Synthesis of new photoresponsive stilbene dendrons and dendrimers

Article abstract of DOI:10.1055/s-2006-926401

A new convergent synthetic route for the synthesis of functionalized photoactive dendrimers having bis-stilbenoid skeletons on planar and tetrahedral cores, endowed with methoxy/methyl group has been developed. Optical spectroscopic techniques have been u

Full text of DOI:10.1055/s-2006-926401

PAPER
1257
Synthesis of New Photoresponsive Stilbene Dendrons and Dendrimers
Synthesis of
N
e
ew Photor
e
r
sponsive
u
S
tilbene
D
e
m
ndrons and
D
endrim
a
ers l Rajakumar,* Manickam Dhanasekaran, Subramaniyan Selvam
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai, Tamil Nadu 600 025, India
E-mail: perumalrajakumar@hotmail.com
Received 5 September 2005; revised 24 November 2005
2 and 3 (Figure 1), from relatively simple starting materi-
als.
Abstract: A new convergent synthetic route for the synthesis of
functionalized photoactive dendrimers having bis-stilbenoid skele-
tons on planar and tetrahedral cores, endowed with methoxy/methyl
group has been developed. Optical spectroscopic techniques have
been used to study absorption and emission properties and isomer-
ization behavior of the stilbene dendrimers.
Our synthesis started with cheap, commercially available
5-hydroxyisophthalic acid, from which the desired dibro-
mide 6 was easily prepared by a four-step literature proce-
dure.17 This dibromide was then treated with triethyl
phosphite at 160 °C for three hours to give the diphospho-
nate ester 7 in 85% yield. The product was pure enough,
as indicated by TLC, for direct use in the subsequent
steps. Bis-stilbenes 8a,b were obtained in good yield, by
Wittig–Horner reaction between diphosphonate ester 7
with p-anisaldehyde/p-tolualdehyde using NaH as base in
THF at room temperature. The benzyl group present in
stilbenes 8a,b was successfully cleaved without affecting
the methoxy and methyl groups, using TiCl4/dioxane18 to
give bis-stilbene phenols 9a,b in 62% and 65% yields, re-
Key words: convergent, Wittig–Horner, photoluminescence
Dendrimers have become an interesting area of research
in recent times due to their unique structures and photonic
applications in numerous devices. Photoresponsive den-
drimers are attractive candidates for photonic applications
such as organic LEDs, optical power limiting devices and
nonlinear optics.1 Various dendritic systems are also
known to function as efficient light-harvesting antennae,2
sensors,3 unimolecular micelles,4 catalysts5 and potential
drug-delivery systems.6
1
spectively (Scheme 1). The characteristic H NMR reso-
nance peak of the vinylic proton of dendrons 8a,b, and
9a,b displayed a large coupling constant (J ~ 16 Hz) indi-
cating the trans-configuration in the stilbene units. The
phenolic stilbenoid skeletons 9a,b so-obtained could
serve as excellent starting material for the convergent syn-
thesis of stilbene dendrimers.
Meier and Lehman7 reported the first stilbenoid dendrim-
er, with the optical response of poly(phenylenevinylene)-8
and
binaphthyl-based
chiral
phenylenevinylene
dendrimers9 utilizing Heck and Horner–Wordsworth–
Emmons reactions subsequently reported. The 5-hydroxy-
isophthalic acid moiety has been used extensively to con-
struct the dendritic architecture, through the combination
of 3,5-aryl branching connectivity.10
OBn
OBn
X
O
ii
i
P(OEt)2
Photochemical and photophysical behavior of stilbenes
have become an important field of research due to their
potential and practical applications.11 Arai and co-
workers12 reported the first synthesis of a series of stilbene
dendrimers and studied their photoisomerization behav-
ior. The same group also reported the synthesis and pho-
tochemical behavior of a serious of water-soluble
dendrimers with carboxylate-terminated dendron
groups.13
Br
Br
O
P(OEt)2
6
R
7
R
8a,b X = OBn
9a,b X = OH
a: R = OMe
b: R = Me
iii
Scheme 1 Reagents and conditions: (i) Triethyl phosphite, 160 °C,
3 h, 85%; (ii) NaH, THF, p-anisaldehyde/p-tolualdehyde, 12 h, 8a
(88%), 8b (92%); (iii) TiCl4, dioxane, reflux, 6 h, 9a (62%), 9b
(65%).
