Quantitative studies in stereochemistry by isotope dilution. C. Electrochemistry. I. Ratio of diastereomeric pinacols formed in the electrolytic bimolecular reduction of acetophenone-7-14C

Dimerization of electrochemically generated ion radicals: mechanisms and reactivity factors

“…The first mechanistic studies of electrodimerization via ion radicals concerned the reduction of aromatic carbonyl compounds such as benzaldehyde and acetophenone [1][2][3][4][5]. Besides examination of the stereochemistry of the coupling reaction to pinacol [1,2], the discussion on mechanism and reactivity mainly dealt with the factors governing the competition between pinacol formation and hydrogenation [3][4][5][6].…”

“…Besides examination of the stereochemistry of the coupling reaction to pinacol [1,2], the discussion on mechanism and reactivity mainly dealt with the factors governing the competition between pinacol formation and hydrogenation [3][4][5][6]. Early applications of cyclic voltammetry to the reduction of aromatic carbonyl compounds [7] were indicative of a mechanism of pinacol formation involving the coupling of two anion radicals to give the pinacolate that protonates further to pinacol [7][8][9].…”

Electrochemical Reduction in an Aprotic Medium of New Functionalized Amphiphilic Molecules Derived from Sugars: Stereoselective Pinacolization and an Example of a Glycosidic Carbon-Oxygen Bond Cleavage

“…The steric interactions of the carbohydrate groups promote a head-to-tail orientation of the two anion-radicals. Coupling from this configuration favors, as postulated by Stocker et al, [18,19] the formation of the meso pinacol (Scheme 3). …”

“…[15] The d,l/meso ratio of 9.5 for the two diastereomeric pinacols 7 is quite high. Bewick et al [16,17] and Stocker et al [18,19] have postulated that this diastereoselectivity can be explained by ion-pair formation between the anion-radical and BuN ϩ from the supporting electrolyte. Thereby the less hindered radical pair with the methyl and phenyl groups facing each other (Scheme 2) leads to the favoured d,l diatereiosomer.…”

“…[18,19] This shift can be explained by a solvation of the anion rad- icals by the hydroxyl groups of the carbohydrate that competes with the ion pair formation by BuN ϩ . The steric interactions of the carbohydrate groups promote a head-to-tail orientation of the two anion-radicals.…”