Synthesis of monohydroxy-functionalized triphenylene discotics: green chemistry approach

Article abstract of DOI:10.1016/j.tet.2007.04.058

This paper presents an environmentally benign procedure for the preparation of monohydroxy-functionalized triphenylenes using simple ionic reagents. Pyridinium hydrochloride, pyridinium hydrobromide, N-methyl pyridinium iodide, N-ethyl pyridinium bromide, and 1-n-butyl-3-methyl imidazolium bromide have been employed to prepare various monohydroxypentaalkoxytriphenylenes, which are valuable precursors for the synthesis of a variety of discotic monomers, dimers, oligomers, and polymers.

Full text of DOI:10.1016/j.tet.2007.04.058

Tetrahedron 63 (2007) 6874–6878
Synthesis of monohydroxy-functionalized triphenylene
discotics: green chemistry approach
*
Santanu Kumar Pal, Hari Krishna Bisoyi and Sandeep Kumar
Raman Research Institute, C.V. Raman Avenue, Bangalore 560 080, India
Received 16 November 2006; revised 4 April 2007; accepted 19 April 2007
Available online 25 April 2007
Abstract—This paper presents an environmentally benign procedure for the preparation of monohydroxy-functionalized triphenylenes using
simple ionic reagents. Pyridinium hydrochloride, pyridinium hydrobromide, N-methyl pyridinium iodide, N-ethyl pyridinium bromide, and 1-
n-butyl-3-methyl imidazolium bromide have been employed to prepare various monohydroxypentaalkoxytriphenylenes, which are valuable
precursors for the synthesis of a variety of discotic monomers, dimers, oligomers, and polymers.
Ó 2007 Elsevier Ltd. All rights reserved.
1
. Introduction
The synthesis of mono-functionalized triphenylenes can
be achieved in different ways. One of the earliest reported
1
0
There has been an ever increasing interest in the field of
discotic liquid crystals (DLCs) in general, and in triphenyl-
ene-based discotic mesogens in particular, since their
methods of monohydroxypentaalkoxytriphenylene syn-
thesis involves partial alkylation of hexaacetoxytriphenyl-
ene to monoacetyl-pentaalkoxytriphenylene in low yield.
This can be hydrolyzed to monohydroxytriphenylene. A
non-selective cleavage of one of the alkoxy group of hexaal-
1
2
,3
4
,5
discovery. DLCs are a unique state of matter possessing
self-organization of disk-shaped molecules. Their supramo-
lecular columnar architecture is of fundamental importance,
not only as models for the study of the energy and charge mi-
gration in organized systems, but also as functional materials
for device applications such as one-dimensional conductors,
photoconductors, light-emitting diodes, photovoltaic solar
cells, gas sensors, etc. Triphenylene derivatives are the most
widely synthesized and well-studied materials in the family
of DLCs, because they show a variety of mesophases, their
derivatives are chemically and thermally stable, and their
chemistry is fairly accessible. Scaled up and improved syn-
thetic routes to the hexa-substituted triphenylene nucleus has
1
1
koxytriphenylene using a calculated amount of 9-Br-BBN
gives a mixture of products containing unreacted hexaalkoxy-
triphenylene (26%), monohydroxytriphenylene (39%), and
a minor amount of dihydroxytriphenylenes (10%). The de-
sired product can be purified by column chromatography.
A selective cleavage of the methyl ether of monomethoxy-
pentaalkoxytriphenylene with lithium diphenylphosphide
The
2
,3
12,13
affords the monohydroxytriphenylene in high yield.
monomethoxytriphenylene can be prepared by the so-called
biphenyl route. The main drawback of this process is the
poor yield of the biphenyl in the classical Ullman coupling
reaction, and the use of highly sensitive and hazardous lith-
ium diphenylphosphide. However, now better but expensive
6
–9
been well documented.
However, because of synthetic
problems in obtaining mono-functionalized triphenylenes,
which are valuable precursor molecules for the synthesis of a
variety of discotic dimers, oligomers, polymers, networks,
and mixed tail derivatives, the potential utility of these in-
triguing materials has not yet been fully explored. Physical
properties of these non-conventional liquid crystals are sig-
nificantly different to those of conventional low molar mass
liquid crystals. A few methods have been developed for the
synthesis of mono-functionalized triphenylenes, but most of
these involve expensive and hazardous reagents.
1
4
methods are available to prepare tetraalkoxybiphenyls.
