Homologation method for preparation of substituted pentacenes and naphthacenes

Article abstract of DOI:10.1021/jo060923y

Multi-substituted pentacenes, such as 1,2,3,4,6,8,9,10,11,13- decasubstituted pentacenes (Type I), 1,2,3,4,6,-13-hexasubstituted pentacenes (Type II), 1,2,3,4-tetrasubstituted pentacenes (Type III), and 2,3-disubstituted pentacenes (Type IV), 1,2,3,4,6,11

Full text of DOI:10.1021/jo060923y

Homologation Method for Preparation of Substituted Pentacenes
and Naphthacenes
Tamotsu Takahashi,*,† Shi Li,† Wenying Huang,† Fanzhi Kong,† Kiyohiko Nakajima,‡
Baojian Shen,§ Takahiro Ohe,¶ and Ken-ichiro Kanno†
Catalysis Research Center and Graduate School of Pharmaceutical Sciences, Hokkaido UniVersity, and
SORST, Japan Science and Technology Corporation (JST), Kita-ku Sapporo 001-0021, Japan, Department
of Chemistry, Aichi UniVersity of Education, Igaya, Kariya, Aichi 448-8542, Japan, Petroleum
UniVersity-Hokkaido UniVersity Joint Lab, Faculty of Chemical Science and Engineering China
UniVersity of PetroleumsBeijing, Changping, Beijing 102249, China, and Materials Laboratories, Sony
Corporation, Okata, Atsugi, Kanagawa 243-0021, Japan
tamotsu@cat.hokudai.ac.jp
ReceiVed May 4, 2006
Multi-substituted pentacenes, such as 1,2,3,4,6,8,9,10,11,13-decasubstituted pentacenes (Type I), 1,2,3,4,6,-
13-hexasubstituted pentacenes (Type II), 1,2,3,4-tetrasubstituted pentacenes (Type III), and 2,3-disubstituted
pentacenes (Type IV), 1,2,3,4,6,11-hexasubstituted naphthacenes (Type V), 1,2,3,4-tetrasubstituted
naphthacenes (Type VI), and 2,3-disubstituted naphthacenes (Type VII), were prepared by a homologation
method. The homologation method involved the conversion of phthalic acid ester derivatives to two ring
extended phthalic acid ester derivatives via diynes and metallacyclopentadienes using transition metals,
such as Zr and Rh. For the formation of pentacenes of Type III and Type IV and naphthacenes of Type
VII, trimethylsilyl-substituted diynes were used for zirconocene-mediated cyclization. Elimination of the
trimethylsilyl groups after the cyclization afforded nonsubstituted position on pentacenes or naphthacenes.
Structures of 1,4,6,8,9,10,11,13-octaethyl-2,3-bis(methoxycarbonyl)pentacene (9a) and 8,9,10,11-tetraethyl-
2,3-bis(methoxycarbonyl)-1,4,6,13-tetrapropylpentacene (9b) were determined by X-ray analysis. The
structure of 9a had the herringbone packing system in the crystal like nonsubstituted pentacene. However,
9b, whose substituents at 1,4,6,13-positions were changed from Et to Pr at 1,4,6,13-positions of 9a, had
the face parallel plane system in the crystal.
Introduction
substituents into pentacene is attractive since its property and
solubility can be controlled by the substituents. The first
substituted pentacene, 6,13-diphenylpentacene, was reported by
Allen et al. in 1942.2 This compound was prepared by the
reaction of PhMgBr and pentacenequinone. In 1949, Clar
reported 6-methylpentacene.3a In 1969, Maulding et al. reported
the formation of 6,13-bis(alkynyl)pentacene and 5,7,12,14-
tetrakis(alkynyl)pentacene derivatives.4 These compounds were
prepared from pentacenequinone derivatives and alkynylmetal
compounds. After these reports, development of a preparation
Acenes, such as pentacene, have attracted much attention as
organic materials with high mobility.1 However, it has a critical
limitation in solubility in organic solvents. Introduction of
† Hokkaido University and SORST, JST.
‡ Aichi University of Education.
§ Petroleum University-Hokkaido University Joint Lab.
¶ Sony Corporation.
(1) (a) Gundlach, D. J.; Lin, Y.-Y.; Jackson, T. N.; Nelson, D. F.; Nelson,
S. F.; Schlom, D. G. IEEE Electron DeVice Lett. 1977, 18, 87. (b) Lin,
Y.-Y.; Gundlach, D. J.; Nelson, D. F.; Jackson, T. N. IEEE Electron DeVice
Lett. 1977, 18, 606. (c) Lin, Y.-Y.; Gundlach, D. J.; Nelson, S. F.; Jackson,
T. N. IEEE Trans. Electron DeVices 1977, 44, 1325. (d) Lin, Y.-Y.;
Gundlach, D. J.; Jackson, T. N. Appl. Phys. Lett. 1998, 72, 1854.
(2) Allen, C. F. H.; Bell, A. J. Am. Chem. Soc. 1942, 64, 1253.
(3) (a) Clar, E. Chem. Ber. 1949, 82, 495. (b) Clar, E.; Wright, J. W.
Nature 1949, 163, 921.
(4) Maulding, D. R.; Roberts, B. G. J. Org. Chem. 1969, 34, 1734.
10.1021/jo060923y CCC: $33.50 © 2006 American Chemical Society
Published on Web 09/21/2006
J. Org. Chem. 2006, 71, 7967-7977
7967

Takahashi et al.
CHART 1. Homologation Method for the Formation of Acenes
CHART 2. Substituted Pentacenes and Naphthacenes
method and characterization of the substituted pentacenes have
not been clearly reported in the literature for more than 30 years,
although some attempt has been reported.5
As mentioned above, in 1997, it was reported that pentacene
showed the highest mobility among organic thin film transistor
devices, and that it was comparable to the mobility of amorphous
silicon.1 Therefore, we believed that the substituted pentacenes
became very important. However, unfortunately, there have been
no systematic preparation methods of substituted pentacene
derivatives, although, historically, some compounds have been
known.2-4 This situation prompted us to develop a systematic
method for the formation of substituted pentacene derivatives.
In 2000, we preliminarily reported a novel homologation method
for the formation of multi-substituted pentacene derivatives,6
which was the first report of the systematic preparation method
of the substituted pentacenes since 1997. After our reports,
several papers on the preparation of substituted pentacenes
appeared in the literature.7-11
Among substituted pentacene derivatives, alkyl-substituted
pentacenes are quite rare. 6-Methylpentacene, as Clar reported,
existed as 6-methylene-6,13-dihydropentacene at room tem-
perature.3b Theoretical calculation of the energy indicated that
6-methylene-6,13-dihydropentacene is more stable than 6-me-
thylpentacene.12 This is one reason for the limited number of
alkyl-substituted pentacene derivatives. Even after our com-
munication, alkyl-substituted pentacenes are quite limited. Only
a few examples, such as 2,3,9,10-tetramethylpentacene deriva-
tives, have been reported.8 Fully characterized higher alkyl
groups, such as Et- or Pr-substituted pentacene derivatives, have
not been reported in the literature.
supported by a theoretical study of [1,5]-sigmatropic hydrogen
rearrangement in substituted 1,3-pentadiene systems, in which
the transition state is destabilized by the introduction of an
electron-withdrawing group in the π-system.13 The tautomer-
ization between 6-methylpentacene and 6-methylene-6,13-
dihydropentacene can also be categorized as a [1,5]-sigmatropic
hydrogen rearrangement, and the stability of the pentacene form
in our reported pentacene can be attributed to the two ester
groups at the 2,3-positions.
The concept of our homologation method involves the ring
extension of the functionalized aromatic compounds using the
reactivity of the functional groups as shown below.In this paper,
we would like to report the details of the homologation method
to control the position of the substituents of the substituted
pentacenes (Types I-IV) and naphthacenes (Types V-VII).
In contrast, our substituted pentacenes reported in a com-
munication could have eight alkyl groups as stable pentacenes.
Such stability can be explained by the existence of electron-
withdrawing groups, such as methoxycarbonyl groups. It is
(5) Hart, H.; Bashir-Hashemi, A.; Luo, J.; Meador, M. A. Tetrahedron
1986, 42, 1641.
(6) Takahashi, T.; Kitamura, M.; Shen, B.; Nakajima, K. J. Am. Chem.
Soc. 2000, 122, 12876.
Results and Discussion
Preparation of Type I and Type II Pentacenes by Ho-
mologation. We have reported a convenient preparative method
of 3,4,5,6-tetrasubstituted phthalate derivative 1 by zirconium-
mediated benzene formation.14 Starting from 3,4,5,6-tetrasub-
stituted phthalate 1, reduction of the two ester groups, bromi-
nation of the resulting diol, alkynylation of dibromide, and
cyclization of diyne with dimethyl acetylenedicarboxylate
(DMAD) afforded dihydroanthracene derivatives 4, as shown
in Scheme 1. Thus formed tricyclic compounds 4 are also
3,4,5,6-tetrasubstituted phthalate derivatives, which are the same
as 1. The tricyclic skeleton of 5 can be again extended to
pentacyclic compounds 8 by the same combination of the
procedures as for 1. Thus Type I pentacenes were prepared.
