One-step, large-scale synthesis of isotruxene

Article abstract of DOI:10.3184/174751918x15403823022089

A concise procedure for the one-step synthesis of isotruxene has been developed. Isotruxene is obtained in around 60% yield on a 150-gram scale through acid-catalysed cyclotrimerisation of equimolar amounts of 1-indanone and 2-indanone. The separation procedure is convenient and is based on different solubilities between isotruxene and side products.

Full text of DOI:10.3184/174751918x15403823022089

556 RESEARCH PAPER
VOL. 42 NOVEMBER, 556–557
JOURNAL OF CHEMICAL RESEARCH 2018
One-step, large-scale synthesis of isotruxene
Cen Zhoua*, Wei Xuana, Shi-Peng Luob and Yue-Hua Baoa
aCollege of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P.R. China
bSchool of Chemical & Environmental Engineering, Jiangsu University of Technology, Changzhou 213001, P.R. China
A concise procedure for the one-step synthesis of isotruxene has been developed. Isotruxene is obtained in around 60% yield on a 150-
gram scale through acid-catalysed cyclotrimerisation of equimolar amounts of 1-indanone and 2-indanone. The separation procedure is
convenient and is based on different solubilities between isotruxene and side products.
Keywords: truxene, oligofluorene, cyclotrimerisation, large-scale synthesis of isotruxene
Isotruxene is an isomer of truxene (structures in Scheme 1). These
two isomers have a similar 2D-extented oligofluorene skeleton but
different arrangements of the phenylene groups and thus different
conjugation effects.1,2 Although truxene and its derivatives have
been widely applied in the field of organic electronics,3–8 the
potential of isotruxene in this field is much less explored,9–11 mostly
duetothelimitedsyntheticmethods. Langetal. reportedasynthetic
procedure for isotruxene more than 50 years ago.12 However, the
harsh conditions (20 atm and 350 °C) applied in the procedure
severely limited its application both in the laboratory and in
industry. Yang et al. developed a synthetic procedure by oxidative
cyclotrimerisation of indene under relatively mild conditions in
2006.13 The yield was 18% after careful flash chromatography.
After that, they reported three modified multistep approaches in
2009.14 The total yields were improved to 27–36% on a 10-gram
scale. Later, two more multistep approaches were reported by Wu
and co-workers15 and Liu et al.16 and the total yields were 18 and
31% on 100-milligram and 1-gram scales respectively. We report
here a one-step facile synthesis of isotruxene on a 150-gram scale
from commercially available starting materials.
Results and discussion
Inspired by the well-developed synthetic procedure for truxene
through cyclotrimerisation of 1-indanone in acetic acid and aqueous
HCl, we designed a strategy for the synthesis of isotruxene (Scheme
1).17 Specifically, equimolar amounts of 1-indanone and 2-indanone,
both commercially available, were mixed and subjected to the
acidic condensation conditions (HOAc/concentrated aqueous HCl).
If the reactivities of the carbonyl groups in both 1-indanone and
2-indanone are equal, the ratio of heterotrimer to homotrimer should
be 3:1, thus making isotruxene the major product and truxene the
minor product. To our delight, isotruxene indeed formed as the
major product after a one-day reflux of the mixture.
The purification procedure was relatively convenient (Scheme
2). The solid residue was easily separated by suction and
washed three times with water. Then, after thorough washing
Scheme 1 Truxene-inspired synthetic strategy to isotruxene.
Scheme 2 Purification of isotruxene and truxene.
* Correspondent. E-mail: miller19850128@163.com

JOURNAL OF CHEMICAL RESEARCH 2018 557
(m, 3 H), 7.42–7.34 (m, 3 H), 4.28 (s, 2 H), 4.01 (s, 4 H); 13C NMR
(100 MHz, CDCl3): δ (ppm) 144.1, 144.0, 143.9, 142.4, 142.0, 141.8,
139.1, 137.5, 136.8, 136.5, 136.1, 135.7, 126.9, 126.8, 126.5, 126.3,
126.2, 126.1, 125.2, 125.1, 125.0, 123.5, 123.3, 122.1, 36.6, 35.9, 35.7;
MS (EI) m/z 342 [M]+; HRMS (EI) m/z calcd for C27H18+: 342.1409;
found: 342.1411.
Truxene: M.p. 370–372 °C (dec.) [lit.18 368–369 °C (dec.)]; 1H NMR
(500 MHz, CDCl3): δ (ppm) 7.97 (d, J = 7.5 Hz, 3 H), 7.71 (d, J = 7.5
Hz, 3 H), 7.51 (t, J = 7.5 Hz, 3 H), 7.40 (t, J = 7.5 Hz, 3 H), 4.30 (s, 6 H);
13C NMR (100 MHz, CDCl3): δ (ppm) 143.8, 141.7, 137.1, 135.3, 126.9,
126.3, 125.1, 121.9, 36.6; MS (EI) m/z 342 [M]+; HRMS (EI) m/z calcd
for C27H18+: 342.1409; found: 342.1405.
with acetone, isotruxene was enriched in the eluent with little
truxene and other polar impurities. This crude product was
briefly purified through a short column over silica gel, then
recrystallised from toluene or xylene, giving isotruxene as a
1
light orange solid in 61% yield. Its H and 13C NMR spectra
were in accordance with those in the literature.13,14 High-
performance liquid chromatography showed that the purity of
the product was over 95%. In addition, truxene was enriched
in the filter cake (15%). The as-obtained light-yellow solid of
truxene was also pure as confirmed by 1H NMR.18
Conclusion
Isotruxene was synthesised on a 150-gram scale simply by one-
step cyclotrimerisation of commercially available 1-indanone
and 2-indanone and easily separated based on different
solubilities between isotruxene and side products. We believe
that this tremendous improvement in the synthesis of isotruxene
will facilitate the research of isotruxene as a building block
for organic electronics, supramolecular chemistry, etc. The
synthetic and separation strategy may also be applied for other
C3h symmetric polycyclic aromatic hydrocarbons and their
isomers.
Acknowledgements
This work was supported by the NSFC (Nos 21722304,
21573181 and 91227111) and the Fundamental Research Funds
for the Central Universities (No. 20720160050) of China. We
thank Prof. Xiao-Yu Cao, Dr Ru-Qiang Lu and Dr Xin-Chang
Wang for helpful discussions.
Received 6 August 2018; accepted 9 October 2018
Paper 1805566
https://doi.org/10.3184/174751918X15403823022089
Published online: 2 November 2018
Experimental
Melting points were determined with a Büchi M-565 apparatus and
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