Bushby and Lu have demonstrated the use of the isopropoxy
masking group in a biphenyl–phenyl oxidative coupling
route for the preparation of monohydroxytriphenylenes.
1
5
The synthesis of monohydroxytriphenylene by directly cou-
pling tetraalkoxybiphenyl and alkoxyphenol using molybde-
num(V) chloride has been reported, but the reaction was
9
sluggish and the isolation of the product was difficult. We
have previously reported that this compound can also be
obtained as a side product in the oxidative trimerization of
9
dialkoxybenzene with MoCl in about 25% yield. Bromo-
5
catecholborane, an alternative to 9-Br-BBN, has been found
to give almost 70% of mono-functionalized triphenylene.
Keywords: Ionic liquids; Triphenylene; Ether cleavage; Discotic liquid crys-
tals; Microwaves.
16
This reaction is highly efficient for the preparation of
mono-, di- and trifunctionalized triphenylene derivatives, but
*
Corresponding author. Tel.: +91 80 23610122; fax: +91 80 23610492;
e-mail: skumar@rri.res.in
0
040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.04.058

S. K. Pal et al. / Tetrahedron 63 (2007) 6874–6878
6875
the reagent is expensive and moisture sensitive. Recently we
presented in the following tables. Pyridinium hydrochloride
and hydrobromide have been prepared by following a closely
1
7
have also reported an economic and convenient method for
the preparation of monohydroxy-functionalized triphenyl-
ene using FeCl in nitromethane. Though it is a one-step pro-
2
2
related method reported in the literature. These have been
known for a long time, and a number of papers on their prop-
erties, chemical reactions, and reactivity are available.
3
2
3
cess, the overall yield in the reaction does not go above 20%.
Because of these problems, we started looking for an alter-
native, inexpensive, and less hazardous method to produce
these materials. We have found that ionic reagents can be
used to prepare these various monohydroxy-functionalized
triphenylenes in moderate yield. This methodology avoids
all type of toxic, volatile, and hazardous reagents.
These simple ionic reagents are very useful to cleave one of
the ether linkages to get mono-functionalized triphenylene
derivatives and a convenient, economic, and environmentally
benign green chemical process for the isolation of the latter.
2. Results and discussion
Developing green chemistry methodologies is one of the
main themes of modern synthetic chemistry. In this context,
the use of ionic liquids and microwaves are powerful tools.
Ionic liquids, a class of organic salts with usually low melt-
When different hexaalkoxytriphenylenes [R¼–C H
4
9
(H4TP), –C H (H5TP), –C H (H6TP)] were treated
6 13
5
11
with various ionic reagents (I–V) (Scheme 1), mono-func-
tionalized triphenylenes were formed in good yields. A sum-
mary of the best yields and conditions is given in Table 1.
More descriptive data are given in supplementary tables.
1
8
ing points, have attracted considerable attention. Due to
their unique characteristics, such as non-volatility, thermal
stability, non-flammability, very low vapor pressure, reus-
ability, and diverse solvating ability, they can be used as en-
vironmentally benign solvent media to replace conventional
First of all, we checked the classical dealkylation reagent,
pyridinium hydrochloride, to prepare mono-functionalized
triphenylene. The hexaalkoxytriphenylene and different
equivalents (1.2–4) of pyridinium hydrochloride were
1
9
volatile organic solvents in many chemical processes.
Ionic liquids serve the dual purpose of solvent as well as re-
agents in many reactions, and allow easy isolation of prod-
ucts. On the other hand, microwave-assisted high-speed
chemical synthesis has attracted much attention in the past
ꢀ
checked at about 165 C at different time intervals (Table
S1, Supplementary data) and the product was isolated by
conventional work-up and purification. The use of 1.2 equiv
of pyridinium hydrochloride furnished almost 16% of the
mono-functionalized triphenylene derivative within 3 h. It
is interesting to note that no side product was formed in
the reaction and the unreacted triphenylene can be isolated
easily. Therefore, the yield of the product 2 based on con-
sumed H4TP was excellent. Increasing the reaction time to
24 h (entry 4, Table S1) resulted in the isolation of about
35% of monohydroxytriphenylene. The best yield was ob-
tained by running the reaction for 48 h. It gives 40% of the
desired monohydroxytriphenylene derivative but the product
was contaminated with about 2% of dihydroxytripheny-
lenes. Increasing the amount of the reagent and keeping
the same reaction time decreases the mono-functionalized
derivative and increases dihydroxy functionalized tripheny-
lene derivatives (6–8%). The same reaction condition has
been used to cleave other triphenylenes. It is clear from
Table 1 that longer chain aryl–alkyl ether gives lower yield
of the product. This could be because of the increased
steric hindrance of longer alkyl chains.
