Synthesis of novel trifluoromethyl-containing heterocycle-fused troponoid compounds

Article abstract of DOI:10.1515/hc-2012-0122

A facile synthesis of novel trifluoromethylcontaining pyrano-, pyrazolo- and isoxazolo-fused tropone compounds 4a,b , 5a,b , and 6a,b , respectively, by cyclizations of ( E )-3-[3-(trifluoromethylphenyl)acryloyl] tropolones 3a,b is described. The substrates 3a,b were prepared by Claisen-Schmidt condensation reaction of 3-acetyltropolone ( 1 ) with 3- or 4-(trifluoromethyl)benzaldehydes 2a,b .

Full text of DOI:10.1515/hc-2012-0122

DOI 10.1515/hc-2012-0122ꢀ
ꢀHeterocycl. Commun. 2012; 18(4): 223–226
Wentao Gao*, Rui Liu and Yang Li
Synthesis of novel trifluoromethyl-containing
heterocycle-fused troponoid compounds
Abstract: A facile synthesis of novel trifluoromethyl- drug discovery (Cavazza et al., 2000; Isakovic et al., 2001;
containing pyrano-, pyrazolo- and isoxazolo-fused Nair et al., 2006). Therefore, the interesting and remark-
tropone compounds 4a,b, 5a,b, and 6a,b, respectively, by able bioactivity surrounding the troponoid moiety con-
cyclizations of (E)-3-[3-(trifluoromethylphenyl)acryloyl] tinues to be a vector in the development of novel and
tropolones 3a,b is described. The substrates 3a,b were interesting types of new drug candidates (Baldwin et al.,
prepared by Claisen-Schmidt condensation reaction of 2003; Mori et al., 2003; Wahlström et al., 2004). In recent
3-acetyltropolone (1) with 3- or 4-(trifluoromethyl)benzal- years, our group has synthesized a number of novel sub-
dehydes 2a,b.
stituted or fused troponoid compounds (Gao et al., 1989,
2009, 2010a,b, 2012; Gao and Zheng, 2000; Li and Gao,
Keywords: aromatic hydrazine; Claisen-Schmidt conden- 2010; Li et al., 2009, 2012a,b). Building upon this evolv-
sation; cyclization; hydroxylamine hydrochloride; trifluo- ing expertise and diversifying our work on the synthesis
romethyl; tropone.
of new troponoid compounds, we would like to report,
herein, the synthesis of a series of novel trifluoromethyl-
containing bicyclic heterocycle-fused troponoid com-
pounds.
*Corresponding author: Wentao Gao, Institute of Superfine
Chemicals, Bohai University, Keji Street, Jinzhou, 121000,
P. R. China, e-mail: bhuzh@163.com
Rui Liu: Institute of Superfine Chemicals, Bohai University, Keji
Street, Jinzhou, 121000, P. R. China
Yang Li: Institute of Superfine Chemicals, Bohai University, Keji
Street, Jinzhou, 121000, P. R. China
Results and discussion
The Claisen-Schmidt condensation of 3-acetyltropolone
(1) with 3- or 4-(trifluoromethyl)benzaldehyde accord-
ing to our previously published methodology (Li et al.,
2009; Chang et al., 2010) furnished the respective (E)-3-
(3-(trifluoromethylphenyl)acryloyl)tropone 3a,b in high
yield (Scheme 1). These compounds served as precursors
Introduction
It is well known that the introduction of a trifluoromethyl for the construction of the desired trifluoromethyl-con-
group into bioactive organic molecules strongly affects taining bicyclic heterocycle-fused troponoid skeleton.
their unique features such as polarity and lipid solubility
Our recent work has shown that the I2/DMSO/H2SO4
(Asahina et al., 2005; Liu et al., 2008; Chowdhury et al., system is an efficient reagent for intramolecular oxidative
2009; Feng et al., 2010). A large volume of synthetic work cyclization of 3-cinnamoyltropolones (Gao et al., 2009; Li
on this subject has been published (Donohue et al., 2002; et al., 2009). In this work, this approach was extended on
Sloop et al., 2002; Loska et al., 2007; Shaaban 2008).
the oxidative cyclization of trifluoromethyl-substituted
By contrast, troponoid-based compounds, espe- tropolones 3a and 3b (Scheme 2). After usual workup fol-
cially heterocycle-fused troponoids, exhibit potent bio- lowed by purification of crude products by crystallization
logical and pharmacological activities such as antiviral from 1,4-dioxane, the desired flavone-like products 4a and
(Nakazawa et al., 2012), antifungal (Angawi et al., 2003) 4b were obtained in yields of 66% and 68%, respectively.
