Shape-persistent elliptic macrocycles composed of polycyclic aromatic hydrocarbons: Synthesis and photophysical properties

Article abstract of DOI:10.1021/ol800505y

(Chemical Equation Presented) Bimolecular coupling/unimolecular cyclization strategies, including McMurry- and Glaser-type homocoupling reactions, were utilized to synthesize two shape-persistent elliptic macrocycles, which consist of polycyclic aromatic

Full text of DOI:10.1021/ol800505y

ORGANIC
LETTERS
2008
Vol. 10, No. 11
2123-2126
Shape-Persistent Elliptic Macrocycles
Composed of Polycyclic Aromatic
Hydrocarbons: Synthesis and
Photophysical Properties
Wen-Jun Liu, Yan Zhou, Qi-Feng Zhou, Yuguo Ma,* and Jian Pei*
The Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry
of Education and the Key Laboratory of Polymer Chemistry and Physics of Ministry of
Education, College of Chemistry and Molecular Engineering, Peking UniVersity,
Beijing 100871, China
jianpei@pku.edu.cn
Received March 6, 2008
ABSTRACT
Bimolecular coupling/unimolecular cyclization strategies, including McMurry- and Glaser-type homocoupling reactions, were utilized to synthesize
two shape-persistent elliptic macrocycles, which consist of polycyclic aromatic hydrocarbon units. The identity and purity of both macrocycles
MC1 and MC2 were verified by 1H and 13C NMR, elemental analysis, as well as MALDI-TOF MS. The photophysical properties of MC1 and MC2
in dilute solution were also investigated.
Considerable attention has recently been devoted to shape-
persistent macrocycles, not only for their aesthetic appearance
but also for their potential applications in supramolecular
and material chemistry.1 A diversity of supramolecular
assemblies, including host-guest complexes,2a discotic liquid
crystals,2b extended tubular channels,2c and organic porous
solids,2d were realized by shape-persistent macrocycles
possessing rigid cyclic backbones. The noncollapsible scaf-
folds and the resultant well-defined cavities were exploited
to reinforce the intermolecular interaction, thus facilitating
(1) (a) Moore, J. S. Acc. Chem. Res. 1997, 30, 402–413. (b) Bunz,
U. H. F.; Rubin, Y.; Tobe, Y. Chem. Soc. ReV 1999, 28, 107–119. (c) Ho¨ger,
S. J. Polym. Sci. Part A: Polym. Chem. 1999, 37, 2685–2698. (d) Grave,
C.; Schlu¨ter, A. D. Eur. J. Org. Chem. 2002, 3075–3098. (e) Zhao, D.;
Moore, J. S. Chem. Commun. 2003, 807–818. (f) Yamaguchi, Y.; Yoshida,
Z. Chem. Eur. J. 2003, 9, 5430–5440. (g) Zhang, W.; Moore, J. S. Angew.
Chem., Int. Ed. 2006, 45, 4416–4439. (h) Song, Y.; Di, C.; Yang, X.; Li,
S.; Xu, W.; Liu, Y.; Yang, L.; Shuai, Z.; Zhang, D.; Zhu, D. J. Am. Chem.
Soc. 2006, 128, 15940–15941.
(2) (a) Kawase, T.; Tanaka, K.; Fujiwara, N.; Darabi, H. R.; Oda, M.
Angew. Chem., Int. Ed. 2003, 42, 1624–1628. (b) Seo, S. H.; Jones, T. V.;
Seyler, H.; Peters, J. O.; Kim, T. H.; Chang, J. Y.; Tew, G. N. J. Am.
Chem. Soc. 2006, 128, 9264–9265. (c) Balakrishnan, K.; Datar, A.; Zhang,
W.; Yang, X.; Naddo, T.; Huang, J.; Zuo, J.; Yen, M.; Moore, J. S.; Zang,
L. J. Am. Chem. Soc. 2006, 128, 6576–6577. (d) Venkataraman, D.; Lee,
S.; Zhang, J.; Moore, J. S. Nature 1994, 371, 591–593.
10.1021/ol800505y CCC: $40.75
Published on Web 05/02/2008
2008 American Chemical Society

