4-Phenylsulfonyl-2-(p-tolylsulfonyl)-1H,8H-pyrrolo[2,3-b]indole

The title compound, C23H18N2O4S2, contains a pyrrolo group fused onto the plane of an indole ring with phenylsulfonyl and p-toluenesulfonyl groups bonded to the indole and pyrrolo rings. The angles between the mean planes of the pyrrolo-indole ring and the phenylsulfonyl and p-toluenesulfonyl rings are 73.7 (6) and 80.6 (0)°, respectively. The dihedral angle between the mean planes of the two benzene rings is 78.7 (4)°. In the crystal, both classical N—H⋯O and non-classical C—H⋯O intermolecular hydrogen-bonding interactions are observed, as well as weak π–π interactions [centroid–centroid distances = 3.6258 (8) and 3.9298 (8) Å], which contribute to the stability of the packing.

JCB wishes to thank the UWI and the Government of Barbados for funding this research. JPJ thanks Dr Ray Butcher and Howard University for assistance with the data collection and acknowledges the NSF MRI program (grant No. CHE-0619278) for funds to purchase the X-ray diffractometer.

Comment
In view of our continued interest in the synthesis of fused indole heterocycles (Gribble et al., 2005) for the construction of more elaborate molecules, such as the potent antibiotics pyrroindomycins A and B (Abbanat et al., 1999;Ding et al., 1994), we have sought to unequivocally confirm the assigned structure of the product formed in the reaction of 3-nitro-1-(phenylsulfonyl)indole with isocyanide. Our previous studies have shown that both pyrrolo[2,3-b]indoles and pyrrolo [3,4b]indoles can be synthesized in one step via this Barton-Zard pyrrole synthesis (Barton & Zard, 1985;Barton et al., 1990) from 3-nitroindoles depending on the N-indole protecting group (Pelkey et al., 1996;Pelkey & Gribble, 1997. Indeed, whereas our proposed fragmentation-rearrangement sequence, to afford the pyrrolo[2,3-b]indole ring system (Pelkey et al., 1996), only occurs with the phenylsulfonyl protecting group, the same reaction with N-benzyl, N-2-pyridyl, and Nethoxycarbonyl protecting groups generates the corresponding pyrrolo[3,4-b]indole ring system. We differentiated these two isomers both by comparison of the NMR coupling constants and through the independent synthesis of the corresponding pyrrolo[2,3-b]indole. (Moody & Ward, 1984a, 1984b. To confirm this structural assignment we now report the crystal structure of the title compound, the product of the reaction of 3-nitro-1-(phenylsulfonyl)indole with tosylmethyl isocyanide, and the first crystal structure of this fused indole ring system.
The title compound contains a pyrrolo group fused onto the plane of an indole ring with phenylsulfonyl and p-toluenesulfonyl groups bonded to the indol and pyrrolo rings. The angles between the mean planes of the pyrrolo-indole ring and the phenylsulfonyl and p-toluenesulfonyl rings are 73.7 (6)° and 80.6 (0)°, respectively. The dihedral angle between the mean planes of the two benzene rings is 78.7 (4)°. The sum of the angles around the indole N atom is 345.2 (4)° indicating slightly distorted sp 2 hybridization. The C3═C10 indole bond length is 1.3760 (17)Å similar to that observed in 3-acetyl-2ethyl-1-(phenylsulfonyl)indole (Jasinski et al., 2010). The remainder of the bonds are in normal ranges (Allen et al., 1987).
These observations support the influence of the hydrogen bonds and π-π interactions as contributing to the stability of crystal packing.

Experimental
This compound was prepared according to the procedure of Pelkey & Gribble (2006). To a stirred solution of 3-nitro-1-(phenylsulfonyl)indole (0.50 g, 1.67 mmol, 1 eq.) in dry THF (30 ml) was added a solution of tosylmethyl isocyanide (0.39 g, 1.99 mmol, 1.20 eq.) dissolved in dry THF (15 ml) followed by the addition of DBU (0.6 ml, 4.01 mmol, 2.4 eq.). The supplementary materials sup-2 solution was allowed to stir for 24 h at room temperature. Removal of the solvent in vacuo gave an orange oil that was purified via flash column chromatography (3:1 hexanes-ethyl acetate) to afford the pyrroloindole (0.46 g, 62%) as a yellow solid. Crystals suitable for the X-ray study were grown from a 1:1 mixture of CH 2 Cl 2 and ether [m.p. 484-487 K; literature value 509-511 K].

Refinement
All the H atoms were discernible in the difference electron density map, however, they were situated into idealized positions. The parameters of all the H atoms have been constrained within the riding atom approximation. C-H bond lengths were constrained to 0.95 or 0.98 Å for aryl or methyl H atoms, and 0.88 for N-H atoms, U iso (H) = 1.17-1.22U eq (C aryl ); U iso (H) = 1.51U eq (C methyl ) or U iso (H) = 1.16U eq (N).  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.