Synthesis, molecular and crystal structure analysis of 1-(4-Methylbenzenesulfonyl)indole-3-carbaldehyde and DFT investigation of its rotational conformers.

Two independent molecules that differ in terms of rotation about the central S-N bond comprise the asymmetric unit of the title compound 1. The molecules have a V-shape with the dihedral angles between the fused ring system and benzene ring being 79.08(6)° and 72.83(5)°, respectively. The packing is mostly driven by p···p interactions occurring between the tolyl ring of one molecule and the C6 ring of the indole fused ring system of the other. DFT and IRC calculations for these and related 1-(arylsulfonyl)indole molecules showed that the rotational barrier about the S-N bond between conformers is within the 2.5-5.5 kcal/mol range. Crystal data for C16H13NO3S (1): Mr = 299.33, space group Pna21, a = 19.6152(4) Å, b = 11.2736(4) Å, c = 12.6334(3) Å, V = 2793.67(13) Å3, Z = 8, Z' = 2, R = 0.034.

3,3-Bis(4-bromo-phenyl-sulfan-yl)-1-methyl-piperidin-2-one.

In the title compound, C18H17Br2NOS2, the conformation of the piperidin-2-one ring is based on a half-chair with the methyl-ene C atom diagonally opposite the N atom being 0.649 (3) Šabove the plane of the remaining five atoms (r.m.s. deviation = 0.1205 Å). The S atoms occupy axial and bis-ectional positions, and the dihedral angle between the benzene rings of 59.95 (11)° indicates a splayed disposition. Helical supra-molecular chains along the b axis sustained by C-H⋯O inter-actions is the major feature of the crystal packing. The chains are connected into a three-dimensional architecture by C-H⋯Br and C-H⋯π inter-actions.

Ethyl (2Z)-3-oxo-2-(3,4,5-tri-meth-oxy-benzyl-idene)butano-ate.

In the title compound, C16H20O6, the conformation about the C=C double bond [1.344 (2) Å] is Z. With respect to this bond, the ketone is almost coplanar [C-C-C-O torsion angle = -179.60 (10)°] and the ester is almost perpendicular [C-C-C-O = 78.42 (13)°]. The meth-oxy substituents of the central benzene ring are either almost coplanar [C-C-O-C = 3.54 (15) and 177.70 (9)°] or perpendicular [C-C-O-C = 80.08 12)° for the central substituent]. In the crystal, the three-dimensional architecture features C-H⋯O and π-π [inter-centroid distance = 3.6283 (6) Å] inter-actions.