Sulfinyl halides

An alternative route to aromatic trifluoromethylsulfonyl and sulfinyl compounds is based on the nucleophilic trifluoromethylation of sulfonyl or sulfinyl halides with Me3SiCF3 [38[ (Scheme 2.178). 

Scheme 2.178 Conversion of sulfonyl and sulfinyl halides to the corresponding trifluoromethyl sulfones and sulfoxides by nucleophilic trifluoromethylation [38].

Benzisothiazoles are formed by the action of ammonia or amines on benzenesulfenyl halides bearing an o-carbonyl function (72AHC 14)43, 80MI41700). Analogous diphenyl disulfides behave similarly (77SST(4)339). Sulfinyl chlorides or phenylsulfoxides produce... 

In the reaction of 88 with -phenethyl bromide, l-phenethyl-3-phenylpropyl methyl sulfoxide and bis-3-phenylpropyl sulfoxide, besides 3-phenylpropyl methyl sulfoxide are obtained . Sulfoxides, bearing a -hydrogen to the sulfinyl function, give olefins upon thermolysis. Utilizing this reaction, Trost and Bridges alkylated benzyl phenyl sulfoxide, 3,4-methylenedioxybenzyl phenyl sulfoxide, phenylthiomethyl phenyl sulfoxide, phenylsulfinylmethyl phenyl sulfoxide and cyanomethyl phenyl sulfoxide with alkyl, allyl and benzyl halides and subjected these sulfoxides to thermolysis, obtaining olefins in one-pot processes. 

As with sulfinyl chloride, the exothermic reaction with limited amounts of water may be dangerously violent under confinement because of rapid gas evolution. See other gas evolution incidents, non-metal halides... 

Alkyl sulfides are not the only nucleophiles that can catalyze the hydrolysis of sulfinyl sulfones. The various halide ions, thiocyanate ion, acetate ion, and thiourea, are very effective catalysts (Kice and Guaraldi, 1968). The mechanism for the hydrolysis as catalyzed by these nucleophiles is shown in... 

The addition of alcohols to carbon disulfide in the presence of a base produces xanthates.106 The base is often OH, but in some cases better results can be obtained by using methyl-sulfinyl carbanion MeSOCH2 .107 If an alkyl halide RX is present, the xanthate ester ROCSSR can be produced directly. In a similar manner, alkoxide ions add to C02 to give carbonate ester salts ROCOO". 

A concerted elimination-cyclization mechansim, involving a sulfenyl halide in a 1,3-butadiene-1-thio system, is the most probable mechanism for the formation of benzo[6 Jthiophenes from cinnamic acids or 4-aryl-2-butanones by treatment with thionyl chloride. The reactions shown in Scheme 5 have been carefully worked out, and the intermediates isolated (75JOC3037). The unique aspect of this synthesis is the reduction of the sulfinyl chloride (a) by thionyl chloride to form the sulfenyl chloride (b). The intermediate (b) was isolated and converted in pyridine to the 3-chlorobenzo[6]thiophene-2-carbonyl chloride in 36% yield (73TL125). The reaction is probably initiated by a sulfenyl ion attack on the aromatic ring, since it is promoted by electron-releasing groups para to the site of ring closure. For example, when X in (36) was N02, a 23% yield of (37), a mixture of 5-and 7-nitro derivatives, was obtained, but when X in (36) was OMe, a 54% yield of (37) was obtained, contaminated with some 3,4-dichloro-5-methoxybenzo[6]thiophene-2-carboxylic acid. 

Sulfoxides and sulfones can be prepared on cross-linked polystyrene by oxidation of thioethers. The most commonly used reagent for this purpose is MCPBA in DCM [8,12,32,57,80-82] or dioxane [50,83] (Table 8.6), but other oxidants such as H2O2 in acetic acid [34], oxone (Entry 7, Table 8.6), or oxaziridines [84] have also been used. PEG-bound thioethers have been converted into sulfones by oxidation with MCPBA in DCM [52,54] or with Os04/NMO [85], The oxidation of thioethers to sulfoxides requires careful control of the reaction conditions to prevent the formation of sulfones. Sulfones have also been prepared by S-alkylation of polystyrene-bound sulfi-nates (Entries 8 and 9, Table 8.6), by a-alkylation of sulfones (BuLi, THF, alkyl halide [86]), and by addition of sulfinyl radicals to resin-bound alkenes or alkynes (Entry 11, Table 8.6). 

A highly stereoselective vinylogous Pummerer rearrangement of a optically active sulfoxide has been shown to proceed by a [l,4]-migration of the sulfinyl oxygen atom via an intermediate intimate ion pair (Scheme 12).16 The reaction occurs with high enantioselectivity when o-sulfinyl-substituted benzyl carbanions are treated with trimethylsilyl halides. 

Nonmetal Halides. Vigorous or explosive reactions occur with phosphorus tribromide on addition of drops of water,20 phosphorus trichloride, phosphorus pentachloride,21 diselenium dichloride,22 sulfur dichloride, boron tribromide, sulfur dibromide,17 seleninyl bromide,23 phosphoryl chloride, sulfinyl fluoride, silicon tetrachloride, and silicon tetrafluoride.24... 

Reduction of sulfoxides to thioethers.1 Use of hydrogen halides for this reduction was first reported in 1909 and is still a viable method. This reduction has assumed importance since chiral sulfinyl groups are valuable in asymmetric syntheses and are eliminated in two steps reduction to the ether followed by catalytic hydrogenation or metal/ammonia reduction. The first step can now be carried out with several reagents, as shown by this comprehensive review (349 references). 

Substituted sulfinyl- and substituted sulfonylquinoxaline 1,4-dioxides are easily converted to 2-haloquinoxaline 1,4-dioxides with aqueous hydrogen halides, in almost quantitative yields. ... 

The Friedel-Crafts sulfonylation of aromatics with alkane- and arenesulfonyl halides and anhydrides has been studied (Eq. 9) [23]. In the reaction of pentafluorobenzenesul-fonyl fluoride with pentafluorobenzene, decafluorodiphenyl sulfone is formed with deca-fluorodiphenyl [23c]. Certain phenylacetylenes react with SO2 and benzene in the presence of SbFs to form benzothiophene 5-oxide [24]. (Eq. 10). Sulfinyl fluoride reacts similarly with arenes under SbFs catalysis to give sulfoxides (Eq. 11) [25]. 

Aromatic sulfonyl chlorides can be prepared directly, by treatment of aromatic rings with chlorosulfuric acid. Since sulfonic acids can also be prepared by the same reagent (11-7), it is likely that they are intermediates, being converted to the halides by excess chlorosulfuric acid. The reaction has also been effected with bromo- and fluorosulfuric acids. Sulfinyl chlorides (ArSOCl) have been prepared by the reaction of thionyl chloride and an aromatic compound on Montmorillonite KIO clay. ii... 

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