Organic Letters
Letter
(4) For earlier computational evaluation of ketene−alkene [2 + 2]
cycloadditions, see: (a) Wang, X.; Houk, K. N. J. Am. Chem. Soc. 1990,
112, 1754. (b) Bernardi, F.; Bottoni, A.; Robb, M. A.; Venturini, A. J.
Am. Chem. Soc. 1990, 112, 2106. (c) Valenti, E.; Pericas, M. A.;
Moyano, A. J. Org. Chem. 1990, 55, 3582. (d) Salzner, U.; Bachrach, S.
M. J. Org. Chem. 1996, 61, 237.
In summary, we have provided both experimental and
computational data that support the proposed pathway for
diastereoselectivity. Subsequent studies will be directed toward
utilizing this knowledge for future iterations of reaction
development.
(5) Wang, Y.; Wei, D.; Li, Z.; Zhu, Y.; Tang, M. J. Phys. Chem. A
2014, 118, 4288.
(6) (a) Tantillo, D. J. J. Phys. Org. Chem. 2008, 21, 561−570.
(b) Williams, A. Concerted Organic and Bio-Organic Mechanisms; CRC
Press: Boca Raton, FL, 2000.
ASSOCIATED CONTENT
* Supporting Information
Experimental data, computational data, and analytical data. This
material is available free of charge via the Internet at http://
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S
(7) (a) Ussing, B. R.; Hang, C.; Singleton, D. A. J. Am. Chem. Soc.
2006, 128, 7594−7607. (b) Gonzalez-James, O. M.; Kwan, E. E.;
Singleton, D. A. J. Am. Chem. Soc. 2012, 134, 1914−1917.
(c) Pemberton, R. P.; Hong, Y. J.; Tantillo, D. J. Pure Appl. Chem.
2013, 85, 1949−1957.
AUTHOR INFORMATION
Corresponding Authors
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(8) Wei, Tang and co-workers also invoke steric effects in
rationalizing the diastereoselectivity for the 5 + 6 reaction (see ref 5).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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We gratefully acknowledge support from UC Davis and the
National Science Foundation (CHE-030089 for computer time
via the XSEDE program). Indiana University is also acknowl-
edged for generous financial support.
REFERENCES
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(1) (a) Rasik, C. M.; Brown, M. K. J. Am. Chem. Soc. 2013, 135, 1673.
For a review, see: (b) Rasik, C.; Brown, M. Synlett 2014, 25, 760.
(2) For excellent reviews, see: (a) Snider, B. B. Chem. Rev. 1988, 88,
793−811. (b) Hyatt, J. A.; Raynolds, P. W. Organic Reactions; Wiley:
New York, NY, 1994. (c) Tidwell, T. T. Ketenes; Wiley: New York,
NY, 1995. (d) Tidwell, T. T. Ketenes II; Wiley-Interscience: Hoboken,
NJ, 2006. (e) Tidwell, T. T. Eur. J. Org. Chem. 2006, 563−576.
(f) Danheiser, R. L. Science of Synthesis: Compounds with Four and
Three Carbon Heteroatom Bonds, Vol. 23; Georg Thieme Verlag KG:
Germany, 2006. (g) Allen, A. D.; Tidwell, T. T. Chem. Rev. 2013, 113,
7287.
(3) Calculations were performed with GAUSSIAN09 (Frisch, M. J. et
al.; full reference in Supporting Information). Geometries were
optimized using the B3LYP and M06-2X methods with the 6-
31G(d) basis set, and all stationary points were characterized as
minima or transition state structures using frequency calculations at
the same level: (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652.
(b) Becke, A. D. J. Chem. Phys. 1993, 98, 1372−1377. (c) Lee, C.;
Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785−789. (d) Stephens, P.
J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994,
98, 11623−11627. (e) Zhao, Y.; Truhlar, D. Theor. Chem. Acc. 2008,
120, 215−241 (this method provides a better treatment of dispersion).
Intrinsic reaction coordinate (IRC) calculations were used for further
characterization of transition state structures: (f) Gonzalez, C.;
Schlegel, H. B. J. Phys. Chem. 1990, 94, 5523−5527. (g) Fukui, K.
Acc. Chem. Res. 1981, 14, 363−368.
Free energies in solution
(toluene (120 °C) and CH2Cl2 (−78 °C) in the absence and presence
of the Lewis acid, respectively) are computed using the integral
equation formalism variant (IEFPCM) with the SMD solvation
method: (h) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. J. Phys.
Chem. B 2009, 113, 6378−6396. Reported free energies are relative to
that of the separate reactants (alkene + ketene for thermal condition
and alkene + Lewis acid−ketene complex for the Lewis acid promoted
reaction). Images of computed structures are created with Ball & Stick:
(i) Muller, N.; Falk, A.; Gsaller, G. Ball & Stick V.4.0a12, molecular
̈
graphics application for MacOS computers; Johannes Kepler University:
Linz, 2004. MeAlCl2 was used as the model Lewis acid. M06-2X results
are described in the text; see Supporting Information for B3LYP
results.
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