Alcohol tosylate from

Problem 16.9 You prepare 5ec-butyl tosylate from alcohol of [aj +6.9 . On hydrolysis with aqueous base, this ester gives A c-butyl alcohol of [a] - 6.9 . Without knowing the configuration or optical purity of the starting alcohol, what (if anything) can you say about the stereochemistry of the hydrolysis step ... 

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... 

Section 8 14 Nucleophilic substitution can occur with leaving groups other than halide Alkyl p toluenesulfonates (tosylates) which are prepared from alcohols by reaction with p toulenesulfonyl chloride are often used... 

Mesylates and tosylates may be used as variants of the 0-sulfate ester. For instance, 55% of aziridine 7 was obtained from base-mediated cyclization of amino mesylate 6. In comparison, the classic Wenker protocol only gave 3% of 7. In another instance, A-tosyl amino alcohol 8 was tosylated to give 9, which was transformed to aziridine 10 in 64% yield, along with 29% of the P-elimination product due to the presence of the ester moiety. Likewise, aziridine 12 was assembled from tosylate 11 in two steps and 60% yield. ... 

Secondary amines are obtained from alcohols when the alcohol is treated with N-methyltosylamine in the presence of triphenylphosphine and diethyl azodicarboxylate56,57 and the tosyl group is then removed from the product 28 by treatment with sodium in liquid ammonia at —70°C (equation 21)58. 

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]. 

Section 7.8). Other classes of derivatives are thus most conveniently prepared from the sulfonyl chloride. Reaction with an alcohol leads to formation of a sulfonate ester. Two common sulfonyl chloride reagents employed to make sulfonate esters from alcohols arep-toluenesulfonyl chloride, known as tosyl chloride, and methanesulfonyl chloride, known as mesyl chloride (see Section 6.1.4). Note the nomenclature tosyl and mesyl for these groups, which may be abbreviated to Ts and Ms respectively. 

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). 

Sulfonates such as mesylates or tosylates are readily prepared from alcohols under mild conditions, and are therefore attractive alternatives to halides as electrophiles. Although sulfonates often undergo clean displacement by nucleophiles, alternative reaction pathways are accessible to these intermediates, which can lead to unexpected results. If the nucleophile used is strongly basic, metalation instead of displacement of the sulfonate can occur. Some potential reactions of such metalated sulfonates include fragmentation into sulfenes and alcoholates, or into sulfmates and carbonyl compounds, or self-alkylation (Scheme4.15). 

We have focussed on alkyl halides but tosylates from TsCl and mesylates from MsCl can be used too. The conversion of alcohols to chlorides and bromides is discussed earlier in this chapter and the combination of reagents used to make thiols is discussed in the next chapter. 

Tosylate, TsO, is an important leaving group made from alcohols... 

Toluenesulfonate esters (tosylates) can be made from alcohols (with TsCl, pyridine). You have already met tosylates in Chapter 17 because they are good electrophiles for substitution reactions with nonbasic nucleophiles. With strong bases such as f-BuOK, NaOEt, DBU, or DBN they undergo very efficient elimination reactions. Here are two examples. 

Tosylate esters may be prepared in the absence of pyridine as solvent by converting the hydroxyl group to a lithium salt by addition of methyl or butyllithium. The resultant lithium alkoxide is then treated with tosyl chloride. This approach is recommended for the preparation of tosylates from very sensitive alcohols, provided that they do not contain other functional groups that react with the alkyl lithium reagents. 

Sulfur example—formation of a tosylate from toluenesulfonyl chloride and an alcohol ... 

Bicyclopropylidene has also been prepared from alcohol 2 via the tosylate instead of the bromide (see Section 5.2.2.3.). ... 

The presence of a nitrogen atom is not essential to transform natural compounds in ionic liquids. Recently, ionic liquids have been synthesized from alcohols and polyhydroxylated compounds (sugars) after transformation of the hydroxyl group on tlie primary carbon(s) in a more efficient leaving group (halogen, tosylate, triflate, and so on). 

C-X disconnection in aliphatic compounds (ii) gives a nucleophile XH and an electrophilic carbon species usually represented by an alkyl halide, tosylate, or mesylate. These compounds can all be made from alcohols (ii) and as alcohols can be made by C-C bond formation (Chapter 10) we shall treat the alcohol as the central functional group (Table 4.2). 

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