Synthesis of novel dendrimers containing pyrimidine units

Article abstract of DOI:10.1016/S0040-4020(03)00462-9

A novel convergent approach to dendritic macromolecules is described in which 4,6-dichloro-2-(4-methoxyphenyl)-pyrimidine is used as the building block. The nucleophilic aromatic substitution reaction at this AB₂-monomer was used as the key step in the propagation of the dendrons. Different core reagents were used to form the dendrimers, including a 5,15-bis(pyrimidyl)porphyrin core. Fourth-generation dendrons and third-generation dendrimers could be synthesized. The presented dendrimers are promising candidates to be used in applications where a more rigid structure and a larger resistance towards the applied conditions is required.

Full text of DOI:10.1016/S0040-4020(03)00462-9

Tetrahedron 59 (2003) 3937–3943
Synthesis of novel dendrimers containing pyrimidine units
Wouter Maes,a David B. Amabilinob and Wim Dehaena
,
*
aDepartment of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium
`
Institut de Ciencia de Materials de Barcelona (CSIC), 08193 Bellaterra, Spain
b
Received 11 October 2002; revised 23 December 2002; accepted 10 January 2003
Abstract—A novel convergent approach to dendritic macromolecules is described in which 4,6-dichloro-2-(4-methoxyphenyl)-pyrimidine
is used as the building block. The nucleophilic aromatic substitution reaction at this AB2-monomer was used as the key step in the
propagation of the dendrons. Different core reagents were used to form the dendrimers, including a 5,15-bis(pyrimidyl)porphyrin core.
Fourth-generation dendrons and third-generation dendrimers could be synthesized. The presented dendrimers are promising candidates to be
used in applications where a more rigid structure and a larger resistance towards the applied conditions is required. q 2003 Elsevier Science
Ltd. All rights reserved.
1. Introduction
of the poor reactivity of the system towards NAS. The
triazine monomer, however, was very reactive towards this
substitution and dendrimers until the third generation could
easily be synthesized. Unfortunately, the triazine system
was so reactive that the deprotecting step (cleavage of a
methylarylether with boron tribromide) caused some extent
of destructive fragmentation in the dendrimer structure,
resulting in a difficult separation of the dendrons of different
generations. Moreover the triazine dendrons also possess a
high reactivity towards all kinds of nucleophiles, such as
water and methanol, therefore demanding extreme caution
when handling this system and limiting its applicability.
The increasing need for highly specialized materials with
new and improved properties, useful in different techno-
logical applications, creates a demand for new macro-
molecules with well controlled architectures. A class of
products that can supply a possible solution to this demand
are the monodisperse dendrimers.1 These relatively novel
macromolecules differ from the classical, linear polymers
by their perfectly branched structure. The synthesis can
occur through a divergent2 or a convergent3 approach to
different sizes or ‘generations’. Due to the large structural
variation that is possible, dendrimers can find application as
synthetic models for biological structures, as exo- and endo-
receptors, as new catalysts, as drug carriers, as unimolecular
micelles and in new biosensors.1
Because of these earlier difficulties we searched for a system
with an intermediate reactivity in order to build up larger
structures. From earlier work on porphyrins,8,9 it is known
that the NAS on 4,6-dichloropyrimidines is possible under
relatively mild conditions (K2CO3 in DMF at 608C for
phenolate substitution). Therefore, a new monomer
suggested for the synthesis of dendrimers through the
NAS approach is the pyrimidine monomer 4,6-dichloro-2-
(4-methoxyphenyl)-pyrimidine 1.
In the synthesis of dendrimers, it is crucial to find reactions
with a large effectivity to reduce the probability of defects in
the large structure and to simplify purification. Recently, we
started to use the nucleophilic aromatic substitution (NAS)
of halides with phenolates as a new convergent strategy
towards dendrimers.4–7 To make this substitution success-
ful it is necessary to have an electron poor (e.g.
heterocyclic) system in the ortho- or para-position of the
aryl halide, but it is even better to place the halide directly
on the heterocyclic structure. In our recent research we
successfully synthesized dendrimers consisting of 1,3,4-
oxadiazoles6 and 1,3,5-triazines7 as heterocyclic building
blocks using this approach. The synthesis of the oxadiazole
dendrimers was restricted to the second generation because
2. Results
2.1. Monomer synthesis
A heterocyclic system with the appropiate AB2-symmetry
that is well-suited for dendrimer construction is 4,6-di-
chloro-2-(4-methoxyphenyl)-pyrimidine 1 (Scheme 1). This
monomer can be synthesized according to a literature
method10 starting from 4-methoxybenzonitrile by conver-
sion into the benzamidine, which can be condensed with
diethyl malonate to the hydroxypyrimidone. Chlorination
then gives the desired monomer 1.
