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Bull. Chem. Soc. Jpn. Vol. 83, No. 7 (2010)
Synthesis and Structure of Boron Compounds
oxaborolan-2-yl)isophthalate (8a). To a THF (1 mL) solution
of 7 (71 mg, 0.20 mmol), n-BuLi (0.14 mL, 1.58 M in hexane,
0.22 mmol) was dropwise added at ¹78 °C under Ar, and the
mixture was stirred for 1 h. To the reaction mixture, THF
(3 mL) solution of 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-di-
oxaborolane (0.10 mL, 0.50 mmol) was dropwise added at
¹78 °C. The mixture was then slowly warmed to room tem-
perature within 15 h. The mixture was extracted with CH2Cl2,
and the organic layer was dried over Na2SO4. After removal of
the solvents by evaporation, co-crystals of 8a and 2-hydroxy-
4,4,5,5-tetramethyl-1,3,2-dioxaborolane suitable for X-ray
analysis (100 mg, 91%) were obtained by recrystallization
from n-hexane/CH2Cl2. The co-crystals were dissolved in
CH2Cl2 and washed with H2O several times, then dried over
Na2SO4. After removal of the solvents by evaporation, analyti-
cally pure 8a¢0.5H2O was obtained; mp 82.5-84.0 °C (dec);
1H NMR (CDCl3, 400 MHz): ¤ 1.48 (s, 12H), 1.57 (s, 18H),
7.37 (t, 1H, J = 7.6 Hz), 7.99 (d, 2H, J = 7.6 Hz); 11B NMR
(CDCl3, 127 MHz): ¤ 30.5; 13C NMR (CDCl3, 100 MHz): ¤
25.7, 28.1, 81.2, 83.7, 128.1, 132.0, 136.7, 166.1, the ipso-
carbon bonded to the central boron atom was not observed;
Anal. Calcd for C22H33BO6 + 0.5H2O: C, 63.93; H, 8.29%.
Found: C, 64.14; H, 8.04%.
400 MHz): ¤ 1.26 (s, 18H), 6.92 (d, 2H, J =7.2 Hz), 7.00 (t,
2H, J =7.2 Hz), 7.23 (t, 2H, J =7.2 Hz), 7.51 (t, 1H, J =
8.0 Hz), 7.64 (d, 2H, J =7.2 Hz), 8.08 (d, 2H, J =8.0 Hz);
11B NMR (CDCl3, 127 MHz): ¤ 13.1; 13C NMR (CDCl3,
100 MHz): ¤ 27.7, 86.4, 119.1, 126.3, 127.0, 127.4, 129.4,
132.1, 134.0, 151.0, 173.2, the two ipso-carbons bonded to the
central boron atom were not observed; Anal. Calcd for
C28H29BO4: C, 76.37; H, 6.64%. Found: C, 76.25; H, 6.37%.
Synthesis of N,N,N¤,N¤-Tetraisopropyl-2-bromoisophthal-
amide (10b). To a CH2Cl2 (5 mL) solution of 2-bromoisoph-
thaloyl dichloride (9) (253 mg, 1.00 mmol), diisopropylamine
(0.60 mL, 4.0 mmol) was slowly added at 0 °C. The mixture
was stirred overnight at room temperature. The mixture was
then extracted with CH2Cl2, and the organic layer was washed
with brine and dried over MgSO4. After removal of the
solvents by evaporation, the crude product was purified by
column chromatography (AcOEt-MeOH = 20:1) to give com-
pound 10b as a white solid (378 mg, 0.919 mmol, 92%); mp
1
220.5-221.0 °C; H NMR (CDCl3, 400 MHz): ¤ 1.03 (d, 12H,
J =6.8 Hz), 1.22 (d, 12H, J =6.8 Hz), 3.53 (sep, 2H, J =6.8
Hz), 3.62 (sep, 2H, J =6.8 Hz), 7.13 (d, 2H, J =7.6 Hz), 7.35
(t, 1H, J =7.6 Hz); 13C NMR (CDCl3, 100 MHz): ¤ 20.0, 20.6,
46.0, 51.2, 115.2, 126.0, 128.1, 141.1, 167.8; Anal. Calcd for
C20H31BrN2O2: C, 58.39; H, 7.60; N, 6.81%. Found: C, 58.72;
H, 7.88; N, 6.74%.
Synthesis of Di-t-butyl 2-(Benzo-1,3,2-dioxaborolan-2-
yl)isophthalate (8b).
To a THF (1 mL) solution of 7
(71 mg, 0.20 mmol), n-BuLi (0.14 mL, 1.58 M in hexane,
0.22 mmol) was dropwise added at ¹78 °C under Ar, and the
mixture was stirred for 1 h. To the reaction mixture, THF
(3 mL) solution of chlorocatecholborane (31 mg, 0.20 mmol)
was dropwise added at ¹78 °C. The mixture was then warmed
to 0 °C and stirred for 4 h. The mixture was extracted with
Et2O, and the organic layer was washed with brine and dried
over Na2SO4. After removal of the solvents by evaporation,
compound 8b was obtained as a white solid (68 mg, 0.15 mmol,
77%). Colorless crystals of 8b suitable for X-ray analysis were
obtained by recrystallization from n-hexane/CH2Cl2; mp
Synthesis of N,N,N¤,N¤-Tetraisopropyl-2-(dihydroxybo-
ryl)isophthalamide (12).
