Synthesis of a halo-methylphenylene periphery-functionalized triazine-based dendritic molecule with a 3,3′-dimethyl-biphenyl linker using tris(halo-methylphenylene)triazines as building blocks

Article abstract of DOI:10.1016/j.tetlet.2009.02.011

A tris(bromo-methylphenylene)triazine and its corresponding phosphine oxide derivative have been synthesized; the latter compound was found to be a potent ligand for the hydroformylation reaction. Suzuki coupling of the mono-pinacolboronate derivative of

Full text of DOI:10.1016/j.tetlet.2009.02.011

Tetrahedron Letters 50 (2009) 1851–1854
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Tetrahedron Letters
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Synthesis of a halo-methylphenylene periphery-functionalized
triazine-based dendritic molecule with a 3,30-dimethyl-biphenyl linker
using tris(halo-methylphenylene)triazines as building blocks
a
b
b
c
Ioannis D. Kostas a, , Fotini J. Andreadaki , Elaine A. Medlycott , Garry S. Hanan , Eric Monflier
*
a National Hellenic Research Foundation, Institute of Organic and Pharmaceutical Chemistry, Vas. Constantinou 48, 116 35 Athens, Greece
b Département de Chimie, Université de Montréal, 2900 Edouard-Montpetit, Pavillon Roger-Gaudry, Montréal, Que., Canada H3T-1J4
c Unité de Catalyse et de Chimie du Solide-UMR 8181, Université d’Artois, rue Jean Souvraz, Lens Cédex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
A tris(bromo-methylphenylene)triazine and its corresponding phosphine oxide derivative have been syn-
thesized; the latter compound was found to be a potent ligand for the hydroformylation reaction. Suzuki
coupling of the mono-pinacolboronate derivative of the former compound with a tris(iodo-methylphen-
ylene)triazine was possible at two of the three iodine atoms, yielding a bromo- and iodo-methylphenyl-
ene periphery-functionalized triazine-based dendritic molecule with a 3,30-dimethyl-biphenyl linker.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 15 December 2008
Revised 26 January 2009
Accepted 4 February 2009
Available online 8 February 2009
Keywords:
Dendrimer
Triazine
Cyclotrimerization
Suzuki coupling
Phosphine oxide
Hydroformylation
Dendrimers and dendritic molecules are the subject of signifi-
cant academic and industrial interest.1,2 Compounds containing
s-triazine units and dendrimers based on triazine have received a
remarkable amount of attention owing to their potential applica-
tions3 and have shown molecular recognition and self-assembly
properties.4 They are of interest for their electroluminescent and
electrochemical properties due to the role of the electron-deficient
triazine unit as an electron transport component5 and also for their
liquid-crystalline and nonlinear optical properties.5b,6 Triazine
dendritic structures, and in particular those based on melamine,
have shown very promising results for drug delivery and can
sequester a range of hydrophobic guests effectively, including can-
didate anticancer drugs, and with the absence of toxicity.7
Triazine dendrimers can be synthesized by various routes based
on divergent and convergent methods. The most common methods
are cycloaddition reactions to form the triazine ring, cyclotrimer-
ization of organic cyanates and nucleophilic aromatic substitution
of cyanuric chloride.1–8 In the great majority of triazine dendritic
molecules, the triazine rings are linked by nitrogen-containing
spacers such as amino groups. In this Letter, we report the synthe-
sis of a halo-methylphenylene periphery-functionalized triazine-
based dendritic molecule with a 3,30-dimethyl-biphenyl linker, by
the use of tris(halo-methylphenylene)triazines as building blocks.
We used compound 2 with a methyl substituent instead of the ana-
logue without the methyl group due to its higher solubility in or-
ganic solvents. Indeed, we found that in boiling toluene, the
solubility of 2 was 2.8 g/100 mL compared to 0.8 g/100 mL for
the analogue without methyl substituents.
