Methyl acetolysis

Higher perfluoroalkanesulfonates are slightly more reactive than triflates toward nucleophilic displacements. The rate constants for acetolysis of methyl nonafluorobutanesulfonate [6401 -03-2J, methyl trifluoromethanesulfonate [333-27-7] and methyl toluenesulfonate [80-48-8] are 1.49 x, ... 

The rate of acetolysis of t-butyl bromide relative to that of i-propyl bromide at 25°C is 10 - , whereas the rate of acetolysis of 2-methyl-2-adamantyl bromide relative to that of 2-adamantyl bromide is 10 ... 

On the other hand the acetolysis of the 6y5,19-ether bridge is a useful reaction in the 6a-methyl-6j9,19-ether series ... 

Barsha and Hibbert16 also demonstrated by meins of methylation, acetylation, acetolysis and hydrolysis experiments that the membranes synthesized by the action of A. xylinum on D-fructose and on glycerol were chemically identical with cotton cellulose. 

Depolymerization of the permethylated carbohydrate is achieved by hydrolysis with acid. Under these conditions, the amino sugar residues are N-deacetylated, and the aminohexosidic linkages become resistant to hydrolysis. Stellner and coworkers29 showed that, when the acid degradation is conducted in 95% acetic acid, the amino sugar residues are also liberated, and can be analyzed by the methylation technique.29 Therefore, acetolysis followed by acid hydrolysis is now commonly used, as it allows the analysis both of hexose and hexosamine residues. 

The partially methylated monosaccharides obtained on depolymerization of the permethylated sample are preferably analyzed as acetates by g.l.c.-m.s., as shown by Bjomdal and coworkers.41,42 The neutral sugars and the amino sugars obtained in acetolysis-acid hydrolysis are reduced, and acetylated for the analysis, and the amino-hexitol and the neuraminic acid residues are acetylated after methanolysis. Identification with the aid of g.l.c.-m.s. has been described for all of the common components of protein- and lipid-linked glycans and oligosaccharides from animal cells, namely, the neutral sugars,41-43 hexitols,44 hexosamines,29,43,45,46 aminohexitols,31,32 and neuraminic acids.33,34,47... 

Figure 4. Products of acetolysis of bicyclo[2.1. l]hexane-5-methyl tosylates.

In contrast, the results obtained in the methanolysis, acetolysis, and trifluoroacetolysis of the tosylate 91 were not the expected ones. Cram obtained the methyl ether 93, the acetate 94 and the trifluoro-acetate 95 with the same configuration and optical purity as in the direct synthesis from the alcohol 92. These solvolyses at the bridge carbon atom of [2.2]paracyclophane therefore proceed with complete retention of configuration. The rate of acetolysis of the tosylate 91 also deviates considerably from that of aliphatic secondary tosylates it is some 100 times faster than that of 2-butyl tosylate and about the same as that of a-phenylneopentyl tosylate, acetolysis of which is only slightly stereospecific. 

Glycosidic linkages may also be cleaved in other solvents, such as methanol. In this case, water is rigorously excluded, so that the elements of a molecule of methanol are added across the glycosidic linkage to afford the methyl glycosides. Methanolysis is usually catalyzed by the addition of dry hydrogen chloride to the methanol. Other solvents, such as acetic anhydride-acetic acid (acetolysis) and formic acid (formolysis), are occasionally used for special purposes. 

Formolysis and acetolysis are not common methods for cleavage of glycosidic linkages. They do have some unique applications, however. For instance, methylated polysaccharides are not generally soluble in hot water, and consequently, hydrolysis is best preceded by formolysis under these circumstances. For example, 5 mg of methylated polysaccharide is dissolved in 3 mL of 90% formic acid, and the solution is kept for 2 h at 100°. The formic acid is removed by evaporation at 40°. The residue is dissolved in 1 mL of 250 mM sulfuric acid and the solution is heated for 12 h at 100°, cooled, the acid neutralized with barium carbonate, the... 

Cycloheptanes.— The C-1—C-2 bond in -y-thujaplicin is essentially single, Co"-/3-thujaplicin-amine complexes have been described, and thermodynamic data on the U -/3-thujaplicin complex have been calculated. The biomimetic cyclization of the silyl enol ether (191) to karahanaenone (192), using methyl-aluminium bis(trifluoroacetate) is almost quantitative (192) is also synthesized by thermolysis followed by desilylation of the silyl enol ether (193) which is readily available from l-bromo-2-methyl-2-vinylcyclopropane and isobutyraldehyde. Dehalogenation of 3-bromo-l-iodo-3-methylbutan-2-one with Zn-Cu couple on alumina in the presence of isoprene yields (192) and minor amounts of the isomers (194) and (195) however, dehalogenation with Fc2(CO)9 favours (195). Acetolysis of karahanaenol tosylate yields anticipated p-menthane derivatives and no filifolene. ... 

Acetolysis of Methyl-(e-tosy1oxyethyl)-nitrosamine (I) and Methyl(y-tosyloxypropyl)-ni trosamine 111... 

Byproducts of this rearrangement are cyclobutenes, cyclopropane derivatives and allenic alcohols. The ratio of these products depends on the substitution of the substrate and on the reaction conditions. For example, 3-methyl-5-tosyloxypenta-l,2-diene (3) gives 75% of 1-methyl-2-methylenecyclobutanol (4) upon hydrolysis with water and calcium carbonate at 100 °C, while acetolysis with acetic acid/sodium acetate at 80 °C, and subsequent treatment with lithium aluminum hydride, provides only 37% of the cyclobutanol.12... 

The product mixture is more complicated when substituents are present on the allenes. When C4 and C5 of the penta-l,2-dien-5-yl system carry different substituents, an apparent exchange of the positions of these substituents occurs during cyclization, owing to competition between homoallyl and 1234 1243 rearrangement (see Section 2.3.).12 Moreover, the cis- and tow. -isomers are formed. This is exemplified in the product distribution obtained from the hydrolysis and acetolysis of 3,4-dimethyl-5-tosyloxypenta-1,2-diene (7, R1 — Me R2 = H) and 3-methyl-5-tosyloxyhexa-1,2-diene (7, R1 = H R2 = Me).12... 

Moreover, the acetolysis of oHt/-7-methyl-s>7i-7-tosyloxybicydo[2.2.1]hept-2-ene in acetic acid/ sodium acetate at 70 °C gave predominantly the regioisomeric exo-4-acetoxybicyclo[3.2.0]hept-2-enes 10 and 11.82... 

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