the formation of these highly ordered rigid structures.
Polycyclic aromatic hydrocarbons (PAHs) are ideal building
blocks for the preparation of cofacially stacked supramo-
lecular structures and display various attractive optoelectronic
properties.3However, the synthesis of rigid macrocycles is still
a great challenge. The desired cyclic structure has to compete
against the statistic distribution of various linear/cyclic oligo-
mers/polymers of different chain lengths in reaction, resulting
in poor reaction yields,1e although many different methodologies
have been developed to overcome such problems.1
Scheme 1. Synthetic Route to 6
In this contribution, we incorporate polycyclic aromatic
hydrocarbon moieties into the shape-persistent marocycles
in order to take advantages of the features of both polycyclic
aromatic hydrocarbons and macrocycles. The strategy of
bimolecular coupling followed by intramolecular cyclization,
as illustrated in Figure 1, which can achieve a better balance
Figure 1. Schematic representation of bimolecular coupling/
unimolecular cyclization strategy.
between the number of synthetic steps and the overall
reaction yield,4 was utilized to approach the shape-persistent
macrocycles from geometrically appropriate polycyclic aro-
matic hydrocarbons.
Scheme 2. Synthetic Route to MC1
Scheme 1 illustrates the synthetic route to polycyclic
aromatic hydrocarbon 6. In order to differentiate the reac-
tivities of two positions in fluorene undergoing the Sono-
gashira cross-coupling reaction, 9,9-dihexyl-2-bromo-7-
iodofluorene (1) was chosen as the starting material, which
was easily prepared through the iodination in high yield
followed by the bromination from commercially available
9,9-dihexylfluorene. Selective Sonogashira cross-coupling
reaction at room temperature between 1 and 2-methyl-3-
butyn-2-ol and subsequent deprotection of tertiary alcohol
with KOH furnished 3, which was then carried on a
Sonogashira cross-coupling reaction with 9,9-dihexyl-2,7-
diiodofluorene to afford 4 in 89% yield. The relatively
unreactive aryl bromides flanking 4 could be further func-
tionalized in the following steps. The Diels-Alder reaction
between 4 and 2,5-diethyl-3,4-diphenylcyclopentadienone
followed by decarbonylation in refluxed 1,2,4-trimethylben-
zene produced 5 in 88% yield. The FeCl3-promoted oxidative
cyclization condition was applied to generate polycyclic
aromatic hydrocarbon 6 in 87% yield.5 This oxidative
(3) (a) Harvey, R. G. Polycyclic Aromatic Hydrocarbons; Wiley-VCH:
New York, 1997. (b) Wu, J.; Pisula, W.; Mu¨llen, K. Chem. ReV. 2007,
107, 718–747. (c) Hill, J. P.; Jin, W. S.; Kosaka, A.; Fukushima, T.; Ichihara,
H.; Shimomura, T.; Ito, K.; Hashizume, T.; Ishii, N.; Aida, T. Science 2004,
304, 1481–1483.
cyclization reaction proceeded effectively despite the pres-
ence of two electron-withdrawing bromide groups, presum-
ably due to the negligible inductive effect of bromide groups
relative to the extended π-conjugated reactant.
(4) (a) Ho¨ger, S.; Enkelmann, V. Angew. Chem., Int. Ed. 1995, 34, 2713–
2716. (b) Tobe, Y.; Utsumi, N.; Kawabata, K.; Naemura, K. Tetrahedron
Lett. 1996, 37, 9325–9328. (c) Zhao, D.; Moore, J. S. J. Org. Chem. 2002,
67, 3548–3554.
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Org. Lett., Vol. 10, No. 11, 2008

After the bimolecular coupling, the intramolecular cy-
clization methodology to shape-persistent macrocycles is
outlined in Scheme 2. From polycyclic aromatic hydrocarbon
6, a Suzuki coupling reaction with 4-formylphenylboronic
acid afforded 7 with two aldehyde functionalities in 73%
yield. The precursor 7 was then subjected to McMurry6
homocoupling reaction to afford MC1 in 29% yields.
As shown in Scheme 3, 7 was further converted to terminal
ethynyl groups to produce 8 in 84% yield through a Corey-
Fuchs reaction. The precursor 8 was then subjected Glaser-
MC1 and MC2 as slightly yellow solids were readily
soluble in common organic solvents, such as dichlo-
romethane, chloroform, tetrahydrofuran, and toluene. The
1
identity and purity of MC1 and MC2 were verified by H
and 13C NMR, MALDI-TOF MS, and elemental analysis.
Comparing the 1H NMR spectra between the precursors and
the macrocycles, we observed the singlet at 10.1 ppm in 7
(Figure 2a) and the singlet at 3.19 ppm in 8 (Figure 2b)
Scheme 3. Synthetic Route to MC2
1
Figure 2
.
(a) H NMR spectra of 7 (black) and MC1 (blue) from
1
7.0-11.0 ppm. (b) H NMR spectra of 8 (black) and MC2 (blue)
from 2.0-3.5 ppm.
belonging to the protons of aldehyde in 7 and ethynyl in 8,
respectively, vanished after the corresponding cyclization,
which clearly indicates the cyclization rather than oligomer-
1
ization of the precursors took place. From the H NMR
spectrum of MC1, we also observed that the double bonds
predominately exist as the E-isomer.8 Furthermore, as shown
in Figure 3, the signals at 3482 Da (100%) for MC1 and at
type homocoupling reactions7 to afford MC2 in 52% yields.
We also tried to convert butadiynylene groups to the
thiophene ring by addition of sulfur; unfortunately, due to
the rigidity of this macrocycle, we did not obtain the target
molecules.
Figure 3. Measured and simulated MALDI-TOF MS spectra of
(5) (a) Zhou, Y.; Liu, W.-J.; Zhang, W.; Cao, X.-Y.; Zhou, Q.-F.; Ma,
Y.; Pei, J. J. Org. Chem. 2006, 71, 6822–6828. (b) Cao, X.-Y.; Zi, H.;
Zhang, W.; Lu, H.; Pei, J. J. Org. Chem. 2005, 70, 3645–3653.
(6) Nakao, K.; Nishimura, M.; Tamachi, T.; Kuwatani, Y.; Miyasaka,
H.; Nishinaga, T.; Iyoda, M. J. Am. Chem. Soc. 2006, 128, 16740–16747.
(7) Siemsen, P.; Livingston, R. C.; Diederich, F. Angew. Chem., Int.
Ed. 2000, 39, 2632–2657.
MC1 and MC2.
3524 Da (100%) for MC2 (see the Supporting Information)
exhibited on the MALDI-TOF MS spectra unambiguously
Org. Lett., Vol. 10, No. 11, 2008
2125

