A STUDY OF PALLADIUM-CATALYZED ARYLATION
Ar
Ar
33
S
S
1. n-BuLi
2. ZrCl4 · 2THF
ZrCl2
Me2Si
Me2Si
S
S
Ar
Ar = Ph (3a), 1-naphtyl (3c)
Ar
Ar = Ph (4a), 1-naphtyl (4b)
Scheme 3.
Thus, in this study we have developed a new diameter and 500 mm long, hexane as eluent) to give
approach to the synthesis of aryl-substituted (cyclo- 2.61 g (42%) of a mixture of 6,6'-isomer (about 60%)
penta[b]thienyl)dimethylsilanes via the palladium-cat- with 4,4'- and 4,6'-isomers (about 40%).
alyzed Negishi arylation of corresponding bromo-sub-
Procedure for the Negishi reaction. A 1.0 M solu-
tion of the corresponding Grignard reagent (26.0 mL,
26.0 mmol) in THF was added to 58.0 mL of a 0.50 M
solution of ZnCl2 (29.0 mmol) in THF at ambient tem-
perature. The reaction mixture was stirred for 1 h, and
then 10.0 mmol of a mixture of compound 2 and
20.0 mL of a 0.02 M solution of Pd(t-Bu3P)2
(0.40 mmol) in THF was added. The mixture was
stirred at 70°C for 5 h, cooled, and passed through a
silica gel bed (30 mm in diameter, 50 mm in height,
THF as eluent). The solvent was removed on a rotary
evaporator. The product (3a, 3b, 3c) was isolated by
flash chromatography on silica gel (40–63 µm, a col-
umn 30 mm in diameter and 100 mm long, hexane as
eluent).
stituted substrates. The initial bromo-substituted bridg-
ing ligands with cyclopenta[b]thienyl fragments are the
mixtures of regioisomers that differ in the position of
the bridging fragment toward the halogen atoms; none-
theless, the resulting products of the Negishi reaction
undergo rearrangement to give a sole isomer necessary
for the synthesis of ansa-metallocenes.
EXPERIMENTAL
All experiments with moisture- and oxygen-sensi-
tive compounds were carried out in an argon atmo-
sphere using the standard Schlenk technique or in a box
with a controlled nitrogen atmosphere. Analyzes were
performed on a Waters Delta 600 chromatograph.
13
1H and C NMR spectra were recorded on a Bruker
General procedure for the preparation of ansa-
zirconocenes. A 2.5 M solution of n-BuLi (7.92 mL,
20.0 mmol) in hexane was added to a solution of
10.0 mmol of ligand 3a or 3c in 220 mL of diethyl ether
at ambient temperature. The reaction mixture was
stirred for 24 h and then cooled to –78°C, and
10.0 mmol of ZrCl4(THF)2 was added. The mixture
was stirred for 24 h at ambient temperature, and the sol-
vent was removed to dryness. Toluene (220 mL) was
added to the residue, the mixture was stirred for 8 h at
90°C, and the hot solution was filtered through a G4
porosity sintered glass filter. The residue was addition-
ally washed with hot toluene (3 × 100 mL). The com-
bined extracts were evaporated to dryness. Product 4a
or 4b was isolated by the crystallization of the residue
from dichloromethane.
Avance 400 DPX spectrometer operating at 400 and
100 MHz, respectively. Elemental analysis was accom-
plished using a Heraeus CHN-O-Rapid analyzer.
5-Methyl-4,5-dihydro-6H-cyclopenta[b]thiophen-6-
one was obtained from thiophene and metacrylic acid
as described in [9]. 3-Bromo-5-methyl-4(5)H-cyclo-
penta[b]thiophene was prepared by the bromination of
5-methyl-4,5-dihydro-6H-cyclopenta[b]thiophen-6-
one followed by reduction and dehydration by the pro-
cedure in [9].
Bis(3-bromo-5-methyl-6H-cyclopenta[b]thien-6-
yl)(dimethyl)silanes (2). A 1.6 M solution of MeLi
(16.0 mL, 25.6 mmol) in diethyl ether was added to a
solution of 5.50 g (25.6 mmol) of 3-bromo-5-methylcy-
clopenta[b]thiophene in 250 mL of ether at –60°C. The
mixture was stirred for 1 h at ambient temperature and
cooled to 0°C, and 1.55 mL (1.65 g, 12.8 mmol) of
Me2SiCl2 was added. The reaction mixture was stirred
for 12 h at ambient temperature, and 50 mL of water
was added. The organic layer was separated and dried
with K2CO3, and the solvent was removed on a rotary
evaporator. The residue was purified by flash chroma-
tography on silica gel (40–63 µm, column 40 mm in
REFERENCES
1. Chen, E.Y.X. and Marks, T.J., Chem. Rev., 2002,
vol. 100, p. 1391.
2. Resconi, L., Cavallo, L., Fait, A., and Piemontesi, F.,
Chem. Rev., 2000, vol. 100, p. 1253.
DOKLADY CHEMISTRY Vol. 424 Part 2 2009