organic papers o2470 Kishbaugh et al. C 19 H 18 N 2 O 6 S doi:10.1107/S1600536807017448 Acta Cryst. (2007). E63, o2470–o2471 Acta Crystallographica Section E Structure Reports Online ISSN 1600-5368 4-Methoxy-4a-nitro-9-(phenylsulfonyl)- 4,4a,9,9a-tetrahydro-1H-carbazol-2(3H)-one T. L. S. Kishbaugh, a Gordon W. Gribble a and Jerry P. Jasinski b * a Department of Chemistry, Dartmouth College, Hanover, NH 03755-3564, USA, and b Department of Chemistry, Keene State College, Keene, NH 03435-2001, USA Correspondence e-mail: jjasinski@keene.edu Key indicators Single-crystal X-ray study T = 296 K Mean (C–C) = 0.015 A ˚ R factor = 0.055 wR factor = 0.255 Data-to-parameter ratio = 13.1 For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e. Received 19 March 2007 Accepted 9 April 2007 # 2007 International Union of Crystallography All rights reserved The crystal structure of the title molecule, C 19 H 18 N 2 O 6 S, confirms the structure of this novel Diels–Alder adduct formed from the reaction of 3-nitro-1-(phenylsulfonyl)indole and 1-methoxy-3-(trimethylsiloxy)-1,3-butadiene (Danishefs- ky’s diene). The angle between the planes of the indoline ring system and the phenylsulfonyl ring is 69.9 (4) . Comment We have found that both 2- and 3-nitroindoles undergo Diels– Alder cycloaddition reactions to afford a simple synthesis of carbazoles (Kishbaugh & Gribble, 2001). Surprisingly, the reaction between 3-nitro-1-(phenylsulfonyl)indole and 1- methoxy-3-(trimethylsiloxy)-1,3-butadiene (Danishefsky’s diene) provided the title initial cycloadduct, 4-methoxy-4a- nitro-9-(phenylsulfonyl)-4,4a,9,9a-tetrahydro-1H-carbazol- 2(3H)-one, (I), as the major product, rather than the expected 2-hydroxy-9-(phenylsulfonyl)carbazole, which was the minor product. The observed regiochemistry of the present Diels– Alder reaction is consistent with the known reactivity of Danishefsky’s diene with nitroalkenes in normal electron- demand reactions (Node et al. , 1996), but the observed exo mode of addition, affording a trans arrangement of nitro and methoxyl groups, rather than an endo mode of addition, was not necessarily expected. We now describe the crystal struc- ture of (I). The X-ray crystallographic analysis confirms the molecular structure and atom connectivity for (I) (Fig. 1) that we had proposed for this compound based on NMR spectroscopy (Kishbaugh & Gribble, 2001). The ketone carbonyl C2—O3 bond is 1.206 (13) A ˚ , which is normal for a cyclohexanone [1.24 (2) A ˚ ; Romers, 1956], and the C1—C2—C3 bond angle of 114.4 (8) compares with the electron diffraction value of 117 (3) for cyclohexanone (Romers, 1956). The angle between the planes of the indoline ring system and the phenylsulfonyl ring is 69.9 (4) . The phenylsulfonyl group is oriented away from the cyclohexanone ring and is disposed towards the nitro group, while the methoxyl group adopts an equatorial position on the cyclohexanone ring. The sum of the