2,6-Bis(9-ethyl-9H-carbazolylmethylene)cyclohexanone

Abstract

The title compound, 2,6-bis(ethyl-9-ethyl-9H-carbazolylmethylene)cyclo­hexanone has been synthesized by condensation of 9-ethylcarbazole-3-aldehyde and cyclohexanone in ethanol in the presence of pyridine. The structure of this new compound was confirmed by elemental analysis, IR, ¹H NMR, ¹³C NMR and EI-MS spectral analysis.

Knoevenagel condensations are among the frequently applied reactions in organic synthesis, providing a good synthetic pathway to form donor-acceptor dienes known as methylene [1]. Compounds with donor-acceptor dienes have become of much interest in recent years in the context of photoelectronics [2], photophotonics [3], photodynamic therapy [4], electrochemical sensing [5], optical limiting [6], langmuir film and photoinitiated polymerization [7]. As evident from the literature, it was noted that a lot of research has been carried out on donor-acceptor dienes, but no work has been done on bis-donor-acceptor dienes. In this paper we report the synthesis of a bis-carbazole from a carbazole aldehyde. With regard to the stereochemistry of the product, we assume the E,E-isomer (only one singulet of the olefinic protons was observed in the ¹H NMR spectrum) for steric reasons, but the Z,Z-isomer cannot be completely excluded.

A mixture of 9-ethylcarbazole-3-aldehyde (1.0 g, 0.0044 mol), cyclohexanone (0.215 g, 0.0022 mol) and a few drops of pyridine in ethanol (15 mL) was heated for 3 h. The progress of the reaction was monitored by TLC. The solid that separated from the cooled mixture was collected and recrystallized from a methanol-chloroform mixture.

Yield: 20%; m.p. 81 °C.

EI-MS m/z (rel. int.%): 509 (50) [M+1]⁺.

IR (KBr) v_max cm^-1: 3053 (C-H_aromatic), 1681 (C=O), 1589 (C=C), 1147 (C-N).

¹H NMR (600 MHz, CDCl₃) δ: 8.17 (H-1, d, J = 7.8 Hz), 8.02 (H-2, d, J = 8.4 Hz), 7.25 (H-3, s), 7.55 (H-4, d, J = 7.2 Hz), 7.49 (H-5, dd, J = 8.4 Hz, 7.8 Hz), 7.34 (H-6, dd, J = 7.2 Hz, 1.2 Hz), 7.55 (H-7, dd, J = 7.2 Hz, 7.8 Hz), 8.65 (H-8, s), 4.43 (CH₃-CH₂-N, t, J = 7.2 Hz), 1.64 (CH₃-CH₂-N, q, J = 7.2 Hz).

¹³C NMR (600 MHz, CDCl₃) δ: 201.74, 198.65, 191.89, 145.15, 143.55, 140.64, 140.33, 139.96, 137.96, 129.06, 128.43, 127.20, 126.72, 126.11, 125.88, 125.11, 124.37, 123.03, 122.84, 121.53, 120.98, 120.30, 119.68, 109.31, 108.94, 108.33, 58.49, 40.17, 37.93, 29.24, 27.35, 23.95, 13.84.

Anal. calc. for C₃₆H₃₂ON₂: C, 85.03, H, 6.29, N, 5.51. Found: C, 84.98, H, 6.24, N, 5.47.