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Novel oxidative cleavage of carbon—carbon bond in hydrazones by oxygenation with cobalt Schiff base complex
Tetrahedron Letters,Vo1.27,No.23,pp Printed in Great Britain
NOVEL
OXIDATIVE
CLEAVAGE
BY OXYGENATION
Akira
Nishinaga,*
Department
OF CARBON-CARBON
WITH COBALT
Shigekazu
of Synthetic
Yoshida,
0040-4039/86 $3.00 + .OO Pergamon Journals Ltd.
2649-2652,1986
Yamazaki,
Kyoto
IN HYDRAZONES
BASE COMPLEX
and Teruo
Chemistry,
Sakyo-ku,
BOND
SCHIFF
Kyoto
Matsuura
University
606, Japan
Summary: Oxygenation of aromatic ketone hydrazones with Co(salen) in methanol resulted unexpectedly in oxidative degradation to give methyl benzoate derivatives. A mechanism involving nucleophilic attack by methanolon a diazo intermediate is discussed.
Oxygenations capable
of organic
of binding
biological
compounds
dioxygen
oxidations
catalyzed
by metal
complexes
which
are received
much attention in connection synthesis. 1,2 In aprotic solvents,
and organic
(II) Schiff base complexes bind gen carriers, 3,4 while function
dioxygen
reversibly,
as model
dioxygenases
providing
cobalt-
synthetic
when organic
are
with
oxy-
compounds
such as phenols,
flavonols, and indoles are put in the reversible dioxygen 5,6 system. These cobalt(I1) Schiff base complexes are, on the other
binding hand,
oxidized
irreversibly
with molecular
oxygen
in alcohols
giving
rise to
hydroxo-
and alkoxo-cobalt(II1) complexes depending on the acidity of the al7 used. Recently, we reported that the reversible dioxygen binding sys-
cohol
tem using
five coordinate
dehydrogenation
that the oxygenation
oxidized, rise
Schiff
base
results
to alkyl
of aromatic
benzoate
solution
under
solution
(1 mmol)
in methanol
with
romethane
and filtered
complex.
The organic
4.
Ratio
an oxygen
(20 ml)
to give
products
(2 mmol)
dropwise
was dissolved
thus obtained of methyl
on the reaction
the slow addition 2649
After
evaporation
of
of dichlothe metal
by silica
1, ketone
conditions
of 1 as well
a To the 1
to remove
was separated
until
of hydrazone
in a small volume
benzoate
reference
for 30 min).
a solution
silca gel column
giving
in methanol
at room temperature (usually
co-
is irreversibly
are available with of hydrazones. 9
of Co(salen)
atmosphere
a short
depended
four coordiante
of the C-C bond
in 1 h at room temperature.
derivatives
1, in methanol
a planar
was obtained
was added
residue
through
of the products
seen from Table
for
with N,N'-ethylene-
Few reports
a suspension
stirring
the resulting
chromatography
was effective
the complex
cleavage
bond breakdown
of Co 111(salen)(OH)7
resulting
the solvent,
complexes
hydrazones
where
in oxidative
derivatives.
experiment,
ketone
[Co(salen)],
in alcohols,
carbon-carbon
(30 ml) was stirred clear
complex
unexpectedly
to such oxidative In a typical
base
ketone
bis(salicylideneiminato)cobalt(II), balt(II)
Schiff
hydrazones, providing a convenient method of aryldiazoalkanes. 8 In this communication, we wish to
for the synthesis report
cobalt(II)
of aromatic
gel layer
3, and azine
(Table 1).
As
as the higher
2650
02/Co(salen) R'OH,
r-t.
-"9roR
+'q,
NNH2
0
0
-1
-2
)
+
C
b
a
-3 e
d
f
g R : Me Me Me Me Et H H _.. ____..___.~~.____._..-~.____ __...___._~..__ ___ _ __..._.. .__...._~___ x Me0 H H Cl Cl Ph NO, ‘
Table 1
1. Oxygenation
[co]'[~l
of Hydrazones
Addition rate of i(mmol/h) 13
la
0.0
la
0.1
1 by Co(salenja
Solvent
1.0
Product/%
(RIOH)
1
3
4
OOH
MeOH
0
0
100
OMe
MeOH
10
56
27
Me 5
0.5
1.0
MeOH
36
la
1.0 1.0
1.0 _=
MeOH
la
MeOH
la
2.0
1.0
MeOH
64
32
and the substituent
la
2.0
0.5
MeOH
70
28
not affect
la
2.0
0.5
EtOH
30
60
cut ratio.
