Aerobic photooxidative cleavage of vicinal diols to carboxylic acids using 2-chloroanthraquinone

Article abstract of DOI:10.1055/s-0032-1316585

We developed the aerobic photooxidative cleavage of vicinal diols to carboxylic acids using 2-chloroanthraquinone in the presence of photoirradiation with a high-pressure mercury lamp. This is the first metal-free reaction using molecular oxygen as the terminal oxidant. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0032-1316585

LETTER
▌2059
lAetteerrobic Photooxidative Cleavage of Vicinal Diols to Carboxylic Acids Using
2
-Chloroanthraquinone
Aerobic Photooxidative Cleavage of Vicinal Diol
Yoko Matsusaki, Tomoaki Yamaguchi, Norihiro Tada, Tsuyoshi Miura, Akichika Itoh*
Gifu Pharmaceutical University, 1-25-4, Daigaku-nishi, Gifu 501-1196, Japan
Fax +81(58)2308108; E-mail: itoha@gifu-pu.ac.jp
Received: 14.05.2012; Accepted after revision: 07.06.2012
edge, there is no metal-free catalytic oxidative cleavage of
vicinal diols to carboxylic acid using molecular oxygen as
the terminal oxidant.
Abstract: We developed the aerobic photooxidative cleavage of
vicinal diols to carboxylic acids using 2-chloroanthraquinone in the
presence of photoirradiation with a high-pressure mercury lamp.
This is the first metal-free reaction using molecular oxygen as the
terminal oxidant.
Recently, we have developed several catalytic photooxi-
dation methods using molecular oxygen as the terminal
8
Key words: photooxidation, aerobic, anthraquinone, vicinal diol,
carboxylic acid
In the course of our study on this photooxidation
oxidant.
protocol, we have found that methyl aromatics were effec-
tively oxidized to the corresponding benzoic acids by pho-
tooxidation with molecular oxygen as the terminal
8
b
Oxidative cleavage of vicinal diols is a key reaction in de- oxidant in the presence of 2-chloroanthraquinone.
termining the carbohydrate structure, which transforms Therefore, we reasoned that, with this photooxidation pro-
various polyhydroxylated substances to carbonyl com- tocol, vicinal diols are oxidatively cleaved to the corre-
pounds. Furthermore, oxidative cleavage can split the car- sponding carboxylic acids with molecular oxygen as the
bon–carbon double bond in combination with terminal oxidant under metal-free conditions. We report
dihydroxylation of olefins, which complements ozonoly- herein the first example of an aerobic, oxidative cleavage
sis or Lemieux–Johnson reaction.
of vicinal diols under metal-free conditions (Scheme 1).
Oxidative cleavage of vicinal diols to aldehyde has been
studied extensively, and generally proceeds with lead tet-
raacetate and periodic acid. On the other hand, oxidative
hν, O2
HO
R1
OH
R2
O
O
1
cat. 2-Cl-AQN
+
R1
OH
HO
R2
cleavage of vicinal diols to carboxylic acid has been also
2
extensively studied, and anodic oxidation was reported.
Scheme 1 Oxidative cleavage of vicinal diols
Furthermore,
a
transition-metal-catalyzed oxidative
cleavage of vicinal diols was reported, which combined a
metal catalyst (Mn, Ru, Ni, W, Mo, and V) and a stoichio-
metric oxidant (NaIO , KHSO , H O , NaOCl, NaBO ,
To explore this approach, we selected 1-phenyl-1,2-eth-
anediol (1a) as the test substrate for optimizing the reac-
tion conditions (Table 1). Although we examined the
reaction conditions with various photosensitizers, the
yields of 2a were unsatisfactory, except for anthracene
and anthraquinone (AQN) derivatives (Table 1, entries 1–
8). Further study of the solvent and the amounts of cata-
lyst revealed that using 2-chloroanthraquinone (0.1 equiv)
in EtOAc for 20 hours were the best conditions (Table 1,
entry 2). Note that this reaction also proceeded in air at-
mosphere (Table 1, entry 18). Addition of H O, K CO ,
4
3
5
2
2
3
H IO , and t-BuOOH). In addition, two metal-free reac-
5
6
tions using stoichiometric amounts of oxidants were re-
4
ported. Recently, a catalytic metal-free reaction was
reported, which proceeds in the presence of 4-iodobenzoic
5
acid, but it requires a stoichiometric amount of Oxone.
