Rhodium-catalyzed hydroarylation of alkynes with arylboronic acids: 1,4-shift of rhodium from 2-aryl-1-alkenylrhodium to 2-alkenylarylrhodium intermediate [12]

Full text of DOI:10.1021/ja0165234

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
9918
J. Am. Chem. Soc. 2001, 123, 9918-9919
Scheme 1
Rhodium-Catalyzed Hydroarylation of Alkynes with
Arylboronic Acids: 1,4-Shift of Rhodium from
2-Aryl-1-alkenylrhodium to 2-Alkenylarylrhodium
Intermediate
Tamio Hayashi,* Kazuya Inoue, Nobukazu Taniguchi, and
Masamichi Ogasawara
Department of Chemistry
Graduate School of Science, Kyoto UniVersity
Sakyo, Kyoto 606-8502, Japan
Table 1. Rhodium-Catalyzed Hydroarylation of Alkynes 1 with
Arylboronic Acid 2a
ReceiVed June 29, 2001
Since Miyaura reported the addition of aryl- and alkenylboronic
acids to R,â-unsaturated ketones in an aqueous solvent under
catalysis by a rhodium-phosphine complex in 1997,1 this
rhodium-catalyzed reaction has been successfully extended to
catalytic asymmetric 1,4-addition by use of binap as a chiral
ligand.2-5 Recently, it has been also reported that the reaction of
arylboronic acids takes place with norbornene giving a multiple
alkylation product6 and with terminal olefins such as styrenes and
vinylpyridines.7 Here we report, as another example of the
rhodium-catalyzed reaction of organoboronic acids, the hydroary-
lation of alkynes which proceeds with high syn-selectivity and
whose catalytic cycle involves an interesting 1,4-shift of rhodium
from an alkenyl carbon to an aryl carbon.
The reaction of 4-octyne (1a) with phenylboronic acid (2m)
was examined under several reaction conditions (Scheme 1). It
was found that hydrophenylation of the alkyne takes place
smoothly in an aqueous solvent in the presence of a bisphos-
phine-rhodium catalyst. Thus, a mixture of 1a, 2m (1.2 equiv
to 1a), and 3 mol % of a rhodium catalyst generated from Rh-
(acac)(C2H4)2 and dppb8 in dioxane/water (10/1) was heated at
100 °C for 3 h. Evaporation of the solvent followed by silica gel
chromatography (hexane) gave 87% yield of (E)-4-phenyl-4-
octene9 (4am), whose isomeric purity determined by NMR
analyses is over 97% (entry 1 in Table 1). The formation of the
E isomer indicates that hydrogen and phenyl add to the triple
bond in a syn fashion. The use of an excess of boronic acid 2m
slightly increased the yield of 4am, the yield being 93 and 95%
with 2.0 and 5.0 equiv of 2m, respectively (entries 2 and 3). Some
other chelating bisphosphine ligands, dppf,8 dppe,8 and binap,8
gave essentially the same high chemical yield as dppb, while the
ArB(OH)2 2 or
(ArBO)3 3
product 4
entry
alkyne 1
ligand
yield (%)b
1c
2d
3
4
5
6
7
8
9
10
11
12e
13
14
15
16
17
18
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1b
1c
1d
1e
1f
2m
2m
2m
2m
2m
2m
2m
3m
2n
2o
3p
3p
2m
2n
dppb
dppb
dppb
dppf
dppe
binap
PPh3
dppb
dppb
dppb
dppb
dppb
dppb
dppb
dppb
dppf
dppf
dppf
4am
4am
4am
4am
4am
4am
4am
4am
4an
4ao
4ap
4ap
4bm
4cn
87
93
95
91
94
95
48
90
93
92
31
97
89
96
96f
81
70
87
2m
2m
2m
2m
4dm
4em
4fm
4gm
1g
a The reaction was carried out with 1 (0.40 mmol) and boronic acid
2 (2.0 mmol) or arylboroxine 3 (0.67 mmol) in 1.0 mL of dioxane and
0.1 mL of water in the presence of 3 mol % of the catalyst generated
from Rh(acac)(C2H4)2 and a phosphine ligand (Rh/P ) 1/2.2) at 100
°C for 3 h, unless otherwise noted. b Isolated yield by silica gel
chromatography. c The amount of phenylboronic acid was 0.48 mmol.
d The amount of phenylboronic acid was 0. 80 mmol. e Reaction at 60
°C for 3 h. f A mixture of (E)-1,2-diphenylpropene (4dm) and its
regioisomer, 1,1-diphenylpropene, in a ratio of 3 to 1.
yield was much lower with triphenylphosphine (entries 4-7).
