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Table 2 Oxidation of several methylquinolines (1b–f) with dioxygena
NHPI + NO Æ PINO + HNO
2 2
(1)
(2)
(3)
(4)
(5)
Run Substrate Catalystb Methodc Conv. (%)d Product Yield (%)d
R − CH + PINO → R − CH ⋅+NHPI
3
2
1
2
3
4
5
6
7
a
1b
1b
1c
1c
1d
1e
1f
A
B
A
C
A
A
A
D
D
E
E
E
D
D
42 (0)
70 (0)
98(21)
65 (0)
89(67)
75(35)
40 (2)
2b
2b
2c
2c
2d
2e
2f
32 (0)
64 (0)
R − CH ⋅+O →→ R − COOH
2
2
87 (10)
61 (0)
81 (50)
60 (26)
35 ( < 1)
HNO Æ1/3 HNO +1/3 H O + 2/3 NO
2
3
2
NO +1/2 O → NO2
2
Substrate (2 mmol) was allowed to react with O
2
in the presence of catalyst
(2 mol%), Mn(OAc)
(10 mol%); B: NHPI (10 mol%) NO (30 mol %); C:
(1 atm), 110 °C, 15 h; E: Air (20
atm), 150 °C, 5 h. The number in parenthesis shows the conversion or
yield in the reaction without NO
This work was partially supported by a Grant-in-Aid for
Scientific Research (S) from the Ministry of Education, Culture,
Sports and Technology (MEXT), Japan.
b
in AcOH (5 mL). A: NHPI (20 mol%), Co(OAc)
0.1 mol%), NO
NHPI (20 mol%) NO
2
2
(
2
2
c
2
(10 mol%). D: O
2
d
2
.
Notes and references
†
A typical reaction was carried out as follows: To a solution of NHPI (0.1
mmol) and transition metal salts in AcOH (5 mL) were added 1a (1 mmol)
and NO (0.1 mmol, using a Hamilton gas-tight syringe). The flask was
equipped with a balloon filled with O (1 atm). The mixture was stirred at
Next, the oxidation of 2-methylquinoline (1b) was run (Table
). No reaction took place under 1 atm of O at 110 °C in the
absence of NO . Although the oxidation of 1a occurred under
0 atm of air without NO , the oxidation of 1b was difficult
under these conditions. However, when 10 mol% of NO was
added to the reaction system, the oxidation furnished 2-quinoli-
necarboxylic acid (2b) in 32% yield (Run 1). Surprisingly, the
oxidation of 1b was efficiently promoted by NHPI in the
2
2
2
2
2
1
10 °C for 15 h.
2
2
1
J. P. Michael, Nat. Prod. Rep., 1997, 14, 605; G. Jones, in
Comprehensive Heterocyclic Chemistry II, eds. A. R. Katritzky, C. W.
Rees and E. F. V. Scriven, Pergamon Press, Oxford, 1996, Vol. 5,
2
1
67–243.
J. N. Kim, H. J. Lee, K. Y. Lee and H. S. Kim, Tetrahedron Lett., 2001,
2, 3737; K. Kobayashi, R. Nakahashi, A. Shimizu, T. Kitamura, O.
2
presence of NO
2
2
without any metal salt. Treatment of 1b with
in the absence
4
O
(1 atm) under the influence of NHPI and NO
2
Morikawa and H. Konishi, J. Chem. Soc., Perkin Trans. 1, 1999, 1547,
and references cited therein.
3 C. K. Cain, J. N. Plampin and J. Sam, J. Org. Chem., 1955, 20, 466.
of any metal salt produced 2b in 64% yield (Run 2). It is
important to note that no nitrated products were formed. This
finding provides a new aerobic oxidation system of methylqui-
nolines by NHPI without the use of a transition metal catalyst.
Other methylquinolines (1c–f) used were successfully oxidized
4
5
6
D. W. Ladner, Synth. Commun., 1986, 16, 157.
S. Paraskewas, Synthesis, 1974, 819.
To the best of our knowledge, there is only one patent work on the
aerobic oxidation of methylquinolines in the presence of KOH: A. N.
Christyakov and L. M. Titov, USSR Pat. 457,701, 1975.
A. Shibamoto, S. Sakaguchi and Y. Ishii, Org. Process. Res. Dev., 2000,
2 2
by the NHPI–Co–Mn–NO or NHPI–NO systems giving the
corresponding carboxylic acids in moderate to good yields.
7
A plausible reaction pathway for the oxidation by the NHPI–
4
, 505.
NO
2
system is outlined in Eqns (1)–(5). It is possible to assume
8 Y. Ishii, S. Sakaguchi and T. Iwahama, Adv. Synth. Catal., 2001, 343,
393.
that the reaction would be initiated by the hydrogen abstraction
from NHPI by NO to form PINO and HNO [Eqn. (1)]. The
PINO thus formed abstracts the hydrogen atom from the methyl
group of the substrate to produce R-CH · (R- = quinolyl-) and
NHPI [Eqn. (2)]. The R-CH · is readily trapped by O affording
9 S. Sakaguchi, Y. Nishiwaki, T. Kitamura and Y. Ishii, Angew. Chem.,
Int. Ed., 2001, 40, 222.
0 Recently, we have shown that NAPI acts as an efficient catalyst for the
aerobic oxidation of p-xylene and requires a lower catalyst loading than
NHPI: Y. Tashiro, T. Iwahama, S. Sakaguchi and Y. Ishii, Adv. Synth.
Catal., 2001, 343, 220.
2
2
1
1
2
2
2
a peroxy radical which is eventually converted into the
corresponding carboxylic acid [Eqn. (3)]. On the other hand,
1 S. Isozaki, Y. Nishiwaki, S. Sakaguchi and Y. Ishii, Chem. Commun.,
2 3 2
may be converted into HNO , H
O and NO [Eqn. (4)].12
HNO
The resulting NO was oxidized with O
is reused for the formation of PINO from NHPI [Eqn. (5)].
2
001, 1352.
2
to generate NO
2
, which
12 K. Jones, in Comprehensive Inorganic Chemistry, ed. A. F. Trotman-
Dickenson, Pergamon Press, New York, 1973, pp. 147-388.
CHEM. COMMUN., 2002, 180–181
181
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