Synthesis of macrocyclic tetraindolyls via oxidative coupling reactions

Article abstract of DOI:10.1016/j.tetlet.2012.04.082

The reaction of 4,6-dimethoxyindoles with stannic chloride results in an oxidative biaryl coupling, producing a series of 2,7′-biindolyls. Reactions of representatives of these biindolyls with p-benzoquinone gave the novel tetraindolyls.

Full text of DOI:10.1016/j.tetlet.2012.04.082

Tetrahedron Letters 53 (2012) 3337–3341
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Tetrahedron Letters
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Synthesis of macrocyclic tetraindolyls via oxidative coupling reactions
⇑
Rui Chen, Mohan Bhadbhade, Naresh Kumar, David StClair Black
School of Chemistry, The University of New South Wales, Sydney, NSW 2052, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 23 April 2012
The reaction of 4,6-dimethoxyindoles with stannic chloride results in an oxidative biaryl coupling, pro-
ducing a series of 2,70-biindolyls. Reactions of representatives of these biindolyls with p-benzoquinone
gave the novel tetraindolyls.
Keywords:
Indoles
Ó 2012 Elsevier Ltd. All rights reserved.
Macrocycles
Aryl coupling
Oxidative coupling
Indorphyrins
The porphyrin structure 1 is a very important framework
among the molecules of life.1–3 Research into porphyrin com-
pounds is expanding to include possibilities for the generation
of new materials.4–6 Ever since we began an investigation of
indoles which were deliberately activated to undergo reaction
at C2 and C7, we have been attracted to the 2,7;2,7;2,7;2,7-tetra-
indolyl structure 2, for which we suggest the name ‘indorphyrin’
(Fig. 1).
The comparative reactivity of C2 and C7 in these systems has been
found to be dependent upon the C3-substitutent, with electron-
withdrawing groups deactivating the C2 position so that C7-substi-
tution is favoured, and electron-donating groups activating the C2
position so that C2-substitution is comparable or preferable to C7-
substitution.13 Synthesis of indorphyrins 2 requires the appropri-
ate direct coupling of either indoles or biindolyls at C2 and C7.
The formation of all types of biindolyls has recently been re-
viewed.14 We have previously reported oxidative coupling of 2,3-
disubstituted-4,6-dimethoxyindoles 3 to give the 7,70-biindolyls 5
under a variety of conditions,15–17 but the corresponding reaction
of 3-substituted-4,6-dimethoxyindoles 4 gave complex mixtures
from which no single product could be isolated (Scheme 1). We
have also developed effective syntheses of 2,70-biindolyls by the
use of 2-indolinone combined with phosphoryl chloride or triflic
anhydride in modifications of the Vilsmeier reaction.18–20 How-
ever, this approach could not be extended satisfactorily to 4,6-
dimethoxy-2-indolinones.
7-Acetyl-4,6-dimethoxy-3-substituted-indoles can be prepared
using N,N-dimethylacetamide and phosphoryl chloride in a modi-
fied Vilsmeier reaction.21 However, in the course of preparing the
7-acetylindole derivative from indole 4a under alternative
Friedel-Crafts acetylation conditions [acetonitrile in dichlorometh-
ane and nitromethane using tin(IV) chloride as catalyst],22 2,70-
biindolyl 6a23 was isolated instead of the 7-acetylindole when the
mixture was heated at reflux overnight. The structure of biindolyl
6a was elucidated from the 1H NMR spectrum, which showed H5
and H2 of the first indole unit as singlets at d 6.50 and d7.13, respec-
tively, and the H50 and H70 protons of the second indole unit as dou-
blets at d 6.28 and d 6.64, respectively. The formation of the 2,70-
linkage was further confirmed from the 13C and 2D NMR spectro-
scopic data (Scheme 2).
The interest in the indorphyrin structure lies in the fact that
while it superficially resembles the porphyrin structure, it does
not contain a cyclic 18-p aromatic ring system. Moreover, such a
cyclic aromatic system cannot be generated without the destruction
of the aromaticity of two of the four indoles. Consequently, the
properties of indorphyrins are likely to be quite different from those
of porphyrins, but no less interesting. The indorphyrin structure has
also been suggested for eumelanin protomolecules.7 For the past
25 years, we have—from time to time—investigated rational but
unsuccessful synthetic routes to examples of this system. Interest-
ingly, we have recently and unexpectedly found a direct synthetic
route to these structures. Our group is not alone in its interest in
the indorphyrin structure, as Nakamura et al. have recently pub-
lished the synthesis of an indorphyrin via an iridium-catalysed C–
H borylation-cross coupling sequence.8 This publication prompts
us to disclose our different, but complementary synthetic route.
