Helvetica Chimica Acta – Vol. 89 (2006)
1073
i
2
. Determination of the Reaction Mixture of Borane and PrOH. To borane·dimethyl sulfide complex
(
1 mmol) in anh. toluene (5 ml) under N was added sequentially 0.1 equiv., 0.1 equiv., 0.2 equiv., 0.4
2
i
equiv., 0.2 equiv., 0.5 equiv., 0.5 equiv., and 1.0 equiv. ofPrOH in this order. The resulting soln. was stirred
for 10 min after each addition and analyzed by GC/MS.
3. (5S)-2,4,4-Triphenyl-3,1,2-oxazaborabicyclo[3.3.0]octane (=(3aS)-Tetrahydro-1,3,3-triphenyl-1H,
3H-pyrrolo[1,2-c][1,3,2]oxazaborole=B-Ph Catalyst; 1b). In a round-bottomed flask equipped with a
1
0-ml pressure-equalizing addition funnel (containing a cotton plug and ca. 10 g of 5- molecular sieves,
and functioning as a Soxhlet extractor), a mixture of (S)-diphenylprolinol (0.05 mmol, 12.7 mg) and phe-
nylboronic acid (0.05 mmol, 6.1 mg) was dissolved under stirring in dry toluene (15 ml). The resulting
soln. was heated to reflux for 12 h. Then, most of the solvent was distilled and the residue (ca. 3 ml)
was cooled to r.t. The addition funnel was removed, and the flask was airproofed quickly to avoid mois-
ture.
4
. General Procedure for the Asymmetric Reduction of Ketones. To a soln. of catalyst 1b (17 mg, 0.05
mmol, 10 mol-%), freshly prepared in dry toluene, 2M borane·dimethyl sulfide complex in THF (0.25 ml,
.5 mmol; or the amount given in Table 1) was added under N at r.t. A soln. of 4-butoxypropiophenone
0
2
(=1-(4-butoxyphenyl)propan-1-one; 7, 103 mg, 0.5 mmol) in toluene (4 ml) was added dropwise over 1 h
or all at once. After the addition, the mixture was stirred for 4 h and then quenched with MeOH (0.5 ml)
in an ice-water bath. After evaporation, the residue was purified by column chromatography (silica gel,
petroleum ether (60–908)/AcOEt 5 :1): chiral secondary alcohol as colorless oil. The spectral and anal.
data of all obtained alcohols were in agreement with those reported in [6c]. The ee value was determined
by chiral HPLC analysis.
REFERENCES
[
1] S. Wallbaum, J. Martens, Tetrahedron: Asymmetry 1992, 3, 1475; V. K. Singh, Synthesis 1992, 605; L.
Deloux, M. Srebnik, Chem. Rev. 1993, 93, 763; E. J. Corey, C. J. Helal, Angew. Chem., Int. Ed. 1998,
37, 1986.
[
2] a) E. J. Corey, R. K. Bakshi, S. Shibata, J. Am. Chem. Soc. 1987, 109, 5551; b) E. J. Corey, R. K. Bak-
shi, S. Shibata, C. Chen, V. K. Singh, J. Am. Chem. Soc. 1987, 109, 7925; c) E. J. Corey, J. O. Link,
Tetrahedron Lett. 1989, 30, 6275.
[
[
3] V. Nevalainen, Tetrahedron: Asymmetry 1991, 2, 63, 429, 827, and 1133.
4] a) T. K. Jones, J. J. Mohan, L. C. Xavier, T. J. Blacklock, D. J. Mathre, P. Sohar, E. T. Jones, R. A.
Reamer, F. E. Roberts, E. J. Grabowski, J. Org. Chem. 1991, 56, 763; b) C. Puigjaner, A. Vidal-Fer-
ran, A. Moyano, M. A. Pericas, A. Riera, J. Org. Chem. 1999, 64, 7902.
[
5] a) D. J. Mathre, A. S. Thompson, A. W. Douglas, K. Hoogsteen, J. D. Carroll, E. G. Corley, E. J. Gra-
bowski, J. Org. Chem. 1993, 58, 2880; b) E. J. Corey, M. Azimioara, S. Sarshar, Tetrahedron Lett.
1992, 33, 3429; c) J. K. Zhao, X. H. Bao, X. M. Liu, B. S. Wan, X. W. Han, C. G. Yang, J. F. Hang,
Y. Feng, B. Jiang, Tetrahedron: Asymmetry 2000, 11, 3351; d) J. X. Xu, T. Z. Wei, S. S. Lin, Q. H.
Zhang, Helv. Chim. Acta 2005, 88, 180.
[
6] a) M. Masui, T. Shioiri, Synlett 1997, 273; b) J. X. Xu, X. B. Su, Q. H. Zhang, Tetrahedron: Asymme-
try 2003, 14, 1781; c) J. X. Xu, T. Z. Wei, Q. H. Zhang, J. Org. Chem. 2003, 68, 10146; d) J. X. Xu, T.
Z. Wei, J. K. Xia, Q. H. Zhang, H. S. Wu, Chirality 2004, 16, 341; e) J. X. Xu, Y. Lan, T. Z. Wei, Q. H.
Zhang, Chin. J. Chem. 2005, 23,1457.
[
7] a) B. T. Cho, Y. S. Chun, J. Chem. Soc., Perkin. Trans. 1 1999, 2095; b) B. T. Cho, Y. S. Chun, Tetra-
hedron: Asymmetry 1999, 10, 1843; c) N. J. Gilmore, S. Jones, Tetrahedron: Asymmetry 2003, 14,
2115.
[
8] a) J. M. Brunel, M. Maffei, G. Buono, Tetrahedron: Asymmetry 1993, 4, 2255; b) G. B. Stone, Tetra-
hedron: Asymmetry 1994, 5, 465; c) Y. Z. Jiang, Y. Qin, A. Q. Mi, Chin. Chem. Lett. 1995, 6, 9; d) K.
R. Prasad, N. N. Joshi, Tetrahedron: Asymmetry 1996, 7, 3147; e) V. Santhi, J. M. Rao, Tetrahedron:
Asymmetry 2000, 11, 3553; f) C. E. Garrett, K. Prasad, O. Repic, T. J. Blacklock, Tetrahedron:
Asymmetry 2002, 13, 1347; g) X. Y. Fu, T. L. McAllister, T. K. Thiruvengadam, C. H. Tann, D. Su,
Tetrahedron Lett. 2003, 44, 801; h) R. E. Huertas, J. A. Corella, J. A. Soderquist, Tetrahedron
Lett. 2003, 44, 4435.