Unsaturated carbohydrates. Part XVI. Isomerisation of allylic 4-azides and 4-thiocyanates and the subsequent synthesis of 2-acetamido-2-deoxyhexopyranoside derivatives

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Abstract
Ethyl 2,3-dideoxy-4,6-di-O-methylsulphonyl-α-D-erythro- and threo-hex-2-enopyranoside on treatment with sodium azide or potassium thiocyanate in NN-dimethylformamide undergo selective displacements of the allylic secondary sulphonyloxy-groups and afford 4-azido- and 4-thiocyanato-derivatives with the threo- and erythro-configurations, respectively. On heating in inert solvents these products isomerise (the azides incompletely and the thiocyanates completely) to give 3,4-unsaturated glycosides having 2-azido- and 2-isothiocyanato-sub-stituents. From these, 2-acetamido-derivatives can be prepared; the reactions offer a new means of introducing this important functional group into carbohydrates. An attempt to introduce a nitrogenous substituent by pyrolysis of an allylic N-phenylcarbamate was not successful, and, similarly, ald-2-enopyranosyl derivatives bearing ester groups at C-4 could not be induced to rearrange.

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