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

• Published in: Organic & biomolecular chemistry 2024-02, Vol.22 (7), p.1426-1433
• Main Authors: Ali, Ahmad, Faraz, Simra, Khan, Abu Taleb
• Format: Article
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/d3ob02051g

The hitherto unreported synthesis of 2-aryl-2 H ,5 H -thiopyrano[2,3- b ]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. The regioselective synthesis of 2-aryl-2 H ,5 H -thiopyrano[2,3- b ]thiochromen-5-ones was achieved using 4-hydroxydithiocoumarins and substituted cinnamaldehydes under metal-free conditions.