C. Heiss, E. Marzi, F. Mongin, M. Schlosser
FULL PAPER
NMR*: δ = 169.0 (m), 155.1 (dd, J = 243, 11 Hz), 150.5 (dd, J =
267, 18 Hz), 136.2 (d, J = 26 Hz), 118.8 (dd, J = 10, 5 Hz), 126.6
(d, J = 3 Hz), 119.8 (d, J = 6 Hz), –1.4 (d, J = 1 Hz, 3 C) ppm.
C10H12F2O2Si (230.29): calcd. C 52.16, H 5.25; found C 52.26, H
5.28.
21 Hz, 2 C), 110.3 (td, J = 24, 3 Hz), 105.7 (td, J = 21, 5 Hz, 2
C), –1.5 (t, J = 3 Hz, 6 C) ppm. C13H19F3O2Si2 (320.46): calcd. C
48.72, H 5.98; found C 48.79, H 6.04.
2-Chloro-5-(trimethylsilyl)benzoic Acid (11-Cl): Prepared, analo-
gously as described above for acid 11-F, from (4-chlorophenyl)tri-
methylsilane (1-Cl; 2.8 mL, 2.8 g, 15 mmol); tiny colorless needles;
m.p. 78–80 °C; yield: 2.45 g (72%). 1H NMR: δ = 8.12 (d, J =
1.6 Hz, 1 H), 7.60 (dd, J = 7.9, 1.6 Hz, 1 H), 7.47 (d, J = 8.0 Hz,
1 H), 0.30 (s, 9 H) ppm. 13C NMR: δ = 171.7, 139.6, 138.7, 137.2,
135.3, 130.7, 127.8, –1.4 (3 C) ppm. C10H13ClO2Si (228.75): calcd.
C 52.51, H 5.73; found C 52.53, H 5.80.
2,5-Difluoro-4-(trimethylsilyl)benzoic Acid (15b-F): (2,5-Difluoro-
phenyl)trimethylsilane (5-F; 3.8 mL, 4.1 g, 15 mmol) was added
to a solution of sec-butyllithium (15 mmol) in cyclohexane (12 mL)
and tetrahydrofuran (20 mL) cooled in a dry ice/ethanol bath. After
45 min at –75 °C, the reaction mixture was poured onto freshly
crushed dry ice before being acidified at +25 °C with 2.0 hydro-
chloric acid (10 mL). According to gas chromatography (see Sec-
tion 3), the crude mixture contained 66% of acid 15b-F and 21%
of acid 15a-F. After extraction with diethyl ether (3ϫ15 mL) and
evaporation of the combined organic layers, the acid 15b-F crys-
tallized as tiny colorless needles; m.p. 144–146 °C (from hexanes);
yield: 3.07 g (89%). 1H NMR*: δ = 7.60 (dd, J = 7.9, 5.3 Hz, 1 H),
7.17 (dd, J = 10.2, 4.0 Hz, 1 H), 0.35 (d, J = 0.9 Hz, 9 H) ppm.
13C NMR*: δ = 167.9, 162.2 (dd, J = 241, 2 Hz), 158.3 (dd, J =
261, 2 Hz), 137.7 (d, J = 35 Hz), 123.1 (dd, J = 24, 12 Hz), 118.9
(dd, J = 12, 3 Hz), 117.7 (d, J = 31 Hz), –1.5 (d, J = 1.5 Hz, 3 C)
ppm. C10H12F2O2Si (230.29): calcd. C 52.16, H 5.25; found C
52.17, H 5.28. The isomeric 2,5-difluoro-3-(trimethylsilyl)benzoic
acid (15a-F) was isolated from the mother liquors by sublimation;
colorless needles (from hexanes); m.p. 88–89 °C; yield: 0.52%
(15%). 1H NMR: δ = 7.68 (ddd, J = 8.0, 5.5, 3.5 Hz, 1 H), 7.31
(dt, J = 7.1, 3.5 Hz, 1 H), 0.36 (d, J = 0.9 Hz, 9 H) ppm.
C10H12F2O2Si (230.29): calcd. C 52.16, H 5.25; found C 52.11, H
5.18.
