The synthesis of pyranocoumarin is reported from 4-hydroxycoumarin, styrene oxide, and DMSO in the presence of -TSA·HO at 110 °C using a three-component reaction. Interestingly, a CH moiety from DMSO gets inserted in this reaction to form the pyranocoumarin ring. The plausible mechanism for this interesting reaction was proposed and validated using quantum chemical methods.
View Article and Find Full Text PDFThe hitherto unreported synthesis of 2-aryl-2,5-thiopyrano[2,3-]thiochromen-5-one derivatives was achieved from 4-hydroxydithiocoumarin and cinnamaldehyde using 20 mol% L-proline, an environmentally benign organocatalyst in methanol under reflux conditions. The current approach involves imine formation, followed by a Mannich reaction, instead of a 1,4-addition or thia-Michael reaction, and finally, cyclization. The salient features of this method are mild reaction conditions, broad substrate scope, good yield, atom economy, and shorter reaction time.
View Article and Find Full Text PDFThe regioselective ring-opening of aryl oxiranes was investigated with various 4-hydroxycoumarins in dimethyl sulfoxide in the presence of 20 mol% FeCl as a catalyst at 110 °C. This approach provided a short and concise synthetic route for the regioselective synthesis of 2-aryl-4-furo[3,2-] coumarin derivatives. Product formation occurred through regioselective ring-opening of the aryl oxirane at a less hindered site, followed by dehydration and concomitant cyclization.
View Article and Find Full Text PDFAn environmentally benign and metal-free synthesis of 4-aryl quinolines is reported by employing readily available arylamine, arylacetylene, and DMSO in the presence of 20 mol% -TSA·HO. In the present protocol, the solvent DMSO serves as a reactant cum solvent for providing the C2 carbon atom of the quinoline skeleton. Notably, the reaction proceeds effectively and efficiently without the involvement of any metal catalyst, ligand, and co-catalyst as additives and inert atmospheric reaction conditions.
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