Our group has previously developed efficient synthetic
methodologies to 4,6-dimethoxyindoles.9–12 2,3-Disubstituted-
4,6-dimethoxyindoles 3 are activated to react at C7. However, 3-
substituted-4,6-dimethoxyindoles 4 are activated at both the C2
and C7 positions towards electrophilic substitution and addition.
⇑
Corresponding author.
E-mail address: d.black@unsw.edu.au (D.StC. Black).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.04.082

3338
R. Chen et al. / Tetrahedron Letters 53 (2012) 3337–3341
OMe
R
OMe
R
OMe
R
N
H
MeO
N
H
Cl Sn Cl
MeO
N
H
MeO
H
N
OMe
9
8
R
OMe
7
Figure 1. Structures of porphyrin and indorphyrin.
Figure 2. Possible intermediates in the formation of 2,70-biindolyls 6.
OMe
R
Cl
Cl
Cl
OMe
R
R
R
N
a
MeO
H
R
H
N
OMe
OMe
MeO
OMe
a = C6H5
N
MeO
H
R
b
= p-MeOC6H4
a
c = CO2Me
NH HN
3
N
H
MeO
MeO
R
OMe
OMe
MeO
HN
NH
5
Cl
NH
Cl
Cl
Scheme 1. Formation of 7,70-biindolyls 5. Reaction conditions: (a) p-benzoquinone,
or DDQ, CH2Cl2, RT, yield = 60–100%.
OMe
MeO
OMe
OMe
OMe
6a
10a
OMe
R
Scheme 3. Synthesis of 10a. Reaction conditions: (a) HCl, p-benzoquinone, CH2Cl2,
RT, 3 h, yield = 50%.
OMe
R
a
N
H
MeO
R
N
H
MeO
tin(IV) chloride added. The reactions were stirred at room temper-
ature for 1 h before being heated at reflux overnight to afford
2,70-biindolyls 6b–d in moderate yields (Scheme 2). Strongly
electron-withdrawing groups were found to inhibit this reaction,
and no reaction occurred with p-nitrophenyl substituted indole 4e.
NH
MeO
4
OMe
6
It is well known that tin(IV) chloride can form p-type electron
donor-acceptor complexes with aryl donors.24 In particular, the
formation of SnCl4ꢀ2C8H7N addition compounds between indoles
and tin(IV) chloride have been reported.22 Mechanistically, it is
therefore proposed that the oxidative coupling proceeds via a tin
complex, and this is supported by the observation that the solution
changed from a light yellow to a dark red colour upon the addition
of tin(IV) chloride.
Substrate
R
Product
Yield (%)
4a
4b
4c
4d
4e
p-ClC6H4
p-BrC6H4
p-MeC6H4
Me
6a
6b
6c
6d
6e
43
50
50
25
0
To elucidate this process further, 1H NMR titration experiments
were performed at room temperature using ratios of activated in-
dole 4a and tin(IV) chloride varying from 1:0 to 1:2 in CDCl3 and in
the presence of a drop of nitromethane. When the ratio was in-
creased to 1:0.5, the H7 proton at d 6.48 disappeared, indicating
the possible formation of a 2:1 indole-tin complex 7 (Fig. 2). The
H2 proton at d 6.25 remained, however, signifying that the biindol-
yl 6a was not produced at room temperature. The observed in-
crease in reaction rate in the presence of nitromethane suggests
that it assists the formation of this tin(IV) complex.
Although no further mechanistic experiments have been per-
formed so far, we hypothesize that 2,70-biindolyls 6 can be gener-
ated from a radical cation 8 or cationic 9 species (Fig. 2). Radical
mechanisms have been proposed in the synthesis of related 7,70-
biindolyl15–17 and 2,70-biindolyl systems,25 but no experimental
confirmation has been obtained. Formation of radical cation 8
would be expected to encourage the potential formation of 7,70-
biindolyl analogues, though none were isolated from the reaction
mixture. Furthermore, treatment of 4,6-dimethoxy-2,3-dipheny-
lindole (3a) under the optimised conditions above did not generate
the corresponding 7,70-biindolyl 5. Alternatively, the coupling reac-
tion might proceed via the cation 9, which could be generated from
p-O2NC6H4
Scheme 2. Synthesis of 2,70-biindolyls 6. Reaction conditions: (a) SnCl4, CH2Cl2,
MeNO2, MeCN, reflux, 12 h.
