Cyclohexanones reduction, dissolving metals

Dissolving metal reductions remain the method of choice, and are frequently the only viable method, for the reduction of sterically hindered cyclohexanones to equatorial alcohols. In the early 1950s it was found that reduction of 11-keto steroids using either Na-propan-l-oP or Li-NHs-dioxane-ethanol gave good yields of the equatorial I la-alcohol. 11-Keto steroids, such as androstan-11-one (29 equation 12) have two axial methyl groups in a 1,3-relationship to the carbonyl group and afford exclusively the axial 11 P-ol (30) on reduction with metal hydrides. 

The electrochemical properties of many functional groups have been described in reviews by Steckhan, Degner (industrial uses of electrochemistry), Kariv-Miller,543 and Feoktistov. The synthetic applications of anodic electrochemistry has also been reviewed. There are interesting differences between dissolving metal reductions (secs. 4.9.B-G) and electrochemical reactions. Cyclohexanone, for example, can be reduced to cyclohexanol (sec. 4.9.B) or converted to the 1,2-diol (556) via pinacol coupling by controlling the reduction potential, the nature of the electrode and the reaction medium. 46 Presumably, the more concentrated conditions favor formation of cyclohexanol via reduction of the carbanion. More dilute solutions appear to favor the radical with reductive dimerization to 556. More important to this process, however, is the difference in reduction potential (-2.95 vs. -2.700 V) and the transfer of two Faradays per mole in the former reaction and four Faradays per mole in the latter. 

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