la
2.0
0.5
i-PrOH
3
81
10
2 also
depended
la
2.0
0.5
t-BuOH
3
66
27
nature
of the solvent.
lb
2.0
0.5
MeOH
73
25
2
lc
2.0
0.5
MeOH
63
24
than methanol
Id
2.0
0.5
MeOH
80
15
tion of the parent
ld
0.5
1.0
MeOH
63
32
2 predominated.
le
2.0
0.5
MeOH
55
33
dative
If lg -
2.0
0.5
MeOH
69
of 1 was observed
2.0
0.5
MeOH
13
19 _d
la
a A solution
of 1 in MeOH(20
wise to a solution MeOH(30 b
noted. added
ml) under
6
56
38
1
ratio
39
48
8
in the higher
ml) was added
of Co(salen)(OH)(2 O2 at r.t. Conv.
d
mm011
[Co]/[l]
Thus,
1(5%)
_d
with
resulted yield
much
where
in
with
on the
cleavage in such as and DMF,
3 was formed
Co(salpr)(OH)7
in meth-
also
with a half amount of Cofsalen) (OH) at a higher addition 5 10 was obtained in 5% yield, and further the oxygenation
Co(salen)(OH)
results
therefore
nately
was quite
of 3.
r
when -Id rate,
of -la These (Table 1).
of the solvent for the present
and coordioxidative
Furthermore, oxygen bubbling through a solution 8 of 1-(4-nitrophenylj-1-diazoethane (6) in methanol containing an equimolar amount
cleavage
Interestingly,
slow to give only compound
suggest that the nucleophilicity III unsaturated Co (OH) species are essential
C-C bond
of 4.
in place
anol resulted
without
along
amount
was oxygenated hydroperoxide
ketone
No oxi-
of Co(salen)(OH) formation
other
the forma-
solvents
a small
of
The use of six coordinate
-la was
Not determined. in the predominant
X did
the prod-
alcohols
dichloromethane
drop-
of 1,
The yield
C-C bond
aprotic
100% otherwise
7% in 72 h. ' Hydrazone
Conv.
at once.
56
reaction.
of Co(salen)(OH)
at room
temperature
for a few minutes
followed
by
2651
pouring the mixture into water gave peroxocobalt(II1) complex 7 as yellow fine 11 which gave hydroperoxide 5 upon treatment with acetic crystals (84% yield), acid or silica gel. In methanol, the diazo compound 6 was stable without Co(salen)(OH), whereas with the cobalt complex under nitrogen was obtained a complex mixture but not a simple product in which methanol was incorporated. On the other hand, compound 6 was oxygenated readily in the presence of Co(salen)(OH) in acetonitrile to give -3d in 94% yield. Therefore, it may be clear that the formation of 7 results from the dioxygen incorporation into 6 in preference to the methanol addition. The peroxo complex 1 was stable against Co(salen)(OH) in methanol, .but decomposed immediately when Co(salen) or hydrazone Id was added to a solution of -7 in methanol under nitrogen to give a (80%) and 3cJ (20%), indicating that 7 is susceptible to one-electron reduction.
From these observations and the fact that 6 is formed from Id at
MeOH, r.t. OOCo(salen) I Co(salen)
N2
1
6
7
t or -Id
-2d
+
-3d
the expense of two equivalents of Co(salen)(OH), 8 the present oxidative cleavage of the C-C bond in 1 is rationalized to proceed by the following mechanism involving the diazo intermediate (Scheme 1).