2
0
decade. Almost all types of organic reactions have been
performed using the efficiency of microwave flash heating.
This is not only due to the fact that the reactions proceed sig-
nificantly faster and more selective than under conventional
thermal conditions, but also because of operational simplic-
ity, high yield of products and cleaner reactions with easier
work-up. We have recently utilized this technology to pre-
pare some conventional calamitic liquid crystalline mate-
21
rials. In this paper, we report a convenient, economic and
environmentally benign green chemical method for the syn-
thesis of monohydroxypentaalkoxytriphenylenes by using
pyridinium and imidazolium-based ionic reagents under
classical as well as microwave heating conditions.
We have applied several pyridinium and imidazolium salts
to examine the possibility of selective ether dealkylation
in hexaalkoxytriphenylenes (Scheme 1) and the results are
OR
OH
OR
OR
OR
RO
RO
RO
RO
Table 1. Preparation of monohydroxypentaalkoxytriphenylene 2 using
ꢀ
Ionic reagent
Heat/Microwaves
reagents I–V at 165–170 C
Entry
1
Reagent (equiv)
Time (h)
2 (%)
a: R = C4H9
b: R = C5H11
1
2
3
4
5
6
7
8
9
1
1
1
1
1
H4TP
H5TP
H6TP
H4TP
H5TP
H6TP
H4TP
H5TP
H4TP
H5TP
H6TP
H4TP
H5TP
H6TP
I (3.0)
I (3.0)
I (3.0)
II (4.0)
II (4.0)
II (4.0)
III (3.2)
III (3.2)
IV (4)
IV (4)
IV (4)
V (4.2)
V (4.2)
V (4.2)
48
48
48
24
24
24
30
30
24
24
24
24
24
24
40
37
34
40
33
29
31
28
37
36
31
33
33
30
1
OR
2
OR
6 13
c: R = C H
OR
Ionic reagents:
N
N
N
Br
N
H
I
N
H
II
N
Cl-
Br-
Br-
I-
-
0
1
2
3
4
III
IV
V
Scheme 1. Synthesis of monohydroxypentaalkoxytriphenylenes using ionic
reagents.

6876
S. K. Pal et al. / Tetrahedron 63 (2007) 6874–6878
ꢁ
To check whether Br cleaves the ether bond in hexaalkoxy-
triphenylenes more effectively than Cl we made simple
The dealkylation of hexaalkoxytriphenylenes was carried
out using an unmodified household microwave oven (LG,
MS-192 W). We examined the effect of microwave power
and time on various hexaalkoxytriphenylenes as described
in Tables S6 and S7. The hexaalkoxytriphenylene and the
ionic reagent were thoroughly mixed and subjected to micro-
wave irradiation for 1 min under the desired power. The vial
was taken out and once again kept back for 1 min and this
procedure was continued up to desired time. Then the vial
was cooled to room temperature. The mixture was dissolved
in dichloromethane and then passed through column to
isolate the pure product.
ꢁ
pyridinium bromide by reacting HBr gas with pyridine.
The cleavage of hexaalkoxytriphenylene using this reagent
was carried out as described above for pyridinium hydro-
chloride and the results are summarized in Table S2 (Supple-
mentary data). It is clear from this table that under identical
reaction conditions (1.2 equiv of the reagent, 3 h), the yield
of mono-functionalized triphenylene derivative increases to
2
1% but the product was contaminated with some amount
of dihydroxy derivative. Increasing the reaction time or
increasing the amount of the reagent does not show any sig-
nificant change. Using 4 equiv of the reagent for 24 h, 40%
of the desired mono-functionalized triphenylene can be iso-
lated in addition to 10% of the dihydroxy derivatives. This
As can be seen from Tables S6 and S7, irradiation of the
reaction mixture at 360 W for 3 min using 3 equiv of the re-
agent generally furnished good yield of the product. Enhanc-
ing the microwave power to 600 W or 800 W did not
increase the yield significantly. Compared to thermal heat-
ing, the yield of monohydroxytriphenylenes was low under
microwave heating conditions but the reaction can be fin-
ished in a very short time.
ꢁ
ꢁ
reflects the higher reactivity of Br compare to Cl .
