1156
T. Korenaga et al. / Journal of Fluorine Chemistry 128 (2007) 1153–1157
with Dean-Stark trap containing molecular sieves 3A. The
solvent was removed under the pressure of <1 mmHg at
3.4. Typical procedure of asymmetric reduction of ketone
3
0 8C for 1 h to give pale yellow solid. After addition of Et O
To a THF (1.0 mL) solution of oxazaborolidine 1a
(0.1 mmol) prepared above was added borane dimethylsulfide
complex (28 mL, 0.30 mmol). After being stirred at room
temperature for 10 min, the solution of acetophenone (8a)
(120 mL, 1.0 mmol) in THF (2.0 mL) was added via syringe
pump over 1.5 h, and then the reaction solution was stirred at
room temperature for 4 h. To the solution was added methanol
(1 mL) and then the solvent was removed under reduced
pressure. After purification through a short column chromato-
2
to the solid, the white suspension was filtered through glass
wool under argon atmosphere. The solvent was removed
under the pressure of <1 mmHg at 40 8C for 1 h to give
(4S,5R)-4,5-diphenyl-2-pentafluorophenyl-1,3,2-oxazaboro-
lidine (1a). This oxazaborolidine 1a was readily used for
asymmetric borane reduction of ketones without further
purification.
1
H NMR (300 MHz, CDCl ) d: 4.53 (br, 1H), 5.21 (d,
3
J = 6.6 Hz, 1H), 6.00 (d, J = 6.6 Hz, 1H), 6.92–7.15 (m, 10H);
1
graphy (SiO , hexane/EtOAc (3:1)), the residue was analyzed
2
3
C NMR (151 MHz, CDCl (except for C F )) d: 64.1, 84.6,
3
by chiral HPLC; Daicel CHIRALCEL OB-H,
ꢀ1
Ø
6 5
1
9
1
26.3, 127.1, 127.3, 127.4, 127.5, 127.8, 137.9, 139.5;
F
4.6 mm ꢂ 25 cm, hexane/i-PrOH (9: 1), 0.4 mL min , UV
NMR (282 MHz, CDCl ) d: ꢀ162.8 to ꢀ162.7 (m, 2F), ꢀ151.1
254 nm, retention time (t ); (S)-8a: 17.5 min (41.4%); (R)-8a:
R
3
1
1
(
t, J = 21 Hz, 1F), ꢀ131.2 to ꢀ131.1 (m, 2F); B NMR
22.9 min (58.6%).
1
(
192 MHz, CDCl ) d: 30.2.
3
H NMR (300 MHz, CDCl ) d: 1.51 (d, J = 6.3 Hz, 3H),
3
1
3
1
.77 (br, 1H), 4.91 (q, J = 6.3 Hz, 1H), 7.25–7.41 (m, 5H);
C
NMR (75 MHz, CDCl ) d: 25.0, 70.2, 125.3, 127.4, 128.5,
3
1
.2. (S)-1-(Pentafluorophenyl)tetrahydro-3,3-diphenyl-
H,3H-pyrrolo[1,2-c][1,3,2]oxazaborole (1b)
3
145.9; IR (CCl ) 537, 903, 998, 1076, 1255, 1463, 1491, 2978
4
ꢀ
1
and 3350 cm
.
(
S)-1-(Pentafluorophenyl)tetrahydro-3,3-diphenyl-1H,3H-
pyrrolo[1,2-c][1,3,2]oxazaborole (1b) was prepared from (S)-
a,a-diphenyl-2-pyrrolidinemethanol following the procedure
described for 1a.
Acknowledgements
1
This work was partially supported by Okayama Foundation
for Science and Technology, and a Grant-in-Aid for Young
Scientists (B) (No. 16750082) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan. We thank the
H NMR (300 MHz, CDCl ) d: 0.93–1.03 (m, 1H), 1.72–
3
1
.80 (m, 1H), 1.81–1.95 (m, 2H), 3.18–3.38 (m, 2H), 4.65 (dd,
J = 5.9, 10.0 Hz, 1H), 7.03–7.43 (m, 8H), 7.42–7.57 (m, 2H);
1
3
C NMR (151 MHz, CDCl (except for C F )) d: 26.3, 30.0,
3
6 5
1
13
19
SC-NMR Laboratory of Okayama University for H, C, F,
4
1
2
3.0, 72.8, 87.6, 126.0, 126.3, 126.4, 127.0, 127.6, 128.0, 144.1,
1
1
and B NMR measurements.
