H.-J. Frohn et al. / Tetrahedron Letters 43 (2002) 8111–8114
8113
Scheme 2.
Table 2. The cross-coupling of K [C6F5BF3] 1 with p-X-
C6H4R 2a–ha
fluoroborates (Scheme 3). In potassium trifluoro-
vinyltrifluoroborate (4) C(1) is less nucleophilic than in
1 caused by the directly bonded fluorine atom. Indeed,
salt 4 was less reactive than the pentafluorophenyl
analogue 1. Thus 4 reacted with 2a to the correspond-
ing tetrafluorostyrene 5 with 63% conversion of 2a
within 3 h and 54% yield. When the reaction time was
increased to 8 h the conversion of 2a reached 100% and
the yield 76%.
Entry
R
X
Conversion of Yield of 3
2 (%)
(%)b,c
1
2
3
4
5
6
7
8
9
F (2a)
F (2b)
NO2 (2c)
H (2d)
CH3 (2e)
CH3O (2f)d
NO2 (2g)e
NO2 (2g)d
C(O)OEt (2h)
I
Br
I
I
I
Br nd
Br nd
Br nd
100
30
100
100
100
92 (76)
28
\98 (81)
\98 (90)
98 (93)
25
36
62
Acknowledgements
I
100
\98 (82)
We gratefully acknowledge financial support by the
Deutsche Forschungsgemeinschaft, the Russian Foun-
dation for Basic Research, and the Fonds der Chemis-
chen Industrie.
a General procedure: 1 (165 mg, 0.6 mmol), Pd(OAc)2 (11 mg, 0.05
mmol), PPh3 (26 mg, 0.1 mmol), Ag2O (140 mg, 0.6 mmol), and
K2CO3 (138 mg, 1 mmol) were placed into the flask under an
atmosphere of dry argon. 2a–h (0.5 mmol) and degassed toluene (2
ml) were added and the reaction mixture was stirred at 100°C for 3
h. After cooling to 20°C, C6H5CF3 (5 ml, 0.041 mmol) was added
and the motherliquor was analysed by 19F NMR. For isolation of
the product the mixture was diluted with pentane and filtrated.
After removing of the solvent practically pure products were
received. The 1H and 19F NMR spectra of the obtained fluorinated
biphenyls coincided with the published spectra of the known com-
pounds.9,12,13
References
1. For reviews, see: (a) Miyaura, N.; Suzuki, A. Chem. Rev.
1995, 95, 2457–2483; (b) Stanforth, S. P. Tetrahedron
1998, 54, 263–303; (c) Suzuki, A. J. Organomet. Chem.
1999, 576, 147–168; (d) Hassan, J.; Sevignon, M.; Gozzi,
C.; Schulz, E.; Lemaire, M. Chem. Rev. 2002, 102, 1359–
1470; (e) Miyaura, N. In Topics in Current Chemistry;
Miyaura, N., Ed. Organoboron Compounds. Springer:
Berlin, 2002; Vol. 219, pp. 11–59.
b Determined by 19F NMR.
c Preparative yields are given in brackets.
d Reaction time 24 h.
e Reaction time 5 h.
2. (a) Frohn, H.-J.; Adonin, N. Yu.; Bardin, V. V.;
Starichenko, V. F. Z. Anorg. Allg. Chem. 2002, accepted
for publication; (b) Sterlin, R. N.; Isaev, V. L.; Zakharov,
G. M.; Martin, B.; Knunyanz, I. L. Zh. Vses. Khim.
Obshchest. 1967, 12, 475–477 (Chem. Abstr. 1968, 68,
13025); This item is also discussed in Ref. 1a, p. 2470.
Unsuccessful attempts with C6F5B(OH)2 in Suzuki reac-
tions were reported by: (c) Havelkova, M.; Hocek, M.;
Cesnek, M.; Dvorak, D. Synlett 1999, 1145–1147; (d)
Tiemann, T.; Umeno, K.; Ohira, D.; Inohae, E.; Sawada,
T.; Mataka, S. New J. Chem. 1999, 23, 1067–1070.
3. (a) Darses, S.; Michaud, G.; Genet, J.-P. Eur. J. Org.
Chem. 1999, 1875–1883; (b) Darses, S.; Genet, J.-P. Tet-
rahedron Lett. 1997, 38, 4393–4396; (c) Darses, S.;
Michaud, G.; Genet, J.-P. Tetrahedron Lett. 1998, 39,
5045–5048.
All iodobenzenes 2a, 2c–e, and 2h readily react with
potassium pentafluorophenyltrifluoroborate giving the
corresponding biphenyls in very high yields (Table 2).
The p-substituted bromobenzenes are less reactive.
Thus, only 30% conversion and 28% yield were
achieved for p-fluorobromobenzene (Table 2, entry 2)
within 3 h, whereas p-bromoanisole needed 25 h to
form the corresponding biphenyl 3f in 25% only (Table
2, entry 6). p-Nitrobromobenzene reacted with potas-
sium pentafluorophenyltrifluoroborate to yield 36% 3g
within 5 h (Table 2, entry 7) and 62% within 24 h
(Table 2, entry 8).
It was a challenge to extend this investigation on cross-
coupling to a prototype of perfluorinated alkenyltri-
Scheme 3.