Synthetic Utility of 2-Furylmethylene-2,3,4,9-Tetrahydrocarbazol-1-Ones: Syntheses of Pyrazolo, Isoxazolo, Pyrido and Pyrimido Annelated Carbazoles

Abstract

2-Furylmethylene-2,3,4,9-tetrahydrocarbazol-1-ones were obtained from the mixed aldol condensation of 2,3,4,9-tetrahydrocarbazole-1-ones and furan-2-carbaldehyde (furfural). The corresponding enones were utilised as the synthons to prepare various heteroannulated pyrazolo[3,4- a]-, isoxazolo[3,4- a]-, pyrido[2,3- a]-, and pyrimido[4,5- a] carbazoles under different conditions using various reagents. Single crystal X-ray diffraction studies of 2-furylmeth-ylene-6-methyl-2,3,4,9-tetrahydrocarbazol-1-one are discussed.