Dihydro-D-glucal

A whole series of isomerization products have been obtained from triacetyl-D-galactal (XLVIII) which are similar to those described in detail for D-glucal this includes diacetyl-D-pseudogalactal (XLIX) and its dihydro derivative, D-isogalactal (L) and D-protogalactal (LI).44 Only... 

Oxidative contraction of glycols.1 Reaction of 3,4-dihydro-2//-pyran (1) with benzeneselenenyl chloride and then with methanol provides the adduct 2, which is oxidized by m-chloroperbenzoic acid to the ring-contracted aldehyde 3 (cf., 12, 120). Application of this sequence to the tribenzyl-D-glucal (4) furnishes the adduct... 

Oxidations catalyzed by platinum oxide are now well known in carbohydrate chemistry, and their marked specificity has been examined with profit. From the reaction with D-glucal, a mixture of products was obtained, from which 2-deoxy-D-orob no-hexose and crystalline 2,3-dihydro-3-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one (32) were obtained.47 Related enones have been encountered among... 

The observation that, under acidic conditions, 2,3-dihydro-4if-pyran will substitute at position 9 of purine derivatives led to the suggestion that nucleosides might be prepared directly from glycals. Although the conditions employed during synthesis of the tetrahydropyranyl derivatives were unsuitable for interaction between 6-chloropurine and 3,4-di-O-acetyl-D-arabinal, when these two compoimds were fused together in the presence of p-toluenesulfonic acid, a mixture of 6-chloro-9-(3,4-di-0-acetyl-2-deoxy-a- and -/3-D-er2/iAro-pentopyranosyl)purines resulted, from which the known a-D anomer was isolated in pure form. Alternatively, an unsaturated nucleoside was obtained from tri-O-acetyl-D-glucal by this method (see p. 91). 

No free 2-hydroxyglycals have yet been identified. 1,5-Anhydro-D-erythro-2,3-h.exodiuioaet bis(phenylhydrazone) (63, R = H, Ri = OH), which has been prepared from the product of deacetylation of 2-acetoxy-tri-0-acetyl-D-glucal, loses water when it is heated in aqueous acetic acid in presence of phenylhydrazine, giving a product believed to have the structure of 2,3-dihydro-6-(hydroxymethyl)-3,4-bis(phenylhydrazono)py-ran (64). This is, however, not identical with the osazone derived from... 

The epoxide 70, derived from D-mannitol, has been converted into the 6-lactone 71 via the key intermediates shown in Scheme 15. This compound is the dihydro-derivative of (H-)-boranolide, the corresponding a,P-unsaturated lactone, and this work constitutes a formal synthesis of the natural product. The enal 72, derived from tri-O-acetyl-D-glucal, has been converted in a multistep process into the unsaturated lactone 73, an analogue of the a,p-unsaturated lactone portion of a number of natural products. ... 

The reaction between tri-O-acetyl-D-glucal 7 and chlorosulfonyl isocyanate has been studied in the past, but neither formation of a cycloadduct nor of a rearranged product has been observed. Isocyanate acted only as acid catalyst causing decomposition of sugar material. On the other hand, [2+2]cycloaddition of active isocyanates to dihydro-2H-pyran and to its derivatives has been widely investigated, under a variety of conditions. The reaction of tosyl isocyanate with dihydro-2H-pyran 1 at low temperature (0 ) led to the formation of bicyclic p-lactam 2. Elevation of the cyclization temperature resulted in the rearrangement of the four-membered ring to the open-chain amide 3 (Scheme 4). 

A report on three reductive syntheses directed towards the preparation of desosamine has been reported (Scheme 18). Thus tri-O-acetyl-D-glucal can be converted via the di-tosylate derivative shown into the D-form of inethoxy-2-methyl-6-dihydro-4,S-... 

Hydrogenation of hexaacetylgentiobial leads to the dihydro derivative, which gives the free dihydrogentiobial upon deacetylation. This compound is split by emulsin into fermentable D-glucose and dihy dro-n-glucal.6... 

The potential use of hydroxylations in S3mthetic work is exemplified by the synthesis of 3,4,6-trideoxyhexoses from 2,3-dihydro-2-methyl-4JI-pyran, and of 3,4,6-tri-O-methyl-D-glucose from 3,4,6-tri-O-methyl-n-glucal. Provided that the products are purified, oxidation of the phenan-threnequinone adducts (see p. 89) offers an additional, specific means of hydroxylation. 

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