Triphenylcyclotriboroxane (3m, phenylboroxine)3e which is a
cyclic anhydride of phenylboronic acid (2m) can be used as well
as the boronic acid (entry 8). Arylboronic acids, 2n and 2o, which
have trifluoromethyl and methyl, respectively, at the 4-position
of the phenyl gave the corresponding hydroarylation products (E)-
4an and -4ao in over 90% yield (entries 9 and 10). In the reaction
with 4-methoxyphenylboronic acid (2p) or its boroxine 3p, the
yield of 4ap was low at 100 °C, because the hydrolysis giving
anisole is fast at this temperature. Lowering the reaction temper-
ature to 60 °C greatly improved the yield of 4ap (97%) (entry
12). The hydroarylation of diphenylethyne (1c) also proceeded
with syn-selectivity, giving (E)-1,2-diphenyl-1-(4-trifluorometh-
ylphenyl)ethene (4cn) (>99% E) in the reaction with 4-trifluo-
romethylphenylboronic acid (2n) (entry 14). In the reaction of
acetylenes substituted with an ester or phosphonate group, the
regio- and syn-selectivity was so high that no regio- or geometrical
isomers were detected by NMR analysis (entries 16-18). The
aryl group was introduced selectively at the â position to the
electron-withdrawing group.
(1) Sakai, M.; Hayashi, H.; Miyaura, N. Organometallics 1997, 16, 4229.
(2) For recent reviews on catalytic asymmetric 1,4-addition: (a) Tomioka,
K.; Nagaoka, Y. In ComprehensiVe Asymmetric Catalysis; Jacobsen, E. N.,
Pfaltz, A., Yamamoto, H., Eds.; Springer: Berlin, 1999; Vol. 3, Chapter 31.1.
(b) Sibi, M. P.; Manyem, S. Tetrahedron 2000, 56, 8033. (c) Krause, N.;
Hoffmann-Ro¨der, A. Synthesis 2001, 171.
(3) (a) Takaya, Y.; Ogasawara, M.; Hayashi, T.; Sakai, M.; Miyaura, N. J.
Am. Chem. Soc. 1998, 120, 5579. (b) Takaya, Y.; Ogasawara, M.; Hayashi,
T. Tetrahedron Lett. 1998, 39, 8479. (c) Takaya, Y.; Senda, T.; Kurushima,
H.; Ogasawara, M.; Hayashi, T. Tetrahedron: Asymmetry 1999, 10, 4047.
(d) Takaya, Y.; Ogasawara, M.; Hayashi, T. Tetrahedron Lett. 1999, 40, 6957.
(e) Hayashi, T.; Senda, T.; Takaya, Y.; Ogasawara, M. J. Am. Chem. Soc.
1999, 121, 11591. (f) Takaya, Y.; Ogasawara, M.; Hayashi, T. Chirality 2000,
12, 469. (g) Hayashi, T.; Senda, T.; Ogasawara, M. J. Am. Chem. Soc. 2000,
122, 10716.
(4) Sakuma, S.; Sakai, M.; Itooka, R.; Miyaura, N. J. Org. Chem. 2000,
65, 5951.
(5) Kuriyama, M.; Tomioka, K. Tetrahedron Lett. 2001, 42, 921.
(6) Oguma, K.; Miura, M.; Satoh, T.; Nomura, M. J. Am. Chem. Soc. 2000,
122, 10464.
(7) Lautens, M.; Roy, A.; Fukuoka, K.; Fagnou, K.; Mart´ın-Matute, B. J.
Am. Chem. Soc. 2001, 123, 5358.
(8) Abbreviations: dppb ) 1,4-bis(diphenylphosphino)butane, dppf ) 1,1′-
bis(diphenylphosphino)ferrocene, dppe ) 1,2-bis(diphenylphosphino)ethane,
binap ) 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl.
It is assumed that the catalytic cycle involves addition of an
arylrhodium intermediate to an alkyne in a syn fashion and
hydrolysis of the resulting alkenylrhodium bond giving the
(9) Gao, Y.; Harada, K.; Hata, T.; Urabe, H.; Sato, F. J. Org. Chem. 1995,
60, 290. The E geometry of 4am was confirmed by NOE experiments
(Supporting Information).
10.1021/ja0165234 CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/18/2001

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Communications to the Editor
J. Am. Chem. Soc., Vol. 123, No. 40, 2001 9919
Scheme 2
Scheme 4
Scheme 3
conditions where an excess of arylboronic acid is used in the
presence of a large excess of water as a solvent, the addition does
take place in the reaction of an arylboroxine with excess alkyne
in the presence of a minimum amount of water. Thus, the reaction
of phenylboroxine (3m) with 8 equiv of 3-hexyne (1b) in the
presence of one equiv (to boron) of water11 and rhodium-dppf
catalyst (3 mol %) in dioxane at 100 °C for 3 h gave 71% yield
of indene 5 together with the hydrophenylation product 4bm
(28%) and diene 6 (41%) (Scheme 4). The formation of indene
5 can be rationalized by the catalytic cycle involving addition of
2-(alkenyl)phenylrhodium species C to 3-hexyne and intramo-
lecular carborhodation in the new alkenylrhodium intermediate
D. â-Hydrogen elimination on the alkylrhodium E followed by
isomerization of the double bond gives indene 5 containing the
allyl group and a hydridorhodium species. The formation of diene
6 may suggest that the hydridorhodium comes back to the catalytic
cycle after it effects the reductive dimerization of alkyne 1b
forming 6.