Keywords: dendrimer synthesis; nucleophilic aromatic substitution;
pyrimidine; porphyrin.
*
Corresponding author. Tel.: þ32-16-327439; fax: þ32-16-327990;
e-mail: wim.dehaen@chem.kuleuven.ac.be
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00462-9

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W. Maes et al. / Tetrahedron 59 (2003) 3937–3943
Scheme 1. Dendron synthesis.
2.2. Dendron synthesis—propagation of the dendrons
boron tribromide. Reiteration of the NAS with the
deprotected first generation dendron 4 and the monomer 1
gave the second generation dendron 5. This sequence could
be repeated as far as the fourth generation dendrons
(Scheme 1).
After the synthesis of the monomer, we constructed the
dendrimers using a convergent method. As a consequence of
the electron poor haloaryl functions of this heterocyclic
building block, NAS was made possible. We intended to use
this reaction as the key reaction for the synthesis of our
dendrimers.
2.3. Dendrimer synthesis
2.3.1. 1,3,5-Benzenetricarbonyl trichloride as core
reagent. The convergent approach for dendrimer synthesis
implies that the synthesized dendrons are attached in the
final step to a central core. In our case, any core molecule
that can be coupled with a phenol functionality can be
applied. An example of such a core is 1,3,5-benzenetri-
carbonyl trichloride 11. Using this core, dendrimers until the
third generation were synthesized easily and in high yields
using mild conditions (triethylamine as base in dichloro-
methane at room temperature). Scheme 2 gives an example
of a third generation dendrimer constructed in this way.
Attempts to prepare the fourth generation dendrimer failed,
probably because of the increased steric hindrance around
the focal group of the G4-dendron 10.
The dendron propagation was started with the substitution
of the two chlorine functions by a phenolate with the desired
peripheral groups. These peripheral groups have a major
influence on the final properties of the dendron or
dendrimer. Initially we chose to insert functionalities
which would give the dendrimers good solubility in order
to be able to perform a complete characterization of the
structure by 1H and 13C NMR spectroscopy as well as mass
spectrometry. Therefore, the compound we used was
3,5-bis-(t-butyl)phenol 2, which is commercially available
at low cost, so we reacted this phenol with monomer 1 to
obtain a first generation dendron 3 (Scheme 1), but
theoretically all compounds bearing a phenol moiety may
be insertable as peripheral groups. The ideal circumstances
for the NAS were investigated (different base–solvent
systems) and the best results were obtained with anhydrous
potassium carbonate base in acetonitrile at reflux.
2.3.2. Synthesis of novel porphyrin dendrimers. Por-
phyrins have already been applied as central building
blocks (cores) in dendrimer chemistry. Inoue et al. described
´
a beautiful example where eight fourth generation Frechet-
The obtained first generation dendron 3 could be activated
again for a second substitution by a deprotecting step using
type dendrons3 were connected to a central porphyrin
core.11 It has been suggested that dendritic porphyrins could

W. Maes et al. / Tetrahedron 59 (2003) 3937–3943
3939
Scheme 2. G3-dendrimer with 1,3,5-benzenetricarbonyl trichloride 11 as core reagent.
act as model systems for natural electron transfer hemo-
proteins like cytochrome C or hemoglobin.12,13
analogous reaction with our dendrons. In this way porphyrin
dendrimers until the third generation were synthesized in
relatively good yields (70–80%). An example of such a
dendrimer is given in Scheme 3. This second-generation
dendrimer could be formed from the G2-dendron 6 and 12 as
core reagent.
