Journal of the American Chemical Society
COMMUNICATION
Scheme 4
Jimꢀenez-Nꢀu~nez, E.; Bu~nuel, E.; Cꢀardenas, D. J.; Echavarren, A. M.
Chem.—Eur. J. 2006, 12, 1694–1702. (c) Jimꢀenez-Nꢀun~ez, E.; Raducan,
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of gold(I) carbenes to react with alkenes in cyclopropanation
reactions.
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We expected that a retro-Buchner reaction of (trans-2,3-
diphenylcyclopropyl)cyclohepta-1,3,5-triene (1l) would gener-
ate cyclopropyl gold(I) carbene 9, which could evolve to
cyclobutene 1027 and subsequently (E,E)-11 by thermal con-
rotatory opening (Scheme 4).28 However, reaction of 1l with
catalyst A led exclusively to (Z,Z)-11. This surprising result
suggests that intermediate 9 evolves by a mechanism analogous
to the skeletal rearrangement of 1,6-enynes,29 bypassing the
formation of cyclobutene 10.
In summary, we have found that cationic Au(I) complexes
promote the retro-Buchner reaction of 1,3,5-cycloheptatrienes to
form substituted gold(I) carbenes that can be trapped by alkenes
in a new cyclopropanation reaction. 1,2,3-Trisubstituted cyclo-
propanes, which are not easily prepared by other methods, can
be synthesized from 1,2-substituted alkenes and readily available
7-substituted 1,3,5-cycloheptatrienes as a safe alternative to the
use of explosive diazo compounds.
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’ ASSOCIATED CONTENT
S
Supporting Information. Additional data, experimental
b
details, characterization data, and crystallographic data (CIF).
This material is available free of charge via the Internet at http://
pubs.acs.org.
’ AUTHOR INFORMATION
(15) Albeck, M.; Tamari, T.; Sprecher, M. J. Org. Chem. 1983, 48,
2276–2278.
(16) For the formation of benzyl-Rh(II) from cycloheptatrienyl-
Rh(I) by a metalloradical process, see: Chan, Y. W.; Chan, K. S. Chem.
Commun. 2011, 47, 4802–4804.
Corresponding Author
’ ACKNOWLEDGMENT
(17) The reaction of 7-ethynylcyclohepta-1,3,5-triene with trifluo-
roacetic acid gives phenylallene by protonation of the alkyne in the
norcaradiene tautomer followed by cyclopropane cleavage to form
the arenium cation. See: (a) Kitagawa, T.; Kamada, J.; Minegishi, S.;
Takeuchi, K. Org. Lett. 2000, 2, 3011–3013. (b) Minegishi, S.; Kamada,
J.; Takeuchi, K.; Komatsu, K.; Kitagawa, T. Eur. J. Org. Chem. 2003,
3497–3504.
(18) 2-Ethoxyethylidene carbene has been generated by photoche-
mical cleavage of a cyclopropanated phenanthrene. See: Graves, K. S.;
Thamattoor, D. M.; Rablen, P. R. J. Org. Chem. 2011, 76, 1584–1591.
(19) (a) Phenyldiazomethane is explosive at room temperature and
should be stored between À20 and À80 °C under N2 or Ar. See: Creary,
X. Org. Synth. 1986, 64, 207–216. (b) Electron-rich p-methoxyphenyl-
diazomethane is shock-sensitive and can detonate. It slowly decomposes
at À80 °C. See: Closs, G. L.; Moss, R. A. J. Am. Chem. Soc. 1964, 86,
4042–4053.
We thank the MICINN (CTQ2010-16088/BQU, Consolider
Ingenio 2010 Grant CSD2006-0003, and FPI Predoctoral Fel-
lowship to C.R.S.-A.), the AGAUR (2009 SGR 47), and the ICIQ
Foundation for financial support.
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