Sulphinate esters

Sulphinate Esters.—A wide variety of synthetic routes to sulphinate esters is represented in the recent literature. A one-step synthesis of alkyl t-alkane-sulphinates from a Grignard reagent and a sulphite has been explored. Among the reports of sulphinate syntheses from sulphinyl halides are three accounts of studies with unusual interest, viz. CF,SOF - CF3S(0)0R, iV-t-butylsulphinyl-oxycarbamates from Bu SOCl and H0NR C(0)0R, and an asymmetric synthesis involving a sulphinyl chloride, an achiral alcohol, and an optically active tertiary amine. In the best experiment an optical purity of 45% was achieved in the asymmetric synthesis.  

Reactions of sulphinates and sulphoxylates with FSOsMe and CFsS03Me proceed via dialkoxysulphonium ions produced, in the former case, by methylation 

Sulphinate Esters.—Methods of preparation from suiphinyl chlorides by reaction with alcohols, with silyl ethers, or with hydroxylamines, from sulphinic acids, - from sulphoxylates l(RO)2S -1- H2C=CHCH2Br (at 105- 

Tamaru, M. Kagotani, R. Suzuki, and Z. Yoshida, Chem. Lett., 1978,1329. 

Federici, G. Spoto, R. M. Matarese, and D. Cavallini, Physiol. Chem., Phys., 1978,10,435. 

Uchino, K. Suzuki, and M. Sekiya, Chem. Pharm. Bull., 1979, 27,1199. 

Further examples of the use of propargyl sulphinates (see Vol. 5, p. 55) in syntheses of allenes by reaction with organocopper reagents (ROuBr)MgX LiBr include a synthesis of (/ )-allenes and one of vinyl-allenes.  

Snlphinate Esters.—new preparation from disulphides involves chlorina-ti(m in alcohol solvents at -20 and a further new route is announced, in which N-alkyl-N -toluene-p-sulphonylhydrazines TolSOjNHNHCHi-CHjR give toluene-p-sulphinates TolSOOCHzCHzR and the alkene RCH==CH2 on oxidation with SeOz, C1O3, or HgO, probably via radical intermediates. Pyrolysis of n-butyl sulphoxylate Bu OSOBu is suggested to involve conversion into the sulphinate as first step, en route to SO2, S, Bu OH, and but-l-ene. Standard routes are illustrated in preparations of phenylmethanesulphinates and amides.  

The 3-cyclodextrin inclusion technique is suitable for the resolution of simple alkyl alkanesulphinates.  

Cleavage of benzylic sulphoxides and t-butyl dialogues with N-bromo- or -chloro-succinimides gives the benzyl or t-butyl halide and an ethyl alkane-pr arene-sulphinate, the ethanol in the CHCh used as solvent providing the nucleophile for attack at sulphur on the intermediate bromosulphoxonium cation. Use of an optically active sulphoxide leads to the conclusion that the reaction is largely of SnI character. 

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Thus, the enantiomeric contents in a pair of sulphoxides can be determined by the NMR chemical shifts in the methine or methylene protons in the two diastereomeric complexes which are stabilized by the hydrogen bond between the hydroxyl and the sulphinyl groups147-151 (Scheme 13). Similarly, the enantiomeric purity and absolute configurations of chiral sulphinate ester can be determined by measuring the H NMR shifts in the presence of the optically active alcohols152. 

Dialkyl thiosulphonates (37) are desulphurized by tris(diethylamino)phos-phine to give sulphoxides. In some cases sulphinate esters are formed as minor products. Diaryl thiosulphonates gave 1 1-adducts of the type (38). Desulphurization of sulphenimides (39) by tris(dimethylaniino)phos-... 

Despite the aversion of the sulphonyl group to function as a nucleophile, there are a limited number of literature reports that deseribe sueh a process . The first of these does not lead to a reduetion at sulphur and is thus not direetly relevant, but the report by Braverman and Duar deseribes reaetions in whieh an acetylenie sulphinate ester ean undergo a [2,3] sigmatropie rearrangement to an allenie t-butyl sulphone. Reaetion of this sulphone with the appropriate eleetrophile, for example bromine, gave a y-sultine, formation of whieh requires the partieipation of the sulphonyl group in an intramoleeular cyclization process. The reactions are outlined in equation (40). 

The chirality exhibited by the pyramidal sulphur compounds (e.g. sulphonium salts, sulphoxides and sulphinic esters) should be noted, but cannot be considered within the scope of this book. 

Clearly, the major primary decomposition processes are loss of SO and loss of CO, both of which require prior formation of a C—0 bond. This virtually demands isomerization to an internal sulphinate ester (7),... 

Enantiomeric distinction can also be achieved using chiral solvents without shift reagents. The determination of enantiomeric purity and the assignment of absolute configuration of cyclic and acyclic sulphinate esters has recently been achieved (573) using chiral l-aryl-2,2,2-trifluoroethanols as solvents. Enhanced enantiomeric distinction has been demonstrated using a combination of both a chiral solvent and an achiral LSR. (514)... 

