Syntheses of Pyrazolo-, Isoxazolo-, Pyrido- and Pyrimido-Carbazoles from 2-(3′,4′-Dimethoxybenzylidene)-2,3,4,9-Tetrahydrocarbazol-1-Ones

Synthesis and crystal structure of 1-hy-droxy-8-methyl-9H-carbazole-2-carbaldehyde

Two crystallographically independent mol-ecules are present in the asymmetric unit of the title compound, C14H11NO2, with virtually identical geometries. The carbazole units are planar. The hy-droxy group at position 1, carbaldehyde group at position 2, and methyl group at position 8 (with the exception of two H atoms) are coplanar with the attached benzene rings. The dihedral angle between the two benzene rings is 2.20 (9)° in mol-ecule A and 2.01 (9)° in mol-ecule B. The pyrrole ring makes dihedral angles of 0.82 (10) and 1.40 (10)° [0.84 (10) and 1.18 (10)° in mol-ecule B] with the (-CH3)-substituted and (-OH and -CHO) substituted benzene rings, respectively. The mol-ecular structure is stabilized by the intra-molecular O-H⋯O hydrogen bonds, while the crystal structure features N-H⋯O and C-H⋯O hydrogen bonds. A range of π-π contacts further stabilizes the crystal structure.

Crystal structure of (E)-2-(furan-2-yl-methyl-idene)-2,3,4,9-tetra-hydro-1H-carbazol-1-one

The title compound, C17H13NO2, crystallizes with two conformationally very similar independent mol-ecules (A and B) in the asymmetric unit. In the crystal, the individual mol-ecules are linked by pairs of N-H⋯O hydrogen bonds forming A-A and B-B inversion dimers, with R22(10) rings. They stack alternately up the a-axis direction and are linked by C-H⋯π inter-actions, forming sheets parallel to the ab plane.

Synthesis, photophysical properties and DFT analysis of highly substituted pyrido carbazole-based “push pull” chromophores

A series of new fluorescent pyrido[2,3-a]carbazole derivatives were synthesized based on a four component reaction with 2,3,4,9-tetrahydro-1H-carbazol-1-one, malononitrile, and aryl/heteroaryl aldehydes in presence of NaOEt.

Solvent-free synthesis of heteroannulated carbazoles: a novel class of anti-tumor agents

A series of novel carbazole analogues that hold pyrido, isoxazolo, pyrimido and pyrazolo templates were designed and synthesised in good yield by grinding conditions. All the synthesised compounds were screened for their anti-tumor activity and displayed enviable selective growth inhibition on HeLa cell line compared to AGS cell line. Among these compounds, compound 2-(3',4'-diethoxy-benzylidene)-6-methyl-2,3,4,9-tetrahydro-carbazol-1-one,6-chloro-2-(3',4'-diethoxy-benzylidene)-2,3,4,9-tetrahydro-carbazol-1one, 2-(3',4'-diethoxy-benzylidene)-8-methyl-2,3,4,9-tetrahydro-carbazol-1-one, 3-(3',4'-diethoxyphenyl)-7-methyl-4,5-dihydro-10H-isoxazolo[3,4-a]carbazole, 7-chloro-3-(3',4'-diethoxyphenyl)-4,5-dihydro-10H-isoxazolo[3,4-a]carbazole, 4-(3',4'-diethoxyphenyl)-2-ethoxy-8-methyl-6,11-dihydro-5H-pyrido[2,3-a]carbazole-3-nitrile, 8-chloro-4-(3',4'-diethoxyphenyl)-2-ethoxy-6,11-dihydro-5H-pyrido[2,3-a]carbazole-3-nitrile, 4-(3',4'-diethoxyphenyl)-2-ethoxy-10-methyl-6,11-dihydro-5H-pyrido[2,3-a]carbazole-3-nitrile were found to have promising anti-tumor properities with reference to the standard ellipticine against the HeLa cancer cell line. All these intermediates showed IC50 outranged the standard ellipticine. The same compounds showed moderate activity against AGS cancer cell lines. The efforts were undertaken to optimize potency and selectivity of this class of compounds.

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

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.

(E)-2-(Furan-2-yl-methyl-idene)-8-methyl-2,3,4,9-tetra-hydro-1H-carbazol-1-one

In the title mol­ecule, C₁₈H₁₅NO₂, the carbazole unit is not planar [maximum deviation from mean plane = 0.236 (2) Å]. The pyrrole ring makes dihedral angles of 1.21 (10) and 16.74 (12)° with the benzene and the furan rings, respectively. The cyclo­hexene ring adopts a half-chair conformation. In the crystal, inversion dimers linked by pairs of N—H⋯O hydrogen bonds generate R₂²(10) loops.