Because of their large size and the possibility of host–guest
interactions, porphyrins represent attractive cores for the
design of dendritic sensors and catalysts. High valent
metalloporphyrins have been employed as catalysts for
the oxidation of organic substrates.14 The introduction of
bulky dendritic polymers at the peripheral positions of
a metal porphyrin results in steric protection of the
metal center and can provide regio- and shape-selective
catalysis.15
All compounds synthesized were fully characterized using
NMR spectroscopy (1H and 13C) and mass spectrometry
(CI, Electrospray and MALDI-TOF). The 1H NMR spectra
of the different generation dendrons clearly show the signals
corresponding with the different monomer layers and the
integration indicates which generation is involved. How-
ever, the signals in the 1H NMR spectrum of the
G3-porphyrin dendrimer were broadened and therefore the
extent of substitution on the porphyrin core could not be
established unambiguously by integration. This broadening
may be caused by restricted movement of the dendron
arms. The uncertainty about the degree of substitution
was confirmed by the MALDI-TOF mass spectrum of this
G3-porphyrin dendrimer. Although the spectrum gives a
proof of the existence of the fully substituted porphyrin
dendrimer, there is also a significant peak corresponding to
the dendrimer lacking one dendron. It is not clear if this
peak is originating from the triple substituted porphyrin
dendrimer or it is generated by fragmentation during
acquisition of the spectrum. The reported 13C NMR data
of the (higher generation) dendrimers do not include all
carbon atoms because the abundance of some (core) signals
was too low. Since the detection limit of our electrospray
ionization (ESI) mass spectrometer was m/e¼4000, the
higher generation dendrons and dendrimers were identified
by their double and triple charged ions or by MALDI-TOF
spectra. The UV-absorption spectra of the different
generation porphyrin dendrimers show the intense absorp-
tion peak of the dendrons (around 285 nm) and the different
porphyrin bands (Soret-band and Q-bands).
Porphyrins and metalloporphyrins are useful photophysical
probes for evaluating the properties of the dendritic
structure due to their sensitivity to the type and the position
of the substitution as well as the presence of neighboring
chromophores.16 Several studies investigating dendrimers
having a porphyrin or metalloporphyrin core functionality
have been reported.11,17–22 Recently, De Schryver et al.
have undertaken a study to correlate the molecular structure
of such compounds with their hydrodynamic and photo-
physical properties in solution.23
A porphyrin molecule that can be used as a dendrimer core
is 5,15-bis(pyrimidyl)porphyrin 12.8 The synthesis of this
A2B2-porphyrin was performed by a McDonald-conden-
sation of mesityldipyrromethane24 with 4,6-dichloro-
pyrimidin-5-carbaldehyde,25 which can be formed from
4,6-dihydroxypyrimidine under Vilsmeier conditions
(DMF, POCl3).
As mentioned earlier, NAS reactions on this porphyrin were
already applied with a large variety of alcoholates and
phenolates.9 For the phenolates this substitution could be
performed under soft conditions (K2CO3, DMF, 608C) and
in high yields (60% and more) so we tried to do an

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W. Maes et al. / Tetrahedron 59 (2003) 3937–3943
Scheme 3. The second generation porphyrin dendrimer.
3. Discussion
4,6-dichloro-2-(4-methoxyphenyl)-pyrimidine 1 as AB2-
monomer and different cores, including a bis(pyrimidyl)-
porphyrin core 12, have been employed to prepare the
pyrimidine dendrimers. At this moment we can routinely
prepare third generation dendrimers and fourth generation
dendrons. The presented dendrimer system provides a new,
promising, rigid dendrimer backbone for various appli-
cations. It therefore presents an alternative to commonly
used dendrimers, containing aliphatic amides or amines,2 or
benzyl ether3 linkages.
The dendrimers presented are promising candidates for use
in several applications. First of all, dendrimers with a range
of functional groups (and chromophores) at the periphery
are easily accessible just by altering the phenol moiety used
to form the first generation dendron (Scheme 1). Any
compound bearing a phenol functionality can (theoretically)
easily be introduced. Since the dendrimers are built in a
convergent way, the core functionality can also be adapted
according to the application needs.
The dendrimers in this project are relatively rigid which
could create larger cavities and thus allow the inclusion of
larger guests. Moreover, the large number of heteroatoms
5. Experimental
could also enable strong complexation. Many of the
3
dendrimers synthesized so far (ex. the Frechet dendrimers )
5.1. Materials and methods
´
are quite unstable in conditions of heat, acids, bases,
oxidation and reduction. The stable functionalities in our
dendrimers could provide a higher resistance towards a
more reactive environment.
