Synthesis of dendritic phenol ether derivatives with a naphthalene core

Article abstract of DOI:10.1080/00397910801913980

A series of dendritic phenol ether derivatives with a naphthalene core were synthesized by the Williamson reaction as a coupling reaction between 1-hydroxymethylnaphthalene and polyether-based dendritic fragments in the presence of phase-transfer catalyst and alkali. The modified method for chlorination of dendritic benzyl alcohol was also developed using PPh3 and CCl4 as reagents and CH2Cl2/CCl4 as solvent. Copyright Taylor & Francis Group, LLC.

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Synthesis of Dendritic Phenol Ether
Derivatives with a Naphthalene Core
Zhonghua Xiang a b c & Derong Cao a
a College of Chemistry , South China University of Technology , Guangzhou,
China
b Guangzhou Institute of Chemistry, Chinese Academy of Sciences ,
Guangzhou, China
c Graduate School of Chinese Academy of Sciences , Beijing, China
Published online: 25 Apr 2008.
To cite this article: Zhonghua Xiang & Derong Cao (2008) Synthesis of Dendritic Phenol Ether Derivatives
with a Naphthalene Core, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 38:9, 1318-1324, DOI: 10.1080/00397910801913980
To link to this article: http://dx.doi.org/10.1080/00397910801913980
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Synthetic Communicationsw, 38: 1318–1324, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910801913980
Synthesis of Dendritic Phenol Ether
Derivatives with a Naphthalene Core
Zhonghua Xiang1,2,3 and Derong Cao1
1College of Chemistry, South China University of Technology,
Guangzhou, China
2Guangzhou Institute of Chemistry, Chinese Academy of Sciences,
Guangzhou, China
3Graduate School of Chinese Academy of Sciences, Beijing, China
Abstract: A series of dendritic phenol ether derivatives with a naphthalene core were
synthesized by the Williamson reaction as a coupling reaction between 1-hydroxy-
methylnaphthalene and polyether-based dendritic fragments in the presence of
phase-transfer catalyst and alkali. The modified method for chlorination of dendritic
benzyl alcohol was also developed using PPh3 and CCl4 as reagents and CH2Cl2/
CCl4 as solvent.
Keywords: Chlorination, dendrimer, naphthalene, Williamson reaction
INTRODUCTION
Uniform (monodisperse) dendrimers represent the connecting link between
organic compounds with low molecular masses and polymers, and they are dis-
tinguished by a number of special properties.[1] Recently, in the dendrimer
series we studied some antenna systems of anthracenes substituted in the
´
9,10-position with Frechet dendrons. Irradiation in the near-UV region
(400 nm ꢀ l ꢀ 300 nm) of an approximately 1023 M solution of the dendri-
mers with both arms in benzene led to the quantitative [4p þ 4p] cycloaddition
reaction between the benzene ring and anthracene ring.[2] The unusual photodi-
merization can be explained by an aggregation of the dendrimers in solution.
Received August 30, 2007
Address correspondence to Derong Cao, College of Chemistry, South China
University of Technology, Guangzhou 510640, China. E-mail: drcao@scut.edu.cn
1318

Dendritic Phenol Ether Derivatives
1319
Naphthalene linked with 3,5-dialkoxy benzene via -CH2OCH2- exhibited also
an unusual intramolecular photocycloaddition reaction to the polycyclic
compound in the diluted solutions under UV irradiation.[3] The quantitative
process is completely reversible by heating or under UV irradiation. Its appli-
cations in materials science seem to be particularly promising in the field of
optical switching processes or data storage systems.[4] To further study the influ-
encing factors of the reaction, a series of dendrimers containing naphthalene as a
core and benzene rings as side chains were synthesized by the reaction of
1-hydroxymethylnaphthalene 1 and the 3,5-dialkoxybenzylchloride 2a–c.
The nucleophilic substitution of the halogen atoms in 2a–c with 1-hydroxy-
methylnaphthalene in an alkaline medium under phase-transfer conditions
provided yields of the dendrimers 3a–c between 31% and 67% (Scheme 1).
RESULTS AND DISCUSSION
Scheme 1 summarizes the preparation of the dendrimers with a naphthalene
core, 3a–c. A mixture of 1 and 2a–c in chlorobenzene/H2O under
Scheme 1. Preparation of the dendrimers 3a–c.

1320
Z. Xiang and D. Cao
Table 1. Yield of 3b at different temperature
Entry
Temperature (8C)
Reaction time (h)
Yield (%)
1
2
3
60
80
90
48
48
48
54
54
57
n-Bu4NBr as phase-transfer catalyst and KOH as alkaline yielded the dendri-
mers 3a–c. An increase in dendron size makes the reaction less effective;
for example, the yields of 2a and 2c were 67% and 31% respectively. To
improve the yield of 3c, we let the alcohol 1 three times excess than
dentritic benzyl chlorides 2, but it did not increase the yield. We studied the
effect of temperature on the yield of 3b (Table 1). The results showed that
the influence of temperature is not remarkable, but the reaction rate is faster
at a higher temperature.
´
Scheme 2 summarizes the preparation of the Frechet-type dendritic
fragments. The convergent synthesis of this dendrimer has been developed
´
by Hawker and Frechet and was successfully used by other groups to
construct monodisperse macromolecules.[5] However, the drawbacks of the
method are that (1) the growth of the dendritic wedges is time-consuming
and (2) the reported yields of 2-Br are not always easy to reproduce and
Scheme 2. Preparation of the dendritic fragments.

