Sulphonate esters

From a study of the partial tosylation of methyl -D-mannopyranoside, the order of substitution was found to be 6 3 2 4. With two equi- 

Kergomard, and S. Vincent, Bull. Soc. chim. France, 1972, 301. 

Alkyl alkanesulphonates react with Na naphthalene to form first the radical anion, which splits into R + O-SOa R , from which alkanols, alkanes, and alkanesulphinic acids are formed, depending on conditions. Photochemical cleavage of tosylated sterols and terpene alcohols at 254 nm proceeds in moderate yield within 3 h, in ether, to give back the alcohol via RSO2 + RO sulphonamides similarly give amines.  

Claisen-type condensation reactions of aralkanesulphonate esters, ArCH2S020Ar ArCH(SO2CH2Ar)S020Ar, have been exemplified further (see also Vol. 1, p. 72), sulphonylation being brought about in the presence of a strong base (e.g. Bu 0 K+-THF).  

Thermal or photo-isomerization of /m 5-PhCH=C(OTs)Ph in MeCN gives the c -isomer, but also PhCH(Ts) CO Ph through a free-radical route,illustrated also by a steroidal vinylogue, TsOC(3)=C(4)—C(5)-=C(6) 0=C(3)—C(4)=C(5)—C(6)Ts. Decarboxylative elimination 

Studies of jS-alkyl- and -aryl-thio-vinyl sulphonates, mainly from a mechanistic point of view but with implications in synthesis, have been reported in a series of papers. - j8-Arylthio-compounds (183) give benzo[6]thiophens (184) by cyclization, spontaneously or by BF3 

Garcia Fraile, A. Garcia Martinez, A. Herrera Fernandez, and J. M. Sanchez Garcia, An. Quim., 1979, 75, 723 A. Garcia Martinez, I. Espada Rios, and E. Teso Vilar, Synthesis, 1979, 382. 

Routine mechanistic studies (solvolysis of 1-cyclobutenyl nonafluorobutanoate via vinyl cations hydrolysis of phenyl methanesulphonates and phenyl-sulphonylacetates, alkyl alkanesulphonates, and toluene-p-sulphonylmethyl benzenesulphonate and arenethiolysis of methyl sulphonates ) have been reported. 

Dimolar tosylation of 1,5-anhydroxylitol gave a mixture of mono-, 

The methods of preparation and uses of perfluoroalkanesulphonic esters in organic chemistry has been reviewed. Applications of triflates in S 2 reactions of sugars, particularly for the synthesis of deoxy-sugars, were illustrated. 

Reference to the use of sulphonates in ring-contraction reactions leading to branched-chain sugars will be found in Chapter 13- 

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Combined Erythrina Alkaloids. The sources of the liberated alkaloids (see above) are now known to be, at least in two cases, the sulphur-containing alkaloids erysothiopine and erysothiovine, which are esters of sulphoacetic acid, HOOC. CHj. SOj. OH, identified as the aniline salt, m.p. 187-9° with erj sopine and erysovine respectively. The sources of erysodine and erysonine have not yet been isolated. These combined alkaloids arc believed to be sulphonic esters, of the type HO. OC. CHj. SOj. 0. R, where R is the alkaloidal residue. ... 

An excellent discussion on derivatization techniques has been given by Lawrence (17) including a detailed discussion on pre-column derivatization (18) and post-column derivatization (19). Probably, the more popular procedures are those that produce fluorescing derivatives to improve detector sensitivity. One of the more commonly used reagents is dansyl chloride (20), 5-dimethylamino-naphthalene-1-sulphonyl chloride (sometimes called DNS-chloride or DNS-C1). The reagent reacts with phenols and primary and secondary amines under slightly basic conditions forming sulphonate esters or sulphonamides. 

Treatment of the sulphonate esters of N-phosphinyl-hydroxylamines with a strong base such as methoxide often results in a Lossen-like rearrangement. Thus with methoxide in methanol,... 

There is a parallel for oxygen abstraction by a sulphonyl radical either from nitrobenzene or by disproportionation thermolysis of benzenesulphonyldiazomethane (54) in benzene gives, among other products, some sulphonate ester (55) 67>, which has been formulated as follows ... 

Exocyclic reactions for aromatic carboxylic esters 174 Exocyclic reactions for aliphatic carboxylic esters 187 Endocyclic reactions for carboxylic esters 191 Carbon acid participation for carboxylic esters 195 Effective molarities 198 Ring size 199 Initiating nucleophile 200 Phosphate and sulphonate esters 200... 

Sulphonic esters have been obtained from the sulphonyl chlorides in high yields under mild conditions for a range of alcohols and phenols [e.g. 18, 19]. Of particular value is the protection of glycosides possessing a free hydroxyl group and hydroxy-steroids, which are tosylated readily under phase-transfer conditions [20-22]. Alkyl sulphinites have been obtained in a similar manner [23]. Alternatively, preformed tetra-rt-butylammonium sulphonates or their alkali metal salts have also been alkylated with haloalkanes or alkyl fluorosulphonates [24,25]. In contrast with more classical procedures, tosylation of alcohols, which are susceptible to E/Z-isomerism, e.g. Z-alk-2-en-l-ols, occurs with retention of their stereochemistry under phase-transfer catalysis [26]. 