and antimalarial (Seephonkai et al., 2001) activities. In In this reaction, to ensure precipitation of the product
particular, a new heterocycle-fused troponoid, namely directly from the reaction mixture, a minimal amount of
cordytropolone, discovered in the culture broth of DMSO was used. Oxidative cyclization was also attempted
Cordyceps sp. BCC 1681, shows promise to be developed using the DMSO-I2 reagent system in the absence of con-
into a new antimalarial drug (Seephonkai et al., 2001). centrated H2SO4, according to the literature method by
The troponoid moiety is an important structural part of Lokhande et al. (2005). This reaction produced products
other biologically important molecules in the area of 4a,b in low yields.
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ꢀW. Gao et al.: Trifluoromethyl-containing heterocycle-fused troponoid compounds
O
O
CHO
OH
O
5% KOH
r. t.
OH
CF3
F3C
O
2a,b
3a,b
1
a
b
: 3-CF3; : 4-CF3
Scheme 1
Isoxazoles and pyrazoles are important classes of
biologically active heterocycles, being readily applied to
drug design, and have a rich chemistry because of their
easy reductive cleavage and susceptibility to ring trans-
formations (Nakamura et al., 2003; Penning et al., 2006).
In this work, the synthesis of trifluoromethyl-substituted
isoxazolo- and pyrazolo-fused troponoids was accom-
plished by cyclization of 3a,b with bifunctional agents
(Scheme 3). The methodology has been used by us previ-
ously for the synthesis of related compounds (Gao et al.,
1989, 2010a, 2012; Li and Gao 2010; Li et al., 2012a,b).
Thus, the treatment of tropolones 3a,b with phenylhy-
drazine hydrochloride or hydroxylamine hydrochloride
in refluxing ethanol under reflux conditions furnished
the respective products 5a,b and 6a,b in acceptable
yields of 54–62%.
Conclusion
The construction of a series of novel trifluoromethyl-con-
taining pyrano-, pyrazolo- and isoxazolo-fused bicyclic
tropones compounds was achieved.
Experimental
All reagents were obtained from Fluka and used without purifica-
tion. Melting points were determined by using WRS-1B melting points
apparatus and are uncorrected. H NMR spectra were recorded on a
Bruker Avance 400 NMR spectrometer at 400 MHz. Electrospray
ionization (ESI) mass spectra were determined using an MSD VL ESI1
spectrometer. Elemental analysis was performed using an Elementar
Vario EL-III element analyzer. The progress of reactions was moni-
tored by thin-layer chromatography (TLC) on silica gel GF254 using
ethyl acetate/petroleum ether (1:4) as eluent.
1
CF3
Preparation of 3-(3-(trifluoromethylphenyl)
acryloyl)tropolones 3a,b
O
O
I2/DMSO/H2SO4
3a,b
110°C
An aqueous solution of 5% KOH (5 mL) was added dropwise to a
stirred solution of 3-acetyltropolone (1, 1 mmol, 164 mg) and 1.5 equi-
molar amount of 3- or 4-(trifluoromethyl)benzaldehyde (2a,b, 1.5
mmol, 261 mg) in 50% aqueous methanol (5 mL). The mixture was
stirred at room temperature for 24 h and then quenched by addition
of water (5 mL) and acidified with 1 M HCl. The resultant precipitate
of 3a,b was collected by filtration, washed with water, dried and
crystallized from methanol.
O
4a,b
a: 3-CF3; b: 4-CF3
Scheme 2
3-(3-(3-(Trifluoromethyl)phenyl)acryloyl)tropolone
(3a)ꢀThis
compound was obtained as bright yellow crystals from 2a (3-(trifluo-
romethyl)benzaldehyde); yield 83%; mp 188–189°C; 1H NMR (CDCl3):
δ 7.02–7.05 (m, 2H), 7.41 (d, 1H, J = 16 Hz), 7.45 (d, 1H, J = 8 Hz), 7.63 (d,
1H, J = 11 Hz), 7.81 (d, 1H, J = 8 Hz), 7.86–7.90 (m, 2H), 8.43 (d, 1H, J = 16
Hz), 8.45 (d, 1H, J = 11 Hz), 10.42 (s, 1H); MS: m/z 321.1 [M+H]+. Anal.
