Catalyst-free regioselective synthesis of benzopyran-annulated thiopyrano[2,3-b]thiochromen-5-(4H)-one derivatives by domino-Knoevenagel-hetero-Diels-Alder reaction of terminal alkynes with 4-hydroxy dithiocoumarin in aqueous medium

The synthesis of novel pentacyclic benzopyran-annulated thiopyrano[2,3-b] thiochromen-5(4H)-ones has been described by domino-Knoevenagel-hetero-Diels-Alder reaction of 4-hydroxy dithiocoumarin and O-propargylated salicylaldehyde in aqueous medium and in the absence of any catalyst. The single step reaction is highly regioselective and provides polycyclic heterocycles in high yields.