Journal of the American Chemical Society
Communication
Figure 3. Calculated reaction pathway of the H-bond directed organocatalytic formal [2 + 2]-cycloaddition. Energies are reported in kcal/mol and
are relative to the energy of the reactant complex, A. Bond distances are reported in Å.
́
(8) (a) Bertelsen, S.; Marigo, M.; Brandes, S.; Diner, P.; Jørgensen, K.
ASSOCIATED CONTENT
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A. J. Am. Chem. Soc. 2006, 128, 12973. (b) Bench, B. J.; Liu, C.; Evett,
C. R.; Watanabe, C. M. H. J. Org. Chem. 2006, 71, 9458. (c) Hong, B.-
C.; Wu, M.-F.; Tseng, H.-C.; Huang, G.-F.; Su, C.-F.; Liao, J.-H. J. Org.
S
* Supporting Information
Screening results, experimental procedures, analytical data,
computational details, NMR spectra, and HPLC traces. This
material is available free of charge via the Internet at http://
Chem. 2007, 72, 8459. (d) de Figueiredo, R. M.; Frohlich, R.;
̈
Christmann, M. Angew. Chem., Int. Ed. 2008, 47, 1450.
(9) (a) Li, J.-L.; Kang, T.-R.; Zhou, S.-L.; Li, R.; Wu, L.; Chen, Y.-C.
Angew. Chem., Int. Ed. 2010, 49, 6418. (b) Li, J.-L.; Zhou, S.-L.; Han,
B.; Wu, L.; Chen, Y.-C. Chem. Commun. 2010, 46, 2665.
(c) Bergonzini, G.; Vera, S.; Melchiorre, P. Angew. Chem., Int. Ed.
AUTHOR INFORMATION
■
2010, 49, 9685. (d) Stiller, J.; Marques
́
-Lop
́
ez, E.; Herrera, R. P.;
Corresponding Author
Frohlich, R.; Strohmann, C.; Christmann, M. Org. Lett. 2011, 13, 70.
̈
(10) For recent reviews on H-bonding catalysis, see: (a) Storer, R. I.;
Notes
́
Aciro, C.; Jones, L. H. Chem. Soc. Rev. 2011, 40, 2330. (b) Aleman, J.;
The authors declare no competing financial interest.
Parra, A.; Jiang, H.; Jørgensen, K. A. Chem.Eur. J. 2011, 17, 6890.
For the first application of squaramide-based catalysts in asymmetric
synthesis, see: (c) Malerich, J. P.; Hagihara, K.; Rawal, V. H. J. Am.
Chem. Soc. 2008, 130, 14416.
ACKNOWLEDGMENTS
■
This work was supported by Aarhus University, FNU
and the Carlsberg Foundation. C.R.-E. thanks the Generalitat
de Catalunya for a Beatriu de Pinos postdoctoral fellowship.
́
F.C.A. thanks CSIC for a predoctoral JAE grant. Dr. Jacob
Overgaard is acknowledged for performing X-ray analysis.
(11) Recently, formal organocatalytic [2 + 2]-cycloaddition between
enamines and nitroolefins has been identified as an undesired reaction
pathway leading to catalyst inhibition. For details, see: (a) Patora-
Komisarska, K.; Benohoud, M.; Ishikawa, H.; Seebach, D.; Hayashi, Y.
́
Helv. Chim. Acta 2011, 94, 719. (b) Bures, J.; Armstrong, A.;
Blackmond, D. G. J. Am. Chem. Soc. 2011, 133, 8822.
(12) For reviews on biologically active and naturally occurring
cyclobutanes, see: (a) Dembitsky, V. M. J. Nat. Med. 2008, 62, 1.
(b) Sergeiko, V. V.; Hanus, L. O.; Dembitsky, V. M. Open Med. Chem.
J. 2008, 2, 26.
(13) Calculations were performed with GAUSSIAN09. Geometries
were optimized without symmetry constraints at the M06-2X/6-
31G(d) level of theory ( Zhao, Y.; Truhlar, D. Theor. Chem. Acc. 2008,
120, 215) in the gas phase. See Supporting Information for the
complete references on theoretical methods.
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