Xylofuranose derivatives

Scheme 10.4 Rh-catalysed hydroformylation of styrene with xylofuranose-derived thioether-phosphite ligands.

The preparation of 1,2-O-cyclohexylidene-a-D-xylofuranose (22) (Expt 5.117) from 1,2-O-cyclohexylidene-a-D-glucofuranose illustrates the use of sodium metaperiodate for the cleavage of carbon-carbon bonds in a-diols (see also Section 4.2.55, p. 454). In this case C-6 is lost as formaldehyde and C-5 is converted into an aldehyde group. This aldehydic product is isolated as a dimer, which is then reduced in methanol solution with sodium borohydride to the xylofuranose derivative (22). 

With the exception of 4-methylxylose all the methyl ethers that are derivable theoretically from D-xylopyranose or D-xylofuranose are known. From the products of hydrolysis of methylated polysaccharides 2-methyl-, 3-methyl-, 2,3-dimethyl-, 2,4-dimethyl-, 3,4-dimethyl- and 2,3,4-tri-methyl-D-xylose have been separated. No D-xylofuranose derivatives have been isolated from a natural source. Unknown at the present time are the 4-methyl-, 4,5-dimethyl-, 2,4,5- and 3,4,5-trimethyl- and... 

To explain the formation of (S )-(+)-/3-methylhydrocinnamic acid by the reaction of the D-xylofuranose derivative 20 with phenylmagnesium bromide in the absence of cuprous chloride, the coordinated adduct 20 was envisaged as the precursor, with attack from the front side of the double bond now giving the acid having the S-configuration. 

Phosgene reacts with xylofuranose derivatives according to [2054] ... 

Kawana et al. used xylofuranose derivates as chiral auxiliaries [7, 13], Through its primary hydroxy function, the auxiliary was loaded to the polystyrene resin. Esterification of the immobilized auxiliary 8 gave a-keto esters. Subsequent nucleophilic additions of Grignard reagents afforded resin-bound a-hydroxy esters. Subsequent saponification afforded the chiral a-hydroxy acids 9 (Scheme 12.5) in 18-84% yields and 36-65% enantiomeric excesses. The recovered polymer supported chiral auxiliaries could be reused without decrease of enantioselectivity. 

Typical applications of the Michaelis-Arbuzov reaction include the conversion of the 5-deoxy-l,2-0-isopropylidene-3-0-methyl-a-D-xylofuranose derivative 298 into 299 with triethyl phosphite" " or with diethyl ethyl- or butyl-phosphonite to give 300 (R = Et or protection at C ) is also feasible with acetyl or benzoyl moieties . Another example is the conversion of 301 with (MeO)3P into 302 (R = Me) in only 30% yield, but with sodium dibenzyl phosphite into 302 (R = CH2Ph) in 80% yield, and thence via 303 to 304" other similar applications may be noted" ". ... 

Branch at C-2 or C-3. - In new and versatile approaches to the synthesis of deuterium or tritium labelled branched tetritols, two separate syntheses of 2-C-methyl-D-erythritol (3) have been described starting from dimethyl fumarate (Me02CCH=CHC02Me, 1) and the xylofuranose derivative (5), respectively. 

A variety of NMR spectroscopic methods have been applied to structural and conformational analyses of the following furanose systems sugar em-dimethyl substituted alkenyl ethers, e.g. a-D-xylofuranose derivatives 13 (see Chapter 5 for synthesis), " the diastereomeric 6-chloro-6-deoxy-l,2-0-isopropylidene-a-D-gulofuranose cyclic 3,5-piperididomonophosphates 14, several 4 -thionucleo-sides, 6-formyl- and 6-(hydroxymethyl)-uridine 5 -carboxaldehydes 15 and 16, respectively, and their 2, 3 -0-isopropylidene derivatives, two double-... 

The efficiency of the stereocontrol in such reactions depends upon the structure of the carbohydrate. With xylofuranose-derived oxazinone templates and diethylaluminium chloride as the catalyst the Diels-Alder reactions give adducts with only low yield and unsatisfying diastereoselectivity. In the course of these investigations, however, we found a new synthesis of P-branched carboxylic acids. 

The xylofuranose-derived N-cinnamoyl oxazinone 2 0 reacts with two equivalents of diethylaluminium chloride to deliver the 3-phenyl-valeric acid derivative 21 in high yield (eq. 8). The stereoselection achieved so far is only moderate. A surprising feature of this new 1,4-addition to carboxylic acid derivatives is revealed, when other dialkylaluminium chlorides are used. 

Reduction of the 3-C-cyano 3-sulphonate derivative (118) with lithium aluminium hydride furnished the branched-chain sugar (119) and the spiro-epimine (120), which, on further reduction and 7V-acetylation, gave 3-acetamido-3-deoxy-l,2 5,6-di-(7-isopropylidene-3-C-methyl-a-D-glucofuranose. The latter branched-chain amino-sugar was also converted into related o-xylofuranose derivatives by a conventional chain-shortening procedure, following removal of the 5,6-0-isopropylidene group. 

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