Analytical, Spectroscopic and Crystallographic Characterization of 3-[(2E)-3-Phenylprop-2-en-1-ylidene]pentane-2,4-dione

Knoevenagel condensation is widely the main method to obtain a carbon–carbon double-bond reacting aldehyde or ketone with organic acid compounds. The condensation between formaldehyde and diethyl malonate, in the presence of diethylamine, appears to be the 1st example of this reaction.1 Doebner modification, for instance, is used to synthesize α-, βunsaturated compounds with advantageous since the reaction can be performed at room temperature, tolerate a variety of functional groups, and avoid unnecessary reactions.2 Another modification of the Knoevenagel reaction is known as the Weiss–Cook reaction, which is an extremely versatile reaction used for the synthesis of a high number of natural products.3,4 The title compound (Fig. 1) was obtained by following the literature.3 Briefly, about 10.3 mL (0.1 mol) of acetylacetone was mixed with 13.3 mL of cinnamaldehyde (0.1 mol), and the mixture was stirred under an ice bath. After 2 h, only one drop of pyrrolidine was added to the reaction solution, and stirring at room temperature (25°C) continued for 10 min. The solution was washed 3 times with a mixture of 10 mL of a HCl aqueous solution (1.0 mol L–1) and 10 mL of CH2Cl2. The organic layer was concentrated, yielding a residue which was purified by column chromatography using n-hexane and ethyl-acetate as an eluent (95:5) to afford the product in solution. Light-yellow crystals were obtained by slow evaporation of the solvent. The yield was 72%, m.p.: 105 – 107o C. Anal. Calcd (%) for C14H14O2: C, 78.5; H, 6.59; Found (%): C, 78.3; H, 6.61. IR bands: νC=O, 1700 cm–1; νC=C + νCCaromatic at 1607, 1541 and 1345 cm–1; νC–O at 1198 cm–1. 1H NMR (500 MHz, DMSO-d6) δ (ppm): 2.34 (s, 3H, CH3) and 2.40 (s, 3H, CH3); 7.035 (dd, 1H, J = 13.5 Hz, –HC=CH–CH=); 7.49 (J = 11.4Hz, 1H, –HC=CH–CH=) and 7.32 (J = 15.4 Hz, 1H, –HC=CH–CH=); 7.61 (d, 2H, J = 7.2, Haromatic); 7.42 (m, 3H, Haromatic). 13C (125 MHz, DMSO-d6) δ (ppm) 203 and 198 (C=O); 145, 142.6 and 124 (–HC=CH–CH=); 142, 135, 128.3, 129.5 and 130.3 (Caromatic and Cnon-hydrogenated). UV-Vis: 332 nm (π-π* transition). The X-ray measurements were performed on an Enraf-Nonius Kappa-CCD diffractometer with graphite-monochromated Mo Kα (λ = 0.71073 Å) radiation. Diffraction data were collected (φ and ω scans with κ-offsets) with COLLECT.5 Integration, scaling and reduction of the diffraction intensities were performed with HKL DENZO-SCALEPACK6 suite of programs. The data were corrected empirically for absorption effects with the multi-scan method.7 The unit cell parameters were obtained by leastsquares refinement based on the angular settings for all collected reflections using HKL SCALEPACK.8 The structure was solved by direct methods with SHELXS-979 and the molecular model refined by the full-matrix least-squares procedure on F2 with SHELXL-97.10 The compound belongs to the monoclinic system. The a, b and c axes are: 12.7006(4)Å, 10.0271(5)Å and 20.1044(10)Å, respectively, and the β angle is 106.525(3)°. Crystallographic data are reported in Table 1 and the some torsion angles are described in Table 2. There is no solvent molecule in this structure, and there are two independent asymmetric units in the unit cell (Z = 8). The slight difference between two asymmetric units could only be observed in the torsion angles of the ketone groups. The C12–C11–C111–C112 angle is –121.3° while in a similar asymmetric unit is –122.2° (C22–C21–C213–C214). Also, the C12–C11–C113–C114 angle is 13.6°, while C22-C21-C211-C212 is 9.4°. An ORTEP 3 representation of only one molecule is represented in Fig. 2. 2020 © The Japan Society for Analytical Chemistry