Triacetyl glucal

B. Fraser-Reid and B. Radatus, 4,6-Di-0-acetyl-aldehydo-2,3-dideoxy-D-eythro-trans-htx-2-enose. A probable reason for the al in Emil Fischer s triacetyl glucal, J. Am. Chem. Soc., 92 (1970) 5288-5290. 

Perrier rearrangement of triacetyl glucal (19), upon reaction with phenols to give 2,3-unsaturated (9-arylglucosides 20, required a reflux in chlorobenzene for several hours. The MORE enabled a rapid access to 20 in 72-83% yields within 1-8 min, in the absence of a solvent (Scheme 5). The stereoselectivity and yields are fairly comparable with that under thermal conditions, but the reaction time was reduced by several fold (94SC2097). 

Methyl 2,3,6-trideoxy-a-D-hex-2-enopyranosid-4-ulose, F2, was readily prepared from triacetyl glucal FI [67], as summarized in Scheme 20. Reaction of this material with Danishefsky s diene [68] gave the annulated pyranoside F3 in 93% yield as a single diastereomer, in keeping with precedents. 

For a recent synthesis of a-multistriatin (31) by Plaumann and Fraser-Reid (75) the starting material was the enone (83) which is readily prepared from glucose as outlined in Scheme 20 (26). However triacetyl glucal (81) is commercially available. The Ferrier reaction with ethanol gives (82 a) as a crystalline substance in excellent yield, and the derived diol (82 b) may be oxidized with manganese dioxide to the hydroxy enone (83 a). Alternatively the primary hydroxyl of the diol may be protected to allow for oxidation with Collins reagent. 

The 1,5-anhydro-hexen-3-ulose (15) obtained from triacetyl glucal gave an equimolar mixture of ribo- and arabino-3-C-methyl branched-chain derivatives (16) on treatment with methyl lithium. 

Hirst and Woolvin169 preferentially methylated positions 3, 4 and 6 by the use of glucal, an unsaturated sugar derivative having a 1,2-olefinic bond, introduced by the reduction of triacetyl-a-D-glucopyranosyl bromide with zinc dust and acetic acid. By the action of an ethereal solution of perbenzoic acid on an aqueous solution of 3,4,6-trimethyl-glucal a sirupy product was obtained. This was shown to contain... 

These key intermediate is accessible from triacetyl-D-glucal 38 in a large-scale adaptable 5-step sequence in an overall yield of 30 % conversion of 38 into hexenoside 39 according to a known two-step procedure (55), tosylation to the chloro-tosylate 40, since the chloride ions formed during the reaction in situ displace the activated allylic tosyloxy function, and, finally, the consecutive reductive removal of tosyloxy- and chloro groups 40 -> 35 (56,57) ... 

In the first attempts at deacetylation of triacetyl-D-glucal, aqueous barium hydroxide was used and an uncrystallizable sirup was obtained2... 

If the mixture of triacetyl-D-glucal dibromides is shaken with silver carbonate or oxide in methanol, the bromine atom at carbon 1 is exchanged for a methoxyl group.3 Here again four isomers are to be expected, which consist of the a. and /3 methyl glycosides of the 2,4,6-triacetyl D-glucose and D-mannose 2-bromohydrins (XI). Two of these methyl triacetyl-2-... 

Chlorine can add to the double bond in triacetyl-D-glucal in a manner similar to that of bromine.311 The resulting dichlorides (XIV) have more tendency to crystallize than the dibromides. However, many of the... 

A tetraacetyl-2-desoxy-2-chloro-D-hexose (XV), which is shown to be homogeneous by its melting point and rotation, can be prepared in good yield from the mixture of triacetyl-D-glucal dichlorides by treatment with silver acetate in glacial acetic acid.3 Likewise, the mixture of... 

The corresponding triacetyl-2-desoxy-2-halogeno-D-hexoses (XVIII) (see page 218) are formed from the triacetyl-D-glucal dihalides by reaction with moist silver carbonate.11 The 2-desoxyaldonic acid (the so-called... 

The oxidation of triacetyl-D-glucal with ozone produced 2,3,5-triacetyl-D-arabinose (XIX),8 which was converted to D-arabinose and the sugar... 

The steric course of the reaction of derivatives of D-glucal that are substituted at the hydroxyl of carbon 3 proceeds in chloroform solution somewhat differently.4-18 For example, triacetyl-D-glucal yielded predominantly l-benzoyl-3,4,6-triacetyl-D-glucose (XXII), which has a... 

When triacetyl-n-glucal is treated with perbenzoic acid in ethyl acetate and water, some D-glucose derivatives are produced in detectable amounts in addition to the predominant D-mannose derivatives. 

Similar results, although with lesser yields, were reported for oxidations with hydrogen peroxide in /erf-butanol in the presence of osmium tetroxide.14 With triacetyl-D-glucal, as well as with free D-glucal, the D-glucose configuration is formed to a greater extent than the D-mannose one. 

The free hydroxyl group of carbon atom 1 of the cyclic tautomeric form can be acetylated. The resulting triacetate (XXV) is different from triacetyl-D-glucal, and it loses the 1-acetyl as a result of boiling with water and is reconverted to diacetyl-D-pseudoglucal.18 (3) The... 

With Dische s reagent for 2-desoxy sugars (diphenylamine in acetic acid and sulfuric acid) triacetyl-D-glucal and a series of other glycals and glycal derivatives give the same or a similar color as the 2-desoxy sugars.25-28... 

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... 

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