Synthesis of pyrenes by twofold hydroarylation of 2,6-dialkynylbiphenyls

Article abstract of DOI:10.1246/cl.2011.40

Cationic gold(I) complexes having Buchwald-type biarylphosphines effectively catalyzed twofold hydroarylation of 2,6-dialkynylbiphenyls to construct pyrene skeletons.

Full text of DOI:10.1246/cl.2011.40

doi:10.1246/cl.2011.40
40
Published on the web November 25, 2010
Synthesis of Pyrenes by Twofold Hydroarylation of 2,6-Dialkynylbiphenyls
Takanori Matsuda,*,³ Taisaku Moriya, Tsuyoshi Goya, and Masahiro Murakami*
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering,
Kyoto University, Katsura, Kyoto 615-8510
(Received October 4, 2010; CL-100850; E-mail: murakami@sbchem.kyoto-u.ac.jp)
Cationic gold(I) complexes having Buchwald-type biaryl-
phosphines effectively catalyzed twofold hydroarylation of 2,6-
dialkynylbiphenyls to construct pyrene skeletons.
(a)
(b)
MeO
OMe
HO
OH
MeO
OMe
(96%)
(64%)
I
2
3
4
Synthesis of polycyclic aromatic hydrocarbons (PAHs)1 has
been the subject of intensive research because PAHs possess
characteristic light-emitting and semiconducting properties.2
Among them, pyrene derivatives are an important class of
compounds that have been used as materials for organic light-
emitting diodes3 and fluorescent probes and sensors.4 Several
established methods are available for the synthesis of 1,3,6,8-
substituted5 and 2,7-substituted pyrenes6 from pyrene. In
contrast, substitution reactions of pyrene at the 4, 5, 9, and 10
positions have been scarcely developed.7 Pyrene derivatives
possessing substituents at these positions are often prepared via
indirect routes involving partial reduction8 and the Diels-Alder
reaction9 of pyrene. Fürstner reported that hydroarylation
reaction10 of 2-alkynylbiphenyls gives phenanthrenes and/or
9-alkylidenefluorenes depending on the catalyst employed.11 We
anticipated that pyrene skeletons could be directly constructed
by twofold hydroarylation of dialkynylbiphenyls.12,13 In this
paper, we report that 4,10-disubstituted pyrenes are synthesized
by gold(I)-catalyzed twofold hydroarylation of 2,6-dialkynylbi-
phenyls.
(c)
(96%)
(d)
TfO
OTf
Me3Si
SiMe3
5
1a
(e)
(46% in 2 steps)
(f)
(up to 90%)
Ar
Ar
1b
1c (Ar = 4-MeOC6H4)
1d (Ar = Ph)
1e (Ar = 4-ClC6H4)
Scheme 1. Conditions: (a) 1.1 equiv PhB(OH)2, 1 mol %
[Pd2(dba)3]¢CHCl3, 2.4 mol % [HP(t-Bu)3]BF4, 3.3 equiv KF,
THF, reflux. (b) 2 equiv BBr3, CH2Cl2, ¹78 °C to rt. (c) 4 equiv
Tf2O, 3 equiv pyridine, CH2Cl2, 0 °C to rt. (d) 3 equiv
Me3SiC≡CH, 20 mol % [PdCl2(PPh3)2], 40 mol % CuI, 2 equiv
Bu4NI, 13 equiv Et3N, DMF, 85 °C. (e) 2.3 equiv K2CO3,
MeOH, rt. (f) 2 equiv ArI, 6 mol % [PdCl2(PPh3)2], 10 mol %
CuI, Et3N, rt.
2,6-Dialkynylbiphenyls 1 requisite for twofold hydroaryla-
tion were prepared as shown in Scheme 1. Palladium-catalyzed
cross-coupling of 2-iodo-1,3-dimethoxybenzene (2) with phen-
ylboronic acid gave 2,6-dimethoxybiphenyl (3). Demethylation
of 3 with BBr3 afforded biphenyl-2,6-diol (4).14 The two
hydroxy groups of 4 were converted to the corresponding
triflates, and subsequent palladium-catalyzed cross-coupling
with trimethylsilylacetylene provided 2,6-bis[(trimethylsilyl)-
ethynyl]biphenyl (1a). The trimethylsilyl groups were removed
under basic conditions, and the resulting 2,6-diethynylbiphenyl
(1b) underwent palladium-catalyzed cross-coupling with aryl
halides to furnish 2,6-bis(arylethynyl)biphenyls 1c-1e in up to
90% yields.15
Table 1. Hydroarylation of diyne 1c
cat.
(ligand)AuNTf2
Ar
Ar
24 h
Ar
Ar
6c
1c (Ar = 4-MeOC6H4)
MeO
i-Pr
i-Pr
P(c-Hex)2
OMe
P(c-Hex)2
i-Pr
P(t-Bu)2
i-Pr
i-Pr
i-Pr
XPhos
t-butylXPhos
SPhos
2,6-Bis[(4-methoxyphenyl)ethynyl]biphenyl (1c) thus ob-
tained was treated with PtCl2 in p-xylene at 140 °C.11 However,
no formation of a pyrene derivative was observed, which led
us to examine a hydroarylation reaction using gold(I) com-
plexes having Buchwald-type biarylphosphine ligands (Table 1).
When diyne 1c was heated in p-xylene in the presence of
(SPhos)AuNTf2 (20 mol %) at 150 °C for 24 h, hydroarylation
successfully occurred on both sides to afford 4,10-bis(4-meth-
oxyphenyl)pyrene (6c) in 83% yield (Entry 1). (XPhos)AuNTf2
worked equally well (Entry 2), and (t-butylXPhos)AuNTf2 gave
the best result giving 6c in 88% yield (Entry 3).16,17 On the other
hand, neutral chlorogold(I) complexes bearing the same biaryl-
phosphine ligands failed to promote the hydroarylation. Both the
Gold(I) catalyst
/mol % Ligand
Entry
Conditions
Yielda/%
1
2
3
4
5
20
20
20
5
SPhos
XPhos
p-xylene, 150 °C
p-xylene, 150 °C
83
83
88
73
48
t-butylXPhos p-xylene, 150 °C
t-butylXPhos DCE, 70 °C
t-butylXPhos DCE, 60 °C
5
aIsolated yield.
catalyst loading and the reaction temperature could be reduced
by the use of 1,2-dichloroethane (DCE) as the solvent; when the
reaction was carried out in DCE at 70 °C with the use of 5 mol %
Chem. Lett. 2011, 40, 40-41
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

