The C3 or O-alkylation of 4-hydroxycoumarin (formation of new C-C and C-O bond) is undoubtedly one of the most important and challenging reactions in synthetic chemistry due to its pharmaceutical utility. In this communication, we report sulfated tin oxide (STO)-catalyzed synthesis of arylated vinyl ethers in moderate to good isolated yields (68-93%) from the reaction of substituted phenyl acetylenes (terminal alkynes) with 4-hydroxy coumarin in polyethylene glycol (PEG 400) as solvent at 110 oC. The catalyst can be recycled up to 5 times without losing the significant yield.

The synthesis of 4-aryl-NH-1,2,3-triazoles in good to excellent isolated yields (75-95%) has been achieved via a [3+2] cycloaddition of aromatic nitroolefins and sodium azide catalyzed by recyclable heterogeneous sulfated tin oxide (STO, 10 mol%) in toluene at 60 0C. Aliphatic nitrooefines proved to be unsuccessful partners in the present methodology.

One significant and elegant method for creating β-amino alcohols, which are useful intermediates for the synthesis of many different natural and synthetic pharmaceutical compounds, is to open the rings of epoxides with amines. When sulfated tin oxide catalyst (2 mol%) is present, epoxides can open their rings and react with amines to produce corresponding β-amino alcohols in good to high yields under mild circumstances. Under clean circumstances and in a short amount of time, the reaction demonstrated high regioselectivity and functioned well with both aromatic and aliphatic amines at room temperature.

Wide range of 2,4,5-trisubstituted imidazoles were synthesized using eco-friendly, readily available, inexpensive Zn(OAc)2•2H2O (5 mol%) under solvent-free conditions in moderate to excellent yields by condensation from aldehyde, ammonium acetate and benzil at 70 0C. The optimized reaction parameters were successfully applied for the synthesis of divergent 1,2,4,5-tetrasubstitued imidazoles using aromatic amine as fourth component. All the imidazole derivatives were sufficiently characterized by IR, NMR and Mass spectral analyses.