There is a pressing need to replace hazardous and harmful solvents with "green" or "sustainable" media. Natural compounds have recently been used to produce deep eutectic solvents, sugar melts, or ionic liquids. This review presents physicochemical data of these reaction media and highlights recent advances in their use in organic synthesis and biotransformations.

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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, b-D-glucosyl-and b-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 b-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.

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Review: 96 refs.