The synthesis of the title dendritic molecule was first attempted
by cyclotrimerization of the corresponding nitrile as shown in
Scheme 1. The tris(bromoaryl)triazine 2 was prepared in high yield
by cyclotrimerization of 4-bromo-3-methylbenzonitrile (1) with
neat trifluoromethanesulfonic acid. The procedure was analogous
to that previously described for the cyclotrimerization of 4-bro-
mobenzonitrile.9 The CH3 resonance in 2 was observed as one sig-
nal in the 1H and 13C NMR spectra at d 2.57 and 23.17, respectively,
indicating the equivalence of the three CH3 groups. Compound 2
could be regarded as the 0th generation of a symmetric halo-meth-
ylphenylene periphery-functionalized triazine dendrimer. In the
next step, cyanation of 2 was achieved by the use of Pd2(dba)3,
dppf and Zn as the catalyst and Zn(CN)2 as the cyanide source, in
accordance with a known protocol for the cyanation of aryl chlo-
rides.10 Although the ratio of Br/CN was kept at 2.5:1, cyanation
was not selective, leading to unreacted 2 (32%) and a mixture of
mono- and dicyanated derivatives 3 and 4, in yields of 30% and
* Corresponding author. Tel.: +30 210 7273878; fax: +30 210 7273831.
E-mail address: ikostas@eie.gr (I.D. Kostas).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.02.011

1852
I. D. Kostas et al. / Tetrahedron Letters 50 (2009) 1851–1854
CN
CN
Br
Br
CF3SO3H
Zn(CN)2, Zn
N
N
N
N
N
N
N
N
+
N
Pd2(dba)3, dppf
CN
DMA, reflux 20 h Br
Br
Br Br
CN
Br
1
2 (90%)
3 (30%)
4 (16%)
CF3SO3H
no cyclotrimerization
Scheme 1.
16%, respectively. Unfortunately, the formation of the 1st genera-
tion dendrimer by cyclotrimerization of 3, as described for 1, was
not possible, probably due to steric hindrance.
ded the dendritic molecule 8 in 79% yield. Although the ratio of B/I
was 1.3:1, coupling to only two of the three iodine atoms was
achieved, presumably due to steric hindrance. This result is in con-
trast to the full coupling of arylboronic acid dendrimer arms to
tribromobenzene14 or the coupling of 4-(2,20-dipyridylami-
no)phenylboronic acid to tris(4-bromophenyl)-1,3,5-triazine.5d
The structure of 8 was determined by spectroscopic techniques.
In the 1H NMR spectrum, the ratio of the total number of aromatic
protons to the total number of CH3 protons was 1:1, and the ratio
of the 5 ꢀ CH3 protons closest to the halogens (d 2.57) to the CH3
protons attached to the other four aromatic rings (d 2.30) was
found to be 15:12, as expected for 8. In the 13C NMR spectrum,
the CH3 resonances were present as three signals at d 29.70,
23.14 and 20.06, which were assigned to the CH3 groups closest
to iodine, bromine and the internal CH3 groups, respectively.
The halogen atoms in compounds 2 and 8 can serve for further
functionalization such as phosphorous-functionalized dendritic
molecules, and thus, these reagents may be regarded as potent li-
gands for transition-metal homogeneous catalysis.15 For example,
we synthesized the phosphine oxide derivative 9 as shown in
Scheme 3.16 Replacement of the bromine atoms by the diphenyl-
phosphine oxide group was achieved by reaction of 2 with potas-
sium diphenylphosphide and subsequent oxidation of the
resulting tris(triarylphosphine)triazine by hydrogen peroxide. The
presence of only one singlet at d 31.84 in the 31P NMR spectrum
