Diethyl [(3-cyano-1-phenylsulfonyl-1H-indol-2-yl)methyl]phosphonate

In the title compound, C20H21N2O5PS, the indole ring is essentially planar, with a maximum deviation of −0.0083 (18) Å. The methyl C atom of the methylphosphonate group and the S atom lie 0.104 (2) and −0.2158 (6) Å, respectively, from the indole mean plane. The sulfonyl-bound phenyl ring is almost perpendicular to the indole ring system, with a dihedral angle of 82.30 (8)°. The ethyl side chains are disordered over two sets of sites, with occupancy factors of 0.737 (5)/0.263 (5) and 0.529 (11)/0.471 (11). In the crystal, molecules are linked into centrosymmetric dimers via C—H⋯O hydrogen bonds, resulting in an R 2 2(18) graph-set motif. The crystal structure is further stabilized by C—H⋯π interactions.

In the title compound, C 20 H 21 N 2 O 5 PS, the indole ring is essentially planar, with a maximum deviation of À0.0083 (18) Å . The methyl C atom of the methylphosphonate group and the S atom lie 0.104 (2) and À0.2158 (6) Å , respectively, from the indole mean plane. The sulfonyl-bound phenyl ring is almost perpendicular to the indole ring system, with a dihedral angle of 82.30 (8) . The ethyl side chains are disordered over two sets of sites, with occupancy factors of 0.737 (5)/0.263 (5) and 0.529 (11)/0.471 (11). In the crystal, molecules are linked into centrosymmetric dimers via C-HÁ Á ÁO hydrogen bonds, resulting in an R 2 2 (18) graph-set motif. The crystal structure is further stabilized by C-HÁ Á Á interactions.
Indoles also have been proved to display high aldose reductase inhibitory activity (Rajeswaran, et al., 1999).
In the benzene ring of the indole ring system, the endocyclic angles at C2 and C5 are contracted to 117.49 (17) and 118.56 (17)° respectively, while those at C1, C3 and C4 are expanded to 121.35 (15)°, 121.69 (18) and 120.69 (17)°, respectively. This would appear to be a real effect caused by the fusion of the smaller pyrrole ring to the six-membered benzene ring and the strain is taken up by the angular distortion rather than by bond-length distortions (Allen, 1981;Sethu Sankar et al., 2002).

Experimental
To a solution of 2-(bromomethyl)-1-phenylsulfonyl-indole-3-carbonitrile (1 mmol) and triethylphosphite (1.2 mmol) in dry dichloromethane (10 ml) at room temperature, ZnBr 2 (0.2 mmol) was added and allowed to stir for 2 h under N 2 . After consumption of the bromo compound (monitored by TLC) volatile components were removed under vacuo. The residual mass was poured over crushed ice (200 g) containing conc. HCl (5 ml). The precipitated solid was filtered, washed with water and dried to give crude phosphonate ester. The crude product was purified by flash column chromatography to provide the title compound which was recrystalized from a mixture of 50% ethylacetate in pure hexane.

Refinement
All the hydrogen atoms weree fixed geometrically and allowed to ride on their parent atoms with C-H distance in the range 0.93Å to 0.97Å and with U iso (H) = 1.5U eq (C) for CH 3 groups and U iso (H) = 1.2U eq (C) for all the other H-atoms.