Palladium-Catalyzed Cross-Coupling of Arenediazonium Salts with Arylboronic Acids

Full text of DOI:10.1021/jo960058p

J . Org. Chem. 1997, 62, 3405-3406
3405
Sch em e 1
P a lla d iu m -Ca ta lyzed Cr oss-Cou p lin g of
Ar en ed ia zon iu m Sa lts w ith Ar ylbor on ic
Acid s
–
N2+BF4
R′
10% Pd(OAc)2
MeOH, ,1 h
+
R′
B(OH)2
Saumitra Sengupta* and Sanchita Bhattacharyya
R
R
Department of Chemistry, J adavpur University,
Calcutta 700 032, India
1
2
3
a; R = p-Cl
a; R′ = H
b; R′ = Me
b; R = o-Me
Received J anuary 9, 1996 (Revised Manuscript Received
October 23, 1996)
c; R = o-OMe
d; R = o-CO2Me
e; R = m-COMe
f; R = p-Me
In recent years, the palladium-catalyzed cross-coupling
reaction has evolved as a powerful synthetic tool for the
construction of unsymmetrical biaryls.1 The reaction,
which is vastly superior to the classical methods of biaryl
synthesis (Gomberg-Bachmann and Ullmann synthe-
sis),2 usually involves an arylmetal species (ArM) acting
upon an aryl electrophile (Ar′X) in presence of a Pd0
catalyst. Numerous versions of this reaction, featuring
various arylmetals (Arm, M ) MgX,3 ZnX,4 SnR3,5
B(OH)2,6 SiFnR3-n7), are known today among which the
aryltins5 and arylboronic acids6 have found widespread
synthetic applications. However, for all practical pur-
poses, the aryl electrophile component (Ar′X) in these
reactions has been limited to the conventional use of
halides (Br, I) and the newly emerged triflates.8 In order
to broaden the scope of the cross-coupling reaction, we
addressed this latter limitation and sought new Ar′X
components as alternatives to the above. Although
O-aryl carbamates,9a aryl sulfones,9b and aryl mesylates9c
have recently been promoted as new Ar′X components,
cross coupling of the former two are limited to selected
Grignard reagents and suffer from harsh reaction condi-
tions and poor functional group tolerence properties,
whereas aryl mesylates give good yields in their Ni-
catalyzed reactions with arylboronic acids. While pursu-
ing a general program on Pd-catalyzed reactions of
g; R = p-OMe
h; R = p-CO2Me
i; R = p-Br
arenediazonium salts,10 we reasoned that these salts
armed with an excellent nucleofuge (N2) would be a
superior alternative to all those mentioned above and
decided to explore them as aryl electrophile components
in cross-coupling reactions. Although arenediazonium
salts have been used in Heck reactions, which we have
recently extended to aqueous reaction conditions,10 their
use in cross-coupling reactions are virtually unknown
except for an isolated report with organostannanes.11 We
have now successfully engaged them in cross-coupling
reaction with arylboronic acids and in this Note, disclose
our preliminary results.
Initial screening of the reaction conditions with the
diazonium salt 1a and PhB(OH)2 (2a ) revealed that the
usual “Suzuki protocol” (DME, Pd(PPh3)4, aqueous Na2-
CO3) caused extensive decomposition of the diazonium
salt, the main culprit being triphenylphosphine. After
much experimentation, the desired cross coupling was
ultimately achieved with 10 mol % Pd(OAc)2 in refluxing
MeOH or EtOH in the absence of any added base to
produce the biaryl 3a in 80% yield (Scheme 1, Table 1).
Alcoholic solvents12 (over DME, DMF, CH3CN) are ab-
solutely essential for this reaction whereas external
bases, thought to be key components in Suzuki-couplings,
are not required and in fact, are detrimental to success.
Ligandless Pd(OAc)2,13 or 10% Pd-C14 (entry 2, Table 1)
were found to be the only effective catalysts for this
reaction.
(1) Reviews: (a) Hegedus, L. S. J . Organomet. Chem. 1993, 457,
167. (b) Kalinin, V. N. Synthesis 1992, 413. (c) Bringmann, G.; Walter,
R.; Weirich, R. Angew. Chem., Int. Ed. Engl. 1990, 29, 977. (d)
Snieckus, V. Chem. Rev. 1990, 90, 879. (e) Altenbach, H. J . Nachr.
Chem. Tech. Lab. 1988, 36, 1324.
(2) Sainsbury, M. T. Tetrahedron 1980, 36, 3327.
(3) Tamao, K.; Kumada, M. In The Chemistry of the Metal-Carbon
Bond; Hartley, F. R., Ed.; Wiley: New York, 1987; Vol 4, p 820.
(4) Reviews: (a) Negishi, E.-i. Acc. Chem. Res. 1982, 15, 340. (b)
Erdik, E. Tetrahedron 1992, 48, 9577, see especially 9599. Cf. recent
works: (c) Quesnelle, C. A.; Familoni, O. B.; Snieckus, V. Synlett 1994,
349. (d) Koch, K.; Chambers, R. J .; Biggers, M. S. Ibid. 1994, 347.