of 9 clearly indicated the equivalence of the three phosphorous
The formation of the 1st generation dendrimer was then at-
tempted via a Suzuki coupling of an aryl halide and a pinacolboro-
nate in a mixture of an organic solvent and an aqueous solution of
Na2CO3 using Pd(PPh3)4 as the catalyst (Scheme 2), in accordance
with the synthesis of hyperbranched polyphenylene by the homo-
coupling of (3,5-dibromophenyl)boronic acid.11 The pinacolboro-
nate 5 was synthesized by the nickel-catalyzed reaction of 2 with
pinacolborane using Ni(dppp)Cl2 in refluxing PhCH3/NEt3, as previ-
ously described for the synthesis of pinacolboronates by reaction of
di- or tribromobenzene with pinacolborane.12 A ratio of Br/B of
2.3:1 afforded 5 in 21% yield after two days refluxing. Palladium-
catalysis
using
Pd2(dba)3/2-dicyclohexylphosphino-20-(N,N-
dimethylamino)biphenyl was also attempted, however, without
any improvement in the yield. In order to avoid homocoupling of
5 to give a mixture of hyperbranched polymers, the Suzuki cou-
pling was performed between 5 and tris(iodoaryl)triazine 7 instead
of the bromo-analogue 2, since it is known that the reaction of
arylboronic acid (or ester) proceeds at a higher rate with iodoare-
nes than with bromoarenes.13 The tris(iodoaryl)triazine 7 was
synthesized as described for 2, by cyclotrimerization of 4-iodo-3-
methylbenzonitrile (6), prepared via bromine–lithium exchange
in 1, and further treatment with iodine. Suzuki coupling of the
boronate 5 with the iodide 7 using Pd(PPh3)4 as the catalyst affor-
O
N
O
N
B
N
O
O
Br
Br
B
H
N
2
N
N
N
N
Ni(dppp)Cl2
PhCH3 /NEt3
reflux, 2 d
Br
Br
5 (21%)
Pd(PPh3)4, o-xylene
2M aq. Na2CO3
reflux, 3 d
I
N
I
Br
I
1. n-BuLi
THF
N
N
N
N
CF3SO3H
1
N
N
2. I2
CN
I
I
6 (56%)
7 (75%)
8 (79%)
Br
Scheme 2.

I. D. Kostas et al. / Tetrahedron Letters 50 (2009) 1851–1854
1853
O
Br
PPh2
1. Ph2PK/THF
N
N
N
N
N
N
2. H2O2/acetone
Br
Br
Ph2P
O
PPh2
O
2
9 (70%)
Scheme 3.
atoms. Initial investigation of 9 as a ligand in the rhodium-cata-
lyzed hydroformylation of styrene provided encouraging prelimin-
ary results, as the chemoselectivity of the reaction for aldehydes
was quantitative and the regioselectivity towards the branched
aldehyde was up to 98%.
In summary, Suzuki coupling of a pinacolboronate bis(bromo-
methylphenylene)triazine to two of the three iodine atoms was
possible with tris(iodo-methylphenylene)triazine 7, yielding a
new dendritic molecule in which the triazine rings are linked by
a 3,30-dimethyl-biphenyl spacer. The presence of the halogen
atoms on the periphery can serve for further functionalization, pro-
viding new reagents which may be useful in a wide range of den-
drimer applications.
and 125.62 (Ar), 116.21 (CN), 23.17 and 20.74 (CH3). Anal. Calcd
for C25H18Br2N4: C, 56.20; H, 3.40; N, 10.49. Found: C, 55.99; H,
3.39; N, 10.30. Compound 4: 1H NMR (300.13 MHz, CDCl3): d
8.65–8.57 (m, 5H, ArH), 8.41 (d, 3J = 7.9 Hz, 1H, ArH), 7.82 (d,
3J = 7.9 Hz, 2H, ArH), 7.75 (d, 3J = 8.6 Hz, 1H, ArH), 2.74 (s, 6H,
CH3), 2.59 (s, 3H, CH3). 13C NMR (75.47 MHz, CDCl3): d 170.65 (tria-
zine C), 142.51, 139.47, 138.72, 134.39, 132.99, 132.87, 130.90,
130.25, 129.86, 127.85, 126.62 and 124.07 (Ar), 116.53 (CN),
23.17 and 20.74 (CH3).
