Imines electroreduction

In a similar type of process, imines have been dimerized to give 1,2-diamines, by a number of procedures, including treatment with TiCLj—In/aqueous EtOH, Zn/aqueous NaOH, Cp2VCl2/Zn/PhMe2SiCl, with Sml2, and I for silylated imines) NbCl4(thf)2. When electroreduction was used, it was even... 

Imines can be stereoselectively hy-drodimerized to 1,2-diamines with rac/ meso rahos of 0.9 to 1.1 similar to the cathodic coupling of carbonyl compounds to pinacols in an acidic medium [304]. With 4,6-dimethylpyrimid-2-one only the meso-diamine was obtained [305]. Electroreduction of diimines prepared from... 

An electroreductive Barbier-type allyla-tion of imines (434) with allyl bromide (429) also occurs inaTHF-PbBr2/Bu4NBr-(Al/Pt) system to give homoallyl amine (436) (Scheme 151) [533]. The combination of Pb(II)/Pb(0) redox and a sacrificial metal anode in the electrolysis system plays a role as a mediator for both cathodic and anodic electron-transfer processes. The metals used in the anode must have a less positive anodic dissolution potential than the oxidation potentials of the organic materials in order to be present or to be formed in situ. In addition, the metal ion plays the role of a Lewis acid to form the iminium ion (437) by associating with imine (435) (Scheme 151). 

Electroreductive hydrodimerization (435— 439) of the imine (435) has been performed in a THF-CF3C02H(TFA)/ PbBr2-(Pt) system using an undivided cell (Scheme 152) [534]. For the conversion, both TFA and PbBr2 are indispensable, since the lack of either of the... 

A new electrolysis system comprising two metal redox couples, Bi(0)/Bi(III) and A1(0)/A1(III), has been shown to be effective for electroreductive Barbier-type allylation of imines [533]. The electrode surface structure has been correlated with the activity towards the electroreduction of hydrogen peroxide for Bi monolayers on Au(III) [578], Electroreductive cycliza-tion of the 4-(phenylsulfonylthio)azetidin-2-one derivative (502) as well as the allenecarboxylate (505) leading to the corresponding cycKzed compounds (504) and (506) has been achieved with the aid of bimetallic metal salt/metal redox systems, for example, BiCh/Sn and BiCh /Zn (Scheme 175) [579]. The electrolysis of (502) is carried out in a DMF-BiCh/Py-(Sn/Sn) system in an undivided cell by changing the current direction every 30 s, giving the product (504)in 67% yield. 

Electroreduction [5b] (with chiral quat as the supporting electrolyte) has been compared with chemical reduction (NaBH4) in the presence of chiral quats for ketone (up to 28% op) and imine (up to 22% op) reductions [57,58], The reduction (NaBH4) of a chiral a,p-enone prostaglandin intermediate in the presence of ephedra-derived catalysts led to the formation of the enol with 70% de [59]. Other reductions with lower asymmetric inductions are noted for ketone [lli,24h,24i,47e,60], imine [5b,57], and hydrodehalogenation of a cyclic a,a-dichlo-roamide [61],... 

Imino lactones, such as (22), can be reduced cleanly to the morpholinone (23) in an aptotic medium using diethyl malonate as a mild proton donor (equation 9). The electroreductive behavior of this class of activated imines is presently under study. 

The electroreductive Barbier-type allylation was applied recently to imines [126] in the following overall reaction ... 

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