Actually, in an early stage of
Scheme 1 Ar >C=NNH~ R
Ar, ,OOCom Co ,,OR, "";', C R co=
')
ArCOOR'
+
R.
or _1 8
2
the oxygenation of A, transient appearance of red color due to the diazo intermediate was generally observed. The fate of radical R. in the final step in Scheme 1 under the oxygenation conditions was clearly demonstrated by the oxygenation of cyclic ketone hydrazones. Thus, the oxygenation of 1-tetralone hydrazone (9) with two equivalents of Co(salen)(OH) in methanol gave compounds -10 (27%), 11 (2781, -12 (3%), and the parent ketone (27%).12
Since compound -11 was not formed from
NNH2 -9
-10
11 -
-12
2652
-10 under the reaction conditions, these products should be formed independently from a common intermediate -13 resulting from breakdown of 8' (refer to s in Scheme
1) and dioxygen incorporation followed by reductive or associative q-. decomposition.l' Similarly, the oxygenation of 2-methyl-1-indanone hydrazone
q--pcq”
-
H-
11 -
13 -
-8' (14) gave compounds 34%, and 10% yield,
15, 16, 17, 18, and the parent ---I2 The formation respectively.
ketone
in 12%, 16%, 15%,
of -17 and -18 is rational-
CQ- QMe QMe cTc:oMe c3r GMe NNH2 14 -
-15
ized by assuming a more
stable
the breakdown
benzyl
The present aromatic tivity
2) 3) 4) 5) 6) :; 9) 10)
whereas
in the oxygenation.
References 1)
radical
of alkoxy species
oxygenolysis
ketones,
17 -
16 -
radical
followed
of hydrazones
aliphatic
ketone
The details
18 intermediate
by the further
is characteristic hydrazones
are under
exhibit
current
-13' -13' leading oxidation.
to
for those
of
different
reac-
investigation.
and Notes
Oxidations of Organic ComR. A. Sheldon and J. K. Kochi, "Metal-Catalyzed Francisco, pounds," Academic Press, New York-London-Toronto-Sydney-San 1981, p. 72. H. Mimoun, J. Mol. Catal., 2, 1 (1980). and F. Basolo, Chem. Rev., 2, 139 (1979). R. D. Jones, D. A. Summerville, E. C. Niederhoffer, J. H. Timmons, and A. E. Martell, Chem. Rev., 84, 137 (1984). T. Matsuura, Tetrahedron, 33, 2869 (1977). A. Nishinaga and H. Tomita, J. Mol. Catal., 2, 179 (1980). A. Nishinaga, T. Kondo, and T. Matsuura, Chem. Lett., 1985, 905. A. Nishinaga, S. Yamazaki, and T. Matsuura, Chem. Lett., 1986, in press. E. G. E. Howkins, J. Chem. Cot.(C), 1971, 1474; M. Utaka, Y. Fujita, and A. Takeda, Chem. Lett., 1982, 1607. 1 6 1.58 (s, 3H), 3.40 (s, 3H), Hydroperoxide 5: m.p. 56-57 'C. HNMR(CDC13) 7.66 (d, 2~, J-= 9Hz), 8.17 (d, ZH, J = 9Hz), 8.33 (brd s, lH, OH). Anal. CgHllN05: C, 20.26%; H, kO.028; N, ?0.02%.
11) Complex
7: Anal.
12) Isolated
yield.
C25H24N307Co H20: C, +0.28%; H, *O-07%; N, 20.02%. 1 HNMR(CDC13) for the products are in good agreement
The
with the structures: 10; 1.59-2.13 (m, 2H), 2.43 (brd s, lH, OH), 3.02 (t, 2H, J = 7Hz), 3.57-(t, 2~, J = ~HZ), 3.84 (s, 3H), 6.97-7.97 (m, 4H). 11; 2.76 ((m, 2H), 3.25 (m, ZH), 3.88 (s, 3H), 7.0-8-O (m, 4H), 9.72 (t, m, J = 1Hz). 12; 1.3-2.1 (m, 4H), 2.5-2.9 (m, 8H), 7.0-7.4 (m, 6H), 8.01.26 (d, 3H, J = 6Hz), 3.05 (d, 2H, J = 8Hz), 3.89 (s, 8.4 (m, 2H). 15 7.0-8.0 (m, 5H). 16; 2.23 (s, 3H), 3.85 (s, 3H), 4.07 3H), 4.00 (m,TH), 3H), 6.24 (St (s, 2H), 7.0-7.5 (m, 3H), 7.8-8.1 (m,lH). -18; 3.57 (s, lH), 7.3-7.9 (m, 4H). 13) J. A. Howard, "The Chemistry of Peroxides," ed. by S. Patai, John Wiley York-Brisbane-Toronto-Singapore, 1983, p. 235. a Sons, Chichester-New (Received
in Japan
6 March
1986)
NOVEL
OXIDATIVE
CLEAVAGE
BY OXYGENATION
Akira
Nishinaga,*
Department
OF CARBON-CARBON
WITH COBALT
Shigekazu
of Synthetic
Yoshida,
0040-4039/86 $3.00 + .OO Pergamon Journals Ltd.