(5) Review: (a) Mitchell, T. N. Synthesis 1992, 803. Recent works:
(b) Forman, F. W.; Sucholeiki, I. J . Org. Chem. 1995, 60, 523. (c)
Segelstein, B. E.; Butler, T. W.; Chenard, B. L. J . Org. Chem. 1995,
60, 12. (d) Farina, V.; Kapadia, S.; Krishnan, B.; Wang, C.; Liebeskind,
L. S. J . Org. Chem. 1994, 59, 5905.
(6) Reviews: (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
(b) Martin, A. R.; Yang, Y. Acta Chem. Scand. 1993, 47, 221. Recent
works: (c) Anderson, J . C.; Namli, H. Synlett 1995, 765. (d) Miura,
Y.; Oka, H.; Momoki, M. Synthesis 1995, 1419. (e) Zoltewicz J . A.;
Cruskie, M. P., J r. Tetrahedron 1995, 51, 11401. (f) Beller, M.; Fischer,
H.; Herrmann, W. A.; Ofele, K.; Brossmer, C. Angew. Chem., Int. Ed.
Engl. 1995, 34, 1848. (g) Fu, J .-M.; Zhao, B. P.; Sharp, M. J .; Snieckus,
V. Can. J . Chem. 1994, 72, 227. (h) Maddaford, S. P.; Keay, B. A. J .
Org. Chem. 1994, 59, 6501. Mechanistic studies: (i) Aliprantis, A. O.;
Canary, J . W. J . Am. Chem. Soc. 1994, 116, 6985.
The synthetic efficacy of this reaction was studied with
a number of arenediazonium salts (1a -i) and the boronic
acids 2a ,b which produced the unsymmetrical biaryls
3a -k in fair to excellent yields (Table 1). While all cross-
(10) (a) Sengupta, S.; Bhattacharya, S. J . Chem. Soc., Perkin Trans.
1 1993, 1943. (b) Bhattacharya, S.; Majee, S.; Mukherjee, R.; Sen-
gupta, S. Synth. Commun. 1995, 25, 651. (c) Sengupta, S.; Bhatta-
charya, S. Tetrahedron Lett. 1995, 36, 4475. For nonaqueous varia-
tions, see (d) Beller, M.; Fischer, H.; Kuhlein, K. Tetrahedron Lett.
1994, 35, 8773. (e) Kikukawa, K.; Nagira, K.; Wada, F.; Matsuda, T.
Tetrahedron 1981, 37, 31.
(11) Kikukawa, K.; Kono, K.; Wada, F.; Matsuda, T. J . Org. Chem.
1983, 48, 1333.
(12) For Suzuki coupling in alcoholic solvents, see (a) Kamikawar,
K.; Watanabe, T.; Uemura, M. J . Org. Chem. 1996, 61, 1375. (b)
Campi, E. M.; J ackson, W. R.; Marcuccio, S. H.; Naesland, C. G. M. J .
Chem. Soc., Chem. Commun. 1994, 2395. (c) Smith, G. B.; Dezeny, G.
C.; Hughes, D. L.; King, A. O.; Verhoeven, T. R. J . Org. Chem. 1994,
59, 8151. For aqueous Stille coupling, see (d) Roshchin, A. I.; Bumagin,
N. A.; Beletskaya, I. P. Tetrahedron Lett. 1995, 36, 125. (e) Rai, R.;
Aubrecht, K. B.; Collum, D. B. Tetrahedron Lett. 1995, 36, 3111.
(13) (a) Wallow, T. I.; Novak, B. M. J . Org. Chem. 1994, 59, 5034.
(b) Beletskaya, I. P. Bull. Acad. Sci. USSR, Div. Chem. Sci. (Engl.
Transl.) 1990, 39, 2013.
(7) Review: (a) Hatanaka, Y.; Hiyama, T. Synlett 1991, 845. Recent
work: (b) Hatanaka, Y.; Goda, K.-i.; Okahara, Y.; Hiyama, T. Tetra-
hedron 1994, 50, 8301.
(8) Ritter, K. Synthesis 1993, 735.
(9) (a) Sengupta, S.; Leite, M.; Raslan, D. S.; Quesnelle, C.; Snieckus,
V. J . Org. Chem. 1992, 57, 4066. (b) Clayden, J .; Cooney, J . J . A.;
J ulia, M. J . Chem. Soc., Perkin Trans. 1 1995, 7. (c) Percec, V.; Bae,
J .-Y.; Hill, D. H. J . Org. Chem. 1995, 60, 6895.
(14) (a) Marck, G.; Villiger, A.; Buchecker, R. Tetrahedron Lett. 1994,
35, 3277. (b) Beller, M.; Kuhlein, K. Synlett 1995, 441.