1
9
47.8; F NMR (282 MHz, CDCl ) d: ꢀ163.1 to ꢀ162.9 (m,
3
1
1
F), ꢀ152.3 (t, J = 21 Hz, 1F), ꢀ130.5 to ꢀ130.4 (m, 2F);
B
NMR (192 MHz, CDCl ) d: 30.0.
3
References
3.3. Meso-2-(pentafluorophenyl)-4,5-diphenyl-1,3,2-
dioxaborolane (5)
[
1] Recent reviews:
(
(
a) B.T. Cho, Tetrahedron 62 (2006) 7621–7643;
b) V.A. Glushkov, A.G. Tolstikov, Russ. Chem. Rev. 73 (2004) 581–608.
[
2] (a) H. Liu, J.X. Xu, J. Mol. Catal. A: Chem. 244 (2006) 68–72;
A 20 mL of dry Schlenk tube was charged with meso-1,2-
diphenyl-1,2-ethanediol (4) (21 mg, 0.10 mmol), pentafluor-
ophenylboronic acid (23 mg, 0.11 mmol) and toluene (2.0 mL)
under an argon atmosphere. After being stirred at room
temperature, the mixture was stirred for 4 h under conditions of
azeotrope with Dean-Stark trap containing molecular sieves
(
(
b) J. Xu, T. Wei, Q. Zhang, J. Org. Chem. 69 (2004) 6860–6866;
c) C.E. Garrett, K. Prasad, O. Repic, T.J. Blacklock, Tetrahedron:
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3] E.J. Corey, C.J. Helal, Angew. Chem. Int. Ed. 37 (1998) 1986–2012.
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5
6 (1991) 763–769.
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340–7343.
3
A. The solvent was removed under reduced pressure to give
white solid. The resulting solid was purified by recrystallization
from petroleum ether–CH Cl to give meso-2-(pentafluoro-
[
7
2
2
[6] Steric effect of fluorine substituents: K. Uneyama, Organofluorine Chem-
istry, Blackwell, Oxford, 2006, pp. 81–90.
phenyl)-4,5-diphenyl-1,3,2-dioxaborolane (5) in quantitative
yield (39 mg, 0.10 mmol).
[
7] (a) C.A. Hunter, K.R. Lawson, J. Perkins, C.J. Urch, J. Chem. Soc., Perkin
Trans. 2 (2001) 651–669;
1
mp 115–117 8C; H NMR (300 MHz, CDCl ) d: 6.01 (s,
3
(
(
b) E.A. Meyer, R.K. Castellano, F. Diederich, Angew. Chem. Int. Ed. 42
2003) 1210–1250.
1
H), 6.90–7.10 (m, 10H); C NMR (75 MHz, CDCl (except
3
2
for C F )) d: 83.6, 126.3, 127.6, 127.8, 136.1; F NMR
3
9
1
6
5
[8] The crystal structure of pentafluorophenylboronic acid was packed by
Hꢁ ꢁ ꢁO hydrogen-bond network: P.N. Horton, M.B. Hursthouse, M.A.
Beckett, M.P. Rugen-Hankey, Acta Crystallogr., Sect. E: Struct. Rep.
Online E60 (2004) o2204–o2206.
(
282 MHz, CDCl ) d: ꢀ162.5 to ꢀ162.2 (m, 2F), ꢀ149.2 (t,
3
1
1
J = 22 Hz, 1F), ꢀ129.4 to ꢀ129.1 (m, 2F); B NMR
(
192 MHz, CDCl ) d: 30.9; IR (KBr) 698, 719, 754, 1209,
3
[
9] N.Y. Adonin, V.V. Bardin, U. Floerke, H.-J. Frohn, Z. Anorg. Allg. Chem.
31 (2005) 2638–2646.
ꢀ1
1255, 1340, 1367, 1412, 1485, 1651, 2950, 3040 cm ; anal.
calcd. for C H BF O : C, 61.58; H, 3.10; found: C, 60.21; H,
6
2
0
12
5
2
[10] When toluene was used for azeotrope solvent, many by-products were
1
observed in H NMR.
3
.37%.