Sub-stoichiometric oxidation of benzylic alcohols with commercially available activated MnO2 under oxygen atmosphere: A green modification of the benzylic oxidation

Article abstract of DOI:10.1016/j.tet.2013.04.109

Benzylic and allylic alcohols were readily converted into aldehydes and ketones in the presence of sub-stoichiometric amounts of activated MnO ₂ under oxygen atmosphere. No over-oxidation to carboxylic acid happened. The present procedure dramatically reduces the amounts of MnO ₂ necessary for the oxidation and provides a greener modification of widely used oxidation method.

Full text of DOI:10.1016/j.tet.2013.04.109

Tetrahedron 69 (2013) 5968e5972
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Sub-stoichiometric oxidation of benzylic alcohols with commercially
available activated MnO under oxygen atmosphere: a green
2
modification of the benzylic oxidation
*
Akio Kamimura , Hiroyuki Komatsu, Takaaki Moriyama, Yuichiro Nozaki
Department of Applied Molecular Bioscience, Graduate School of Medicine, Yamaguchi University, Ube 755-8611, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Benzylic and allylic alcohols were readily converted into aldehydes and ketones in the presence of sub-
Received 26 March 2013
Received in revised form 19 April 2013
Accepted 21 April 2013
2
stoichiometric amounts of activated MnO under oxygen atmosphere. No over-oxidation to carboxylic
acid happened. The present procedure dramatically reduces the amounts of MnO necessary for the
2
oxidation and provides a greener modification of widely used oxidation method.
Available online 6 May 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Manganese oxide
Benzylic oxidation
Green oxidation
Aerobic oxidation
1. Introduction
2
to 1/40 comparing with the conventional MnO oxidation; 1 equiv
or less amounts of the oxidant gave good results. During the course
of our research, we thought that commercially available activated
MnO might perform the oxidation under similar reaction condi-
2
tions, and such modification would provide a much greener
method to organic synthesis. In this paper we show reduced
Oxidation of alcohols to aldehydes or ketones is an important
1
transformation in organic synthesis. Use of various oxidation
2
3
methods, such as PCC or PDC oxidation, Swern oxidation, TPAP
oxidation,4 Dess-Martin periodate, TEMPO6 and AZADO, and
5
7
8
MnO
2
based oxidation reaction, are currently used widely for or-
2
amounts of activated MnO also serves as a good oxidation reagents
ganic synthesis. Among of these methods, MnO
a unique position because it selectively oxidizes benzylic and allylic
alcohols to the corresponding aldehydes and ketones. Although it
2
oxidation occupies
for benzylic and allylic alcohols. A dramatic reduction of the
amounts of manganese oxide for the oxidation is demonstrated.
provides a simple reaction procedure, MnO
2
should be activated
2. Results and discussion
beforehand; so far several activation methods are known, such as
Attenborough method. Instead of these methods, commercially
We first examined various conditions for the oxidation of
benzhydrol 1. The results are summarized in Table 1.
9
available activated MnO
2
has been recently used as a convenient
oxidant. Another drawback of the reaction is that it requires a large
excess amount of MnO reagents, a heavy metallic reagent, for
achieving the sufficient oxidation results. Recently we have de-
Benzhydrol 1 was readily oxidized under conventional reaction
2
conditions employing large excess amounts of MnO , and benzo-
2
phenone 2 was isolated in quantitative yield (entry 1). Use of re-
1
0
11
veloped birnessite MnO
2
as a new reagent for the oxidation. We
under oxygen atmo-
duce amounts of MnO , however, failed the smooth oxidation and
2
reported that cobalt-doped birnessite MnO
2
compound 2 was detected only 7% (entry 2). This was almost the
sphere achieved dramatic reduction of the amounts of the oxidant;
the oxidation of benzylic and allylic alcohols was achieved using
only the sub-stoichiometric amounts of the manganese oxidant.
The necessary amounts of the manganese reagents reached 1/30
same for the reaction performed under oxygen atmosphere (entry
3). Heating of the reaction mixture improved the yield of 2 to 60%
under nitrogen atmosphere (entry 4). Benzophenone 2 was ob-
12
tained in quantitative yield when compound 1 was treated with
ꢀ
sub-stoichiometric amounts of MnO
2
at 110 C in toluene under air
or oxygen atmosphere (entry 5 and 6). The amounts of MnO
reduced to 50 mg/mmol without loss of the yields of 2 (entry 7),
2
were
*
Corresponding author. Tel.: þ81 836 85 9231; fax: þ81 836 85 9201; e-mail
address: ak10@yamaguchi-u.ac.jp (A. Kamimura).
0
040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.04.109

