Sulfmate

Simple a-fluorosulfides are reduced to the fluoroalkanes by sodium-ethanol [9J (equation 75). Clean conversion of bis(trifluoromethyl) diiulfide to trifluoromethyl mercaptan is accomplished with hydrogen sulfide and ultraviolet irradiation (941 (equation 76). Perfluoroalkanesulfonyl fluondes are converted to the sulfmate salts by hydrazine [95] (equauon 77)... 

The nucleophilic displacement of halogens by pentafluorophenoxide ion resulted in the formation of the corresponding esters [31] (equation 29) (Table 12). Reactions of trifluoromethanesulfinyl fluoride with fluoro alcohols in the presence of sodium fluoride or cesium fluoride are used to prepare sulfmates [32] (equation 30) (Table 12). 

Cyclodextrins, toroidal molecules composed of 6, 7 and 8 D-glucose units, are now commercially available at reasonable cost. They form inclusion compounds with a variety of molecules and often differentially include sulfoxide enantiomers29,30. This property has been used to partially resolve some benzyl alkyl, phenyl alkyl and p-tolyl alkyl sulfoxides. The enantiomeric purities after one inclusion process ranged from 1.1 % for t-butyl p-tolyl sulfoxide to 14.5% for benzyl r-butyl sulfoxide. Repeating the process on methyl p-tolyl sulfoxide (10) increased its enantiomeric purity from 8.1% to 11.4% four recrystallizations raised the value to 71.5%. The use of cyclodextrins in asymmetric oxidations is discussed in Section II.C.l and in the resolution of sulfmate esters in Section II.B.l. 

Preparation of the appropriate optically active sulfmate ester is initially required for reaction with a Grignard or other organometallic reagent. If the method is to produce homochiral sulfoxides, the precursor sulfmate ester must be optically pure. An exception to this statement occurs if the reaction yields a partially racemic sulfoxide which can be recrystallized to complete optical purity. 

Preparation of enantiomerically pure sulfmate esters has most often been accomplished by making menthyl esters of arenesulfinic acids, particularly of p-toluenesulfinic acid. This... 

Compounds 45 exhibit, in addition to sulfone-sulfmate rearrangements1 2 4-6 11, alkyl sulfone cleavages4,6,27, intramolecular Smiles-type rearrangements33 and extrusion of S023,5,29,30, an exceptional mode of remote group interaction which leads to the loss of... 

TABLE 2. Sulfones from S-acylations of sulfmate anions RSOz... 

Electrochemical oxidation of disulfides and trapping of intermediately formed sulfmates by alkylation yields sulfones in good yields494. 

The zinc chloride is acting here as a Lewis acid. Similarly, thiirane dioxides react with metal halides such as lithium and magnesium chlorides, bromides and iodides in ether or THF to give the halo-metal sulfmates (130) in fair yields157. 

The softer, less basic potassium bromide and iodide did not react with the thiirene dioxide 19b. The latter was also inert towards potassium thiocyanate, selenocyanate or nitrile. It did react, however, with potassium thiophenoxide in DMF at room temperature to yield, most probably, the vinyl sulfmate 138 isolated as the corresponding sulfone39 (equation 56). 

The reaction of 16a on heating with methanol to give the sulfenic acid intermediate 142 and the sulfmate 143 (which was further transformed into the disulfide 144) was interpreted in terms of the mechanism shown in equation 58161. 

Dimethyl-benzene-sulfmate Chloride1 Thiocyanate Thionbenzoate1 ... 

Braverman and Reisman111 have found that addition of a carbon tetrachloride solution of bromine to bis-y,y-dimethylallenyl sulfone 20 at room temperature unexpectedly resulted in spontaneous and quantitative fragmentation of the sulfone, with formation of the cyclic a, /3-unsaturated sulfmate (y-sultine) 43a and the tribromo products 44 and 45 (equation 38). Analogously, treatment of the same sulfone with trifluoroacetic acid gives rise to y-sultine 43b. It is interesting to note that from a synthetic point of view it is not even necessary to prepare the diallenyl sulfone 20, since one can use its sulfinate precursor (equation 24) to obtain exactly the same results, under the same conditions. The authors suggested that the fragmentation-cyclization of sulfone 20 may take place by the mechanism depicted in equation 39. 

