Methyl furanosides, synthesis

Hoppe, D, Tarara, G, Wikens, M, Jones, P G, Schmidt, D, Stezowski, J J, Enantioselective synthesis of methyl furanosides of unnatural 3,6-dideoxy-3-methylaldohexoses form lactates hy homoaldol reactions, Angew. Chem. Int. Ed. Engl., 26, 1034-1035, 1987. 

Several methyl furanosides have been prepared in this way in yields considerably higher than those previously recorded in the literature for example, methyl a-D-iibofuranoside, 69% (lit., 4%) methyl j8-D-lyxofuran-oside, 31% (lit. 3-5%) and methyl ) D-talofuranoside, 54% (previously unknown). This increase in yield, spectacular in some cases, is due not only to the shift in the equilibrium but also to the separation, without substantial losses, of the desired component by the calcium column. In the synthesis of methyl -D-mannofuranoside, complexing is used for a third time when the compound is isolated as its readily crystallizing complex with calcium chloride. ... 

Currently this reaction is often the starting point in the multi-step synthesis of hexofuranoside-containing bioactive targets. Thus, galactose was converted to anomeric methyl furanosides 12 via this ferric... 

Methyl 5-0-benzyl-2,3-dideoxypent-2-enofuranoside (626), an intermediate in this synthesis, was epoxidized337 with m-ehloroperoxy-benzoic acid, furnishing methyl 2,3-anhydro-5-0-benzyl-D-pento-furanosides of the fi-ribo (629) and a-tyxo (631) configurations. 

O. Schulze, J. Voss, and G. Adiwidjaja, Preparation of methyl 2,3-anhydro- and 2,3-0-sulfinylfuranosides from unprotected furanosides using the Mitsunobu reaction, Synthesis, (2001) 229-234. 

P. A. McNicholas, M. Batley, and J. W. Redmond, Synthesis of methyl pyranosides and furanosides of 3-deoxy-D-marcrco-oct-2-ulosonic acid (KDO) by acid-catalysed solvolysis of the acetylated derivatives, Carbohydr. Res., 146 (1986) 219-231. 

A synthetic route for the synthesis of 2-deoxy-C-aryl glycosides using an umpolung strategy has been reported by Aidhen and co-worker (Scheme 1.7). The synthetic endeavour led to a versatile intermediate aryl ketone 1.13, which has paved the way for two important classes of C-glycosides, i.e. C-alkyl furanosides 1.14 and methyl 2-deoxy-C-aryl pyranosides 1.15. 

The intervention of episulphonium ion intermediates in the synthesis of azidosugars has been postulated by Christensen and Goodman in order to rationalize the product (140), formed on interaction of azide ion with the furanoside (141). Direct replacement with inversion at C(2) did not occur rather, a mixture of the diazides 140 2ind 142 was obtained by nucleophilic attack of azide ion on the episulphonium ion (143). A similar episulphonium intermediate (144) has been invoked to rationalize the conversion of methyl 4,6-0-benzylidene-... 

One fraction was obtained in the crystalline state in a yield of 20%. It was assigned the structure (42), which was based not only on elemental and methoxyl analyses but also on the following observations. The two -d-glycosidic linkages were indicated by a high dextrorotation ([a]o + 262°). It was hydrolyzed at a rate comparable with that of furanosides, and methylation followed by hydrolysis and borohydride reduction gave 2,5-di-O-methyl-D-mannitol (43). The structure of (43) was established by synthesis and by lead tetraacetate oxidation it consumed one mole of oxidant, with the formation of 2-0-methyl-D-glyceraldehyde (44). 

This exocyclic keto-aldoside was obtained in a good yield (73%) in the liquid state by the oxidation of methyl 2,3-0-isopropylidene-L-rhamno-furanoside with chromium trioxide/pyridine. The compound was only characterized by some of its physical properties, but its structure was evident from the mode of synthesis and from its further reactions. 

Epoxidation of the olefin occurs with high diastereofacial selectivity to give carbamoyl-oxirane 945. This epoxide is not extremely stable, and is treated directly with methanesulfonic acid to afford the j5-D- a/o-furanoside 946. The stereocenter at C-2 must be inverted to match the configuration of the natural product. This is accomplished by triflate formation followed by an Sn2 reaction with cesium acetate. Hydrolysis of the OAc group furnishes the desired P D-ga/ac o-furanoside (947). 0-Methylation, benzyl group hydrogenolysis, acidic hydrolysis, and dithioacetal formation completes the synthesis of 948 in 11 steps and 5.7% overall yield from 929 [252]. 

Application of the azidomercuration-demercuration procedure to the 5-ene (9) gave the 6- and 5-azides (10) and (11) in the ratio 1 4 (Scheme 1). The synthesis of azido-sugars via 2,3-anhydro-furanosides has been reported. Methyl 2,3-anhydro-0 -D-lyxofuranoside (12) gave the 3-azide (13) in 95% yield, and its 5-0-tosyl ester (14) gave the 3,6-diazide (15) in 84% yield. In contrast, the 2,3-anhydro-riboside (16) gave a mixture of the 2- and 3-azides (17) and (18) in the ratio 3 2. However, substitution at C-5 of (16) resulted in steric hindrance of the approach to C-3 and consequently the 5-tosylate (19) afforded the 2,6-... 

The oxidation of aldose phenylosazones to aldos-2-uloses (osones) and the g.l.c. separation of the TMS ethers of the products have been examined in the cases of the D-f/ reo-pentose, D-arabino-, D-lyxo-, L-xy/o-hexose compounds, and two disaccharide derivatives. A new approach to the synthesis of ketonic carbohydrate derivatives involves the treatment of amino-compounds with sterically hindered quinones to prepare imines which rearrange as shown in Scheme 1 to give products which undergo hydrolysis to ketones. The method gave the 2- and 3-ulosides, respectively, when applied to methyl 2-amino-2-deoxy-a- and 3-D-glucopyranoside and methyl 3-amino-3-deoxy-j3-D-allo-furanoside. ... 

In a de novo synthesis of the 2-deoxy-L-ara6iho-hexose derivative 7 the dihydropyran ring was formed by asymmetric [2+4]-heterocycloaddition of enone 5 to chiral vinyl ether 6, as shown in Scheme 22 Chain-extension at C-5 of methyl 2,3-0-isopropylidene-p-D-r/Z>o-pentodialdo-l,4-furanoside with meth-oxymethylenetriphenylphosphorane and subsequent hydrolysis, reduction and... 

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