A. Kamimura et al. / Tetrahedron 69 (2013) 5968e5972
5969
Table 1
Table 3
Oxidation of benzhydrol 1 under various conditions
Oxidation of benzylic alcohols 3 to aldehydes 4
Entry
Ar
MnO
2
(g/mmol)
4; Yield (%)a
Entry
Amounts of
MnO (mg/mmol)
Atmosphere
Time
(h)
Temp
( C)
2; Yield
(%)
1
2
3
4
5
6
7
8
9
4-MeO
3-MeO
3,4-(OCH O)C H
2 6 3
3,4-(MeO)
2-Naphthyl
2-Furyl
50
100
50
70
100
70
70
70
100
70
100
70
4b; 93
4c; 93c
4d; 84
4e; 99
4f; 89
ꢀ
a
2
1
2
3
4
5
6
7
8
9
1750
100
100
100
100
100
50
N
2
N
2
O
2
N
2
3
3
3
3
3
3
8
8
8
25
25
25
110
110
110
110
110
110
53
7
8
60
98
100
98
65
42
2
C
6
H
3
4g; 34 (23)b
4h; 89
4i; 75
4-NO
2-NO
2
C
C
6
H
H
4
Air
O
O
O
O
2
2
2
2
2
6
4
4-ClC
4-BrC
2,6-Cl
3-BrC
6
H
4
4j; 64
4k; 74
4l; 29
4m; 61
4n; 90
4o; 66
4p; 85
10
11
12
13
14
15
6
H
4
30
10
2
C
6
H
3
6
H
4
a
Isolated yield.
4-MeC
3-MeC
2-MeC
6
6
6
H
H
H
4
4
4
70
70
70
while the yield decreased very much when 30 or 10 mg/mmol of
MnO was employed (entry 8 and 9).
a
b
c
Isolated yield.
Recovery of starting benzylic alcohol 3.
2
We next examined these conditions for the oxidation of benzyl
Use of 70 mg/mmol of MnO
2
gave 4c in 54%.
alcohol 3a. The results are summarized in Table 2.
HOH2C
OHC
MnO2
toluene/O2/110 ºC
X
X
Table 2
Oxidation of benzyl alcohols 3a to benzaldehydes 4
4h; 32% (10 mg/mmol) 4k; 23% (10 mg/mmol)
3
h; X = NO2
6
7
8
2% (30 mg/mmol)
2% (50 mg/mmol)
9% (70 mg/mmol)
54% (30 mg/mmol)
61% (50 mg/mmol)
74% (70 mg/mmol)
3k; X = Br
2
Scheme 1. Oxidation of 3h and 3k with various amounts of MnO .
ꢀ
4a; Yield (%)a
The present reaction conditions were useful for the other sub-
strates (Scheme 2). For example, p-methylphenylethyl alcohol 5a
was readily oxidized to give acetophenone 6a in 88% yields. Cin-
namyl alcohol underwent slow oxidation, giving cinnamaldehyde
8a in 34% yield. Other allylic alcohol 7b also gave unsaturated al-
dehyde 8b in poor yield. Saturated aliphatic alcohol 7c was inert
toward the present reaction conditions and compound 7c was re-
covered in 95% yield. Double oxidation smoothly occurred when
benzyldiol 9a was used for the reaction, but slightly more amounts
Entry
Temp ( C)
Atmosphere
1
2
3
4
5
25
25
110
110
110
N
2
O
2
N
2
2
3
32
42
85
Air
O
2
a
GC yield.
As expected, almost no oxidation occurred in the reaction at
room temperature (entry 1 and 2). Benzaldehyde 4a was obtained
in 32% yield by the reaction under heating conditions under ni-
trogen atmosphere (entry 3). The yield of 4a was slightly improved
under air atmosphere (entry 4). Satisfactory yield of 4a was finally
obtained by the oxidation under oxygen atmosphere (entry 5).
With the optimized conditions in hand, we examined the
present reaction conditions for the oxidation of various types of
benzyl alcohols 3. The results are summarized in Table 3.
Anisalcohol 3b was smoothly oxidized to give anisaldehyde 4b
in 93% yield (entry 1). No over oxidation to benzoic acid was ob-
served under the present reaction conditions. The reaction com-
pleted in 8 h. Isolation work was readily achieved by the filtration
followed by concentration. Occasionally chromatographic purifi-
cation was necessary for obtaining pure aldehydes 4. Some benzyl
alcohols that have an electron withdrawing substituents un-
derwent slow oxidation and the reaction requires slightly more
2
of MnO were required and mono-oxidized products 11a were
obtained as a side product. The yield of 10a was improved to 76%
when the diol was exposed to the reaction mixture for 17 h.
The present oxidation happens when MnO
der oxygen atmosphere. Use of oxygen atmosphere in the absence
of MnO did not promote the oxidation reaction. Thus, benzalde-
hyde 3a was treated under O atmosphere in the presence of MnO
for 10 min. Then the reaction mixture was divided into two, one
contained MnO and the other was supernatant without MnO . The
atmosphere
2
was employed un-
2
2
2
2
2
two reaction flasks were again maintained under O
and heated to 110 C for additional 5 h. The flask containing MnO
2
ꢀ
2
gave benzaldehyde 4a in quantitative yield, while the yield of 4a
was unchanged for the supernatant solution. These results clearly
show that the oxidation occurs only in the presence of MnO and O
2 2
was not the direct oxidant for 3a (Scheme 3).
The amounts of MnO
hydes so that partial re-oxidation of MnO
is a possibility of a catalytic cycle of MnO
catalytic cycle should be very inefficient so that sub-stoichiometric
amounts of MnO were required for obtaining satisfactory yield of
aldehydes. We examined reuse of the MnO for the oxidation of 1a,
2
were slightly less than the yield of alde-
should occur, and there
could exist. However, the
amounts of MnO
2
to give corresponding aldehydes 4 in lower re-
2
activity and in moderate yields (entries 2, 5, and 9). Sterically
demanded alcohol, such as 2,6-dicholorobenzyl alcohol gave the
aldehyde 4l in low yield (entry 11). Heteroaromatic alcohols also
gave corresponding aldehydes, but due to its volatility the isolated
yield remained in moderate level (entry 6).
We used 3h and 3k to examine necessary amounts of MnO for
2
completion of the reaction (Scheme 1). In both cases, 70 mg/mmol
was the optimized amounts for the oxidation, and use of less
2
2
2
but the oxidation did not complete to give 2a in 42% for the second
time, 24% for the third time, and 16% for the fourth time (Scheme 4).
In conclusion, we have successfully developed a new method for
the oxidation of benzylic alcohols in sub-stoichiometric amounts of
amounts of MnO
2
gave 4h and 4k in moderate to low yields.
2 2
MnO . The activated MnO used here is normally commercially