2649-2652,1986
Yamazaki,
Kyoto
IN HYDRAZONES
BASE COMPLEX
and Teruo
Chemistry,
Sakyo-ku,
BOND
SCHIFF
Kyoto
Matsuura
University
606, Japan
Summary: Oxygenation of aromatic ketone hydrazones with Co(salen) in methanol resulted unexpectedly in oxidative degradation to give methyl benzoate derivatives. A mechanism involving nucleophilic attack by methanolon a diazo intermediate is discussed.
Oxygenations capable
of organic
of binding
biological
compounds
dioxygen
oxidations
catalyzed
by metal
complexes
which
are received
much attention in connection synthesis. 1,2 In aprotic solvents,
and organic
(II) Schiff base complexes bind gen carriers, 3,4 while function
dioxygen
reversibly,
as model
dioxygenases
providing
cobalt-
synthetic
when organic
are
with
oxy-
compounds
such as phenols,
flavonols, and indoles are put in the reversible dioxygen 5,6 system. These cobalt(I1) Schiff base complexes are, on the other
binding hand,
oxidized
irreversibly
with molecular
oxygen
in alcohols
giving
rise to
hydroxo-
and alkoxo-cobalt(II1) complexes depending on the acidity of the al7 used. Recently, we reported that the reversible dioxygen binding sys-
cohol
tem using
five coordinate
dehydrogenation
that the oxygenation
oxidized, rise
Schiff
base
results
to alkyl
of aromatic
benzoate
solution
under
solution
(1 mmol)
in methanol
with
romethane
and filtered
complex.
The organic
4.
Ratio
an oxygen
(20 ml)
to give
products
(2 mmol)
dropwise
was dissolved
thus obtained of methyl
on the reaction
the slow addition 2649
After
evaporation
of
of dichlothe metal
by silica
1, ketone
conditions
of 1 as well
a To the 1
to remove
was separated
until
of hydrazone
in a small volume
benzoate
reference
for 30 min).
a solution
silca gel column
giving
in methanol
at room temperature (usually
co-
is irreversibly
are available with of hydrazones. 9
of Co(salen)
atmosphere
a short
depended
four coordiante
of the C-C bond
in 1 h at room temperature.
derivatives
1, in methanol
a planar
was obtained
was added
residue
through
of the products
seen from Table
for
with N,N'-ethylene-
Few reports
a suspension
stirring
the resulting
chromatography
was effective
the complex
cleavage
bond breakdown
of Co 111(salen)(OH)7
resulting
the solvent,
complexes
hydrazones
where
in oxidative
derivatives.
experiment,
ketone
[Co(salen)],
in alcohols,
carbon-carbon
(30 ml) was stirred clear
complex
unexpectedly
to such oxidative In a typical
base
ketone
bis(salicylideneiminato)cobalt(II), balt(II)
Schiff
hydrazones, providing a convenient method of aryldiazoalkanes. 8 In this communication, we wish to
for the synthesis report
cobalt(II)
of aromatic
gel layer
3, and azine
(Table 1).
As
as the higher
2650
02/Co(salen) R'OH,
r-t.
-"9roR
+'q,
NNH2
0
0
-1
-2
)
+
C
b
a
-3 e
d
f
g R : Me Me Me Me Et H H _.. ____..___.~~.____._..-~.____ __...___._~..__ ___ _ __..._.. .__...._~___ x Me0 H H Cl Cl Ph NO, ‘
Table 1
1. Oxygenation
[co]'[~l
of Hydrazones
Addition rate of i(mmol/h) 13
la
0.0
la
0.1
1 by Co(salenja
Solvent
1.0
Product/%
(RIOH)
1
3
4
OOH
MeOH
0
0
100
OMe
MeOH
10
56
27
Me 5
0.5
1.0
MeOH
36
la
1.0 1.0
1.0 _=
MeOH
la
MeOH
la
2.0
1.0
MeOH
64
32
and the substituent
la
2.0
0.5
MeOH
70
28
not affect
la
2.0
0.5
EtOH
30
60
cut ratio.
