Furanoside, branched

Kassou, M. Castillon, S., Ring Contraction Vs Fragmentation in the Intramolecular Reactions of 3-0-(Trifluoromethanesulfonyl) Pyranosides - Efficient Synthesis of Branched-Chain Furanosides. J. Org. Chem. 1995,60, 4353-4358. 

Z)-awh-4-Hydroxy-l-aIkenyl carbamates 363, when subjected to substrate-directed, vanadyl-catalysed epoxidation , lead to diastereomerically pure epoxides of type 364 (equation 99)247,252,269 qqjggg epoxides are highly reactive in the presence of Lewis or Brpnsted acids to form -hydroxylactol ethers 366 in some cases the intermediate lactol carbamates 365 could be isolated . However, most epoxides 364 survive purification by silica gel chromatography . The asymmetric homoaldol reaction, coupled with directed epoxidation, and solvolysis rapidly leads to high stereochemical complexity. Some examples are collected in equation 99. The furanosides 368 and 370, readily available from (/f)-0-benzyl lactaldehyde via the corresponding enol carbamates 367 and 369, respectively, have been employed in a short synthesis of the key intermediates of the Kinoshita rifamycin S synthesis . 1,5-Dienyl carbamates such as 371, obtained from 2-substituted enals, provide a facile access to branched carbohydrate analogues . 

An efficient method for large-scale preparation of apiose was developed by Koos et al. [21], using an Aldol-Cannizzaro reaction as a key step. 2,3-0-isopropylidene-L-t/2rco-tetrodialdose acetal 24 was reacted with excessive formaldehyde and gave 3-C-(hydroxymethyl)-2,3-0-iso-propylidene-D- /ycero-tetrose acetal 25, which was deprotected to afford apios 26. Besides, treatment of 27 with formaldehyde in the presence of sodium hydroxide yielded branched furanoside 28 under the same conditions [22] (O Scheme 9). It is worth noting that the prod-... 

Synthesis from o-arabinose (35, 55 )-Quinuclidine-3,5-diol (2) has been synthesized from D-arabinose by conversion to the furanoside 21 in 59% overall yield (Schemes 4) Oxidation of the C-3 hydroxyl group with pyridinium chlorochromate followed by treatment with [(methoxycarbonyl)methylene]triphenylphosphorane and subsequent hydrogenation gave the corresponding ester, which upon reduction, mesylation and nucleophilic displacement of the mesylate group by azide ion afforded the branched azi-doethyl lyxofuranoside 22. Two pathways were used to convert 22 into 2. Acid hydrolysis of... 

The Ramirez dioxaphosphole condensation has been successfully applied to the synthesis of branch ed-chain 1-deoxyhexuloses. The dioxaphosphole (13) and 2,3-C-isopropylidene-D-glyceraldehyde afforded, after hydrolysis and methanolysis, a mixture of methyl l-deoxy-3-C-methyl- 8-D-r/Z)o-hexulopyrano-side and the corresponding furanoside (Scheme 5). The nature of the product obtained could be varied by the use of different dioxaphospholes. ... 

The conversion of 4,5-hexadienoic acids to furanones and of 4,5-hexadienals to furanosides was achieved in a one-pot acetalization-cyclization-methoxycarbonylation procedure (Scheme 21). Trialkylsiloxy substituents in /3-position induce high stereo selectivities. This method was applied in a synthesis of nucleoside analogs bearing a branched difunctional side chain. ]... 

The preparation of the branched C-formyl furanoside derivatives by opening of an epoxide with phenylthiomethyl lithium or 2-lithio-l,3-dithiane has been described (Scheme 3). ... 

The preparation of the doubly C-branched derivative of D-allose 34 by the use of enantiomerically enriched (Z)-anti-3,5 -dialkyl-4-hydroxy-1,5-alkadieny 1 N -diisopropy Icarbamates, obtained by the homoaldol approach, in a similar way to that described in Vol. 25, Chapter 14, ref. 31, has been reported." Other furanosides are also described. 

N.mj. spectroscopy and molecular modelling allowed the unequivocal structural assignments of the diacetoneglucose-derived, branched derivatives 2 and 3. Conformational analysis on a number of tetro- and pento-furanosides, based on values expressed as a function of the pseudorotation parameters, has been reported. ... 

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. 

The intramolecular oxypalladation of 3-r-butyldimethyIsilyloxy-4,S hexadienal 68 (prepared in 7 steps from 1,3-propanediol) gave the 2-deoxy-erythro-furanoside 69 as a potential side-chain-branched nucleoside/ ... 

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