Cyclic acetals, properties

This article is limited to the reactions involving cyclic acetals of aldoses and aldosides. However, for comprehensiveness, or for their potential usefulness in carbohydrate chemistry, some properties of cyclic acetals not directly relevant to aldoses and aldosides are included. It may be recalled that the chemistry of dithioacetals had already been reviewed in this Series.7... 

The reactivity of functional groups presenting some similarities to cyclic acetals, such as cyclic orthoesters, and stannylidene and amide acetals, falls outside the scope of the present article, but attention has to be drawn to the fact that they may be considered to be special types of acetals having distinct properties, and a growing interest is focused... 

The polar properties of the alpha-C-H bonds and their reactivity towards hydrogen atom abstraction in acetals are enhanced by the presence of two ether groups. These hydrogens are susceptible to abstraction by excited carbonyl compounds (77). Cleavage of C—0 bonds in acetals occurs readily when an acetal radical is formed (38) even at room temperature. It has been shown that irradiation of cyclic acetals of aldehydes at room temperature in the presence of acetone leads to the appropriate carboxylic esters (22),... 

The properties of ring systems discussed above may be used to answer two questions raised by the use of cyclic-acetal groupings for the selective masking of hydroxyl groups in carbohydrates. What is the most probable ring structure of the acetals obtainable from a particular polyhydroxy compound For a given acetal, how many diastereoisomers are likely to be stable ... 

He and his students then tried to s oithesize simple analogs of the above monomeric unit, an endeavor which proved fruitless, but, in the course of their studies, they accumulated a large amount of knowledge regarding the preparation and properties of cyclic acetals. Thus, they found that a trace of acid catalyzes the formation of a polymer from 5,6-dihydroxy-2-hexanone, and that aliphatic aldehydes (RCHO) readily combine with chloral to give polymers of the general formula (2 RCHO -j- CUCCHO). ... 

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... 

Khimicheskie Svoistva 1,3-Dioksanov. Chast 2. Tsiklicheskie Atsetali. Spravochnik (Physico-Chemical Properties of 1,3-Dioxanes. Part 2. Cyclic Acetals. Handbook). Khimiya, Moscow, 1984. 

VI. Tables of Properties of Cyclic Acetals of the Aldoses and Aldosides. 209... 

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