2,3-Dichloro-5-(trimethylsilyl)benzoic Acid (13-Cl): Prepared, anal-
ogously as described above for acid 11-F, from (3,4-dichlorophen-
yl)trimethylsilane (3-Cl; 2.7 mL, 3.3 g, 15 mmol); tiny colorless
needles; m.p. 166–168 °C (from hexanes); yield: 3.35 g (85%). 1H
NMR: δ = 7.95 (d, J = 1.5 Hz, 1 H), 7.75 (d, J = 1.5 Hz, 1 H),
0.33 (s, 9 H) ppm. 13C NMR: δ = 170.2, 141.2, 138.7, 134.7, 134.6,
132.8, 130.4, –1.4 (3 C) ppm. C10H12Cl2O2Si (263.20): calcd. C
45.64, H 4.60; found C 45.15, H 4.52.
2,3-Dichloro-4-(trimethylsilyl)benzoic Acid (14-Cl): Prepared, anal-
ogously as described above for acid 11-F, from (2,3-dichlorophen-
yl)trimethylsilane (4-Cl; 3.3 g, 15 mmol); tiny colorless needles;
1
m.p. 121–123 °C (from hexanes); yield: 3.39 g (86%). H NMR*: δ
= 7.81 (d, J = 7.7 Hz, 1 H), 7.45 (d, J = 7.5 Hz, 1 H), 0.37 (s, 9 H)
ppm. 13C NMR*: δ = 170.9, 146.8, 140.8, 133.0, 132.5, 131.4,
129.0, –0.91 (3 C) ppm. C10H12Cl2O2Si (263.20): calcd. C 45.64, H
4.60; found C 45.46, H 4.40.
2,5-Dichloro-4-(trimethylsilyl)benzoic Acid (15b-Cl): Prepared,
analogously as described above for acid 11-F, from (2,5-chlo-
rophenyl)trimethylsilane (5-Cl; 2.6 mL, 3.3 g, 15 mmol); tiny color-
less needles; m.p. 114–116 °C (from hexanes); yield: 2.68 g (68%).
1H NMR*: δ = 7.97 (s, 1 H), 7.53 (s, 1 H), 0.41 (s, 9 H) ppm. 13C
NMR*: δ = 169.2, 146.7, 139.0, 138.2, 132.5, 129.6, –1.2 (s, 3 C)
ppm. C10H12Cl2O2Si (263.20): calcd. C 45.69, H 4.61; found C
45.57, H 4.50. – According to gas chromatography (see Section 3),
the crude reaction mixture contained 74% of acid 15b-Cl and 15%
of acid 15a-Cl. A 1: 1 composition isolated from mother liquors
enabled the structural assignment of the minor component 15a-Cl.
1H NMR: δ = 7.88 (d, J = 0.6 Hz, 1 H), 7.56 (d, J = 0.7 Hz, 1 H),
0.41 (s, 9 H) ppm.
2,6-Difluoro-4-(trimethylsilyl)benzoic Acid (16-F): Analogously, as
described above for acid 11-F, from (3,5-difluorophenyl)trimethyl-
silane (6-F; 4.7 g, 25 mmol); colorless needles; m.p. 105–107 °C
(from hexanes); yield: 5.29 g (92%). 1H NMR*: δ = 7.09 (d, J =
8.0 Hz, 2 H), 0.30 (s, 9 H) ppm. 13C NMR*: δ = 167.5 (s), 160.6
(dd, J = 262, 5 Hz, 2 C), 150.3 (t, J = 5 Hz), 116.3 (symm. m),
109.3 (t, J = 16 Hz, 2 C), 1.8 (3 C) ppm. C10H12F2O2Si (230.29):
calcd. C 52.16, H 5.25; found C 52.28, H 5.24.
2,6-Difluoro-3-(trimethylsilyl)benzoic Acid (17-F): As described
above for acid 11-F, but starting from (2,4-difluorophenyl)trimeth-
ylsilane (4.7 g, 25 mmol); colorless needles; m.p. 98–100 °C (from
hexanes); yield: 5.07 g (88%). 1H NMR: δ = 7.50 (dt, J = 6.4,
1.6 Hz, 1 H), 6.97 (td, J = 6.7, 1.6 Hz, 1 H), 0.35 (t, J = 1.5 Hz, 9
H) ppm. 13C NMR*: δ = 168.0, 165.0 (dd, J = 251, 5 Hz), 162.2
(dd, J = 260, 6 Hz), 138.9 (dd, J = 15, 5 Hz), 123.0 (dd, J = 32,
4 Hz), 112.0 (dd, J = 21, 4 Hz), 109.3 (dd, J = 15, 5 Hz), –1.2 (3
C) ppm. C10H12F2O2Si (230.29): calcd. C 52.16, H 5.54; found C
51.89, H 5.19.
