Efficient preparation of beta-D-glucosyl and beta-D-mannosyl ureas and other N-glucosides in carbohydrate melts

Sugar melts or solvent-free systems have been used to react simple unprotected hexoses at the C-1 atom with urea and urea derivatives to sugar-ureides by acid catalysis and with short reaction times. In one step, beta-D-glucosyl- and beta-D-mannosyl urea 2a/b were obtained in high yields. D-Galactose 6, N-acetyl-D-glucosamine 7, L-rhamnose 8 and 2-deoxy-D-glucose 9 were converted likewise to glycosyl ureas. Additionally, urea-related nucleophiles were investigated as melt components. N, N'-Ethylene urea 15, N, N'-allylurea 16 and ethyl carbamate 18 were beta-selectively converted with D-glucose in good yield, giving the corresponding N-glycosides. Under these conditions, however, the condensation product with N-octylurea 17 was not accessible.