Organic Letters
Letter
(7) Only three reports of enantioselective organocatalytic Michael
additions to α-alkyl nitroalkenes are available (a) Han, Y.; Zheng, B.;
Peng, Y. Adv. Synth. Catal. 2015, 357, 1136. (b) Kimmel, K. L.;
Weaver, J. D.; Lee, M.; Ellman, J. A. J. Am. Chem. Soc. 2012, 134, 9058.
(c) Zheng, B.; Wang, H.; Han, Y.; Liu, C.; Peng, Y. Chem. Commun.
2013, 49, 4561. For stoichiometric reactions of preformed α-
nitrostyrene with achiral enamines, see: (d) Bradamante, P.; Pitacco,
G.; Risaliti, A.; Valentin, E. Tetrahedron Lett. 1982, 23, 2683.
(e) Benedetti, F.; Drioli, S.; Nitti, P.; Pitacco, G.; Valentin, E.
ARKIVOC 2001, v, 140.
ASSOCIATED CONTENT
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S
* Supporting Information
The Supporting Information is available free of charge on the
Experimental methods and spectroscopic data for all
(8) (a) Kunetsky, R. A.; Dilman, A. D.; Struchkova, M. I.;
Tartakovsky, V. A.; Ioff, S. L. Tetrahedron Lett. 2005, 46, 5203.
AUTHOR INFORMATION
(b) Lese
Commun. 1973, 38, 459.
́
̌ ́
ticky, L.; Fidler, V.; Prochazka, M. Collect. Czech. Chem.
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Corresponding Author
(9) For application in the conjugate additions of thiols, see: Baricordi,
N.; Benetti, S.; Bertolasi, V.; De Risi, C.; Pollini, G. P.; Zamberlan, F.;
Zanirato, V. Tetrahedron 2012, 68, 208.
Notes
(10) Nitroacetate 2a was prepared by acetylation of the nitro alcohol,
which was obtained by reaction of the corresponding epoxide with
NaNO2 employing a modification of the reported method, see: Borah,
J. C.; Gogoi, S.; Boruwa, J.; Barua, N. C. Synth. Commun. 2005, 35,
873. Nitroacetates 2b and 2c were prepared by acetylation of the
corresponding nitro alcohols. These were obtained by hydroxymethy-
lation of the respective aryl nitromethanes. See the Supporting
(11) (S)-Proline, (1R,2R)-1,2-diphenylethylenediamine, and (S)-3-
methyl-N-(pyrrolidin-2-ylmethyl)butan-1-amine also provided 4a but
in lower yield and with lower ee as compared to 3. (1R,2S)-Ephedrine
summary of the optimization studies.
(12) Pansare, S. V.; Pandya, K. J. Am. Chem. Soc. 2006, 128, 9624.
(13) The enantiomeric excess of the minor diastereomers is typically
low (50−55% ee). Treatment of pure 4a (92% ee) with catalyst 3 (20
mol %) in the presence of ketone 1 (5 equiv) did not result in any loss
of enantiomeric excess of 4a under the conditions employed for the
Michael addition. The minor diastereomer could not be detected in
this reaction mixture. These observations suggest that the Michael
adduct 4a does not revert back to 1 and the nitroalkene and also that
the minor diastereomer is not obtained by epimerization of the major
diastereomer under the reaction conditions.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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These investigations were supported by the Natural Sciences
and Engineering Research Council of Canada and the Canada
Foundation for Innovation. We thank Dr. Hilary A. Jenkins,
McMaster University, for X-ray crystallography of the nitro-
ketone 4a.
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