Design of new synthetic strategies to cyclophanes via ring-closing metathesis

Article abstract of DOI:10.1016/j.tetlet.2014.10.092

A simple synthetic methodology to cyclophanes containing hydroxyl groups has been reported. The key steps involved here are: Grignard reaction, double Claisen rearrangement, and ring-closing metathesis. The strategy reported here is protecting group-free synthesis.

Full text of DOI:10.1016/j.tetlet.2014.10.092

Tetrahedron Letters 55 (2014) 6972–6975
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Design of new synthetic strategies to cyclophanes via ring-closing
metathesis
⇑
Sambasivarao Kotha , Mukesh E. Shirbhate
Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai 400 076, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple synthetic methodology to cyclophanes containing hydroxyl groups has been reported. The key
steps involved here are: Grignard reaction, double Claisen rearrangement, and ring-closing metathesis.
The strategy reported here is protecting group-free synthesis.
Received 9 September 2014
Revised 7 October 2014
Accepted 9 October 2014
Available online 22 October 2014
Ó 2014 Elsevier Ltd. All rights reserved.
Keywords:
Cyclophanes
Macrocycles
Ring-closing metathesis
Grignard reaction
Claisen rearrangement
Pyridine derivatives
Cyclophanes are endowed with unique molecular architecture
and interesting chemical properties.1–12 More importantly, mole-
cules containing pyridine moiety or free hydroxyl groups have
received much attention due to their unique complexing abilities
with various metal ions.13 Cyclophanes are versatile building
blocks in organic, inorganic as well as supramolecular chemistry
shown in Figure 1. The scheme reported here, are devoid of
protecting groups usage.
42
Results and discussion
To realize the strategy shown in Figure 1, the commercially avail-
able 4-bromophenol (1) and the allyl bromide were reacted in the
1
4–19
and therefore their synthesis is of considerable interest.
20
Several popular reactions such as aldol condensation, Baylis–
presence of K
in acetonitrile to generate the corresponding O-allyl phenol (2) in
8% yield. Later, a readily available 2,6-pyridinedicarbonitrile (3)
2 3
CO . The allylation reaction proceeds efficiently at rt
2
1
22
Hillman reaction, Beckmann rearrangement, Claisen rearrange-
2
3
24
25
ment,
Diels–Alder reaction,
coupling, Negishi coupling, Hay coupling, and Sonogashira
McMurry coupling,
Suzuki
9
2
6
27
28
4
3
was reacted with the Grignard reagent, prepared from the O-allyl
bromophenol (2) and an active magnesium turning in the presence
of catalytic quantities of iodine in THF. The desired bis-O-allyl deriv-
ative was not characterized due to the presence of some impurities
and further, it was directly subjected to the Claisen rearrangement
2
9
coupling have been employed as key steps to synthesize intricate
cyclophane derivatives. However, utilization of Grignard reaction,
Claisen rearrangement, and ring-closing metathesis (RCM) or com-
bination of any of these two reactions for cyclophane synthesis is
rarely found in the literature. As a part of the major program aimed
(Scheme 1). We attempted to purify bis-O-allyl derivative 5 by
at the synthesis of various macrocycles and cyclophanes by adopt-
column chromatography which led to the decomposition. When
the bis-O-allyl derivative 5 was subjected to the Claisen rearrange-
ment at 180 °C in 1,2-dichlorobenzene (DCB) for 8 h, a rearranged
product 6 was obtained. DCB turned out to be a better solvent than
decalin and N,N-dimethylaniline (Scheme 1). The structure of the
ing a simple methodology,3
0–35
herein, we report a new synthetic
strategy to assemble cyclophane derivatives by utilizing the Grig-
nard reaction, a double Claisen rearrangement,3
6,37
and RCM
38–40
as key steps. Claisen rearrangement is a useful tool for the incorpo-
4
1
1
13
ration of C–C bond in various polycycles and natural products.
Claisen rearrangement product 6 was confirmed by H NMR,
C
The strategy based on these three reactions is unique and concise
in nature. The retrosynthetic scheme to cyclophane derivatives is
NMR spectral data and further supported by HRMS data. Later, the
di-allyl derivative 6 was further subjected to RCM protocol using
the Grubbs second generation catalyst (G-II). In order to optimize
the reaction condition for RCM, we have picked dichloromethane
(DCM) as the solvent, but the cyclization failed because compound
⇑
Corresponding author. Fax: +91 (22)25723480.