The addition of an aryl group and hydrogen to alkynes has
been attained, for example, by nickel-catalyzed addition of aryl-
magnesium or -zinc reagent12,13 followed by hydrolysis, or pal-
ladium-catalyzed cross-coupling of aryl halides with alkenylmetal
reagents generated by hydroboration14 or titanium-catalyzed hy-
drozincation of alkynes.9,15 From a synthetic point of view, the
present hydroarylation of alkynes has advantages over other
methods in that it is carried out in an aqueous solvent, functional
groups such as ester are intact during the reaction, and the syn-
selectivity at the addition is very high.
hydroarylation product. In this catalytic cycle, the hydrogen on
the vinylic carbon should come from water. To confirm this
catalytic cycle, the reaction of 4-octyne (1a) with phenylboroxine
(3m) was carried out in D2O ((a) in Scheme 2). Rather surpris-
ingly, the hydrophenylation product 4am-d1, which was formed
in 87% yield, did not incorporate the deuterium (<2%) on the
vinylic carbon, and the deuterium was observed at the ortho
position (98%) of the phenyl group instead. It follows that
rhodium moved from the vinylic position of the alkenylrhodium
intermediate (B in Scheme 3) to the ortho position of the phenyl,
probably by way of a rhodium(III) intermediate formed by
oxidative addition of a C-H bond on the phenyl to rhodium(I),
and the 2-(alkenyl)phenylrhodium intermediate C undergoes the
hydrolysis with water giving the hydrophenylation product
(Scheme 3). The reaction of 1a with C6D5B(OH)2 (2m-d5) in H2O
gave the hydrophenylation product 4am-d5 where one of the
deuterium atoms on the ortho position of the pentadeuteriophenyl
moved to the vinylic position ((b) in Scheme 2). This 1,4-shift
of the deuterium also supports the rearrangement of the alkenyl-
rhodium intermediate B into the 2-(alkenyl)phenylrhodium in-
termediate C. A similar 1,4-shift of rhodium has been reported
by Miura6 in the reaction of norbornene with arylboronic acids,
where rhodium moves from alkyl sp3 carbon to aryl sp2 carbon
and the arylrhodium species further reacts with another molecule
of norbornene. In our hydroarylation of alkynes, rhodium moves
from alkenyl sp2 carbon to phenyl sp2 carbon10 before hydrolysis.
For the catalytic cycle to be completed to give a high yield of
the hydrophenylation product, the addition of the phenylrhodium
intermediate A must occur before its hydrolysis with water, and
the 2-(alkenyl)phenylrhodium intermediate C, generated by the
phenylrhodation of alkyne followed by the 1,4-rearrangement,
must undergo the hydrolysis rather than insertion of alkyne. The
high selectivity in giving the one-to-one hydroarylation products
observed here may be ascribed to the 1,4-rearrangement of
rhodium forming the 2-(alkenyl)phenylrhodium intermediate C
which is less reactive toward the alkyne insertion than phenyl-
rhodium A or alkenylrhodium intermediate B because of its steric
bulkiness.
Acknowledgment. This work was supported by “Research for the
Future” Program, the Japan Society for the Promotion of Science and a
Grant-in-Aid for Scientific Research, the Ministry of Education, Japan.
Supporting Information Available: Experimental procedures, spec-
troscopic and analytical data for the products (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
JA0165234
(11) Since arylboroxine and water is in an equilibrium with arylboronic
acid under the reaction conditions, the reaction starting from arylboronic acid
and that starting from arylboroxine and water (1 equiv to boron) should result
in the same outcome. Nevertheless, the combination of the boroxine and water
was used in this experiment, because the ratio of boron to water can be kept
more precisely. Chemically pure arylboroxines can be readily obtained by
dehydration of arylboronic acids by azeotropic removal of water from their
benzene solution, while arylboronic acids obtained by recrystallization from
water are usually contaminated with arylboroxines to some extent. For a
review: Lappert, M. F. Chem. ReV. 1956, 56, 959.
(12) For a review on the nickel-catalyzed addition: Houpis, I. N.; Lee, J.
Tetrahedron 2000, 56, 817.
(13) For a review on the organozinc reagents: Knochel, P.; Almena Perea,
J. J.; Jones, P. Tetrahedron 1998, 54, 8275.
Although the 2-(alkenyl)phenylrhodium intermediate C does
not add to another molecule of alkyne under the reaction
(14) For a review on the cross-coupling of organoboron reagents: Miyaura,
N.; Suzuki, A. Chem. ReV. 1995, 95, 2457.
(15) For a review on the organotitanium reagents: Sato, F.; Urabe, H.;
Okamoto, S. Chem. ReV. 2000, 100, 2835.
(10) A similar migration of vinylic palladium(II) to arylpalladium(II) has
been proposed in the palladium-catalyzed synthesis of 9-alkylidene-9H-
fluorenes: Tian, Q.; Larock, R. C. Org. Lett. 2000, 2, 3329.