demonstrated that their structures containing two polycyclic
aromatic hydrocarbons were linked by different spacers. We
can still recognize the similar isotopic distributions between
measured and simulated results regardless of the sensitivity
of the facility.
Figure 4 illustrates the photophysical behaviors of the
shape-persistent macrocycles MC1 and MC2 in dilute THF
solution (10-5 M), and their photophysical properties are
the diacetylene unit.9 Furthermore, we compared the mac-
rocycles with compound 9,5a which has been investigated
in our previous work (see the Supporting Information).6 The
absorption peak has been significantly red-shifted by 68 and
57 nm in comparison to compound 9 for MC1 and MC2,
respectively. Such red shift shows the conjugation length of
the molecules have been extended after the macrocyclization.
The emission spectrum showed the same trend. The maxi-
mum emission peak was red-shifted by 48 and 39 nm from
387 nm for MC1 and MC2, respectively. The vibration
emission peak of 9 turned to be a shoulder peak in MC1
and MC2. More specifically, the Stokes shift decreased from
72 to 53 nm after the cyclization, indicating that the rigidity
of the molecule enhanced after the cyclization. The fluores-
cence quantum yields (ΦF) of MC1 and MC2 in dilute THF
solution were 0.94 and 0.82, respectively, using 9,10-
diphenylanthracene as the standard.
In summary, two shape-persistent elliptic macrocycles
composed of polycyclic aromatic hydrocarbons (MC1 and
MC2) have been designed and synthesized in a relatively
straightforward manner. FeCl3-promoted oxidative cycliza-
tion and bimolecular coupling followed by unimolecular
cyclization strategy are adopted to construct the polycyclic
aromatic hydrocarbons and shape-persistent macrocycles,
respectively. Geometrical conformation of the precursors is
demonstrated to play a key role in the formation of the
desired macrocycles. The investigation of the synthetic route
and the photophysical behaviors of MC1 and MC2 gives
insight into the rational design of rigid macromolecules, as
well as the fine-tuning of their photophysical properties.
Figure 4. Absorption and emission spectra of 9, MC1, and MC2
in dilute THF solution (10-5 M). Emission spectra were obtained
upon excitation at absorption maximum.
summarized in Table 1. The absorption of MC1 show a
maximum at 382 nm, which red-shifted by 11 nm in
comparison with MC2 (λmax ) 371 nm). The emission of
Acknowledgment. This work was supported by the
National Basic Research Program (No. 2006CB921602 and
2007CB808000) from the Ministry of Science and Technol-
ogy, and National Natural Science Foundation of China
(NSFC 20425207, 50473016, 20521202, and 20604001).
Table 1. Photophysical Properties of Macrocycles MC1 and
MC2 in Dilute THF Solution
macrocycles
ꢀ (M-1 cm-1
)
λmax abs (nm)
λmax PL (nm)
MC1
MC2
6.5 × 105
5.4 × 105
382
371
435, 459
426
Supporting Information Available: Experimental pro-
cedures and 1H and 13C NMR spectra for all new compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
MC2 peaked at 426 nm while MC1 exhibit emission
maximum at 435 nm with a small shoulder at 459 nm.
The emission maximum of MC1 red-shifted by 9 nm
relative to that of MC2. Such red shifts in both absorption
and emission spectra of MC1 implied that ethylene unit is
superior in extending the effective conjugation length than
OL800505Y
(8) Jiang, Y.; Wang, J.-Y.; Ma, Y.; Cui, Y.-X.; Zhou, Q.-F.; Pei, J. Org.
Lett. 2006, 8, 4287–4290.
(9) Cao, X.-Y.; Zhang, W.; Zi, H.; Pei, J. Org. Lett. 2004, 6, 4845–
4848.
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