Crystal Structure of 5,6-Dihydro-7H-benzo[c]carbazole

Carbazole derivatives display a range of biological activities, making them attractive compounds to synthetic and medicinal chemists. They also have an important role in the synthesis of indole alkaloids, in which their synthetic derivatives, possessing useful pharmacological properties, are currently under investigation. The benzo[c]carbazoles, containing an aromatic ring fused to the c-face of the carbazole nucleus, show promising profiles for intracyclin-dependent kinase selectivity.1 The title compound may be an interesting intermediate in the synthesis of benzo[c]carbazoles.1 It was prepared from a b-tetralone (2.00 g, 13.70 mmol) and phenylhydrazine hydrochloride (2.18 g, 15.07 mmol) mixture in absolute ethanol (50 ml), which was refluxed for 7 h under a nitrogen atmosphere. After cooling to room temperature, the solvent was removed under reduced pressure. The crude product was dissolved in chloroform and washed with hydrochloric acid (50 ml, 10%) and potassium carbonate (50 ml, 10%). The organic layer was dried with anhydrous magnesium sulfate, the solvent was evaporated and the residue was crystallized from methanol (yield, 2.15 g, 72%, m.p. 377 K). X-ray analysis results are given in Tables 1 – 3. H10(C10), H11A(C11), H12A(C12) and H13(C13) atoms were positioned geometrically and a riding model was used during the refinement process; the remaining ones were located by a difference synthesis and refined isotropically. The title molecule (Fig. 2) contains a benzoato group fused to the c-face of the carbazole skeleton. In the carbazole skeleton, ring A (C1 – C4a/C9a) is not planar, having a total puckering amplitude, QT, of 0.453(4)Å. It adopts a twisted conformation [j = –140.7(5) ̊ and q = 176.74(3) ̊].2 Rings B (C4a/C5a/C8a/ N9/C9a), C (C5a/C5–C8/C8a) and D (C3/C4/C10–C13) are, of course, planar. Rings B and C are nearly coplanar with a dihedral angle of B/C = 1.95(9) ̊ and the coplanar ring system is oriented with respect to benzene ring D at a dihedral angle of 20.82(9) ̊. In crystal packing, the molecules are elongated along the b axis and stacked in parallel to the c-axis. The benzoato group, fused to the c-face of the carbazole skeleton, causes notable changes in the geometry of the carbazole core, leading to increases in the angles C5a–C8a–C8, C1–C9a–N9, C8–C8a–N9, C5–C5a–C4a, C4–C4a–C5a, C1–C9a–C4a, C13–C4– C4a and decreases in the C9a–C1–C2, C1–C2–C3, C3–C4–C4a, X-ray Structure Analysis Online