(7) For 6,13-alkynyl-substituted pentacene derivatives, see: (a) Anthony,
J. E.; Brooks, J. S.; Eaton, D. L.; Parkin, S. R. J. Am. Chem. Soc. 2001,
123, 9482. (b) Payne, M. M.; Delcamp, J. H.; Parkin, S. R.; Anthony, J. E.
Org. Lett. 2004, 6, 1609. (c) Payne, M. M.; Delcamp, J. H.; Parkin, S. R.;
Anthony, J. E. Org. Lett. 2004, 6, 3325. (d) Swartz, C. R.; Parkin, S. R.;
Bullock, J. E.; Anthony, J. E.; Mayer, A. C.; Malliaras, G. G. Org. Lett.
2005, 7, 3163.
(8) Meng, H.; Bendikov, M.; Mitchell, G.; Helgeson, R.; Wudl, F.; Bao,
Z.; Siegrist, T.; Kloc, C.; Chen, C.-H. AdV. Mater. 2003, 15, 1090.
(9) For perfluoropentacene, see: Sakamoto, Y.; Suzuki, T.; Kobayashi,
M.; Gao, Y.; Fukai, Y.; Inoue, Y.; Sato, F.; Tokito, S. J. Am. Chem. Soc.
2004, 126, 8138.
(10) For 2,3-substituted pentacene derivatives, see: (a) Miano, Q.;
Lefenfeld, M.; Nguyen, T.-Q.; Siegrist, T.; Kloc, C.; Nuckolls, C. AdV.
Mater. 2005, 17, 407. (b) Chan, S. H.; Lee, H. K.; Wang, Y. M.; Fu, N.
Y.; Chen, X. M.; Cai, Z. W.; Wong, H. N. C. Chem. Commun. 2005, 66.
(11) For 6- or 6,13-aryl-substituted pentacenes, see: (a) Vets, N.; Smet,
M.; Dehaen, W. Synlett 2005, 217. Very recently multi-phenyl-substituted
pentacenes were reported. See: (b) Miao, Q.; Chi, X.; Xiao, S.; Zeis, R.;
Lefenfeld, M.; Siegrist, T.; Steigerwald, M. L.; Nucholls, C. J. Am. Chem.
Soc. 2006, 128, 1340.
(13) Saettel, N. J.; Wiest, O. J. Org. Chem. 2000, 65, 2331.
(14) (a) Takahashi, T.; Kotora, M.; Xi, Z. J. Chem. Soc., Chem. Commun.
1995, 361. (b) Takahashi, T.; Xi, Z.; Yamazaki, A.; Liu, Y.; Nakajima, K.;
Kotora, M. J. Am. Chem. Soc. 1998, 120, 1672. (c) Takahashi, T.; Tsai,
F.-Y.; Li, Y.; Nakajima, K.; Kotora, M. J. Am. Chem. Soc. 1999, 121, 11093.
(12) (a) Herr, M. L. Tetrahedron 1972, 28, 5139. (b) Bartmess, J. E.;
Griffith, S. S. J. Am. Chem. Soc. 1990, 112, 2931.
7968 J. Org. Chem., Vol. 71, No. 21, 2006

Homologation of Pentacenes and Naphthacenes
SCHEME 1
SCHEME 2
When 8a-c were treated with DDQ (2,3-dichloro-5,6-
dicyano-1,4-benzoquinone) at 100-150 °C, some amounts of
DDQ adducts of the desired pentacene derivatives 9a-c were
formed as byproducts14 along with the desired pentacenes 9a-c
and some unidentified species. The unidentified species could
not be separated by column chromatography in some cases.
Fortunately, these byproducts and the unidentified species were
soluble in methanol, but the products 9a-c were not soluble in
methanol. Therefore, addition of methanol to the reaction
mixture of 8a-c with DDQ afforded blue precipitates of 9a-
c. In the sequence of the pentacene synthesis of Type I, the
aromatization of the corresponding 5,7,12,14-tetrahydropenta-
cene with 2 equiv of DDQ was attempted. The amount of the
byproducts, however, increased and resulted in failure for
isolation of the desired pentacene. Then, the stepwise procedure
of DDQ aromatization was chosen in the synthesis.
ature as described above. Structures of 9a,b were determined
by X-ray analysis (vide infra).
Type II pentacene derivatives could be prepared using
dibromo-o-xylene which is commercially available as the
starting material in a similar way to Type I pentacene deriva-
tives, as shown in Scheme 2. The product 9d was obtained as
a blue solid.
Preparation of Type III and Type IV Pentacenes by
Introduction and Elimination of the Trimethylsilyl Group.
To obtain Types III and IV pentacenes, it was necessary to
consider the solubility of the intermediates. Zirconium-mediated
cyclization usually requires the existence of substituents on
diynes. Therefore, silylated diynes were used, and after cycliza-
tion, the silyl groups were removed.
Reaction of dibromo-o-xylene (2b) with trimethylsilylethy-
nyllithium or magnesium halide did not lead to the clean
formation of the desired diyne 3e. Therefore, 2b was converted
to diiodo-o-xylene 2c. Diiodo-o-xylene (2c) cleanly reacted with
trimethylsilylethynylmagnesium bromide in the presence of
CuCl to give the desired diyne 3e. The diyne 3e was treated
with Cp2ZrBu2 (Negishi reagent) followed by the reaction with
DMAD in the presence of CuCl to afford dihydroanthracene
derivative 4e. The structure of 4e was verified by X-ray analysis.
Desilylation of 4e with Bu4NF in THF gave a mixture of
The alkyl-substituted pentacenes 9a-c prepared here were
stable under nitrogen15 and did not show any conversion to its
tautomer, 6-alkylidene-6,13-dihydropentacene, at room temper-
(15) In general, naphthacenes and pentacenes should be treated in the
absence of oxygen because they react with molecular oxygen in the presence
of light to afford the corresponding endoperoxides. We previously reported
such oxidation reactions with substituted pentacenes. See: Zhou, X.;
Kitamura, M.; Shen, B.; Nakajima, K.; Takahashi, T. Chem. Lett. 2004,
33, 410.
J. Org. Chem, Vol. 71, No. 21, 2006 7969

Takahashi et al.
SCHEME 3
SCHEME 4
SCHEME 5
desilylated dihydroanthracene and its aromatized one. Fortu-
nately, reduction of 4e with LiAlH4, hydrolysis, and successive
bromination with PBr3 gave cleanly 2,3-bis(bromomethyl)-9,-
10-dihydroanthracene (4f) as a separable major product. The
NMR analyses of these steps showed that the protodesilylation
occurred at the bromination step, probably due to HBr generated
from the reaction of the alcohol with PBr3 or contaminated in
it. Aromatization of 4f with DDQ gave 6e. Further reactions
from 6e for preparation of 9e were the same as described for
the formation of 9d. Alkynylation of 6e with 1-hexynyllithium
afforded 7e. Aromatization of dihydroanthracene 4e gave the
corresponding anthracene 5e. Cyclization of 7e using Cp2ZrBu2
and DMAD in the presence of CuCl produced 8e, which was
aromatized with DDQ to give 9e.
ethoxycarbonyl)tetrahydropentacenes 12a,b were obtained.
Treatment of 11a with TBAF instead of the combination
of Me3SiCl, NaI, and H2O in CH3CN resulted in the for-
mation of a 1:1 mixture of 12a and its dihydropentacene
derivative, which was partially the aromatized product of
12a. Fortunately, in contrast to the synthesis of Types I-III
pentacenes shown in Schemes 1-3, the double aromatization
of the tetrahydropentacenes 12 worked well, and the desired
pentacenes were able to be isolated in good yields. Aromati-
zation of 12a,b with 2 equiv of DDQ afforded the desired
pentacene diesters 9f,g, as shown in Scheme 6. When 11a was
treated with a 1:3 mixture of LiAlH4 and AlCl3, benzofuran
derivative 12d was obtained. After desilylation of 12d
with trifluoroacetic acid, thus formed tetrahydropentacene 12e
was aromatized in the similar way to afford the pentacene 9i
having a cyclic ether moiety. Reduction of 11a with LAH and
bromination with PBr3 afforded bis(bromomethyl)tetrahydro-
pentacene 12c, which was aromatized with DDQ in a manner
similar manner to produce bis(bromomethyl)pentacene in high
yield.
To prepare Type IV pentacenes, 4f was converted to diiodide
4h. Aromatization of 4h caused a problem for the second
desilylation step at the dihydropentacene stage. Therefore, the
alkynylation of 4h was carried out without aromatization of 4h,
as shown in Scheme 4. The zirconium-mediated cycloadditions
of diyne 10 with dimethyl or diethyl acetylenedicarboxylates
afforded the corresponding tetrahydropentacenes 11a,b.