NMR spectra were acquired on commercial instruments
(Bruker Avance 300 MHz or Bruker AMX 400 MHz) and
chemical shifts (d) are reported in parts per million
referenced to internal residual solvent protons (1H) or the
carbon signal of deuterated solvents (13C). Mass spec-
trometry data were obtained with an HP MS apparatus
5989A (chemical ionization (CI), CH4) or a Micromass
Quattro II apparatus (ESI, solvent mixture: CH2Cl2/
MeOHþNH4OAc). MALDI-TOF mass spectra were
recorded on a KRATOS ANALYTICAL (Manchester,
UK) KOMPACT MALDI-2K-PROBE instrument in posi-
tive high (20 kV) mode, which uses a 3 ns pulse from a
nitrogen laser (l¼337 nm) at a target area of 100 mm in
diameter and pulse extracts the ions down a linear flight tube
(2 m), employing a-cyano-4-hydroxy-cinnamic acid as a
matrix. UV–Vis spectra were taken on a Perkin–Elmer
Lambda 20 spectrometer. IR spectra were obtained on a
Perkin–Elmer 1600 instrument as KBr pellets. Melting
points (not corrected) were determined using a Reichert
Thermovar apparatus.
In recent publications it has been shown that polymers
consisting of heterocyclic building blocks can be used in
organic light-emitting diodes (LEDs) because of their
electroluminescent properties.26 Since the heterocyclic
dendrimers in this project are very similar to these
polymers, they could also be used for this purpose. The
major advantage of dendrimers27 (over linear polymers) in
these organic LEDs is that the electronic and physical
properties could be optimized independently. The prepared
macromolecules are therefore candidates to be incorporated
in the construction of organic LEDs.
4. Conclusion
The NAS reaction has been used to build up dendrimers
based on pyrimidine as a heterocyclic building block.
A convergent approach to dendrimers is described with
˚
DMF was dried on molecular sieves 4 A. Other solvents
were used without further purification.

W. Maes et al. / Tetrahedron 59 (2003) 3937–3943
3941
5.2. General procedure for the synthesis of the protected
dendrons (R5CH3)
121.2, 119.4, 115.6, 113.7, 89.5 88.4, 55.3, 35.0, 31.4; MS
(ESI) m/z¼1344.0 [(Mþ)þH]; UV–Vis (CH2Cl2) lmax
(log 1)¼227 (4.692), 282 (4.959).
The Gx-dendron (3,5-bis-(t-butyl)phenol 2, 4, 6 or 8)
(2.2 equiv.) in CH3CN solution was stirred at room
temperature for 0.5 h with an excess of anhydrous K2CO3
(5.5 equiv.). After another 0.5 h of reflux, the monomer 1
(1 equiv.) was added and the mixture was refluxed for 4
days. After evaporation of the solvent, water was added and
the mixture was extracted with CH2Cl2 and dried over
MgSO4. The products were purified by column chroma-
tography (silica, eluent CH2Cl2) and obtained as white
solids.
5.3.4. G2 (R5H) 6. Rf (CH2Cl2) 0.10; 1H NMR (400 MHz,
CDCl3) d¼8.39 (d, 4H, J¼8.8 Hz), 8.00 (d, 2H, J¼8.8 Hz),
7.30 (t, 4H, J¼1.6 Hz), 7.22 (d, 4H, J¼8.8 Hz), 7.06 (d, 8H,
J¼1.6 Hz), 6.74 (d, 2H, J¼8.8 Hz), 6.15 (s, 1H), 5.98 (s,
2H), 5.53 (s(br), 1H), 1.32 (s, 72H); 13C NMR (100 MHz,
CDCl3) d¼172.4, 171.3, 164.0, 163.7, 158.6, 155.3, 152.7,
152.2, 133.9, 130.5, 130.0, 129.2, 121.2, 119.4, 115.6,
115.3, 89.5, 88.5, 35.0, 31.4; MS (ESI) m/z¼1329.6
[(Mþ)þH]; UV–Vis (CH2Cl2) lmax (log 1)¼226 (4.888),
282 (4.947).
