C. Heiss, M. Schlosser
(10): Diisopropylamine
FULL PAPER
17 Hz), 124.9 (dd, J ϭ 17, 4 Hz) ppm. C7H2BrF3O2 (254.92): calcd.
1,2,3-Tribromo-4,5,6-trifluorobenzene
C 32.97, H 0.79; found C 33.19, H 0.86.
(3.5 mL, 2.5 g, 25 mmol) and 1,5-dibromo-2,3,4-trifluorobenzene
(3.2 mL, 7.2 g, 25 mmol) were added consecutively to a solution
of butyllithium (25 mmol) in hexanes (16 mL) and tetrahydrofuran
(35 mL) cooled in a methanol/dry ice bath. After 2 h at Ϫ75 °C,
the mixture was poured into a precooled (Ϫ75 °C) solution of tetra-
bromomethane (10 g, 30 mmol) in tetrahydrofuran (30 mL). After
rapidly turning dark and then black, the mixture was absorbed on
basic alumina (15 mL) and eluted with hexanes (20 mL). After
evaporation of the volatiles, the residue was crystallized from eth-
anol (10 mL) to give yellowish fine needles; m.p. 67Ϫ69 °C (ref.[18]
m.p. 72 °C); yield 6.2 g (67%). 13C NMR: δ ϭ 148.4 (ddd, J ϭ 251,
12, 5 Hz), 139.4 (td, J ϭ 262, 18 Hz), 122.9 (d, J ϭ 6 Hz), 109.7
(symm. m) ppm. C6Br3F3 (368.74): calcd. C 19.54, H 0.00; found
C 19.71, H 0.00.
2-Bromo-3,4,5-trifluorobenzoic Acid (5): An analogous reaction was
carried out with 2-bromo-3,4,5-trifluoro-1-iodobenzene (14; see
Section 2; 3.4 g, 10 mmol); colorless needles; m.p. 101Ϫ103 °C
1
(from hexanes); yield: 2.3 g (90%). H NMR: δ ϭ 7.78 (ddd, J ϭ
10.0, 7.8, 2.6 Hz, H) ppm. 13C NMR: δ ϭ 165.5 (s), 151.3 (dd, J ϭ
251, 10 Hz), 150.7 (dd, J ϭ 248, 11 Hz), 143.5 (dt, J ϭ 258, 17 Hz),
131.6 (s), 116.5 (dd, J ϭ 19, 3 Hz), 107.0 (dd, J ϭ 20, 3 Hz) ppm.
C7H2BrF3O2 (254.92): calcd. C 32.97, H 0.79; found C 32.96, H
0.80.
2. Haloarenes without Functional Groups (6؊14)
2,3,4-Trifluoro-1,5-phenylenebis(triethylsilane) (6): A solution of
1,2,3-trifluorobenzene (7.7 mL, 9.9 g, 75 mmol) and sec-butyl-
lithium (75 mmol) in cyclohexanes (52 mL) and tetrahydrofuran
(0.15 L) was kept for 45 min at Ϫ75 °C. Always at Ϫ75 °C, chloro-
triethylsilane (13 mL, 11 g, 75 mmol) and, at 45 min intervals, more
sec-butyllithium (75 mmol) in cyclohexane (52 mL) and chlorotri-
ethylsilane (13 mL, 11 g, 75 mmol) were added. The product was
isolated by immediate distillation as a colorless oil; b.p. 103Ϫ105
°C/0.5 Torr; n2D0 ϭ 1.4656; d420 ϭ 1.101; yield: 24.6 g (91%). 1H
NMR: δ ϭ 7.03 (td, J ϭ 7.0, 2.5 Hz, 1 H), 0.96 (t, J ϭ 7.4 Hz, 18
H), 0.83 (q, J ϭ 7.4 Hz, 12 H) ppm. 13C NMR: δ ϭ 156.4 (ddd,
J ϭ 247, 8, 3 Hz), 139.5 (dt, J ϭ 256, 18 Hz), 135.2 (ddd, J ϭ 17,
11, 2 Hz), 120.6 (symm. m), 7.1 (s), 3.6 (s) ppm. C18H31F3Si2
(360.60): calcd. C 59.95, H 8.66; found C 56.96, H 8.68.
