- ANODIC FUNCTIONALIZATION OF VINYL SULFIDES. FORMAL ACCESS TO GEM OR VICINAL ARYL THIOETHER DICATIONS
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The anodic oxidation of a number of vinyl thioethers has been performed in CH3CN-Et3N,3HF.Results clearly show that the reactivity of the vinyl sulfide radical cation depends on several factors as structure of substrates and nucleophilic conditions.For example a dimerization occurred from the unsubstituted vinyl sulfide 1a (CH2=CH-SPh) whereas α,β- and/or β,β-difluoro sulfides were obtained from substituted homologues.In order to understand this reactivity the anodic behaviour of 1a and 1b (Ph-CH=CH-SPh) has been especially analysed in two other nucleophilic media (CH3OH/Et3N,3HF and AcOH/AcOK) leading respectively to methoxylation and acetoxylation of starting compounds.Comparison with electrofluorination results has allowed us to propose a mechanism involving an intermediary episulfonium ion which could explain the formation and ratio of the products isolated.Key Words: vinyl sulfides; enol thioethers; anodic oxidation; electrochemistry; fluorination; methoxylation; acetoxylation; formal dication; fluorosulfides
- Andres, Didier F.,Laurent, Eliane G.,Marquet, Bernard S.,Benotmane, Hassiba,Bensadat, Abdelkader
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p. 2605 - 2618
(2007/10/02)
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- Additive Pummerer reactions of vinylic sulfoxides. Synthesis of γ-hydroxy-α,β-unsaturated esters, α-hydroxyketones, and 2-phenylsulfenyl aldehydes and primary alcohols
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Treatment of β-monosubstituted vinylic sulfoxides 1 with trifluoroacetic anhydride in dichloromethane gave excellent yields of 1,2-bis(trifluoroacetoxy)thioethers 6. Mildly basic methanolysis of 2-alkyl-substituted 6 gave α-hydroxyaldehydes 11 as monomer-dimer mixtures; similar treatment of the 2-aryl analogues afforded aryl (hydroxymethyl) ketones 12. Compounds 11 underwent Wittig reactions with methoxycarbonylmethylenetriphenylphosphorane to give high yields of γ-hydroxy-α,β-unsaturated esters 13, predominantly as the E-isomers. β-Monosubstituted vinylic sulfoxides 1 possessing a β-aryl group, and β-disubstituted vinylic sulfoxides 3 reacted with trifluoromethanesulfonic anhydride-sodium acetate in acetic anhydride to give 2-(phenylsulfenyl) acylals 14. These gave 2-phenylsulfenyl aldehydes 15 upon basic methanolysis, and the corresponding primary alcohols 16 on reduction with sodium borohydride. Reaction of both geometric isomers of enantiomerically pure vinylic sulfoxide 1o with TFAA gave racemic 6o as a mixture of diastereomers. Reaction of optically pure (E)- and (Z)-1p with trifluoromethanesulfonic anhydride-sodium acetate in acetic anhydride gave acylal 19 in 10.5 and 23% e.e., respectively.
- Craig, Donald,Daniels, Kevin,MacKenzie, A. Roderick
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p. 11263 - 11304
(2007/10/02)
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- Peculiar Aspects of the Anodic Oxidation of Vinylic Sulfides
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In the anodic oxidation of vinylic sulfides on platinum in acetonitrile, a non-classical sulfonium ion explains satisfactorily the transfer of the thioether group leading to an aldehyde in the presence of water, or its acetal in the presence of methanol.Some other reactions depend on the structure of the substrate, particularly the dimerization into anodically inactive forms likely to decompose during the work-up, to lead in some cases to masked ketenes having the structure of a gem-disulfide.
- Guillanton, Georges Le,Simonet, Jacques
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p. 437 - 444
(2007/10/02)
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