Synthesis of meso-substituted tetraarylalkynylporphyrins via rhenium-catalyzed formation of naphthalene units

Article abstract of DOI:10.1055/s-0030-1261199

Rhenium-catalyzed synthesis of naphthalene-substituted aryl bromides or iodides via C-H bond activation, and its use for palladium-catalyzed cross-coupling reactions with tetraethynylporphyrin are described. A series of novel meso-substituted tetraalkynyl

Full text of DOI:10.1055/s-0030-1261199

LETTER
2177
Synthesis of meso-Substituted Tetraarylalkynylporphyrins via Rhenium-
Catalyzed Formation of Naphthalene Units
Synthesis of
m
eso
-
l
Substit
i
uted
T
etraary
S
lalkynylporph
a
yrins marat,a Yoichiro Kuninobu,*b Kazuhiko Takai*b
a
University of Carthage, Faculty of Sciences of Bizerte, Jarzouna 7021, Bizerte, Tunisia
Division of Chemistry and Biochemistry, Graduate School of Natural Science and Technology, Okayama University,
Tsushima, Kita-ku, Okayama 700-8530, Japan
b
Fax +81(86)2518094; E-mail: kuninobu@cc.okayama-u.ac.jp; E-mail: ktakai@cc.okayama-u.ac.jp
Received 11 July 2011
derivative 3a in 92% yield (Scheme 1). The isobenzofu-
ran 3a was trapped with diethyl maleate (4a) by a Diels–
Alder reaction to afford Diels–Alder adduct 5a in only
18% yield due to its instability. In fact, 5a was decom-
posed during the purification by column chromatography
on silica gel. Therefore, the problem can be solved by one-
pot operation as described in Table 1 (entry 1). The Diels–
Alder adduct was exposed to acidic conditions causing de-
hydrative aromatization, and the functionalized naphtha-
lene derivative with a bromine atom (6a) was obtained
quantitatively. The bromine atom was retained in these re-
action steps.
Abstract: Rhenium-catalyzed synthesis of naphthalene-substituted
aryl bromides or iodides via C–H bond activation, and its use for
palladium-catalyzed cross-coupling reactions with tetraethynylpor-
phyrin are described. A series of novel meso-substituted tetraalky-
nylporphyrins with naphthalene moieties were obtained.
Key words: rhenium catalyst, C–H bond activation, naphthalene
derivative, Sonogashira coupling, meso-substituted tetraalkynyl-
porphyrin
The continuing interest in porphyrins can be explained by
their peculiar optical and electronic properties that make
them attractive targets as physiologically active
compounds1 and for a variety of applications.2 Thus, por-
phyrin derivatives with conjugated connections at the
meso positions have attracted much interest for their po-
tential applications in electronic materials such as nonlin-
ear optics3,4 and light harvesting.5 Electronic distributions
in the porphyrin rings can be easily modified by changing
the peripheral substituents, which influence the physico-
chemical and conformational properties of the porphyrin
derivatives.6 The synthesis of meso-tetraarylporphyrins
has been intensively studied.7 In contrast, extending the p-
conjugate systems of porphyrin cores with aryl groups by
linking them with acetylene bridges is one of the most ef-
ficient methods for extending the p-conjugate systems be-
tween aryl substituents and porphyrin macrocycles.5,8
Since the acetylene cores are linear, the structures cannot
be twisted to break the conjugation with the porphyrin
skeletons. In this paper, we present our strategy for the
synthesis of functionalized aryl halides that could be cou-
pled with meso-tetraethynylporphyrin to afford a new
family of meso-tetraarylalkynylporphyrins.
H
O
Ph
Ph
[ReBr(CO)3(thf)]2 (2.5 mol%)
4 Å MS
N
+
toluene, 115 °C, 48 h
1
Br
2a (2.0 equiv)
Ph
Ph
EtO2C
CO2Et
CO2Et
O
O
(4a, 1.2 equiv)
CO2Et
toluene, 115 °C, 12 h
Br
Br
3a 92%
5a 18%
Ph
CO2Et
CO2Et
H2SO4
AcOH
CH2Cl2
Recently, we reported a rhenium-catalyzed synthesis of
naphthalene skeletons via C–H bond activation.9 Due to
our continuing interests in rhenium-catalyzed synthesis of
multisubstituted aromatic compounds,10 we decided to in-
vestigate the synthesis of our target molecules based on
this C–H bond transformation. Treatment of aromatic
ketimine 1, 4-bromobenzaldehyde (2a), and molecular
sieves with a catalytic amount of a rhenium complex, [Re-
Br(CO)3(thf)]2, in toluene at 115 °C gave isobenzofuran
25 °C, 2 h
Br
6a >99%
Scheme 1
By the reaction of aromatic ketimine 1, 4-iodobenzalde-
hyde (2b), and N-methylmaleimide (4b) as a dienophile in
the presence of catalytic amounts of the rhenium complex
and molecular sieves, the Diels–Alder adduct 5b was iso-
lated in 91% yield. Diene formation was not affected by
the presence of maleimide 4b. The Diels–Alder adduct
SYNLETT 2011, No. 15, pp 2177–2180
x
x
.x
x
.2
0
1
1
Advanced online publication: 30.08.2011
DOI: 10.1055/s-0030-1261199; Art ID: U05111ST
© Georg Thieme Verlag Stuttgart · New York

