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 met hylenes having an alpha-cyano or alpha-keto group to give thiopyranocoumari n derivatives 3-9. The reaction of compound 1 with different ketene N,S-ace tals, afforded the corresponding thiazino(5,4c)coumarin derivatives 10,13 a nd 16. On reacting compound 10 or 13 with malononitrile, spiro pyran-4,2'-t hiazino(5,4-c)coumarin 11 or 14 were obtained, while the reaction of compou nd 16 with malononitrile gave spiro cyclobutene-1,2'-thiazino(5,4-c)coumari n derivative 17. Treating of compounds 10, 13 or 16 with cyclohexylidenemal ononitrile afforded spiro naphthyl-1,2'-tkiazino(5,4-c) coumarin derivative s 12,15 or 18 respectively. Treatment of compound I with CS2 and malononitr ile 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 sp iro naphthyl-1,'2-(1,3)dithiano(5,4-c)coumarin 21 derivatives, respectively .