ORGANIC
LETTERS
2005
Vol. 7, No. 24
5397-5400
Nonracemic
Asymmetric Propargylation with the
10-Trimethylsilyl-9-borabicyclo[3.3.2]decanes†
Eliud Hernandez and John A. Soderquist*
r-Allenyl Carbinols from
UniVersity of Puerto Rico, Department of Chemistry,
Rio Piedras, Puerto Rico 00931-3346
Received August 5, 2005
ABSTRACT
The asymmetric propargylboration of aldehydes at
−78 °C in <3 h with 1 provides silylated r-allenyl carbinols 6 (60−87%) in high ee (94% to
>98% ee). The reagents 1 are easily prepared in both enantiomeric forms with a simple Grignard procedure and air-stable borinate complexes
2. The ozonolysis of 6 proceeds smoothly through an acylsilane intermediate to give a TMS ester, which is hydrolyzed to the
quantitatively with water.
r-hydroxy acid
The asymmetric propargylboration of aldehydes provides a
convenient route to nonracemic R-allenyl carbinols. The first
successful asymmetric propargylboration was accomplished
by Corey with 1,3,2-diazaborolanes prepared through Sn/B
exchange and 1,3-transposition with allenyltributyltin.1 These
proved to be highly effective and enantioselective reagents
for the asymmetric synthesis of these useful alcohols.2
phenomenon was elegantly utilized by Wang, who took
advantage of the steric bulk of the trimethylsilyl (TMS) group
to prepare γ-silylated propargylboranes cleanly free of allen-
ylic impurities.4 This route to R-allenyl carbinols was later
developed by Brown into a second effective asymmetric pro-
cess using his diisopinocampheylborane reagents ((Ipc)2B-
CH2CtCTMS).5 Moreover, the R-TMS group in the prod-
ucts can be easily removed to provide the parent R-allenyl
carbinols. Compared to alternative routes,6 the propargylbo-
ration process is unrivaled in convenience and selectivity.
However, issues that could be addressed with new systems
include (1) a more direct route to the reagents through simple
Grignard procedures avoiding other organometallic interme-
diates, (2) the use of air-stable precursors to simplify the
experimental operations, and (3) the inclusion of effective
recovery procedures to recycle the chiral borane moiety. The
The racemic version of propargylboration was first re-
ported by Zweifel.3 He clearly demonstrated the use of
substitution to control propargyl- versus allenylboration under
either kinetic or thermodynamic reaction conditions. This
† This work is belatedly dedicated to Professor Elias J. Corey on the
occasion of his 77th birthday.
(1) Corey, E. J.; Yu, C.-M.; Lee, D.-H. J. Am. Chem. Soc. 1990, 112,
878.
(2) (a) Friesen, R. W.; Giroux, A. Tetrahedron Lett. 1993, 34, 1867. (b)
Friesen, R. W.; Kolaczewska, A. E. J. Org. Chem. 1991, 56, 4888. (c)
Marshall, J. A.; Pinney, K. G. J. Org. Chem. 1993, 58, 7180. (d) Friesen,
R. W.; Blouin, M. J. Org. Chem. 1993, 58, 1653. (e) Lautens, M.; Delanghe,
P. H. M. J. Org. Chem. 1993, 58, 5037. (f) Corey, E. J.; Jones, G. B.
Tetrahedron Lett. 1991, 32, 5713. (g) Yoneda, E.; Zhang, S.-W.; Zhou,
D.-Y.; Onitsuka, K.; Takahashi, S. J. Org. Chem. 2003, 68, 8571. (h) ,
Friesen, R. W.; Blouin, M. J. Org. Chem. 1996, 61, 7202.
(3) Zweifel, G.; Backlund, S. J.; Leung, T. J. Am. Chem. Soc. 1978,
100, 5561.
(4) (a) Wang, K. K.; Nikam, S. S.; Ho, C. D. J. Org. Chem. 1983, 48,
5376. (b) Wang, K. K.; Liu, C. J. Org. Chem. 1985, 50, 2578.
(5) (a) Brown, H. C.; Khire, U. R.; Narla, G. J. Org. Chem. 1995, 60,
8130. (b) Kulkarni, S. V.; Brown, H. C. Tetrahedron Lett. 1996, 37, 4125.
(6) (a) Marshall, J. A.; Adams, M. D. J. Org. Chem. 1997, 62, 8976. (b)
Nakajima, M.; Saito, M.; Hashimoto, S. Tetrahedron: Asymmetry 2002,
13, 2449. (c) Yu, C.-M.; Yoon, S. K.; Back, K.; Lee, J.-Y. Angew. Chem.,
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10.1021/ol051886k CCC: $30.25
© 2005 American Chemical Society
Published on Web 11/04/2005