We recently reported the synthesis of permanent fluores-
cence-sensing hyperbranched dendritic architectures14 as
well as the bactericidal efficacy of some novel
dendrimers15 and the electrochemical properties of den-
drimers with m-terphenyl as the peripheral group.16
The first-generation dendron 1, containing two bis-stil-
benoid skeletons, was obtained in 76% yield from the cou-
pling reaction of 9a with dibromide 6 in DMF, in the
presence of K2CO3. In order to make a comparative study
of the effect of stilbene units on photochemical behavior,
dendrimers 2 and 3 were prepared by similar methodology
using 1,3,5-tris(bromomethyl)benzene19 as the planar
core and pentaerythritol tetrabromide20 as the tetrahedral
core (Scheme 2). Dendron 1 and dendrimers 2 and 3 were
characterized completely using spectral and analytical
techniques.
In view of the emerging importance of stilbene dendrim-
ers with their interesting photophysico-chemical proper-
ties, we wish to report herein the synthesis and optical
properties of new stilbene dendrons 1, 4, 5 and dendrimers
SYNTHESIS 2006, No. 8, pp 1257–1262
x
x
.
x
x
.2
0
0
6
Advanced online publication: 27.03.2006
DOI: 10.1055/s-2006-926401; Art ID: Z16505SS
© Georg Thieme Verlag Stuttgart · New York
The allyl-protected dendron 4, with methyl surface
groups, was synthesized similarly in good yield by the re-

1258
P. Rajakumar et al.
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Dendrons
Me
Me
Me
O
O
O
Me
Me
Me
O
O
O
Me
Me
1
4
Me
Me
O
O
Me
Me
O
O
O
O
O
Me
Me
Me
Me
5
Dendrimers
OMe
OMe
MeO
OMe
O
OMe
O
CH2
MeO
O
C
H2C
O
CH2
O
OMe
OMe
O
H2C
MeO
MeO
O
MeO
2
OMe
OMe
OMe
3
Figure 1 The structures of stilbene dendrons and dendrimers
1 (76%)
action of one equivalent of allyl-protected dibromide 10
with 2.2 equivalents of phenol 9b in the presence K2CO3
in DMF under nitrogen (Scheme 3). The desired allyl-
protected dibromide 10 was synthesized by a convention-
al procedure from 5-hydroxyisophthalic acid.21
The 1H NMR spectrum of dendron 4 displayed a twelve-
proton singlet at d = 2.25 corresponding to the four methyl
groups, a two-proton doublet at d = 4.47 (J = 5.0 Hz) for
the O-methylene protons of the allyl moieties, a four-pro-
ton singlet at d = 5.01 for benzylic protons, a set of one-
proton doublets at d = 5.19 with a cis coupling constant of
OBn
i
Br
Br
6
Br
OH
Br
Br
MeO
C(CH2Br)4
2 (62%)
3 (73%)
i
i
9a
OMe
Scheme 2 Reagents and conditions: i) K2CO3, DMF, 60 °C, 48 h.