2178
A. Samarat et al.
LETTER
was treated with sulfuric acid and acetic acid in dichlo-
romethane at room temperature for 2 hours. As a result,
the desired naphthalene derivative bearing an iodine atom
(6b) was afforded in 78% yield (Scheme 2). These reac-
tions proceeded without loss of the iodine atom.
Table 1 One-Pot Synthesis of Naphthalene Derivatives with a
Halogen Atoma
H
O
Ph
[ReBr(CO)3(thf)]2 (2.5 mol%)
4 Å MS
R
R
Ph
N
+
+
toluene, 115 °C, 48 h
1
4
H
O
Ph
O
X
Ph
R
Ph
[ReBr(CO)3(thf)]2 (2.5 mol%)
4 Å MS
2
N
N
Me
+
+
toluene, 115 °C, 48 h
R
H2SO4, AcOH
25 °C, 2 h
1
O
I
2b
(2 equiv)
4b
(1.2 equiv)
Ph
O
Ph
O
O
X
6
H2SO4, AcOH
N
Me
N
O
Me
Entry Aldehyde 2 Olefin 4
Product 6
Yield (%)
CH2Cl2, 25 °C, 2 h
O
1
2
3
4
5
6
2a X = Br 4a R = CO2Et
6a
78
64
66
58
71
34
2a
4c R = CO2Me 6c
I
I
2b X = I
2b
4a R = CO2Et
6d
5b 91%
6b 78%
4c R = CO2Me 6e
4d R = CO2n-Bu 6f
Scheme 2
2b
The generality of this methodology was further extended
to the one-pot synthesis of naphthalene derivatives with a
halogen atom. Treatment of aromatic ketimine 1, 4-bro-
mobenzaldehyde (2a), olefin 4a, and molecular sieves (4
Å) with a catalytic amount of [ReBr(CO)3(thf)]2 in tolu-
ene at 115 °C for 48 hours and successive dehydration un-
der acidic conditions led to the corresponding naphthalene
derivative 6a in 78% yield without isolation of the formed
Diels–Alder adduct 5a (Table 1, entry 1). The one-pot
synthesis of the naphthalene derivative bearing a halogen
atom is advantageous compared with the stepwise method
(Scheme 1) from the viewpoint of easy procedure and
good total yield. By using this method, the corresponding
naphthalene derivatives 6 with several types of substitu-
ents were obtained in good to excellent overall yields
(Table 1, entries 2–8). Substituents such as esters and
amides were tolerated under the reaction conditions and
no significant electronic and/or steric effects were ob-
served for the olefin substituents. In addition, it is note-
worthy that aryl halides remain intact under the rhenium
catalysis.
2b
4e R = n-Pr
6g
O
N
Me
7
8
2b
2b
6b
72
94
O
4b
4f
6h
a Conditions: aldehyde 2 (2 equiv), olefin 4 (1.2 equiv).
Pd2(dba)3 and AsPh3, resulting in efficient formation of
the desired meso-substituted tetraarylalkynylporphyrin 9a
in 92% yield (Table 2, entry 1). UV-vis spectra of meso-
tetraethynylporphyrin 8 and meso-tetraarylalkynylpor-
phyrin 9a were measured. As a result, the absorptions
were observed at l = 450 nm and 475 nm, respectively,
and long-wavelength shift was caused by introducing the
naphthalene moieties. These results indicate that the p-
conjugate system is expanded by the connection between
porphyrin and naphthalene skeletons using the alkyne
moieties. In a similar manner, other meso-substituted tet-
raarylalkynylporphyrins 9b–f could be synthesized in
moderate to good yields (Table 2, entries 2–6).
The preparation of 5,10,15,20-meso-tetraethynylporphy-
rin 8 by desilylation of porphyrin derivative 711 using tet-
rabutylammonium fluoride is a key step for applying the
Sonogashira cross-coupling towards the construction of
the extended conjugated porphyrin derivatives.12 When
naphthalene derivatives with bromine atoms (6a and 6c)
were used to couple with 5,10,15,20-meso-tetraethy-
nylporphyrin 8, a complex mixture of porphyrins was ob-
tained. In contrast, the desired porphyrin derivatives could
be synthesized easily using the naphthalene-substituted
aryl iodides as shown in Table 2. The coupling reaction of
porphyrin 8 with aryl iodide 6d was carried out in a mix-
ture of triethylamine and THF using palladium complex
In summary, we have succeeded in the one-pot synthesis
of naphthalene derivatives with a bromine or iodine atom
via C–H bond activation by the reaction of N-(diphenyl-
methylene)aniline and 4-halobenzaldehydes with dieno-
philes in the presence of the rhenium catalyst
[ReBr(CO)3(thf)]2 and successive dehydration.13 The cou-
Synlett 2011, No. 15, 2177–2180 © Thieme Stuttgart · New York

