Ring Opening and Recyclization Reactions with Chromone-3-carbonitrile

Chemical transformations of chromone-3-carbonitrile (1) with some substituted hydrazines, namely, thiosemicarbazide, S-methyl/benzyldithiocarbazate, 7-chloro-4-hydrazinoquinoline, and 3-hydrazino-5,6-diphenyl-1,2,4-triazine, led to substituted pyrazoles 2, 5-8. Ring opening of carbonitrile 1 followed by recyclization with 3-amino-1,2,4-triazole and 2-aminobenzimidazole gave triazolo[1,5-a]pyrimidine 9 and pyrimido[1,2-a]benzimidazole 10, respectively. Treatment of carbonitrile 1 with some heterocyclic amines produced 2-amino-3-substituted-chromones 11 and 12. The novel 3-hydroxychromeno[4,3-b]pyrazolo[4,3-e]pyridin-5(1H)-one (13) was efficiently synthesized from the ring conversion of carbonitrile 1 with cyanoacetohydrazide. A mixture of chromeno[2,3-b]naphthyridine 14 and chromeno[4,3-b]pyridine 15 was obtained from base catalyzed transformation of carbonitrile 1 with malononitrile dimer. A diversity of novel annulated chromeno[2,3-b]pyridines 16-22 was also synthesized. Chromeno[2,3-b]pyrrole-2-carboxylate 23 was obtained from the reaction of carbonitrile 1 with ethyl chloroacetate. Structures of the new synthesized products were deduced on the basis of their analytical and spectral data.