2-[4-(4,40,5,50-Tetramethyl-1,3,2-dioxaborolyl)]-4,6-di(4-bromo-3-
methyl-phenylene)-1,3,5-triazine (5):
A solution of 2 (7.42 g,
12.62 mmol), 4,40,5,50-tetramethyl-1,3,2-dioxaborolane (pinacolbo-
rane) (2.40 mL, 16.54 mmol), Ni(dppp)Cl2 (0.21 g, 0.39 mmol) in
toluene (300 mL) and triethylamine (7 mL) was refluxed under ar-
gon for 2 d, during which time a precipitate was formed, presum-
ably NEt3ꢁHBr. After cooling to room temperature, the mixture
was quenched with saturated aqueous NH4Cl solution (120 mL),
the organic layer was separated, diluted with dichloromethane
(200 mL) and washed with saturated aqueous NH4Cl solution
(120 mL). The combined aqueous layers were extracted with
dichloromethane (200 mL). The combined organic layers were
washed with water (120 mL) and dried over Na2SO4. After filtration,
the filtrate was passed through a pad of Celite and the solvents
were removed by evaporation. Column chromatography over silica
gel using dichloromethane/hexane (1:1) and then dichloromethane
as eluent yielded the starting material 2 (3.02 g, 41%) and 5 as a
white solid (1.68 g, 21%).17 1H NMR (300.13 MHz, CDCl3): d 8.42–
8.37 (m, 4H, ArH), 8.26 (d, 3J = 8.6 Hz, 2H, ArH), 7.91 (d,
3J = 7.3 Hz, 1H, ArH), 7.63 (d, 3J = 8.6 Hz, 2H, ArH), 2.68 (s, 3H, Ar–
CH3), 2.51 (s, 6H, Ar–CH3), 1.40 (s, 12H, C(CH3)2). 13C NMR
(75.47 MHz, CDCl3): d 171.53 and 170.72 (triazine C), 145.00,
138.11, 137.59, 135.97, 135.07, 132.54, 130.73, 129.89, 129.63,
127.63 and 125.01 (Ar), 83.70 (C(CH3)2), 24.92 (C(CH3)2), 23.11
(Ar–CH3), 22.39 (Ar–CH3). Anal. Calcd for C30H30BBr2N3O2: C,
56.73; H, 4.76; N, 6.62. Found: C, 57.01; H, 4.95; N, 6.34.
2,4,6-Tris(4-bromo-3-methyl-phenylene)-1,3,5-triazine (2): 4-
Bromo-3-methylbenzonitrile (1) (11.0 g, 56.0 mmol) was added
in small portions over 4 h to stirred trifluoromethanesulfonic acid
(18.0 mL, 203.4 mmol) under argon at 0–5 °C, and then stirring was
continued at this temperature for an additional 1 h and at room
temperature for 1 h. The resulting orange solution was allowed
to stand at room temperature overnight and then poured onto
ice, yielding a white solid. The mixture turned alkaline on addition
of 25% aqueous ammonium hydroxide, and the solid precipitate
was removed by filtration, washed several times with water and
dried under vacuum at 100 °C. The final traces of water were re-
moved by azeotropic distillation with toluene, and the product
was recrystallized from boiling toluene and dried under vacuum
at 100 °C, yielding 2 as a white solid (9.9 g, 90%).17 1H NMR
(300.13 MHz, CDCl3): d 8.54 (d, 4J = 1.8 Hz, 3H, ArH), 8.38 (dd,
3J = 8.5 Hz, 4J = 1.8 Hz, 3H, ArH), 7.72 (d, 3J = 8.5 Hz, 3H, ArH), 2.57
(s, 9H, CH3). 13C NMR (75.47 MHz, CDCl3): d 171.11 (triazine C),
138.40, 135.04, 132.77, 130.86, 130.18 and 127.76 (Ar), 23.17
(CH3). Anal. Calcd for C24H18Br3N3: C, 49.01; H, 3.08; N, 7.14.
Found: C, 48.74; H, 2.96; N, 6.92.
