Benzimidazole and benzothiazole sugar derivatives
Simple aldehydosugars such as 1 or 2, by reaction with o‐phenylenediamine, gave the corresponding benzimidazoles 3 and 4. Whereas the unperturbed α, β‐unsaturated aldehydosugar D gave the benzodiazepine E upon treatment with o‐phenylenediamine, the formyl‐bearing alkenyl acetals 5 and 8 led, in the same conditions, to the benzimidazoles 6 and 9 respectively or, on reaction with o‐aminothiophenol, to the benzothiazoles 7 and 10 respectively. This difference in reactivity is explained by the electrondonor ability of the oxygen atom of the alkenyl acetal function as shown by the 13C‐RMN. spectra.