Alkyl tosylates sulfonates

Trifluoromethanesulfonates of alkyl and allylic alcohols can be prepared by reaction with trifluoromethanesulfonic anhydride in halogenated solvents in the presence of pyridine.3 Because the preparation of sulfonate esters does not disturb the C—O bond, problems of rearrangement or racemization do not arise in the ester formation step. However, sensitive sulfonate esters, such as allylic systems, may be subject to reversible ionization reactions, so that appropriate precautions must be taken to ensure structural and stereochemical integrity. Tertiary alkyl tosylates are not as easily prepared nor as stable as those from primary and secondary alcohols. Under the standard conditions, tertiary alcohols are likely to be converted to the corresponding alkene. 

Substrates susceptible to Sn 1 attack and those bearing leaving groups other than halides have also been employed in the Michaelis-Arbuzov reaction, for example, dialkyl sulfates, alkyl mesylates, alkyl tosylates, quaternary ammonium species, activated acetates as have other electrophiles, for example, alkyl fluoroborates, lactones, lactams, aziridines, sulfones, iminium cations, and orf/io-quinonoids.6,13-15,18... 

Let us look at another example of solvolysis. A very commonly studied system is one in which the solvent is acetic acid (HOAc) and the substrates are alkyl esters of sulfonic acids ROTs, alkyl tosylates (alkyl p-toluenesulfonates) ROBs, alkyl... 

Desulfonylation. Various sulfonyl groups are reductively removed by Mg/MeOH. These include alkenyl sulfones, alkyl tosylates, and A -Boc-arenesulfonamides (p-toluenesulfonhydrazides, V-tosylaziridines ). But when the V-tosylaziridine contains an electron-withdrawing group, ring cleavage to give p-(V-tosylamino) derivatives takes precedence to detosylation. ... 

The photochemical reaction of ArgSb with styrenes in the presence of Oy results in the formation of 1,2-diarylethanols via peroxyantimony(V) intermediates (Scheme 14.54) [122]. The irradiation of a mixture of Ph2SbSbPh2 and iodoalkaries in air produces alcohols via alkyl diphenylstibonates [123]. Alkyl aryl sulfones are obtained by the BugSb-promoted reaction of tosyl chloride with alkyl hahdes [124]. 

The first catalytic arylation of an alkyl sulfonate was reported by Schlosser and coworkers during the early 1970s, when they showed that a primary alkyl tosylate... 

Several sulfonyl chlorides are available to activate OH groups. The most common one is para-toluenesulfonyl chloride (abbreviated as TsCl). The sulfonate ester formed from the reaction of TsCl and an alcohol is called an alkyl tosylate (abbreviated as ROTs). 

Sulfonate esters are subject to the same limitations as alkyl halides Competition from elimination needs to be considered when planning a functional group transforma tion that requires an anionic nucleophile because tosylates undergo elimination reactions just as alkyl halides do... 

An advantage that sulfonate esters have over alkyl halides is that their prepara tion from alcohols does not involve any of the bonds to carbon The alcohol oxygen becomes the oxygen that connects the alkyl group to the sulfonyl group Thus the configuration of a sulfonate ester is exactly the same as that of the alcohol from which It was prepared If we wish to study the stereochemistry of nucleophilic substitution m an optically active substrate for example we know that a tosylate ester will have the same configuration and the same optical purity as the alcohol from which it was prepared... 

The preparation of esters can be classified into two main categories (1) carboxy-late activation with a good leaving group and (2) nucleophilic displacement of a caiboxylate on an alkyl halide or sulfonate. The latter approach is generally not suitable for the preparation of esters if the halide or tosylate is sterically hindered, but there has been some success with simple secondaiy halides and tosylates (ROTs, DMF, K2CO3, 69-93% yield). ... 

In contrast to phosphorus esters, sulfur esters are usually cleaved at the carbon-oxygen bond with carbon-fluorine bond formation Cleavage of esteri nf methanesulfonic acid, p-toluenesidfonic acid, and especially trifluoromethane-sulfonic acid (tnflic acid) by fluoride ion is the most widely used method for the conversion of hydroxy compounds to fluoro derivatives Potassium fluoride, triethylamine trihydrofluoride, and tetrabutylammonium fluoride are common sources of the fluoride ion For the cleavage of a variety of alkyl mesylates and tosylates with potassium fluoride, polyethylene glycol 400 is a solvent of choice, the yields are limited by solvolysis of the leaving group by the solvent, but this phenomenon is controlled by bulky substituents, either in the sulfonic acid part or in the alcohol part of the ester [42] (equation 29)... 

Alkyl sulfates, tosylates, and other esters of sulfuric and sulfonic acids can be converted to alkyl halides with any of the four halide ions. Neopentyl tosylate... 

Sulfonic esters are most frequently prepared by treatment of the corresponding halides with alcohols in the presence of a base. The method is much used for the conversion of alcohols to tosylates, brosylates, and similar sulfonic esters. Both R and R may be alkyl or aryl. The base is often pyridine, which functions as a nucleophilic catalyst, as in the similar alcoholysis of carboxylic acyl halides (10-21). Primary alcohols react the most rapidly, and it is often possible to sulfonate selectively a primary OH group in a molecule that also contains secondary or tertiary OH groups. The reaction with sulfonamides has been much less frequently used and is limited to N,N-disubstituted sulfonamides that is, R" may not be hydrogen. However, within these limits it is a useful reaction. The nucleophile in this case is actually R 0 . However, R" may be hydrogen (as well as alkyl) if the nucleophile is a phenol, so that the product is RS020Ar. Acidic catalysts are used in this case. Sulfonic acids have been converted directly to sulfonates by treatment with triethyl or trimethyl orthoformate HC(OR)3, without catalyst or solvent and with a trialkyl phosphite P(OR)3. ... 

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