LETTER
Synthesis of meso-Substituted Tetraarylalkynylporphyrins
2179
pling reaction of the naphthalene derivatives with meso- devices. Optical and electrochemical properties of synthe-
tetraethynylporphyrin provided a series of extended con- sized meso-tetraarylalkynylporphyrins are under way.
jugated meso-tetraarylalkynylporphyrins.14 These new
compounds are expected to show high potential as new
functional materials for optical memories and solar cell
Table 2 Coupling Reactions of meso-Tetraethynylporphyrin 8 with Aryl Iodides 6
H
TMS
N
N
N
N
N
N
N
n-Bu4NF (6.0 equiv)
CH2Cl2, 25 °C
H
TMS
Zn
Zn
H
TMS
N
Ar
H
TMS
7
8
ArI (6, 6.5 equiv)
Pd2(dba)3 (10 mol%)
AsPh3 (1.8 equiv)
N
N
N
N
Ph
R1
R2
Ar
Zn
Ar
Et3N–THF (1:2)
50 °C, 4 h
ArI =
Ar
I
9
Entry
ArI
6d
6e
R1
R2
Yield (%)
9a 92
1
2
3
CO2Et
CO2Et
CO2Me
CO2n-Bu
n-Pr
CO2Me
9b 93
6f
CO2n-Bu
n-Pr
9c 86
4
5
6g
6b
6h
9d 51
9e 56
O
O
C N C
Me
6
–(CH2)6–
9f 81
(3) (a) Anderson, H. L.; Martin, S. J.; Bradley, D. C. C. Angew.
Chem., Int. Ed. Engl. 1994, 33, 655. (b) Martin, S. J.;
Anderson, H. L.; Bradley, D. C. C. Adv. Mater. Opt.
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(b) Priyadarshy, S.; Therien, M. J.; Beratan, D. N. J. Am.
Chem. Soc. 1996, 118, 1504.
Acknowledgment
This work was supported by Okayama University.
References and Notes
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Synlett 2011, No. 15, 2177–2180 © Thieme Stuttgart · New York