2,4-Bis(4-bromo-3-methyl-phenylene)-6-(4-cyano-3-methyl-phe-
nylene)-1,3,5-triazine (3) and 2-(4-bromo-3-methyl-phenylene)-4,6-
bis(4-cyano-3-methyl-phenylene)-1,3,5-triazine (4): A mixture of 2
(2.94 g, 5.00 mmol), Zn dust (0.04 g, 0.60 mmol), Zn(CN)2 (0.35 g,
3.00 mmol), Pd2(dba)3 (0.09 g, 0.10 mmol), dppf (0.11 g,
0.20 mmol) and DMA (100 mL) was heated at reflux under argon
for 20 h. After cooling to room temperature, the reaction mixture
was diluted with dichloromethane (500 mL), washed with 2 N aq
NH4OH solution (100 mL) and brine (100 mL) and dried over
Na2SO4. After filtration, the filtrate was passed through a pad of Ce-
lite and the solvents were removed by evaporation. Column chro-
matography over silica gel using mixtures of dichloromethane/
hexane (initially 1:1, then 3:1, then 5:1) and finally dichloro-
methane yielded the starting material 2 (0.94 g, 32%) and the cya-
nated products 3 (0.81 g, 30%)17 and 4 (0.39 g, 16%).17 Compound
3: 1H NMR (300.13 MHz, CDCl3): d 8.62–8.54 (m, 4H, ArH), 8.38
(d, 3J = 8.6 Hz, 2H, ArH), 7.79 (d, 3J = 7.9 Hz, 1H, ArH), 7.73 (d,
3J = 8.6 Hz, 2H, ArH), 2.72 (s, 3H, CH3), 2.57 (s, 6H, CH3). 13C NMR
(75.47 MHz, CDCl3): d 171.43 (triazine C), 142.41, 139.79, 138.56,
134.71, 132.90, 132.80, 130.90, 130.54, 130.18, 127.79, 126.56
4-Iodo-3-methylbenzonitrile (6): To a solution of 1 (5.00 g,
25.50 mmol) in THF (150 mL) under argon was added n-BuLi
(1.78 M in methylcyclohexane, 15.50 mL, 27.59 mmol) at ꢂ65 °C,
and the solution was stirred at this temperature for 2 h. Next, ex-
cess solid iodine (13.58 g, 53.50 mmol) and additional THF
(40 mL) were added, and the reaction mixture was warmed slowly
to room temperature and stirred overnight, after which an aqueous
solution of sodium thiosulfate (40.00 g, 161.17 mmol in 100 mL of
water) was added. The volatile materials were removed by evapo-
ration, the residue was extracted with dichloromethane
(2 ꢀ 200 mL), the combined organic layers were washed with
water (50 mL), dried over Na2SO4, filtered and evaporated to dry-
ness to yield a yellow–brown solid, which was recrystallized from
ethanol yielding 6 as a white solid (3.46 g, 56%), mp 73–75 °C. 1H
NMR (300.13 MHz, CDCl3): d 7.92 (d, 3J = 8.5 Hz, 1H, ArH), 7.47 (s,
1H, ArH), 7.13 (d, 3J = 7.9 Hz, 1H, ArH), 2.46 (s, 3H, CH3). 13C NMR
(75.47 MHz, CDCl3): d 143.09, 139.86, 132.25 and 130.18 (Ar),
118.28 (CN), 112.13 (Ar–C–CN), 107.25 (Ar–C–I), 28.05 (CH3).

1854
I. D. Kostas et al. / Tetrahedron Letters 50 (2009) 1851–1854
GC–MS (EI): m/z (relative intensity) 243 (M+, 100), 116 ([M–I]+, 21),
89 (17), 63 (8). Anal. Calcd for C8H6IN: C, 39.53; H, 2.49; N, 5.76.
Found: C, 39.78; H, 2.57; N, 5.53.
2,4,6-Tris(4-iodo-3-methyl-phenylene)-1,3,5-triazine (7): Reac-
tion of 6 (2.16 g, 8.89 mmol) with trifluoromethanesulfonic acid
(2.80 mL, 31.64 mmol) as described for the synthesis of 2 yielded
7 as a white solid (1.61 g, 75%).17 1H NMR (300.13 MHz, CD2Cl2):
d 8.60 (s, 3H, ArH), 8.26–8.23 (m, 3H, ArH), 8.06 (d, 3J = 8.0 Hz,
3H, ArH), 2.62 (s, 9H, CH3). Anal. Calcd for C24H18I3: C, 39.53; H,
2.49; N, 5.76. Found: C, 39.40; H, 2.24; N, 5.84.
Dendritic molecule 8: A solution of 7 (0.25 g, 0.34 mmol), 5 (0.85 g,
1.34 mmol) and Pd(PPh3)4 (0.06 g, 0.05 mmol) in o-xylene (25 mL)
and aqueous Na2CO3 (2 M, 2.60 mL, 5.20 mmol) was refluxed under
argon for 3 d. After cooling to room temperature, the mixture was
quenched with saturated aqueous NH4Cl solution (50 mL) and di-
luted with dichloromethane (300 mL). The organic layer was sepa-
rated, washed with water (50 mL) and dried over Na2SO4. After
filtration, the filtrate was passed through a pad of Celite and the sol-
vents were removed by evaporation. Column chromatography over
silica gel using dichloromethane/hexane (1:1) as eluent yielded 8 as
a white solid (0.40 g, 79%).17 1H NMR (300.13 MHz, CDCl3): d 8.74–
8.59 (m, 17H, ArH), 7.71 (m, 5H, ArH), 7.39 (m, 5H, ArH), 2.57 (s,
15H, CH3), 2.30 (s, 12H, CH3). 13C NMR (75.47 MHz, CDCl3): d
171.69 and 171.11 (triazine C), 145.52, 138.37, 136.27, 135.65,
135.26, 132.77, 130.93, 130.47, 130.12, 129.53, 127.79 and 126.56
(Ar), 29.70, 23.14 and 20.06 (CH3).
