C. Heiss, F. Cottet, M. Schlosser
FULL PAPER
3,5-Dichloro-4-(triethylsilyl)benzoic Acid (5):[3] Methyl ester: color-
less oil; b.p. 98–100 °C/0.3 Torr; n2D0 = 1.4946; d420 = 1.223; yield:
(98%). 1H NMR: δ = 7.86 (s, 2 H), 3.92 (s, 3 H), 1.0 (m, 15 H)
ppm. 13C NMR: δ = 164.9, 142.5, 140.9, 132.5, 129.1, 52.5, 7.7 (3
C), 5.9 (3 C) ppm. C14H20Cl2O2Si (319.27): calcd. C 52.66, H 6.31;
found C 52.64, H 6.26.
continued for 45 min at +25 °C. The aqueous phase was extracted
with diethyl ether (3×10 mL). The combined organic layers were
dried and evaporated; small needles (from methanol); m.p. 36–
38 °C (ref.[13] 37–39 °C); yield: 2.30 g (90%). 1H NMR: δ = 7.50 (d,
J = 2.2 Hz, 1 H), 7.40 (m, 1 H), 7.37 (m, 2 H), 7.30 (td, J = 8.5,
2.1 Hz, 2 H), 7.24 (d, J = 8.5 Hz, 1 H) ppm.
3-Chloro-2-(triethylsilyl)benzoic Acid (3): At –75 °C, (2-bromo-6- 2,4,4Ј-Trichlorobiphenyl (8b): Prepared analogously from 4-chloro-
chlorophenyl)triethylsilane (see following paragraph; 4.6 g,
25 mmol) was treated with butyllithium (25 mmol) in tetra-
phenylboronic acid[14] (1.6 g, 10 mmol) and 2,4-dichloro-1-iodo-
benzene (1.3 mL, 2.7 g, 10 mmol); colorless needles from methanol;
hydrofuran (40 mL) and hexanes (10 mL). After 15 min at –75 °C, m.p. 53–55 °C (ref.[14] 55 °C); yield: 2.45 g (95%). 1H NMR: δ =
the mixture was poured onto an excess of freshly crushed dry ice.
After addition of a 2.0 ethereal solution of hydrogen chloride
(30 mL), the volatiles were evaporated. The residue was extracted
with hot hexanes (3×25 mL) and the filtrate concentrated to afford
7.50 (m, 1 H), 7.42 (d, J = 8.5 Hz, 2 H), 7.35 (d, J = 8.5 Hz, 2 H),
7.25 (d, J = 8.5 Hz, 2 H) ppm.
3,3Ј,5-Trichlorobiphenyl (9a): Prepared analogously from 3-chloro-
phenylboronic acid (1.6 g, 10 mmol) and 3,5-dichloro-1-iodo-
benzene (2.7 g, 10 mmol); colorless needles from ethanol; m.p. 78–
79 °C (ref.[13] 78–79 °C); yield: 2.44 g (96%). 1H NMR: δ = 7.51
(m, 1 H), 7.42 (d, J = 1.9 Hz, 2 H), 7.4 (m, 4 H) ppm.
1
colorless needles; m.p. 37–39 °C; yield: 3.80 g (94%). H NMR: δ
= 7.61 (dd, J = 7.3, 1.0 Hz, 1 H), 7.48 (dd, J = 8.0, 1.3 Hz, 1 H),
7.32 (t, J = 7.7 Hz, 1 H), 1.0 (m, 15 H) ppm. 13C NMR: δ = 175.8,
142.8, 141.0, 136.5, 132.8, 129.7, 127.0, 7.8 (3 C), 5.1 (3 C) ppm.
