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Experimental
All reagents were commercially obtained without further purification. The melting
point was recorded on a WSR-I capillary melting point apparatus and was
1
uncorrected. H-NMR and 13C-NMR data were recorded on a Bruker 400 MHz
spectrometer operating near 400 (1H) or 100 (13C) MHz in CDCl3 solutions and
TMS was used as the internal standard.
To a well-stirred reaction vessel, which was kept in an ice water bath to
maintain a temperature of 0–5 °C, was added aluminum chloride (4.6 g,
0.035 mol), N-ethylcarbazole (9.75 g, 0.05 mol) and dichloroethane (65 mL). To
the content, the solution of o-methyl benzoyl chloride (6.5 mL, 0.05 mol) and
dichloroethane (15 mL) was added dropwise over 0.5 h. Upon completion of the
addition, the mixture was kept at 0–5 °C for an additional 0.5 h. Then, the ice
water bath was removed and warmed slowly to room temperature. A mixture of
aluminum chloride (3.4 g, 0.025 mol) and acetyl chloride (4.5 mL, 0.06 mol) was
added and the content was kept at this temperature for another 0.5 h. Then, the
mixture was poured into water. After the phase separation, the organic layer was
successively washed with saturated sodium carbonate solution and water to
neutralization and dried over Na2SO4. Then, the solvent was completely evaporated
under reduced pressure and the residue was extracted with acetone (3 9 20 mL).
The combined acetone solution was cooled in the refrigerator to maintain a
temperature of 0 °C and kept for 12 h and, thereupon, 3-acetyl-6-(o-methyl
benzoyl)-N-ethylcarbazole was crystallized as a white solid (15.2 g, 85.6% yield),
mp. 162.1–163.2 °C.
3-Acetyl-6-(o-methyl benzoyl)-N-ethylcarbazole: 1H-NMR (400 MHz, CDCl3) d
(ppm): 1.46–1.50 (t, 3H, –CH2–CH3), 2.35 (s, 3H, –CH3), 2.70 (s, 3H, –CO–CH3),
4.41–4.43 (q, 2H, –CH2–), 7.29–7.48 (m, 6H, Ar–H), 8.09–8.11 (m, 1H, Ar–H),
8.14–8.17 (m, 1H, Ar–H), 8.54–8.55 (m, 1H, Ar–H), 8.68–8.69 (m, 1H, Ar–H).
13C-NMR (100 MHz, CDCl3) d (ppm): 13.81 (–CH2–CH3), 19.83 (–CH3), 26.69
(–CO–CH3), 38.16 (–CH2–), 108.69 (–Ar), 108.82 (–Ar), 122.08 (–Ar), 122.90
(–Ar), 122.93 (–Ar), 124.21 (–Ar), 125.30 (–Ar), 127.07 (–Ar), 127.97 (–Ar),
128.63 (–Ar), 129.71 (–Ar), 129.83 (–Ar), 129.93 (–Ar), 130.89 (–Ar), 136.16
(–Ar), 139.48 (–Ar), 143.37 (–Ar), 143.53 (–Ar), 197.50 (Ar–CO–Ar), 198.17
(–CO–CH3).
Conclusion
3-Acetyl-6-(o-methyl benzoyl)-N-ethylcarbazole was prepared in 85.6% yield
through two successive different acylations of N-ethylcarbazole. In the o-methyl
benzoylation of N-ethylcarbazole, less than N-ethylcarbazole molar dosage of
aluminum chloride was enough to obtain high conversion, and which was effective
to restrain the multi-acylation. The total molar dosage of aluminum chloride of two
successive acylations was reduced to 1.2 times that of N-ethylcarbazole for the
recycling of aluminum chloride in o-methyl benzoylation and the two successive
acylations in one pot.
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