Preparation of Hexa- (Type V), Tetra- (Type VI), and
Disubstituted Naphthacenes (Type VII). As for substituted
naphthacene derivatives, many examples have been reported in
the literature.6,17,18 5,6,11,12-Tetraphenylnaphthacene is com-
It is well-known that cyclization of diyne derivatives can be
done with other transition metal catalysts. In Scheme 5, Rh-
catalyzed transformation of 3e to 4h is demonstrated.
The product 11a,b could be converted into various penta-
cene derivatives of Type IV, as shown in Scheme 6. The direct
desilylation of 11a,b was successful with the combination
of Me3SiCl, NaI, and H2O in CH3CN.16 2,3-Bis(methoxy- or
(16) Olah, G. A.; Narang, S. C.; Gupta, B. G. B.; Malhotra, R. J. Org.
Chem. 1979, 44, 1247.
7970 J. Org. Chem., Vol. 71, No. 21, 2006

Homologation of Pentacenes and Naphthacenes
SCHEME 6
SCHEME 7
mercially available, well-known as rubrene, and very attractive
as an organic material.19-21 Its derivatives have been prepared.18
In our homologation method, we have already reported the
formation of hexasubstituted naphthacene derivatives (Type V).6
Naphthacenes of Types VI and VII were prepared from 2,3-
naphthalenedicarboxylic anhydride, which was used as the
commercially available starting material. Reduction, iodination,
and alkynylation of 2,3-naphthalenedicarboxylic anhydride
afforded 14 via 13, as shown in Scheme 7. Cyclization of 14
with Cp2ZrBu2 gave 15a, which could be aromatized with DDQ
to give naphthacene 16a. Reduction and bromination of 15a
afforded 15b. Aromatization of 15b gave 16b.
Effect of the Substituents on the Packing System of
1,2,3,4,6,8,9,10,11,13-Decasubstituted Pentacenes. Structures
of 9a and 9b were determined by X-ray analysis. Those
structures are shown in Figure 1. It is well-known that
nonsubstituted pentacene has the herringbone structure22 which
has an important role for its physical properties, such as FET
mobility. According to the theoretical study, the parallel stacking
of pentacenes can have better properties.23 However, it is not
(17) (a) Fieser, L. F.; Hershberg, E. B. J. Am. Chem. Soc. 1940, 62, 49.
(b) Meek, J. S.; Dewey, F. M. J. Org. Chem. 1970, 35, 1315. (c) Sy, A.;
Hart, H. J. Org. Chem. 1979, 44, 7. (d) Gribble, G. W.; Perni, R. B. J.
Org. Chem. 1985, 50, 2934. (e) Odom, S. A.; Parkin, S. R.; Anthony, J. E.
Org. Lett. 2003, 5, 4245. (f) Moon, H.; Zeis, R.; Borkent, E.-J.; Besnard,
C.; Lovinger, A. J.; Siegrist, T.; Kloc, C.; Bao, Z. J. Am. Chem. Soc. 2004,
126, 15322. (g) Chen, Z.; Muller, P.; Swager, T. M. Org. Lett. 2006, 8,
273.
(18) (a) Dodgge, J. A.; Chamberlin, R. Tetrahedron Lett. 1988, 29, 1359.
(b) Dodge, J. A.; Bain, J. D.; Chaberlin, A. R. J. Org. Chem. 1990, 55,
4190 and references therein. (c) Smyth, N.; Van Engen, D.; Pascal, R. A.,
Jr. J. Org. Chem. 1990, 55, 1937.
(19) Hurcules, D. M.; Lansbury, R. C.; Roe, D. K. J. Am. Chem. Soc.
1966, 88, 4578.
(20) Freedman, D. A.; Matachek, J. R.; Mann, K. R. Inorg. Chem. 1993,
32, 1078.
(21) Sundar, V. C.; Zaumseil, J.; Podzorov, V.; Menard, E.; Willet, R.
L.; Someya, T.; Gershenson, M. E.; Rogers, J. A. Science 2004, 303, 1644.
(22) Mattheus, C. C.; Dros, A. B.; Baas, J.; Meetsma, A.; de Boer, J. L.;
Palstra, T. T. M. Acta Crystallogr. 2001, C57, 939.
J. Org. Chem, Vol. 71, No. 21, 2006 7971

Takahashi et al.
FIGURE 1. Perspective views of pentacenes 9a and 9b.
FIGURE 2. Packing systems of 9a and 9b.
clear which factors control the packing system of substituted
pentacenes. Most of the substituted pentacenes have the her-
ringbone structures. Only alkynyl-substituted or phenyl-
substituted pentacenes have the parallel stacking system.7,11b
There has been no information how to control the stacking
system.
As shown in Figure 2, 9a has clearly the same herringbone
system as that of nonsubstituted pentacene and most of
substituted pentacenes. Surprisingly, when only the substituent
was changed from Et to Pr at 1,4,6,13-positions from 9a to 9b,
the molecular order could be changed from the herringbone to
(23) Deng, W.-Q.; Goddard, W. A., III. J. Phys. Chem. B 2004, 108,
8614.
7972 J. Org. Chem., Vol. 71, No. 21, 2006

Homologation of Pentacenes and Naphthacenes
Preparation of 1,4-Dipropyl-2,3-bis(methoxycarbonyl)-5,6,7,8-
tetraethyl-9,10-dihydroanthracene (4b) from 3b. To a solution
of Cp2ZrCl2 (436 mg, 1.49 mmol) in 5 mL of THF was added
n-BuLi (1.58 M hexane solution, 1.9 mL, 3.0 mmol) at -78 °C,
and the solution was stirred for 1 h. To the solution was added
1,2-bis(2-hexynyl)-3,4,5,6-tetraethylbenzene (3b, 435 mg, 1.24
mmol), and the mixture was warmed to room temperature by
removal of the cooling bath. After stirring for 3 h, CuCl (246 mg,
2.48 mmol) and DMAD (0.46 mL, 3.7 mmol) were added to the
mixture, and the mixture was stirred for 3 h at room temperature.
The mixture was quenched with aqueous 3 N HCl and extracted
with ethyl acetate. The combined organic phase was washed with
water, saturated aqueous NaHCO3 solution, and brine. The solution
was dried over anhydrous Na2SO4. The solvent was evaporated,
and the resulting brown viscous oil was purified by a flash
chromatography (silica gel, hexane:ethyl acetate ) 5:1 as eluent)
to afford the title compound 4b as colorless crystals (412 mg, 67%
yield).
face parallel stacking, as shown in Figure 2, although the
neighbor long axes of pentacene 9b are not parallel in the crystal.
In the herringbone packing system of 9a, the distance between
the two least-squares planes of neighboring pentacenes (d1) is
5.4 Å, and the dihedral angle (Θ) is 115.6°. The distance is
considerably longer than those for nonsubstituted pentacene (2.1
and 2.6 Å).23 It seems that the ethyl groups cause the strong
intermolecular steric hindrance in the packing system. The
dihedral angle of the two least-squares planes of neighboring
nonsubstituted pentacene is 128.0°. On the other hand, 9b has
the parallel stacking system (d2 ) 3.6 Å).
Conclusion
In conclusion, we developed a homologation method for the
preparation of substituted pentacene and naphthacene derivatives
starting from substituted phthalic acid ester compounds and
naphthalenedicarboxylic anhydride, respectively. Introduction
and elimination of trimethylsilyl groups could control the
position of substituents on pentacenes and naphthacenes. Multi-
substituted alkylpentacenes were obtained as stable compounds
with electron-withdrawing groups, such as methoxycarbonyl
groups under N2. Structures of the alkyl-substituted pentacenes
were determined. Slight change of the alkyl groups from the Et
group to the Pr group of some substituents caused the change
of packing system from herringbone to parallel in the crystal.
4b: 1H NMR (CDCl3, δ) 1.05 (t, J ) 7 Hz, 6 H), 1.19 (t, J ) 7
Hz, 6 H), 1.24 (t, J ) 7 Hz, 6 Hz), 1.64 (tq, J ) 8, 8 Hz, 4 H),
2.69 (q, J ) 8 Hz, 4 H), 2.73-2.87 (m, 8 H), 3.84 (s, 6 H), 3.92
(s, 4 H); 13C NMR (CDCl3, δ) 14.6, 15.3, 15.9, 22.28, 22.31, 24.4,
29.5, 32.6, 52.2, 130.0, 132.4, 135.2, 136.4, 137.9, 139.3, 169.6.
HRMS calcd for C32H44O4: 492.3240. Found: 492.3242.
Preparation of 1,4-Dipropyl-2,3-bis(methoxycarbonyl)-5,6,7,8-
tetraethylanthracene (5b) from 4b. 9,10-Dihydroanthracene 4b
(475 mg, 0.96 mmol) and DDQ (240 mg, 1.06 mmol) were
dissolved in 5 mL of toluene, and the mixture was heated to 100
°C for 3 h. A colorless precipitate of 2,3-dichloro-5,6-dicyanohy-
droquinone was observed. After cooling to room temperature, the
precipitate was removed by filtration, and the filtrate was concen-
trated in vacuo. The residue was dissolved in CHCl3 (30 mL) and
filtered to remove the remaining hydroquinone. The solvent was
removed in vacuo, the residue was dissolved in 1 mL of CHCl3,
and the mixture was put into 10 mL of MeOH. The mixture was
stirred for 10 min to produce a pale-yellow precipitate of the title
compound 5b, which was collected by filtration (161 mg). The
filtrate was concentrated in vacuo and was purified by silica gel
column chromatography (CHCl3) to afford the additional product
(163 mg). The total isolated yield was 69%.