Calcd for C17H11F3O3: C, 63.75; H, 3.46. Found: C, 63.53; H, 3.31.
O
N
N
PhNHNH2 HCl
EtOH, reflux
3a,b
CF3
5a,b
O
O
N
NH2OH HCl
EtOH, reflux
3-(3-(4-(Trifluoromethyl)phenyl)acryloyl)tropolone (3b)ꢀThis
compound was obtained as bright yellow crystals from 2b (4-(trifluo-
romethyl)benzaldehyde); yield 87%; mp 209–210°C; 1H NMR (CDCl3):
δ 7.14–7.19 (m, 1H), 7.34 (d, 1H, J = 16 Hz), 7.36–7.42 (m, 1H), 7.57 (d, 1H,
J = 11 Hz), 7.63–7.66 (m, 2H), 8.19 (d, 1H, J = 16 Hz), 7.97–8.07 (m, 2H),
CF3
6a,b
a
b
: 3-CF3; : 4-CF3
Scheme 3
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W. Gao et al.: Trifluoromethyl-containing heterocycle-fused troponoid compoundsꢀ
ꢀ225
1
8.38 (d, 1H, J = 11 Hz), 10.39 (1H, s); MS: m/z 321.0 [M+H]+. Anal. Calcd yield 54%; mp 195–197°C; H NMR (DMSO-d6): δ 7.66–7.71 (m, 7H),
for C17H11F3O3: C, 63.75; H, 3.46. Found: C, 63.47; H, 3.51.
7.74 (d, 1H, J = 16 Hz), 7.91 (d, 1H, J = 11 Hz), 7.95 (d, 1H, J = 16 Hz),
7.98–8.01 (m, 3H), 8.41 (s, 1H), 8.87 (d, 1H, J = 8 Hz); MS: m/z 392.9
[M+H]+. Anal. Calcd for C23H15F3N2O: C, 70.40; H, 3.85; N, 7.14. Found:
C, 70.26; H, 4.13; N, 6.93.
Preparation of 2-[3- or 4-(trifluoromethyl)
1-Phenyl-3-[4-(trifluoromethyl)styryl]cyclohepta[c]pyrazol-
8(1H)-one (5b)ꢀThis compound was obtained as a yellowish-brown
solid from 3b (3-(3-(4-(trifluoromethyl)phenyl)acryloyl)tropolone);
yield 58%; mp 204–206°C; 1H NMR (DMSO-d6): δ 6.92 (d, 1H, J = 12 Hz),
6.99–7.03 (m, 1H), 7.42–7.50 (m, 6H), 7.65 (d, 1H, J = 16 Hz), 7.76 (d, 2H,
J = 8 Hz), 7.95 (d, 1H, J = 16 Hz), 8.01 (d, 2H, J = 8 Hz), 8.17 (d, 1H,
J = 11 Hz); MS: m/z 393.1 [M+H]+. Anal. Calcd for C23H15F3N2O: C, 70.40;
H, 3.85; N, 7.14. Found: C, 70.22; H, 3.95; N, 7.03.
phenyl]cyclohepta[b]pyran-4,9-diones (4a,b)
A mixture of compound 3a,b (1 mmol, 320 mg), DMSO (8 mL) and 2–4
drops of concentrated H2SO4 was stirred at 110°C for 15 min and then
treated with I2 (0.1 mmol, 25.4 mg) and stirred for an additional 12 h.
After completion of the reaction as monitored by TLC, the mixture
was cooled to room temperature. The resulting precipitate of 4a,b
was collected by filtration and crystallized from 1,4-dioxane.
2-[3-(Trifluoromethyl)phenyl]cyclohepta[b]pyran-4,9-dione
(4a)ꢀThis compound was obtained as a yellowish-brown solid from
3a (3-(3-(3-(trifluoromethyl)phenyl)acryloyl)tropolone); yield 66%;
Preparation of 3-[3- or 4-(trifluoromethyl)
1
mp 203–205°C; H NMR (DMSO-d6): δ 7.53 (s, 1H), 7.67 (d, 1H, J = 11
styryl]-8H-cyclohepta[d]isoxazol-8-ones (6a,b)
Hz), 7.82–7.86 (m, 2H), 7.97 (s, 1H), 8.07 (d, 1H, J = 8 Hz), 8.32–8.40 (m,
3H); MS: m/z 318.9 [M+H]+. Anal. Calcd for C17H9F3O3: C, 64.16; H, 2.85.
