organic papers Acta Cryst. (2007). E63, o1623–o1625 doi:10.1107/S1600536807006939 O ¨ zbey et al. C 17 H 19 NO 5 S o1623 Acta Crystallographica Section E Structure Reports Online ISSN 1600-5368 Ethyl 2-(9-methylsulfonyl-1-oxo-2,3,4,9- tetrahydro-1H-carbazol-2-yl)acetate Su ¨heyla O ¨ zbey, a * Arzu Karayel, a Ayhan Yılmaz b and Nesimi Uludag ˘ c a Hacettepe University, Faculty of Engineering, Department of Engineering Physics, Beytepe 06800, Ankara, Turkey, b Hacettepe University, Faculty of Education, Department of Science, Beytepe 06800, Ankara, Turkey, and c Cumhuriyet University, Faculty of Education, Department of Science, 58140 Sivas, Turkey Correspondence e-mail: sozbey@hacettepe.edu.tr Key indicators Single-crystal X-ray study T = 295 K Mean (C–C) = 0.006 A ˚ R factor = 0.070 wR factor = 0.223 Data-to-parameter ratio = 14.4 For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e. Received 6 February 2007 Accepted 9 February 2007 # 2007 International Union of Crystallography All rights reserved The title compound, C 17 H 19 NO 5 S, crystallizes with two molecules per asymmetric unit; these do not exhibit the same pattern of hydrogen bonds. The indole part of the carbazole skeleton is almost planar, while the cyclohexenone ring is twisted. Comment Pyridocarbazole alkaloids such as olivacine and ellipticine are some of the most potent drugs for the treatment of a variety of cancers. Thus a number of methods have been developed for the synthesis of ellipticine and its analogues (Pelletier, 1970), including the use of the non-protected ethyl 2-(1-oxo-2,3,4,9- tetrahydro-1H-carbazole-2-yl)acetate derivative of the title compound, (I), as the starting material (Wenkert & Dave, 1962). Furthermore, after transformation of the title compound into 4-oxo-tetrahydrocarbazole derivatives, useful intermediates for the synthesis of the azocino[4.3-b]indole system may be obtained (Magnus et al. , 1992). As shown in Fig. 1, there are two molecules (molecule 1 and molecule 2) in the asymmetric unit of (I). The indole part of the carbazole skeleton is almost planar; the dihedral angles between the mean planes of the pyrrole (ring B) and the benzene rings (ring A), which are both planar as expected, are 1.7 (2) and 4.3 (2) for molecule 1 and 2, respectively. These values are comparable to those of ethyl (3-ethyl-1-oxo-1,2,3,4- tetrahydrocarbazol-2-yl)acetate [1.3 (2) ; Kaynak et al., 2004] and N 0 -[(1E)-1-methyl propylidene]-5-methyl-3-phenyl-1H- indole-2-carbohydrazide (1.89 ; Kaynak et al., 2005). Rings A and C (C2/C3/C9–C12) in the carbazole system are slightly bent away from the central five-membered ring in the opposite direction, with torsion angles of 179.0 (4) (C2—C1—C4— C5) and 172.0 (3) (C12—C3—C2—C1) for molecule 1 [174.7 (4) and 167.4 (4) for molecule 2]. Ring C is not planar; the ring puckering parameters (Cremer & Pople, 1975) for this ring in molecule 1 and 2 are Q = 0.484 (5) and 0.429 (5) A ˚ , = 45.7 (6) and 44.6 (7) , ’ = 211.4 (8) and 220.8 (7) , respectively. In molecule 2, atoms N1 0 , C3 0 , C12 0 , C11 0 and O1 0 are almost coplanar, but atoms C9 0 and C10 0