Acknowledgements
This investigation was supported by the General Secretariat of
Research and Technology of Greece and by the Université de
Montréal.
References and notes
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2,4,6-Tris(4-diphenylphosphinyl-3-methyl-phenylene)-1,3,5-triazine
(9): A solution of potassium diphenylphosphide in THF (0.5 M, 7 mL,
3.50 mmol) was added to
a white suspension of 2 (0.59 g,
1.00 mmol) in THF (15 mL) at room temperature under argon, and
then heated at reflux for 48 h. The reaction mixture was cooled to
room temperature, diluted by the addition of dichloromethane
(60 mL), washed with 10% aqueous NaOH (2 ꢀ 20 mL), then with
brine and dried over Na2SO4. The volatiles were evaporated and
the residue was evacuated at 180 °C. The remaining very viscous
oil turned to a solid on addition of ether/hexane (1:1, 10 mL), and
the solid was removed by filtration, washed with ether/hexane
and dried under vacuum at 180 °C. The solid was mixed with ace-
tone (50 mL) and 30% hydrogen peroxide (9 mL, 88.15 mmol) and
refluxed for 1 h in air. After cooling to room temperature, the vola-
tiles were evaporated under reduced pressure, the residue was dis-
solved in a minimum amount of dichloromethane, and slow
diffusion of ether afforded a solid which was then washed twice
with ether/dichloromethane (10:1) and then with ether yielding 9
(0.67 g, 70% based on 2).17 1H NMR (300.13 MHz, CDCl3): d 8.57–
8.46 (m, 6H, ArH), 7.67–7.19 (m, 33H, ArH), 2.58 (s, 9H, CH3). 13C
NMR (75.47 MHz, CDCl3): d 171.27 (triazine C), 144.00–125.56
(Ar), 21.88 (CH3). 31P NMR (121.50 MHz, CDCl3): d 31.84 (s). Anal.
Calcd for C60H48N3O3P3: C, 75.70; H, 5.08; N, 4.41. Found: C,
75.92; H, 5.03; N, 4.67.
14. Miller, T. M.; Neeman, T. X.; Zayas, R.; Bair, H. E. J. Am. Chem. Soc. 1992, 114,
1018–1025.
15. Selected reviews (a) Oosterom, G. E.; Reek, J. N. H.; Kamer, P. C. J.; van Leeuwen,
P. W. N. M. Angew. Chem., Int. Ed. 2001, 40, 1828–1849; (b) Astruc, D.; Chardac,
F. Chem. Rev. 2001, 101, 2991–3023; (c) van Heerbeek, R.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M.; Reek, J. N. H. Chem. Rev. 2002, 102, 3717–3756; (d) Méry,
D.; Astruc, D. Coord. Chem. Rev. 2006, 250, 1965–1979.
16. Phosphine oxides can be superior ligands in catalysis compared to the
phosphine analogues (a) Tolis, E. I.; Vallianatou, K. A.; Andreadaki, F. J.;
Kostas, I. D. Appl. Organomet. Chem. 2006, 20, 335–337; (b) Abu-Gnim, C.; Amer,
I. J. Chem. Soc., Chem. Commun. 1994, 115–117; (c) Abu-Gnim, C.; Amer, I. J.
Organomet. Chem. 1996, 516, 235–243; (d) Basoli, C.; Botteghi, C.; Cabras, M. A.;
Chelucci, G.; Marchetti, M. J. Organomet. Chem. 1995, 488, C20–C22.
17. The mp apparatus used has an upper limit of 200 °C. Compounds 2–5 and 7–9
did not melt below 200 °C.