Methyl 6-chloro-4,6-dideoxy preparation

Some of the rare sugars that have been prepared by way of chloro-deoxy derivatives are 4,6-dideoxy-3-0-methyl-D-xyZo-hexose (D-chal-cose), 3,6-dideoxy-D-n foo-hexose (paratose), 3,6-dideoxy-D-arafcmo-hexose (tyvelose), methyl 2,3-dideoxy-/3-D-glr/cero-hex-2-enopyrano-sid-4-ulose, and certain aminodeoxy sugars. 

Osmylation of the chirally masked 2-alkoxypent-3-enal 1 and subsequent functional group manipulations furnished enantiopure 5-deoxy-L-lyxose and -xylose derivatives. A new preparation of 5-deoxyribonolactone derivative 2 from ribonolactone by tributyltin hydride reduction of a 5-chloro-5-deoxy intermediate has been published. Conversion of compound 2 to a 5 -deoxy-nucleoside analogue is covered in Chapter 20. A multistep synthesis of methyl 5-0-benzoyl-2,3-dideoxy-P-D-g/ycero-pentofuranose (4) from D-xylose involving Raney nickel desulfurization of compound 3 (see Chapter 11) has been described. Several deoxy-ketoses have been prepared by Raney nickel desulfurization of 1-thio-ketose derivatives obtained by enzyme-catalysed aldol condensations (see Vol. 29, Chapter 2, Scheme 1). An example is given in Scheme 1. ... 

Besides the 0-glycosides mentioned so far, also attention has been paid to the synthesis of N- and S-analogues. The p-nitrophenyl N-glycoside of a-N-acetylneuraminic acid has been prepared by silver carbonate-promoted reaction of 4,7,8,9-tetra-0-acetyl-2-chloro-2-deoxy-p-N-acetylneuraminic acid methyl ester with p-nitroaniline and subsequent deprotection (Privalova and Khorlin 1969). Treatment of the same precursor with sodium azide, followed by de-esterification, led to the formation of 2-azido-2-deoxy-a-N-acetylneuraminic acid (Supp et al. 1980). The same authors reported also the preparation of the p-form. The azides can readily be converted into the 2-amino derivatives of N-acetylneuraminic acid. Subsequently, the amino function has been benzoylated. Data on the syntheses of the methyl and p-nitrophenyl S-glycosides of a-N-acetylneuraminic acid have been presented by Privalova and Khorlin (1969), whereas Ponpipom et al. (1980) have described a method for the synthesis of 5-acetamido-2-S-[6-(5-cholesten-3p-yloxy)hexyl]-3,5-dideoxy-2-thio-p-D-g/vccro-D-ga/acto-2-nonulopyranosonic acid. 

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