Sulphinic acid esters have also been oxidized, to the sulphonic acid ester, with hydrogen peroxide although the reaction usually proceeds in poor yield345,346. This resistance to oxidation is also evident when other oxidants are used233,347. A much improved procedure for the oxidation of aromatic sulphinate esters uses potassium permanganate in aqueous solution, as oxidant345,348,349, as shown in equation 79. Mefa-chloroperbenzoic acid has also been used with success for the oxidative preparation of sulphonate esters. Indeed, it has resulted in the preparation of unstable sulphonate esters that are hard to form by other means350. 

Aryl sulphonyl chlorides may also be synthesized from the sulphinyl chloride, by oxidation with chlorine, in 80% yield573 (equation 146) or dimethyl sulphoxide574. Sulphinate esters may also be utilized as the precursor to sulphonyl halide via oxidative halogenation. For example, methyl methanesulphinate is converted to methanesulphonyl chloride in excellent yield at 0°C568. 

It has been proposed54 that oxidative cyclizations such as these occur via the formation of the cyclic sulphinate esters (sultines) with subsequent oxidation to the corresponding sultone as shown in equation 34 for the formation of 16. 

Sultines (cyclic sulphinate esters) can be readily oxidized to sultones by hydrogen peroxide or potassium peroxysulphate. The first example of such a synthesis was reported by King and De Mayo and their associates69 who prepared l,2-oxathiole-2,2-dioxide (22)... 

The reactions of phosphorylated carbanions have been extended to include those with sulphinate esters as a route to phosphoryl sulphoxides . The interaction of dimethyl... 

Reactions of arenesulphenyl chlorides with hydroxyl functions of nucleosides have been investigated with N phthalimido-2, 3 -0-isopropylideneadenosine, o-nitrophenyl sulphenyl chloride gave the 5 -0-sulphenyl ester, whilst other sulphenyl chlorides without an o-nitro group gave mixtures of sulphinate esters and 5 -deoxy-5 -chloro compound. Mechanisms were suggested. ... 

Alternatively, the allyl sulphinyl anion (8) gave the threo adduct (9), which underwent sulphoxide - sulphinate ester rearrangement, leading to the hex-2-enitol derivative (10)(Scheme 4) the threo isomer predominated by non-chelation control, which has previously been difficult to achieve. ... 

Higher temperature and the presence of alcohols would cause further oxidation of the disulphide and formation of sulphinic esters . ... 

References to addition reactions of sulphenyl halides with alkenes and alkynes are given in the Sulphides section. An incidental bonus from a study of the addition of PhSCl to adamantylideneadamantane is the formation of the 4e-chloro-derivative and PhSSPh, via an intermediate thiiranium salt. Sulphenyl and selenenyl chlorides have been used for the dehydration of aldoximes to nitriles. Whereas sulphinyl chlorides yield sulphinate esters with alkoxytri-methylsilanes, no reaction occurs with sulphenyl chlorides. ... 

Four-membered Rings.—Open-chain sulphinate esters are readily prepared but their cyclic analogues are less easily come by. [2 + 2]Cycloadditions involving SO2 are limited to a few specialized examples, and it has been suggested that it is this mode of reaction that leads to the initially formed adduct (274) between SO2 and ketenimines. These compounds are unstable and rearrange to thiazetidine 5-oxides (275) in 90% yield. A versatile approach has been... 

Reactions.—A variety of interesting and useful syntheses have been published involving the reaction of dimsyl anion [MeS(0)CHa ] with esters and lactones,with disulphides, with chlorosilanes, with sulphinate esters, with organoboranes, and with stilbenes. Simple and functionalized a-sulphinyl carbanions can be condensed with carbonyl compounds or alkylated, often in a stereocontrolled manner, as in a nicely conceived synthesis of biotin. Considerable attention has been given to methods for the removal of the sulphoxide function following carbon-carbon bond formation. Among the methods used are reduction by aluminium amalgam (with j3-keto-sulphoxides), reduction with Raney nickel, pyrolytic elimination of sulphenic acid, elimination of sulphur dioxide from sultines, e.g. (64), and sulphoxide-... 

Sulphines are formed by the oxidation of thiones with peroxy-acids, but they then react further, albeit much more slowly, to give the ketone, sulphur, and sulphur dioxide. This latter reaction is kinetically similar to many other oxidations with peroxy-acids, and the results are consistent with electrophilic attack of the peroxy-acid on the C=S double bond to give a cyclic sulphinate ester (4), which rapidly decomposes to give the ketone and sulphur monoxide. In contrast, oxidation of thiobenzanilide 5-oxide with m-chloroperoxybenzoic acid gives products derived from the sulphene PhC(NHPh)=SOa. Further examples of the reaction between diarylsulphines and aryldiazomethanes to give epi-sulphoxides have been reported. ... 

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