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X. Yu, X. Lu / Tetrahedron Letters 52 (2011) 2076–2079
sponding 9-aminofluorene derivatives in moderate to high yield.
Treating the tosylimine 1 with a methyl group at the para or meta
position of the arene moiety also gave the corresponding product
in excellent yield (Table 2, entries 2 and 3). Substrate with a methyl
group at ortho position of the arene gave 2d in a slightly lower 72%
yield probably due to the steric hindrance (Table 2, entry 4). On the
other hand, when the benzene ring was substituted by a methoxy,
a phenyl, a trifluoromethoxy, or a chlorine atom in the para posi-
tion, the reactions go smoothly in all cases (Table 2, entries 5–8).
However, when an electron-withdrawing substituent, such as tri-
fluoromethyl group or a fluorine atom was placed in the para posi-
tion, the reaction also occurred smoothly to give rise to the product
in 88% and 94% yield, respectively (Table 2, entries 9 and 10). These
results illustrated the catalytic reactions showed high substrates
tolerance, affording a series of diverse in general excellent yields.
To broaden the applicability and scope of the present reaction,
o-heterocycle substituted N-tosylbenzaldimines were tested. The
results were shown in Scheme 2. When thiophene was used as
the heteroaromatic nucleophile, the reaction provided the addition
product 2n in 88% yield after 12 h. While using the furan as the
corresponding heteroaromatic moiety, the substrate decomposed
at 80 °C or room temperature probably due to the strong coordina-
tion of the Cu(OTf)2 with oxygen atom.
In addition, under the appropriate reaction conditions, the scope
of the methodology was investigated with other substituted N-
tosylimines in order to give access to a series of novel derivatives.
The experiments were illustrated in Scheme 3. Disappointingly,
no addition product was formed under the optimized reaction con-
ditions with the substrate 1p. However, when using 1q as the reac-
tant, the product 3q was obtained in 40% yield without any 9-amino
derivative. A chaÀnge of counterions of the copper(II) Lewis acid
from TfOÀ to ClO4 gave the same product. Combined with the re-
sults of substrate 1o in Scheme 2, it was supposed that the more Le-
wis basic oxygen atom in the substrates might coordinate with the
copper catalyst giving the product in lower yield.
Acknowledgments
We thank the National Basic Research Program of China
(2009CB825300), National Natural Science Foundation of China
(20732005), and Chinese Academy of Sciences for financial support.
Supplementary data
Supplementary data (experimental procedures and data for
products) associated with this article can be found, in the online
References and notes
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NHTs
NTs
Cu(OTf)2 (10 mol %)
toluene, 80 o
C
X
X
1n
2n
, 88%
2o, 0%
, X=S
1o, X=O
Scheme 2. Cu(OTf)2 catalyzed reaction of o-heterocycle substituted
N-tosylbenzaldimines.
NTs
Cu(OTf)2 (10 mol %)
no product
toluene, 80 oC
1p
11. Fan, C.; Xu, J.; Chen, W.; Dong, B. J. Phys. Chem.
C 2008, 112, 12012–
O
O
.
NTs
Cu(OTf)2 or Cu(ClO4)2 6H2O
12017.
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(10 mol %)
toluene, 80 oC
O
1q
3q
40%
Scheme 3. The reaction of other N-tosylbenzaldimines.