Sulfides, -fluoro

By the way, trifluoroacetaldehyde is a versatile fluoro building block. However the chemical or electrochemical oxidative transformation of trifluoro-ethanol to trifluoroacetaldehyde has been unsuccessful. Trifluoroacetaldehyde is therefore generally produced by the reduction of trifluoroacetic acid ester or acid chloride using an excess of LAH. The anodic substitution at fluoroaikyl phenyl sulfides is a useful alternative because it realizes the transformation of economical trifluoroethanol to highly valuable trifluoroacetaldehyde equivalents as shown in Scheme 6.5. 

Fuchigami and co-workers utilized the regioselective anodic fluorination of aryl propargyl sulfides 301 for the preparation of fluorinated alkyne intermediates, which were subsequently isomerized by sodium ethoxide to furnish 1-fluoro-l-arylthioallenes 302 (Scheme 8.80) [166]. 

In most oases, the fluoro Pummerer reaction can be carried out with 1.33 to 2.0 equiv of DAST and a "catalytic" amount of antimony trichloride in either refluxing methylene chloride or chloroform at room temperature or 50°C. In the synthesis of fluoromethyl phenyl sulfide, however, the induction period makes room temperature conditions the preferred method for large scale synthesis. 

The a- and /3-cyclodextrins have been found to accelerate the Smiles rearrangement of 4-nitrophenyl salicylate. The reaction of 2,4-dinitrobenzenesulfonamide with acyl chlorides in the presence of excess triethylamine has been found to produce the corresponding nitrile in good yield. Mechanistic studies have indicated that the reaction proceeds via a Smiles rearrangement of the initially formed iV-(2,4-dinitrobenzenesulfonyl)amide to form the nitrile, 2,4-dinitrophenol, and sulfur dioxide (see Scheme 12). l-Chloro-3-fluorophenothiazines have been prepared by Smiles rearrangement of 3-chloro-5-fluoro-2-formamido-2 -nitrophenyl sulfides in alcoholic... 

A detailed study of the interaction of diaryl sulfides with AICI3 (unsubstituted and p-chloro, methoxy, and fluoro) at -60°C showed the corresponding thianthrene radical ions(H-) to have been formed. Bis (4-nitrophenyl)disulfide produced thianthrene radical ion(l-l-) itself. The... 

D.F. Andres, U. Dietrich, E.G. Laurent, B.S. Marquet, Anodic fluorination of vinyl sulfides - synthesis of a-fluoro- -thio-a, -unsaturated carbonyl compounds. Tetrahedron 53 (1997) 647-658. 

The reactions of perfluorinated cyclic sulfides, e.g. perfluorotetrahydrothiophene, per-fluoro-l,3-dithietane, and perfluoro-l,4-dithiane. proceed in a similar way.98... 

The electrochemical oxidation of sulfides R CH2SR2 in acetonitrile in the presence of triethylamine trishydrofluoride leads to the a-fluoro sulfide products R CHFSR2.52... 

Similarly, butan-2-one, pentan-3-one, 2,2-difluorobutane and 3,3-difluoropentane can be converted by the sulfur tetrafluoride/hydrogen fluoride/disulfur dichloride system into fluoro sulfides and fluoro disulfides.240... 

The reaction of 3,3,3-trifluoropropene with a sulfur tetrafluoride/hydrogen fluoride/disul-fur dichloride system proceeds at 20 C to give a mixture of diastereomers of bis[2-fluoro-l-(tri-fluoromethyl)ethyl] sulfide (18) in high yield.243... 

Bis[2-fluoro-l-(trifluoromethyl)ethyl] Sulfide (18) Single Procedure 243... 

The reaction of sulfides bearing an a-hydrogen with 1-fluoropyridinium salts results in the facile formation of a-fluoro sulfides 7.53... 

Table 4. Elimination of Hydrogen Fluoride with Base from a-Fluoro Ethers and Sulfides"...

In organo-fluorine compounds fluorine atoms can be eliminated by nucleophilic sulfur species to form C —S bonds. In principle, the fluorine to be eliminated can be bonded to aliphatic or araliphatic compounds, as well as to aromatic or heterocyclic compounds however, the replacement proceeds more efficiently the more the fluorine is activated. Therefore, the synthetic usefulness of these reactions is the broadest with fluoroaromatic compounds, including heteroaromatics, with which the reactions often proceed smoothly under mild conditions. The nucleophilic sulfur compound to be reacted is. in most cases, an aliphatic or aromatic thiol or a metal sulfide, but reactions with, for example, thiourea or ammonium thiocyanate have also been described. The sulfur introduced this way can be either oxidized or removed by reduction, opening additional possibilities for modifications of the original fluoro compounds. 

The broad applicability of dimethylformamide as the reaction medium is further shown by the reaction of other types of fluoroheterocycles. such as 3-fluoro- or 4-fluorophthalic anhydride, with substituted benzenethiols, which at low temperatures and with weak bases, e.g. sodium carbonate, provides the respective sulfides in excellent yield.25... 

On the pages which follow, general methods are illustrated for the synthesis of a wide variety of classes of organic compounds including acyl isocyanates (from amides and oxalyl chloride p. 16), epoxides (from reductive coupling of aromatic aldehydes by hexamethylphosphorous triamide p. 31), a-fluoro acids (from 1-alkenes p. 37), 0-lactams (from olefins and chlorosulfonyl isocyanate p. 51), 1 y3,5-triketones (from dianions of 1,3-diketones and esters p. 57), sulfinate esters (from disulfides, alcohols, and lead tetraacetate p. 62), carboxylic acids (from carbonylation of alcohols or olefins via carbonium-ion intermediates p. 72), sulfoxides (from sulfides and sodium periodate p. 78), carbazoles... 

Addition of a sulfenyl chloride to an alkene in the presence of silver fluoride affords (3-fluoro sulfides, as shown in equation (2).18 The same trans adducts can also be prepared from the sulfenyl chloride adducts and silver fluoride. An alternative procedure for the formal addition of methanesulfenyl fluoride to alkenes involves the use of dimethyl(methylthio)sulfonium tetrafluoroborate and triethylamine tris(hy-drofluoride) as in equation (3).19... 

The ultrasonic irradiation of aqueous sulfide solutions was conducted with a Branson 200 sonifier operating at 20 kHz by Kotronarou et al. (1992). Reactions were performed in a 50-mL water-jacketed, stainless-steel cell from Sonics Materials. The temperature inside the reaction vessel was kept constant at 25°C. All irradiations were carried out in air-saturated solutions at t = 0. A Haake A80 water circulating and temperature-controlling system was used for temperature control. Hydrogen peroxide was analyzed fluoro-metrically. Deionized water was used to prepare all the solutions. 

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