Microwave assisted synthesis of indole-annulated dihydropyrano[3,4-c]chromene derivatives via hetero-Diels-Alder reaction

An efficient two-step synthesis of indole-annulated dihydropyrano[3,4-c]chromene derivatives is achieved via Knoevenagel condensation of O-propargylated salicylaldehyde derivatives with indolin-2-ones followed by a microwave-assisted intramolecular-hetero-Diels-Alder reaction of the resulting (Z)-3-(2-(prop-2-ynyloxy)benzylidene)indolin-2-ones in the presence of 20 mol % CuI in acetonitrile.