A Study of the Crystal Structure and Hydrogen Bonding of 3-Trifluoroacetyloxime Substituted 7-Acetamido-2-aryl-5-bromoindoles

• Main Author: Malose J. Mphahlele
• Format: Article
• Language: English
• Published: MDPI AG 2018-06-01
• Series: Crystals
• Subjects: 7-acetyl-2-aryl-5-bromo-3-(trifluoroacetyl)indoles; oximation; Beckmann rearrangement; hydrogen bonds; XRD; DFT
• Online Access: http://www.mdpi.com/2073-4352/8/7/274

The 7-acetyl-2-aryl-5-bromo-3-(trifluoroacetyl)indoles 1a-d were reacted with hydroxylamine hydrochloride (2.2 equiv.) in the presence of pyridine in ethanol under reflux to afford the corresponding diketo oxime derivatives 2a-d. Beckmann rearrangement of the latter with trifluoroacetic acid under reflux afforded the corresponding 7-acetamido-2-aryl-5-bromo-3-(trifluoroacetyloxime)indoles 3a-d. The structures of the prepared compounds were characterized using a combination of NMR (1H & 13C), IR, and mass spectrometric techniques. The molecular structure of the 3-trifluoroacetyloxime substituted 7-acetamido-2-aryl-5-bromoindoles was unambiguously confirmed by the single crystal X-ray diffraction data of 3d. Structural studies of 3d in the solid state by X-ray crystallography provided evidence of hydrogen bonding networks and π-stacking of the indole moiety. Compound 3d was crystallized in the trigonal space group R-3:H with unit cell dimensions a = 25.1614(13), b = 25.1614(13), c = 17.3032(9) Å, α = β = 90°, γ = 120°, V = 9486.9(11) Å3, Z = 6. The density functional theory (DFT) structural parameters (bond lengths, bond angles, and torsion angles) of the optimized geometry calculated using the B3LYP/6-311G basis set were found to compare favourably with those of the X-ray crystal structure.