2,6-Dichloro-4-(trimethylsilyl)benzoic Acid (16-Cl): Prepared, anal-
ogously as described above for acid 11-F, from (3,5-dichlorophen-
yl)trimethylsilane (6-Cl; 5.5 g, 25 mmol); colorless needles; m.p.
160–162 °C (from hexanes); yield: 5.92 g (92%). 1H NMR*: δ =
7.43 (s, 2 H), 0.30 (s, 9 H) ppm. 13C NMR*: δ = 170.4, 146.6, 132.3
(2 C), 132.1 (2 C), 131.3, –1.5 (3 C) ppm. C10H12Cl2O2Si (263.20):
calcd. C 45.64, H 4.60; found C 45.57, H 4.50.
2,4,6-Trifluoro-3-(trimethylsilyl)benzoic Acid (18-F): Prepared,
analogously as described above for acid 11-F, from silane 8-F
(2.6 mL, 3.1 g, 15 mmol); colorless needles; m.p. 76–77 °C (from
2,6-Dichloro-3-(trimethylsilyl)benzoic Acid (17-Cl): Prepared, anal-
ogously as described above for acid 11-F, from (2,4-dichlorophen-
yl)trimethylsilane (7-Cl; 5.5 g, 25 mmol). Extraction with hexanes
(3ϫ25 mL), evaporation of the combined organic layers and
crystallization of the residue from hexanes (10 mL) afforded color-
1
hexanes); yield: 2.56 g (69%). H NMR: δ = 6.69 (ddd, J = 10.3,
8.7, 1.7 Hz, 1 H), 0.39 (t, J = 1.5 Hz, 9 H) ppm. 13C NMR: δ =
167.2 (ddd, J = 251, 20, 5 Hz), 166.8 (s), 165.7 (ddd, J = 205, 17,
8 Hz), 162.9 (ddd, J = 212, 16, 8 Hz), 111.0 (td, J = 36, 4 Hz),
106.2 (ddd, J = 19, 16, 6 Hz), 100.9 (ddd, J = 31, 4, 2 Hz), –1.7 (t,
J = 3 Hz, 3 C) ppm. C10H11F3O2Si (248.28): calcd. C 48.38, H
4.47; found C 48.17, H 4.21.
1
less needles; m.p. 152–154 °C; yield: 5.79 g (88%). H NMR*: δ =
7.44 (d, J = 8.3 Hz, 1 H), 1.33 (d, J = 8.3 Hz, 1 H), 0.38 (3 C) ppm.
13C NMR*: δ = 171.1, 138.6, 137.3, 137.0, 132.8, 132.3, 127.1, –1.0
(3 C) ppm. C10H12Cl2O2Si (263.20): calcd. C 45.64, H 4.60; found
C 45.66, H 4.47.
2,4,6-Trifluoro-3,5-bis(trimethylsilyl)benzoic Acid (19-F): Prepared,
analogously as described above for acid 11-F, from silane 9-F
(3.5 mL, 4.1 g, 15 mmol); colorless needles; m.p. 153–155 °C (from
hexanes); yield: 2.70 g (56%). 1H NMR*: δ = 0.37 (s) ppm. 13C
NMR*: δ = 172.8 (dt, J = 246, 30 Hz), 167.7, 167.0 (dt, J = 255,
2,4,6-Trichloro-3-(trimethylsilyl)benzoic Acid (18-Cl): Prepared,
analogously as described above for acid 11-F, from silane 8-Cl
(3.5 mL, 4.1 g, 15 mmol); colorless needles; m.p. 112–114 °C (from
hexanes); yield: 4.06 g (91%). 1H NMR*: δ = 7.40 (s, 1 H), 0.54 (s,
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Eur. J. Org. Chem. 2007, 669–675