These reactions typically involve the use of heavy metals
or non-atom-economical stoichiometric oxidants. Conse-
quently, they generate large amounts of waste and are not
environmentally benign.
2
2
3
and PTSA had little effect on this reaction (Table 1, en-
tries 19–21). A lower yield of 2a was observed when fluo-
rescent or xenon lamps were used instead of an Hg lamp
Due to the increasing demand for a more environmentally
benign synthesis, molecular oxygen has received much at-
tention as the ultimate oxidant because it is photosynthe-
sized by plants, produces little waste, is inexpensive, and
(
Table 1, entries 22 and 23). The fact that 2a was not ob-
tained or was obtained only in low yield without 2-Cl-
AQN, irradiation or molecular oxygen shows the necessi-
ty of these ingredients for this reaction (Table 1, entries
6
has greater atom efficiency than that of other oxidants.
The catalytic oxidative cleavage of vicinal diols to car-
boxylic acid using molecular oxygen as terminal oxidant
has been reported. However, these reactions must use
24–26).
7
Table 2 shows the scope and limitations of the oxidative
metal catalysts (Co, Ru), and to the best of our knowl-
9
cleavage of vicinal diols under the optimized conditions.
Generally, the corresponding carboxylic acids were ob-
tained in high yields regardless of the electron-donating or
electron-withdrawing group on the benzene ring (Table 2,
entries 1–6). On the other hand, the 2-naphthyl derivative
SYNLETT 2012, 23, 2059–2062
Advanced online publication: 26.07.2012
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0032-1316585; Art ID: ST-2012-U0418-L
Georg Thieme Verlag Stuttgart · New York
©

2060
Y. Matsusaki et al.
LETTER
was a poor substrate and resulted in low yield with many
minor byproducts (Table 2, entry 7). Aliphatic vicinal di-
ols were also converted into the corresponding carboxylic
acids in moderate to good yields (Table 2, entries 9–11).
Cyclic vicinal diol yielded the corresponding dicarboxylic
acid (Table 2, entry 12). In these aliphatic substrates, fur-
ther prolonging of reaction time resulted in lower yields.
Moreover, tetrasubstituted vicinal diol was converted into
the corresponding ketone in good yield (Table 2, entry 8).
Table 1 Study of Reaction Conditions
OH
O
hν (400-W Hg lamp), O2
OH
catalyst (equiv)
OH
solvent (3 mL), 20 h
1a (0.3 mmol)
2a
Entry
Catalyst (equiv)
Solvent
Yield (%)a
1
2
3
4
5
6
7
8
9
1-Cl-AQN (0.1)
2-Cl-AQN (0.1)
2-t-Bu-AQN (0.1)
2-Br-AQN (0.1)
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
MeCN
acetone
hexane
40
82
82
75
74
65
0
We studied the time course of the oxidative cleavage of 1a
to clarify the reaction mechanism (Figure 1). It was re-
vealed that 2-hydroxyacetophenone (3a) and phenylgly-
1
oxal (4a) were detected in the H NMR spectra.
AQN-2-CO H (0.1)
2
anthracene (0.1)
rose bengal (0.1)
methylene blue (0.1)
2-Cl-AQN (0.1)
2-Cl-AQN (0.1)
2-Cl-AQN (0.1)
2-Cl-AQN (0.1)
2-Cl-AQN (0.1)
2-Cl-AQN (0.1)
2-Cl-AQN (0.1)
2-Cl-AQN (0.05)
2-Cl-AQN (0.2)
2-Cl-AQN (0.1)
2-Cl-AQN (0.1)
2-Cl-AQN (0.1)
2-Cl-AQN (0.1)
2-Cl-AQN (0.1)
2-Cl-AQN (0.1)
–
0
68
61
74
1
1
1
1
1
1
1
1
1
1
2
2
0
1
2
3
4
5
6
7
8b
cyclohexane 70
H O
6
68
63
65
68
60
78
84
80
59
74
21
0
2
AcOH
i-Pr O
2
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
Figure 1 Time course
O
O
9c
hν (400-W Hg lamp), O2
-Cl-AQN (0.1 equiv)
OH
2
0d
OH
OH
(
(
1)
2)
EtOAc (3 mL), 20 h
1e
3
a
2a 72%
2 f
O
O
2
OH
hν (400-W Hg lamp), O2
3g
2
2
2
EtOAc (3 mL), 20 h
4
3
a
2a 28%
5h
2-Cl-AQN (0.1)
2-Cl-AQN (0.1)
O
O
hν (400-W Hg lamp), O2
2-Cl-AQN (0.1 equiv)
2 i
O
6
1
OH
OH
⋅
H2O
(3)
a 1
b
EtOAc (3 mL), 10 h
H NMR yields.