E-mail address: srk@chem.iitb.ac.in (S. Kotha).
http://dx.doi.org/10.1016/j.tetlet.2014.10.092
040-4039/Ó 2014 Elsevier Ltd. All rights reserved.
0

S. Kotha, M. E. Shirbhate / Tetrahedron Letters 55 (2014) 6972–6975
6973
MgBr
O
O
NC
X
O
O
O
OH
OH
OH
X
X
X
O
OH
X = CH or N
Figure 1. Retrosynthetic approach to cyclophane derivatives.
NC
O
O
O
Br
O
Br
CN
N
CN
N
O
O
(i)
(ii)
N
O
CN
O
O
OH
O
4
5
1
2
3
(
iii)
O
O
O
OH
OH
OH
OH
OH
OH
(v)
N
(iv)
N
N
O
O
O
8
7
6
Scheme 1. Synthesis of cyclophane derivative (8) by using DCR and RCM strategies. Reagents and conditions: (i) K
2
CO
3
, CH
3
CN, allyl bromide, rt, 6 h, 98%; (ii) Mg, I
2
, THF, rt,
1
2 h, 59%; (iii) 1,2-dichlorobenzene, 8 h, 190 °C, 81%; (iv) G-II, 5 mol %, toluene, reflux, 18 h, 62%; (v) Pd/C, (10 mol %), MeOH, rt, 12 h, 81%.
6
has low solubility in DCM and hence the starting material was
would play an important role in coordination chemistry and may
serve as useful building blocks in molecular recognition.
recovered. So we switched over to toluene in which the cyclization
proceeded at reflux temperature to give the RCM product 7 in 62%
yield as a mixture of cis and trans isomers almost in an equal ratio.
After several attempts we were successful in crystallization of the
trans isomer of RCM product 7 in methanol and acetonitrile (1:1).
Later, hydrogenation of the unsaturated cyclophane derivative 7
using activated Pd/C (10 mol %) in the presence of hydrogen in
anhydrous methanol furnished the saturated cyclophane derivative
Experimental
General procedure for Grignard reaction
To a stirred mixture of Mg turnings, (2.5 equiv) in THF a crys-
tal of iodine was added, and the reaction mixture was stirred at
rt. Later, the brown color disappears. Then, O-allyl bromobenzene
(2) (2.5 equiv) was added, and the reaction mixture was stirred
for 30 min. Then 2,6-pyridinedicarbonitril (3) (or isophthalonitrile
9) (1.0 equiv) was added, and the resulting mixture was stirred
for 6 h, at rt. At the conclusion of the reaction (TLC monitoring),
the reaction mixture was quenched with EtOAc (10 mL), diluted
8
(81% yield, Scheme 1).
The cyclophane structure 7 was further confirmed by a single
crystal X-ray diffraction studies (Fig. 2),4 which clearly established
its trans configuration.
4
Adopting the same methodology, isophthalonitrile (9) was con-
verted to benzene containing cyclophane derivative 13 in four
steps (Scheme 2). The Grignard reaction, yielded the mono-addi-
tion product 10, (35% yield) and the di-addition product 11, (55%
yield). On subjection of the O-allyl benzene derivative 11 to double
Claisen rearrangement in DCB the rearranged product 12, (73%
yield) was generated. Compound 12 on treatment with G-II cata-
lyst gave the RCM product 13, (54% yield) as cis and trans isomers
with H
2
O (10 mL), and extracted with EtOAc (3 Â 10 mL). The
organic layer was washed with brine and dried over Na
2
SO
4
.
The solvent was removed under reduced pressure, and the crude
product obtained was purified by column chromatography (silica
gel 5% EtOAc–petroleum ether) to obtain the O-allyl product 10
and 11.
À1
(Scheme 2). Later, it occurred to us that O-allyl benzene derivative
10: (mp decomposed at 91 °C); IR (KBr, cm ) 616, 1123, 1503,
1
1
1 is also a useful substrate for cyclophane synthesis. Therefore, 11
2111, 2854, 3340; H NMR (400 MHz, CDCl
3
) d = 4.60–4.63 (m, 2H),
was subjected to the RCM sequence in the presence of G-II catalyst
to generate the cyclophane derivative. Interestingly, when the
O-allyl benzene derivative 11 was subjected to the metathesis
sequence, we found that dimer 14 (48% yield) was formed in
contrast to the Claisen rearranged product 12 (Scheme 2).
In conclusion, we have developed a simple and protecting group
free approach to cyclophane derivatives containing hydroxyl
groups. The methodology reported here involves a sequential use
of the Grignard reaction, the Claisen rearrangement, and the RCM
as the key steps. We anticipate that the reported compounds
5.30–5.45 (m, 2H), 5.99–6.09 (m, 1H), 6.96–6.98 (m, 2H), 7.67 (t,
7.1 Hz, 1H) 7.75 (d, 1.3 Hz, 2H), 7.81 (d, 1.4 Hz, 1H), 7.95–7.99
(m, 2H), ppm.; C NMR (100.6 MHz, CDCl ): d = 69.09, 112.73,
3
1
3
114.53, 114.74, 118.48, 129.04, 129.41, 132.38, 132.64, 133.20,
133.69, 134.99, 139.38, 162.93, 193.15 ppm.; HRMS (Q-ToF): m/z
+
calcd: 264.0965 for C17
H14NO
2
[M+H] ; found 264.0960.
À1
11: (mp decomposed at 83 °C); IR (KBr, cm ) 627, 1094, 1452,
1574, 2634, 3349; H NMR (400 MHz, CDCl ) d = 4.60–4.63 (m, 4H),
3
1
5.30–5.46 (m, 4H), 6.00–6.08 (m, 2H), 6.96–7.01 (m, 4H), 7.56
(t, J = 7.7 Hz, 1H), 7.81–7.84 (m, 4H), 7.94 (d, J = 1.7 Hz, 2H), 8.08

6
974
S. Kotha, M. E. Shirbhate / Tetrahedron Letters 55 (2014) 6972–6975
Figure 2. X-ray crystal structure of 7 with 50% probability.
Br
O
CN
CN
CN
O
(i)
O
O
O
O
O
10
11
2
9
O
O
O
OH
OH
O
OH
OH
(
ii)
(iii)
O
O
O
O
12
11
13
O
O
O
O
O
(iii)
O
O
O
O
O
O
O
14
11
Scheme 2. Synthesis of cyclophane derivatives 13 and 14 by using DCR and RCM strategies. Reagents and conditions: (i) Mg, I
ii) 1,2-dichlorobenzene, 8 h, 190 °C, 73%; (iii) G-II, 5 mol %, toluene, reflux, 18 h, (13, 54%), (14, 48%).
2
, THF, rt, 12 h; 35% and 55%;
(
(
1
1
t, J = 1.5 Hz, 1H), ppm.; 13C NMR (100.6 MHz, CDCl
3
): d = 69.03,
14.53, 118.38, 128.48, 129.76, 130.70, 132.50, 132.67, 132.84,
38.41, 162.60, 194.74 ppm.; HRMS (Q-ToF): m/z calcd: 399.1598
chromatography. Elution of the column with 20% EtOAc–petro-
leum ether gave 2-allyl phenol (6, 81% yield).
À1
6: (mp decomposed at 176 °C); IR (KBr, cm ) 624, 918, 1280,
+
1
for C26
H
23
O
4
[M+H] ; found 399.1591.
1597, 1632, 3208, 3340; H NMR (400 MHz, (CD
3
2
) SO) d = 3.27
(
d, J = 6.5 Hz, 4H), 4.93–4.98 (m, 4H), 5.78–5.88 (m, 2H), 6.88 (d,
J = 8.4 Hz, 2H), 7.82 (dd, J = 10.5, 2.1 Hz, 2H), 7.85 (d, J = 1.9 Hz,
H), 8.08 (d, J = 7.2 Hz, 2H), 8.20 (t, J = 8.1 Hz, 1H), 10.56 (br s,
General procedure for Claisen rearrangement
2
1
3
O-Allyl phenol 5 (3 mmol) was dissolved in 1,2-dichloroben-
zene and the reaction mixture was heated at 170–180 °C for 8 h
in a sealed tube. After completion of the reaction (TLC monitoring),
the reaction mixture was cooled and purified by silica gel column
3 2
2H) ppm.; C NMR (100.6 MHz, (CD ) SO): d = 33.59, 114.53,
115.94, 125.93, 126.28, 126.91, 131.68, 133.10, 136.33, 138.90,
154.40, 160.37, 190.97 ppm.; HRMS (Q-ToF): m/z calcd: 422.1368
+
for C25
H
21NNaO
4
[M+Na] ; found 422.1363.

