Velu Saravanan

Synthesis of Cyclo[b]fused Carbazoles via SnCl4-Mediated Domino Reaction of 2-Indolylmethylpivalates with Arenes and Heteroarenes

A straightforward synthesis of aryl and heteroaryl-annulated cyclo[b]carbazoles has been developed via SnCl4-mediated one-pot arylation, cyclization and aromatization reaction sequence from 3-acetyl/aroyl-2-pivaloyloxymethylindoles. The starting material is easily accessible from commercially available 2-methylindole via Friedel-Crafts acylation, bromination and pivaloylation. Remarkably, electron withdrawing/donating aroyl units including heterocyclic systems are well tolerated in the present domino reaction protocol. Furthermore, this methodology could be extended to the synthesis of dibenzofurocarbazole via bis-annulation of 2,5-bis(2-pivaloyloxymethyl)pyrrole.

(E)-1-[2-(2-Nitro­styr­yl)-1-phenyl­sulfonyl-1H-indol-3-yl]propan-1-one

In the title compound, C25H20N2O5S, the phenyl ring makes dihedral angles of 89.88 (8) and 13.98 (8)°, respectively, with the indole ring system and the nitrobenzene ring. The dihedral angle between the indole ring system and the nitrobenzene ring is 88.48 (11)°. The molecular structure is stabilized by a weak intramolecular C—H⋯O interaction. In the crystal, π–π interactions, with centroid–centroid distances of 3.6741 (18) and 3.8873 (17) Å, link the molecules into layers parallel to the ab plane.

2-(4-Chloro-2-nitrophenyl)-4-methoxy-9-phenylsulfonyl-9H-carbazole-3-carbaldehyde

In the sterically hindered title compound, C26H17ClN2O6S, the carbazole ring has a maximum deviation from planarity of 0.067 (4) Å for the C atom connected to the aldehyde group. The carbazole moiety forms a dihedral angle of 72.8 (1)° with the nitro-substituted benzene ring. The O atom of the methoxy group deviates by 0.186 (1) Å from the adjacent carbazole moiety. The phenylsulfonyl group forms intramolecular C—H⋯O bonds between sulfone O atoms and the carbazole moiety, resulting in two S(6) rings. In the crystal, the nitrated benzene rings are linked via C—H⋯O interactions forming infinite C(7) chains along [100]. The crystal packing is also characterized by C—H⋯π interactions, which result in inversion dimers.

3-Iodo-2-methyl-1-phenyl­sulfonyl-1H-indole

In the title compound, C15H12INO2S, the sulfonyl-bound phenyl ring forms a dihedral angle 82.84 (9)° with the indole ring system. The molecular structure is stabilized by a weak intramolecular C—H⋯O hydrogen bond. The crystal structure exhibits weak intermolecular C—H⋯π interactions and π–π interactions between the indole groups [centroid–centroid distance between the five-membered and six-membered rings of the indole group = 3.7617 (18) Å].

2-(4,5-Dimeth-oxy-2-nitro-phen-yl)-4-meth-oxy-9-phenyl-sulfonyl-9H-carbazole-3-carbaldehyde.

In the title compound, C28H22N2O8S, the carbazole ring system is roughly planar, with a maximum deviation of 0.084 (3) Å for the C atom connected to the 4,5-dimethoxy-2-nitrophenyl ring. The dihedral angle between the carbazole system and the dimethoxy-substituted nitrophenyl ring is 57.05 (10)°. The aldehyde C atom deviates by 0.164 (5) Å from its attached carbazole ring system. The molecular structure is stabilized by C—H⋯O interactions which generate two S(6) and one S(7) ring motif. In the crystal, molecules are linked by C—H⋯O hydrogen bonds, forming R 3 3(15) ring motifs, which are further crosslinked by R 3 2(19) ring motifs, resulting in (002) layers. The crystal packing also features C—H⋯π interactions.

2-(4,5-Di­chloro-2-nitro­phen­yl)-4-meth­oxy-3-methyl-9-phenyl­sulfon­yl-9H-carbazole

In the title compound, C26H18Cl2N2O5S, the carbazole ring system is essentially planar with a maximum deviation of 0.0498 (16) Å for the N atom. The carbazole ring system is almost orthogonal to the phenylsulfonyl and dichloro-substituted nitrophenyl rings, making dihedral angles of 84.23 (7) and 85.46 (12)°, respectively. The molecular structure features intramolecular C—H⋯O interactions, which generate two S(6) ring motifs. In the crystal, molecules are linked by C—Cl⋯O halogen bonds [3.016 (3) Å, 166.63 (5)°], which generate infinite C(8) chains running parallel to [010].

2-(4-Fluoro-2-nitro­phen­yl)-4-hy­droxy-9-phenyl­sulfonyl-9H-carbazole-3-carbaldehyde

In the title compound, C25H15FN2O6S, the carbazole ring system is essentially planar, with a maximum deviation of 0.1534 (16) Å for the C atom connected to the 4-fluoro-2-nitrophenyl ring. It is almost orthogonal to the phenylsulfonyl and nitrophenyl rings, making dihedral angles of 88.45 (8) and 79.26 (7)°, respectively. The molecular structure is stabilized by O—H⋯O and C—H⋯O hydrogen bonds, which generate three S(6) ring motifs. In the crystal, molecules are linked by two C—H⋯O hydrogen bonds, which generate C(6) and C(9) chains running in the [100] and [010] directions, respectively, so forming a two-dimensional network lying parallel to (001). There are also supramolecular R 4 3(28) graph-set ring motifs enclosed within these networks.

(E)-2-Bromo-1-[2-(2-nitro-styr-yl)-1-phenyl-sulfonyl-1H-indol-3-yl]ethanone.

In the title compound C24H17BrN2O5S, the phenyl ring makes dihedral angles of 85.4 (2) and 8.8 (2)° with the indole ring system and the nitrobenzene ring, respectively, while the indole ring system and nitrobenzene ring make a dihedral angle of 80.1 (2)°. In the crystal, weak C—H⋯O interactions link the molecules, forming a two-dimensional network parallel to the bc plane.

(Z)-3-(1-Chloro-prop-1-en-yl)-2-methyl-1-phenyl-sulfonyl-1H-indole.

In the title compound, C18H16ClNO2S, the indole ring system forms a dihedral angle of 75.07 (8)° with the phenyl ring. The molecular structure is stabilized by a weak intramolecular C—H⋯O hydrogen bond. In the crystal, molecules are linked by weak C—H⋯O hydrogen bonds, forming a chain along [10-1]. C—H⋯π interactions are also observed, leading to a three-dimensional network.

1-(2-Bromo-meth-yl-1-phenyl-sulfonyl-1H-indol-3-yl)propan-1-one.

In the title compound, C18H16BrNO3S, the dihedral angle between the phenyl ring and the indole ring system is 89.91 (11)°. The molecular structure features weak C—H⋯O and C—H⋯Br hydrogen bonds. In the crystal, molecules are linked by weak C—H⋯O hydrogen bonds, forming chains along the a-axis direction. The chains are further linked by C—H⋯π interactions, forming a layer parallel to the ab plane.