Experimental Section
Preparation of 1,2-Bis(iodomethyl)benzene (2c). A mixture of
1,2-bis(bromomethyl)benzene (25.0 g, 95 mmol), NaI (85 g, 0.57
mol), and acetone (500 mL) was refluxed for 12 h. After cooling
to room temperature, the solvent was removed in vacuo. To the
resulting solid was added water (500 mL), and the mixture was
stirred for 30 min. The resulting precipitate was filtered and washed
with 10% aqueous Na2S2O3 solution, water, and MeOH. The solid
was dried in vacuo to afford the title compound as pale-yellow
powder (31 g, 91% yield). All spectral data were identical to the
reported ones.24
5b: 1H NMR (CDCl3, δ) 1.22 (t, J ) 7 Hz, 6 H), 1.30 (t, J ) 7
Hz, 6 H), 1.42 (t, J ) 7 Hz, 6 H), 1.78-1.95 (m, 4 H), 2.91 (q, J
) 7 Hz, 4 H), 3.18-3.33 (m, 8 H), 3.93 (s, 6 H), 8.86 (s, 2 H); 13
C
Preparation of 1,2-Bis(2-hexynyl)-3,4,5,6-tetraethylbenzene
(3b) from 2a. To a solution of 1-pentyne (0.79 mL, 8.0 mmol) in
10 mL of THF was added n-BuLi (1.58 M hexane solution, 5.1
mL, 8.0 mmol) at -78 °C, and the mixture was warmed to room
temperature. After stirring for 1 h, the solution was re-cooled to
-78 °C, and DMPU (0.96 mL, 8.0 mmol) and 1,2-bis(bromom-
ethyl)-3,4,5,6-tetraethylbenzene (2a, 752 mg, 2.0 mmol) were added
to the mixture. The resulting mixture was warmed to room
temperature by removal of the cooling bath and stirred for 3 h.
The mixture was quenched with saturated NH4Cl solution and
extracted with CHCl3. The combined organic phase was washed
with water, saturated aqueous NaHCO3 solution, and brine. The
solution was dried over anhydrous MgSO4. The solvent was
evaporated, and the resulting yellow oil was purified by a flash
chromatography (silica gel, hexane to hexane:ethyl acetate ) 50:1
as eluent) to afford the title compound 3b as a pale-yellow oil (647
mg, 92% yield).
NMR (CDCl3, δ) 14.7, 15.4, 15.8, 20.0, 23.0, 24.7, 32.5, 52.3,
121.4, 126.5, 128.9, 130.3, 135.1, 137.6, 138.8, 169.8. HRMS calcd
for C32H42O4: 490.3083. Found: 490.3087.
Preparation of 1,4-Dipropyl-2,3-bis(bromomethyl)-5,6,7,8-
tetraethylanthracene (6b) from 5b. LiAlH4 (46 mg, 1.2 mmol)
was added to 5 mL of THF and cooled to 0 °C. To the suspension
was added a solution of 2,3-bis(methoxycarbonyl)-1,4-dipropyl-
5,6,7,8-tetraethylanthracene (5b, 294 mg, 0.60 mmol) in 7 mL of
THF dropwise for 15 min. The mixture was warmed to room
temperature and stirred for 1 h. After cooling to 0 °C, to the mixture
was slowly added aqueous 3 N HCl. It was extracted with CHCl3.
The combined organic phase was washed with brine and dried over
anhydrous Na2SO4. Removal of the solvent in vacuo gave the
corresponding diol as a pale-yellow solid in almost quantitative
yield. The solid was dissolved in 10 mL of 1,2-dichloroethane and
treated with phosphorus tribromide (53 µL, 0.56 mmol) and stirred
at room temperature for 1 h. The mixture was quenched with water
and extracted with CHCl3. The combined organic phase was washed
with brine and dried over Na2SO4. After removal of the solvent in
vacuo, the residue was dissolved in 2 mL of CHCl3, and it was put
into 20 mL of MeOH. The resulting yellow precipitate was collected
by filtration and dried in vacuo to afford the pure title compound
6b (233 mg, 69% yield).
3b: 1H NMR (CDCl3, δ) 0.93 (t, J ) 7 Hz, 6 H), 1.18 (t, J ) 8
Hz, 6 H), 1.22 (t, J ) 8 Hz, 6 H), 1.48 (tq, J ) 7, 7 Hz, 4 H), 2.08
(tt, J ) 7, 2 Hz, 4 H), 2.65 (q, J ) 8 Hz, 4 H), 2.74 (q, J ) 8 Hz,
4 H), 3.61 (t, J ) 2 Hz, 4 H); 13C NMR (CDCl3, δ) 13.6, 15.4,
15.7, 19.2, 21.0, 22.3, 22.4, 22.7, 78.4, 80.4, 132.9, 138.3, 138.9.
HRMS calcd for C26H38: 350.2973. Found: 350.2966.
6b: 1H NMR (CDCl3, δ) 1.23 (t, J ) 7 Hz, 6 H), 1.32 (t, J ) 7
Hz, 6 H), 1.41 (t, J ) 8 Hz, 6 H), 1.72-2.00 (m, 4 H), 2.90 (q, J
(24) Inaba, S.; Wehmeyer, R. M.; Forkner, M. W.; Rieke, R. D. J. Org.
Chem. 1988, 53, 339.
) 8 Hz, 4 H), 3.18-3.36 (m, 8 H), 5.00 (s, 4 H), 8.77 (s, 2 H); 13
C
J. Org. Chem, Vol. 71, No. 21, 2006 7973

Takahashi et al.
NMR (CDCl3, δ) 14.9, 15.4, 15.8, 22.0, 23.0, 24.4, 30.0, 31.5,
120.7, 129.1, 129.2, 129.9, 135.0, 138.3, 138.7. HRMS calcd for
C30H40Br2: 558.1497. Found: 558.1493.
137.6, 138.2, 169.7. HRMS calcd for C46H58O4: 674.4335.
Found: 674.4343.
Preparation of 1,2-Bis(3-trimethylsilyl-2-propynyl)benzene
(3e) from 2c. To a solution of trimethylsilylacetylene (13.6 mL,
96 mmol) in 100 mL of THF was added ethylmagnesium bromide
(0.96 M THF solution, 100 mL, 96.0 mmol) slowly, and the mixture
was heated to 40 °C for 1 h. To the resulting solution were added
CuCl (1.19 g, 12 mmol) and 1,2-bis(iodomethyl)benzene (2c, 8.59
g, 24 mmol), and the mixture was heated to reflux for 3 h. After
cooling to room temperature, the mixture was quenched with
aqueous saturated NH4Cl and extracted with hexane. The combined
organic phase was washed with water and brine and dried over
anhydrous Na2SO4. After removal of the solvent, the residue was
purified by silica gel chromatography (hexane:ethyl acetate ) 50:
1) to afford the title compound 3e (5.59 g, 78% yield) as a colorless
oil.
Preparation of 1,4-Dipropyl-2,3-bis(2-hexynyl)-5,6,7,8-tetra-
ethylanthracene (7b) from 6b. n-BuLi (1.56 M hexane solution,
0.90 mL, 1.40 mmol) was added dropwise to a solution of 1-pentyne
(0.14 mL, 1.42 mmol) in 5 mL of THF at -78 °C. The mixture
was warmed to room temperature and stirred for 1 h. The mixture
was cooled to -78 °C, and to the mixture was added 2,3-bis-
(bromomethyl)-1,4-dipropyl-5,6,7,8-tetraethylanthracene (6b, 203
mg, 0.36 mmol). The mixture was warmed to room temperature
and heated to 50 °C for 3 h. After cooling to room temperature,
the mixture was quenched with aqueous 3 N HCl and extracted
with CHCl3. The combined organic phase was washed with water,
saturated NaHCO3 solution, and brine and dried over Na2SO4. After
removal of the solvent in vacuo, the residue was dissolved in 1
mL of CHCl3, and it was put into 10 mL of MeOH. The resulting
yellow precipitate was collected by filtration and dried in vacuo to
afford the pure title compound 7b (144 mg, 75% yield).
1
3e: H NMR (CDCl3, δ) 0.19 (s, 18 H), 3.65 (s, 4 H), 7.25-
7.28 (m, 2 H), 7.45-7.48 (m, 2 H); 13C NMR (CDCl3, δ) 0.1, 23.9,
87.4, 103.4, 127.2, 128.6, 134.2. Anal. Calcd for C18H26Si2: C,
72.41; H, 8.78. Found: C, 72.32; H, 8.84.