Found: C, 63.89; H, 3.01.
A solution of tropolone 3a or 3b (1 mmol, 320 mg) in ethanol (10 mL)
was stirred and treated with hydroxylamine hydrochloride (104 mmg,
1.5 mmol). The mixture was heated under reflux for 24 h, then cooled
to room temperature and quenched with water. The resultant precipi-
tate of 6a,b was collected by filtration and crystallized from ethanol.
2-[4-(Trifluoromethyl)phenyl]cyclohepta[b]pyran-4,9-dione
(4b)ꢀThis compound was obtained as a yellowish-brown solid from
3b (3-(3-(4-(trifluoromethyl)phenyl)acryloyl)tropolone); yield 68%;
1
3-[3-(Trifluoromethyl)styryl]-8H-cyclohepta[d]isoxazol-8-one
(6a)ꢀThis compound was obtained as a yellowish-brown solid from
3a (3-(3-(3-(trifluoromethyl)phenyl)acryloyl)tropolone); yield 62%;
mp 216–218°C; H NMR (CF3COOD): δ 7.56 (s, 1H), 7.63–7.67 (m, 2H),
7.81 (d, 1H, J = 12 Hz), 7.92 (d, 2H, J = 7 Hz), 8.26 (d, 2H, J = 7 Hz), 8.53
(d, 1H, J = 11 Hz); MS: m/z 319.1 [M+H]+. Anal. Calcd for C17H9F3O3: C,
64.16; H, 2.85. Found: C, 64.43; H, 2.66.
1
mp 197–199°C; H NMR (DMSO-d6): δ 7.12–7.25 (m, 2H), 7.28 (d, 1H,
J = 16 Hz), 7.58–7.81 (m, 4H,), 8.05 (d, 1H, J = 11 Hz), 8.12–8.27 (m, 2H);
MS: m/z 318.0 [M+H]+. Anal. Calcd for C17H10F3NO2: C, 64.36; H, 3.18;
N, 4.41. Found: C, 64.56; H, 3.00; N, 4.20.
Preparation of 1-phenyl-3-[3-
(trifluoromethyl)styryl]cyclohepta[c]pyrazol-
8(1H)-ones (5a,b)
A solution of 3a,b (1 mmol, 320 mg) in ethanol (10 mL) was stirred
and treated with phenylhydrazine hydrochloride (217 mmg,
1.5 mmol). The mixture was heated under reflux for 24 h, then
cooled to room temperature and quenched with water. The result-
ing precipitate of 5a,b was collected by filtration and crystallized
from ethanol.
3-[4-(Trifluoromethyl)styryl]-8H-cyclohepta[d]isoxazol-8-one
(6b)ꢀThis compound was obtained as a yellowish-brown solid from
3b (3-(3-(4-(trifluoromethyl)phenyl)acryloyl)tropolone); yield 56%;
mp 215–216°C; 1H NMR (DMSO-d6): δ 7.12–7.15 (1H, m), 7.27 (1H, d,
J = 16 Hz), 7.62 (1H, d, J = 16 Hz), 7.64 (1H, d, J = 11 Hz), 7.78–7.82
(3H, m), 7.98–8.05 (3H, m); MS: m/z 318.1 [M+H]+. Anal. Calcd for
C17H10F3NO2: C, 64.36; H, 3.18; N, 4.41; Found: C, 64.15; H, 3.36; N, 4.19.
Acknowledgments: The authors would like to thank the
Natural Science Foundation of Liaoning Province for
financial support (Grant No. 201202001).
1-Phenyl-3-[3-(trifluoromethyl)styryl]cyclohepta[c]pyrazol-
8(1H)-one (5a)ꢀThis compound was obtained as a yellowish-brown
solid from 3a (3-(3-(3-(trifluoromethyl)phenyl)acryloyl)tropolone); Received August 13, 2012; accepted September 8, 2012
References
Angawi, R. F.; Swenson, D. C.; Gloer, J. B.; Wicklow, D. T. Malettinin
A: a new antifungal tropolone from an unidentified fungal
colonist of Hypoxylon stromata (NRRL 29110). Tetrahedron Lett.
2003, 44, 7593–7596.