Dendritic Phenol Ether Derivatives
1321
Table 2. Yield of 2b in different solvents
Entry
Temperature (8C)
Reagents
Solvent
Yield (%)
1
2
3
rt
PPh3 and CBr4
PPh3 and CCl4
PPh3 and CCl4
THF
CCl4
62
71
80
80
50
CH2Cl2/CCl4
great care is necessary, especially with the higher generation bromides.
Several methods have been reported to avoid the difficult step of bromina-
tion.[6–8] In our hands, we synthesized 3,5-bis(benzyloxy)benzyl chloride
2a using CCl4 and PPh3 in high yield (93%). Here CCl4 is both reagent and
solvent. Stimulated by the success of preparation of 2a, we prepared 2b in
the same way. However, the yield of 2b was not as high as 2a. And we
found that the mixture was heterogeneous in the end of the reaction. Also
´
we synthesized 2b-Br by following Frechet’s method, and the reported
yield was hard to achieve.
We considered that the low yield of the chlorination might be due to the
heterogeneous system. It might be possible to improve the yield of 2b by intro-
ducing some solvent to make the homogeneous mixture. CH2Cl2 is a good
choice. Table 2 showed that the yield increased when CH2Cl2/CCl4 was used
as the solvent. The yield of the higher generation 2c was also desired (90%).
EXPERIMENTAL
General Procedure for the Synthesis of Dendritic Benzyl Alcohols
2-OH
A mixture of the appropriate benzyl chloride (2.00 equiv), 3,5-dihydroxyben-
zyl alcohol (1.00 equiv), dried potassium carbonate (2.50 equiv), and
18-crown-6 (0.20 equiv) in dry acetone was heated at reflux and stirred vigor-
ously under nitrogen for 48 h. The mixture was allowed to cool and filtrate.
The residue was washed with CH2Cl2 three times. The combined organic
liquids were then evaporated and dried. The crude product was purified as
outlined in the following text.
General Procedure for the Synthesis of Dendritic Benzyl Chlorides 2
Triphenylphosphine was added to a mixture of the dendritic benzyl alcohol
2-OH with appropriate amount solvent, and the mixture was heated at
reflux and stirred under nitrogen for 24 h. For higher generation, a larger
amount of triphenylphosphine was required. After the reaction was

1322
Z. Xiang and D. Cao
completed, the reaction mixture was evaporated and dried. The crude product
was purified as outlined in the following text.
Compound 2a-OH was prepared from benzyl chloride. The residue was
purified by flash chromatography with petroleum ether (bp 60–90 8C)/ethyl
acetate (v/v, 4:1) as the eluent to give 2a-OH as a white crystalline solid:
yield 91%; mp 78–79 8C.
Compound 2a was prepared from 2a-OH (1.00 equiv) and triphenylpho-
sphine (1.50 equiv) in CCl4. The residue was purified by flash chromatography
with petroleum ether (bp 60–90 8C)/ethyl acetate (v/v, 10:1) as the eluent to
give 2a as a white crystalline solid: yield 93%: mp 72–74 8C.
Compound 2b-OH was prepared from 2a. The residue was purified by flash
chromatography with petroleum ether (bp 60–90 8C)/ethyl acetate (v/v, 2:1) to
give 2b-OH as a white crystalline solid: yield 92%; mp 108–110 8C.
Compound 2b was prepared from 2b-OH (1.00 equiv) and triphenylpho-
sphine (2.00 equiv) in CCl4 and CH2Cl2 (v/v, 1:1). The residue was purified
by flash chromatography with petroleum ether (bp 60–90 8C)/CH2Cl2 (v/v,
2:1) to give 2b as a white crystalline solid: yield 80%; mp 110–112 8C.
Compound 2c-OH was prepared from 2b and purified by flash chromato-
graphy with CH2Cl2 as the eluent to give 2c-OH as a colorless glass: yield 83%.
Compound 2c was prepared from 2c-OH (1.00 equiv) and triphenylpho-
sphine (2.50 equiv) in CCl4 and CH2Cl2 (v/v, 1:1). The residue was purified
by flash chromatography with petroleum ether (bp 60–90 8C)/CH2Cl2 (v/v,
1:2) as the eluent to give 2c as a colorless glass: yield 90%.
General Procedure for the Synthesis of the Dendrimers 3
A mixture of 1 (2-methoxy-1-naphthalenemethanol) (1.00 equiv), the corre-
sponding benzyl chloride 2 (1.00 equiv), KOH (1.20 equiv), and n-Bu4NBr
(0.05 equiv) in chlorobenzene and water (v/v, 30:1) was heated at 90 8C
and stirred vigorously under nitrogen for 48 h. Then CH2Cl2 and water
were added to the mixture. The separated water layer was extracted three
times with CH2Cl2. The combined organic layers were then evaporated and
dried. The crude product was purified as outlined in the following text.
1-(Benzyloxymethyl)naphthalene 3a was prepared from 2a and purified
by flash chromatography with petroleum ether (bp 60–90 8C)/ethyl acetate
(v/v, 8:1) as the eluent to give 3a as a white crystalline solid: mp 86–
1
88 8C, yield 67%. H NMR (400 MHz, CDCl3): d ¼ 3.93 (s, 3H, OCH3),
4.55 (s, 2H, CH2), 4.97 (s, 4H, CH2), 5.06 (s, 2H, CH2), 6.52 (t, 1H,
aromat. H), 6.62 (d, 2H, aromat. H), 7.25–7.48 (m, 13H, aromat. H), 7.76–
7.84 (m, 2H, aromat. H), 8.10 (m, 1H, aromat. H); 13C NMR (100 MHz,
CDCl3): d ¼ 56.7, 62.2, 70.0, 71.9, 101.4, 106.7, 113.3, 118.6, 123.6, 124.0,
126.8, 127.5, 127.9, 128.2, 128.5, 129.2, 130.3, 133.8, 137.0, 141.4, 155.7,
159.9; MS (FD): m/z ¼ 490 (Mþ†). Anal. calcd. for C33H30O4 (490.59): C,
80.79; H, 6.16. Found: C, 80.69; H, 6.17.

