Organic Letters
Letter
proposed to occur through a PdII/PdIV catalytic cycle involving a
concerted migration−fluorination process to furnish the final
product. Further mechanistic research is in progress by our group
to examine details of the reaction.
16354. (c) Yuan, Z.; Wang, H.; Mu, X.; Chen, P.; Guo, Y.; Liu, G. J. Am.
Chem. Soc. 2015, 137, 2468. (d) He, Y.; Yang, Z.; Thornbury, R. T.;
Toste, F. D. J. Am. Chem. Soc. 2015, 137, 12207.
(8) For selected C−CF3 bond constructions via high-valent palladium
catalysis, see: (a) Mu, X.; Wu, T.; Wang, H.; Guo, Y.; Liu, G. J. Am.
Chem. Soc. 2012, 134, 878. (b) Zhang, L.; Chen, K.; Chen, G.; Li, B.;
Luo, S.; Guo, Q.; Wei, J.; Shi, Z. Org. Lett. 2013, 15, 10.
(9) Boontanonda, P.; Grigg, R. J. Chem. Soc., Chem. Commun. 1977, 583.
(10) For selected examples of the anchimeric assistance of the phenyl
group in Wagner−Meerwein rearrangement, see: (a) Cram, D. J. J. Am.
Chem. Soc. 1949, 71, 3863. (b) Geary, G. C.; Hope, E. G.; Stuart, A. M.
Angew. Chem., Int. Ed. 2015, 54, 14911.
ASSOCIATED CONTENT
* Supporting Information
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S
The Supporting Information is available free of charge on the
Detailed experimental procedures and characterization
data for all new compounds (PDF)
X-ray data for compound 2a (CIF)
(11) See ref 2d−f and references cited therein.
(12) For selected reports of C−H activation at PdIV, see: (a) Hull, K.
L.; Lanni, E. L.; Sanford, M. S. J. Am. Chem. Soc. 2006, 128, 14047.
(b) Rosewall, C. F.; Sibbald, P. A.; Liskin, D. V.; Michael, F. E. J. Am.
Chem. Soc. 2009, 131, 9488. (c) Wang, X.; Leow, D.; Yu, J. Q. J. Am.
Chem. Soc. 2011, 133, 13864. For a recent review, see ref 2a.
(13) Compounds 2a and 2a′ were also speculated to form via a
pathway in Scheme S16 in the SI, see (a) Ilchenko, N. O.; Tasch, B. O.;
X-ray data for compound 8 (CIF)
AUTHOR INFORMATION
Corresponding Authors
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Notes
́
Szabo, K. J. Angew. Chem., Int. Ed. 2014, 53, 12897. (b) Reference 10b.
(14) When substrate 3a or 3j was subjected to the control experiment in
the absence of Pd catalyst, product 4a′ (36%) or 4j′ (77%) was obtained
as the major product along with some polymerization products.
(15) A similar reaction involving different conditions was reported
The authors declare no competing financial interest.
recently; see: Ulmer, A.; Brunner, C.; Arnold, A. M.; Pothig, A.; Gulder,
T. Chem. - Eur. J. 2016, 22, 3660.
̈
ACKNOWLEDGMENTS
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We are grateful for financial support bythe National Natural
Science Foundation ofChina (21332005, 21472085) and program
A for outstanding PhD candidates of Nanjing University.
(16) For selected examples, see: (a) Winstein, S.; Morse, B. K.;
Grunwald, E.; Schreiber, K. C.; Corse, J. J. Am. Chem. Soc. 1952, 74,
1113. (b) Brown, H. C.; Kim, C. J. J. Am. Chem. Soc. 1968, 90, 2082. In
some cases, 1,2-alkyl shift was more favorable over 1,2-aryl shift to form a
́
́
more stable carbocation transition state, see: (c) Gutierrez-Bonet, A.;
REFERENCES
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Flores-Gaspar, A.; Martin, R. J. Am. Chem. Soc. 2013, 135, 12576.
(17) For a similar reaction analogous to formation of 6, see: Matsuura,
B. S.; Condie, A. G.; Buff, R. C.; Karahalis, G. J.; Stephenson, C. R. J. Org.
Lett. 2011, 13, 6320.
(1) Negishi, E., Ed. Handbook of Organopalladium Chemistry for
Organic Synthesis; Wiley: New York, 2002; Vols. 1−2.
(2) For reviews on high valent palladium complex, see: (a) Topczewski,
J. J.; Sanford, M. S. Chem. Sci. 2015, 6, 70. (b) Bonney, K. J.;
Schoenebeck, F. Chem. Soc. Rev. 2014, 43, 6609. (c) Hickman, A. J.;
Sanford, M. S. Nature 2012, 484, 177. (d) Sehnal, P.; Taylor, R. J. K.;
Fairlamb, I. J. S. Chem. Rev. 2010, 110, 824. (e) Xu, L.; Li, B.; Yang, Z.;
(18) It also corresponds to the general observation that weak
coordinating nucleophiles prefer anti nucleophilic palladation to olefins.
See: McDonald, R. I.; Liu, G.; Stahl, S. S. Chem. Rev. 2011, 111, 2981 and
references cited therein.
