Journal of the American Chemical Society
Communication
Soc. 2002, 124, 7982. (d) Aechtner, T.; Dressel, M.; Bach, T. Angew.
radical intermediates as catalyst-bound adducts. The surprising
stability of these noncovalent complexes allows them to
effectively serve as a basis for asymmetric induction in a
subsequent C−C bond-forming step. We anticipate that these
features of PCET activation will be transferable to other substrate
classes and transformations, providing new opportunities for the
further development of catalytic asymmetric radical chemistry.
Chem., Int. Ed. 2004, 43, 5849. (e) Bauer, A.; Westkamper, F.; Grimme,
̈
S.; Bach, T. Nature 2005, 436, 1139. (f) Muller, C.; Bauer, A.; Bach, T.
̈
Angew. Chem., Int. Ed. 2009, 48, 6640. (g) Muller, C.; Bauer, A.; Maturi,
M. M.; Cuquerella, M. C.; Miranda, M. A.; Bach, T. J. Am. Chem. Soc.
2011, 133, 1668.
̈
(8) For a discussion of the energetic role of precursor and successor H-
bonds in bimolecular PCET reactions, see: Mader, E. A.; Mayer, J. M.
Inorg. Chem. 2010, 49, 3685.
ASSOCIATED CONTENT
* Supporting Information
(9) For a recent review on reductive couplings of ketones and imine
derivatives, see: Burchak, O. N.; Py, S. Tetrahedron 2009, 65, 7333.
(10) For selected examples, see: (a) Corey, E. J.; Pyne, S. G.
Tetrahedron Lett. 1983, 24, 2821. (b) Sturino, C. F.; Fallis, A. G. J. Am.
Chem. Soc. 1994, 116, 7447. (c) Sturino, C. F.; Fallis, A. G. J. Org. Chem.
1994, 59, 6514. (d) Tormo, J.; Hays, D. S.; Fu, G. C. J. Org. Chem. 1998,
201. For chiral auxiliary approaches: (e) Zhong, Y.-W.; Dong, Y.-Z.;
Fang, K.; Izumi, K.; Xu, M.-H.; Lin, G.-Q. J. Am. Chem. Soc. 2005, 127,
11956. (f) Wang, B.; Wang, Y.-J. Org. Lett. 2009, 11, 3410.
(11) Selected examples of aza-pinacol reactions in synthesis:
(a) Nicolaou, K. C.; Hao, J.; Reddy, M.; Rao, P.; Rassias, G.; Snyder,
S.; Huang, X.; Chen, D.; Brenzovich, W.; Giuseppone, N.; Giannakakou,
P.; O’Brate, A. J. Am. Chem. Soc. 2004, 126, 12897. (b) Riber, D.; Hazell,
R.; Skrydstrup, T. J. Org. Chem. 2000, 65, 5382.
■
S
Experimental procedures, characterization data, computational
data, and crystallographic data (CIF). This material is available
AUTHOR INFORMATION
Corresponding Author
■
Notes
The authors declare no competing financial interest.
(12) For a recent example of catalytic asymmetric ketyl reactivity, see:
Streuff, J.; Feurer, M.; Bichovski, P.; Frey, G.; Gellrich, U. Angew. Chem.,
Int. Ed. 2012, 51, 8661.
(13) For a review of enantioselective radical chemistry, see: Sibi, M. P.;
Manyem, S.; Zimmerman, J. Chem. Rev. 2003, 103, 3263.
(14) Lowry, M. S.; Goldsmith, J. I.; Slinker, J. D.; Rohl, R.; Pascal, R. A.;
Malliaras, G. G.; Bernhard, S. Chem. Mater. 2005, 17, 5712.
(15) Zhu, X.; Li, H.; Li, Q.; Ai, T.; Lu, J.; Yang, Y.; Cheng, J. Chem.
Eur. J. 2003, 9, 871.
ACKNOWLEDGMENTS
■
We acknowledge LeeAnn Love for the preparation of catalyst ent-
8, Benjamin Liu for preliminary experiments, and Phil Jeffrey for
X-ray crystallographic analysis. The MacMillan group is
acknowledged for the generous use of their analytical
instrumentation. Financial support was provided by Princeton
University and the American Chemical Society Petroleum
Research Fund (52252-DNI).
(16) Fukuzumi, S.; Ishikawa, K.; Hironaka, K.; Tanaka, T. J. Chem. Soc.,
Perkin Trans. 2 1987, 751.
REFERENCES
■
(17) This value is based on a calculated ketyl O−H BDFE of 26 kcal/
mol and a formal BDFE of 29.1 for the IrII(ppy)2(dtbpy)/phosphoric
acid PCET pair. For details on the use of formal BDFE values in
determining PCET thermochemistry, see: (a) Waidmann, C. R.; Miller,
A. J. M.; Ng, C. A.; Scheuermann, M. L.; Porter, T. R.; Tronic, T. A.;
Mayer, J. A. Energy Environ. Sci. 2012, 5, 7771. (b) Reference 3.
(18) See Supporting Information for thermochemical cycle used in
calculating the potential of the HEH radical.
(19) Storer, R.; Carrera, D.; Ni, Y.; MacMillan, D. W. C. J. Am. Chem.
Soc. 2006, 128, 84.