An investigation into the reaction conditions was performed in
order to identify the role of the reagents and solvents in the forma-
tion of biindolyl 6a. The results showed that the acetylating source,
acetonitrile, could be removed without changing the reaction out-
come. The use of dichloromethane was important to the reaction as
no biindolyl products were found using alternative solvents such
as tetrahydrofuran or carbon tetrachloride. Tin(IV) chloride was
also critical to this coupling process, as reactions using other Lewis
acids such as iron(III) chloride or copper(II) chloride yielded only
trace amounts of biindolyl. The use of nitromethane was found
to influence the rate of the reaction, with 1H NMR titration exper-
iments in CDCl3 showing the disappearance of the H7 proton at d
6.48 within 1 h in the presence of nitromethane instead of over
12 h in its absence.
A variety of activated indoles 4 were subsequently dissolved in
a mixture of dichloromethane and nitromethane and 0.5 equiv of

R. Chen et al. / Tetrahedron Letters 53 (2012) 3337–3341
3339
Figure 3. ORTEP diagram of structure 10a: top view and side view.
Me
OMe
N
H
MeO
MeO
Me
NH
OMe
Me
Me
6c
Me
Me
OMe
OMe
a
OMe
OMe
OMe
MeO
MeO
N
H
HN
NH
NH
HN
HN
H
Me
N
OMe
MeO
MeO
NH
OMe
Me
OMe
Me
OMe
MeO
OMe
OMe
10c
Scheme 4. Synthesis of 10c and 11c. Reaction conditions: (a) HCl, p-benzoquinone, CH2Cl2, RT, 3 h, yield for 10c = 18%; yield for 11c = 25%.
Me
11c
the tin complex 7 upon reduction assisted by mild heat. Subse-
quent reaction of the tin complex 7 with cation 9 could then gen-
erate the 2,70-linkage, and cleavage of the indole-tin bond could
restore aromaticity to produce the biindolyls 6.
In an attempt to extend this methodology to the development of
indorphyrins, biindoyls 6 were subsequently subjected to tin(IV)
chloride under the optimised conditions reported previously, but
no reaction was apparent. Conversely, oxidative coupling at room
temperature for 3 h in the presence of p-benzoquinone and acidified
dichloromethane13,14 successfully afforded the 2,2;7,2;7,7;2,7-
tetraindolyl compound 10a26 in 50% yield (Scheme 3).
The structure of 10a showed the inclusion of two molecules of
methanol, with one above and one below the centre of the macro-
cyclic ring and each coordinated to two opposite indole NH atoms
via two sets of hydrogen bonds. Hydrogen bond distances between
the four indole NH atoms and the two methanol oxygen atoms
were 2.28, 2.30, 2.12 and 2.22 Å and the two HꢀꢀꢀOꢀꢀꢀH bond angles
were 99.1° and 95.5°.
It is proposed that the head-to-head compound 10a was prefer-
entially produced due to the deactivation of the indole C2 position
by the electron-withdrawing p-ClC6H4 group at C3. This could re-
sult in preferential formation of the 7,70-linkage, and then a slower
oxidative coupling of the C2 positions. Accordingly, use of a biind-
olyl with an electron-donating group at C3 would be more likely to
give rise to the 2,7;2,7;2,7;2,7-tetraindolyl compound or indorph-
yrin 11. Thus the biindolyl 6c, with a p-MeC6H4 group at C3, was
treated with p-benzoquinone under the same conditions reported
above and was found to give a mixture of the head-to-head tetra-
indolyl compound 10c and head-to-tail indorphyrin 11c27 in 18%
and 25% yields, respectively (Scheme 4). The 1H NMR spectrum
The 1H NMR spectrum of 10a suggested that 2,20- and 7,70- link-
ages were formed between the two biindolyl units as there were two
sets of signals for each of the indole NH, aromatic, H5, and methoxy
protons. The two NH signals appeared (in CDCl3) at d 8.27 and d 8.15,
and the two H5 signals appeared at d 6.50 and d 6.16. The structure of
the head-to-head coupled tetraindolyl 10a was further confirmed by
X-ray crystallography (Fig. 3) of a crystal obtained from a mixture of
methanol, dichloromethane and n-hexane.

3340
R. Chen et al. / Tetrahedron Letters 53 (2012) 3337–3341
Figure 4. ORTEP diagram of structure 11c: top view and side view.
