Furanosides, rearrangement

Unlike w-pentenyl p)ranosides, the corresponding furanosides have attracted comparatively little attention. Sharma and Rao reported the preparation of -pentenyl D-allo-, and D-gulo-furanosides 143 and 146, respectively (O Scheme 19) [55]. They made use of an efficient acid-induced rearrangement of diacetonides 142 and 145, in the presence of -pentenyl alcohol. The ensuing pent-4-enyl diacetonides 143 and 146, were chemoselectively cleaved to hemiacetals 144 and 147. 

The Merck Frosst approach to optically pure 11,12-LTA4 employs the versatile route from 2-deoxy-D-ribose (Scheme 4.12)." The tosylate 29 was prepared from the methyl furanoside, and Wittig reaction with hexylidene triphenylphosphorane resulted in the in situ formation of epoxy alcohol 30, which does not rearrange under the reaction conditions. The Paine rearrangement occurs upon treatment of 30 with MeONaTMeOH to epoxy alcohol 31, which is then carried on in a similar fashion to the LTA4 route to optically pure 11,12-LTA4. 

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. ... 

Scheme 20.8 Application nf Pummerer rearrangement to the synthesis nf modified furanosides.

The allyl ketene acetal Claisen rearrangement of uronic acid derivatives with furanoside structures has been studied. The Claisen rearrangement of alkenyl-substituted ketene acetals (84), produced in situ by selenoxide elimination from the corresponding phenylselenoacetaldehyde-derived acetals (83) of enantiomericaUy pure... 

In the area of aryl -furanosides it has been shown that Q-furanosides with a dimethyl(p-tolyl)silyl ether group at Q-2, on treatment with tin (IV) chloride, give 1,2-fiis-related p-tolyl -glycofuranosides. In similar fashion Q-vinyl glycosides can be made. A related rearrangement occurs as indicated in Scheme 26. ... 

The preparation of some fused [3.3.0] furanoside nucleosides such as (73) is mentioned in Chapter 20 and that of branched-chain ( )-canadaK>soIide from D-glucose is mentioned in Chapter 24. The n paration of 3,5-carbohydrates from 3-C-methyl aldoses by Gaisen rearrangement is described in Chapter 2. The addition of nitromethane anion to unsaturated derivative (74) is described in Chapter 13. 

Further examples of rearrangements involving cyclic sulphonium ions have been reported. Thus 2,3,5-tri-0-methyl-4-0-toluene-/>-sulphonyl-D-ribose diethyl dithioacetal (184) and dibenzyl dithioacetal (185) gave 4- S -ethyl-2,3,5-tri-0-methyl-4-thio-L-lyxose (186) and benzyl 2,3,5-tri-0-methyl-l,4-dithio-a-L-lyxo-furanoside (187) (Scheme 46) when heated either in aqueous pyridine or with sodium iodide in acetone similar rearrangements to the 4-thiofuranosides were observed with 2,3,5-tri-0-methyl-4-0-toluene-p-sulphonyl-D-xylose and -lyxose... 

On heating in boiling water the lumazine nucleoside 5 -sulphonate (429) rearranged to 5 -deoxy-5 -(lumazin-8-yl)-D-ribofuranose (430), which could be converted into methyl furanoside, dialkyl dithioacetal, and osazone derivatives. ... 

One of the most common methods of the formation of the carbocyclic ring from the normal sugar ring is undoubtedly the Ferrier-H rearrangement discovered by Ferrier in 1979 [10]. It is based on an HgCl2-catalyzed rearrangement of unsaturated sugars with the C5-C6 (for pyranosides) or C4-C5 (for furanosides) exo-cyclic double bond. This method is discussed in many excellent reviews [11-13]. Such unsaturated... 

SCHEME 13.18 (a) Acid-catalyzed ring-opening of glycal derived gem-dibromo-cyclopropane derivative 58 and (b) rearrangement of halo-oxepines to C-furanosides 61 and 62 [30],... 

Sugimura, H., Hasegawa, Y, and Osumi, K. (2000) Studies relating to the synthesis of laurenenynes Construction of the alkylidene side chain via [2,3]-Wittig-Still rearrangement at the anomeric center of a furanoside derivative. Heterocydes, 52, 99-102. 

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