J. Am. Chem. Soc. 2001, 123, 10407-10408
10407
Scheme 1
Palladium-Catalyzed Arylative Carbon-Carbon
Bond Cleavage of r,r-Disubstituted Arylmethanols
Yoshito Terao, Hiroyuki Wakui, Tetsuya Satoh,
Masahiro Miura,* and Masakatsu Nomura
Department of Applied Chemistry, Faculty of Engineering
Osaka UniVersity, Suita, Osaka 565-0871, Japan
ReceiVed August 22, 2001
ReVised Manuscript ReceiVed September 4, 2001
Transition metal-catalyzed organic reactions involving the
cleavage of C-C single bonds have recently attracted much
attention.1 Although the cleavage is energetically unfavorable,
various unique catalytic transformations including ring-expansion
or ring-contraction, fragmentation, and coupling with another
molecule can be realized when appropriately designed. Besides
the reactions via oxidative addition of low-valent transition metals
to a C-C bond,1,2 catalytic cycles involving â-carbon elimination
of heteroatom-coordinated species such as M-O-C-C may be
constructed. Utilizing the latter cleavage to form M-C species
and ketones (or aldehydes), Pd-catalyzed ring-opening reactions
of cyclic allylic carbonates,3 cyclobutanols,4 and cyclopropanols5
and a Ru-catalyzed fragmentation of homoallyl alcohols6 have
recently been developed. The driving force of these reactions
originates from release of ring-strain or formation of a relatively
stable π-allylmetal intermediate. In the course of our study of
Pd-catalyzed new arylative C-C bond formation reactions,7 it
has been found that certain R,R-disubstituted arylmethanols, even
acyclic ones, efficiently react with aryl bromides to give biaryls
via cleavage of the sp2-sp3 C-C bond (eq 1),4a,8,9 which is
described herein.
Scheme 2
bromobenzene (1a) (Scheme 1). When 2a (0.5 mmol) was treated
with 1a (1 mmol) in the presence of Pd(OAc)2 (0.025 mmol),
PPh3 (0.15 mmol), and Cs2CO3 (1 mmol) in refluxing o-xylene
for 3 h, mono- and diphenylated products, 5 (62%) and 6 (15%),
were produced along with o-terpheyl (4) (19%) (yields by GC
based on the amount of 2a). This suggests that in the key
alkoxypalladium intermediate, not only anticipated ortho-phen-
ylation of 2a to produce 5 and 6 but also â-carbon elimination
leading to 4 competitively occurs in a rate ratio of 8:2. By starting
with 2-phenyl-2-propanol (2b) a mixture of biphenyl (3a), 2a,
and 4-6 was obtained, showing that the reaction similarly
proceeds (Scheme 2). It was quite interesting that the reaction of
2-(2-methylphenyl)-2-propanol (2c) selectively proceeded via
â-carbon elimination to give 2-methylbiphenyl (3b) (77%) as the
single major product, 2c (20%) being recovered. The reaction of
triphenylmethanol (2d) with 1a (3 equiv) also gave mechanisti-
cally important information (eq 2).10 The product distribution
We previously reported that phenolic compounds as well as
aromatic carbonyl compounds undergo ortho-arylation on treat-
ment with aryl halides under the influence of palladium catalysts.7a,b
For example, the phenylation of 2-phenylphenol with iodobenzene
takes place regioselectively at the 2′-position. The reaction is a
unique catalytic aryl-aryl coupling via cleavage of the aromatic
C-H bond in which coordination of the phenolic oxygen to
phenylpalladium(II) species is the key. To see the applicability
of an alcohol function as the directing group in the arylation, we
examined the reaction of 2-(biphenyl-2-yl)-2-propanol (2a) with
(1) Reviews: (a) Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1999, 111,
918. (b) Murakami, M.; Ito, Y. In ActiVation of UnreactiVe Bonds and Organic
Syntheis; Murai, S., Ed.; Springer: Berlin, Germany, 1999; p 97.
(2) Recent examples: (a) Murakami, M.; Tsuruta, T.; Ito, Y. Angew. Chem.,
Int. Ed. 2000, 39, 2484. (b) Jun, C.-H.; Lee, H.; Lim, S.-G. J. Am. Chem.
Soc. 2001, 123, 751. (c) Chatani, N.; Ie, Y.; Kakiuchi, F.; Murai. S. J. Am.
Chem. Soc. 1999, 121, 8645. (d) Satoh, T.; Jones, W. D. Organometallics
2001, 20, 2916 and references therein.
(3) Harayama, H.; Kuroki, T.; Kimura, M.; Tanaka, S.; Tamaru, Y. Angew.
Chem., Int. Ed. Engl. 1997, 36, 2352.
indicates that both the processes via ortho-phenylation and
â-carbon elimination occur in the initial step as in the reactions
of 2a and 2b, and in this case, the successively ortho-phenylated
products further undergo coupling with 1a via â-carbon elimina-
(4) (a) Arylative ring-opening of cyclobutanols: Nishimura, T.; Uemura,
S. J. Am. Chem. Soc. 1999, 121, 11010. (b) Nishimura, T.; Ohe, K.; Uemura,
S. J. Org. Chem. 2001, 66, 1455. (c) Nishimura, T.; Uemura, S. J. Am. Chem.
Soc. 2000, 122, 12049. (d) Larock, R. C.; Reddy, C. K. Org. Lett. 2000, 2,
3325.
(5) (a) Park S.-B.; Cha, J. K. Org. Lett. 2000, 2, 147. (b) Okumoto, H.
Jinnai, T.; Shimizu, H.; Harada, Y.; Mishima, H.; Suzuki, A. Synlett 2000,
629.
(6) Kondo, T.; Kodoi, K.; Nishinaga, E.; Okada, T.; Morisaki, Y.;
Watanabe, Y.; Mitsudo, T. J. Am. Chem. Soc. 1998, 120, 5587.
(7) (a) Satoh, T.; Kawamura, Y.; Miura, M.; Nomura, M. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 1740. (b) Kawamura, Y.; Satoh, T.; Miura, M.;
Nomura, M. Chem. Lett. 1999, 961. (c) Terao, Y.; Kametani, Y.; Wakui, H.;
Satoh, T.; Miura, M.; Nomura, M. Tetrahedoron 2001, 57, 5967. (d) Dyker,
G.; Heiermann, J.; Miura, M.; Inoh, J.; Pivsa-Art, S.; Satoh, T.; Nomura, M.
Chem. Eur. J. 2000, 6, 1889.
(8) Pd-catalyzed Sonogashira-type reaction of aryl halides with 2-alkynyl-
propanols is known. The reaction is generally considered to involve in situ
generation of terminal alkynes, while it would proceed partly via â-carbon
elimination. (a) Huynh, C.; Linstrumelle, G. Tetrahedron 1988, 44, 6337. (b)
Chow, H.-F.; Wan, C.-W.; Low, K.-H.; Yeung, Y.-Y. J. Org. Chem. 2001,
66, 1910. (c) Choi, C.-K.; Tomita, I.; Endo, T. Chem. Lett. 1999, 1253.
(9) Ir-catalyzed fragmentation of benzopinacols: Hou, Z.; Koizumi, T.;
Fujita, A.; Yamazaki, H.; Wakatsuki, Y. J. Am. Chem. Soc. 2001, 123, 5812.
(10) The fact that the total yield of 3a and 4 is somewhat greater than
100% may be due to the participation of homo-coupling of 1a to some extent.
However, formation of homo-coupling products was not observed or negligible
(less than 2%) in the other reactions.
10.1021/ja016914i CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/27/2001