Synthesis 2006, No. 8, 1257–1262 © Thieme Stuttgart · New York

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Synthesis of New Photoresponsive Stilbene Dendrons and Dendrimers
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OBn
10.2 Hz and d = 5.33 with a trans coupling constant of
17.2 Hz for terminal methylene (olefin) protons of the al-
lyl moiety, a one-proton multiplet at d = 5.92 to 6.02 due
to the methine (-CH-) of the allyl moiety and two eight-
proton doublets at d = 7.06 and d = 7.31 (J = 7.8 Hz) for
para-disubstituted benzene protons, in addition to other
aromatic and olefinic protons. The 13C NMR spectrum of
4 showed methyl carbon at d = 21.3 and methylene car-
bons at d = 68.9 and 69.9, in addition to 16 aromatic car-
bons from d = 111.7 to 159.3. The FAB mass spectrum of
4 showed a peak at m/z 811 corresponding to the molecu-
lar ion.
OH
i
9b
iv
O
O
5
EtO2C
CO2Et
E
E E
E
11a E = CO2Et
11b E = CH2OH
11c E = CH2Cl
ii
iii
Scheme 4 Reagents and conditions: (i) 6, (0.5 equiv), K2CO3,
DMF, 60 °C, 48 h, 78%; (ii) LiAlH4, THF, 6 h, 80% (iii) SOCl2, Py,
CH2Cl2, 8 h, 64%; (iv) K2CO3, DMF, 60°C, 48 h, 30%.
O
and the data obtained are summarized in Table 1. The stil-
bene dendron 1 and dendrimers 2 and 3 showed similar
absorption spectra with maxima at 308 nm in CHCl3. The
intensity of absorption becomes much stronger (Figure 2)
as the number of light-absorbing stilbene units increases.
Hence the dendrimer 3, with four bis-stilbenoids, showed
a relatively high molar extinction co-efficient of 9.4 × 104
M–1 cm–1 (Table 1).
K2CO3
8b
4 (63%)
+
DMF, 60 °C
Br
Br
10
Scheme 3
Encouraged by the synthesis of first-generation dendrons
1 and 4 and dendrimers 2 and 3 by a convergent approach, Stilbene dendron 1, and dendrimers 2 and 3 exhibited sim-
we focused our attention on the synthesis of the second- ilar strong fluorescence, with maxima at 398 nm (lexc 308
generation stilbenoid dendron 5. Reaction of one equiva- nm). However, on increasing the number of stilbenoid
lent of dibromide 6 with 2.1 equivalents of ethyl 5-hy- units, the emission spectra showed fluorescence quench-
droxyisophthalate in the presence of K2CO3 in DMF gave ing (Figure 2). Hence the fluorescence intensity for the
the tetraester 11a, which was then reduced using LiAlH4 dendrimer 3 is substantially lower than that of correspond-
in THF to give the tetraalcohol 11b. Treatment of 11b ing dendron 1. Similar behavior has been previously
with SOCl2 and pyridine in CH2Cl2 led to the desired tet- observed22 for structurally rigid dendrons and has been ac-
rachloride 11c, which was coupled with 4.4 equivalents of counted for by the number of modes by which the excita-
phenol 9b in the presence of K2CO3 in DMF to afforded tion energy is dissipated in larger dendrons, a property
the second-generation stilbene dendron 5 in 30% yield that enhances the non-radiative decay. The through-space
(Scheme 4).
interactions between the fluorescence units become sig-
nificant with increasing molecular size, providing addi-
tional fluorescence quenching pathways.
The optical properties of the dendron 1 and dendrimers 2
and 3 were investigated by UV-Vis and fluorescence
spectral studies. The absorption and photoluminescence Therefore, as far as the peak positions are concerned, the
(PL) spectra of stilbene dendrimers are shown in Figure 2 absorption and emission spectra of dendrimers 2 and 3
Figure 2 a) Absorption spectra and b) fluorescence spectra of dendron 1, dendrimers 2 and 3 in 1 × 10–5 M CHCl3 solution at room
temperature.
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P. Rajakumar et al.
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photoisomerization behavior of stilbene units in dendron
1 and dendrimers 2 and 3.
