1-(1-Hydroxy-9H-carbazol-2-yl)-3-methylbut-2-en-1-one

The title compound, C17H15NO2, was prepared as one of two products of the AlCl3/POCl3-catalysed reaction of 9-carbazol-1-ol with 3,3-dimethyacrylic acid. It crystallizes with two crystallographically independent molecules, A and B, which are virtually superimposable but not related by any translational or other pseudosymmetry. Both independent molecules are almost planar [r.m.s. deviations from planarity = 0.053 (1) and 0.079 (1) Å in A and B, respectively] and contain an intramolecular O—H⋯O hydrogen bond. Each type of molecules is connected via pairs of N—H⋯O hydrogen bonds, forming centrosymmetric A 2 and B 2 dimers which are, in turn, arranged in offset π-stacks extending along the a-axis direction. The offset of the dimers and the tilt angle of the molecules allows the formation of alternating C—H⋯π interactions between A and B molecules of parallel stacks.

The title compound, C 17 H 15 NO 2 , was prepared as one of two products of the AlCl 3 /POCl 3 -catalysed reaction of 9-carbazol-1-ol with 3,3-dimethyacrylic acid. It crystallizes with two crystallographically independent molecules, A and B, which are virtually superimposable but not related by any translational or other pseudosymmetry. Both independent molecules are almost planar [r.m.s. deviations from planarity = 0.053 (1) and 0.079 (1) Å in A and B, respectively] and contain an intramolecular O-HÁ Á ÁO hydrogen bond. Each type of molecules is connected via pairs of N-HÁ Á ÁO hydrogen bonds, forming centrosymmetric A 2 and B 2 dimers which are, in turn, arranged in offset -stacks extending along the a-axis direction. The offset of the dimers and the tilt angle of the molecules allows the formation of alternating C-HÁ Á Á interactions between A and B molecules of parallel stacks.

Related literature
For synthetic strategies for the synthesis of carbazole and its derivatives, see: Chakraborty (1993). For the isolation of pyranocarbazoles from various plant species, see: Knö lker & Reddy (2002, and references therein). For the synthesis of related compounds, see: Kavitha & Rajendra Prasad (2003a,b); Patel (1982). For the structure of the second product of the reaction yielding the title compound, see: Sridharan et al. (2008).  Table 1 Hydrogen-bond geometry (Å , ).

Experimental
Cg1, Cg2 and Cg3 are the centroids of the phenyl rings C1B-C6B, C7A-C12A and C1A-C6A, respectively. 1-(1-Hydroxy-9H-carbazol-2-yl)-3-methylbut-2-en-1-one M. Zeller, M. Sridharan, K. J. Rajendra Prasad and A. Ngendahimana Comment A number of carbazole alkaloids with intriguing novel structures and useful biological activities were isolated from natural sources over the past decades, which led towards the development of new synthetic strategies for the synthesis of carbazole and its derivatives (Chakraborty, 1993). Among the physiologically active carbazoles found aree pyranocarbazole alkaloids, which have a C-13, C-18 or C-23 framework (Knölker & Reddy, 2002). The basic unit is the C-12 carbazole nucleus with one carbon attached as a methyl, formyl, carboxylic or ester group. This C-13 unit then leads to C-18 or C-23 carbazole alkaloids depending on whether it combines with a hemi-terpenoid or a mono-terpenoid unit. Another observation is that in all the pyranocarbazole derivatives isolated so far, the oxygen atom of the pyran ring is attached to carbon-2 of the carbazole nucleus to form essentially pyrano[3,2-a]carbazole as in grinimbine. Patel (1982, and references therein) has reported the synthesis of indolo[3,2-h]chromanones from 1-hydroxycarbazoles which were then converted to isomers of grinimbine. Here the yields of compound were reported to be moderate since it was obtained along with the respective 2-acryloyl-1-hydroxycarbazole.
The title compound crystallizes in a triclinic setting with two crystallographically independent molecules, A and B ( Figure   2). The two molecules are virtually superimposable (see overlay of the two structures in Figure 3) but a PLATON symmetry check did not reveal any translational or other pseudosymmetry even when using relaxed tolerances (Spek, 2009). Both independent molecules are planar, r.m.s. deviations from planarity are 0.053 and 0.079 Å 2 , respectively, and they are tilted against each other within the structure with a dihedral angle of the planes of the A and B molecules of 53.11 (2)°.
Each molecule exhibits a strong intramolecular O-H···O hydrogen bond between the phenolic hydroxyl group and the keto oxgen atom (Table 1). In addition each type of molecules is connected via pairs of N-H···O hydrogen bonds to another molecule of the same type to form centrosymmetric A 2 and B 2 dimers (the planes of the dimers are parallel but slightly shifted against each other, Figure 4). The dimers are in turn arranged in offset π-stacks that are extending along the a axis direction. The metrics of the interaction are best given for the interaction of the phenol rings C7A to C12A and C7B to C12B with their respective symmetry equivalent counterparts at 2 -x, -y, 1 -z and 1 -x, -y, 2 -z. For these the centroid to centroid distances are 4.083 (1) and 4.089 (1) Å, the interplanar distances are 3.2985 (6) and 3.2992 (7) Å, and the slippages are 2.407 and 2.415 Å, respectively. The offset of the dimers and the tilt angle of the molecules allows for the formation of supplementary materials sup-2 alternating C-H···π interactions between A and B molecules of parallel stacks. C-H···π interactions are given in Table 1, with ring centroids 1, 2 and 3 being the phenyl rings C1B to C6B, C7A to C12A and C1A to C6A, respectively.

Experimental
The title compound was synthesized as described previously by Sridharan et al. (2008): 9-Carbazole-1-ol (0.001 mol) and 3,3-dimethylacrylic acid (0.001 mol) were dissolved in the mixture of an ice-cold solution of AlCl 3 /POCl 3 (400 mg/ 6 ml) and kept at room temperature for 24 h. The reaction process as monitored by TLC indicated the formation of two compounds. After completion of the reaction (disappearance of starting material), the residue was poured onto ice water.