2180
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LETTER
(7) (a) Zhou, X.; Tse, M. K.; Wan, T. S. M.; Chan, K. S. J. Org.
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0.500 mmol), 4-bromobenzaldehyde (2a, 1.00 mmol) or 4-
iodobenzaldehyde (2b, 1.00 mmol), olefin (4, 0.600 mmol),
4 Å MS (200 mg), [ReBr(CO)3(thf)]2 (10.6 mg, 0.0125
mmol), and toluene (1.0 mL) was stirred at 115 °C for 48 h.
Then, AcOH (3.0 mL) and H2SO4 (1.0 mL) were added, and
the mixture was stirred at r.t. for 2 h. The crude product was
extracted with hexane and purified by column
(8) (a) Lin, V. S.-Y.; DiMagno, S. G.; Therien, M. J. Chem. Eur.
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chromatography on silica gel or recrystallized from EtOH to
give naphthalene derivative 6.
(14) Typical Procedure for the Synthesis of meso-Substituted
Tetraarylalkynylporphyrin 9a
Porphyrins 711 and 812a were prepared according to the
reported methods. To a degassed solution of zinc(II)
5,10,15,20-tetraethynylporphyrin (8, 10 mg, 0.021 mmol),
1-(4-iodophenyl)-4-phenylnaphthalene-2,3-dicarboxylic
acid diethyl ester (6d, 75.4 mg, 0.137 mmol), and AsPh3 (12
mg, 0.038 mmol) in a mixture of anhyd THF (10 mL) and
Et3N (5.0 mL) was added Pd2(dba)3 (2.0 mg, 0.0020 mmol).
The reaction mixture was stirred at 50 °C for 4 h under an
argon atmosphere. The solvent was evaporated under
reduced pressure, and the crude product was purified by
column chromatography on silica gel using CHCl3 as an
eluent to give a dark green solid 9a (41.7 mg, 92%). 1H NMR
(400 MHz, CDCl3): d = 0.96 (t, J = 7.2 Hz, 12 H), 1.17 (t,
J = 7.2 Hz, 12 H), 4.03 (q, J = 7.2 Hz, 8 H), 4.19 (q, J = 7.2
Hz, 8 H), 7.43–7.55 (m, 28 H), 7.68–7.71 (m, 12 H), 7.85 (d,
(11) Anderson, H. L. Tetrahedron Lett. 1992, 33, 1101.
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H.; Peng, S.-M.; Yeh, C.-Y. Org. Lett. 2006, 8, 4239.
(b) Kuo, M.-C.; Li, L.-A.; Yen, W.-N.; Lo, S.-S.; Lee, C.-
W.; Yeh, C.-Y. Dalton Trans. 2007, 1433.
J = 8.4 Hz, 4 H), 8.27 (d, J = 8.0 Hz, 8 H), 9.48 (s, 8 H). 13
C
NMR (100 MHz, CDCl3): d = 13.6, 13.9, 61.4, 61.6, 66.7,
92.8, 96.9, 102.7, 123.7, 127.1, 127.5, 127.8, 127.9, 128.1,
129.0, 129.2, 130.2, 130.7, 131.2, 131.5, 132.6, 132.8,
137.7, 138.3, 138.4, 139.3, 151.3, 168.3, 168.4. IR (Nujol):
480, 771, 941, 1132, 1166, 1222, 1300, 1676, 1685, 1716,
1734, 2213, 2924 cm–1.
(13) General Procedure for the Synthesis of Naphthalene
Derivatives 6 by One-Pot Reaction
A mixture of N-(diphenylmethylene)aniline (1, 129 mg,
Synlett 2011, No. 15, 2177–2180 © Thieme Stuttgart · New York

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