Reaction was conducted under air.
4a
2
a 64%
c
d
e
f
Reaction was conducted in the presence of H O (50 μL).
Reaction was conducted in the presence of K CO (0.5 equiv).
Reaction was conducted in the presence of PTSA (0.5 equiv).
Reaction was conducted using a fluorescent lamp.
Reaction was conducted using a Xe lamp.
Reaction was conducted in the dark.
2
O
O
2
3
O
hν (400-W Hg lamp), O2
(
4)
⋅H2O
EtOAc (3 mL), 10 h
g
h
i
4
a
2a 70%
Reaction was conducted under Ar.
Scheme 2 Study of reaction mechanism
When 3a was used as substrate under the optimal condi-
tions, benzoic acid (2a) was obtained in high yields
(
Scheme 2, equation 1). On the other hand, 3a afforded 2a
Synlett 2012, 23, 2059–2062
© Georg Thieme Verlag Stuttgart · New York

LETTER
Aerobic Photooxidative Cleavage of Vicinal Diol
2061
in low yield in the absence of 2-chloroanthraquinone
hν
AQN*
(
Scheme 2, equation 2). These results suggest that 3a is
AQN
the intermediate in this reaction, and anthraquinone is re-
quired for the oxidation of 3a. Furthermore, when phenyl-
glyoxal (4a), a plausible reaction intermediate, was used
as the substrate under the standard conditions, benzoic
acid (2a) was obtained in good yields (Scheme 2, equation
AQN*
OH
AQH•
AQH•
OO•
OH
AQN
OH
OH
O2 HO
R
•
OH
R
R
1
5
6
3
). On the other hand, 4a afforded higher yields of benzoic
acid (2a) in the absence of 2-chloroanthraquinone
Scheme 2, equation 4).
AQH•
AQN *
O
O
HO
R
OOH
OH
O2
OH
O
(
OH
R
H2O2
R
•
7
3
Scheme 3 shows a plausible path for this reaction, which
is postulated by considering the requirement of continu-
ous irradiation, a catalytic amount of anthraquinone, and
molecular oxygen. Excited anthraquinone abstracts the
hydrogen radical at the benzyl position of vicinal diol to
produce radical 5, which traps the molecular oxygen. 2-
Hydroxyacetophenone (3) is formed via peroxyradical 6
and hydroperoxide 7, and then it is transformed to hydro-
peroxide 8 via abstraction of the hydrogen radical by the
excited anthraquinone and followed by oxidation. Phenyl-
glyoxal (4) is produced by the elimination of hydrogen
peroxide. Next, phenylglyoxal produces the acyl radical 9
by Norrish I reaction, which traps the molecular oxygen.
Carboxylic acid 2 is formed through the peroxy radical 10
and peracid 11.
AQH•
AQN
O
O
O
hν
OH
OO•
OH
OOH
R
R
R
R
H2O2
8
4
O
O
O
O
O2
•
R
OO•
R
OOH
R
OH
9
10
11
2
Scheme 3 Plausible path of oxidative cleavage of vicinal diol
chloroanthraquinone and photoirradiation from a high-
pressure mercury lamp. This method is of interest from
the viewpoint of green chemistry because of the use of
molecular oxygen and anthraquinones as organocatalysts.
