10.1002/ejoc.201800809
European Journal of Organic Chemistry
COMMUNICATION
A gram-scale reaction of 1d afforded 2d in 88% yield when 5
mol % of catalyst was added. When the catalyst loading
decreased to 3 mol %, 2d was obtained in a slight lower yield
(eq 2). The Boc group was easily removed when 2d was
subjected to LiBr or HCl conditions. Especially when 2d was
treated with HCl in ethyl acetate (EA), 2e was obtained in nearly
quantitative yield (95%, eq 3).
(GK201703022) are greatly appreciated. We thank Xuetong Li
for reproducing the preparation of 2d, 2j and 2p (Scheme 2).
Keywords: gold catalysis • diazo compounds • dimerization •
isoindigo • coupling
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Boc
O
N
N2
XPhosAuCl/AgPF6
CH3CN, rt.
O
(2)
N
N
Boc
O
Boc
2d
1d
0.8177 g, 88% yield (5 mol % catalyst)
0.7489 g, 81% yield (3 mol % catalyst)
1.037 g (4 mmol)
Boc
H
O
O
N
N
Conditions
(3)
N
N
O
O
[2]
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Boc
H
2d
2e
Condition A: LiBr (3 equiv), CH3CN, 65 oC, 5 h, 76% yield
Condition B: HCl, EA, rt, 6 h, 95% yield
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Conclusions
In conclusion, a highly efficient gold-catalyzed dimerization of 3-
diazooxindoles was developed. The reaction shows its
advantage in rapid construction of various substituted isoindigos
in gram-scale under mild conditions. Taking the importance of
isoindigos into account, the reaction shows its potent application
in both pharmaceuticals and material science.
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Experimental Section
General procedure for the gold-catalyzed dimerization of 3-
Diazooxindoles
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3-Diazooxindole (0.3 mmol) was added successively to
a stirring
suspension of XPhosAuCl (10.6 mg, 15.0 µmol) and AgPF6 (3.8 mg, 15.0
µmol) in acetonitrile (3.0 mL) at room temperature. The solution was then
stirred at room temperature for 12 hours. After evaporation, the residue
was purified by column chromatography on silica gel (dichloromethane
was used as the eluting solvent) affording the desired product.
(E)-1,1'-Dibenzyl-[3,3'-biindolinylidene]-2,2'-dione (2a)[17] : Yield: 75%, 1H
NMR (CDCl3, 400 MHz): δ = 9.23 (d, 2 H, J = 7.8 Hz), 7.33-7.25 (m, 12
H), 7.04 (t, 2 H, J = 7.8 Hz), 6.71 (d, 2 H, J = 7.8 Hz), 5.02 (s, 4 H) ppm.
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Acknowledgements
Financial support by the National Natural Science Foundation of
China (21502110, 21542002), the 111 Project (B14041) and the
Fundamental Research Funds for the Central Universities
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