Asahina, Y.; Araya, I.; Iwase, K.; Iinuma, F.; Hosaka, M.; Ishizaki,
T. Synthesis and antibacterial activity of the 4-quinolone-3-
carboxylic acid derivatives having a trifluoromethyl group as a
novel N-1 substituent. J. Med. Chem. 2005, 48, 3443–3446.
Baldwin, J. E.; Mayweg, A. V. W.; Pritchard, G. J.; Adlington, R. M.
Expedient synthesis of a highly substituted tropolone via a
3-oxidopyrylium [5+2] cycloaddition reaction. Tetrahedron Lett.
2003, 44, 4543–4545.
Cavazza, M.; Guella, G.; Pietra, F. Synthesis of 1-oxaazulan-2-ones
and furanotropones from troponoids: a reexamination and
extension to colchicinoids. Tetrahedron 2000, 56,
1917–1922.
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226ꢀ
ꢀW. Gao et al.: Trifluoromethyl-containing heterocycle-fused troponoid compounds
Chang, M. Q.; Li, Y.; Zhang, H.; Gao, W. T. A facile and general
synthesis of tropolonyl-substituted chalcone derivatives.
J. Chem. Res. 2010, 34, 269–273.
Li, Y.; Sun, M. C.; Gao, W. T. Synthesis and characterization of
bromo-, arylazo-, and heterocyclic-fused troponoids containing
a 1,3-benzodioxole system. J. Heterocycl. Chem. 2012b, 49,
167–172.
Chowdhury, M. A.; Abdellatif, K. R. A.; Dong, Y.; Das, D.; Suresh,
M. R.; Knaus, E. E. Synthesis of celecoxib analogues
possessing a N-difluoromethyl-1,2-dihydropyrid-2-one
5-lipoxygenase pharmacophore: biological evaluation as
dual inhibitors of cyclooxygenases and 5-lipoxygenase with
anti-inflammatory activity. J. Med. Chem. 2009, 52, 1525–1529.
Donohue, B. A.; Michelotti, E. L.; Reader, J. C.; Reader, V.; Stirling,
M.; Tice, C. M. Design, synthesis, and biological evaluation
of a library of 1-(2-thiazolyl)-5-(trifluoromethyl)pyrazole-4-
carboxamides. J. Comb. Chem. 2002, 4, 23–32.
Feng, M. L.; Li, Y. F.; Zhu, H. J.; Zhao, L.; Xi, B. B.; Ni, J. P. Synthesis,
insecticidal activity, and structure-activity relationship of
trifluoromethyl-containing phthalic acid diamide structures.
J. Agric. Food Chem. 2010, 58, 10999–11006.
Gao, W. T.; Zheng, Z. Study on synthesis of heterocycle-fused
troponoid compounds. Chin. Chem. Lett. 2000, 11, 503–504.
Gao, W. T.; Jin, Z. T.; Yin, B. Z.; Imafuku, K. Synthesis and reactions
of halo-, nitro-, and arylazo-substituted 3-cinnamoyl-
tropolones. Formation of styryl-substituted heterocycle-fused
troponoid compounds. J. Heterocycl. Chem. 1989, 26, 371–375.
Gao, W. T.; Li, Y.; Zhang, H.; Chang, M. Q.; Imafuku, K. Oxidative
cyclization of 3-cinnamoyltropolones with I2/DMSO/H2SO4
system. J. Heterocycl. Chem. 2009, 46, 1107–1112.
Gao, W. T.; Sun, M. C.; Li, Y. Synthesis and reactions of halo-,
arylazo-substituted 3-(3-(1-naphthyl)acryloyl)tropolones.
Formation of (naphthalen-1-yl)vinyl)substituted heterocycle-
fused troponoid compounds. Chin. J. Chem. 2010a, 28,
1409–1416.
Gao, W. T.; Zhang, X. F.; Li, Y.; Liu, H. Y.; Imafuku, K. First synthesis of
2-tropolonylquinoline-4-carboxylic acid derivatives via Pfitzinger
reaction in water. Heterocycles 2010b, 81, 1689–1696.
Gao, W. T.; Yan, Y.; Li, Y. Synthesis of conjugated (E,E)-1,3-diene-
containing troponoid-based compounds. Chem. Pap. 2012, 66,
691–698.
Liu, A.; Wang, X.; Ou, X.; Huang, M.; Chen, C.; Liu, S.; Huang, L.;
Liu, X.; Zhang, C.; Zheng, Y.; et al. Synthesis and fungicidal
activities of novel bis(trifluoromethyl)phenyl-based
strobilurins. J. Agric. Food Chem. 2008, 56, 6562–6566.