Dendritic Phenol Ether Derivatives
1323
Compound 3b was prepared from 2b and purified by flash chromatography
with petroleum ether (bp 60–90 8C)/CH2Cl2 (v/v, 1:2) as the eluent to give 3b
as a white crystalline solid: yield 57%, mp 100–102 8C. 1H NMR (400 MHz,
CDCl3): d ¼ 3.91 (s, 3H, OCH3), 4.53 (s, 2H, CH2), 4.90 (s, 4H, CH2), 5.01
(s, 8H, CH2), 5.06 (s, 2H, CH2), 6.55–6.65 (m, 9H, aromat. H), 7.30–7.41
(m, 22H, aromat. H), 7.46 (m, 1H, aromat. H), 7.75–7.81 (m, 2H, aromat.
H), 8.08 (m, 1H, aromat. H); 13C NMR (100 MHz, CDCl3): d ¼ 56.7, 62.2,
69.9, 70.1, 71.9, 101.4, 101.5, 106.4, 106.7, 113.3, 118.5, 123.6, 123.9, 126.8,
127.5, 128.0, 128.2, 128.6, 129.2, 130.4, 133.8, 136.8, 139.4, 141.4, 155.7,
159.8, 160.1; MS (FAB): m/z ¼ 915 (Mþ† þ 1), 171, 91. Anal. calcd. for
C61H54O8 (914.38): C, 80.06; H, 5.95. Found: C, 79.90; H, 5.74.
Compound 3c was prepared from 2c and purified by flash chromato-
graphy with petroleum ether/CH2Cl2/ether (v/v/v, 300:150:1) as the eluent
1
to give 3c as a colorless glass: yield 31%. H NMR (400 MHz, CDCl3):
d ¼ 3.89 (s, 3H, OCH3), 4.53 (s, 2H, CH2), 4.88 (s, 4H, CH2), 4.93 (s, 8H,
CH2), 4.99 (s, 16H, CH2), 5.05 (s, 2H, CH2), 6.52–6.66 (m, 21H, aromat.
H), 7.28–7.40 (m, 42H, aromat. H), 7.45 (t, 1H, aromat. H), 7.72 (m, 1H,
aromat. H), 7.78 (m, 1H, aromat. H), 8.08 (m, 1H, aromat. H); 13C NMR
(100 MHz, CDCl3): d ¼ 56.6, 62.2, 70.0, 70.1, 71.9, 101.3, 101.6, 106.4,
106.7, 113.2, 118.4, 123.6, 123.9, 126.8, 127.5, 128.0, 128.2, 128.5, 129.1,
130.3, 133.8, 136.7, 139.2, 139.4, 141.4, 155.6, 159.8, 160.0, 160.1 (the
signals partially overlap in the 13C NMR of data 3c); MS (FAB): m/
z ¼ 1592, 154, 91. Anal. calcd. for C117H102O16 (1762.72): C, 79.66; H,
5.83. Found: C, 79.60; H, 5.57.
ACKNOWLEDGMENT
This work was supported by the National Natural Science Foundation of
China (20572111) and the Guangdong Natural Science Foundation of China
(06025664).
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