Cyclic Acetal Derivatives

The cyclic acetals of sugars constitute an important class of compounds, and their value as synthetic intermediates is well recognized.100 The reaction of methyl /3-maltoside with benzaldehyde in the presence of zinc chloride has been reported to give the crystalline methyl 4, 6 -0-benzylidene-/3-maltoside.52 Similar benzylidenation of l,6-anhydro-/8-maltose affords the corresponding 4, 6 -0-benzylidene derivative in 63% yield.82 

The kinetic-acetonation procedure previously reported,107 employing alkyl isopropenyl ethers in N,N-dimethylformamide, and applied to the common pentoses and hexoses, has been extended to various hexuloses, oligosaccharides, and other sugar systems.108 Maltose gave the 4, 6 -monoacetal, isolated as the crystalline hexaacetate, on treatment with isopropenyl methyl ether inN,N-dimethylformamide in the presence of p-toluenesulfonic acid. 

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Diols that bear two hydroxyl groups m a 1 2 or 1 3 relationship to each other yield cyclic acetals on reaction with either aldehydes or ketones The five membered cyclic acetals derived from ethylene glycol (12 ethanediol) are the most commonly encoun tered examples Often the position of equilibrium is made more favorable by removing the water formed m the reaction by azeotropic distillation with benzene or toluene... 

Write the structures of the cyclic acetals derived from each of... 

The reaction of sucrose with a combination of 2,2-dimethoxy-propane-N,N-dimethylformamide-p-toluenesulfonic acid has been exploited to give various, interesting, cyclic acetal derivatives.32,83-85 This combination of reagents for acetonation is known to give strained, and otherwise inaccessible, acetals of monosaccharides.86-89 Treatment of sucrose with 2,2-dimethoxypropane in N,N-dimethyl-formamide in the presence of a catalytic proportion of p-toluenesul-fonic acid for 80 min at room temperature afforded a mixture containing 4,6-O-isopropylidenesucrose, 2,1 4,6-di-O-isopropyli-... 

Cyclic acetals derived from diols and o-nitrobenzaldehyde produce hydroxynitrosobenzoates upon irradiation (see Scheme 26). Early studies of this reaction demonstrated that acetals involving carbohydrates and o-nitrobenzaldehyde experience facile, photochemical... 

With due consideration of the explanations just presented for the observed, relative stabilities of cyclic acetals derived from polyols, in terms of their constitution and conformation, nearly all of the following observations on the selective hydrolysis of cyclic acetals of alditols and dialkyl dithioacetals may be readily understood. 

A. B. Foster, Cyclic acetals derivatives of sugars and alditols. The Carbohydrates Chemistry, Biochemistry, Vol. 1A, (W. Pigman and D. Horton, eds.), Academic Press, New York, 1972,p. 391. 

SAMPLE SOLUTION (a) The cyclic acetals derived from ethylene glycol contain a five-membered 1,3-dioxolane ring. 

The addition of certain glycols and polyols to acrolein leads to the production of cyclic acetal derivatives. 

Splitting by hydrogenolysis is not a property unique to benzyl ethers among the groups often employed in carbohydrate chemistry. The tri-phenylmethyP ethers and the cyclic acetals derived from benzalde-hyde are also cleaved by this means. This property of these... 

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