Mesylate anion

Pyridopyrrolopyrimidine 156 was obtained from compound 155 by removal of the protecting group followed by elimination of the mesylate anion (Equation 8) <2001TL315, 2003JOC10020, 2003TL6191, 2004ARK74, 2004M615>. 

These observations are in accord with a scheme involving a reversible electron transfer, followed by a reaction that depletes the concentration of the initially formed reduced species, R. They are also reminiscent of the observations made earlier in regard to the electrohydrocyclization process. The greater the rate of the follow-up process, the more significant its effect on the concentration of R in a given time period, that associated with the CV scan rate, for example. From a moments consideration of the Nernst equation, it is clear that this event should manifest itself in terms of a shift in the peak potential to a more positive value, as observed for 255 and 257b [4]. In the present instance, it is suggested that a rapid or concerted loss of the mesylate anion in the reductive cyclization is likely to be associated with this so-called kinetic shift of the peak potentials [69]. 

Explain why the trifluoromethanesulfonate anion is a better leaving group than the mesylate anion. 

Ionic polymers 120 containing a mesylate anion were prepared by the quaterniza-tion of poly(4-vinylpyridine/styrene) 118 with tri(ethylene glycol) monomesylate monomethyl ether 119. These polymers were used to immobilize OSO4, as shown in Scheme 3.33. The resultant polymer 122 showed excellent catalytic performance in the Sharpless asymmetric dihydroxylation of styrene derivatives [63]. For example, 123 was dihydroxylated to styrene glycol 124 in 88% yield with 99% ee. 

Thomas investigated the chemistry of 8-azabicyclo[1.2.1]octanes, the core structure of the tropane alkaloids, and unexpectedly observed a Grob fragmentation instead of the predicted elimination reaction. Upon treatment of mesylate 27 with potassium /-butoxide in dimethyl sulfoxide, silyl cleavage affords alkoxide 28 which fragments to yield formaldehyde, a mesylate anion, and bicycle 29. Exposure of 27 to DBU in acetonitrile leads to the desired E2 reaction with complete suppression of the Grob fragmentation. ... 

As discussed in Section 10.5D, a special value of p-toluenesulfonic (tosylate) and meth-anesulfonic (mesylate) esters is that in forming them, an —OH is converted from a poor leaving group (hydroxide ion) in nucleophilic displacement to an excellent leaving group, the p-toluenesulfonate (tosylate) or methanesulfonate (mesylate) anions. 

Where possible, the leaving group (Y ) should be as hydrophilic as possible good candidates are Cl and mesylate. Anionic leaving groups that are particularly hydrophobic such as iodide and p-toluenesulfonate, tend to form tighter ion pairs with the quat cation and slow down or stop the PTC process. 

Activity is also retained when oxygen at the 21 position is replaced by sulfur. Preparation of one of these compounds follows a route quite analogous to the foregoing thus, displacement of the mesylate group in the cortisone (56) derivative 57 with the anion from thiopivalic acid affords thioester 58. Reduction of the 11-ketone by means of borohydride affords tixocortol pivalate (59)[13j. 

Intermediate 10 must now be molded into a form suitable for coupling with the anion derived from dithiane 9. To this end, a che-moselective reduction of the benzyl ester grouping in 10 with excess sodium borohydride in methanol takes place smoothly and provides primary alcohol 14. Treatment of 14 with methanesulfonyl chloride and triethylamine affords a primary mesylate which is subsequently converted into iodide 15 with sodium iodide in acetone. Exposure of 15 to tert-butyldimethylsilyl chloride and triethylamine accomplishes protection of the /Mactam nitrogen and leads to the formation of 8. Starting from L-aspartic acid (12), the overall yield of 8 is approximately 50%, and it is noteworthy that this reaction sequence can be performed on a molar scale. 

Stereoinversion Stereoinversion can be achieved either using a chemoenzymatic approach or a purely biocatalytic method. As an example of the former case, deracemization of secondary alcohols via enzymatic hydrolysis of their acetates may be mentioned. Thus, after the first step, kinetic resolution of a racemate, the enantiomeric alcohol resulting from hydrolysis of the fast reacting enantiomer of the substrate is chemically transformed into an activated ester, for example, by mesylation. The mixture of both esters is then subjected to basic hydrolysis. Each hydrolysis proceeds with different stereochemistry - the acetate is hydrolyzed with retention of configuration due to the attack of the hydroxy anion on the carbonyl carbon, and the mesylate - with inversion as a result of the attack of the hydroxy anion on the stereogenic carbon atom. As a result, a single enantiomer of the secondary alcohol is obtained (Scheme 5.12) [8, 50a]. 

