4
Tetrahedron Letters
Supplementary Material
H 2 N
CH 2
Ag 2 CO 3
O
N
N
O
N
Spectral and analytical data including the H NMR and 13 C
1
(2.0 equiv.)
H
H
+
H
H
Ag
1,4-dioxane
O
O
O
Ag
NMR spectra of all compounds given in Table 2 were given in
the Supplementary Section. Crystallographic data of the
compound 2l (CCDC 1011536) also been deposited at the
Cambridge Crystallographic Database Centre and these data can
O
Ag
C
B
O
OAg
1a
(1.5 mmol) (1 mmol)
1b
A
[Ag] I
N
O
1,4-dioxane
50 ºC, 8 hrs
(I)
N
H
[Ag] I . [Ag] I
O
2a
D
D
References and notes
CHO
O
(II) Hydrolysis
H 2
+
O
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O
3a
1a
Scheme 3. Extended experiments with 9,10-phenanthra-
quinone , 1a and benzylamine, 1b .
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Although, a stoichiometric amount of Ag 2 CO 3 was employed
in reaction course, the silver species after the reaction was re-
synthesized simply by filtration and treating with nitric acid
followed by Na 2 CO 3 (Scheme 4). 3a The regenerated Ag 2 CO 3
(yield 82%) was also successfully reused in the C(sp 3 )-H
functionalization followed by oxidative C-O coupling reaction
between 9,10-phenanthraquinone, 1a and benzylamine, 1b under
the standard reaction condition with almost similar activity
(Scheme 5).
2005 , 127 , 6968-6969 .
HNO 3
Na 2 CO 3
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Ag salts
AgNO 3
Ag 2 CO 3
Scheme 4. Regeneration experiment of Ag 2 CO 3 .
H 2 N
Recyclized Ag 2 CO 3
(2.0 equiv.)
O
O
N
O
+
solvent, temp
12 hrs
2a
1a
(1.5 mmol)
1b
(1 mmol)
Isolated yield: 86%
Scheme 5. Reaction between 9,10-phenanthraquinone, 1a
and benzylamine, 1b with recyclized Ag 2 CO 3 .
3. Conclusion
In summary, we have successfully developed a highly
efficient silver (I) mediated C(sp 3 )-H functionalization of primary
amines followed by cyclization through oxidative C-O coupling
to form the the 2,4.5-triaryl oxazole derivatives as well as 2-
alkyl-4,5-diaryl oxazole derivatives. The studied reaction has
been also demonstrated a straightforward and practical route for
construction of the significantly diverse 2,4,5-trisubstituted
oxazoles, in good to excellent yields. In this reaction protocol, we
have successfully utilized electron-rich as well as electron
deficient benzyl amines and aliphatic primary amines to construct
the 2,4,5- trisubstituted oxazole derivatives. The significant
features of this methodology include its operational simplicity
and recyclability of the silver (I) salt, makes the protocol more
general and acceptable.
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Acknowledgments
One of the authors (RS) thanks the Council of Scientific and
Industrial Research (CSIR), New Delhi, for his fellowship (SRF).
We also thank the CAS Instrumentation Facility, University of
Calcutta for the spectral data.