Organic Letters
Letter
Notes
Scheme 3. Cu(I)−NHC Catalyzed Asymmetric Silyl Transfer
a
to N-Tosyl α,β-Unsaturated Amides
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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We thank The Leverhulme Trust (V.P.) and the EPSRC (J.P.R.)
for funding and Robyn Bullough (University of Manchester) for
assistance optimizing the conversion of 1−2.
REFERENCES
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a
Yields are for isolated products.
oxiracetam, a nootropic drug employed in the treatment of
diseases related to Alzheimer’s.22
Thus, lactam 2, the product of Cu(I)−NHC asymmetric silyl
transfer, underwent efficient removal of the N-tosyl group upon
treatment with SmI2 (Scheme 4).23 The resulting N-H lactam 7
(3) Xu, L.-W.; Li, L.; Lai, G.-Q.; Jiang, J.-X. Chem. Soc. Rev. 2011, 40,
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Scheme 4. Asymmetric Synthesis of (R)-Oxiracetam
(5) (a) Matsumoto, Y.; Hayashi, T.; Ito, Y. Tetrahedron 1994, 50, 335.
(b) Hayashi, T.; Matsumoto, Y.; Ito, Y. J. Am. Chem. Soc. 1988, 110,
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underwent N-alkylation to give 8 in 74% yield. Subsequent
oxidation under Fleming−Tamao conditions24 gave (R)-
oxiracetam (αD = +34.2 (c = 1.0, H2O); lit. + 36.4 (c = 1.0,
H2O))22 in 78% yield (Scheme 4).
In summary, the first Cu(I)−NHC catalyzed asymmetric silyl
transfer from PhMe2SiBpin to unsaturated lactams and amides
gives the corresponding β-silylated lactams and amides in good
yields and enantioselectivities. While C2-symmetric NHC ligands
give the best results for 5-membered lactams and acyclic amides,
C1-symmetric NHC ligands work best for 6- and 7-membered
lactam substrates. The protocol has been exploited in a short
asymmetric synthesis of (R)-oxiracetam.
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For asymmetric allylic silylation using a Cu(I)−NHC system and
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́
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Lett. 2007, 9, 3187.
ASSOCIATED CONTENT
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S
* Supporting Information
Experimental procedures, characterization data, H and 13C
1
spectra. This material is available free of charge via the Internet at
AUTHOR INFORMATION
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dx.doi.org/10.1021/ol4033623 | Org. Lett. 2014, 16, 476−479