A nucleophilic attack at an allene system of the type of 417 was described for the first time by Cainelli et al. [172], namely at 444 with the chloride ion as the nucleophile (Scheme 6.91). After the treatment of the mesylate 443 with triethylamine in the presence of lithium, sodium or tetrabutylammonium chloride, mixtures of the vinyl chlorides 445 and 447 were isolated in high yields. Since the reaction did not proceed in the absence of triethylamine, the first step should be a /3-elimination of methanesulfonic acid from 443 to generate 444, which would accept a chloride ion at the central allene carbon atom. A proton transfer to either allyl terminus of the anion thus formed (446) would lead to the products 445 and 447. 

Bell el al., 1974. The reference intermolecular reaction is of the anion of p-hydroxy-acetophenone with EtCOCHjBr under the same conditions As for note j except that the reference reaction is alkylation of the guaiacol anion m Borchardt and Cohen, 1972. EM s based on relative rates assuming equal EM s for the bromide and mesylate, B.5.10 and B.5.12... 

The almost instantaneous intramolecular ether formation by reaction of phenoxy anions, generated from the silyl ethers with a stoichiometric amount of tetra-n-butylammonium fluoride, on mesylate esters has been used to synthesize labile benzo-0-2-isocephams (>90%) [20]. 

Further variations on the epoxyketone intermediate theme have been reported. In the first (Scheme 9A) [78], limonene oxide was prepared by Sharpless asymmetric epoxidation of commercial (S)-(-)- perillyl alcohol 65 followed by conversion of the alcohol 66 to the crystalline mesylate, recrystallization to remove stereoisomeric impurities, and reduction with LiAlH4 to give (-)-limonene oxide 59. This was converted to the key epoxyketone 60 by phase transfer catalyzed permanganate oxidation. Control of the trisubstituted alkene stereochemistry was achieved by reaction of the ketone with the anion from (4-methyl-3-pentenyl)diphenylphosphine oxide, yielding the isolable erythro adduct 67, and the trisubstituted E-alkene 52a from spontaneous elimination by the threo adduct. Treatment of the erythro adduct with NaH in DMF resulted... 

Carbohydrate anisyl tellurides are easily prepared by treatment of the corresponding mesylates or tosylates with the anisyl teUurolate anion. By irradiation of these tellurocarbohy-drates in the presence of M-acetoxythiopyridone and the electrophilic olefin, the tandem addnct is formed. The oxidative elimination of the thiopyridine moiety leads to the trans-olefms. ... 

Direct nucleophilic SN2 exchanges F/leaving group (mesylate, tosylate, nosy-late, triflate, iodide or bromide) in a complex structure using [ Fj fluoride anion are more frequent in aliphatic than in aromatic series. The choice of the leaving group is strongly dependent on the substrate to label [206] and it is often neces-... 

Intermolecular reactions of hydroxylamines with secondary alkyl halides and mesylates proceed slower than with alkyl triflates and may not provide sufficiently good yield and/or stereoselectivity. A nseful alternative for these reactions is application of more reactive anions of 0-alkylhydroxamic acids or 0-alkoxysulfonamides ° like 12 (equation 8) as nucleophiles. The resulting Af,0-disubstituted hydroxamic acids or their sulfamide analogs of type 13 can be readily hydrolyzed to the corresponding hydroxylamines. The same strategy is also helpful for synthesis of hydroxylamines from sterically hindered triflates and from chiral alcohols (e.g. 14) through a Mitsunobu reaction (equation 9). 

Metallation of 3,4-dimethyl-l,2,5-thiadiazole (55) to the anion (56) was accomplished with the use of a nonnucleophilic base, lithium diisopropylamide <82JHC1247>. Nucleophilic attack at sulfur resulted in an alkyllithium reagent <70CJC2006>. The lithiomethyl derivative (56) was carboxylated to (57) with carbon dioxide and converted to the vinyl derivative (58) via an esterification, reduction, mesylation, and base elimination sequence (Scheme 12). 

The direct anionic cyclization of 2-alkynylbenzonitriles 45 was applied to the synthesis of isoquinolinones <99T13193> and phenanthridines <990L767>. A bw-alkylation process of an amine with a hii-mesylate afforded the tetrahydroisoquinoline ring system <99SC645>. 

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