Sulphonate esters alkyl

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]. 

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). 

Sulphones, 500, 1078 Sulphonephthaleins, 989, 990 Sulphonic acids, 548, 557, 1077 see also under Aromatic sulphonic acids alkyl esters of, 1079 ... 

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. 

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. 

Reaction of hydroxy- and alkoxy-substituted aromatic compounds with methyl fluorosulphonate leads to the preparation of a sulphonate ester by carbon-sulphur bond formation342, as shown in equation 77. In the case of the hydroxy-substituted aromatic compounds, the synthetic utility is limited since side-reactions involving O-alkylation readily occur. 

Sulphonate esters may be formed by a transalkylation reaction involving an alcohol and another sulphonate ester. One such reaction of some novelty proceeds in the presence of ultra-violet light via a sulphene as shown in equation 80351. Alkyl group exchange may also be accomplished by reaction of alkyl halides with methyl tosylates, by heating in the presence of tetraalkylammonium salts352. 

Alkylation of sulphonic acids with a wide variety of reagents produces sulphonate esters. Diazomethane378,390 and other diazoalkanes358,391 produce the sulphonate ester in good yield, presumably via the carbene, as shown in equation 88. In a similar manner, ft-... 

In reactions that resemble the pinacol rearrangement, thiopyranoside sulphonate esters undergo ring contraction and expansion reactions via the intermediacy of sulphonium ions, e.g. equations 37 and 38102. Similarly, cyclic sulphonates are able to trap oxime anions at the carbon atom (equation 39)103. Such carbon alkylation of oxime ions is rare, and by suitable choice of substrate both ring-contraction and ring-expansion reactions are possible103. 

Intramolecular alkylation of an a-sulphonyl anion in the methyl sulphonate ester 53 is potentially possible. Though the rearrangement (equation 40) is observed, deuterium labelling experiments reveal that the reaction involves intermolecular methyl transfer104. This is attributed to the preference of SN2 reactions for backside attack at the tetrahedral carbon atom. 

Protonation of sulphonate esters in aqueous sulphuric acid mixtures appears to increase the rates of S l reactions in solvent compositions of about 60% w/w or more, although the extent of protonation of substrates was estimated to be only 1% (increasing, but still less than 30% protonation, in 98% sulphuric acid)10. Solvolyses of primary alkyl sulphonates have been examined in sulphuric acid and in fluorosulphuric acid, containing 1M potassium fluorosulphate130,131 under these conditions, it was roughly estimated130 that ethyl tosylate would be only about 0.1% protonated. 

The reactions of lithiophosphide reagents with alkyl halides or sulphonate esters have continued to find wide application in the synthesis of new phosphines. A series of phosphino-ethers, e.g., (22), has been prepared from the reactions of chloromethyl-substituted ethers with lithium diphenylphosphide. " A one-step synthesis of macrocyclic phosphino-ethers and -thioethers (23) is afforded by the reactions of dilithio-organophosphides with bis(j8-chloroethyl)-ethers and -thioethers derived from ethane-1,2-diol and ethane-1,2-dithiol, respectively. " A new family of water soluble phosphonio-phosphine ligands (24) has been prepared by the reaction of a,o)-dihaloalkanes with one mole of lithium diphenylphosphide, followed by quatemisation of the intermediate w-haloalkylphosphine with trimethylphosphine. The new ligand system (25) has been prepared by the reaction of chloromethylbenzene-chromium tricarbonyl with... 

Dithiepins.—There are two new variations on the preparation of dithiepins by migration of a thio-group in 1,3-dithians. Treatment of the l,3-dithian-2-yl-methanols (164 R = C02Me or H) with methanesulphonyl chloride gave the 1,4-dithiepin (165), presumably by ring-expansion of the sulphonate ester. Another example is provided by the oxidation of the 2-ethylidene-l,3-dithian (166) with lead tetra-acetate the yields if R = alkyl or aralkyl varied between 34 and 67%, but if R = phenyl only (167) was produced, and not the thiepin enol acetate, as stated earlier by another group. ... 