Table 1 Absorption Maxima, Extinction Coefficients and Fluores-
cence Maxima of Stilbene Dendrimers
Compound
l
max(abs)a (nm)
e (M–1 cm–1)
58600
l
max(fl)a (nm)
On UV irradiation at 254 nm at room temperature, the
trans-dendron 1, trans-dendrimers 2 and 3 underwent
isomerization at the carbon–carbon double bond to give
the cis isomers as revealed by the decrease of the
absorbance23 (Figure 3).
1
2
3
308.4
308.4
308.4
398
399
398
63900
93700
In summary, we have developed a new convergent syn-
thetic route to dendrimeric compounds that combines bis-
stilbenoid skeletons obtained from relatively simple start-
ing materials. The synthesis of stilbenoid building blocks
9a,b makes use of the Wittig–Horner reaction, and paves
the way for the convergent synthesis of higher-generation
dendrimeric systems. The synthesis and photophysical
properties of such systems, with bis-stilbenoid skeletons,
are in progress.
a All spectra were recorded in CHCl3 at room temperature at c = 1 ×
10–5 M.
virtually mimic those of the dendron 1. Thus, all stilbene
units present in these dendrimers behave as isolated chro-
mophores.
The photoisomerization behavior of the stilbene core in a
dendritic molecule is well known and has been thoroughly
studied.13 However, the photoisomerization behavior of
peripheral stilbenoid skeletons in dendritic molecules re-
mains to be explored. Hence, it is of interest to study the
All melting points were uncorrected. Reagents were purchased from
commercial sources and used as received without purification. Sol-
vents were dried by standard procedures. Column chromatography
was carried out on silica gel (grade 60, mesh size 230–400, Merck).
Figure 3 Change of absorption spectrum of (a) trans-1, (b) trans-2 and (c) trans-3 upon UV-irradiation with 254 nm light in 1 × 10–5 M CHCl3
solution at room temperature.
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Synthesis of New Photoresponsive Stilbene Dendrons and Dendrimers
1261
1
IR spectra were recorded on a Shimadzu 8300 instrument. H and
13C NMR spectra were recorded on a Jeol 400 MHz spectrometer
with solvent signals as internal standard. Mass spectra were ob-
tained on a Jeol DX-303 (electron impact, 70 eV) and a Jeol SX 102/
DA (FAB, NBA matrix) spectrometer, respectively. Elemental
analyses were carried out on a Perkin-Elmer 240B analyzer. UV-
Vis spectra were recorded on a Shimadzu UV 260 spectrophotome-
ter. Fluorescence spectra were recorded on a Perkin-Elmer LS 5B
luminescence spectrophotometer.
(2 × 100 mL), and brine solution (1 × 100 mL). The organic layer
was dried (Na2SO4) and evaporated to give the crude product that
was purified by column chromatography (silica gel, hexane–
EtOAc, 2:3) to yield the phenol.
Phenol 9a
Yield 62%; pale-brown solid; mp 185–188 °C.
IR (KBr): 3485 cm–1 (O–H).
1H NMR (400 MHz, CDCl3): d = 3.76 (s, 6 H), 6.78 (s, 2 H), 6.84
(d, J = 8.8Hz, 4 H), 6.85 (d, J = 16.6 Hz, 2 H), 7.00 (d, J = 16.6 Hz,
2 H), 7.10 (s, 1 H), 7.39 (d, J = 8.8 Hz, 4 H).
13C NMR (100 MHz, CDCl3): d = 55.3, 111.7, 114.2, 117.8, 126.1,
127.8, 128.9, 129.9, 139.5, 156.0, 159.4.
MS (EI, 70 eV): m/z = 57, 121, 179, 218, 248, 358 (100%) [M+].
