21 as major product and almost none of the valence tautomerized product 22 (equation 29)139. Photomediated electron transfer apparently differs here from alternative electron transfer processes, since in lithium/liquid ammonia and electrochemical reductions 22 is produced. 

Cathodic reduction of diphenyl diselenide produces a benzeneselenolate, which catalyzes the reduction of a, -epoxy carbonyl compounds into -hydroxy carbonyl compounds in the presence of a proton source (Scheme 16) [21]. This electrochemical method is applicable to the selenation of haloalkanes, epoxides, and enones [22]. Electrochemical reduction of elemental selenium to diselenide dianion (Se ) and selenide dianion (Se ) is also possible [23]. 

Methods for reduction of enones may be divided conveniently into four historically based classes. The earliest procedures employed dissolving metals more recent developments, such as reduction with low-valent transition metal compounds and electrochemical processes, may also be included in this category as they all proceed via sequential addition of electrons and protons to the substrate molecule. These methods are discussed in Section 3.5.2. 

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