Thiosulfine acid

The esters of thiosulfinic acid R -SO,-S-R are used as fungicides and antibacterial prepai ations. These compounds have similar stiaicture fragments to allicin - natural insecticide from garlic with following structure (CH =CH-CH ),[SO-S] (http //www.ALLICIN.com). For deter-mination of ethyl S-ester of 4-aminobenzenthiosulfinic acid (esulan) in the ointment RP-HPLC was proposed [1] with acetonitrile water=30 70 as eluent. For seai ching bioactive compounds the synthesis of new esters of thiosulfinic acid is perspective that was confirmed by results of recent studies as instance [2]. Therefore requirements ai e existed for investigation HPLC sepai ations of these substances. 

In analogy to hydroformylation, alkenes react with SO2 and H2 to give a so-called hydrosulftnation product, sulfinic acids [116]. Cationic Pd(II) and Pt(II) complexes bearing bidentate phosphine ligands are effective catalyst precursors. A plausible mechanism for the hydrosulfination involves formation of alkyl intermediates by olefin insertion into metal hydrides, subsequent insertion of SO2, and reformation of the hydrides with the release of sulfinic acids (Scheme 7.19). However, ahphatic sulfinic acids readily undergo disproportionation to give thiosulfinic acid esters, sulfonic acids, and water at the reaction temperature. The unstable sulfinic acids can be conveniently converted into y-oxo sulfones by addition of a,-unsaturated carbonyl compounds as Michael acceptors to the reaction mixtine (Eq. 7.23) [117]. 

The thermolysis of acyclic- and/or six- and larger ring sulfoxides to yield olefins and sulfenic acids is well documented . The formation of allylic sulfenic acids and thiosulfinates in the thermolysis of thiirane oxides containing hydrogen on the a-carbon of the ring substituent (which is syn to the S—O bond) has been discussed previously in terms of /i-elimination of hydrogen, which is facilitated by relief of strain in the three-membered ring (Section llI.C.l). 

We noted earlier that the sulfinyl group of a thiolsulfinate is believed to have a basicity somewhat less than that of a sulfoxide but somewhat greater than that of a sulfinate ester (Engberts and Zuidema, 1970).+Thus, in an acid solution a thiosulfinate will be protonated to some extent to RS(OH)SR. A whole series of reactions is known that are initiated by attack of a nucleophile on the dico-ordinate sulfur of RS(OH)SR with cleavage of the S—S bond and displacement of RSOH. 

Let us return now to a brief further consideration of the acid- and nucleophile-catalyzed reactions of thiosulfinates. We have seen that in the various acid- and nucleophile-catalyzed reactions of PhS(0)SPh the attack of... 

Optically active aromatic thiosulfinates were first prepared by asymmetric oxidation of diaryl disulfides with (+)-percamphoric acid (105,112). Apart from the fact that the optical purity of diaryl... 

Much attention has been devoted to the acid- and nucleophile-catalyzed racemization of thiosulfinates. As a result of the extensive studies by Kice and his co-workers (112) and by Fava (281), it is clear now that the easy racemization of thiosulfinates caused by acids and bases (e.g., pyridine) is related to the scission of the sulfur-sulfur bond and the formation of sulfenic acid or its anion as an achiral intermediate. As expected, introduction of steric hindrance... 

The oxidation of sulfoxides by aliphatic peroxy acids is first order in both reactants the solvent effects have also been investigated. Thiosulfinates are oxidized by peroxy acids to thiosulfonates and not disulfoxides. It had previously been proposed that the disulfoxides are formed first but homolytically cleave and recombine to give thiosulfonates. A series of ab initio calculations were performed (at the 3-210 and 6-3IG levels) which indicate little difference in the rate of oxidation of S over S(0) in the gas phase but faster S(0) oxidation in a reaction cluster. ... 

A further approach for the synthesis of nonsymmetrically protected lanthionines is the conversion of thiosulfinates of symmetrically protected cystine derivatives into nonsymmetrically protected cystines via a reaction with a cysteine derivative and subsequently the conversion of the resulting unsymmetrically protected cystine into the nonsymmetrically protected lanthionines with a tris(dialkylamino)phosphineJ26l The oxidation of the symmetrically protected cystine, e.g. A,AT-bis(benzyloxycarbonyl)-L-cystine diethyl ester, of one stereochemical configuration to the thiosulfinate with m-chloroperoxybenzoic acid is essentially quantitative. The nonsymmetrical cystine is then formed in a subsequent step by the addition of the /V-/er/-butoxycarbonyl-L-cysteine tert-butyl ester derivative to give N-Z-N -Boc-L-cystine ethyl ferf-butyl diester. The desired 2f ,6f -lanthionine is then formed in the presence of P(NEt2)3 in yields of >50%. 