la
2.0
0.5
i-PrOH
3
81
10
2 also
depended
la
2.0
0.5
t-BuOH
3
66
27
nature
of the solvent.
lb
2.0
0.5
MeOH
73
25
2
lc
2.0
0.5
MeOH
63
24
than methanol
Id
2.0
0.5
MeOH
80
15
tion of the parent
ld
0.5
1.0
MeOH
63
32
2 predominated.
le
2.0
0.5
MeOH
55
33
dative
If lg -
2.0
0.5
MeOH
69
of 1 was observed
2.0
0.5
MeOH
13
19 _d
la
a A solution
of 1 in MeOH(20
wise to a solution MeOH(30 b
noted. added
ml) under
6
56
38
1
ratio
39
48
8
in the higher
ml) was added
of Co(salen)(OH)(2 O2 at r.t. Conv.
d
mm011
[Co]/[l]
Thus,
1(5%)
_d
with
resulted yield
much
where
in
with
on the
cleavage in such as and DMF,
3 was formed
Co(salpr)(OH)7
in meth-
also
with a half amount of Cofsalen) (OH) at a higher addition 5 10 was obtained in 5% yield, and further the oxygenation
Co(salen)(OH)
results
therefore
nately
was quite
of 3.
r
when -Id rate,
of -la These (Table 1).
of the solvent for the present
and coordioxidative
Furthermore, oxygen bubbling through a solution 8 of 1-(4-nitrophenylj-1-diazoethane (6) in methanol containing an equimolar amount
cleavage
Interestingly,
slow to give only compound
suggest that the nucleophilicity III unsaturated Co (OH) species are essential
C-C bond
of 4.
in place
anol resulted
without
along
amount
was oxygenated hydroperoxide
ketone
No oxi-
of Co(salen)(OH) formation
other
the forma-
solvents
a small
of
The use of six coordinate
-la was
Not determined. in the predominant
X did
the prod-
alcohols
dichloromethane
drop-
of 1,
The yield
C-C bond
aprotic
100% otherwise
7% in 72 h. ' Hydrazone
Conv.
at once.
56
reaction.
of Co(salen)(OH)
at room
temperature
for a few minutes
followed
by
2651
pouring the mixture into water gave peroxocobalt(II1) complex 7 as yellow fine 11 which gave hydroperoxide 5 upon treatment with acetic crystals (84% yield), acid or silica gel. In methanol, the diazo compound 6 was stable without Co(salen)(OH), whereas with the cobalt complex under nitrogen was obtained a complex mixture but not a simple product in which methanol was incorporated. On the other hand, compound 6 was oxygenated readily in the presence of Co(salen)(OH) in acetonitrile to give -3d in 94% yield. Therefore, it may be clear that the formation of 7 results from the dioxygen incorporation into 6 in preference to the methanol addition. The peroxo complex 1 was stable against Co(salen)(OH) in methanol, .but decomposed immediately when Co(salen) or hydrazone Id was added to a solution of -7 in methanol under nitrogen to give a (80%) and 3cJ (20%), indicating that 7 is susceptible to one-electron reduction.
From these observations and the fact that 6 is formed from Id at
MeOH, r.t. OOCo(salen) I Co(salen)
N2
1
6
7
t or -Id
-2d
+
-3d
the expense of two equivalents of Co(salen)(OH), 8 the present oxidative cleavage of the C-C bond in 1 is rationalized to proceed by the following mechanism involving the diazo intermediate (Scheme 1).