12. Black, D. StC.; Gatehouse, B. M. K. C.; Theobald, F.; Wong, L. C. H. Aust. J. Chem.
1980, 33, 343–350.
13. Black, D. StC.; Bowyer, M. C.; Kumar, N.; Mitchell, P. S. R. J. Chem. Soc., Chem.
Commun. 1993, 819–821.
14. Black, D. StC.; Kumar, N. Adv. Heterocycl. Chem. 2010, 101, 97–123.
15. Black, D. StC.; Choy, A.; Craig, D. C.; Ivory, A. J.; Kumar, N. J. Chem. Soc., Chem.
Commun. 1989, 111–112.
16. Black, D. StC.; Keller, P. A.; Kumar, N. Tetrahedron 1992, 48, 7601–7608.
17. Black, D. StC.; Bowyer, M. C.; Catalano, M. M.; Ivory, A. J.; Keller, P. A.; Kumar,
N.; Nugent, S. J. Tetrahedron 1994, 50, 10497–10508.
18. Black, D. StC.; Kumar, N. J. Chem. Soc., Chem. Commun. 1982, 977–979.
19. Black, D. StC.; Ivory, A. J.; Kumar, N. Tetrahedron 1996, 52, 4697–4708.
20. Black, D. StC.; Ivory, A. J.; Kumar, N. Tetrahedron 1996, 52, 7003–7012.
21. Wahyuningsih, T. D.; Pchalek, K.; Kumar, N.; Black, D. StC. Tetrahedron 2006, 62,
6343–6348.
of the indorphyrin 11c was very simple, showing one NH signal (in
CDCl3) at d 8.87 and one H5 signal at d 6.20.
A single crystal of the indorphyrin 11c was obtained from a
mixture of methanol, dichloromethane and n-hexane and the
structure was confirmed by X-ray crystallography (Fig. 4). Two
methanol molecules were also found to be associated with each
macrocycle. Each methanol forms two hydrogen bonds with NH
atoms of two opposite indoles. Hydrogen bond distances between
the four indole NH atoms and the two methanol oxygen atoms
were 2.14, 2.03, 2.12, and 2.16 Å, and the two HꢀꢀꢀOꢀꢀꢀH bonds an-
gles were 83.6° and 87.6°. Interestingly, two indorphyrins form a
cavity with two methanol molecules attached inside. These meth-
anol molecules are not only held by hydrogen bonds, but also show
22. Ottoni, O.; Neder, A. deV. F.; Dias, A. K. B.; Cruz, R. P. A.; Aquino, L. B. Org. Lett.
2001, 3, 1005–1007.
23. Biindolyl 6a was obtained as a white solid in 43% yield. mp 242 °C. (Found: C,
the presence of CH-p bonds.
66.90; H, 4.69; N, 4.74; C32H26Cl2N2O4 requires C, 67.02; H, 4.57; N, 4.88%). 1
H
In summary, 2,70-biindolyls have been prepared via a tin(IV)
chloride mediated oxidative coupling of 3-substituted-4,6-
dimethoxyindoles. Subsequent treatment of these 2,70-biindolyls
with p-benzoquinone gave rise to both 2,2;7,2;7,7;2,7-tetraindol-
yls and 2,7;2,7;2,7;2,7-tetraindolyls (indorphyrins). Further exam-
ples of these new systems are currently under preparation and an
investigation of their properties and reactivity is actively being car-
ried out. It is interesting that the macrocycles 10a and 11c demon-
strate an ability to bind neutral substrates such as alcohol
molecules. The two independent and complementary syntheses
of the new indorphyrin system, by Nakamura et al.8 and by us,
establish the viability of a structure which has the potential to be-
come an important scaffold for future development.
