ETUDE DU COMPORTEMENT ELECTROCHIMIQUE DE COMPOSES POLYFONCTIONNELS ET DE DERIVES COMPORTANT UN GROUPEMENT XANTHATE

摘要

Electrosynthesis is presented in a detailed manner with an emphasis on reactive electro-generated species and on their interactions (and those of the substrate) with the medium constituents (solvent, ions of electrolyte, constituents of the electrodes). These can act upon the regioselectivity when polyfonctionnal compounds are being processed. This approach has been applied (a) to natural products bearing different carbonyl groups (Chap.3) and (b) to xanthate derivatives (Chap.4 to 8). - On the first substrates (a), it was confirmed that the cation of the electrolyte exerts a preponderant effect upon the regioselectivity of the cathodic reductions. However, it has not been possible to pinpoint the respective role of the solvent or the cation. It is also possible that the anion has an effect on the reactivity of the cation. At the same time, we have conceived and tested a range of reactors of different sizes (from 1 to 50 cm3), with separate compartments, suited for use with solid electrodes (Chap.2). - With the second substrates (b), we present our electrochemical approaches for tree types of reactions: the introduction of the xanthate group, its elimination and the initiation of radical additions (Chap.4 to 8). - Attempts at the synthesis of xanthates by electrogeneration of tertiary radicals in presence of a bis-xanthate have failed. The latter was too easily reduced or oxidised under the Kolbe conditions (Chap.5). - The cathodic reduction of xanthates gave good yields but only with the derivatives of acetophenones. The anodic oxidation did not lead to cyclisation into tetralones (Chap.6). - The initiation of radical additions onto olefins by group transfer failed when using cathodic reduction of alkyl iodides. However, we observed a new reaction when operating with cathodes possessing a strong electro-catalytic activity (Ag, Au, Pd). It consists in the addition of the radical from ethyl iodo-acetate onto a primary xanthate, followed by a cyclisation (Chap.7). In addition, we conceived and tested systems with electric relays for inverting the polarity of the electrodes in order to clean their surfaces when adsorption inhibited the flow of current. - The initiation reactions gave promising results in the case of anodic oxidation of partially neutralised malonic acid. But the yields must be improved further (yield : 45 %; corrected intermediate yield : 75 %) (Chap.8).