Tri-O-acetyl-D-galactal

Deoxy-2-[ F]fluoro-D-galactose can be prepared through an addition reaction to tri-O-acetyl-D-galactal (465), but better through Sn2 reaction (K F-Kryptofix 222 in MeCN) of methyl 3,4-0-isopropylidene-2-0-triflyl-6-0-trityl-y -D-talopyranoside (220 see Section 11,2), according to the cold synthesis. 

B. Shanmugasundaram, A. K. Boseb, and K. K. Balasubramanian, Microwave-induced, montmorillonite KlO-catalyzed Ferrier rearrangement of tri-O-acetyl-D-galactal Mild, eco-friendly, rapid glycosidation with allylic rearrangement, Tetrahedron Lett., 43 (2002) 6795-6798. 

The silicic acid used for column chromatography and the Amberlite resin were Silicar CC-7 100-200 mesh purchased from Mallinckrodt Chemical Works, St. Louis, Mo. The 5% palladium on charcoal catalyst was purchased from Engelhard Industries Ltd., Newark, N. J. The tri-O-acetyl-D-glucal and the tri-O-acetyl-D-galactal (as a 70% solution in benzene) were purchased from Raylo Chemicals Limited, Edmonton, Alberta. 

Korytnyk and coworkers have shown that reactions of xenon difluoride with acetylated glycals in the presence of boron trifluoride are a convenient route for the synthesis of 1,2-difluoro sugars, while the addition of fluorine to the double bond occurred predominantly from the less hindered side and cis adducts were mainly formed75, 76. Stereoselective transformation of tri-O-acetyl-D-galactal with xenon difluoride at -20 to +5 °C, without a catalyst in CFC13, after hydrolysis, afforded 2-deoxy-2-fluoro-D-galactose in 63% yield77. 

Reaction between the cyclic phosphorodithioic acid and 3,4,6-tri-O-acetyl-D-galactal carried out in benzene at room temperature is complete within 48 hours giving quantitatively a mixture of a- and -isomers in an 85 15 ratio. The a-isomer is isolated by crystallization in 80% yield14. 

From the oxo reaction of 3,4,6-tri-O-acetyl-D-galactal (36) (after deacetylation of the mixture of products), there was obtained, in almost quantitative yield, 2,6-anhydro-3-deoxy-D-golacto-heptitol (37) and 2,6-anhydro-3-deoxy-D-foio-heptitol (38). - Structural investigations of these anhydrodeoxyalditols paralleled those on the alditols obtained from 3,4,6-tri-O-acetyl-D-glucal. The absolute structures of compounds (37) and (38) were unequivocally established by correlation, as shown, with 2,6-anhydro-3-deoxy-D-gZuco-heptitol (27). Prior structural work" on compound (37), with the aid of periodic acid degradations only, had led to an incorrect, tentative assignment of structure. 

The partially deuterated analogs of compounds (37) and (38) were obtained when 3,4,6-tri-O-acetyl-D-galactal was allowed to react with carbon monoxide and deuterium. The use of the latter compounds in aiding in the structural assignments of compounds (37) and (38) is described in the following Section. 

Ciment, D M, Ferrier, R J, Unsaturated carbohydrates. Part IV. Allylic rearrangement reactions of 3, 4,6-tri-O-acetyl-D-galactal, J. Chem. Soc. C, 441-445, 1966. 

Grynkiewicz, G, Priebe, W, Zamojski, A, Synthesis of alkyl 4,6-di-0-acetyl-2,3-dideoxy-a-D-t/ireo-hex-2-enopyranosides from 3,4,6-tri-0-acetyl-l,5-anhydro-2-deoxy-D-fyjco-hex-l-enitol (3,4,6-tri-O-acetyl-D-galactal), Carbohydr. Res., 68, 33-41, 1979. 

The C22-C27 segment 149 was prepared from tri-O-acetyl-D-galactal (151) ( Scheme 16). Treatment of 151 with methanol in the presence of SnCl4 afforded 152 (Ferrier-t) e 0-glyco-sidation). Deacetylation of 152 followed by monosilylation provided 153. Hydroxy-direct-... 

The model monosaccharides just listed were prepared from common precursor IV.l (Scheme 39), which was readily obtained by azidonitration of 3,4,6-tri-O-acetyl-D-galactal followed by deacetylation with sodium methoxide. Treatment of IV.l with acetone and toluene p-sulfonic acid monohydrate at room temperature led to predominant formation of the thermodynamically favored 3,4-O-isopropylidene (IV.2) in 61% yield while also producing 27% of the 4,6-O-isopropylidene derivative IV.3. The position of the isopropylidene IV.2 was verified by the use of NMR chemical shift analysis to confirm the position of the acetate group in the resultant acetylated adduct IV.4. Synthesis of the 4-O-sulfate derivative (IV.7) from IV.2 utilized a step that differentiated the 3-OH and 4-OH positions after benzylation and de-isopro-pylidination of IV.2, a selective methylation at the 3-OH of diol IV.5 was achieved via a tin procedure [91] to give methyl glycoside IV.6. Conversion of the azide into... 

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