New Synthetic Approaches to Condensed and Spiro Coumarins: Coumarin-3-Thiocarboxamide as Building Block for the Synthesis of Condensed and Spiro Coumarins

Coumarin-3-thiocarboxamide 1 was reacted with malononitrile, cyanoacetamide or cyanothioacetamide to give the corresponding thiopyrano(3,4-c)coumarin-1-carbonitrile 2. Also, compound 1 was reacted with a variety of active methylenes having an δ-cyano or δ-keto group to give thiopyranocoumarin derivatives 3–9. The reaction of compound 1 with different ketene N.S-acetals, afforded the corresponding thiazino(5,4-c)coumarin derivatives 10,13 and 16. On reacting compound 10 or 13 with malononitrile, spiro pyran-4,2′-thiazino(5,4-c)coumarin 11 or 14 were obtained, while the reaction of compound 16 with malononitrile gave spiro cyclobutene-1,2′-thiazino(5,4-c)coumarin derivative 17. Treating of compounds 10,13 or 16 with cyclohexylidenemalononitrile afforded spiro naphthyl-1,2′-thiazino(5,4-c) coumarin derivatives 12,15 or 18 respectively. Treatment of compound 1 with CS2 and malononitrile under PTC condition afforded 1,3-dithiano(5,4-c) coumarin derivative 19, which in turn reacted with malononitrile or cyclohexylidenemalononitrile to afford spiro cyclobut-2-enyl-1,2′-(1,3)dithiano(5,4-c)coumarin 20 and spiro naphthyl-1,′2-(1,3)dithiano(5,4-c)coumarin 21 derivatives, respectively.