Reference electrode Ag/Agl/I 0.1m in DMF working electrode stirred Hgpool of 10cm2 area mass of substrate cleaved l-2g. In all cases the produced sulfmate anion is methylated by CH3I at the end of the electrolysis. Ts - p-MeC6H4S02. ... 

The picolylsulfone 5 is obtained by a reaction involving the conversion of a sulfonate sodium salt 2 into a sulfmate sodium salt 4 and reaction of the latter with 2-picolyl chloride (refs 6,7 eqn. 1). 

A major problem with the sulfoxide synthesis using menthyl sulfmates is its failure to produce optically pure dialkyl sulfoxides. The prerequisite menthyl alkanesulfinates are oils which have resisted separation into the individual epimers. The menthyl phenyl methanesulfmates are an exception the R epimer is crystalline . One solution to this problem, at least for preparing methyl alkyl sulfoxides, was achieved using cholesteryl methanesulfmates (27) . Both epimers were crystalline and could be separated by fractional crystallization, although in poor yield. Treatment of the epimers with n-propyl, n-butyl, isobutyl, p-tolyl and benzyl magnesium halides yielded the respective methyl alkyl sulfoxides (28) in greater than 95% e.e. and in 32 to 53% yields. 

Mikolajczyk and coworkers have summarized other methods which lead to the desired sulfmate esters These are asymmetric oxidation of sulfenamides, kinetic resolution of racemic sulfmates in transesterification with chiral alcohols, kinetic resolution of racemic sulfinates upon treatment with chiral Grignard reagents, optical resolution via cyclodextrin complexes, and esterification of sulfinyl chlorides with chiral alcohols in the presence of optically active amines. None of these methods is very satisfactory since the esters produced are of low enantiomeric purity. However, the reaction of dialkyl sulfites (33) with t-butylmagnesium chloride in the presence of quinine gave the corresponding methyl, ethyl, n-propyl, isopropyl and n-butyl 2,2-dimethylpropane-l-yl sulfinates (34) of 43 to 73% enantiomeric purity in 50 to 84% yield. This made available sulfinate esters for the synthesis of t-butyl sulfoxides (35). 

Enolates derived from various imino compounds have been sulfmylated in reactions analogous to those shown by equations (14) and (15). Some representative examples are shown in equations 16-18. Here again, these compounds have been utilized in asymmetric syntheses. Addition of sulfmate ester 19 to a THE suspension of a-lithio-Al,JV-dimethylhydrazones, derived from readily available hydrazones of aldehydes and ketones, leads to a-sulfmylhydrazones in good yield, e.g. 53 and 54 (equations 16 and 17) . Compounds 53 and 54 were obtained in a 95/5 and 75/25 E/Z ratio, respectively. The epimer ratio of compound 53 was 55/45. Five other examples were reported with various E/Z and epimeric ratios. 

The lithium enolate of ethyl N-methoxyacetimidate (55) was also successfully sulfiny-lated by treatment with sulfmate ester 19 (equation 19) . Sulfoxide 56 was used in an asymmetric synthesis of some / -hydroxy esters. 

In view of the successful preparation of so many homochiral sulfoxides via the reaction of nucleophilic species with sulfmate ester 19, it appears likely that the reaction is capable of extension to provide still more examples of potentially useful sulfoxides. 

Although carbanionic and enolate species are most often sulfinylated using sulfmate esters, particularly homochiral ester 19, other tricoordinate S(1V) compounds may be used in their place. Sulfmamides (66) and cyclic sulfite ester-amides (67) are two examples of such compounds. 

Principally, both unifold and twofold transformation types ensue in these cases. A unifold transformation occurs in the case of the rearrangement of cumyl benzenesulfmate, which arises from the conversion of cumyl hydroperoxide with benzenesulfenyl chloride (equation 2). Closely related sulfoxylate-sulfone rearrangements, which pass intermediate sulfmate steps similarly, are equally known . 

Nucleophilic substitutions of halogen by the addition-elimination pathway in electron-deficient six-membered hetarenes by sulfmate anions under formation of sulfones have been described earlier . The corresponding electron-poor arenes behave similarly (equation 30). A special type of this reaction represents the inverse Smiles rearrangement in equation 31. ... 

The usual sulfone synthesis by displacement of halide by sulfmate is assumed to have a nucleophilic 8 2 mechanism However, in special cases of alkyl halides with additional, electron-withdrawing substituents a radical substitution pathway has been observed (equation 32). Correspondingly, substitutions under formation of sulfones take... 

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