Angewandte
Chemie
the addition, and the solution was concentrated under vacuum by
using standard techniques to prevent the exposure of the borane to
the open atmosphere. The residue was washed with pentane (6
10 mL), and the extracts were filtered through a celite pad. The
filtrate was concentrated to afford 2 in essentially quantitative yield.
The compounds (Æ )-2 were also prepared by a similar procedure
from (Æ )-B-MeO-10-TMS-9-BBD.
[2] a) E. Canales, K. G. Prasad, J. A. Soderquist, J. Am. Chem. Soc.
2005, 127, 11572; b) E. Canales, E. Hernandez, J. A. Soderquist,
J. Am. Chem. Soc. 2006, 128, 8712; c) E. Hernandez, C. H.
Burgos, E. Alicea, J. A. Soderquist, Org. Lett. 2006, 8, 4089.
[3] A. Z. Gonzalez, E. Canales, J. A. Soderquist, Org. Lett. 2006, 8,
3331.
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J. Am. Chem. Soc. 1990, 112, 878.
Synthesis of 1: Trimethylsilyldiazomethane (4 mmol, 2m in
hexanes) was added dropwise to a solution of 2 (2.9 mmol) in
pentane (5 mL) at room temperature. After 3 h (11B NMR (pentane):
d = 78 ppm), concentration of the mixture gave 1 in quantitative yield.
Representative procedure: A solution of 1 (2.9 mmol) in THF
(10 mL) was cooled to À788C, PrCHO (2.7 mmol) was added
dropwise, and the mixture was stirred for 3 h. Oxidative workup:
After the mixture had warmed to 258C, a phosphate buffer solution
(pH 7.2, 10 mL) was added dropwise. Aqueous NaOH (2.0 mL, 3m)
and H2O2 (0.9 mL, 30%) dropwise were also added, and the mixture
was heated at reflux for 2 h. It was then extracted with brine (3
20 mL), and the organic phase was dried over MgSO4 and filtered.
The product was purified by column chromatography on silica gel
(hexane/ether/NEt3 95:4:1) to give 7b (0.48 g, 90%). Workup with
pseudoephedrine: After warming to 258C, the mixture was concen-
trated in vacuo to give the borinate 5, which was dissolved in CH3CN
(7 mL). (1R, 2R)-Pseudoephedrine was added, and the mixture was
refluxed for 12 h, then cooled slowly to provide crystalline (À)-(S)-6.
The crystals were washed with pentane (3 5 mL) and dried under
vacuum to give (À)-(S)-6 (0.86 g, 80%). The supernatant was then
purified by column chromatography on silica gel (hexane/ether/NEt3
95:4:1) to afford 7b (0.48 g, 90%).
[6] a) W. R. Roush, P. T. Grover, X. Lin, Tetrahedron Lett. 1990, 31,
7563; b) W. R. Roush, A. N. Pinchuk, G. C. Micalizio, Tetrahe-
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[8] A. Alexakis, S. Mutti, P. Mangeney, J. Org. Chem. 1992, 57, 1224.
[9] The 10-Ph analogue of (Æ )-2b was prepared. It reacted
vigorously with TMSCHN2 to give two diastereomeric silyl
allenyl boranes (13C NM R: d = 216.3 and 216.4 ppm). These
boranes underwent addition to PrCHO to give 7 f, the 13C NM R
spectrum of which contained an additional set of alkynyl,
O-methinyl, and TMS signals relative to that of 7 f formed from
(Æ)-1b. The 31P NMR spectrum of the corresponding ester
derivatives formed by the protocol of Alexakis et al.[8] contained
additional signals for the esters derived from anti-7 f (d = 85.4,
86.6 ppm) which are completely absent in the spectrum of the
esters formed from syn-7 f derived from (Æ )-1b (d = 85.9,
86.3 ppm). The formation of enantiomeric rather than diaste-
reomeric alcohols is puzzling. We can only speculate that they
may be formed from an open transition state.
Received: August 24, 2006
Published online: December 5, 2006
[10] P. F. Hudrlik, A. M. Hudrlik, A. K. Kulkarni, J. Am. Chem. Soc.
1982, 104, 6809.
Keywords: asymmetric synthesis · boranes · borotropic
rearrangement · cumulenes · homopropargylic alcohols
.
[11] a) T. Yoshida, R. M. Williams, E. Negishi, J. Am. Chem. Soc.
1974, 96, 3688; b) E. Negishi, T. Yoshida, A. Abramovitch, G.
Lew, R. M. Williams, Tetrahedron 1991, 47, 343; c) K. K. Wang,
B. Liu, Y. Lu, J. Org. Chem. 1995, 60, 185; d) H.-F. Chow, X.-P.
Cao, M.-K. Leung, J. Chem. Soc. Perkin Trans. 1 1995, 193; e) H.
Kleijn, M. Tigchelaar, R. J. Bullee, C. J. Elsevier, J. Meijer, P.
Vermeer, J. Organomet. Chem. 1992, 440, 329; see also: f) I.
Saito, K. Yamaguchi, R. Nagata, E. Murahashi, Tetrahedron Lett.
1990, 31, 7469.
[1] a) C. H. Burgos, E. Canales, K. Matos, J. A. Soderquist, J. Am.
Chem. Soc. 2005, 127, 8044; b) C. Lai, J. A. Soderquist, Org. Lett.
2005, 7, 799; c) E. Hernandez, J. A. Soderquist, Org. Lett. 2005,
7, 5397; see also: d) M. L. Maddess, M. Lautens, Org. Lett. 2005,
7, 3557; e) E. Hernandez, E. Canales, E. Gonzalez, J. A.
Soderquist, Pure Appl. Chem. 2006, 78, 1389.
Angew. Chem. Int. Ed. 2007, 46, 397 –399
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