Synthesis of Pyranocoumarin through MCRs: Modulation of this Approach as a Function of Substituent Effect Forms the Furocoumarin and 4-Hydroxy-3-styryl Coumarin as a Function of Solvent Effect.

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.

L-Proline-catalysed synthesis of 2-aryl-2,5-thiopyrano[2,3-] thiochromen-5-ones from 4-hydroxydithiocoumarins and cinnamaldehyde derivatives.

The 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.

FeCl-catalyzed regioselective ring-opening of aryl oxirane with 4-hydroxycoumarin for the synthesis of furo[3,2-]coumarins.

The 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.

-TSA·HO catalyzed metal-free and environmentally benign synthesis of 4-aryl quinolines from arylamine, arylacetylene, and dimethyl sulfoxide.

An 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.