5.3. General procedure for the synthesis of the
deprotected dendrons (R5H)
5.3.5. G3 (R5CH3) 7. Rf (CH2Cl2) 0.75; 1H NMR
(400 MHz, CDCl3) d¼8.41 (d, 8H, J¼8.8 Hz), 8.21 (d,
4H, J¼8.8 Hz), 8.04 (d, 2H, J¼8.8 Hz), 7.28 (t, 8H, J¼
1.6 Hz), 7.24 (d, 8H, J¼8.8 Hz), 7.17 (d, 4H, J¼8.8 Hz),
7.05 (d, 16H, J¼1.6 Hz), 6.81 (d, 2H, J¼8.8 Hz), 6.20 (s,
2H), 6.10 (s, 1H), 5.96 (s, 4H), 3.80 (s, 3H), 1.30 (s, 144H);
13C NMR (100 MHz, CDCl3) d¼172.3, 171.5, 171.2, 164.1,
163.6, 163.5, 162.2, 155.3, 155.1, 152.6, 152.1, 134.1,
133.4, 130.2, 130.1, 129.9, 128.9, 121.4, 121.2, 119.4,
115.6, 113.6, 90.1, 89.2, 88.5, 55.2, 35.0, 31.7; MS (ESI)
m/z¼2840.6 [(Mþ)þH], 1421.2 [(M2þ)þH]; UV–Vis
(CH2Cl2) lmax (log 1)¼230 (4.980), 284 (5.260).
To a solution of the protected Gx-dendron 3, 5, 7 or 9
(1 equiv.) in CH2Cl2 an excess of BBr3 (1 M in CH2Cl2,
5 equiv./generation) was added at 2788C under dry
conditions and then the mixture was placed in the freezer
(2188C). After 4 days of reaction at 2188C, ice water was
added. After separation of the organic layer, the aqueous
phase was extracted with CH2Cl2. The organic layers were
collected, dried over MgSO4 and evaporated in vacuum.
The products were purified by column chromatography
(silica, eluent CH2Cl2) and obtained as white solids.
5.3.1. G1 (R5CH3) 3. Rf (CH2Cl2) 0.75. Mp 194–1978C;
1H NMR (300 MHz, CDCl3) d¼8.28 (d, 2H, J¼8.8 Hz),
7.28 (t, 2H, J¼1.6 Hz), 7.04 (d, 4H, J¼1.6 Hz), 6.87 (d, 2H,
J¼8.8 Hz), 5.88 (s, 1H), 3.84 (s, 3H), 1.31 (s, 36H); 13C
NMR (75 MHz, CDCl3) d¼172.2, 164.2, 162.1, 152.6,
152.2, 130.2, 129.4, 119.3, 115.7, 113.5, 87.6, 55.3, 35.0,
31.4; MS (CI) m/z¼595 [MHþ, 100], 579 [M2CH3, 12]; IR
(KBr) nmax¼3431.9, 3073.6, 2961.5, 2870.0, 1654.3,
1567.5, 1423.9, 1367.4, 1297.5, 1263.5, 1198.9, 1149.1,
1033.6, 973.4, 871.7, 818.1, 784.0, 705.0, 589.9; UV–Vis
(CH2Cl2) lmax (log 1)¼227 (4.427), 292 (4.462). Anal.
calcd for C39H50N2O3: C, 78.75%; H, 8.47%; N, 4.71%.
Found: C, 78.65%; H, 8.58%; N, 4.59%.
5.3.6. G3 (R5H) 8. Rf (CH2Cl2) 0.15; 1H NMR (400 MHz,
CDCl3) d¼8.42 (d, 8H, J¼8.8 Hz), 8.20 (d, 4H, J¼8.8 Hz),
8.00 (d, 2H, J¼8.8 Hz), 7.28 (t, 8H, J¼1.6 Hz), 7.25 (d, 8H,
J¼8.8 Hz), 7.18 (d, 4H, J¼8.8 Hz), 7.03 (d, 16H, J¼
1.6 Hz), 6.76 (d, 2H, J¼8.8 Hz), 6.21 (s, 2H), 6.11 (s, 1H),
5.96 (s, 4H), 5.44 (s(br), 1H), 1.30 (s, 144H); 13C NMR
(100 MHz, CDCl3) d¼172.3, 171.5, 171.2, 164.0, 163.6,
163.6, 158.5, 155.3, 155.2, 152.6, 152.2, 134.1, 133.5,
130.5, 130.1, 129.9, 129.1, 121.4, 121.2, 119.4, 115.6,
115.2, 90.1, 89.2, 88.5, 35.0, 31.4; MS (ESI) m/z¼2827.7
[(Mþ)þH], 1415.0 [(M2þ)þH]; UV–Vis (CH2Cl2) lmax
(log 1)¼225 (5.213), 283 (5.185).