Pyridinium derivatives where alkyl groups are directly at-
tached to the nitrogen of the pyridinium moiety have been
rarely used for ether dealkylation. We have prepared some
pyridine derivatives containing Br and I having an ethyl
and methyl group, respectively. These reagents were pre-
pared followinga closelyrelated literature procedure. Their
ꢁ
ꢁ
2
2
2
4
properties have already been described in the literature.
3. Conclusion
These reagents were also used to cleave one of the ether link-
ages of hexaalkoxytriphenylene as described above for pyri-
dinium hydrochloride. As expected, these reagents produce
less amounts of mono-functionalized triphenylene, and sur-
prisingly the latter one does not give any mono-functional-
ized triphenylene derivative using 3 equiv of the reagent
over 3 h. Tables S3 and S4 summarize the results of mono-
functionalized triphenylene synthesis using these reagents.
In conclusion, 30–40% yields of the valuable mono-func-
tionalized triphenylenes can be isolated using a simple ionic
liquid in thermal as well as microwave flash heating condi-
tions. The use of 3 equiv of pyridinium hydrochloride for
48 h gives the best yield of mono-functionalized triphenyl-
ene. Using microwave flash heating, these materials can be
prepared in a few minutes in moderate yield. In all cases,
no side reaction occurred and the unreacted starting material
can be isolated easily, and can be recycled. The process
reported here is an economic and green synthesis method
for the preparation of monohydroxyhexaalkoxytriphenylene
derivatives.
The imidazolium-based ionic liquid was prepared following
2
5
the literature method, and found to be effective to cleave
the ether bond. The hexaalkoxytriphenylene and different
equivalents of imidazolium bromide were heated at about
ꢀ
1
65 C for different time intervals (Table S5), and the prod-
uct was isolated by conventional work-up and purified
through column chromatography using neutral alumina.
The best yield of mono-functionalized triphenylene was
4. Experimental
4.1. General
3
3% after 24 h with 11% of dihydroxy derivative. The
amount of reagent, reaction time, and temperature are sum-
marized in Table S5.
Chemical and solvents were obtained locally from E. Merck
and used as such without any purification. Column chroma-
tographic separations were performed on neutral aluminum
oxide. TLC was performed on aluminum sheets precoated
with silica gel (Merck, Kieselgel 60 F254). NMR spectra
were recorded on a 400 MHz Bruker NMR spectrometer.
The transition temperatures and associated enthalpy values
were determined using a differential scanning calorimeter
(DSC; Perkin–Elmer, Model Pyris 1D), which was operated
We have also applied all the reagents (I–V) to prepare mono-
functionalized triphenylene derivative under microwave ir-
radiation. While reagents I, III, and IV did not give any
mono-functionalized triphenylene under microwave heating
condition for more than 5–10 min, reagents II and V pro-
duced the desired product. A summary of the best yields
and conditions is given in Table 2. More descriptive data
are given in supplementary Tables S6 and S7.
ꢀ
ꢁ1
at a scanning rate of 5 C min both on heating and cooling.
ꢀ
The apparatus was calibrated using indium (156.6 C) as
a standard.
Table 2. Preparation of monohydroxypentaalkoxytriphenylene 2 using
reagents II and V under microwave heating
Entry
1
Reagent (equiv) MW power (W) Time (min) 2 (%)
4.2. Synthesis of mono-functionalized triphenylenes
under thermal conditions
1
2
3
4
5
6
H4TP II (3.0)
H5TP II (3.0)
H6TP II (3.0)
H4TP V (3.0)
H5TP V (3.0)
H6TP V (3.0)
360
360
600
600
360
600
5
5
3
3
5
3
36
34
28
26
30
30
In a typical reaction, the hexaalkoxytriphenylene 1 (H5TP,
500 mg, 0.675 mmol) was taken in a round-bottomed flask
with appropriate equivalents of the ionic reagent. The mix-
ꢀ
ture was heated at 165–170 C under sealed conditions for

S. K. Pal et al. / Tetrahedron 63 (2007) 6874–6878
6877
different periods of time as shown in Table 1. The crude
Supplementary data
product was purified by column chromatography over neu-
tral aluminum oxide. Elution of column with 2–5% ethyl
acetate in petroleum ether afforded the hexaalkoxytriphenyl-
ene 1, while the elution with 10% ethyl acetate in petroleum
ether furnished the pure monohydroxypentaalkoxytriphenyl-
enes 2.
Supplementary data associated with this article can be found
in the online version, at doi:10.1016/j.tet.2007.04.058.