7b: 1H NMR (CDCl3, δ) 0.93 (t, J ) 7 Hz, 6 H), 1.20 (t, J ) 7
Hz, 6 H), 1.29 (t, J ) 7 Hz, 6 H), 1.37-1.55 (m, 10 H), 1.75-
1.92 (m, 4 H), 2.05-2.18 (m, 4 H), 2.89 (q, J ) 7 Hz, 4 H), 3.19-
3.33 (m, 8 H), 3.87 (s, 4 H), 8.73 (s, 2 H); 13C NMR (CDCl3, δ)
13.5, 14.9, 15.3, 15.9, 20.1, 20.9, 22.0, 22.4, 23.0, 24.1, 31.7, 78.5,
81.0, 119.7, 129.0, 129.2, 131.1, 134.6, 134.8, 137.0. HRMS calcd
for C40H54: 534.4226. Found: 534.4226.
Preparation of 1,4,6,13-Tetrapropyl-2,3-bis(methoxycarbo-
nyl)-8,9,10,11-tetraethyl-5,14-dihydropentacene (8b) from 7b.
Cp2ZrCl2 (1.27 g, 4.34 mmol) was dissolved in 40 mL of THF.
The solution was cooled to -78 °C. n-BuLi (1.58 M hexane
solution, 5.5 mL, 8.7 mmol) was added dropwise to the solution
and stirred for 1 h. To the mixture was added 1,4-dipropyl-2,3-
bis(2-hexynyl)-5,6,7,8-tetraethylanthracene (7b, 2.30 g, 4.30 mmol),
and it was warmed to room temperature. After stirring for 3 h,
CuCl (0.87 g, 8.8 mmol) and DMAD (1.61 mL, 13.1 mmol) were
added to the mixture at 0 °C, and it was stirred at room temperature
for 12 h. The mixture was quenched with aqueous 3 N HCl and
extracted with hexane three times. The combined organic phase
was washed with water, saturated NaHCO3 solution, and brine and
dried over MgSO4. After removal of the solvent, the residue was
purified by silica gel chromatography (hexane:ethyl acetate ) 10:
1) to afford the title compound 8b as a colorless powder (1.76 g,
60% yield).
1,4-Bis(trimethylsilyl)-2,3-bis(methoxycarbonyl)-9,10-dihy-
droanthracene (4e) from 3e. To a solution of Cp2ZrCl2 (365 mg,
1.25 mmol) in 5 mL of THF was added n-BuLi (1.56 M hexane
solution, 1.60 mL, 2.50 mmol) at -78 °C, and the mixture was
stirred for 10 min. The solution was warmed to -40 °C for 30 min
and then re-cooled to -78 °C. After 10 min, diyne 3e (298 mg,
1.0 mmol) was added to the solution, and it was warmed to room
temperature by removal of the cooling bath. After stirring for 3 h,
CuCl (297 mg, 3.0 mmol) and DMAD (0.48 mL, 3.9 mmol) were
added to the mixture, and it was stirred for 6 h at room temperature.
The mixture was quenched with 3 N HCl and extracted with ethyl
acetate. The combined organic phase was washed with water,
saturated aqueous NaHCO3 solution, and brine. The solution was
dried over anhydrous Na2SO4. The solvent was evaporated, and
the resulting brown viscous oil was purified by a flash chroma-
tography (silica gel, hexane:ethyl acetate ) 5:1 as eluent) to afford
the title compound 4e as colorless crystals (171 mg, 39% yield).
1
4e: H NMR (CDCl3, δ) 0.46 (s, 18 H), 3.85 (s, 6 H), 4.04 (s,
4 H), 7.23-7.27 (m, 2 H), 7.32-7.35 (m, 2 H); 13C NMR (CDCl3,
δ) 1.7, 38.4, 52.3, 126.2, 126.4, 135.6, 135.9, 137.2, 145.9, 170.5.
HRMS calcd for C24H32O4Si2: 440.1839. Found: 440.1845.
Preparation of 2,3-Bis(bromomethyl)-9,10-dihydroanthracene
(4f) from 4e. 1,4-Bis(trimethylsilyl)-9,10-dihydroanthracene-2,3-
dicarboxylic acid dimethyl ester (4e, 440 mg, 1.0 mmol) was added
to LiAlH4 (83.6 mg, 2.2 mmol) in 10 mL of diethyl ether at 0 °C.
After stirring for 3 h at room temperature, hydrolysis with water
was performed carefully. The mixture was treated with aqueous 2
N H2SO4 and extracted with diethyl ether. The extract was washed
with brine and dried over Na2SO4, and then the solvent was
removed. Phosphorus tribromide (0.28 mL, 3.0 mmol) was added
dropwise to the residue in 10 mL of CHCl3 at 0 °C. After stirring
for 1 h at room temperature, the mixture was treated with water at
0 °C and extracted with CHCl3. The extract was washed with brine
and dried over Na2SO4. Chromatography on silica gel (hexane:
ethyl acetate ) 20:1 as eluent) gave 328 mg of the title compound
4f as pale-yellow crystals in 90% isolated yield.
8b: 1H NMR (CDCl3, δ) 1.11 (t, J ) 7 Hz, 6 H), 1.22 (t, J ) 7
Hz, 6 H), 1.29 (t, J ) 7 Hz, 6 H), 1.43 (t, J ) 7 Hz, 6 H), 1.61-
1.93 (m, 8 H), 2.78-2.97 (m, 8 H), 3.20-3.42 (m, 8 H), 3.85 (s,
6 H), 4.14 (s, 4 H), 8.76 (s, 2 H); 13C NMR (CDCl3, δ) 14.7, 14.9,
15.3, 15.9, 22.0, 23.0, 24.3, 24.6, 30.4, 31.1, 32.9, 52.2, 119.6,
128.8, 128.9, 130.2, 131.2, 131.7, 134.7, 135.1, 137.1, 139.8, 169.5.
HRMS calcd for C46H60O4: 676.4492. Found: 676.4497.
Preparation of 1,4,6,13-Tetrapropyl-2,3-bis(methoxycarbo-
nyl)-8,9,10,11-tetraethylpentacene (9b) from 8b. 1,4,6,13-Tetra-
propyl-2,3-bis(methoxycarbonyl)-8,9,10,11-tetraethyl-5,14-dihy-
dropentacene (8b, 600 mg, 0.89 mmol) and DDQ (221 mg, 0.97
mmol) were dissolved in 12 mL of toluene. Under nitrogen
atmosphere, the solution was heated to reflux for 24 h. After cooling
to room temperature, the solvent was removed in vacuo. The residue
was put into 120 mL of degassed MeOH. The resulting blue
precipitate was collected by filtration under nitrogen. The precipitate
was dissolved in 20 mL of CHCl3 and purified by chromatography
of silica gel (deactivated with 10 wt % of water). After removal of
the solvent, the residue was crystallized from hexane to afford the
title compound 9b as blue fluffy solid (207 mg, 35% yield).
9b: 1H NMR (CDCl3, δ) 1.20 (t, J ) 7 Hz, 6 H), 1.28 (t, J ) 7
Hz, 6 H), 1.32 (t, J ) 8 Hz, 6 H), 1.50 (t, J ) 8 Hz, 6 H), 1.87-
2.14 (m, 8 H), 2.90 (q, J ) 7 Hz, 4 H), 3.15-3.41 (m, 8 H), 3.85-
4.05 (m, 4 H), 3.94 (s, 6 H), 9.13 (s, 2 H), 9.19 (s, 2 H); 13C NMR
(CDCl3, δ) 14.9, 15.1, 15.2, 15.8, 22.1, 23.1, 24.6, 25.1, 31.1, 32.7,
52.3, 120.1, 122.8, 126.2, 127.6, 127.9, 128.4, 129.7, 133.9, 134.6,
4f: 1H NMR (CDCl3, δ) 3.93 (s, 4 H), 4.68 (s, 4 H), 7.19-7.31
(m, 6 H); 13C NMR (CDCl3, δ) 30.3, 35.7, 126.3, 127.4, 130.1,
134.3, 135.7, 138.3. HRMS calcd for C16H14Br2 363.9461. Found:
363.9464.
Preparation of 2,3-Bis(bromomethyl)anthracene (6e) from 4f.
DDQ (1.16 g, 5.11 mmol) was added to 2,3-bis(bromomethyl)-9,-
10-dihydroanthracene (4f, 1.7 g, 4.6 mmol) in toluene, and the
mixture was stirred at 90 °C for 3 h. After filtration, the filtrate
was evaporated to dryness and washed with MeOH, and the pale-
yellow powder product 6e was obtained in 78% yield.
1
6e: H NMR (CDCl3, δ) 4.94 (s, 4 H), 7.50 (dd, J ) 6.0, 3.0
Hz, 2 H), 8.00 (dd, J ) 6.0, 3.0 Hz, 2 H), 8.04 (s, 2 H), 8.38 (s, 2
7974 J. Org. Chem., Vol. 71, No. 21, 2006

Homologation of Pentacenes and Naphthacenes
H); 13C NMR (CDCl3, δ) 31.6, 126.1, 126.6, 128.3, 131.0, 131.2,
132.5, 133.1. HRMS calcd for C16H12Br2: 361.9305. Found:
361.9318.