5.3.7. G4 (R5CH3) 9. Rf (CH2Cl2) 0.80; 1H NMR
(400 MHz, CDCl3) d¼8.40 (d, 16H, J¼8.8 Hz), 8.23 (d,
8H, J¼8.8 Hz), 8.23 (d, 4H, J¼8.8 Hz), 7.99 (d, 2H, J¼
8.8 Hz), 7.28 (t, 16H, J¼1.6 Hz), 7.23 (d, 16H, J¼8.8 Hz),
7.19 (d, 8H, J¼8.8 Hz), 7.19 (d, 4H, J¼8.8 Hz), 7.04 (d,
32H, J¼1.6 Hz), 6.75 (d, 2H, J¼8.8 Hz), 6.18 (s, 4H), 6.16
(s, 1H), 6.10 (s, 2H), 5.97 (s, 8H), 3.72 (s, 3H), 1.30 (s,
288H); 13C NMR (100 MHz, CDCl3) d¼172.3, 171.6,
171.1, 164.0, 163.9, 163.5, 162.1, 155.4, 155.2, 155.1,
152.6, 152.2, 134.1, 133.8, 133.3, 132.5, 130.9, 130.1,
130.0, 129.0, 128.8, 121.4, 121.3, 121.2, 119.4, 115.7,
113.7, 90.1, 89.6, 88.6, 55.2, 35.0, 31.4; MS (ESI) m/
z¼2918.0 [(M2þ)þH], 1945.9 [(M3þ)þH]; UV–Vis
(CH2Cl2) lmax (log 1)¼226 (5.412), 283 (5.503).
1
5.3.2. G1 (R5H) 4. Rf (CH2Cl2) 0.15. Mp 95–97 8C; H
NMR (400 MHz, CDCl3) d¼8.23 (d, 2H, J¼8.8 Hz), 7.28
(t, 2H, J¼1.6 Hz), 7.03 (d, 4H, J¼1.6 Hz), 6.80 (d, 2H,
J¼8.8 Hz), 5.88 (s, 1H), 5.18 (s(br), 1H), 1.31 (s, 36H); 13C
NMR (100 MHz, CDCl3) d¼172.2, 164.1, 158.3, 152.6,
152.2, 130.6, 129.7, 119.3, 115.7, 115.1, 87.6, 35.0, 31.4;
MS (CI) m/z¼581 [MHþ, 100], 565 [M2CH3, 13]; IR
(KBr) nmax¼3413.7, 2961.5, 2869.9, 2364.4, 1555.6,
1372.3, 1292.8, 1248.5, 1198.3, 1146.1, 1036.7, 972.1,
871.6, 822.4, 705.2; UV–Vis (CH2Cl2) lmax (log 1)¼224
(4.492), 287 (4.371). Anal. calcd for C38H48N2O3: C,
78.58%; H, 8.33%; N, 4.82%. Found: C, 77.93%; H, 8.32%;
N, 4.65%.
5.3.3. G2 (R5CH3) 5. Rf (CH2Cl2) 0.70; 1H NMR
(400 MHz, CDCl3) d¼8.40 (d, 4H, J¼8.8 Hz), 8.06 (d,
2H, J¼8.8 Hz), 7.29 (t, 4H, J¼1.6 Hz), 7.23 (d, 4H, J¼
8.8 Hz), 7.06 (d, 8H, J¼1.6 Hz), 6.83 (d, 2H, J¼8.8 Hz),
6.14 (s, 1H), 5.98 (s, 2H), 3.81 (s, 3H), 1.32 (s, 72H); 13C
NMR (100 MHz, CDCl3) d¼172.3, 171.3, 163.9, 163.6,
162.2, 155.2, 152.6, 152.1, 133.8, 130.1, 130.0, 129.0,
5.3.8. G4 (R5H) 10. Rf (CH2Cl2) 0.80; 1H NMR (400 MHz,
CDCl3) d¼8.44 (d, 16H, J¼8.8 Hz), 8.23 (d, 8H, J¼
8.8 Hz), 8.22 (d, 4H, J¼8.8 Hz), 7.99 (d, 2H, J¼8.8 Hz),
7.30 (t, 16H, J¼1.6 Hz), 7.27 (d, 16H, J¼8.8 Hz), 7.20 (d,
12H, J¼8.8 Hz), 7.07 (d, 32H, J¼1.6 Hz), 6.83 (d, 2H,
J¼8.8 Hz), 6.26 (s, 4H), 6.19 (s, 1H), 6.19 (s, 2H), 6.01 (s,
8H), 1.32 (s, 288H); 13C NMR (100 MHz, CDCl3) d¼172.3,

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W. Maes et al. / Tetrahedron 59 (2003) 3937–3943
171.5, 170.8, 164.0, 163.8, 163.6, 163.4, 155.5, 155.3,
155.2, 152.6, 152.2, 134.1, 134.0, 133.7, 133.0, 130.0,
129.9, 128.8, 121.4, 121.3, 119.4, 115.6, 115.3, 90.2, 89.8,
88.5, 35.0, 31.4; MS (ESI) m/z¼2912.0 [(M2þ)þH], 1941.7
[(M3þ)þH]; MALDI m/z¼5861.6; UV–Vis (CH2Cl2) lmax
(log 1)¼228 (5.264), 282 (5.542).