The reaction of 4-oxochromanones 282 with thionyl chloride gives a-chlorosulfenyl chlorides 283. Treatment of these sulfenyl chlorides with potassium iodide or thioacetic acid followed by morpholine gives rise to the chroman-4-one thiosulfine intermediates 284, which can dimerize in a Diels-Alder reaction to give the chromeno[3,4-r ]-l,3,4-oxa-dithiin+-one 285, for example, R, R = (0+2)6, R = R = H, in low yield (Scheme 48) <1998)009840, 2002ZNB922>. 

Products of the LOX pathway or compounds formed by autoxidation of fatty acids (Scheme 7.2) are also important for leek aroma [31, 163]. Volatile compounds of the LOX pathway are not pronounced in the aroma profile of freshly cut leeks owing to a high content of thiosulfinates and thiopropanal-S-oxide [30]. In processed leeks that have been stored for a long time (frozen storage), however, these aliphatic aldehydes and alcohols have a greater impact on the aroma profile owing to volatilisation and transformations of sulfur compounds [31, 165]. The most important volatiles produced from fatty acids and perceived by GC-O of raw or cooked leeks are pentanal, hexanal, decanal and l-octen-3-ol (Table 7.5) [31, 35, 148, 163, 164]. 

Buffer catalysis of the hydrolysis of phenyl (311 R = Ph) and methyl (311 R = Me) benzenesulfinates to give the sulfinic acid (312) and alcohol ROH is strongly accelerated by both carboxylate and amine components of the buffer which give Bronsted /i values of approximately unity on separate lines. The carboxylates are about 44 tunes more effective than amines of similar basicity. A concerted. S n2 mechanism with a hypervalent intermediate (313) is proposed for the nucleophilic reaction of these esters.286 The reaction of the thiosulfinate esters (314) with sulfenyl chlorides RSCI and sulfenate esters (315) to give sulfinyl chlorides and disulfides and sulfinate esters and disulfides, respectively, has been studied.287 Hydrolysis of 2-(3-aminophenyl)sulfonyl-ethanol hydrogensulfate gives under different conditions various products such as the ether (316) and the sulfone (317).288... 

Another simple elimination reaction on the thiosulfinate ester makes another molecule of the sulfenic acid and a highly unstable unsaturated thioaldehyde, which promptly dimerizes to give a thioacetal found in garlic as a potent platelet aggregation inhibitor. 

In onions, things start much the same way but the initial amino acid is not quite the same. The skeleton is the same as that of the garlic compound but the double bond is conjugated with the sulfoxide. Elimination and dimerization of the sulfenic acid produce an isomeric thiosulfinate. 

Oxidation of the thiosulfinate ester up to the sulfonate level gives the compound responsible for the lell of raw onions, while a hydrogen shift on the conjugated sulfenic acid (not possible with the garlic impound) gives a sulfine, the sulfur analogue of a ketene. The compound has the Z configuration cted from the mechanism and is the lachrymator that makes you cry when you cut into a raw onion. 

Thiosulfinate 129 has been used for the synthesis of various chiral sulfinyl derivatives such as sulfoxides, sulfmamides, and sulfinimines in good yield, tert-Butanesulfinyl ketimines have been successfully used for the asymmetric synthesis of a,a-dibranched aminesI09h as well as for the synthesis of o.p. amino acids.109 ... 

Sulfane oxides are compounds of type R2S Om ( > 1, m = 1, 2, 3...) with the oxygen atoms present as sulfoxide or sulfone groups. For the nomenclature of organic sulfur-oxygen compounds see Table 2 for reviews on oxidized sulfur chains and rings, see Steudel. Disulfane 1-oxides, RS(0)-SR, are also known as thiosulfinates and the 1,1-dioxides are usually termed as thiosulfonates. Trisulfane 1-oxides and 1,3-dioxides, as well as tetrasulfane 1-oxides and 1,4-dioxides, have been obtained by stepwise oxidation of the corresponding sulfanes by peroxy acids (equations 151 153) 67,101,123,127,262 26s... 

Oxaziridines. Davis has developed the use of chiral 2-sulfonyloxaziridines derived from camphorsulfonic acid as chiral auxiliaries in the asymmetric oxidation reactions. Although other oxaziridines may be preferable, the camphor-derived oxaziridines can be used for the oxidation of sulfides and disulfides to sulfoxides and thiosulfinates as well as for the epoxidation of alkenes. On the other hand, the camphoryloxaziridines are the preferred reagents for hydroxylation of lithium enolates of esters, amides, and ketones, as utilized in the synthesis of kjellmanianone (eq 17). ... 

---