Actually, in an early stage of
Scheme 1 Ar >C=NNH~ R
Ar, ,OOCom Co ,,OR, "";', C R co=
')
ArCOOR'
+
R.
or _1 8
2
the oxygenation of A, transient appearance of red color due to the diazo intermediate was generally observed. The fate of radical R. in the final step in Scheme 1 under the oxygenation conditions was clearly demonstrated by the oxygenation of cyclic ketone hydrazones. Thus, the oxygenation of 1-tetralone hydrazone (9) with two equivalents of Co(salen)(OH) in methanol gave compounds -10 (27%), 11 (2781, -12 (3%), and the parent ketone (27%).12
Since compound -11 was not formed from
NNH2 -9
-10
11 -
-12
2652
-10 under the reaction conditions, these products should be formed independently from a common intermediate -13 resulting from breakdown of 8' (refer to s in Scheme
1) and dioxygen incorporation followed by reductive or associative q-. decomposition.l' Similarly, the oxygenation of 2-methyl-1-indanone hydrazone
q--pcq”
-
H-
11 -
13 -
-8' (14) gave compounds 34%, and 10% yield,
15, 16, 17, 18, and the parent ---I2 The formation respectively.
ketone
in 12%, 16%, 15%,
of -17 and -18 is rational-
CQ- QMe QMe cTc:oMe c3r GMe NNH2 14 -
-15
ized by assuming a more
stable
the breakdown
benzyl
The present aromatic tivity
2) 3) 4) 5) 6) :; 9) 10)
whereas
in the oxygenation.
References 1)
radical
of alkoxy species
oxygenolysis
ketones,
17 -
16 -
radical
followed
of hydrazones
aliphatic
ketone
The details
18 intermediate
by the further
is characteristic hydrazones
are under
exhibit
current
-13' -13' leading oxidation.
to
for those
of
different
reac-
investigation.
and Notes
Oxidations of Organic ComR. A. Sheldon and J. K. Kochi, "Metal-Catalyzed Francisco, pounds," Academic Press, New York-London-Toronto-Sydney-San 1981, p. 72. H. Mimoun, J. Mol. Catal., 2, 1 (1980). and F. Basolo, Chem. Rev., 2, 139 (1979). R. D. Jones, D. A. Summerville, E. C. Niederhoffer, J. H. Timmons, and A. E. Martell, Chem. Rev., 84, 137 (1984). T. Matsuura, Tetrahedron, 33, 2869 (1977). A. Nishinaga and H. Tomita, J. Mol. Catal., 2, 179 (1980). A. Nishinaga, T. Kondo, and T. Matsuura, Chem. Lett., 1985, 905. A. Nishinaga, S. Yamazaki, and T. Matsuura, Chem. Lett., 1986, in press. E. G. E. Howkins, J. Chem. Cot.(C), 1971, 1474; M. Utaka, Y. Fujita, and A. Takeda, Chem. Lett., 1982, 1607. 1 6 1.58 (s, 3H), 3.40 (s, 3H), Hydroperoxide 5: m.p. 56-57 'C. HNMR(CDC13) 7.66 (d, 2~, J-= 9Hz), 8.17 (d, ZH, J = 9Hz), 8.33 (brd s, lH, OH). Anal. CgHllN05: C, 20.26%; H, kO.028; N, ?0.02%.
11) Complex
7: Anal.
12) Isolated
yield.
C25H24N307Co H20: C, +0.28%; H, *O-07%; N, 20.02%. 1 HNMR(CDC13) for the products are in good agreement
The
with the structures: 10; 1.59-2.13 (m, 2H), 2.43 (brd s, lH, OH), 3.02 (t, 2H, J = 7Hz), 3.57-(t, 2~, J = ~HZ), 3.84 (s, 3H), 6.97-7.97 (m, 4H). 11; 2.76 ((m, 2H), 3.25 (m, ZH), 3.88 (s, 3H), 7.0-8-O (m, 4H), 9.72 (t, m, J = 1Hz). 12; 1.3-2.1 (m, 4H), 2.5-2.9 (m, 8H), 7.0-7.4 (m, 6H), 8.01.26 (d, 3H, J = 6Hz), 3.05 (d, 2H, J = 8Hz), 3.89 (s, 8.4 (m, 2H). 15 7.0-8.0 (m, 5H). 16; 2.23 (s, 3H), 3.85 (s, 3H), 4.07 3H), 4.00 (m,TH), 3H), 6.24 (St (s, 2H), 7.0-7.5 (m, 3H), 7.8-8.1 (m,lH). -18; 3.57 (s, lH), 7.3-7.9 (m, 4H). 13) J. A. Howard, "The Chemistry of Peroxides," ed. by S. Patai, John Wiley York-Brisbane-Toronto-Singapore, 1983, p. 235. a Sons, Chichester-New (Received
in Japan
6 March
1986)