5.5.1. G1-dendrimer. Rf (CH2Cl2) 0.80; 1H NMR
(400 MHz, CDCl3) d¼8.97 (d, 4H, J¼4.7 Hz), 8.81 (s,
2H), 8.77 (d, 4H, J¼4.7 Hz), 8.18 (d, 8H, J¼8.8 Hz), 7.31
(s, 4H), 7.24 (t, 8H, J¼1.6 Hz), 6.97 (d, 8H, J¼8.8 Hz), 6.96
(d, 16H, J¼1.6 Hz), 5.86 (s, 4H), 2.67 (s, 6H), 1.85 (s, 12H),
1.26 (s, 144H), 22.45 (s(br), 2H); 13C NMR (100 MHz,
CDCl3) d¼172.1, 169.8, 163.4, 157.8, 155.1, 152.5, 152.1,
139.5, 138.0, 137.8, 133.9, 129.8, 127.8, 121.1, 119.3,
118.7, 115.7, 108.7, 106.0, 88.4, 35.0, 31.4, 21.9, 21.5; IR
(KBr) nmax¼3440.7, 2960.6, 2869.1, 1554.4, 1506.3,
1420.1, 1373.1, 1294.3, 1200.8, 1147.9, 1039.7, 970.2,
867.8, 705.4; MS (ESI) m/z¼3015.9 [(Mþ)þH], 1508.2
[(M2þ)þH]; UV–Vis (CH2Cl2) lmax (log 1)¼227 (5.115),
278 (5.124), 420 (5.582), 515 (4.380), 549 (3.923), 591
(3.834), 648 (3.569).
5.4. General procedure for the synthesis of dendrimers
with 1,3,5-benzenetricarbonyl trichloride core 11
To a solution of the Gx-dendron 4, 6 or 8 (3.3 equiv.) in
CH2Cl2, Et3N (3.6 equiv.) was added and the mixture was
stirred for 0.5 h at room temperature. 1,3,5-Benzenetri-
carbonyl trichloride (1 equiv.) was added to this solution
and the mixture was stirred for another 6 h and then
evaporated in vacuum. After purification through column
chromatography (silica, eluent CH2Cl2) the title compounds
were obtained.
5.5.2. G2-dendrimer. Rf (CH2Cl2) 0.75; 1H NMR
(400 MHz, CDCl3) d¼8.93 (d, 4H, J¼4.7 Hz), 8.74 (d,
4H, J¼4.7 Hz), 8.74 (s, 2H), 8.33 (d, 16H, J¼8.8 Hz), 8.03
(d, 8H, J¼8.8 Hz), 7.27 (t, 16H, J¼1.6 Hz), 7.21 (s, 4H),
7.14 (d, 16H, J¼8.8 Hz), 7.04 (d, 32H, J¼1.6 Hz), 6.94 (d,
8H, J¼8.8 Hz), 6.06 (s, 4H), 5.98 (s, 8H), 2.54 (s, 6H), 1.80
(s, 12H), 1.29 (s, 288H), 22.47 (s(br), 2H); 13C NMR
(100 MHz, CDCl3) d¼172.3, 171.4, 169.9, 163.5, 155.1,
152.6, 152.2, 139.4, 134.0, 130.0, 129.8, 121.5, 121.1,
119.3, 115.6, 88.6, 35.0, 31.4, 21.8, 21.4; MS (ESI) m/z¼
3004.9 [(M2þ)þH], 2004.0 [(M3þ)þH]; MALDI m/z¼
6011.4; UV–Vis (CH2Cl2) lmax (log 1)¼226 (5.410), 282
(5.479), 420 (5.638), 515 (4.334), 550 (3.860), 592 (3.784),
646 (3.546).