C13H19ClO2Si (270.80): calcd. C 57.66, H 7.07; found C 57.69, H
3,4Ј,5-Trichlorobiphenyl (9b): Prepared analogously from 4-chloro-
phenylboronic acid (1.6 g, 10 mmol) and 3,5-dichloro-1-iodo-
benzene (2.7 g, 10 mmol); colorless needles from pentanes; m.p. 87–
7.06. Methyl ester: colorless oil; b.p. 80–82 °C/0.3 Torr; n2D0
=
1.4089; d420 = 1.136; yield: 4.10 g (96%). H NMR: δ = 7.41 (dd, J
= 8.0, 1.3 Hz, 1 H), 7.40 (dd, J = 8.0, 1.2 Hz, 1 H), 7.28 (d, J =
8.0 Hz, 1 H), 3.87 (s, 3 H), 0.9 (m, 15 H) ppm. 13C NMR: δ =
169.8, 142.3, 135.1, 131.6, 129.5, 126.3 (2 C), 52.0, 7.5 (3 C), 4.5 (3
C) ppm. C14H21ClO2Si (284.83): calcd. C 59.03, H 7.43; found C
59.13, H 7.39.
1
1
88 °C (ref.[15] 88 °C); yield: 2.39 g (93%). H NMR: δ = 7.44 (d, J
= 8.5 Hz, 2 H), 7.42 (d, J = 8.5 Hz, 2 H), 7.40 (d, J = 2.0 Hz, 2
H), 7.35 (t, J = 2.0 Hz, 1 H) ppm.
Consecutive Reaction of (2,6-Dichlorophenyl)trimethylsilane with
sec-Butyllithium, Methanol and Tetrabutylammonium Fluoride Hy-
drate: At –100 °C, (2,6-dichlorophenyl)trimethylsilane (9.1 mL,
11 g, 50 mmol) was added to a solution of sec-butyllithium
(50 mmol) in cyclohexane (40 mL) and tetrahydrofuran (60 mL).
After 45 min at –100 °C and another 45 min at –75 °C, the reaction
mixture was treated with methanol (2.1 mL, 1.9 g, 60 mmol). Ac-
cording to gas chromatographic analysis (30 m, DB-1, 80 °C; 1 m,
5% SE-30, 80 °C; nonane as an internal calibrated standard), the
crude material contained 6.5% of (2-chlorophenyl)trimethylsilane
and 58% of (2,6-dichlorophenyl)trimethylsilane. Evaporation and
extraction with hot hexanes (3×50 mL) gave a yellowish oil (9.85 g)
which was distilled under reduced pressure. The first fraction was
essentially composed of (2-chlorophenyl)trimethylsilane (b.p. 45–
47 °C/6 Torr; ref.[16] 207–208 °C/740 Torr); yield: 0.15 g (3.4%). The
second fraction consisted of (2,6-dichlorophenyl)trimethylsilane
(b.p. 53–54 °C/3 Torr; ref.[16] 79–81 °C/4 Torr); yield: 3.01 g (55%).
A third fraction, a yellowish oil (b.p. 161–164 °C/0.2 Torr), con-
tained four high molecular weight products in the ratio of 2:3:6:9
according to gas chromatographic analysis (2 m, 10% PFO, 130 °C;
1 m, 2% C-20M, 180 °C; 2,2Ј,6,6Ј-tetrabromobiphenyl as an in-
ternal calibrated standard); yield: 3.22 g (32%). The third fraction
(3.0 g, 7.5 mmol) was treated with an excess of tetrabutylammo-
nium fluoride trihydrate (4.7 g, 15 mmol) in dimethylformamide
(50 mL) at 25 °C during 24 h. Evaporation, extraction with hot
hexanes (3×50 mL) and distillation (b.p. 139–145 °C/0.3 Torr) af-
forded a viscous oil; yield: 1.91 g (99%). According to gas chroma-
tographic analysis (same conditions as specified above) using au-
thentic samples for retention time comparison, it was composed of
3,3Ј,5-trichlorobiphenyl (9a), 2,4,4Ј-trichlorobiphenyl (8b), 2,3Ј,4-
trichlorobiphenyl (8a) and 3,4Ј,5-trichlorobiphenyl (9b) in a 2:3:6:9
ratio. An aqueous 88% solution of formic acid (2.6 mL, 5.0 mmol)
in water (2.6 mL) was added dropwise over 45 min to a refluxing
solution containing the four trichlorobiphenyls (1.3 g, 5.0 mmol),
sodium carbonate (5.3 g, 50 mmol) and 10% palladium on char-
coal (0.5 g) in toluene (20 mL). After 15 min at 100 °C, the reaction
mixture was washed with brine (3×10 mL). The organic phase was
dried and concentrated to leave behind 0.74 g (96%) of biphenyl;
m.p. 70–71 °C (ref.[17] 70.5 °C).
