Tosyl esters

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... 

One of the more important approaches to 1-azirines involves a similar base-induced cycloelimination reaction of a suitably functionalized ketone derivative (route c. Scheme 1). This reaction is analogous to route (b) (Scheme 1) used for the synthesis of aziridines wherein displacement of the leaving group at nitrogen is initiated by a -carbanionic center. An example of this cycloelimination involves the Neber rearrangement of oxime tosylate esters (357 X = OTs) to 1-azirines and subsequently to a-aminoketones (358) (71AHC-(13)45). The reaction has been demonstrated to be configurationally indiscriminate both syn and anti ketoxime tosylate esters afforded the same product mixture of a-aminoketones... 

Replacement of a primary or secondary hydroxyl function with deuterium is usually carried out by first converting the alcohol into a mesylate or tosylate ester, which can then be displaced by treatment with lithium aluminum deuteride. The... 

Other examples of the successful displacement of tosylates are the preparation of 31 -, 16a-,16j - and27- labeled steroids. This displacement reaction fails, however, with certain C-18 and C-19 alcohol derivatives which give mainly O—S instead of C—O bond cleavage. Unsatisfactory results were also obtained with sterically hindered tosylate esters at C-11, C-12 and C-20, which give considerable amounts of olefinic products in addition to O—S bond cleavage. ... 

Cleavage of mesyl or tosyl esters with K F in the presence of 18-crown-6 ether [46] or Kryptofix 222 [47] provides a reliable method for the preparation of F-labeled biologically active compounds... 

The elimination of water from a fluorinated compound generally follows a reaction path similar to that of its nonfluorinated counterpart, although the presence of the highly electronegative fluorine atoms may have unexpected effects Various monofluoro alcohols can be dehydrated via their tosyl esters at 75 C by using potassium rert-butoxide [80] (equation 50)... 

The inference is that the hydrofuranol ring of XL can never be directly formed by the saponification of a 3-tosyl ester of D-glucose, but only indirectly by the intermediate formation and scission of an anhydro ring of the ethylene oxide type. The sequence of reactions involved in the conversion of methyl 3-tosyl-jS-D-gIueoside into methyl 3,6-anhydro-n-glucoside is shown by XXXVI to XL. 

A rapid O-tosylation of a primary alcohol with tosyl chloride (1 equivalent) in the presence of 4-(N,N-dimethylamino)pyridine (1 equivalent) has been reported by Botta and coworkers (Scheme 6.118) [236], Microwave heating of the reaction mixture at 50 °C for 5 min provided the desired tosyl ester in 95% yield. 

Tipson devoted most of his years in Levene s laboratory accomplishing seminal work on the components of nucleic acids. To determine the ring forms of the ribose component of the ribonucleosides he applied Haworth s methylation technique and established the furanoid structure for the sugar in adenosine, guanosine, uridine, and thymidine. He showed that formation of a monotrityl ether is not a reliable proof for the presence of a primary alcohol group in a nucleoside, whereas a tosyl ester that is readily displaced by iodide affords clear evidence that the ester is at the 5-position of the pentofuranose. Acetonation of ribonucleosides was shown to give the 2, 3 -C -isopropyl-idene derivatives, which were to become extensively used in nucleoside and nucleotide chemistry, and were utilized by Tipson in the first chemical preparation of a ribonucleotide, inosinic acid. 

Recent studies on the solvolysis of the diastereomeric tosylates 107 support this hypothesis. The acetolysis and formolysis of these compounds proceed with high retention of configuration 90> while in ordinary simple acetolysis of tosyl esters of secondary alcohols containing no neighboring groups, inversion predominates. 

Treatment of the 11 P-hydroxysteroid with tosyl chloride produces a tosylate ester, providing a good leaving group for a base-catalysed E2 elimination (see Section 6.4.1). The favoured product is the more-substituted 9, 11-alkene (see Section 6.4.1). A consideration of the steroid shape (see Box 3.19) shows that the 9a-proton and the 1 Ip-tosylate are both axial and, therefore, anti to each other they are thus ideally positioned for an elimination... 

Another recurrent theme of the Richardson-Hough team was the selective sulfo-nylation of disaccharide derivatives, which led to many interesting papers, some involving trehalose and others sucrose. For example, in 1986, they reported (with Mukund K. Gurjar and Lee V. Sincharoenkul) that selective tosylation of 6,l 6 -tri-<9-tritylsucrose at room temperature for 2 days afforded the 2-tosyl ester in 52% yield... 

Scheme 22) and not the 3-tosyl ester that had originally been claimed in 1971 by Jezo as the major product of this reaction. Indeed, when Richardson repeated Jezo s exact conditions, which involved heating 6,l 6 -tri-0-tritylsucrose with TsCl and pyridine at 55 °C, the product obtained had identical spectroscopic properties to those reported for the Jezo product, and this material was, in turn, shown to be identical to the 2-tosyl ester prepared in improved yield under Richardson s new conditions (Scheme 22). 

Richardson and Hough s assertion that it was the 2-tosyl ester that had been prepared, and not the 3-tosylate claimed by Jezo. 

Thiophene-fused benzoquinones, such as 23, can be easily alkylated to produce dialkoxybenzodithiophene compounds 111 on reaction with tosyl esters (Equation 28) <2002SM(130)139>. 

Problem 13.18 (a) Why are sulfonate esters such as p-toluenesulfonyl (tosyl) esters widely used in S 2 reactions (b) How is this reaction used for indirect displacement of —OH from ROH ... 

Probitm 16.95 Reaction of the (R)-tosyl ester of a-phenylethyl alcohol (C H,CHMeOTs) with CH,COOH yields a mixture of (S)- and rac-acetate. Explain. 

Alcohols react with inorganic acids to form esters, e.g. tosylate esters (see Section 5.5.3) and phosphate esters. Phosphate esters are important in nature since they link the nucleotide bases together in DNA (see Section 4.8). 

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