D-Galactal

Subsequently this route to 3-deoxy sugars was developed by further work in our laboratory by Ferrier and Sankey (23). They demonstrated that although tetra-O-acetyl-2-hydroxy-D-galactal undergoes rearrangement in boiling acetic acid, and that reaction is speeded up and goes to completion if catalytic amounts of methanesulfonic acid are added, the... 

From the rearrangement of tetra-O-acetyl-2-hydroxy-D-galactal in boiling acetic acid it was possible to isolate l,2,4,6-tetra-0-acetyl-2,3-dide-h.ydro-3-deoxy-a-jy-threo-hexose (32) (58%) and a small amount of 1,2,3,4,6-penta-O-acetyl-jS-D-galactopyranose. In the reaction mixture the presence of some a-pentaacetate was demonstrated chromatographically but NMR spectroscopy indicated no resonances corresponding to the / anomer of compound 32. These spectral measurements indicate that compound 32 constituted 80% of the mixture of products. 

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. 

D-/yAc>-hexoside from D-galactal, a reaction which defines the stereospecificity of glycosyl transfer to the acceptor oxygen atom. 

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 use of other peroxides in the epoxidation of glycals is limited by selectivities that are often inferior to those achieved with DMDO. One notable exception is the use of the wCPBA (m-chloroperbenzoic acid)/KF combination and its recent successful application in one-pot epoxidation alcoholysis (Scheme 5.66) [197]. This involved treatment of benzylated D-galactal 36 in dichloromethane/methanol with a mixture of wCPBA and KF (2 1) in anhydrous dichloromethane to give methyl-2-hydroxygalactoside 165. 

Nitroglycals65 are excellent Michael-type acceptors,66 where O-, N-, S-, C- and P-nucleophiles can be used as donors.67 An application of this kind of reaction was reported by Schmidt et al. for a new synthesis of 2-deoxy-2-nitro-D-galactose nucleoside 86 and of /V-acetyl-D-galactosamine nucleoside 88, based on addition reactions to 3,4,6-tri-0-benzyl-2-nitro-D-galactal 85 (Scheme 28).68... 

Sugars are also useful starting materials for the preparation of cyclic ethers. Maarten H.D. Postema, now at the Josephine Ford Cancer Center, Detroit, prepared (J. Org. Chem. 2005, 70, 829) the ester 4 from D-galactal. Methylenation of the ester carbonyl followed by ring-closing metathesis returned 5. Hydroboration of the enol ether then delivered the C-glycoside 6 in high diastereomeric purity. 

Unsaturated sugars, namely glycals, such as 3,4,6-tri-Oacetyl-l, 5-anhydro-2-dcoxy-D-r//v/-/w7o-hex-1-enetol and the d-/v.yo epimer react with xenon difluoride in the presence of a boron trifluoride-diethyl ether complex to give a mixture of C2 epimeric fluorides.45,46 Tri-O-acctyl-D-galactal treated with xenon difluoride in trichlorofluoromcthane below 5 C forms after hydrolysis (0.5 M HC1) 2-deoxy-2-fluoro-D-galactose in 63% overall yield.47... 

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