1,2-Dibromo-3,4,5-trifluorobenzene
(11):
Diisopropylamine
(7.0 mL, 5.1, 50 mmol) and 1,5-dibromo-2,3,4-trifluorobenzene (9,
6.4 mL, 14 g, 50 mmol) were added consecutively to a solution of
butyllithium (50 mmol) in hexanes (30 mL) and tetrahydrofuran
(70 mL) stored in a methanol/dry ice bath. After 2 h at Ϫ75 °C,
methanol (5.0 mL, 4.0 g, 0.12 mol) was added. The volatiles were
evaporated and the residue directly distilled; b.p. 37Ϫ39 °C/3 Torr.
The colorless oil obtained was composed of isomer 11 and its pre-
cursor 9 in a 7:1 ratio as evidenced by gas chromatography: (2 m,
2% FFAP, 120 °C; 2 m, 2% OV-17, 150 °C); 1H NMR of the major
component: δ ϭ 7.38 ppm (dd, J ϭ 6.6, 2.1 Hz, 1 H). The dibromo
compound 11 was obtained without regioisomeric contamination,
when, at Ϫ75 °C, 1,2,3-tribromo-4,5,6-trifluorobenzene (10, 5.5 g,
15 mmol) was added to a solution of butylmagnesium chloride
(5.0 mmol) and butyllithium (10 mmol) in tetrahydrofuran
(3.5 mL), hexanes (6.5 mL), and toluene (30 mL) and the mixture,
after having been kept for 45 min at 0 °C, was treated with meth-
anol (0.7 mL, 0.6 g, 20 mmol). Direct distillation gave a colorless
oil; b.p. 41Ϫ45 °C/3 Torr; n2D0 ϭ 1.3320; d420 ϭ 2.219; yield: 4.0 g
(92%). 1H NMR: δ ϭ 7.38 (dd, J ϭ 6.6, 2.1 Hz, 1 H) ppm. 13C
NMR: δ ϭ 150.3 (ddd, J ϭ 255, 12, 3 Hz), 149.6 (ddd, J ϭ 253,
15, 3 Hz), 139.5 (dt, J ϭ 257, 16 Hz), 118.7 (dd, J ϭ 9, 5 Hz), 116.7
(dd, J ϭ 21, 2 Hz), 109.3 (dd, J ϭ 20, 4 Hz) ppm. C6HBr2F3
(289.88): calcd. C 24.86, H 0.35; found C 24.50, H 0.25.
Bromo-2,3,4-trifluorobenzene (7): A solution of sec-butyllithium
(20 mmol) in cyclohexane (15 mL) was added dropwise to a solu-
tion of 1,2,3-trifluorobenzene (2.0 mL, 2.6 g, 20 mmol) in THF
(40 mL) at Ϫ75 °C. After 45 min at Ϫ75 °C, bromine (1.1 mL,
3.2 g, 20 mmol) was added. Immediate distillation under reduced
pressure afforded a colorless oil; b.p. 58Ϫ60 °C/30 Torr; n2D0
ϭ
1.4863; d420 ϭ 1.709; yield: 4.0 g (95%); H NMR: δ ϭ 7.30 (ddd,
J ϭ 7.9, 5.2, 2.5 Hz, 1 H), 6.93 (dddd, J ϭ 9.5, 8.1, 2.2, 2.1 Hz, 1
H) ppm.
