Y. Matsumura et al. / Tetrahedron Letters 45 (2004) 8221–8224
8223
+
-
NaNO2
+
2CF CO H
NO CF CO
+
CF CO Na
2
+ H O
3
2
3
2
3
2
O2-. + H+
O2
NO+
HNO
OH
OH
O
NO+
- H+
-
H+
1
a
3
a
3a'
H
O
N
O
N
OH
O
O
O
HO
HO
N
H2O
C
A
B
O2-. + H+
O2
NO+
O
HNO
O
HO
O
HO
H2O
OH
CHO
- H+
-
NH2OH
2
a
D
Scheme 1. Plausible mechanism for oxidation of cyclohexanol (1a) by NANO
2
in CF
3
CO
2
H.
In order to clarify the reaction mechanism, oxidation of
1
The method presented herein is very promising from a
practical viewpoint for oxidation of alcohols since the
reaction conditions are mild, yields are high, sodium
nitrite is a very cheap oxidizing reagent, and most of tri-
fluoroacetic acid can be recovered. Further application
of this method to other organic compounds than alco-
hols is now under investigation.
a to 2a was carried out under an atmosphere of oxygen,
air, and nitrogen, respectively. The results are shown in
Table 3.
Under an atmosphere of nitrogen, 4equiv of NaNO2
were necessary to complete the conversion of 1a to 2a
(
a mixture of 2a and 3a (entries 3 and 4), and the use
of less than 1equiv of NaNO resulted in formation of
2
entry 5), while the use of 2 or 3equiv of NaNO gave
2
References and notes
cyclohexyl trifluoroacetate (4a) and/or recovery of some
amount of 2a (entries 1 and 2). Aerobic atmosphere con-
dition improved the efficiency of NaNO as an oxidant
1
2
. (a) Smith, J. R. L.; Loeppky, R. N. J. Am. Chem. Soc.
1967, 89, 1147–1157; (b) Olah, G. A.; Ho, T.-L. Synthesis
1976, 609–610; (c) Olah, G. A.; Ho, T.-L. Synthesis 1976,
610–611.
2
(
than 1equiv of NaNO completed the conversion of 1a
entries 6–8), and under an oxygen atmosphere more
2
. (a) Ho, T.-L.; Olah, G. A. J. Org. Chem. 1977, 42, 3097–
098; (b) Olah, G. A.; Shih, J. G.; Singh, B. P. J. Org.
Chem. 1983, 48, 3356–3358.
to 2a (entries 10 and 11), suggesting a regeneration of
NO by oxidation of HNO with the oxygen atom, while
3
+
a mixture of 2a and 3a was formed by a half equivalent
of NaNO under an oxygen atmosphere (entry 9).
3. (a) Rogi c´ , M.; Vitrone, J.; Swerdloff, M. D. J. Am. Chem.
Soc. 1975, 97, 3848–3850; (b) Shiue, C.-Y.; Clapp, L. D. J.
Org. Chem. 1971, 36, 1169–1170; (c) Rogi c´ , M.; Vitrone,
J.; Swerdloff, M. D. J. Am. Chem. Soc. 1977, 99, 1156–
1171.
2
On the basis of these results and the reported mecha-
nism for the nitric acid oxidation of 1a, we pro-
pose a plausible mechanism for the oxidation of 1a to 2a
8a,10b,d,e
4
. (a) Tovrog, B. S.; Diamond, S. E.; Mares, F.; Szalkiewicz,
A. J. Am. Chem. Soc. 1981, 103, 3522–3526; (b) Nyarady,
S. A.; Sievers, R. E. J. Am. Chem. Soc. 1985, 107, 3726–
by NaNO in CF CO H as shown in Scheme 1, where
2
2
3
1
1
intermediates A–D may be involved. The fact that
more than 1equiv of NaNO was necessary for the com-
3727; (c) Nishiguchi, T.; Asano, F. J. Org. Chem. 1989, 54,
1531–1535.
2
pletion of the oxidation of 1a to 2a suggests a consump-
tion of 1equiv of NaNO as hydroxylamine, though
hydroxylamine was not detected.
5
. Cornelis, A.; Laszlo, P. Synthesis 1985, 909–918.
2
6. Bandgar, B. P.; Sadavarte, V. S.; Uppalla, L. S. J. Chem.
Soc., Perkin Trans. 1 2000, 3559–3560.