C O M M U N I C A T I O N S
questions. Further studies of these transformations may lead to new
paths for developing efficient C-H activation methodologies and
a better understanding of both gold chemistry and C-N bond
formation processes.
Acknowledgment. This research was supported by the Alfred
P. Sloan Foundation and the University of Chicago.
Supporting Information Available: Experimental details and
supplemental figures. This material is available free of charge via the
Internet at http://pubs.acs.org.
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Figure 1. Amination of benzylic C-H groups catalyzed by AuCl3 and
a 1
isotope labeling experiments. H NMR ratio and conversion.
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performed with 1,3,5-triisopropylbenzene and a stoichiometeric
3 4 2
amount of AuCl in CCl . The reaction was quenched with D O
1
after several hours and analyzed by H NMR, which showed
disappearance of proton signal from both the aromatic and benzylic
(
e) Chanda, B. M.; Vyas, R.; Bedekar, A. V. J. Org. Chem. 2001, 66,
9
positions (eq 5, Figure 1). These results suggest activation of the
3
0-34. (f) Lebel, H.; Huard, K. Org. Lett. 2007, 9, 639-642. (g) A very
benzylic protons by gold(III), resulting in H-D scrambling.
We propose a mechanism (Scheme 1) to account for the observed
recent paper on intramolecular activation of aromatic C-H bonds with
acrylate azides: Stokes, B, J.; Dong, H.; Leslie, B. E.; Pumphrey, A. L.;
Driver, T. G. J. Am. Chem. Soc. 2007, 129, 7500-7501.
reactivity pattern. First, the arylgold(III) species is generated from
(6) (a) Thu, H.-Y.; Yu, W.-Y.; Che, C.-M. J. Am. Chem. Soc. 2006, 128,
3
the reaction of AuCl
3
and an aromatic C-H bond. PhIdNNs is
9
048-9049. (b) Chen, X.; Hao, X. S.; Goodhue, C. E.; Yu, J. Q. J. Am.
then activated by interaction with the gold(III) center. This
Chem. Soc. 2006, 128, 6790-6791.
activiation leads to attack on the carbon of the arylgold(III) species
resulting in product and the formation of AuCl . This mechanism
3
(7) (a) D ´ı az-Requejo, M. M.; Belderra ´ı n, T. R.; Carmen-Nicasio, M.;
Trofimenko, S.; P e´ rez, P. J. J. Am. Chem. Soc. 2003, 125, 12078-12079.
(
b) Fructos, M. R.; Trofimenko, S.; D ´ı az-Requejo, M. M.; P e´ rez, P. J. J.
helps to explain the unique chemoselectivity of this reaction;
formation of the arylgold(III) species is key and required for the
selective aromatic C-H nitrene insertion. In the presence of very
weak benzylic C-H bonds, our isotope experiment (eq 5) suggests
that gold(III) displaces a weak benzylic proton to form a carbon-
gold(III) bond, which subsequently undergoes the nitrene insertion
Am. Chem. Soc. 2006, 128, 11784-11791.
(
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(
9) After mesitylene-d12 was treated with a stoichiometeric amount of AuCl
in CCl at room temperature for several hours the reaction was quenched
3
4
with water. We detected the H-D exchange for both aromatic and benzylic
protons with exchange predominantly occurring on the aromatic position.
We then tested triisopropylbenzene and quantified the H-D exchange
(Scheme 1). Arylgold(III) may form first before gold(III) migrates
to the benzylic position. Formations of benzylic-gold species are
known and have been reported in the past.10 Although other
mechanistic possibilities cannot be excluded at this time, our
1
ratio by H NMR. Please see Supporting Information for details.
(
10) (a) Bennett, M. A.; Hoskins, K.; Kneen, W. R.; Nyholm, R. S.; Mason,
R.; Hitchcock, P. B.; Robertson, G. B.; Towl, A. D. C. J. Am. Chem.
Soc. 1971, 93, 4592-4593. (b) Parish, R. V. Gold Bull. 1997, 30, 3-12.
experiments suggest that a nearby aromatic C-H is required for
the benzylic C-H amination to occur.11
(11) We prepared pentamethylisopropylbenzene in a 1:1 mixture with pen-
tamethylbenzene. This mixture was subjected to the amination reaction,
and the benzylic insertion for the fully substituted pentamethylisopropy-
lbenzene was not detected. Also, 1,4-diisopropylbenzene only gave trace
amount of products.
In closing, we report here a gold-catalyzed nitrene insertion into
aromatic and benzylic C-H bonds at room temperature. Currently,
this chemistry has a narrow scope limited to simple arenes, but the
unique activity and chemoselectivity present intriguing mechanistic
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