1
(5-Bromo-2,3,4-trifluorophenyl)triethylsilane (8): Diisopropylamine
(21 mL, 15 g, 0.15 mol) and 1-bromo-2,3,4-trifluorobenzene
(21 mL, 32 g, 0.15 mol) were added consecutively to a solution of
butyllithium (0.15 mol) in hexanes (0.10 L) and tetrahydrofuran
(0.25 L) cooled in a methanol/dry ice bath. After 2 h at Ϫ75 °C,
chlorotriethylsilane (25 mL, 23 g, 0.15 mol) was added. Immediate
5-Bromo-1,2,3-trifluorobenzenes (12): A precooled solution of the
1:7 mixture (see above; 12 g, 40 mmol) of 1,5-dibromo-2,3,4-tri-
fluorobenzene (9) and 1,2-dibromo-3,4,5-trifluorobenzene (11) in
diethyl ether (10 mL) was added to butyllithium (35 mmol) in hex-
anes (20 mL) and diethyl ether (70 mL) kept at Ϫ100 °C. After
15 min, methanol (5.0 mL, 4.0 g, 0.12 mol) was added. Evaporation
of the volatiles and direct distillation of the residue gave a colorless
oil; b.p. 41Ϫ43 °C/15 Torr; n2D0 ϭ 1.3731; d420 ϭ 1.711; yield 6.3 g
distillation afforded a colorless oil; b.p. 71Ϫ73 °C/2 Torr; n2D0
ϭ
1.4967; d420 ϭ 1.289; yield: 45 g (92%). 1H NMR: δ ϭ 7.23 (ddd,
J ϭ 7.5, 4.9, 2.6 Hz, 1 H), 0.95 (t, J ϭ 7.1 Hz, 9 H), 0.83 (q, J ϭ
7.1 Hz, 6 H) ppm. 13C NMR: δ ϭ 154.7 (dd, J ϭ 243, 8 Hz), 149.6
(ddd, J ϭ 254, 11, 3 Hz), 140.4 (dt, J ϭ 260, 18 Hz), 132.1 (dd,
J ϭ 12, 3 Hz), 122.8 (d, J ϭ 30 Hz), 105.2 (d, J ϭ 17 Hz), 7.3 (s),
3.6 (s) ppm. C12H16BrF3Si (325.24): calcd. C 44.31, H 4.96; found
C 44.29, H 4.90.
1
(75%). H NMR: δ ϭ 7.18 (t, J ϭ 6.5 Hz, 2 H) ppm. 13C NMR:
δ ϭ 151.2 (ddd, J ϭ 255, 11, 4 Hz), 139.4 (dt, J ϭ 255, 15 Hz),
116.2 (symm. m), 114.8 (ddd, J ϭ 10, 6, 4 Hz) ppm. C6H2BrF3
(210.98): calcd. C 34.16, H 0.96; found C 34.25, H 1.00. When pure
1,2-dibromo-3,4,5-trifluorobenzene (11, 10 mmol) was consecut-
ively treated with butyllithium (10 mmol) in diethyl ether (20 mL)
and hexanes (5.0 mL) at Ϫ100 °C for 15 min, and afterwards with
methanol (0.50 mL, 0.40 g, 12 mmol), the product 12 was formed
in yield 1.1 g (89%).
1,5-Dibromo-2,3,4-trifluorobenzene (9): A solution of (5-bromo-
2,3,4-trifluorophenyl)triethylsilane (8, 25 mL, 33 g, 0.10 mol) and
bromine (10 mL, 32 g, 0.20 mol) in tetrachloromethane (0.10 L)
was heated under reflux for 36 h. The product was immediately
isolated by distillation as a colorless oil; b.p. 37Ϫ38 °C/3 Torr; 1-Bromo-2,3,4-trifluoro-5-iodobenzene (13): Diisopropylamine
n2D0 ϭ 1.5320 (ref.[17] n2D0 ϭ 1.5330); d420 ϭ 2.275 (ref.[17] d420 ϭ 2.27); (14 mL, 10 g, 0.10 mol) and 1-bromo-2,3,4-trifluorobenzene (7,
yield 27 g (93%). 1H NMR: δ ϭ 7.59 (td, J ϭ 7.0, 2.4 Hz, 1 H) 12 mL, 21 g, 0.10 mol) were consecutively introduced into a solu-
ppm. The same compound was obtained when bis(silane) 6
tion of butyllithium (0.10 mol) in hexanes (63 mL) and tetrahy-
(8.2 mL, 9.0, 25 mmol) was analogously treated with elemental drofuran (0.14 L) cooled in a methanol/dry ice bath. After 2 h at
bromine (2.6 mL, 8.0 g, 0.10 mol); yield: 6.9 g (95%).
450
Ϫ75 °C, a precooled solution of iodine (25 g, 0.10 mol) in tetrahy-
Eur. J. Org. Chem. 2003, 447Ϫ451