To a THF (15 mL) solution of
10b (206 mg, 0.50 mmol), n-BuLi (0.32 mL, 1.58 M in hexane,
0.50 mmol) was dropwise added at ¹78 °C under Ar, and the
mixture was stirred for 1 h. To the reaction mixture, trimethyl
borate (0.10 mL, 0.90 mmol) was dropwise added at ¹78 °C
and stirred for 3 h at the same temperature. The mixture was
slowly warmed to room temperature within 15 h. To the
reaction mixture, 10% HCl aq. was added and the mixture was
stirred for 1 h. The mixture was extracted with CH2Cl2, and the
organic layer was washed with brine and dried over Na2SO4.
After removal of the solvents by evaporation, compound 12
was obtained as a white solid (179 mg, 0.476 mmol, 95%). The
crude product of 12 was used without further purification.
Synthesis of N,N,N¤,N¤-Tetraisopropyl-2-(4,4,5,5-tetra-
1
158.0-159.0 °C (dec); H NMR (CDCl3, 400 MHz): ¤ 1.40 (s,
18H), 7.07-7.09 (m, 2H), 7.21-7.24 (m, 2H), 7.59 (t, 1H, J =
8.0 Hz), 8.19 (d, 2H, J =8.0 Hz); 11B NMR (CDCl3, 127 MHz):
¤ 31.4; 13C NMR (CDCl3, 100 MHz): ¤ 28.0, 82.9, 112.0,
121.6, 129.5, 132.7, 136.6, 149.2, 166.4, the ipso-carbon
bonded to the central boron atom was not observed; Anal.
Calcd for C22H25BO6: C, 66.69; H, 6.36%. Found: C, 66.66; H,
6.56%.
Synthesis of Di-t-butyl 2-(5H-Dibenzoborol-5-yl)iso-
phthalate (8c). To a THF (3 mL) solution of 7 (350 mg,
1.00 mmol), n-BuLi (0.63 mL, 1.58 M in hexane, 1.00 mmol)
was dropwise added at ¹78 °C under Ar, and the mixture was
stirred for 1 h. To the reaction mixture, a THF (10 mL) solution
of 9-chloro-9-borafluorene (198 mg, 1.00 mmol) was dropwise
added at ¹78 °C. The mixture was then slowly warmed to room
temperature within 15 h. The mixture was extracted with Et2O,
and the organic layer was washed with brine and dried over
Na2SO4. After removal of the solvents by evaporation, the
crude product was purified by column chromatography
(CH2Cl2-n-hexane =1:1) to give compound 8c as a white
solid (194 mg, 0.440 mmol, 44%). Colorless crystals of 8c
suitable for X-ray analysis were obtained by recrystallization
from n-hexane/CH2Cl2; mp >300 °C; 1H NMR (CDCl3,
methyl-1,3,2-dioxaborol-2-yl)isophthalamide (13a).
A
mixture of 12 (92 mg, 0.24 mmol), pinacol (29 mg, 0.25 mmol),
and anhydrous MgSO4 (100 mg) in THF (6 mL) was refluxed
for 15 h under N2. After the mixture was filtered to remove the
solid materials, the solvents were removed by evaporation. The
crude product was recrystallized from dry n-hexane/CH2Cl2
to afford compound 13a as colorless crystals suitable for
X-ray analysis (71 mg, 0.156 mmol, 65%); mp 223.0-234.0 °C;
1H NMR (CDCl3, 400 MHz): ¤ 1.12 (d, 12H, J =6.8 Hz), 1.27
(s, 12H), 1.54 (d, 12H, J =6.8 Hz), 3.48 (sep, 2H, J =6.8 Hz),
3.78 (sep, 2H, J =6.8 Hz), 7.08 (d, 2H, J =7.6 Hz), 7.31 (t, 1H,
J =7.6 Hz); 11B NMR (CDCl3, 127 MHz): ¤ 30.7; 13C NMR
(CDCl3, 100 MHz): ¤ 20.2, 20.4, 24.6, 45.6, 51.1, 84.2, 124.0,
129.1, 145.7, 171.4, the ipso-carbon bonded to the central
boron atom was not observed; Anal. Calcd for C26H43BN2O4:
C, 68.12; H, 9.45; N, 6.11%. Found: C, 68.31; H, 9.27; N,
5.98%.
Synthesis of N,N,N¤,N¤-Tetraisopropyl-2-(benzo-1,3,2-
dioxaborolan-2-yl)isophthalamide (13b). A mixture of 12