41
Table 2. Hydroarylation of 1 catalyzed by (t-butylXPhos)-
AuNTf2
dimethylpyrene (6h) in good yield (Entry 5). On the other hand,
the reaction of 1b having terminal ethynyl groups suffered the
formation of a by-product derived from the competing 5-exo
cyclization to afford pyrene (6b) in low yield (Entry 6).
Trimethylsilyl-substituted substrate 1a also afforded 6b through
desilylation that occurred during the course of the reaction
(Entry 7).19
a
cat.
(t-butylXPhos)AuNTf2
R
R
24 h
R
R
1
6
In summary, we have established a new entry to 4,10-
substituted pyrenes via gold(I)-catalyzed twofold hydroarylation
of 2,6-dialkynylbiphenyls. Further studies to explore the
reactivities peculiar to dialkynylbiphenyls are underway and
the results will be reported in due course.
Yieldb/%
Entry
1
1
R
6
A
B
1f
6f
89
95
R
R
References and Notes
Me
Me
³
1
2
Present address: Department of Applied Chemistry, Tokyo University
of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601
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(R = 4-MeOC6H4)
2
1g
6g
92
96
R
R
t-Bu
3
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(R = 4-MeOC6H4)
3
4
5
6
7
1d
1e
1h
1b
1a
Ph
6d
6e
6h
6b
6b
47c
1d
70
30
16
4-ClC6H4
Me
52
86
18
42
4
5
6
7
H
SiMe3
aMethod A: 5 mol % catalyst in DCE at 80 °C. Method B:
20 mol % catalyst in p-xylene at 150 °C. bIsolated yield.
c20 mol % of catalyst was used. dA mixture with monohy-
droarylated phenanthrene (22%).
of (t-butylXPhos)AuNTf2, pyrene 6c was produced in 73% yield
(Entry 4). However, incomplete conversion was observed when
the reaction was carried out at 60 °C for 24 h (Entry 5), and no
reaction occurred at room temperature.
8
9
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The twofold hydroarylation was examined with various
2,6-dialkynylbiphenyls 1 in DCE (80 °C) and/or in p-xylene
(150 °C) (Table 2). A distinct electronic effect was observed
with the hydroarylation of 2,6-bis(arylethynyl)biphenyls. Elec-
tron-rich aryl substituents appended to a 2,6-bis[(4-methoxy-
phenyl)ethynyl]phenyl group accelerated the hydroarylation
reaction; the reaction of diynes 1f and 1g having additional
alkyl substituents on the biphenyl backbone gave high yields of
the corresponding pyrenes 6f and 6g, respectively (Entries 1 and
2). The reaction of phenyl-substituted derivative 1d was slower
than that of the 4-methoxyphenyl-substituted derivative 1c, and
pyrene 6d was isolated in 47% yield with the use of 20 mol % of
the catalyst in DCE (Entry 3).18 In the case of diyne 1e equipped
with 4-chlorophenyl groups, the reaction was even more
sluggish, and when carried out in p-xylene at 150 °C, produced
pyrene 6e in moderate yield (Entry 4). No reaction occurred
with a diyne having nitro groups on the para-positions of the
phenyl rings. Thus, the reactivity of 2,6-bis(arylethynyl)biphen-
yls was highly dependent on the electronic character of the aryl
groups. The hydroarylation reaction proceeded more facilely
with more electron-donating aryl groups. In addition to those
with arylethynyl substituents, 2,6-di(prop-1-ynyl)biphenyl (1h)
also participated in the hydroarylation reaction to give 4,10-
G.-P. Blümer, M. Zander, Monatsh. Chem. 1979, 110, 1233.
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12 For the synthesis of 10a-aza-10b-borapyrenes by analogous twofold
hydroarylation, see: M. J. D. Bosdet, W. E. Piers, T. S. Sorensen, M.
Parvez, Angew. Chem., Int. Ed. 2007, 46, 4940.
13 For recent examples on the synthesis of PAHs by hydroarylation, see:
a) J. Storch, J. Sýkora, J. Čermák, J. Karban, I. Císařová, A. Růžička,
J. Org. Chem. 2009, 74, 3090. b) T.-A. Chen, T.-J. Lee, M.-Y. Lin,
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15 Supporting Information is available electronically on the CSJ-Journal
Web site, http://www.csj.jp/journals/chem-lett/index.html.
16 Gold complex [(4-CF3C6H4)3P]AuNTf2 exhibited a similar catalytic
activity (20 mol %, p-xylene, 150 °C, 84%).
17 The reaction in p-xylene required a higher temperature to proceed than
in DCE.
18 The reaction in the presence of 5 mol % gold(I) catalyst in DCE at
80 °C resulted in the formation of a mixture of pyrene 6d (20%) and
monohydroarylated phenanthrene (13%).
19 The reaction of 1a was also accompanied by the formation of some
unidentified by-products.
Chem. Lett. 2011, 40, 40-41
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/