Angewandte
Chemie
DOI: 10.1002/anie.200800924
Direct Coupling
Fluorescent Naphthyl- and Anthrylazoles from the Catalytic Coupling
of Phenylazoles with Internal Alkynes through the Cleavage of
À
Multiple C H Bonds**
Nobuyoshi Umeda, Hayato Tsurugi, Tetsuya Satoh,* and Masahiro Miura*
Polycyclic aromatic and heteroaromatic compounds have
attracted considerable attention because of their electro-
chemical and photochemical properties, and their application
as p-conjugated functional materials such as organic semi-
conductors and luminescent materials.[1] Polyarylated deriv-
atives with condensed aromatic cores are of particular interest
because of their stability, their enhanced ability to transport
charge, and their fluorescent properties in the solid-state that
are brought about by the aryl groups.[2–4] Among the
interesting examples is 1,3,6,8-tetraphenylpyrene, which was
shown to be applicable to organic light-emitting diodes with
field-effect transistor characteristics.[2] Recently, more steri-
cally congested tetraarylpyrenes were synthesized and their
solid-state emission properties were examined.[3]
Multiply arylated compounds are usually prepared by
bromination of the parent aromatic compounds with subse-
quent cross-coupling with arylmetal reagents. Since the cross-
coupling reaction is usually hampered by steric bulk, the
construction of more densely arylated arenes by this method
is problematic.[5] An alternative strategy includes the Diels–
Alder reaction between polyarylated benzynes and cyclo-
pentadienones.[4] This method enables the synthesis of
exhaustively arylated naphthalene and anthracene units,
however, the product yields are low because of steric
repulsion between the bulky reagents.[6] Compared to ben-
zyne, diarylacetylenes are more effective and readily avail-
able building blocks. Thus, transition-metal-catalyzed aro-
matic homologation[7] by the coupling of ArX with two alkyne
molecules has been developed as an efficient and easily
tunable synthetic protocol for highly substituted arenes
possessing extended aromatic cores.[8] Herein, we report our
new findings that phenylazoles undergo an advanced type of
À
aromatic homologation, by the cleavage of two C H bonds
[9,10]
under rhodium catalysis,[8g,h] to give (1,2,3,4-tetraaryl-
naphthalen-5-yl)azoles; the heterocycle functions as an effec-
tive directing group and enhances the fluorescent properties
of the products (vide infra). Furthermore, similar treatment of
a suitable phenylazole substrate with four equivalents of an
À
alkyne leads to the cleavage of four C H bonds to afford a
polyarylated anthracene (1:4coupling product) that is highly
fluorescent.
In an initial attempt, 1-phenylpyrazole (1a) was used as a
typical azole substrate for the reaction with diphenylacety-
lene (2a). The examination of different reaction conditions
(see the Supporting Information) revealed that
[{Cp*RhCl2}2]/C5H2Ph4 (1,2,3,4-tetraphenylcyclopentadiene)
and Cu(OAc)2·H2O are suitable choices for the catalyst and
the oxidant, respectively. Thus, under optimal conditions
(1 mol% [{Cp*RhCl2}2], 4mol% C 5H2Ph4, 1 equiv Cu-
(OAc)2·H2O in DMF at 808C for 6 h under N2) the 1:2
coupling product, 1-(1,2,3,4-tetraphenylnaphthalen-5-yl)pyr-
azole (3a), was obtained in 93% yield (R1 = R2 = H, R3 =
R4 = Ph in Equation (1); Table 1, entry 1).
Table 1 also summarizes the results for the coupling
reactions that employed different 1-phenylpyrazoles and
internal alkynes with the [{Cp*RhCl2}2]/C5H2Ph4 catalyst
system. The reaction of 1a with diarylacetylenes 2b–d
proceeded efficiently to produce the corresponding 1-
(1,2,3,4-tetraarylnaphthalen-5-yl)pyrazoles 3b-d in good
yields (Table 1, entries 2–4). 1-Phenyl-1-hexyne (2e) also
reacted with 1a to give 1-(1,4-dibutyl-2,3-diphenylnaphtha-
len-5-yl)pyrazole (3e) predominantly, along with a small
amount of an unidentified isomer (Table 1, entry 5). From the
reaction of 1-phenyl-1-propyne (2 f) with 1a, 1-(1,4-dimethyl-
2,3-diphenylnaphthalen-5-yl)pyrazole (3 f) was obtained in a
moderate yield (Table 1, entry 6). 1-Phenyl-3-methylpyrazole
(1b) and 1-phenyl-3,5-dimethylpyrazole (1c) underwent the
coupling with 2a in a similar manner to that of 1a to produce
the corresponding 1-naphthylpyrazoles 3g and 3h in good
yields (Table 1, entries 7 and 8).
[*] N. Umeda, Dr. H. Tsurugi, Prof. Dr. T. Satoh, Prof. Dr. M. Miura
Department of Applied Chemistry
Faculty of Engineering
Osaka University
Suita, Osaka 565-0871 (Japan)
Fax: (+81)6-6879-7362
E-mail: satoh@chem.eng.osaka-u.ac.jp
index-Eng.htm
[**] We thank Prof. Dr. N. Tohnai, Osaka University, for fluorescence
quantum efficiency measurements and helpful discussions. This
work was partly supported by Grants-in-Aid from the Ministry of
Education, Culture, Sports, Science, and Technology (Japan) and the
Sumitomo Foundation.
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2008, 47, 4019 –4022
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4019
Umeda, Nobuyoshi
