ORGANIC
LETTERS
2010
Vol. 12, No. 21
4772-4775
B(C6F5)3-Promoted Tandem Silylation
and Intramolecular Hydrosilylation:
Diastereoselective Synthesis of
Oxasilinanes and Oxasilepanes
Roman Shchepin,† Chunping Xu,† and Patrick Dussault*
Department of Chemistry, UniVersity of Nebraska-Lincoln, Lincoln,
Nebraska 68588-0304, United States
Received August 10, 2010
ABSTRACT
B(C6F5)3 promotes regio- and stereoselective cyclizations of unsaturated alkoxysilanes to generate oxasilinanes and oxasilepanes. The same
products are available directly from alkenols via tandem silylation and hydrosilylation.
Intramolecular hydrosilylation of alkenes is an important
transformation in organic synthesis.1 Initially investigated
for unsaturated silanes,2 the methodology is now often
applied to unsaturated alkoxy- and aminosilanes,3 where
stereospecific oxidative cleavage of the newly formed C-Si
bond enables stereodefined synthesis of diols and aminoal-
cohols.4,5 The majority of examples involve metal-catalyzed
5-endo or 5-exo ring closures, although six-membered
cyclizations have been reported.1,3,6 We now report regio-
and stereoselective formation of oxasilinanes and oxas-
ilepanes via formation and cyclization of unsaturated alkox-
ysilanes in the presence of a nonmetal catalyst.
In the course of investigations into the influence of Lewis
acids on the ozonolysis of unsaturated silanes, we found that
addition of B(C6F5)3 to a solution of unsaturated alkoxysilane
1-Pr resulted in regioselective formation of oxasilinane 2-Pr
with high 3,5-trans diastereoselectivity (Table 1).7,8 The
cyclization proceeded efficiently at -78 °C or rt and in the
presence of either stoichiometric or catalytic B(C6F5)3.
Cyclization was also observed for the dimethylsilyl ether (not
shown),9 but the hydrolytic instability of this class of
† These authors contributed equally to this work.
(1) (a) Yamamoto, K.; Hayashi, T. In Transition Metals for Organic
Synthesis, 2nd ed.; Beller, M., Bolm, C., Eds.; Wiley-VCH: Weinheim,
2004; pp 167-191. (b) Marciniec, B. In Hydrosilylation: A ComprehensiVe
ReView on Recent AdVances; Marciniec, B., Ed.; Springer: New York, 2009;
pp 3-51.
(6) Cyclizations to form six- or seven-membered rings: (a) Widenhoefer,
R. A. Acc. Chem. Res. 2002, 35, 905. (b) Xin, S.; Harrod, J. F. J. Organomet.
Chem. 1995, 499, 181. (c) DeCamp, A. E.; Mills, S. G.; Kawaguchi, A. T.;
Desmond, R.; Reamer, R. A.; DiMichele, L.; Volante, R. P. J. Org. Chem.
1991, 56, 3564. (d) Sibi, M. P. e-EROS Encyclopedia of Reagents for
Organic Synthesis; John Wiley & Sons: New York, 2001. (e) Widenhoefer,
R. A.; Krzyzanowska, B.; Webb-Wood, G. Organometallics 1998, 17, 5124.
(7) Reviews of B(C6F5)3: (a) Piers, W. E. AdV. Organomet. Chem. 2005,
(2) Benkeser, R. A.; Mozden, E. C.; Muench, W. C.; Roche, R. T.;
Siklosi, M. P. J. Org. Chem. 1979, 44, 1370.
(3) Varchi, G.; Ojima, I. Curr. Org. Chem. 2006, 10, 1341.
(4) See, for example: (a) Mak, S. Y. F.; Curtis, N. R.; Payne, A. N.;
Congreve, M. S.; Francis, C. L.; Burton, J. W.; Holmes, A. B. Synthesis
2005, 3199. (b) Li, F.; Roush, W. R. Org. Lett. 2009, 11, 2932
.
(5) Oxidative cleavage: (a) Jones, G. R.; Landais, Y. Tetrahedron 1996,
52, 7599. (b) Smitrovich, J. H.; Woerpel, K. A. J. Org. Chem. 1996, 61,
52, 1. (b) Erker, G. Dalton Trans. 2005, 1883.
(8) Stereochemical assignments are based upon 3JH couplings, NOE
correlations, and a literature correlation for diol 21.
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10.1021/ol1018757 2010 American Chemical Society
Published on Web 10/04/2010