Hydroxyethyl esters can be prepared from the free acid by reaction with ethylene carbonate. During an attempt to protect the ketone group of a keto-acid by 1,3-dioxolane formation, it has been found that mixed carboxylate sulphonate esters [e.g. (121) from ethylene glycol and tosic acid] can easily be formed extensions of this reaction show it to have a general applicability. In the presence of fluoride ions, carboxylic acids become sufficiently nucleophilic to attack alkyl halides. Thus, reaction between an acid and 1,3-dibromopropane leads to diesters (122). Molecular sieves have been recommended as suitable absorbants... 

Reactions.—New systems for the reduction of alkyl halides to alkanes include mixtures of lithium aluminium hydride with transition-metal chlorides (such as Ni or Co" chlorides) and some complex metal hydrides of copper, especially the THF-soluble Li4CuHs. Details of the application of sodium cyanoborohydride to the reduction of halides (and sulphonate esters) in dipolar aprotic solvents have been published. Virtually all other functional groups are inert to this convenient, mild, and efficient system, which has been used to develop a one-pot deoxygenation of primary alcohols (Scheme 39) via the iodides. The alternative cyanoborohydride reagents (55) and the polymeric (56) are also discussed. ... 

In the preparation of various unsaturated amides, the dianion of -phenyl-2-(phenyIsulphonylmethyl)propenamide (49) proved to be a versatile synthon. Borohydride reduction of alkylation products of the dianion occurred in high yield to afford moderate overall yields of ,B-unsaturated amides.The dianion of the corresponding phenyl sulphide alkylated poorly giving small amounts of oth a- and y-alkylation products, whereas the sulphone-ester corresponding to (49) was found to be labile under the deprotonation conditions. Compound (49) was also employed in the development of a general strategy for the synthesis of 3,4-epoxy-2-methylene-alkanoic acid amides (Scheme 29). ... 

Polystyrene (soluble), incorporating an arylsul-phonyl chloride group Polymer-saccharide (C-6) sulphonate ester" O-Alkyl fission of sulphonate ester AcOK-DMF /3-D-Gentiobiose octaace-tate Guthrie e/a/., 1971, 1973... 

Methods reported this year for the reduction of alkyl halides to alkanes include the potassium-dicyclohexyl-18-crown-6 reduction of alkyl fluorides, sodium borohydride reduction of alkyl chlorides, bromides, and iodides (or sulphonate esters) under liquid-liquid phase-transfer conditions, and the selective reduction of tertiary alkyl, benzyl, and allyl halides with the borate (61). Continuing... 

Natural Cyclopropanes.—Ficini etal. have outlined a new approach to chrysaU themic acid ester (11) from commercially available 2,5-dimethyl-3-hexyn-2,5-diol, which has as a key stage the palladium-catalysed alkylation of the sulphone ester (10) with the acetate (9) (Scheme 3). cw-Chrysanthemic acid (14, R = H), is obtained by hydrogenation of the cyclopropene (13) produced by addition of diazopropane to the enyne (12). ... 

Little work has been done on the pyridine-sulphonic acids. Alkyl halides do not react with pyridine-2-sulphonic acid or its amide, and with its silver salt give the iV-alkyl betaines which are incapable of forming salts s. With methyl iodide, potassium pyridine-3-sulphonate may have given the methyl ester methiodide, although working up produced the iV-methyl-... 

Sulphonic acid esters Alkyl aryl sulphonic acid esters, such as ethyl p-toluene sulphonate, have two strong characteristic bands near 1350 cm ( 7.41 pm) and 1180cm ( 8.47pm) in their infrared spectra. Aryl esters of alkyl sulphonic acids normally have a strong absorption near 865-650cm (11.56-15.38pm) due to aromatic CH out-of-plane deformation vibrations and in this respect their spectra are similar to those of aryl sulphonamides but, of course, sulphonamides have additional bands due to their NH stretching vibrations. 

Developments of standard uses of sulphonate esters in synthesis include the use of magnesium halides MgBrj " and Mgli" for conversion into alkyl... 

---