(E)-1-([1,1′-Biphenyl]-4-yl)-2-(1,3,3-trimethylindolin-2-ylidene)ethanone

The title compound, C25H23NO, consists of a biphenyl-4-carbonyl unit attached to an exocyclic double bond group at position 2 of an indole unit, which presents methyl groups as substituents at positions 1 and 3. The molecular conformation is s-cis with an E configuration, supported by weak intramolecular C—H⋯O contacts involving the methyl groups and the carbonyl function. The rings of the biphenyl group are twisted by 37.13 (5)°. In the crystal, C—H⋯O and C—H⋯π interactions link the molecules.

The title compound, C 25 H 23 NO, consists of a biphenyl-4carbonyl unit attached to an exocyclic double bond group at position 2 of an indole unit, which presents methyl groups as substituents at positions 1 and 3. The molecular conformation is s-cis with an E configuration, supported by weak intramolecular C-HÁ Á ÁO contacts involving the methyl groups and the carbonyl function. The rings of the biphenyl group are twisted by 37.13 (5) . In the crystal, C-HÁ Á ÁO and C-HÁ Á Á interactions link the molecules.
We are grateful for funding from CONACyT (project No. 52115-Y).
Products with different skills to work as switches have been used in optoelectronics (Shimkin et al., 2006), as organic electroluminescent materials (Cui & Kim, 2004) and dyes (Song et al., 2005). Moreover, the enaminoketone derivatives of the Fischer base, like the title compound, are important intermediates for the synthesis of spiropyrans and spirooxazines (Corns et al., 2009), as well as for the preparation of acetylenic products via enaminoketone fragmentation (Tarshits et al., 2005).
Moreover, despite the molecule presents high conjugation degree, the molecule is not planar; the benzene group (C12···C17) is rotated with respect to indole group (N1···C9) with the dihedral angle of 33.19 (5)°, while the biphenyl rings presents rotation showed by the dihedral angle of 37.13 (5)°.
The intermolecular assembly presents an antiparallel arrangement in a head-to-tail stacking mode especially favored by edge-to-face weak C-H···π interaction between 2.739 to 2.891 Å (see Table 2). Moreover, the weak C-H···O interaction formed by C24-H24C···O1 propagates in the ac plane (Fig. 2).

Experimental
A mixture of 4-biphenylcarboxylic acid (9.59 g, 48.38 mmol) and thionyl chloride (1.5 eq., 8.63 g, 72.57 mmol) in 24 ml of dry benzene was refluxed for 1.5 h, afterward the solvent and the excess of thionyl chloride was evaporated under vacuum.
For complete removal of the thionyl chloride, 24 ml of petroleum ether was added to the residue and then eliminated under vacuum. The 4-biphenyl-carbonyl chloride thus obtained was dissolved in 60 ml of dry benzene, then added to a mixture of the Fischer base 1,3,3-trimethyl-2-methyleneindoline (1 eq., 8.38 g, 48.38 mmol) and triethylamine (1.2 eq., 5.81 g, 58.04 mmol) in 60 ml of dry benzene. The reaction mixture was maintained at 40 °C for 2 h, after that it was allowed to stand overnight at room temperature. The final reaction mixture was first washed with water and the organic phase was separated and removed under vacuum. The resulting solid was washed successively with isopropyl alcohol. The crude product was purified using a column chromatography with chloroform as a mobile phase. Suitable crystals for X-ray diffraction were obtained from toluene by slow evaporation.

Refinement
The positional parameters of H atoms were calculated geometrically (C-H = 0.93 Å for aromatic CH and 0.96 Å for methyl CH 3 ). The displacement parameters for H atoms were fixed as U iso (H) = 1.2U eq (carrier atom) or U iso (H) = 1.5U eq (carrier atom). Fig. 1. The molecular structure of the title compound. Displacement ellipsoids for non-H atom are drawn at the 30% of probability level.