Lokhande, P. D.; Sakate, S. S.; Taksande, K. N.; Navghare, B. Dimethyl-
sulfoxide-iodine catalysed deprotection of 2′-allyloxychalcones:
synthesis of flavones. Tetrahedron Lett. 2005, 46, 1573–1574.
Loska, R.; Majcher, M.; Makosza, M. Synthesis of trifluoromethylated
azines via nucleophilic oxidative substitution of hydrogen by
trifluoromethyl carbanions. J. Org. Chem. 2007, 72, 5574–5580.
Mori, A.; Kawakami, H.; Kato, N.; Wu, S. P.; Takeshitaa, H.
Photochemical reactions of 2-bromotropone and 2,7-
dibromotropone with 9,10-dicyanoanthracene. Org. Biomol.
Chem. 2003, 1, 1730–1736.
Nakamura, T.; Sato, M.; Kakinuma, H.; Miyata, N.; Taniguchi,
K.; Bando, K.; Koda, A.; Kameo, K. Pyrazole and isoxazole
derivatives as new, potent, and selective 20-hydroxy-
5,8,11,14-eicosatetraenoic acid synthase inhibitors. J. Med.
Chem. 2003, 46, 5416–5427.
Nakazawa, T.; Ohmae, T.; Fujimuro, M.; Ito, M.; Nishinaga, T.;
Iyoda, M. Syntheses, molecular structures, and antiviral
activities of 1- and 2-(2′-deoxy-d-ribofuranosyl) cyclohepta[d]
[1,2,3]triazol-6(1H)-ones and 1-(2′-deoxy-d-ribofuranosyl)
cyclohepta[b] pyrrol-8(1H)-one. Tetrahedron 2012, 68,
5368–5374.
Nair, V.; Poonoth, M.; Vellalath, S.; Suresh, E.; Thirumalai, R. An
N-heterocyclic carbene-catalyzed [8 + 3] annulation of tropone
and enals via homoenolate. J. Org. Chem. 2006, 71,
8964–8965.
Penning, T. D.; Khilevich, A.; Chen, B. B.; Russell, M. A.; Boys, M. L.;
Wang, Y.; Duffin, T.; Engleman, V. W.; Finn, M. B.; Freeman,
S. K.; et al. Synthesis of pyrazoles and isoxazoles as potent
αvβ3 receptor antagonists. Bioorg. Med. Chem. Lett. 2006, 16,
3156–3161.
Seephonkai, P.; Isaka, M.; Kittakoop, P.; Trakulnaleamsai, S.;
Rattanajak, R.; Tanticharoen, M.; Thebtaranonth, Y. A new
tropolone from the insect pathogenic fungus Cordyceps sp.
BCC 1681. J. Antibiot. 2001, 54, 751–752.
Isakovic, L.; Ashenhurst, J. A.; Gleason, J. L. Application of Lewis
acid catalyzed tropone [6+4] cycloadditions to the synthesis of
the core of CP-225,917. Org. Lett. 2001, 3, 4189–4192.
Li, Y.; Gao, W. T. Synthesis of 5,7-dibromotropono[c]pyrazole
derivatives. Heterocycles 2010, 81, 2617–2623.
Li, Y.; Chang, M. Q.; Sun, M. C.; Li, W.; Gao, W. T. Synthesis of novel
bromo-substituted favone-like troponoid compounds from
oxidation cyclization of 3-cinnamoyl-5,7-dibromotropolones
using I2/DMSO/H2SO4 system. Chin. J. Chem. 2009, 27,
2073–2078.
Li, Y.; Li, F.; Gao, W. T. Novel synthesis of 1,4-phenylene bridged
bis-heterocyclic tropone compounds. Heterocycles 2012a, 85,
911–917.
Shaaban, M. R. Microwave-assisted synthesis of fused heterocycles
incorporating trifluoromethyl moiety. J. Fluorine Chem. 2008,
129, 1156–1161.
Sloop, J. C.; Bumgardner, C. L.; Loehle, W. D. Synthesis of
fluorinated heterocycles. J. Fluorine Chem. 2002, 118,
135–147.
Wahlström, N.; Stensland, B.; Bergman, J. Synthesis of the marine
alkaloid caulersin. Tetrahedron 2004, 60, 2147–2153.
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