In conclusion, we have developed the aerobic photooxida-
tive cleavage of vicinal diols to carboxylic acids using 2-
Table 2 Scope and Limitations
hν (400-W Hg lamp), O2
2
-Cl-AQN (0.1 equiv)
substrate
0.3 mmol)
product
(
EtOAc (3 mL)
Entry
Substrate
Time (h)
Product
Yield (%)a
OH
O
1
2
3
4
1a R = H
20
20
20
20
2a
2b
2c
2d
86
89
80
82
OH
1b R = Cl
1c R = t-Bu
1d R = OMe
OH
R
R
OH
O
5
6
OH
1e R = Me
1f R = Ph
30
30
2a
81
80
OH
b
2
a
R
OH
O
OH
7
1g
1h
30
30
OH
2g
2h
30
HO
Ph
OH
O
8
9
0
1
70c
75
Ph
Ph
Ph
Ph
Ph
OH
1i n = 7
1j n = 9
1k n = 11
20
30
30
O
2i
2j
2k
d
1
1
OH
OH
58
OH
d
n
n
52
O
O
1
2
1l
50
2l
59d
HO
OH
4
OH
a
b
c
d
Isolated yields.
Compound 2a (0.48 mmol) was obtained.
Compound 2h (0.43 mmol) was obtained.
Substrates were recovered in 10% (entry 10), 8% (entry 11), and 18% (entry 12) yields, respectively.
©
Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2059–2062

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Y. Matsusaki et al.
LETTER
References and Notes
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9) General Procedure
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chloroanthraquinone (0.03 mmol) in dry EtOAc (3 mL) in a
Pyrex test tube, purged with an O balloon, was stirred and
2
irradiated externally with a 400 W high-pressure mercury
lamp for 20 h. The reaction mixture was concentrated in
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1
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CHCl –MeOH = 9:1) provided benzoic acid (R = 0.6, 31.4
3
f
mg, 86%).
Benzoic Acid (2a)
1
H NMR (400 MHz, CDCl ): δ = 8.13 (d, J = 7.4 Hz, 2 H),
.62 (t, J = 7.4 Hz, 1 H), 7.48 (t, J = 7.4 Hz, 2 H). C NMR
3
13
7
(
100 MHz, acetone-d ): δ = 172.6, 133.9, 130.3, 129.4,
6
128.6.
4
-Chlorobenzoic Acid (2b)
(m) Ishii, Y.; Yamawaki, K.; Yoshida, T.; Ura, T.; Ogawa,
1
H NMR (500 MHz, acetone-d ): δ = 8.01 (d, J = 8.6 Hz, 2
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6
13
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4
-tert-Butylbenzoic Acid (2c)
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13
7.49 (d, J = 8.7 Hz, 2 H), 1.35 (s, 9 H). C NMR (125 MHz,
CDCl ): δ = 172.6, 157.7, 130.2, 126.7, 125.6, 35.3, 31.2.
3
1
981, 46, 3936. (r) Wolfe, S.; Hasan, K. S.; Campbell, J. R.
4
-Methoxybenzoic Acid (2d)
J. Chem. Soc., Chem. Commun. 1970, 1420.
1
H NMR (500 MHz, acetone-d ): δ = 7.96 (d, J = 9.2 Hz, 2
H), 7.00 (d, J = 9.2 Hz, 2 H), 3.85 (s, 3 H). C NMR (100
6
(
4) (a) Khurana, J. M.; Sharma, P.; Gogia, A.; Kandpal, B. M.
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13
MHz, acetone-d ): δ = 167.5, 164.4, 132.5, 123.7, 114.5,
6
55.8.
2
-Naphthoic Acid (2g)
(
(
5) Thottumkara, P. P.; Vinod, T. K. Org. Lett. 2010, 12, 5640.
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1
H NMR (400 MHz, acetone-d ): δ = 8.66 (s, 1 H), 8.07 (dd,
6
J = 8.5, 1.7 Hz, 2 H), 7.99 (dd, J = 8.5, 5.6 Hz, 2 H), 7.66–
13
7
1
1
.57 (m, 2 H). C NMR (100 MHz, acetone-d ): δ = 168.9,
6
34.9, 134.2, 132.3, 131.3, 129.4, 128.4, 127.9, 127.0,
26.7, 125.5.