S0022-3263(96)00058-8 CCC: $14.00 © 1997 American Chemical Society

3406 J . Org. Chem., Vol. 62, No. 10, 1997
Notes
Ta ble 1. Cr oss-Cou p lin g of Ar en ed ia zon iu m Sa lts 1 w ith
Ar ylbor on ic Acid s 2 (Sch em e 1)
Since the present cross-coupling reactions do not
require an external base which, on the contrary, is
essential for Suzuki couplings with aryl bromides, the
(p-bromophenyl)diazonium salts (1i) can be selectively
cross-coupled at the diazonium end to give p-bromobi-
phenyl (3i) in high yield (entry 10). This opens up new
synthetic options toward differential cross-coupling reac-
tions employing two different arylboronic acids. As
expected of boronic acid couplings, the reaction shows
good functional group tolerance properties and successful
cross-couplings to sterically hindered ortho,ortho′-biaryls
3j,k can also be achieved, albeit in moderate yields
(entries 11 and 12). Nitro-substituted diazonium salts,
however, failed to participate in this reaction probably
due to their relatively high redox-potentials and a prefer-
ence for homolytic dediazonization pathways.10a
1
2
biaryl 3
yield,a
80
%
Ph
1
1a
2a
3a
Cl
2
3
1a
1b
2a
2a
3a
73b
90
Ph
3b
3c
3d
Me
Ph
4
5
1c
1d
2a
2a
75
OMe
70c
Ph
CO2Me
Ph
6
1e
2a
3e
65
In summary, we have introduced a new cross-coupling
reaction using arenediazonium salts as the aryl electro-
phile component. The reaction holds several advantages
over the existing cross-coupling repertoire: it is opera-
tionally simple, uses alcoholic reaction conditions, and
starts with anilines which in many cases are more readily
available than the halides and phenols. These, together
with the option for selective cross-coupling in bromo-
substituted arenediazonium salts, promises wide applica-
tion of this new regime in unsymmetrical biaryl synthe-
sis.16
COMe
7
8
9
1f
1g
1h
2a
2a
2a
Ph
3f
3g
3h
86
82
75
Me
Ph
MeO
MeO2C
Ph
10
11
1i
2a
2b
Ph
3i
3j
80
40
Br
Exp er im en ta l Section
Me
1c
Gen er a l P r oced u r e for Cr oss-Cou p lin g of Ar en ed ia zo-
n iu m Sa lts w ith Ar ylbor on ic Acid s. A solution of arylboronic
acid (2.0 mmol), arenediazonium salt (2.2 mmol), and Pd(OAc)2
(0.2 mmol) in methanol (5 mL) was heated under reflux for 1 h.
After being cooled to room temperature, it was filtered through
Celite, and the filtrate was diluted with water and extracted
with ether (3 × 10 mL). Removal of ether followed by silica gel
chromatography (0-10% EtOAc in petroleum ether) gave the
respective biaryls 3a -c,e-j. For 3d and 3k , the same procedure
was followed except that the diazonium salt 1d was added last
to the mixture of arylboronic acid and Pd(OAc)2 in MeOH and
stirred at 25 °C for 8 h.
OMe
12
1d
2b
Me
3k
45c
CO2Me
a
b
Isolated yield. 10% Pd-C used as catalyst. c At 25 °C.
couplings studied are extremely rapid (1 h) in refluxing
methanol, some can be equally facile at room temperature
especially when highly activated diazonium salts are
used (entries 5 and 12). Cross-couplings with PhB(OH)2
are not affected by ortho substituents on the diazonium
component. Thus, yields in the para series (entries 7-9)
are only a shade better than the corresponding ortho
isomers (entries 3-5). Only in the cases of ortho,ortho′-
disubstituted biaryls (3j,k ), do steric effects come into
play causing lowering of yields (entries 11, 12). In sharp
contrast to Suzuki couplings with aryl halides,6a the
present reaction shows only marginal electronic effects.
For a given substitution pattern, diazonium salts having
strongly electron-withdrawing substituents (e.g., CO2Me)
produced slightly lower yields than those having electron-
donating groups (e.g. Me or OMe) (cf. entries 3-5 and
7-9). These results suggest that oxidative addition of
PdLn to the diazonium salts may not be the rate-limiting
step for these reactions.15
Ack n ow led gm en t. Financial support from DST
(SYS program) (SR/OY/C-17/92) is gratefully acknowl-
edged. The authors are thankful to a referee for helpful
suggestions.
Su p p or tin g In for m a tion Ava ila ble: General experimen-
tal procedure and spectral data for 3a -k (2 pages). This
material is contained in libraries on microfiche, immediately
follows this article in the microfilm version of the journal, and
can be ordered from the ACS; see any current masthead page
for ordering information.
J O960058P
(15) Oxidative addition of PdLn to aryl iodides has been proposed
as the rate-limiting step in Suzuki couplings: see ref 12c.
(16) While this manuscript was under the reviewing process, a
similar work appeared in the literature: Darses, S.; J effery, T.; Genet,
J .-P.; Brayer, J .-L.; Demoute, J .-P. Tetrahedron Lett. 1996, 37, 3857.