NMR (300 MHz, acetone-d6): d 10.17 (1H, s, NH), 9.87 (1H, s, NH), 7.59 (2H, d,
J = 8.31 Hz, ArH), 7.36 (2H, d, J = 2.0 Hz, ArH), 7.33 (2H, d, J = 2.0 Hz, ArH), 7.13
(1H, s, H2), 7.10–7.09 (2H, m, ArH), 6.64 (1H, d, J = 2.60 Hz, H7), 6.50 (1H, s,
H5), 6.28 (1H, d, J = 2.60 Hz, H50), 3.89 (3H, s, OCH3), 3.85 (3H, s, OCH3), 3.78
(3H, s, OCH3), 3.66 (3H, s, OCH3), 13C NMR (75 MHz, acetone-d6): d 157.3 (C6),
155.3 (C60), 154.8 (C4), 154.6 (C40), 138.6 (ArC), 138.3 (ArC), 135.8 (ArC), 135.4
(ArC), 131.9 (ArCH), 130.6 (Ar-CH), 130.4 (Ar-C), 130.1 (ArC), 127.3 (ArCH)
126.5 (ArCH) 122.2 (C2), 122.0 (C20), 116.7 (ArC), 114.7 (ArC), 111.6 (ArC),
110.0 (ArC), 98.2 (C7), 91.6 (C70), 89.2 (C5), 87.0 (C50), 56.0 (OCH3), 54.8 (OCH3),
54.5 (OCH3), 54.3 (OCH3). IR (KBr): mmax 3456, 2923, 2360, 1593, 1540, 1509,
1467, 1412, 1403, 1329, 1201, 1152, 1136, 1125, 1101, 1077, 1050, 1012, 966,
796, 525, 506 cmꢁ1. UV–vis (MeOH): kmax 202 nm (
(70,025), 241 (56,646), 307 (21,705). HRMS (+ESI) m/z 595.1150 (M+Na+,
32H26Cl2N2O4Na, requires 595.107).
e
90,588 cmꢁ1 Mꢁ1), 219
C
24. Bruggermann, K.; Kochi, J. K. J. Org. Chem. 1992, 57, 2956–2960.
25. Yepuri, N. R.; Haritakul, R.; Keller, P. A.; Skelton, B. W.; White, A. H. Tetrahedron
Lett. 2009, 50, 2501–2504.
26. Tetraindolyl macrocycle 10a was obtained as a pale green solid in 50% yield.
mp >300 °C. (Found: C, 67.14; H, 4.50; N, 4.66; C64H48Cl4N4O8 requires C,
67.26; H, 4.23; N, 4.90%). 1H NMR (300 MHz, DMSO-d6): d10.64 (2H, s, NH),
10.55 (2H, s, NH), 7.36 (4H, d, J = 8.48 Hz, ArH), 7.28 (4H, d, J = 8.78 Hz, ArH),
7.08 (8H, s, ArH), 6.51 (2H, s, H5), 6.31 (2H, s, H5), 3.78 (6H, s, OCH3), 3.72 (6H,
s, OCH3), 3.69 (6H, s, OCH3), 3.44 (6H, s, OCH3), 13C NMR (75 MHz, DMSO-d6): d
155.3 (ArC), 154.7 (ArC), 154.0 (ArC), 153.5 (ArC), 139.6 (Ar-C), 139.4 (Ar-C),
136.6 (Ar-C), 134.7 (Ar-C), 132.1 (Ar-CH), 131.7 (Ar-CH), 130.5 (Ar-C), 129.8
(Ar-C), 127.34 (Ar-CH), 127.32 (ArC), 127.0 (Ar-CH), 126.8 (ArC), 114.6 (ArC),
113.2 (ArC), 112.0 (C2), 110.4 (C2), 99.8 (C7), 97.6 (C7), 89.8 (C5), 89.7 (C5),
Acknowledgments
Research support from the Australian Research Council and the
University of New South Wales is gratefully acknowledged.
References and notes
57.2 (OCH3), 56.6 (OCH3), 55.7 (OCH3), 55.6 (OCH3). IR (KBr):
mmax 3406, 2932,
1. Dolphin, D. The Porphyrins; Academic Press: New York, 1978. Vols. I–VII.
2. Shelnutt, J. A.; Song, X.-Z.; Ma, J.-G.; Jia, S.-L.; Jentzen, W.; Medforth, C. J. Chem.
Soc. Rev. 1998, 27, 31–42.
3. Momenteau, M.; Reed, C. A. Chem. Rev. 1994, 94, 659–698.
4. D’Souza, F.; Ito, O. Chem. Soc. Rev. 2012, 41, 86–96.
5. Kurotobi, K.; Kim, K. S.; Noh, S. B.; Kim, D.; Osuka, A. Angew. Chem., Int. Ed. 2006,
45, 3944–3947.