Alternative Method for the Preparation of 2,3-Bis(iodom-
ethyl)-9,10-dihydroanthracene (4h) from 4e. To a suspension of
LiAlH4 (1.52 g, 40.0 mmol) in diethyl ether (150 mL) at 0 °C was
added 1,4-bis(trimethylsilyl)-2,3-bis(methoxycarbonyl)-9,10-dihy-
droanthracene (4e, 8.82 g, 20.0 mmol). The mixture was warmed
to room temperature and stirred for 1 h. After cooling to 0 °C, the
mixture was slowly added with aqueous 3 N HCl and extracted
with CHCl3. The combined organic phase was washed with brine
and dried over anhydrous Na2SO4. Removal of the solvent in vacuo
afforded the corresponding diol as a colorless solid in a quantitative
yield. NaI (12.1 g, 80.7 mmol) was added to the mixture, and it
was dissolved in 100 mL of acetonitrile. To the mixture was added
chlorotrimethylsilane (10.2 mL, 80.4 mmol), and it was stirred at
room temperature for 1 h.16 The mixture was quenched with water
and extracted with CHCl3. The combined organic phase was washed
with brine and dried over MgSO4. After removal of the solvent in
vacuo, the residue was dissolved in 16 mL of CHCl3, and it was
put into 160 mL of MeOH. The resulting pale-yellow precipitate
was collected by filtration and dried in vacuo to afford the pure
title compound 4h (6.14 g, 67% yield for two steps).
Preparation of 2,3-Bis(2-heptynyl)anthracene (7e) from 6e.
2,3-Bis(bromomethyl)anthracene (6e, 1.24 g, 3.41 mmol) was added
to 17.1 mmol 1-hexynyllithium solution, which was prepared from
1-hexyne and butyllithium in THF/toluene (1/1) solution. The
resulting mixture was stirred at 50 °C for 3 h and hydrolyzed with
3 N HCl (aq). The reaction mixture was extracted with ethyl ether,
washed with NaHCO3 (aq) and brine and dried over MgSO4.
Column chromatography (silica gel, hexane/ethyl ether ) 10/1 as
eluent) gave 1.01 g of the title compound 7e as yellow-green
powder in 81% isolated yield.
1
7e: H NMR (CDCl3, δ) 0.95 (t, J ) 6.6 Hz, 6 H), 1.52 (m, 8
H), 2.29 (t, J ) 7.2 Hz, 4 H), 3.76 (s, 4 H), 7.42 (dd, J ) 6.0, 3.0
Hz, 2 H), 7.98 (dd, J ) 6.0, 3.0 Hz, 2 H), 8.06 (s, 2 H), 8.36 (s, 2
H); 13C NMR (CDCl3, δ) 13.7, 18.6, 22.0, 23.3, 31.1, 76.8, 83.9,
125.1, 125.5, 126.9, 128.1, 131.0, 131.7, 133.6. HRMS calcd for
C28H30: 366.2348. Found: 366.2349.
Preparation of 1,4-Dibutyl-2,3-bis(methoxycarbonyl)penta-
cene (9e) from 8e. DDQ (13.6 mg, 0.06 mmol) in 2 mL of toluene
was dropwise added to 8e (30.5 mg, 0.06 mmol) in 1 mL of toluene
at 100 °C over 12 h. Then the mixture was filtered through Celite,
and the filtrate was kept at -30 °C overnight to afford the title
compound 9e as violet-blue crystals (15 mg, 49% yield).
Preparation of 2,3-Bis(3-trimethylsilylprop-2-ynyl)-9,10-di-
hydroanthracene (10) from 4h. To a solution of trimethylsily-
lacetylene (12.9 mL, 91.3 mmol) in 100 mL of THF was added
ethylmagnesium bromide (0.91 M THF solution, 100 mL, 91
mmol). The mixture was heated to 40 °C for 1 h. CuCl (1.13 g,
11.4 mmol) and diiodide 4h (13.99 g, 30.4 mmol) were added to
the mixture, and it was heated to reflux overnight. After cooling to
room temperature, the mixture was quenched with aqueous saturated
NH4Cl and extracted with hexane. The combined organic phase
was washed with water. After addition of 1 mg of BHT, the solution
was washed with brine and dried over Na2SO4. After removal of
the solvent, the residue was purified by silica gel chromatography
(hexane:ethyl acetate:triethylamine ) 50:1:1 as eluent) to afford a
colorless viscous oil, which was further purified by recrystallization
from hexane. After drying in vacuo, the title compound 10 was
obtained as a colorless solid (8.48 g, 70% yield).
1
9e: H NMR (CDCl3, δ) 1.04 (t, J ) 7.2 Hz, 6 H), 1.60 (m, 4
H), 1.85 (m, 4 H), 3.23 (t, J ) 8.1 Hz, 4 H), 3.93 (s, 6 H), 7.35
(dd, J ) 6.6, 3.3 Hz, 2 H), 7.94 (dd, J ) 6.6, 3.3 Hz, 2 H), 8.65
(s, 2 H), 8.88 (s, 2 H), 8.95 (s, 2 H); 13C NMR (CDCl3, δ) 14.0,
23.3, 30.1, 33.3, 52.3, 125.5, 125.7, 126.5, 127.0, 128.4, 129.0,
129.6, 129.9, 130.6, 131.9, 138.0, 169.6. HRMS calcd for
C34H34O4: 506.2457. Found: 506.2465.
Preparation of 2,3-Bis(hydroxymethyl)-9,10-dihydroanthracene
(4g) from 3e Using a Rhodium Catalyst. K2CO3 (13.3 g, 96 mmol)
was added to 1,2-bis(3-trimethylsilyl-2-propynyl)benzene 3e (7.17
g, 24 mmol) in 300 mL of degassed MeOH/ethyl ether (1/1) solvent.
The reaction mixture was vigorously stirred for 3 h at room
temperature. Then 50 mL of water was introduced and kept stirring
for another 10 min. Then the reaction mixture was extracted by
ether. The organic phase was washed with water and brine and
dried over Na2SO4. The solvent was removed by evaporation below
40 °C to afford a yellow liquid of the desilylated diyne. The residue
was added with BHT (ca. 10 mg). In another flask, 2-butyne-1,4-
diol (8.26 g, 95.9 mmol) and RhCl(PPh3)3 (444 mg, 0.48 mmol)
were dissolved into 250 mL of degassed ethanol and slowly heated
to reflux. To the solution was added the desilylated diyne dropwise
within 5 h. Then the reaction mixture was refluxed for 1 h. After
removal of the solvent, 50 mL of cold ether was added to it. The
mixture was filtered, and the resulting solid was washed with 200
mL of water to afford deep colored powder of the crude product
4g (2.27 g, 44% yield).
1
10: H NMR (CDCl3, δ) 0.24 (s, 18 H), 3.65 (s, 4 H), 3.92 (s,
4 H), 7.17-7.24 (m, 2 H), 7.26-7.31 (m, 2 H), 7.36 (s, 2 H); 13
C
NMR (CDCl3, δ) 0.1, 23.6, 35.6, 87.1, 103.9, 126.0, 127.4, 127.9,
131.8, 135.3, 136.4. HRMS calcd for C26H32Si2: 400.2043.
Found: 400.2037.
Preparation of 2,3-Bis(bromomethyl)-5,7,12,14-tetrahydro-
pentacene (12c) from 11a. Diester 11a (542 mg, 1.0 mmol) was
added to 10 mL of a diethyl ether solution of LiAlH4 (83.6 mg,
2.2 mmol) at 0 °C. After stirring for 3 h at room temperature,
hydrolysis with water and 2 N H2SO4 was performed carefully.
The mixture was extracted with diethyl ether. The extract was
washed with brine and dried over Na2SO4, and then the solvent
was removed. Phosphorus tribromide (0.28 mL, 3.0 mmol) was
added dropwise to the residue in 10 mL of CHCl3 at 0 °C. After
stirring for 1 h at room temperature, the mixture was treated with
water at 0 °C then extracted with CHCl3. The extract was washed
with brine and dried over Na2SO4. After chromatography on silica
gel (hexane:ethyl acetate ) 20:1 as eluent), 429 mg of title
compound 12c was obtained as yellow crystals in 92% isolated
yield.
4g: HRMS calcd for C16H16O2: 240.1150. Found: 240.1145.
Preparation of 2,3-Bis(iodomethyl)-9,10-dihydroanthracene
(4h) from 4g. 2,3-Bis(hydroxymethyl)-9,10-dihydroanthracene (4g,
2.27 g, 9.45 mmol) was put in 160 mL of anhydrous acetonitrile.
Then NaI (8.45 g, 56.4 mmol) and chlorotrimethylsilane (7.12 mL,
56.1 mmol) were introduced.16 After usual workup, the title
compound 4h was obtained (3.04 g, 70% yield).
