E. Laurent

Anodic fluorination of vinyl sulfides-synthesis of α-fluoro-β-thio-α,β-unsaturated carbonyl compounds

A series of new title compounds 3 was synthesised in moderate to excellent yield, by anodic fluorination of their corresponding hudrogenated homologues 1 in Et3N,3HF/CH3CN, followed by a chemical dehydrofluorination step. From vinyl sulfides, we showed that anodically generated vicinal difluoro adducts 2 were easily dehydrofluorinated by an E1cB mechanism, leading to 3 with high stereoselectivity in most cases. In contrast, the anodic behaviour of a thio flavone in the same media was slightly different, giving rise to the formation of vinylic fluoride 3 during the anodic fluorination.

Diastereoselective fluorination at benzylic position by anodic oxidation

Abstract By anodic oxidation of benzylic derivatives 1 in Et3N,3HF/CH3CN, diastereoselective fluorination in the α position of the electron withdrawing group is obtained. The observed stereoselectivities are discussed in connection with the inductor group. The role of the anode is also examined.

Anodic functionalization of vinyl sulfides. Formal access to gem or vicinal aryl thioether dications

Abstract The anodic oxidation of a number of vinyl thioethers has been performed in CH 3 CN-Et 3 N,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 (CH 2 =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 (CH 3 OH/Et 3 N,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.

Fluoration anodique dans le chlorure de methylene (polymethyl- et vinylbenzenes)

Abstract The anodic oxidation of polymethyl and of ethylenic derivatives of benzene in CH 2 Cl 2 /Et 4 NF, 3HF or Et 3 N, 3HF has been studied. The fluoro compounds are obtained in good yields. With the ethylenic compounds cis-addition products predominate.

Le groupe thioéther: Un bon substituant pour les fluorations oxydatives

Abstract Regiospecific monofluorinations of α-thio α-Eirylesters and α-thioacids were obtained by anodic and/or chemical oxidation in fluorinating media. This procedure provided a convenient synthesis of α-fluoroesters via the C-S bond cleavage induced by anodic process while chemical or electrochemical oxidation of α-thioacids underwent a fluoro decarboxylation, affording α-fluorothioethers.

ETUDE DE LA REGIOSELECTIVITE EN FLUORATION ANODIQUE DE DERIVES BENZYLIQUES

By anodic oxidation of paramethylbenzylsulfonate, ester and nitrite 1 in Et3N,3HF/CH3CN, regioselective functionalization at benzylic positions is obtained (benzylic fluorides 2 and acetamides 3 are formed). In order to examin the determining factors of the chemioselectivity. It was compared to those obtained in bromination of the same compounds by 1,3-dibromo 5,5-dimethylhydantoin (DBH)/2.2′-azobis(isobutyronitrile) (AIBN) in CCl4.

Synthesis of pure enantiomers of cis- and trans-3-(trifluoromethyl) pyroglutamic esters

Abstract The addition of the racemic Schiff base ethyl N-(diphenylmethylene)glycinate (2), from glycine ester, to ethyl-4,4,4-trifluorocrotonate gives, according to the experimental conditions, one or two Michael adducts. Acidic hydrolysis gives the cis/trans-3-(trifluoromethyl) pyroglutamates. The enantiomerically pure Schiff base, prepared from chiral 2-hydroxy-3-pinanone and t-butyl glycinate, reacts with trans-ethyl-4,4,4-trifluorocrotonate to produce four diastereoisomers which may be separated and hydrolysed to give enantiomerically pure cis- and trans-3-(trifluoromethyl)pyroglutamate.

Un nouveau moded'accès aux α-fluorocétones : l'oxydation anodique des acétates d'énol en présence d'ions fluorures

Abstract We describe a new route to α-fluoroketones : anodic oxidation of enol-acetates in presence of Et 3 N, 3HF as agent of fluorination and supporting-electrolyte

A new synthesis of enaminoketones

Abstract A new and efficient synthesis of enaminoketones is described. E,Z β-chloroacroleine derivatives react with secondary amines to produce enaminoketones. The reaction was essentially studied with β-trifluoromethylacroleines.

Reaction of thioglycolate with α-fluoro-β-(phenylthio)enones (or -enals): Synthesis of substituted α-carboxy-γ-fluorothiophenes

Abstract A new synthetic method to substituted α-carboxy-γ-fluorothiophenes 2F is reported. They were prepared by the reaction between two equivalents of methyl thioglycolate anion and α-fluoro-β-(phenylthio)enones (or -enals) 1F , in DMSO (70°C) in yields ranging from 41% to 85%. We show from the reaction of (Z) -α-fluoro-β-(phenylthio)but-enone 1aF , that cyclisation to fluorothiophene 2aF occurs via the formation of stable enolates of α-fluoro-β-(dithianyl)butanone.