Benzophenone (2h)
(
(
1
H NMR (500 MHz,CDCl ): δ = 7.80 (d, J = 8.0 Hz, 4 H),
.58 (t, J = 8.0 Hz, 2 H), 7.48 (t, J = 8.0 Hz, 4 H). C NMR
3
13
7
(
125 MHz, CDCl ): δ = 196.8, 137.8, 132.5, 130.2, 128.4.
3
Nonanoic Acid (2i)
8) For recent reports, see: (a) Tada, N.; Ban, K.; Nobuta, T.;
Hirashima, S.; Miura, T.; Itoh, A. Synlett 2011, 1381.
1
H NMR (500 MHz,CDCl ): δ = 2.35 (t, J = 7.6 Hz, 2 H),
3
1
3
2
.70–1.60 (m, 2 H), 1.39–1.22 (m, 10 H), 0.89 (t, J = 6.9 Hz,
(b) Tada, N.; Hattori, K.; Nobuta, T.; Miura, T.; Itoh, A.
13
H). C NMR (125 MHz, CDCl ): δ = 181.0, 34.5, 32.2,
3
Green Chem. 2011, 13, 1669. (c) Nobuta, T.; Hirashima, S.;
Tada, N.; Miura, T.; Itoh, A. Org. Lett. 2011, 13, 2576.
9.6, 29.5, 29.5, 25.1, 23.1, 14.5.
Undecanoic Acid (2j)
(
d) Tada, N.; Matsusaki, Y.; Miura, T.; Itoh, A. Chem.
1
H NMR (500 MHz,CDCl ): δ = 2.35 (t, J = 7.5 Hz, 2 H),
3
Pharm. Bull. 2011, 59, 906. (e) Tada, N.; Ban, K.; Ishigami,
T.; Nobuta, T.; Miura, T.; Itoh, A. Tetrahedron Lett. 2011,
1
3
2
.66–1.59 (m, 2 H), 1.35–1.21 (m, 14 H), 0.88 (t, J = 6.6 Hz,
13
H). C NMR (100 MHz, CDCl ): δ = 179.8, 32.0, 29.6,
3
5
2, 3821. (f) Nobuta, T.; Tada, N.; Hattori, K.; Hirashima,
S.; Miura, T.; Itoh, A. Tetrahedron Lett. 2011, 52, 875.
g) Tada, N.; Cui, L.; Okubo, H.; Miura, T.; Itoh, A. Chem.
9.5, 29.4, 29.3, 29.2, 29.1, 24.7, 22.7, 14.2.
Tridecanoic Acid (2k)
(
1
H NMR (500 MHz,CDCl ): δ = 2.35 (t, J = 7.5 Hz, 2 H),
3
Commun. 2010, 46, 1772. (h) Tada, N.; Ban, K.; Yoshida,
M.; Hirashima, S.; Miura, T.; Itoh, A. Tetrahedron Lett.
1
3
2
.65–1.55 (m, 2 H), 1.34–1.20 (m, 18 H), 0.88 (t, J = 6.9 Hz,
13
H). C NMR (125 MHz, CDCl ): δ = 179.8, 33.8, 31.6,
3
2
010, 51, 6098. (i) Tada, N.; Cui, L.; Okubo, H.; Miura, T.;
9.4, 29.3, 29.2, 29.1, 29.0, 28.8, 24.4, 22.4, 13.8.
Itoh, A. Adv. Synth. Catal. 2010, 352, 2383. (j) Hirashima,
S.; Nobuta, T.; Tada, N.; Miura, T.; Itoh, A. Org. Lett. 2010,
Adipic Acid (2l)
1
H NMR (500 MHz, DMSO-d ): δ = 2.22–2.18 (m, 4 H),
6
1
2, 3645. (k) Tada, N.; Ban, K.; Hirashima, S.; Miura, T.;
13
1
.52–1.47 (m, 4 H). C NMR (125 MHz, DMSO-d ): δ =
6
Itoh, A. Org. Biomol. Chem. 2010, 8, 4701. (l) Kanai, N.;
Nakayama, H.; Tada, N.; Itoh, A. Org. Lett. 2010, 12, 1948.
174.5, 33.5, 24.2.
(
m) Nobuta, T.; Hirashima, S.; Tada, N.; Miura, T.; Itoh, A.
Synlett 2012, 23, 2059–2062
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