Tetraethyl [[5-(Benzyloxy)-1,3-phenylene]di(methyl-
ene)]bis(phosphonate) (7)
The dibromide 6 (1.9 g, 5.14 mmol) was stirred with triethylphos-
phite (2.6 mL, 15.4 mmol) for 3 h under nitrogen atmosphere at
160 °C. The reaction mixture was then cooled to room temperature,
poured into ice-water (100 mL) and then extracted with EtOAc
(2 × 150 mL). The combined extracts were washed with H2O
(2 × 50 mL), dried (Na2SO4) and evaporated under reduced pressure
to give 7, as a pale-yellow liquid in 85% yield. The product was
pure enough as indicated by TLC and used as such for the subse-
quent step.
Anal. Calcd for C24H22O3: C, 80.42; H, 6.19. Found: C, 80.21; H,
6.12.
Phenol 9b
Yield 65%; pale-brown solid; mp 172–175 °C.
IR (KBr) 3455 cm–1 (O–H).
Synthesis of Bis-stilbenes; General Procedure
1H NMR (400 MHz, CDCl3): d = 2.11 (s, 6 H), 6.82 (s, 1 H), 6.94
(d, J = 16.2 Hz, 2 H), 7.02 (d, J = 16.2 Hz, 2 H), 7.10 (d, J = 8.0 Hz,
4 H), 7.18 (s, 2 H), 7.30 (d, J = 8.0 Hz, 4 H).
13C NMR (100 MHz, CDCl3): d = 21.2, 112.1, 117.5, 126.4, 127.3,
129.0, 134.3, 137.5, 139.2, 156.6.
To a stirred suspension of NaH (0.68 g, 28.5 mmol) in dry THF (100
mL), a solution of the diphosphonate ester 7 (2.3 g, 4.75 mmol) in
dry THF (50 mL) was added dropwise, under nitrogen atmosphere.
The mixture was stirred for 30 min and then added over 1 h to a so-
lution of p-substituted benzaldehyde (10.4 mmol) in dry THF (20
mL) The reaction was stirred for 12 h at r.t., then the excess NaH
was quenched with ice-cold H2O (5 mL) and the solvent was re-
moved under reduced pressure. The crude product was purified by
column chromatography (SiO2, hexane–CHCl3, 9:1) and afforded
the bis-stilbene as a colorless solid.
MS (EI, 70 eV): m/z = 55, 115, 165, 219, 278, 326 (100%) [M+] .
Anal. Calcd for C24H22O: C, 88.16; H, 6.79. Found: C, 88.23; H,
6.60.
Construction of Dendrons and Dendrimers; General Procedure
A mixture of the di/tri/tetrabromide (1 equiv), bis-stilbene phenol
(1.1 equiv for each bromide unit) and potassium carbonate (3 equiv
with respect to phenol) in dry DMF (25 mL) was vigorously stirred
at 80 °C under nitrogen atmosphere for 60 h. The reaction mixture
was allowed to cool to r.t. and poured into ice-water (100 mL). The
resulting precipitate was dissolved in CHCl3 (100 mL). The organic
layer was separated, washed with H2O (3 × 100 mL), brine (2 × 100
mL) and dried (Na2SO4) and evaporated to give the crude product,
which was purified by column chromatography (SiO2, hexane–
CHCl3, 3:2).
Bis-stilbene 8a
Yield: 88%; colorless solid; mp 138–140 °C.
1H NMR (400 MHz, CDCl3): d = 3.76 (s, 6 H), 5.06 (s, 2 H), 6.83
(d, J = 8.8 Hz, 4 H), 6.87 (d, J = 16.1 Hz, 2 H), 6.93 (br s, 2 H), 7.00
(d, J = 16.1 Hz, 2 H), 7.15 (s, 1 H), 7.27–7.35 (m, 5 H), 7.38 (d,
J = 8.8 Hz, 4 H).
13C NMR (100 MHz, CDCl3): d = 55.3, 70.1, 111.4, 114.2, 117.8,
126.4, 127.6, 127.8, 128.0, 128.6, 128.7, 130.0, 137.0, 139.3, 159.4.
MS (EI, 70 eV): m/z = 57, 91 (100%), 129, 173, 256, 448 [M+].