(19) Previous reports showed that configurational retention of C−F
bond-forming reductive elimination from the F−PdIV complex was
observed. However, a SN2-type reductive elimination may also operate
during the process, which causes the decline of ee or dr values;
see: Emer, E.; Pfeifer, L.; Brown, J. M.; Gouverneur, V. Angew. Chem., Int.
Ed. 2014, 53, 4181. (b) See ref 7b.
Shi, Z. Chem. Soc. Rev. 2010, 39, 712. (f) Muniz, K. Angew. Chem., Int. Ed.
̃
2009, 48, 9412. (g) Canty, A. J. Acc. Chem. Res. 1992, 25, 83.
(3) For selected stoichiometric studies on reductive elimination
behavior of PdIV complex, see: (a) Dick, A. R.; Kampf, J. W.; Sanford, M.
S. J. Am. Chem. Soc. 2005, 127, 12790. (b) Whitfield, S. R.; Sanford, M. S.
J. Am. Chem. Soc. 2007, 129, 15142. (c) Ball, N. D.; Sanford, M. S. J. Am.
Chem. Soc. 2009, 131, 3796. (d) Ball, N. D.; Kampf, J. W.; Sanford, M. S.
J. Am. Chem. Soc. 2010, 132, 2878. (e) Furuya, T.; Benitez, D.;
Tkatchouk, E.; Strom, A. E.; Tang, P.; Goddard, W. A., III; Ritter, T. J.
Am. Chem. Soc. 2010, 132, 3793. (f) Lee, E.; Kamlet, A. S.; Powers, D. C.;
Neumann, C. N.; Boursalian, G. B.; Furuya, T.; Choi, D. C.; Hooker, J.
M.; Ritter, T. Science 2011, 334, 639.
(4) For selected stoichiometric studies on reductive elimination
behavior of bimetallic PdIII complex, see: (a) Powers, D. C.; Ritter, T.
Nat. Chem. 2009, 1, 302. (b) Powers, D. C.; Geibel, M. A. L.; Klein, J. E.
M. N.; Ritter, T. J. Am. Chem. Soc. 2009, 131, 17050. (c) Powers, D. C.;
Benitez, D.; Tkatchouk, E.; Goddard, W. A., III; Ritter, T. J. Am. Chem.
Soc. 2010, 132, 14092.
(5) β-Elimination, including β-carbon elimination and β-H elimi-
nation, is inhibited for the PdIV complex. See ref 2d,e,g and references
cited therein.
(6) For selected C-heavy halogen bond constructions via high valent
palladium catalysis, see: (a) Giri, R.; Chen, X.; Yu, J. Q. Angew. Chem.,
Int. Ed. 2005, 44, 2112. (b) Kalyani, D.; Sanford, M. S. J. Am. Chem. Soc.
2008, 130, 2150. (c) Yin, G.; Liu, G. Angew. Chem., Int. Ed. 2008, 47,
5442. (d) Kalyani, D.; Satterfield, A. D.; Sanford, M. S. J. Am. Chem. Soc.
2010, 132, 8419.
(20) Substrate 1a with stoichiometric Pd(OAc)2 in the absence of
Selectfluor resulted almost no reaction (Table 1, entry 6). It suggests the
tBu group leaving should occur after the oxidation step.
(21) The migration should proceed anti-periplanar to metal, analogous
́
́
to the Baeyer−Villiger reaction: (a) Cardenas, R.; Cetina, R.; Lagunez-
Otero, J.; Reyes, L. J. Phys. Chem. A 1997, 101, 192. (b) Okuno, Y. Chem.
- Eur. J. 1997, 3, 212.
(22) The fluorine source may also come from the BF4− counteranion;
see ref 13a.
(23) As far as we know, β-alkyl elimination without an additional
driving force (such as ring strain release) has never been reported for
transition-metal complexes. For relative reviews involving the topic of
transition-metal-mediated β-carbon elimination, see: (a) (a) Jun, C.-H.
Chem. Soc. Rev. 2004, 33, 610. (b) Ruhland, K. Eur. J. Org. Chem. 2012,
2012, 2683. Even for the Wacker process (hydrogen shift), evidence
shows the migration proceeds via 1,2-hydride shift-type mechanism
instead of β-H elimination. See: (c) Mimoun, H.; Charpentier, R.;
Mitschler, A.; Fischer, J.; Weiss, R. J. Am. Chem. Soc. 1980, 102, 1047.
(d) Cornell, C. N.; Sigman, M. S. J. Am. Chem. Soc. 2005, 127, 2796.
Moreover, the evidence that the cyclopropylmethylene group is also able
to migrate without decomposition further excludes this process
(Scheme 2, substrate 1s).
(7) For selected C−F bond constructions via high-valent palladium
catalysis, see: (a) Wang, X. S.; Mei, T. S.; Yu, J. Q. J. Am. Chem. Soc. 2009,
131, 7520. (b) Wu, T.; Yin, G.; Liu, G. J. Am. Chem. Soc. 2009, 131,
D
Org. Lett. XXXX, XXX, XXX−XXX