S. Kotha, M. E. Shirbhate / Tetrahedron Letters 55 (2014) 6972–6975
6975
20NO
À1
1
2: (mp decomposed at 170 °C); IR (KBr, cm ) 627, 1094, 1338,
192.22 ppm.; HRMS (Q-ToF): m/z calcd: 374.1388 for C23
H
4
1
+
1
425, 1574, 1634, 3349; H NMR (400 MHz, (CD
3
)
2
SO) d = 3.32 (d,
[M+H] ; found 374.1387.
J = 6.9 Hz, 4H), 5.00–5.07 (m, 4H), 5.74–5.99 (m, 2H), 6.92 (d,
J = 8.4 Hz, 2H), 7.53 (dd, J = 8.3, 2.2 Hz, 2H), 7.59 (d, J = 2.0 Hz, 2H),
Acknowledgments
7
2
.69 (t, J = 7.7 Hz, 1H), 7.89 (d, J = 1.5 Hz, 1H), 7.91 (d, J = 1.4 Hz,
H), 10.55 (br s, 2H) ppm.; 1 C NMR (100.6 MHz, (CD
3
We thank the DST, New Delhi, India for the financial support
and SAIF, Mumbai for recording the spectral data. MES thanks
the IIT-Bombay for the award of a research fellowship. SK thanks
the DST for the award of a J. C. Bose fellowship.
) SO):
3 2
d = 33.52, 114.64, 116.04, 126.61, 127.53, 128.78, 129.78, 130.78,
32.07, 132.28, 136.39, 138.07, 160.05, 193.72 ppm. HRMS
1
+
(Q-ToF): m/z calcd: 421.1414 for C26
H
22NaO
4
[M+Na] ; found 421.1410.
Supplementary data
General procedure for RCM
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2014.10.
Claisen rearrangement product 6 (0.2 mmol) was dissolved in
dry toluene (10 mL) and degassed with nitrogen for 15 min. Then,
Grubbs second generation catalyst (10 mg, 5 mol %) was added and
the reaction mixture was refluxed overnight. At the conclusion of
the reaction (TLC monitoring), the crude mixture product was fil-
tered through Celite pad, washed with EtOAc, and concentrated
under reduced pressure. The crude product was purified by column
chromatography (silica-gel 20% EtOAc–petroleum ether) to afford
0
92. These data include MOL files and InChiKeys of the most
important compounds described in this article.
References and notes
1
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6
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À1
7: (mp decomposed at above 300 °C); IR (KBr, cm ) 628, 1074,
1
1
423, 1574, 3274.; (cis/trans isomer ratio = 1:1):
H NMR
4
5
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(
400 MHz, (CD SO) d = 3.27 (s, 2H), 3.38 (s, 2H), 5.53–5.77 (m,
3 2
)
2
2
1
H), 6.96–7.01 (m, 2H), 7.60 (d, J = 1.5 Hz, 1H), 7.80 (d, J = 12 Hz,
H), 7.85–7.90 (m, 2H), 8.00 (d, J = 7.7 Hz, 1H), 8.16–8.24 (m,
H), 10.68 (br s, 2H) ppm.; 1 C NMR (100.6 MHz, (CD
3
6. Vogtle, F. Cyclophane Chemistry: Synthesis, Structures, and Reaction; John Wiley
3
)
2
SO):
and Sons: Chichester, U.K., 1991.
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7
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1
1
C
27.75, 128.85, 129.22, 130.00, 133.99, 134.82, 139.12, 155.82,
9.
