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 2,3,4,9tetrahydrocarbazole-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-furylmethylene-6-methyl-2,3,4,9-tetrahydrocarbazol-1-one are discussed.

Crystal structure of (E)-2-(furan-2-ylmethylidene)-2,3,4,9-tetrahydro-1H-carbazol-1-one

“…Most heteroaryl carbazoles reported contain a heteroaryl moiety fused with a carbazole moiety; however, there are few reports where the heteroaryl unit is substituted with a carbazole unit (Sridharan et al, 2008). We have reported the synthesis of 1-oxo-2-arylidene-2,3,4,9-tetrahydrocarbazoles from potential precursors of the 2,3,4,9-tetrahydrocarbazole-1-one type and these synthons were utilized to derive a diverse variety of heteroannelated carbazoles (Sridharan et al, 2008;Sridharan & Rajendra Prasad, 2011;Archana et al, 2010a,b;Thiruvalluvar et al, 2013). Herein, we report on the crystal structure of one such compound, synthesized by the base-initialized reaction of 2,3,4,9-tetrahydrocarbazol-1-one with furan-2-carbaldehyde.…”