1
12c: H NMR (CDCl3, δ) 3.79 (s, 4 H), 3.81 (s, 4 H), 4.56 (s,
4 H), 7.04-7.21 (m, 8 H); 13C NMR (CDCl3, δ) 30.3, 35.3, 35.8,
126.0, 126.4, 127.4, 130.1, 133.5, 134.2, 134.8, 136.7, 138.5. HRMS
calcd for C24H20Br2: 465.9931. Found: 465.9934.
Preparation of 2,3-Bis(iodomethyl)-9,10-dihydroanthracene
(4h) from 4f. Dihydroanthracene 4f (364 mg, 1.0 mmol) in 25 mL
of acetone was refluxed with NaI (900 mg, 6.0 mmol) for 3 h.
After removing the solvent, the reaction mixture was treated with
Na2S2O3 and extracted with CHCl3. The extract was washed with
brine and then dried over Na2SO4. After evaporation of the solvent,
414 mg of title compound 4h was obtained as yellow crystals in
90% isolated yield.
Preparation of 4,15-Bis(trimethylsilyl)-1,3,5,7,12,14-hexahy-
dro-2-oxacyclopenta[b]pentacene (12d) from 11a. LiAlH4 (114
mg, 3.0 mmol) was mixed with AlCl3 (1.20 g, 9.0 mmol) at 0 °C
for 0.5 h. Diester 11a (542 mg, 1.0 mmol) was added to the mixture.
After stirring for 3 h at room temperature, hydrolysis with water
and 2 N H2SO4 was performed carefully at 0 °C. The mixture was
extracted with ethyl acetate. The extract was washed with NaHCO3
and brine then dried over Na2SO4. After column chromatography
4h: 1H NMR (CDCl3, δ) 3.87 (s, 4 H), 4.58 (s, 4 H), 7.18-7.28
(m, 6 H); 13C NMR (CDCl3, δ) 2.2, 35.7, 126.3, 127.4, 129.7, 135.1,
135.9, 137.9. HRMS calcd for C16H14I2: 459.9185. Found: 459.9182.
J. Org. Chem, Vol. 71, No. 21, 2006 7975

Takahashi et al.
on silica gel (AcOEt:hexane ) 1:10 as eluent), 332 mg of title
compound 12d was obtained as colorless crystals in 71% isolated
yield.
Preparation of 2,3-Bis(ethoxycarbonyl)pentacene (9g) from
12b. A mixture of a mesitylene (2 mL) solution of tetrahydropen-
tacene diethyl ester 12b (426 mg, 1.0 mmol) and 2,3-dichloro-5,6-
dicyanobenzoquinone (454 mg, 2.0 mmol) was heated for 3 h at
150 °C. After addition of degassed MeOH (40 mL), a blue
precipitate was observed. Filtration under nitrogen gave 338 mg
of the title compound 9g as blue crystals. Isolated yield was 80%.
9g: 1H NMR (CDCl3, 323 K, δ) 1.43 (t, J ) 7.2 Hz, 6 H), 4.43
(q, J ) 7.2 Hz, 4 H), 7.35-7.38 (m, 2 H), 7.94-7.98 (m, 2 H),
8.36 (s, 2 H), 8.70 (s, 2 H), 8.74 (s, 2 H), 9.00 (s, 2 H); 13C NMR
(CDCl3, δ) 14.3, 61.5, 125.7, 126.6, 127.4, 127.9, 128.5, 128.8,
130.0, 130.78, 130.80, 131.9, 132.2, 167.6. HRMS calcd for
C28H22O4: 422.1518. Found: 422.1514. Anal. Calcd for
C28H22O4: C, 79.60; H, 5.25. Found: C, 79.97; H, 4.96.
Preparation of 2,3-Bis(bromomethyl)pentacene (9h) from 12c.
A degassed mesitylene solution (2 mL) of 2,3-bis(bromomethyl)-
5,7,12,14-tetrahydropentacene (466 mg, 1.0 mmol) and 2,3-dichloro-
5,6-dicyanobenzoquinone (454 mg, 2.0 mmol) was heated at 120
°C for 3 h. After addition of degassed MeOH (40 mL), a formed
precipitate was collected by filtration under nitrogen followed by
drying in vacuo to afford the title compound as blue powder (407
mg, isolated yield 88%).
9h: 1H NMR (o-dichlorobenzene-d4, 393 K, δ) 5.02 (s, 4H), 7.97
(s, 2H), 7.97-8.02 (m, 2H), 8.59 (s, 2H), 8.70 (s, 2H), 8.98 (s,
2H); a multiplet (2H) was overlapped with the solvent peaks.
Thermal stability of the compound was relatively low, and
decomposition was observed during the measurement of 1H NMR
spectrum at 393 K. HRMS calcd for C24H16Br2: 461.9618. Found:
461.9623. Anal. Calcd for C24H16Br2: C, 62.10; H, 3.47. Found:
C, 62.42; H, 3.59.
Preparation of 2,3-Bis(iodomethyl)naphthalene (13). To a
suspension of LiAlH4 (1.52 g, 40.0 mmol) in THF (40 mL) was
added naphthalene 2,3-dicarboxylic anhydride (3.96 g, 20.0 mmol)
at 0 °C and stirred at room temperature for 1 h. The mixture was
carefully quenched with water and 3 N HCl solution and extracted
with CHCl3. The organic phase was washed with water, saturated
NaHCO3 solution, and brine and dried over Na2SO4. Removal of
the solvent in vacuo provided the corresponding diol as a colorless
solid (3.45 g, 92% yield). The solid was added with NaI (11.0 g,
73.4 mmol) and dissolved in 200 mL of acetonitrile. The mixture
was added with chlorotrimethylsilane (9.3 mL, 73 mmol) and stirred
at 70 °C for 1 h. After cooling to room temperature, the mixture
was quenched with water and extracted with CHCl3 three times.
The combined organic phase was washed with brine and dried over
MgSO4. After removal of the solvent in vacuo, the residue was
washed with 100 mL of MeOH and dried in vacuo to afford the
pure title compound 13 (5.27 g, 70% yield). The spectral data were
identical to the literature ones.25
12d: 1H NMR (CDCl3, δ) 0.45 (s, 18 H), 3.92 (s, 4 H), 3.97 (s,
4 H), 5.09 (s, 4 H), 7.19-7.27 (m, 6 H); 13C NMR (CDCl3, δ) 2.1,
35.9, 37.8, 74.4, 125.2, 126.0, 127.3, 130.9, 134.5, 136.0, 136.8,
141.5, 143.3. HRMS calcd for C30H36OSi2: 468.2305. Found:
468.2304.
Preparation of 1,3,5,7,12,14-Hexahydro-2-oxacyclopenta[b]-
pentacene (12e) from 12d. Ether (12d, 468 mg, 1.0 mmol) was
reacted with trifluoroacetic acid (0.37 mL, 5.0 mmol) in CHCl3 (5
mL) at 50 °C for 3 h. After evaporation of the solvent, 262 mg of
the title compound 12e was obtained as colorless crystals in 81%
isolated yield.
1
12e: H NMR (CDCl3, δ) 3.94 (s, 8 H), 5.10 (s, 4 H), 7.17-
7.30 (m, 8 H); 13C NMR (CDCl3, δ) 35.8, 36.1, 73.4, 119.8, 126.0,
126.2, 127.4, 134.45, 134.51, 136.3, 136.8, 137.0. HRMS calcd
for C24H20O: 324.1514. Found: 324.1513.
Preparation of 1,3-Dihydro-2-oxacyclopenta[b]pentacene (9i)
from 12e. A mixture of mesitylene (2 mL) solution of ether 12e
(324 mg, 1.0 mmol) and 2,3-dichloro-5,6-dicyanobenzoquinone
(454 mg, 2.0 mmol) was heated for 3 h at 120 °C. After addition
of degassed MeOH (40 mL), a precipitate was formed. After
filtration, 304 mg of the title compound 9i was obtained as blue
crystals in 95% isolated yield.
1
9i: H NMR (nitrobenzene-d5, 423 K, δ) 5.15 (s, 4H), 7.30-
7.33 (m, 2H), 7.71 (s, 2H), 7.91-7.94 (m, 2H), 8.60 (s, 2H), 8.62
(s, 2H), 8.92 (s, 2H). HRMS calcd for C24H16O: 320.1201.
Found: 320.1199.
Preparation of 2,3-Bis(methoxycarbonyl)-5,7,12,14-tetrahy-
dropentacene (12a) from 11a. 1,4-Bis(trimethylsilyl)-5,7,12,14-
tetrahydropentacene-2,3-dicarboxylic acid dimethyl ester (11a, 542
mg, 1.0 mmol) was mixed with NaI (600 mg, 4.0 mmol) and
chlorotrimethylsilane (0.51 mL, 4.0 mmol) in acetonitrile at room
temperature. After 0.5 h, water (72 µL, 4.0 mmol) was added, and
then the mixture was heated to 70 °C for 0.5 h. The reaction was
quenched by aqueous Na2S2O3 at 0 °C and extracted with CHCl3
(15 mL, three times). The combined extract was washed with brine
and then dried over Na2SO4. Column chromatography on silica gel
(AcOEt:hexane ) 1:5 as eluent) afforded 247 mg of the title
compound 12a as colorless crystals in 62% isolated yield.