(20) See Supporting Information for details.
(21) pKa of hydrazone estimated by NMR methods in MeCN-d3. See
Supporting Information for details.
(22) (a) Kalia, J.; Raines, R. T. Angew. Chem., Int. Ed. 2008, 47, 7523.
(b) More O’Ferrall, R. A.; O’Brien, D. J. Phys. Org. Chem. 2004, 17, 631.
(23) (a) Friestad, G. K. Tetrahedron 2001, 57, 5461. (b) Reference 9c.
(1) For recent reviews, see: (a) Teply, F. Collect. Czech. Chem.
́
Commun. 2011, 76, 859. (b) Tucker, J. W.; Stephenson, C. R. J. J. Org.
Chem. 2012, 77, 1617. (c) Prier, C. K.; Rankic, D. A.; MacMillan, D. W.
C. Chem. Rev. 2013, 113, 5322. (d) Yoon, T. P. ACS Catal. 2013, 3, 895.
(2) (a) Nicewicz, D. A.; MacMillan, D. W. C. Science 2008, 322, 77.
(b) Nagib, D. A.; Scott, M. E.; MacMillan, D. W. C. J. Am. Chem. Soc.
2009, 131, 10875. (c) Shih, H.-W.; Vander Wal, M. N.; Grange, R. L.;
MacMillan, D. W. C. J. Am. Chem. Soc. 2010, 132, 13600. (d) DiRocco,
D. A.; Rovis, T. J. Am. Chem. Soc. 2012, 134, 8094. (e) Pirnot, M. T.;
Rankic, D. A.; Martin, D. B.; MacMillan, D. W. C. Science 2013, 339,
1593. (f) Cecere, G.; Konig, C. M.; Alleva, J. L.; MacMillan, D. W. C. J.
̈
Am. Chem. Soc. 2013, 135, 11521. (g) Bergonzini, G.; Schindler, C.;
Wallentin, C.-J.; Jacobsen, E. N.; Stephenson, C. R. J. Chem. Sci. 2013,
DOI: 10.1039/C3SC52265B.
(3) Tarantino, K. T.; Liu, P.; Knowles, R. R. J. Am. Chem. Soc. 2013,
135, 10022.
(24) Kutt, A.; Leito, I.; Kaljurand, I.; Soovali, L.; Vlasov, V. M.;
̈
(4) (a) Weinberg, D. R.; Gagliardi, C. J.; Hull, J. F.; Murphy, C. F.;
Kent, C. A.; Westlake, B. C.; Paul, A.; Ess, D. H.; McCafferty, D. G.;
Meyer, T. J. Chem. Rev. 2012, 112, 4016. (b) Mayer, J. M. Annu. Rev.
Phys. Chem. 2004, 55, 363. (c) Reece, S. Y.; Nocera, D. G. Annu. Rev.
Biochem. 2009, 78, 673. (d) Reece, S. Y.; Hodgkiss, J. M.; Stubbe, J.;
Nocera, D. G. Phil. Trans. R. Soc. London, Ser. B 2006, 361, 1351.
(e) Meyer, T. J.; Huynh, M. H. V.; Thorp, H. H. Angew. Chem., Int. Ed.
2007, 46, 5284. (f) Stubbe, J.; Nocera, D. G.; Yee, C.; Chang, M. Chem.
Rev. 2003, 103, 2167. (g) Kaila, V. R. I.; Verkhovsky, M. I.; Wikstrom, M.
Chem. Rev. 2010, 110, 7062. (h) Hatcher, E.; Soudachov, A.; Hammes-
Schiffer, S. J. Am. Chem. Soc. 2004, 126, 5763.
(5) Rueping, M.; Nachtsheim, B. J.; Ieawsuwan, W.; Atodiresei, I.
Angew. Chem., Int. Ed. 2011, 50, 6706.
Yagupolskii, L. M.; Koppel, I. A. J. Org. Chem. 2006, 71, 2829.
(25) It is plausible that a bifurcated H-bond between the neutral ketyl,
phosphate, and hydrazone nitrogen may also be operative in the
addition transition state. Efforts to evaluate this possibility are ongoing.
For examples of H-bond activation in asymmetric radical additions to
imine derivatives, see: (a) Cho, D. H.; Jang, D. O. Chem. Commun. 2006,
5045. (b) Kim, S. Y.; Kim, S. J.; Jang, D. O. Chem.Eur. J. 2010, 16,
13046.
̈
(26) Preliminary kinetic studies indicate that product inhibition in the
model reaction is not significant. We tentatively attribute this
observation to diminished basicity resulting from intramolecular H-
bonding between the alcohol and hydrazine functionalities in the
product.
(6) pKa value obtained from a known reduction potential of −2.48 V vs
Fc and a calculated O−H bond dissociation free energy (CBS-QB3) of
26 kcal/mol. For details, see ref 3.
(7) (a) Curran, D. P.; Kuo, L. H. J. Org. Chem. 1994, 59, 3259.
(b) Bach, T.; Bergmann, H.; Harms, K. Angew. Chem., Int. Ed. 2000, 39,
2302. (c) Bach, T.; Bergmann, H.; Grosch, B.; Harms, K. J. Am. Chem.
D
dx.doi.org/10.1021/ja4100595 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX