Arylazo-glycenosides. Part 8. Synthesis and reactions of some 2- and 3-arylazo-derivatives of methyl 4,6-O-benzylidene-2,3-dideoxy-D-threo-hex-2-enopyranosides

Abstract

Preparations are described of the α- and β-anomers of methyl 4,6-O-benzylidene-2,3-dideoxy-2-phenylazo-D-threo-hex-2-enopyranoside and of methyl 4,6-O-benzylidene-2,3-dideoxy-3-phenylazo-α-D-threo-hex-2-enopyranoside using D-galactose as the initial material. The procedures adopted for the syntheses are essentially those developed in our laboratory for the preparation of phenylazo-derivatives of sugars, as described in Part 1 of this series of papers.

The 1,4-addition reactions of the new phenylazo-derivatives with a range of nucleophiles have been investigated and the results have been compared with those obtained previously with analogous compounds having the D-erythro configuration. The adducts from the benzylidenated phenylazo-glycenosides in which the acetal and pyranoid rings are cis-fused are found to be relatively unstable in solution and readily revert to the parent phenylazo-glycenoside.

From methyl 4,6-O-benzylidene-2,3-dideoxy-2-phenylazo-α-D-threo-hex-2-enopyranoside, isolable adducts were obtained in reactions with methylamine, dimethylamine, benzylamine, or hydride ion. Also, stable products were formed in the 1,4-addition reactions of methyl 4,6-O-benzylidene-2,3-dideoxy-3-phenylazo-α-D-threo-hex-2-enopyranoside with benzylamine, benzenethiol, dimethylamine, or ammonia (followed by acetylation of the ammonia adduct).