Acetolysis acetal

After isolation as sedoheptulosan, the free sugar can be recovered through its acetate. Acetolysis of sirupy sedoheptulosan tetraacetate, in the presence of a catalytic proportion of perchloric acid, gives a crystalline sedoheptulose hexaacetate which, since its ultraviolet spectrum shows no ketonic absorption, was designated hexa-O-acetyl-a-n-alfro-heptulopyra-nose. Cautious deacetylation of this product gave sirupy sedoheptulose,... 

This interpretation is supported by results on the acetolysis of the bicyclic tosylates 9 and 10. With 9, after three months in acetic acid at 150°C, 90% of the starting material was recovered. This means that both ionization to a cyclopropyl cation and a concerted ring opening must be extremely slow. The preferred disrotatory ring-opening process would lead to an impossibly strained structure, the /ran -cyclohexenyl cation. In contrast, the stereoisomer 10 reacts at least 2x10 more rapidly because it can proceed to a stable cis-cyclohexenyl cation ... 

Acetolysis of 3/ -methoxy-19-hydroxy-androst-5-en-17-one 19-methane-sulfonate (68b) in the presence of 4 equivalents of potassium acetate at 100° for 16 hr followed by basic hydrolysis gives 3/ -methoxy-7) -hydroxy-B-homo-estr-5(10)-en-17-one (70a) in 77% yield and 8% of 3/ -methoxy-5, 19-... 

Methoxy-7)5-hydroxy-B-homo-estr-5(10)-en-17-one (70a) ° The buffered acetolysis solution is prepared by heating at reflux overnight a solution prepared from anhydrous potassium carbonate (3.5 g), acetic anhydride (5 ml) and glacial acetic acid (250 ml). 

A vinyl cation is probably an intermediate in the acetolysis of 6-phenyl-5-hexynyl brosylate, 86. At 80°, despite the inductive effect of the triple bond, the rate of acetolysis of 86 is comparable to that of the saturated analog and yields, besides the acyclic acetate 87, 36% of the rearranged acetate 88 (83). The exclusive formation of the five-membered ring rearranged product with none of... 

Solvolysis of either 178a or 178b in 80% aqueous ethanol in the presence of p-toluenethiolate or benzylthiolate gives a 1 1 mixture of cis and trans products. A 1 1 ds trans product ratio also was observed in acetic acid in the presence of either sodium acetate or silver acetate. The 1 1 product ratio was observed as early as 10% reaction and remained constant throughout the reaction. The acetolysis is accompanied by extensive ion-pair return, which causes cis trans, 178a 178b, isomerization. However, this isomerization... 

Vicinal iodo carboxylates may also be prepared from the reaction of olefins either with iodine and potassium iodate in acetic acid/ or with N-iodosuccinimide and a carboxylic acid in chloroform. " A number of new procedures for effecting the hydroxylation or acyloxylation of olefins in a manner similar to the Prevost or Woodward-Prevost reactions include the following iodo acetoxylation with iodine and potassium chlorate in acetic acid followed by acetolysis with potassium acetate reaction with iV-bromoacetamide and silver acetate in acetic acid reaction with thallium(III) acetate in acetic acid and reaction with iodine tris(trifluoroacetate) in pentane. ... 

Acetolysis of LXXIV gives, as might be expected, a mixture of the acetates of n-mannose and D-idose and as the dianhydro sugar has a free hydroxyl on C2, it should prove to be a source of 2-substituted n-mannose or D-idose and of 2,4-derivatives of n-mannose and 2,3-derivatives of D-idose. 

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... 

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. 

The acetolysis of hexamine closely resembles that of hexamine nitrolysis. Accordingly, acidity is of key importance, with high concentrations of acetic acid favouring the formation of the 6-membered 1,3,5-triacetyl-1,3,5-triazacyclohexane (TRAT) and weakly acidic conditions favouring the 8-membered l,3,5,7-tetraacetyl-l,3,5,7-tetraazacyclooctane (TAT). ... 

Buffered acetolysis of tosylate 420 gives diene 421 as the major product along with unrearranged acetate. In buffered formolysis, the cis formate 422 evolves as the principal component. The structural assignments were confirmed by the chemical intercorrelations shown... 

Acetic acid, trifluoro-, anhydride, applications of, in carbohydrate chemistry, 16, 59-84 Acetolysis, 22, 11-23 Aconitic acid, 6, 231-249 Action pattern,... 

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