60.64, 192.37 ppm.; HRMS (Q-ToF): m/z calcd: 372.1237 for
+
10. Boyle, M. M.; Gassensmith, J. J.; Whalley, A. C.; Forgan, R. S.; Smaldone, R. A.;
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18, 10312.
23
H18NO
4
[M+H] ; found 372.1230.
À1
1
3: (mp decomposed above 300 °C); IR (KBr, cm ) 687, 1086,
1
1
444, 1564, 3234.; (cis/trans isomer ratio = 1:1):
H
NMR
11. Elacqua, E.; MacGillivray, L. R. Eur. J. Org. Chem. 2010, 6883.
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(
400 MHz, (CD
3
)
2
SO) d = 3.28 (s, 2H), 3.44 (s, 2H), 5.68–5.83 (m,
1
2
7
H), 6.99–7.00 (m, 2H), 7.55 (d, 1.9 Hz, 2H), 7.65 (d, 11 Hz, 1H),
.70–7.87 (m, 2H), 7.92 (d, 1.5 Hz, 2H), 7.93–8.00 (m, 1H), 10.52
1
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1
3
(
br s, 2H) ppm.;
3 2
C NMR (100.6 MHz, (CD ) SO): d = 30.60,
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1
1
15.76, 115.95, 126.26, 127.51, 129.01, 130.02, 130.18, 132.26,
2006, 14, 7458.
33.38, 137.23, 138.09, 159.83, 160.35, 193.39, 193.71 ppm.; HRMS
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+
(
Q-ToF): m/z calcd: 371.1279 for C24
H
19
O
4
[M+H] ; found 371.1278.
1
1
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À1
1
4: (mp decomposed at above 198 °C); IR (KBr, cm ) 682,
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1
1
3
) d = 4.83 (s,
2
2
2
0. Lorenzi-Riatsch, A.; Waelchli, R.; Hesse, M. Helv. Chim. Acta 1985, 68, 2177.
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8
H), 5.83 (s, 4H), 6.93 (d, J = 8.6 Hz, 8H), 7.41 (s, 2H), 7.55 (d,
J = 8.6 Hz 8H), 7.73 (t, J = 7.6 Hz, 2H), 8.28 (dd, J = 7.7, 1.6 Hz, 4H)
1
3
ppm.; C NMR (100.6 MHz, CDCl
1
1
3
): d = 68.14, 115.49, 128.73,
29.88, 131.04, 131.42, 132.91, 136.96, 137.14, 160.82,
95.76 ppm.; HRMS (Q-ToF): m/z calcd: 763.2302 for C48 36NaO
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2
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4
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+
[
M+Na] ; found 763.2302.
2
General procedure for hydrogenation
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3
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Olefinic compound 7 (45 mg, 0.12 mmol) was dissolved in dry
methanol (10 mL) and (10 mol %) Pd/C catalyst was added. Then,
the reaction mixture was stirred at rt under hydrogen atmosphere
3
3
3
(
1 atm) for overnight. After completion of the reaction (TLC moni-
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EtOAc–petroleum ether) to give the hydrogenated product 8
34. Kotha, S.; Waghule, G. T.; Shirbhate, M. E. Eur. J. Org. Chem. 2014, 984.
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3
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014, 138.
3
(
36 mg, 81% yield)
À1
8
: (mp decomposed at 289 °C); IR (KBr, cm ) 623, 1072, 1413,
2
1
1
564, 3264; H NMR (400 MHz, (CD
3
)
2
SO) d = 1.51 (s, 4H), 2.63–
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.68 (m, 4H), 6.95 (d, J = 8.6 Hz, 2H), 7.78–7.82 (m, 2H), 7.86 (d,
4
4
3. Kurosawa, W.; Kan, T.; Fukuyama, T. J. Am. Chem. Soc. 2003, 125, 8112.
4. CCDC-1011914 (7) contains the supplementary crystallographic data for this
Letter. This data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
J = 1.9 Hz, 2H), 7.96 (d, J = 1.9 Hz, 2H), 8.23 (t, J = 1.8 Hz, 1H)
1
3
ppm.; C NMR (100.6 MHz, (CD
3 2
) SO): d = 26.39, 27.52, 115.88,
1
26.07, 126.44, 127.77, 128.93, 136.76, 139.15, 155.23, 160.75,