[摘要]：Knoevenagel condensation of 3,4-push-pull-substituted thiophene-2-carbaldehydes 4 with malononitrile gives the gem-dicyanovinylthiophenes 5, followed by a Michael addition of dimedone and a subsequent cyclization to 4-(2-thienyl)-5,6,7,8-tetrahydro-4H-chromen-5-ones 6. Protonolysis of the latter in methanol led to a mixture of four heterocycles 7-10, the main product being the novel tricyclic 9-(2-thienyl)-6,7-dihydro-5H-thieno[3,2-b]chromen-8(9H)-one derivative 7. A mechanism of the protonolysis reaction is proposed, the structures of the two products 7a/8a have been confirmed by X-ray analysis.
