Stereochemistry electroreduction

The products and stereochemistry of the electroreduction of 1-bromo-l-phenylethane (24) and ( )-l-deuterio-1-bromo-l-phenylethane (24-d) have been investigated using DMF at mercury and glassy carbon electrodes (equation 23)50. The products, obtained in nearly quantitative yield, were strongly potential dependent as shown in Table 2. 

The electrochemical reduction of cyclopropyl halides has been widely investigated mainly in relation to its stereochemistry. No ring-opened products have been reported yet but substitution of the halogen by a hydrogen usually proceeds in high yields. Both monohalocyclopropanes, mostly bromide derivatives, and gem-dihalocyclopropanes were investigated. Several groups have studied the stereochemistry of the electroreduction... 

Recently Tallec and coworkersinvestigated the stereochemistry of electroreductions of l-substituted-2,2-diphenylcyclopropenyl bromides in aqueous media at various pHs and in the presence of strongly adsorbed alkaloids (Table 6). Their study shows that the existence of interaction between the alkyl bromides and nitrogen cations makes the two-electron cleavage of the C-X bond easier (sometimes by up to 400 mV). In general, poor optical yields were obtained in the presence of each of the five alkaloids tested. However, the optical yield went up to 42 % when the alkaloid inducer could act as a proton donor. It was also found that the alkaloids were efficient at low concentrations (10 " to 5 x 10 " m) indicating that the induction is a surface phenomenon. 

Cross-Coupling with Carbonyl Compounds. The electroreductive cross-coupling of olefins with carbonyl compounds, which are initially reduced to radical or anion intermediates to attack the olefins, is synthetically useful. The stereochemistry of this type of intermolecular reaction has lately been examined less [70-72] than that of intramolecular cyclization [73-77]. 

Iverson and Madsen [193] reported a synthetically interesting electroreductive ringopening reaction of cyclic quaternary ammonium salts. The stereochemistry of products is greatly affected by pH ... 

Stereoselective electroreduction of some organometal complexes has been reported. The reduction of o -oxotetramethylene-cyclopentadienyl-iron - 7 -benzenes in an acidic solution occurs specifically from the exo side to give only the en /o-alcohol, as in Eq. (38) in alkaline solution the corresponding stereoisomeric (d, 1 and mso) pinacols are formed but the stereochemistry has not been determined [257]. 

Regarding the chemical behavior of (-)-emetine (1), the stereochemistry of asymmetric electroreductions of bromocyclopropanes at a mercury cathode in the presence of adsorbed 1 has been studied 95,96). Bertz et al. (97) have reported asymmetrie induction (with 70 30 R/S ratio, but in only 6% chemical yield) that occurred in the conjugate addition of an (-)-emetine-incorporating phenylamidocuprate to 2-cyclohexenone. Fraser-Reid s group 98,99) has reported that the NH group of 1 is readily protected as the A-pent-4-enoyl derivative, which can be rapidly... 

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