References and notes
4.3. Synthesis of mono-functionalized triphenylenes
under microwave irradiation
1. For a recent review on DLCs see, e.g.: (a) Kumar, S. Chem. Soc.
Rev. 2006, 35, 83; (b) Donnio, B.; Deschenaux, R.; Bruce, D. W.
Compr. Coord. Chem. 2003, 7, 357; (c) Bushby, R. J.; Lozman,
O. R. Curr. Opin. Colloid Interface Sci. 2002, 7, 343; (d)
Tschierske, C. Annu. Rep. Prog. Chem., Sect. C 2001, 97, 191;
(e) Handbook of Liquid Crystals; Demus, D., Goodby, J., Gray,
G. W., Spiess, H.-W., Vill, V., Eds.; Wiley-VCH: Weinheim,
1998; Vol. 2B; (f) Chandrasekhar, S. Liq. Cryst. 1993, 14, 3;
(g) Chandrasekhar, S.; Kumar, S. Sci. Spectra 1997, 8, 66.
2. Kumar, S. Liq. Cryst. 2004, 31, 1037.
H4TP (330 mg, 0.5 mmol) was taken in a glass vial,
bmin]Br (330 mg, 1.5 mmol) was added, and the mixture
[
was thoroughly mixed and irradiated for 1 min under the de-
sired microwave power. The vial was taken out and once
again kept back for 1 min and this procedure was continued
up to desired time. Then the vial was cooled to room temper-
ature. The mixture was dissolved in dichloromethane and
then passed through a column to isolate the pure product.
3. Kumar, S. Liq. Cryst. 2005, 32, 1089.
4
5
. Chandrasekhar, S.; Sadashiva, B. K.; Suresh, K. A. Pramana
1977, 9, 471.
. Billard, J.; Dubois, J. C.; Tinh, N. H.; Zann, A. Nouv. J. Chim.
1978, 2, 535.
4
.4. Characterization
The monohydroxypentaalkoxytriphenylene derivatives were
characterized from their spectral data, phase behavior, and
by direct comparison with authentic samples. Spectral data
of all the mono-functionalized derivatives with different pe-
ripheral chain lengths were found to be in accordance with
6. Destrade, C.; Mondon, M. C.; Malthete, J. J. Phys. Colloq. C3
1979, 40, 17.
7. Boden, N.; Borner, R. C.; Bushby, R. J.; Cammidge, A. N.;
Jesudason, M. V. Liq. Cryst. 1993, 15, 851.
8. Kumar, S.; Vaeshney, S. K. Liq. Cryst. 1999, 26, 1841.
1
2,13,16,26
the literature data.
Selected data are as follows.
9
. Kumar, S.; Manickam, M. Chem. Commun. 1997, 1615.
1
Compound 2a: H NMR (400 MHz, CDCl ): d 7.96 (s, 1H),
3
10. Kreuder, W.; Ringsdorf, H. Makromol. Chem., Rapid Commun.
1983, 4, 807.
11. Closs, F.; Haussling, L.; Henderson, P.; Ringsdorf, H.;
Schuhmacher, P. J. Chem. Soc., Perkin Trans. 1 1995, 1059.
12. Henderson, P.; Ringsdorf, H.; Schuhmacher, P. Liq. Cryst.
1995, 18, 191.
13. Boden, N.; Bushby, R. J.; Cammidge, A. N.; El-Mansoury, A.;
Martin, P. S.; Lu, Z. J. Mater. Chem. 1999, 9, 1391.
14. Rose, A.; Lugmair, C. G.; Swager, T. M. J. Am. Chem. Soc.
2001, 123, 11298.
7
1
.83 (m, 4H), 7.78 (s, 1H), 5.90 (br s, 1H), 4.24 (m, 10H),
.94 (m, 10H), 1.58 (m, 10H), 1.04 (t, J¼7.2 Hz, 15H);
1
3
C NMR (100 MHz, CDCl ): d 149.0, 148.8, 145.9,
3
1
6
2
1
45.3, 124.0, 123.7, 123.3, 123.0, 107.3, 106.6, 104.4,
9.6, 69.3, 68.8, 31.5, 19.4, 14.0; IR (KBr, all the derivatives
a–2c showed similar spectra): nmax 3545, 2953, 2928, 2858,
616, 1518, 1437, 1389, 1352, 1261, 1171, 1074, 835 cm
UV–vis data (CHCl all the derivatives 2a–2c show similar
3
ꢁ
1
;
,
spectrum): l
276.8, 303.2, 344.0 nm; DSC (peak temper-
max
ꢀ
ature in C and associated enthalpy changes J/g in parenthe-
ses, Cr¼crystals, I¼isotropic): Cr 112.0 (56) I; Elemental
analysis: calculated for C H O : C 75.47, H 8.66%; found:
15. Bushby, R. J.; Lu, Z. Synthesis 2001, 763.
16. Kumar, S.; Manickam, M. Synthesis 1998, 1119.
17. Kumar, S.; Lakshmi, B. Tetrahedron Lett. 2005, 46, 2603.
18. (a) Ionic Liquids in Synthesis; Wasserscheid, P., Welton, T.,
Eds.; Wiley-VCH: Weinheim, 2002; (b) Rogers, R. D.;
Seddon, K. R. Ionic Liquids: Industrial Applications to
Green Chemistry; Rogers, R. D., Seddon, K. R., Eds.; ACS
Symposium Series 818; American Chemical Society:
Washington, DC, 2002; p XIII.
3
8 52 6
C 75.18, H 9.10%.
1
Compound 2b: H NMR (400 MHz, CDCl ): d 7.96 (s,
3
H), 7.83 (m, 4H), 7.78 (s, 1H), 5.90 (br s, 1H), 4.24
m, 10H), 1.94 (m, 10H), 1.50 (m, 20H), 0.98 (m, 15H);
1
(
1
3
C NMR (100 MHz, CDCl ): d 149.2, 149.0, 148.8,
3
1
1
1
45.9, 145.3, 124.0, 123.7, 123.3, 123.0, 107.6, 107.3,
06.5, 104.3, 69.9, 69.6, 69.1, 29.2, 29.0, 28.4, 22.6,
4.1; DSC: Cr 64 (28), Cr 82 (27) I; Elemental analysis: cal-
19. For reviews on applications of ionic liquids in Organic
Synthesis, see: (a) Seddon, K. R. J. Chem. Technol.
Biotechnol. 1997, 68, 351; (b) Welton, T. Chem. Rev. 1999,
99, 2071; (c) Wasserscheid, P.; Keim, W. Angew. Chem., Int.
Ed. 2000, 39, 3772; (d) Sheldon, R. Chem. Commun. 2001,
culated for C H O : C 76.52, H 9.26%; found: C 76.29, H
4
9
3
62
6
.60%.
2
399; (e) Dupont, J.; de Souza, R. F.; Suarez, P. A. Z. Chem.
1
Compound 2c: H NMR (400 MHz, CDCl ): d 7.96 (s,
3
Rev. 2002, 102, 3667; (f) Corma, A.; Garcia, H. Chem. Rev.
2003, 103, 4307; (g) Song, C. E. Chem. Commun. 2004, 1033.
20. For recent reviews on MW-assisted Organic Synthesis, see: (a)
Kappe, C. O. Angew. Chem., Int. Ed. 2004, 43, 6250; (b)
Wiesbrock, F.; Hoogenboom, R.; Schubert, U. S. Macromol.
Rapid Commun. 2004, 25, 1739; (c) Nuchter, M.;
Ondruschka, B.; Bonrath, W.; Gum, A. Green Chem. 2004, 6,
128; (d) Bose, A. K.; Manhas, M. S.; Ganguly, S. N.;
Sharma, A. H.; Banik, B. K. Tetrahedron 2001, 57, 9225; (e)
1
1
(
H), 7.83 (m, 4H), 7.78 (s, 1H), 5.90 (br s, 1H), 4.29 (m,
0H), 1.94 (m, 10H), 1.57 (m, 10H), 1.40 (m, 20H), 0.93
m, 15H); C NMR (100 MHz, CDCl ): d 149.1, 148.8,
3
45.9, 145.3, 124.0, 123.7, 123.2, 123.0, 107.7, 107.5,
07.3, 106.5, 104.4, 69.9, 69.7, 69.2, 31.7, 29.4, 29.3,
5.8, 22.7, 14.1; DSC: Cr 65 (63) I; Elemental analysis:
1
3
1
1
2
calculated for C H O : C 77.38, H 9.74%; found: C
4
8 72 6
7
7.31, H 9.98%.

6878
S. K. Pal et al. / Tetrahedron 63 (2007) 6874–6878
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Liagre, M.; Loupy, A.; Luche, J. L.; Petit, A. Tetrahedron 1999,
5, 10851; (g) Loupy, A.; Petit, A.; Hamelin, J.; Texier-Boullet,
F.; Jacquault, P.; Mathe, D. Synthesis 1998, 1213; (h) Caddick,
S. Tetrahedron 1995, 51, 10403.
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