1
12a: H NMR (CDCl3, δ) 3.93 (s, 4 H), 3.94 (s, 4 H), 3.96 (s,
6 H), 7.19 (s, 2 H), 7.22-7.25 (m, 2 H), 7.28-7.35 (m, 2 H), 7.66
(s, 2 H); 13C NMR (CDCl3, δ) 35.3, 35.7, 52.5, 126.0, 126.3, 127.3,
128.0, 129.7, 132.7, 134.9, 136.6, 140.3, 168.1. HRMS calcd for
C26H22O4: 398.1518. Found: 398.1518.
Preparation of 2,3-Bis(ethoxycarbonyl)-5,7,12,14-tetrahydro-
pentacene (12b) from 11b. The compound 12b was prepared in
76% isolated yield from 11b by the same way as described for
dimethyl ester 12a.
Preparation of 1,4-Bis(trimethylsilyl)-2,3-bis(methoxycarbo-
nyl)-5,12-dihydronaphthacene (15a) from 14. To a solution of
Cp2ZrCl2 (365 mg, 1.25 mmol) in 5 mL of THF was added n-BuLi
(1.56 M hexane solution, 1.60 mL, 2.50 mmol) at -78 °C, and the
mixture was stirred for 10 min. The solution was warmed to -40
°C for 30 min and then re-cooled to -78 °C. After 10 min, to the
solution was added diyne 14 (348 mg, 1.0 mmol), and it warmed
to room temperature by removal of the cooling bath. After stirring
for 3 h, CuCl (297 mg, 3.0 mmol) and DMAD (0.48 mL, 3.9 mmol)
were added to the mixture at 0 °C. After stirring for 6 h at room
temperature, the mixture was hydrolyzed with 3 N HCl and
extracted with ethyl acetate. The extract was washed with NaHCO3
and brine and dried over Na2SO4. Column chromatography (silica
gel, hexane:ethyl acetate ) 10:1 as eluent) gave 215 mg of the
title compound 15a as colorless crystals in 44% isolated yield.
15a: 1H NMR (CDCl3, δ) 0.45 (s, 18 H), 3.81 (s, 6 H), 4.18 (s,
1
12b: H NMR (CDCl3, δ) 1.44 (t, J ) 7.2 Hz, 6 H), 3.85 (s, 4
H), 3.91 (s, 4 H), 4.45 (q, J ) 14.1, 7.2 Hz, 4 H), 7.11 (s, 2 H),
7.22-7.25 (m, 2 H), 7.31-7.34 (m, 2 H), 7.65 (s, 2 H); 13C NMR
(CDCl3, δ) 14.0, 35.2, 35.6, 61.4, 125.9, 126.2, 127.2, 127.8, 129.9,
132.6, 134.6, 136.5, 140.1, 167.7. HRMS calcd for C28H26O4:
426.1831. Found: 426.1834.
Preparation of 2,3-Bis(methoxycarbonyl)pentacene (9f) from
12a. A mixture of mesitylene (2 mL) solution of tetrahydropenta-
cene dimethyl ester 12a (398 mg, 1.0 mmol) and 2,3-dichloro-5,6-
dicyanobenzoquinone (454 mg, 2.0 mmol) was heated for 3 h at
150 °C. After addition of degassed MeOH (40 mL), a blue
precipitate was observed. After filtration under nitrogen, 342 mg
of the title compound 9f was obtained as blue crystals. Isolated
yield was 87%.
1
9f: H NMR (DMSO-d6, 373 K, δ) 3.92 (s, 6 H), 7.42-7.45
4 H), 7.42-7.45 (m, 2 H), 7.73 (s, 2 H), 7.79-7.82 (m, 2 H); 13
C
(m, 2 H), 8.05-8.08 (m, 2 H), 8.47 (s, 2 H), 8.90 (s, 2 H), 9.04 (s,
2 H), 9.21 (s, 2 H). HRMS calcd for C26H18O4: 394.1206. Found:
394.1205. Anal. Calcd for C26H18O4: C, 79.17; H, 4.60. Found:
C, 78.82; H, 4.65.
NMR (CDCl3, δ) 1.8, 38.6, 52.3, 124.3, 125.5, 127.3, 132.5, 135.5,
(25) Taillemite, S.; Fichou, D. Eur. J. Org. Chem. 2004, 4981.
7976 J. Org. Chem., Vol. 71, No. 21, 2006

Homologation of Pentacenes and Naphthacenes
135.7, 136.0, 145.7, 170.5. HRMS calcd for C28H34O4Si2: 490.1996.
Found: 490.1989.
as eluent) gave 375 mg of the title compound 15b as yellow crystals
in 90% isolated yield.
1
15b: H NMR (CDCl3, δ) 4.07 (s, 4 H), 4.68 (s, 4 H), 7.35 (s,
Preparation of 1,4-Bis(trimethylsilyl)-2,3-bis(methoxycarbo-
nyl)naphthacene (16a) from 15a. 2,3-Dichloro-5,6-dicyanoben-
zoquinone (250 mg, 1.1 mmol) was added to a toluene solution of
15a (490 mg, 1.0 mmol), and then the mixture was refluxed for 3
h. After filtration, the mixture was evaporated in vacuo. Crystal-
lization from CHCl3/MeOH afforded 307 mg of the title compound
16a as orange crystals. NMR yield was 97%. Isolated yield was
63%.
2 H), 7.41-7.44 (m, 2 H), 7.75 (s, 2 H), 7.77-7.80 (m, 2 H); 13
C
NMR (CDCl3, δ) 30.2, 36.4, 125.4, 125.5, 127.2, 130.0, 132.3,
134.4, 134.6, 138.7. HRMS calcd for C20H16Br2: 413.9618.
Found: 413.9627.
Preparation of 2,3-Bis(bromomethyl)naphthacene (16b) from
15b. A mixture of a toluene solution (10 mL) of 2,3-dichloro-5,6-
dicyanobenzoquinone (250 mg, 1.1 mmol) and 2,3-bis(bromom-
ethyl)-5,12-dihydronaphthacene (15b, 414 mg, 0.99 mmol) was
refluxed for 3 h. After filtration, the solvent was evaporated in
vacuo. Then degassed MeOH was added, and 280 mg of the title
compound 16b precipitated as orange crystals in yield 68%.
1
16a: H NMR (CDCl3, δ) 0.59 (s, 18 H), 3.91 (s, 6 H), 7.43-
7.46 (m, 2 H), 8.01-8.04 (m, 2 H), 8.66 (s, 2 H), 9.05 (s, 2 H);
13C NMR (CDCl3, δ) 2.2, 52.5, 125.7, 126.4, 128.3, 129.3, 129.6,
132.1, 132.7, 135.6, 139.4, 170.6. HRMS calcd for C28H32O4Si2:
488.1839. Found: 488.1845.
1
16b: H NMR (CDCl3, 323 K, δ) 4.94 (s, 4 H), 7.41-7.44 (m,
2 H), 7.99-8.02 (m, 2 H), 8.04 (s, 2 H), 8.62 (s, 2 H), 8.66 (s, 2
H); 13C NMR (CDCl3, 323 K, δ) 31.7, 125.7, 126.7, 127.0, 128.4,
130.8, 130.9, 131.5, 132.2, 133.0. HRMS calcd for C20H14Br2:
411.9461. Found: 411.9463.
Preparation of 2,3-Bis(bromomethyl)-5,12-dihydronaph-
thacene (15b) from 15a. Diester 15a (490 mg, 1.0 mmol) was
added to an anhydrous Et2O solution (10 mL) of LiAlH4 (83.6 mg,
2.2 mmol) at 0 °C. After stirring for 3 h at room temperature,
hydrolysis with water and 2 N H2SO4 was performed carefully.
The mixture was extracted with diethyl ether. The extract was
washed with brine and dried over Na2SO4, and then the solvent
was removed. Phosphorus tribromide (0.28 mL, 3.0 mmol) was
added dropwise to the residue in 10 mL of CHCl3. After stirring
for 1 h, the mixture was treated with water and extracted with
CHCl3. The extract was washed with brine and dried over
Na2SO4. Chromatography on silica gel (hexane:ethyl acetate ) 20:1
Supporting Information Available: Spectral data of com-
pounds 3c, 4c,d, 5a,c-e, 6a,c,d, 7a,c,d, 8a,c-e, 9a,c,d, 11a,b, and
14. NMR charts for all new compounds. UV-vis absorption spectra
of pentacenes 9a-d,g (in solution) and 9f,h,i (in solid). Crystal-
lographic data for 9a and 9b. This material is available free of
charge via the Internet at http://pubs.acs.org.
JO060923Y
J. Org. Chem, Vol. 71, No. 21, 2006 7977