October 1998
SYNLETT
1079
TiCl (OTf) Catalyses the Efficient Conversion of Acetophenones to 1,3,5-Triaryl Benzenes.
3
N. Iranpoor*, B. Zeynizaded
Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454, Iran
Received 2 June 1998
Abstract: The quantitative conversion of different substituted
In order to compare the catalytic efficiency of TiCl (OTf) with
3
acetophenones to their corresponding 1,3,5-triaryl benzenes was
alternative Lewis acids, the trimerization of acetophenone with 10-20
o
achieved in the presence of catalytic amounts of TiCl (OTf) in sealed
mole% of different metal chlorides in sealed tubes at 90-100 C was
3
tubes at 90-100°C.
investigated. The results obtained are displayed in Table 2.
1
,3,5-Triaryl benzenes are important compounds with particular
1
,2
application in electrode and electroluminescent devices.
Their
preparation via condensation of acetophenones has been regarded as a
useful general method and has been extensively studied in the presence
3
of acidic catalysts such as sulfuric acid/sodium pyrosulfate,
4
,5,6
5b
aniline hydrochloride,7
hydrochloric acid,
K S O /H SO ,
2
2
7
2
4
8
9
sulfoacetic acid and ion exchange resin. The use of an alcoholic
hydrochloride system has also been investigated as a suitable reaction
media for this trimerization, but the yields obtained in this manner are
usually very low and the reaction times are 18 and 30 days for different
5a
10
substrates. The use of other catalysts such as Al O at 200-300 °C
2
3
1
1
and oxides of Ti, Cr and Mn at 350-360 °C, are also reported for this
transformation but afford only moderate yields of products. Very
recently an interesting article reported the use of acetyl chloride in the
presence of SmCl3 as catalyst for the conversion of acetophenone
diethylketals to triaryl benzenes in moderate to good yields.12 In this
paper, we report the quantitative conversion of different substituted
acetophenones to their corresponding 1,3,5-triaryl benzenes with 10-20
mole% of TiCl (OTf) under solvent free conditions in sealed tubes at
3
9
0-100°C (scheme).
The results obtained in Table 2 demonstrate that TiCl (OTf) is by far the
3
As shown in Table 1, acetophenones carrying either electron-releasing
or electron-withdrawing groups can be efficiently converted to their
corresponding triaryl benzenes in quantitative yields.
most effective Lewis acid for the trimerization reaction reported in this
paper.
Experimental: Products were characterized by comparison of their
physical data ie. Mp, IR, NMR and mass spectra with those reported in
the literature. Infrared spectra were recorded on a Perkin Elmer IR-157
G and a Perkin Elmer 781 spectrometer. NMR spectra were recorded on
a Bruker Avance DPX-250. Mass spectra were recorded on a Shimadzu
GCMS-QP 1000 EX.
Typical Procedure for Conversion of Acetophenone to 1,3,5-
Triphenyl Benzene: Acetophenone (0.12 g, 1 mmol) and TiCl (OTf)
3
(0.03 g, 0.1 mmol) were added to a tube. Then the tube was sealed and
heated in an oil bath at 90-100ºC for 10 h. After cooling, the sealed tube
was opened. The reaction mixture was chromatographed on a short
column of silica gel using CCl4 as eluent. The pure 1,3,5-triphenyl
benzene was obtained in a quantitative yield (99%, 0.101 g).
Acknowledgment: We are thankful to Shiraz University Research
Council for partial support of this work. The assistance of Mr. N. Maleki
for running NMR spectra and Dr. A. A. Jarahpoor for running mass
spectra is also acknowledged.
References:
(1) Lindeman, S. V.; Struchkov, Yu. T.; Michailov, V. N.; Rusanov, A.
L. Izu. Akad. Nauk. Ser. Khim. 1994, 1986; Chem. Abstr. 1995,
1
23, 32717.
(2) Aslam. M.; Aguilar, D. A.; PCT Int. Appl. WO 93 14, 065; Chem.
Abstr. 1993, 119, 270793.