The arene sulphonyl chloride (0.11 mol) in PhH (50 ml) is added dropwise at 20°C to a two-phase system of the alcohol (or phenol) (0.1 mol) and TEBA-Cl (0.91 g, 4 mmol) in PhH (100 ml) and aqueous NaOH (30%, 50 ml). The mixture is stirred at 20°C for 5-8 h, and the organic phase is then separated, washed well with HzO until the washings are neutral, dried (Na2S04), and fractionally distilled to yield the sulphonic ester. 

When 1,2-diols are subjected to the same reaction conditions required for the formation of sulphonic esters, oxiranes are produced [27]. Presumably, the mono ester is initially formed and, under the basic conditions, intramolecular elimination occurs to produce the oxirane. Partial hydrolysis and ring-closure of a,p-di(tosyloxy) compounds under basic phase-transfer catalytic conditions provides a convenient route to carbohydrate oxiranes [e.g. 28, 29]. Oxiranes have been produced by an analogous method via carbonate esters from partially protected carbohydrates [30],... 

Selected examples of the hydrogenolysis of haloalkanes and alkane sulphonic esters... 

Even sulphonate esters 109 are powerful directing groups, competing well with tertiary amides. No substitution accompanies ortholithiation of ethyl or isopropyl benzene-sulphonate by BuLi. Hydrolysis and chlorination of the products 110 gives functionalized sulphonyl chlorides 111 (Scheme 48) °°. 

Alcohols react with sulphonyl chlorides to yield sulphonate esters via Sn2 reaetions. Tosylate esters (alkyl tosylates) are formed from alcohols from the reaetion with p-toluenesulphonyl ehloride (TsCl). The reaction is most commonly carried out in the presenee of a base, e.g. pyridine or triethyla-mine (Et3N). 

Thus, condensation with ethyl 4-bromo-3-methyl-2-butenoate (2E/2Z 50/50) provided the sulphone-ester, as a mixture of isomers (13 /13Z 50/50). Elimination to the ethyl 9-methylene-retinoate (2E/2Z 50/50) was done by treating the crude mixture with EtONa in cyclohexane, Fig. (42). 

Shiner and coworkers also studied optically active acyclic secondary sulphonate esters and found rate accelerations of about 100 in solvolysis in TFA at 25 °C compared with the alkyl reference (Table 8)93-95. From the product distribution and the stereochemical outcome of the solvolysis Shiner and coworkers proposed the reaction course outlined in equation 37 for the brosylate 23994. The transition state for the ionization adopts the W conformation and, to a smaller extent, the ewrfo-Sickle conformation and results in the formation of /-silicon carbocation which is stabilized by a percaudal interaction. The incoming nucleophile attacks the bridged ion from the front side94. 

The alcoholic hydroxyl group may be protected by conversion into, for example, the acetate, benzoate, p-nitrobenzoate, or toluene-p-sulphonate esters. Suitable specific and general procedures are described in Expts 5.142, 6.46, 6.163 and in Section 9.6.4, p. 1241. Esters may be hydrolysed under basic or acidic conditions, suitable procedures are described in Section 9.6.17, p. 1266. 

This sequence serves to exemplify the formation and aspects of reactivity of toluene-p-sulphonate esters in monosaccharide systems, and further to illustrate the selective protection afforded to hydroxyl groups by the formation of cyclic acetals by reaction with carbonyl compounds. Thus reaction of methyl a-D-glucopyranoside (26) with benzaldehyde in the presence of zinc chloride gives the 4,6-acetal (27) (Expt 5.118), wherein two fused six-membered rings of the frans-decalin type are present. As a cognate preparation the reaction of benzaldehyde with methyl a-D-galactopyranoside results in a similar conversion to a 4,6-acetal, but in this case the product is the conformationally flexible system of the cis-decalin type, the most likely conformation being that shown below. 

Since the 4,6-acetal grouping and the glycosidic grouping (27) are stable under basic conditions, though unstable in the presence of acid, the remaining two hydroxyl groups may be suitably protected by reactions that are base catalysed. TTius (27) may be converted into the 2,3-di-O-toluene-p-sulphonyl derivative (28) by reaction with toluene-p-sulphonyl chloride in the presence of pyridine (Expt 5.119) this reaction is analogous to the formation of sulphonate esters of alcohols or phenols. 

The value of the sulphonate esters in carbohydrate chemistry lies in their ability to undergo cleavage by reaction with nucleophiles in one of two possible ways, (i) cleavage of the S—O bond with regeneration of the hydroxyl group as a result of SN2 attack at the sulphur atom, and (ii) cleavage of the C—O bond as a result of SN2 attack at the carbon atom. 

The following structures indicate the range of aromatic sulphonic acids (1), sulphinic acids (2), sulphonyl chlorides (3), sulphonamides (4) and sulphonate esters (5) to be discussed below. 

These sulphonate esters cannot be made by direct esterification of the sulphonic acids since further reaction of the ester with the alcohol gives rise to an ether by means of an alkyl-oxygen fission process. 

The neutral sulphur compounds include sulphides or thioethers, disulphides, sulphoxides and sulphones, sulphate and sulphonate esters, and isothiocyanates. Acidic sulphur compounds, i.e. sulphonic and sulphinic acids, thiols and thio-phenols, and the primary sulphonamides have already been discussed. The sulphates of amines are converted by aqueous sodium hydroxide into the free bases the sulphate anion can be detected in the resulting aqueous solution as barium sulphate in the usual manner. 

These are sulphonates with some atypical properties and are more complex in that they are polyfunctional, containing sulphonate, ester and, in the case of the half-ester, carboxylate groups. Sulphosuccinates are valued as very mild surfactants in personal care applications and, as the diester, also as highly effective oil-soluble wetting agents. 

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