(2-Bromo-6-chlorophenyl)triethylsilane: 2,2,6,6-Tetramethylpiperi-
dine (17 mL, 14 g, 0.10 mol) and 1-bromo-3-chlorobenzene
(12 mL, 19 g, 0.10 mol) were added consecutively to a solution of
butyllithium (0.10 mol) in hexanes (55 mL) and tetrahydrofuran
(0.15 L) kept in a dry ice/methanol bath. After 2 h at –75 °C, chlo-
rotriethylsilane (17 mL, 15 g, 0.10 mol) was added. Immediate dis-
tillation afforded a colorless oil; b.p. 80–82 °C/1 Torr; n2D0 = 1.5555;
d420 = 1.317; yield: 26.7 g (87%). H NMR: δ = 7.46 (dd, J = 8.0,
1
1.0 Hz, 1 H), 7.27 (dd, J = 8.0, 1.0 Hz, 1 H), 7.05 (t, J = 8.0 Hz, 1
H), 1.1 (m, 15 H) ppm. 13C NMR: δ = 142.6, 137.3, 132.5, 131.5,
130.7, 129.3, 7.9 (3 C), 6.3 (3 C) ppm. C12H18BrClSi (306.57):
calcd. C 47.01, H 5.92; found C 47.18, H 5.93.
Consecutive Reaction of (2,6-Dichlorophenyl)triethylsilane with Vari-
ous Strong Bases and Carbon Dioxide: At –100 °C, (2,6-dichlo-
rophenyl)triethylsilane (5.4 mL, 6.5 g, 25 mmol) was added to a
solution containing the metalating reagent (25 mmol) and, where
appropriate, a complexand (PMDTA, KOR) in stoichiometric
amounts in tetrahydrofuran (30 mL) and a hydrocarbon (20 mL)
such as hexanes or cyclohexane. After 45 min or, when LITMP
served as the base, after 2 h at –100 °C, the mixture was poured
onto an excess of freshly crushed dry ice. The slurry was worked
up analogously as in the case of (2,6-dibromophenyl)triethylsilane
derivatives (see above) and the product compositions (see Table 1)
were quantified by gas chromatography (30 m DB-Wax, 220 °C;
30 m DB-1; internal calibrated standard: tridecane).
4. Derivatives of (2,6-Dichlorophenyl)trimethylsilane
(2,6-Dichlorophenyl)trimethylsilane, 2,4-dichloro-3-(trimethylsilyl)-
benzoic acid and 3,5-dichloro-4-(trimethylsilyl)benzoic acid have
been described previously.[3]
2,3Ј,4-Trichlorobiphenyl (8a): 3-Chlorophenylboronic acid[13] (1.6 g,
10 mmol), 2,4-dichloro-1-iodobenzene (1.3 mL, 2.7 g, 10 mmol),
tetrakis(triphenylphosphane)palladium(0) (0.34 g, 0.30 mmol),
benzene (20 mL) and a 2.0 aqueous solution of sodium carbon-
ate (10 mL) were stirred at +25 °C for 12 h. Then, 35% aqueous
hydrogen peroxide solution (10 mL) was added and the stirring was
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Eur. J. Org. Chem. 2005, 5236–5241