Glucal 2-hydroxy

It was noted (23) that the NMR spectrum of compound 32 was identical with that published (34) for the third product (assigned structure 29) isolated from the reaction of tetra-O-acetyl-2-hydroxy-D-glucal with acetic anhydride and zinc chloride. The identity of the compounds was fully established and a revised structure proposed for this third product. In the presence of zinc chloride, therefore, epimerization can occur at an allylic site and the quasi-equatorial C-4 acetoxy group in the erythro isomers 27 and 28 can assume the favored quasi-axial orientation (24). 

In similar manner 3,6-dideoxyhexoses have been prepared from esteri-fied 6-deoxy-2-hydroxyglycals. 2,3,4-Tri-0-acetyl-6-deoxy-2-hydroxy-D-glucal was converted into the a and / forms of l,2,4-tri-0-acetyl-2,3-didehydro-3,6-dideoxy-D-en/t/iro-hexose. The a anomer was the main product (77%, 55% isolated crystalline) and, in addition to the ft anomer (19%), a small amount (4%) of saturated products was obtained. On hydrogenation, the major product also suffered some hydrogenolysis but afforded two tri-0-acetyl-3,6-dideoxyhexoses which were shown by NMR spectroscopy to be present in the ratio 12 13 and to have the a configuration. Deacetylation of the reduction products gave... 

Neher and Lewis177 obtained 2-furaldehyde from 2,3,4-tri-O-methyl-L-arabinose by heating with dilute acid after preliminary enolization with alkali. Isbell83 proposed a mechanism for this conversion similar to that for the conversion of tetra-0-methyl-(2-hydroxy-D-glucal) into 5-(hydroxymethyl)-2-furaldehyde XLIV was suggested as an intermediate. In Hurd and Isenhour s178 scheme for the formation of 2-furaldehyde from free pentose, the enol (XLV) of a 3-deoxypentosone was regarded as an inter-... 

Zervas48 through the catalytic reduction of 2,3,4,6-tetraacetyl-2-hydroxy-D-glucal, has recently been prepared by the reductive desulfurization of ethyl tetraacetyl-l-thio-/ -D-mannopyranoside (XL),47 a substance which has been obtained through the mercaptolysis of mannosidostreptomycin48 and may be prepared through the prolonged action of ethyl mercaptan and hydrochloric acid on D-mannose. 

Apparently these names were chosen solely upon the assumption that the course of the reduction of the acetates of the two substituted 2-hydroxy-glucals had been similar to that of 2,3,4,6-tetraacetyl-2-hydroxy-D-glucal... 

It was presumed that the third product (26) results from elimination of the elements of hydrogen chloride, in addition to deacetylation, by the strong base, to give a 2-hydroxy-D-glucal (1,5-anhydro-D-arabino-hex-l-enitol) anion (27) which then adds phenyllithium... 

Somewhat surprisingly, particularly in view of the proposed means of formation of the glycosid-3-ulose derivative 2,1,5-anhydro-2,3,4,6-tetra-O-benzoyl-D-arah/no-hex-1 -enitol (tetra-O-benzoyl-2-hydroxy-D-glucal) does not undergo bromination at the allylic C-3 atom the only products isolated following attempted photobromination with N-bromosucdnimide were two dibromides produced by addition reactions.50... 

In accord with the reactions undergone by, for example, tetra-0-acetyl-a-D-glucopyranosyl bromide (23) with bases, and with zinc - acetic acid, which give tetra-0-acetyl-1,5-anhydro-D-arabino-hex-1 -enitol ( tetra-0-acetyl-2-hydroxy-D-glucal ) (158) and tri-O-acetyl-1,5-anhydro-2-deoxy-D-ara >/ o-hex-I-enitol ( tri-O-acetyl-D-glucal ) (159), respectively (see Scheme 24),... 

Today you can purchase D-galactal 5, D-glucal 10 and D- or L-fucal 20 e. g. peracetylated or with unprotected hydroxy groups. 

On the basis of the above directions but with variations in amounts, solvents, length of reaction time, and method of recovery, the following other substances have been made 2,3,4,6-tetra-0-acetyl-(2-hydroxy-D-galactal),2 9 yield 10% 2,3,4,6-tetra-0-benzoyl-(2-hydroxy-D-glucal),10 yield 65% 2,3,4-tri-0-acetyl-(2-hydroxy-D-xylal),n yield 28% 2,3,4-tri-0-benzoyl-(2-hydroxy-D-xylal),12 yield 11% 2,3,4-tri-0-benzoyl-(2-hy-droxy-L-xylal)12 2,3,4,2,3,4,6 -hepta-0-acetyl-(2-hydroxygentiobial),18 yield 50% 2,3,6,2,3, 4,6 -hepta-0-acetyl-(2-hydroxycellobial),9 yield 58% and 2,3,6,2, 3,4, 6/-hepta-0-acetyl-(2-hydroxylactal),8 yield 44%. Major and Cook12 reported their failure to obtain a crystalline tri-O-acetyl-(2-hydroxyxylal). Fletcher and Hudson crystallized the D-isomer from acetic acid by the addition of water. 

Addition of water to the double bond of the hydroxy-D-glucal would produce D-glucose. Although such addition, catalyzed by sulfuric acid,... 

Tetra-0-acetyl-(2-hydroxy-D-glucal) has been compared with several other anhydro-sugars with respect to absorption spectra and heats of combustion.42... 

The acetates of 2-hydroxyglycals are soluble in ethanol, ether, chloroform, benzene, and ethyl acetate moderately soluble in hot water and insoluble in petroleum ether or cold water.2 2,3,4,6-Tetra-0-methyl-(2-hydroxy-D-glucal) is soluble in water, acetone, ether, dioxane, ethanol, and chloroform.29... 

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