2837, 2360, 1593, 1519, 1491, 1463, 1397, 1326, 1210, 1148, 1090, 994, 830,
545 cmꢁ1. UV–vis (MeOH): kmax 202 nm ( 209400 cmꢁ1 Mꢁ1), 220 (161600),
e
245 (120500), 345 (35800). HRMS (+ESI) m/z 1142.2172 (M+, C64H48Cl4N4O8,
requires 1142.2197). Single crystals were obtained from a mixed-solvent of
CH2Cl2, n-hexane and MeOH: C68.75H61Cl8N4O10
a = 12.0294(8) Å, b = 13.9578(9) Å, c = 41.743(3) Å,
= 90.00°, V = 7006.2(8) Å3, T = 155(2) K, space group P2(1)/c, Z = 4, 48942
reflections measured, 12305 independent reflections (Rint = 0.0624). The final
R1 values were 0.1076 (I > 2
(I)). The final wR(F2) values were 0.2961
(I > 2
(I)). The final R1 values were 0.1613 (all data). The final wR(F2) values
,
M = 1386.82, monoclinic,
a
= 90.00°, b = 91.552(2)°,
c
6. Davis, N. K. S.; Thompson, A. L.; Anderson, H. L. J. Am. Chem. Soc. 2010, 133, 30–
31.
r
7. Kaxiras, E.; Tsolakidis, A.; Zonios, G.; Meng, S. Phys. Rev. Lett. 2006, 97, 218102.
8. Nakamura, S.; Hiroto, S.; Shinokubo, H. Chem. Sci. 2012, 3, 524–527.
9. Black, D. StC.; Kumar, N.; Wong, L. C. H. Aust. J. Chem. 1986, 39, 15–20.
10. Black, D. StC.; Bowyer, M. C.; Bowyer, P. K.; Ivory, A. J.; Kim, M.; Kumar, N.;
McConnell, D. B.; Popiolek, M. Aust. J. Chem. 1994, 47, 1741–1750.
11. Pchalek, K.; Jones, A. W.; Wekking, M. M. T.; Black, D. StC. Tetrahedron 2005, 61,
77–82.
r
were 0.3174 (all data). Crystallographic data for 10a have been deposited with
the Cambridge Crystallographic Data Centre as supplementary publication
CCDC-859149. Copies of the data can be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: +44 1223 336 033;
email: deposit@ccdc.cam.ac.uk].

R. Chen et al. / Tetrahedron Letters 53 (2012) 3337–3341
MeOH: 70 50H70ClN4O10
3341
27. Tetraindolyl macrocycle 11c was obtained as a greenish yellow solid in 25%
yield. mp >300 °C. (Found: C, 76.32; H, 5.95; N, 5.07; C68H60N4O8. 0.1CH2Cl2
requires C, 76.46; H, 5.67; N, 5.24%). 1H NMR (300 MHz, CDCl3-d6): d 8.87 (4H,
s, NH), 7.42 (8H, d, J = 8.15 Hz, ArH), 7.13 (8H, d, J = 7.99 Hz, ArH), 6.20 (4H, s,
H5), 3.79 (12H, s, OCH3), 3.18 (12H, s, OCH3), 2.39 (12H, s, CH3), 13C NMR
(CDCl3): d 155.0 (ArC), 153.4 (ArC), 137.8 (ArC), 134.8 (ArC), 133.7 (ArC), 130.2
(ArCH), 127.7 (ArCH), 127.0 (ArC), 117.2 (ArC), 113.1 (ArC), 97.9 (C5), 90.3 (C5),
56.1 (OCH3), 55.4 (OCH3). IR (KBr): mmax 3453, 2931, 2836, 2363, 1609, 1553,
1522, 1461, 1431, 1328, 1341, 1210, 1140, 1093, 994, 822, 794 cmꢁ1. UV–vis
C
.
,
M = 1168.75,
monoclinic,
a = 15.540(4) Å,
b = 23.655(6) Å, c = 18.404(5) Å,
a
= 90.00°, b = 92.854(7)°,
c = 90.00°,
V = 6757(3) Å3, T = 151(2) K, space group P2(1)/c, Z = 4, 41426 reflections
measured, 11604 independent reflections (Rint = 0.2573). The final R1 values
were 0.1542 (I > 2r r(I)). The final
(I)). The final wR(F2) values were 0.3801 (I > 2
R1 values were 0.4587 (all data). The final wR(F2) values were 0.5270 (all data).
Crystallographic data for 11c have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication CCDC-859150.
Copies of the data can be obtained free of charge on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK [fax: +44 1223-336-033; email:
deposit@ccdc.cam.ac.uk].
(MeOH): kmax 202 nm (e
195000 cmꢁ1 M-1), 220 (138900), 245 (134400), 355
(48300). HRMS (+ESI) m/z 1061.4480 (M+, C68H60N4O8, requires 1061.4445).
Single crystals were obtained from a mixed-solvent of CH2Cl2, n-hexane and