supplementary materials

Nitrogen-containing heterocyclic compounds are the key building blocks used to develop compounds of biological and medicinal interest to chemists. Among nitrogen heterocycles, carbazole alkaloids represent an important class of natural products. The Indian medicinal plant Murraya koenigii spreng (Rutaceae) has been found to be a rich source of many carbazole alkaloids (Iyer & Devi, 2008). A number of carbazole alkaloids with intriguing novel structures and useful biological activities were isolated from natural sources over the past decades which had attracted chemists to frame novel synthetic strategies towards the synthesis of carbazole and its derivatives. The continuous increase of isolable natural products as well as pharmacological action of these carbazole derivatives has generated synthetic interest; consequently the syntheses of carbazoles have been a vigorously active area of study (Knölker & Reddy, 2002, and references therein; Choi et al. 2008).

Based on the structural, biological and pharmacological importance of the carbazole derivatives, the present investigation was aimed to devise a viable synthetic route to prepare these classes of compound using different synthetic methodologies. For our synthetic strategy 2,3,4,9-tetra-hydro-1H-carbazol-1-ones, prepared in our laboratory as potential precursors, have opened new avenues for the synthesis of highly functionalized carbazole derivatives. Based on these facts we have developed and reported an efficient syntheses of novel indoloacridines and have reported the crystallographic behavior of some of these compounds (Sridharan et al., 2009a,b). The current contribution presents the synthesis (Fig. 1) and crystal structure of the title compound which represents one such indoloacridine.

The compound undergoes a destructive phase change upon cooling at varying temperatures between 270 and 200 K, depending on cooling rate and disturbance by vibration, thus indicating supercooling of the room-temperature phase. To guarantee collection of a whole dataset the collection was thus performed at room temperture. An ORTEPstyle plot of the molecule is shown in Fig. 2.

The overall planarity of the indolo[3,2-c]acridine part of the molecule is interrupted by the saturated ethylene group of C9 and C10. The planes formed by C1 to C9, C19 and N1 as well as the plane made up of atoms C10 to C18, C20 and N2 are overall planar with r.m.s. deviations from planarity of only 0.01 and 0.03 Å, respectively. With each other the two planes form an angle of 22.05 (6)°. C10 deviates from the first plane by 0.807 (3) Å, C9 from the second by 0.476 (3) Å. The phenyl ring is at an angle to the first plane of 77.81 (6)°.

The N—H group does not form a classical hydrogen bond in the solid state and no strong π–π stacking interactions are observed. Other than van der Waals dispersive forces the packing of the compound in the solid state is dominated by C—H···π interactions (Fig. 3). The two most prominent such interactions are between C10—H10B and the centroid Cg1 of the ring built by atoms C1 to C6 (the chlorine-substituted phenyl ring), and between C26—H26 and the centroid Cg2 of the indole ring with H···Cg distances of 2.96 and 2.51 Å (Table 1). Additional very weak C—H···C and N—H···C interactions are indicated in Fig. 3.

In a recent publication (Sridharan et al., 2009b) we reported the structure of the dehydrogenated derivative of the title compound. It crystallizes in a primitive inversion symmetric setting with a similar volume as for the structure of the title compound. There are however no further reaching similarities between the structures of the two compounds. The hydrogenated molecule is essentially planar and packing, shape of the unit cell and location of the inversion centers are different for the two related compounds (Fig. 4).