Anal. Calcd for C31H28O3: C, 83.01; H, 6.29. Found: C, 82.87; H,
6.18.
Dendron 1
Yield 76%; colorless solid; mp 182–185 °C.
1H NMR (400 MHz, CDCl3): d = 3.75 (s, 12 H), 5.05 (s, 2 H), 5.07
(s, 4 H), 6.82 (d, J = 8.8 Hz, 8 H), 6.87 (d, J = 16.1 Hz, 4 H), 6.93
(s, 4 H), 7.02 (s, 2 H), 7.12 (s, 1 H), 7.14 (s, 2 H), 7.25–7.33 (m,
5 H), 7.00 (d, J = 16.1 Hz, 4 H), 7.38 (d, J = 8.8 Hz, 8 H).
13C NMR (100 MHz, CDCl3): d = 55.3, 69.9, 111.4, 113.4, 114.2,
117.9, 126.4, 127.6, 127.8, 128.0, 128.6, 128.8, 130.0, 132.5, 139.3,
159.4.
Bis-stilbene 8b
Yield 92%; colorless solid; mp 150–152 °C.
1H NMR (400 MHz, CDCl3): d = 2.26 (s, 6 H), 5.01 (s, 2 H), 6.90
(s, 1 H), 6.92 (d, J = 16.3 Hz, 2 H), 7.00 (d, J = 16.3 Hz, 2 H), 7.07
(d, J = 8.3 Hz, 4 H), 7.11–7.38 (m, 7 H), 7.32 (d, J = 8.3 Hz, 4 H).
13C NMR (100 MHz, CDCl3): d = 55.3, 70.1, 111.4, 114.2, 117.8,
126.4, 127.6, 127.8, 128.0, 128.6, 128.7, 130.0, 137.0, 139.3, 159.4.
MS (FAB): m/z = 925 [M+].
MS (EI, 70 eV): m/z = 57, 91 (100%), 105, 155, 179, 265, 297, 325,
416 [M+].
Anal. Calcd for C63H56O7: C, 81.79; H, 6.10. Found: C, 81.51; H,
5.88.
Anal. Calcd for C31H28O: C, 89.38; H, 6.78. Found: C, 89.55; H,
6.52.
Dendrimer 2
Yield 62%; colorless solid; mp 202–208 °C.
Synthesis of Bis-stilbenephenols
1H NMR (400 MHz, CDCl3): d = 3.80 (s, 18 H), 5.20 (s, 6 H), 6.88
(d, J = 8.6 Hz, 12 H), 6.92 (d, J = 16.3 Hz, 6 H), 7.01 (s, 6 H), 7.06
(d, J = 16.3 Hz, 6 H), 7.20 (s, 3 H), 7.43 (d, J = 8.6 Hz, 12 H) 7.58
(s, 3 H).
A solution of benzylic ether 8a or 8b (2.4 mmol) in dry dioxane
(100 mL) was treated with TiCl4 (1.4 g, 7.2 mmol) under nitrogen
atmosphere. The reaction mixture was refluxed for 6 h, then the
mixture was poured over ice (150 mL ) and extracted with EtOAc
(3 × 100 mL). The combined organic layers were washed with H2O
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P. Rajakumar et al.
PAPER
13C NMR (100 MHz, CDCl3): d = 55.3, 69.9, 111.5, 114.2, 118.0,
126.0, 126.4, 127.8, 128.8, 130.0, 138.1, 139.3, 159.3, 159.4.
References
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MS (FAB): m/z = 1189 [M+].
Anal. Calcd for C81H72O9: C, 81.79; H, 6.10. Found: C, 81.94; H,
6.33.
Dendrimer 3
Yield 73%; pale-yellow solid; mp 146–152 °C.