5.4.1. G1-dendrimer. Rf (CH2Cl2) 0.75; 1H NMR
(400 MHz, CDCl3) d¼9.22 (s, 3H), 8.41 (d, 6H, J¼
8.8 Hz), 7.30 (t, 6H, J¼1.6 Hz), 7.29 (d, 6H, J¼8.8 Hz),
7.06 (d, 12H, J¼1.6 Hz), 6.00 (s, 3H), 1.33 (s, 108H); 13C
NMR (100 MHz, CDCl3) d¼172.3, 163.3, 163.0, 152.8,
152.6, 152.2, 136.1, 135.0, 131.2, 130.0, 121.2, 119.4,
115.7, 88.6, 35.0, 31.4; MS (ESI) m/z¼1896.7 [(Mþ)þH],
948.9 [(M2þ)þH]; UV–Vis (CH2Cl2) lmax (log 1)¼226
(4.950), 271 (4.900).
5.4.2. G2-dendrimer. Rf (CH2Cl2) 0.70; 1H NMR
(400 MHz, CDCl3) d¼9.22 (s, 3H), 8.42 (d, 12H, J¼
8.8 Hz), 8.23 (d, 6H, J¼8.8 Hz), 7.29 (t, 12H, J¼1.6 Hz),
7.24 (d, 12H, J¼8.8 Hz), 7.22 (d, 6H, J¼8.8 Hz), 7.06 (d,
24H, J¼1.6 Hz), 6.15 (s, 3H), 5.98 (s, 6H), 1.32 (s, 216H);
13C NMR (100 MHz, CDCl3) d¼172.3, 171.5, 163.6, 163.4,
162.9, 155.1, 152.9, 152.6, 152.2, 136.1, 134.5, 134.1,
131.1, 130.1, 130.0, 121.5, 121.2, 119.4, 115.6, 90.3, 88.6,
35.0, 31.4; MS (ESI) m/z¼2071.1 [(M2þ)þH]; UV–Vis
(CH2Cl2) lmax (log 1)¼226 (5.318), 278 (5.365).
5.5.3. G3-dendrimer. Rf (CH2Cl2) 0.80; 1H NMR
(400 MHz, CDCl3) d¼8.96 (br), 8.73 (br), 8.43 (d), 8.21
(d), 8.01 (d), 7.27 (m), 7.08 (m), 6.77 (d), 6.22 (s), 6.11 (s),
5.97 (s), 2.57 (br), 1.81 (br), 1.31 (s), 22.45 (br); MALDI
m/z¼11998.4, 9209.6; UV–Vis (CH2Cl2) lmax (log 1)¼228
(5.597), 283 (5.787), 420 (5.537), 515 (4.217), 549 (3.803),
592 (3.738), 648 (3.550).
5.4.3. G3-dendrimer. Rf (CH2Cl2) 0.75; 1H NMR
(400 MHz, CDCl3) d¼9.20 (s, 3H), 8.39 (d, 24H, J¼
8.8 Hz), 8.28 (d, 6H, J¼8.8 Hz), 8.22 (d, 12H, J¼8.8 Hz),
7.25 (t, 24H, J¼1.6 Hz), 7.22 (d, 30H, J¼8.8 Hz), 7.17 (d,
12H, J¼8.8 Hz), 7.03 (d, 48H, J¼1.6 Hz), 6.18 (s, 6H), 6.06
(s, 3H), 5.96 (s, 12H), 1.28 (s, 432H); 13C NMR (100 MHz,
CDCl3) d¼172.3, 171.6, 171.5, 163.5, 163.4, 155.2, 155.1,
152.6, 152.2, 134.1, 133.8, 130.8, 130.2, 130.1, 121.3,
121.2, 119.3, 115.6, 90.1, 88.6, 35.0, 31.4; MALDI m/z¼
8636.4; UV–Vis (CH2Cl2) lmax (log 1)¼226 (5.626), 280
(5.659).
Acknowledgements
We thank the Katholieke Universiteit Leuven, the F. W. O.
Vlaanderen and the Ministerie voor Wetenschapsbeleid for
their continuing support.
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