1
382 Bull. Chem. Soc. Jpn., 75, No. 6 (2002)
© 2002 The Chemical Society of Japan
Table 2. Fast Palladium-Catalyzed Cross-Coupling Reaction
of NaBPh with Aroyl and Cinnamoyl Chlorides under
Microwave Irradiation
4
a),b)
c)
Entry
Product
COC
Yield /%
1
2
3
4
5
6
7
8
9
C
6
H
5
6
H
5
(3a)
(3b)
(3c)
(3d)
(3e)
(3f)
(3g)
(3h)
(3i)
97
90
95
92
96
91
90
92
92
90
2-ClC
4-ClC
6
H
H
4
COC
COC
6
H
H
5
6
4
6
5
3-BrC
4-BrC
6
H
H
4
COC
COC
6
H
H
5
6
4
6
5
3-NO
4-NO
2
C
6
H
H
4
COC
COC
6
H
H
5
5
2
C
6
4
6
4-CH
4-CH
3
3
C
OC
6
H
4
COC
6
H
5
6
H
4
COC
6
H
5
1
0
C
6
H
5
CHwCHCOC
6
H
5
(3j)
Scheme 2.
a) The reactions were carried out in the presence of KF/
Al using [PdCl (PPh ] as a catalyst in acetone at 525
W for 5 min under nitrogen. b) Mole ratio: NaBPh :aroyl
= 1:4.1:0.03:2.1. c)
2
O
3
2
3 2
)
4
time.
chloride:[PdCl
2 3 2 2 3
(PPh ) ]:KF/Al O
Experimental
Isolated yield.
General Procedure for the Prepartion of Compounds 3a:
A mixture of sodium tetraphenylborate (1 mmol ), benzoyl
diation and conventional heating was compared, and the re-
sults showed that microwave irradiation accelerated the reac-
tion by 156 times over conventinal heating, thus quantifying
the microwave heating effect.
In order to define the scope and limitation of this method for
unsymmetrical ketone synthesis, the reactions of various acyl
chlorides and sodium tetraphenylborate in the presence of KF/
2 3 2 2 3
chloride (4.1 mmol ), [PdCl (PPh ) ] (0.03 mmol), KF/Al O
(
2.1 mmol) and acetone (10 mL) was irradiated at 525 W for 5
min by microwaves under a nitrogen atmosphere. The precipi-
tate was filtrated and the filtrate was poured into a saturated
aqueous sodium chloride (50 mL) and extracted with diethyl
ether (3×20 mL), The extracts were washed with water (3×20
mL) and then dried over magnesium sulfate. The solution was
concentrated to yield a crude product, which was purified by
column chromatography on silica gel (eluent: petroleum/ethyl
acetate = 15:1) to afford benzophenone 3a in 97% yield.
2 3 2 3 2
Al O catalyzed by [PdCl (PPh ) ] were examined, as shown
in Table 2.
The results in Table 2 show that the reaction of aromatic and
unsaturated acyl chlorides give the corresponding symmetrical
and unsymmetrical ketones in over 90% yield (entry 1–10). In
this reaction, the four phenyl groups of sodium tetraphenylbo-
rate are available for transfer. The reaction is not sensitive to
the structure of acyl chlorides. Various substituents on the
phenyl ring, either electron-withdrawing or electron-donating,
such as 4-methyl, 4-methoxy, 2- or 4-chloro, 3- or 4-bromo,
and 3- or 4-nitro, could be tolerated with little effect on the
yields (entry 2–9). Unsaturated acid chloride, such as cin-
namoyl chloride, reacted similarly and provided the corre-
sponding unsymmetrical ketone in excellent isolated yield (en-
try 10).
We thank the National Natural Science Foundation of China
and the Northwest Normal University Science and Technology
Development Foundation of China for financial support.
References
1
A. Suzuki, “Metal-Catalyzed Cross Coupling Reactions,”
ed by F. Driederich, and P. J. Stang, Wiley-VCH, Weinheim, Ger-
many (1998).
2
a) A. Suzuki, Pure. Appl. Chem., 63, 419(1991). b) S.-K.
Kang, H.-W. Lee, S.-B. Jang, and P. S. Ho, J. Org. Chem., 61,
720 (1996). c) S. Saito, M. Sakai, and N. Miyaura, Tetrahedron
Lett., 37, 2993(1996).
The reaction may proceed via the catalytic cycle shown in
Scheme 2. The oxidative addition of acid chloride to palladi-
um(0) affords acylpalladium(Ⅱ) chloride. When a palladi-
um(Ⅱ) catalyst is used, it may be converted into some palladi-
4
3
a) N. Miyaura, and A. Suzuki, Chem. Rev., 95, 2457
(
1995). b) D. De, and D. J. Krogstad, Org. Lett., 2, 879 (2000). c)
7
um(0) species, probably via side reactions forming biphenyl.
R. Kakino, I. Shimizu, and A. Yamamoto, Bull. Chem. Soc. Jpn.,
4, 371 (2001). d) M. Haddach, and J. R. McCarthy, Tetrahedron
Lett., 40, 3109(1999).
4
The transfer of the phenyl group from NaBPh to palladium
7
with a concomitant elimination of BCl , followed by reductive
3
elimination, gives the corresponding phenyl ketones. A similar
catalytic cycle was already proposed in the reactions with
4
Y. Kobayash, T.Shimazaki,H. Taguchi, and F. Sato, J. Org.
Chem., 55, 5324(1990).
3c
13
arylboron and triphenylbismuth compounds.
5
W. C. Shieh and J. A. Carlson, J. Org. Chem., 57,
In summary, we have developed a simple, efficient and fast
procedure for a cross-coupling reaction of sodium tetraphe-
nylborate with aroyl chlorides and cinnamoyl chloride on pal-
3
79(1992).
6
B. A. Lorsbach, J. T. Bagdanoff, R. B. Miller, and M. J.
Kurth, J. Org. Chem., 63, 2244(1998).
N. A. Bumagin and D. N. Korolev, Tetrahedron Lett., 40,
3057(1999).
ladium-doped KF/Al
O
2 3
under microwave irradiation condi-
7
tions. This method is superior to previously reported methods
in terms of high yields, purity of products, and short reaction