1H NMR (400 MHz, CDCl3): d = 3.78 (s, 24 H), 4.55 (s, 8 H), 6.84
(d, J = 8.6 Hz, 16 H), 6.90 (d, J = 16.3 Hz, 8 H), 7.03 (s, 8 H), 7.06
(d, J = 16.3 Hz, 8 H), 7.16 (s, 4 H), 7.40 (d, J = 8.6 Hz, 16 H).
13C NMR (100 MHz, CDCl3): d = 55.3, 67.1, 111.6, 114.2, 118.2,
126.4, 128.8, 128.8, 130.1, 139.3, 159.4, 159.6.
MS (FAB): m/z = 1497 [M+].
Anal. Calcd for C101H92O12: C, 80.99; H, 6.19. Found: C, 80.71; H,
6.43.
Dendron 4
Yield 63%; colorless solid; mp 172–176 °C.
1H NMR (400 MHz, CDCl3): d = 2.25 (s, 12 H), 4.47 (d, J = 5.0 Hz,
2 H), 5.01 (s, 4 H), 5.19 (d, J = 10.2 Hz, 1 H), 5.33 (d, J = 17.2 Hz,
1 H), 5.92–6.02 (m, 1 H), 6.87–7.13 (m, 13 H), 6.95 (d, J = 14.8 Hz,
4 H), 7.06 (d, J = 7.8 Hz, 8 H), 7.31 (d, J = 7.8 Hz, 8 H).
(7) Meier, H.; Lehmann, M. Angew. Chem. Int. Ed. 1998, 37,
13C NMR (100 MHz, CDCl3): d = 21.3, 69.0, 69.9, 111.7, 113.3,
117.9, 118.2, 118.8, 126.6, 127.5, 129.2, 129.5, 133.1, 134.4, 137.7,
139.0, 139.2, 159.2, 159.3.
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Gómez, R.; Segura, J. L.; Martín, N. Org. Lett. 2000, 2,
3651.
MS (FAB): m/z = 811 [M+].
Anal. Calcd for C59H54O3: C, 87.37; H, 6.71. Found: C, 87.18; H,
6.88.
(10) (a) Kwock, E. W.; Neenan, T. X.; Miller, T. M. Chem.
Mater. 1991, 3, 775. (b) Miller, T. M.; Kwock, E. W.;
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2003, 94. (b) Hayakawa, A.; Momotake, A.; Arai, T. Chem.
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(14) Rajakumar, P.; Ganesan, K. Synlett 2004, 2236.
(15) Rajakumar, P.; Ganesan, K.; Jayavelu, S.; Murugesan, K.
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Dendron 5
Yield 30%; pale-brown solid; mp 142–146 °C.
1H NMR (400 MHz, CDCl3): d = 2.25 (s, 24 H), 4.96 (s, 2 H), 5.00
(s, 4 H), 5.02 (s, 8 H), 6.92 (s, 4 H), 6.96 (d, J = 15.6 Hz, 8 H),
7.01–7.17 (m, 30 H), 7.06 (d, J = 7.8 Hz, 16 H), 7.31 (d, J = 7.8 Hz,
16 H).
13C NMR (100 MHz, CDCl3): d = 21.2, 69.8, 69.9, 111.7, 113.3,
126.5, 127.4, 127.5, 128.0, 128.5, 129.1, 129.4, 132.7, 134.3, 137.6,
138.8, 139.1, 159.2.
MS (FAB): m/z = 1750 [M+].
Anal. Calcd for C127H112O7: C, 87.15; H, 6.45. Found: C, 86.99; H,
6.28.
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Acknowledgment
(20) Herzog, H. L. Org. Synth., Coll. Vol. IV 1963, 743.
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Rapp, B. A.; Wheeler, D. L. Nucleic Acids Res. 2000, 28, 15.
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5, 1.
The authors thank DST, UGC-Special Assistance Program to the
Department of Organic Chemistry and CSIR (SRF to MD) for fi-
nancial assistance.
Synthesis 2006, No. 8, 1257–1262 © Thieme Stuttgart · New York