Acetals of ketoses

Methods in Structural Polysaccharide Chemistry, 15, 53-89 Brady, Robert F., Jr., Cyclic Acetals of Ketoses, 26, 197-278 Bray, H. G., D-Glucuronic Acid in Metabolism, 8, 251-275... 

R. R Brady, Jr., Cyclic acetals of ketoses, Adv. Carbohydr. Chem Biochem 26 197 (1971). J. A. Mills, The stereochemistry of cyclic derivatives of carbohydrates, Adv. Carbohydr. Chem 10 1 (1955). 

Cyclic acetals of ketoses are important and useful compounds. Among other applications, they can be used as intermediates in the synthesis of numerous, useful sugar derivatives and as substrates for studies of conformational principles in fused-ring, heterocyclic A personal contribution by the author. 

General reviews on cyclic acetals of carbohydrates have appeared. The cyclic acetals of the aldoses and aldosides have been treated in this Series by de Beider, but inclusion of cyclic acetals of ketoses was beyond the scope of his Chapter. Other articles, by Barker and Bourne, Mills, and Ferrier and Overend, have been concerned with the stereochemistry and conformation of cyclic acetals of the carbohydrate group. The purpose of the present article is to supplement de Beider s Chapter with a description of the pertinent original work, optimal laboratory preparations, properties, and applications of the cyclic acetals of ketoses, and to provide a summary of the known theoretical aspects of their formation, rearrangement, and hydrolysis. 

Emil Fischer first described the condensation of D-fructose with acetone in 1895, and most of the early work on cyclic acetals of ketoses was performed with D-fructose. In 1934, Reichstein and Griissner published their classic synthesis of L-ascorbic acid (vitamin C), in which L-sorbose was converted into 2,3 4,6-di-0-isopropylidene-a-L-sorbofuranose or other di-alkylidene acetals. The emphasis of research activity then shifted to L-sorbose, and to the elucidation of an optimal procedure for preparing such diacetals. At about the same time, Levene and Tipson used isopropylidene acetals as derivatives for the purification of L-cri/thro-pentulose (as the di-isopropylidene acetal) and D-thrco-pentulose (as the monoisopropyli-dene acetal). Soon thereafter, Reichstein and coworkers used diisopropylidene acetals of D- and L-psicose, and D-tagatose, to purify the respective sugars. 

Cyclic acetals of ketoses are prepared most commonly from acetone or benzaldehyde formaldehyde, acetaldehyde, butanone, and cyclohexanone have been used occasionally. These carbonyl reagents are frequently used directly, although such derivatives as 2,2-di-methoxy- or 2,2-diethoxy -propane (acetone dialkyl acetals), or l,l-dimethoxyethane (acetaldehyde diethyl acetal), are often employed in experiments in which intermediate acetals are of interest,or in which the presence of water in the reaction mixture adversely affects the yield of products. A polymeric form of an aldehyde is the reagent to be preferred whenever the monomer is volatile for example, acetaldehyde is often used in the form of a trimer, paraldehyde, and formaldehyde is employed as formalin solution, as paraformaldehyde, or as polyoxymethylene. An excess of the carbonyl reagent is generally used as the solvent, and the condensation is usually effected at room temperature. 

De Beider has reviewed the stability of cyclic acetals of the aldoses and aldosides to heat, light, bases, and oxidants and reductants. His Chapter gives many examples of the kinds of reactions that may be expected to occur when cyclic acetals of ketoses are subjected to such conditions. 

The acid-catalyzed hydrolysis of cyclic acetals of ketoses is best effected by use of 0.1 M aqueous oxalic acid or 50-80% aqueous acetic as the hydrolyst, because the use... 

The following Tables do not constitute a comprehensive list of all of the known derivatives of acetals of ketoses. In order to keep the Tables within manageable proportions, only the more common esters and ethers of the acetals have been included. Halogen-containing compounds and thioethers, and most of the deoxy and anhydro sugars, phosphorus-containing compounds, and esters of inorganic acids have been omitted. Some of these compounds may be found in the Tables of Barry and Honeyman. ... 

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