5970
A. Kamimura et al. / Tetrahedron 69 (2013) 5968e5972
CHOHCH3
MnO2 (70 mg/mmol)
toluene/O2/110 ºC
COCH3
5a
6a; 88%
Ph
MnO2 (70 mg/mmol)
toluene/O2/110 ºC
CHO
Ph
OH
7a
8a; 34%
MnO2 (100 mg/mmol)
toluene/O2/110 ºC
CHO
OH
OH
7b
8b; 36%
MnO2 (70 mg/mmol)
toluene/O2/110 ºC
Ph
CHO
8c; 0% (recovery of 7c; 95%)
Ph
7c
HOH2C
MnO2 (140 mg/mmol)
toluene/O2/110 ºC
OHC
OHC
+
CH2OH
CHO
8 h 10a; 62%
7 h 76%
CH2OH
11a; 36%
9a
1
Scheme 2. Oxidation of secondary benzyl alcohol and allylic alcohols.
CHO
presence
of MnO2
O2, 110°C
lower part
5h
4
a; 100 %
MnO2 (60 mg)
O2, 110°C,
1
0 min, toluene
supernatant
2
O , 110°C
CHO
CH2OH
CHO
absence
of MnO2
5h
4a; 7%
3a
4a; 7%
2
Scheme 3. Oxidation in the presence or absence of MnO .
OH
O
activated MnO2
(
50 - 100 mg/mmol)
Supernatant of the reaction mixture was scooped by pipet. Addi-
tional toluene (5 mL) was added to solid residue and washed the
solid then the supernatant was scooped by pipet. This washing
procedure was repeated for four times. All of toluene solution was
combined and concentrated. Crude product was purified by flash
chromatography (silica gel/hexaneeEtOAc 3:1) to give 2 in 98%
O2, toluene, 110 ºC
.5 - 6 h
4
2
1
1
3
st, 98%; 2nd, 42%;
rd, 24%; 4th, 16%
2
Scheme 4. Recycling use of MnO .
2
yield (0.373 g, 2.05 mmol). MnO residue was examined for the
recycling use of the oxidant (Scheme 4, see below). White solid; mp
available. Present modification dramatically reduced the necessary
amounts of MnO for the smooth oxidation. The reduction reached
almost 1/30 of the conventional method. We hope the present
methods will contribute a green transformation reaction in organic
synthesis.
ꢀ
ꢀ
1
47e48 C (lit. 47e51 C); H NMR (500 MHz, CDCl
3
) d 7.80 (dd,
2
J¼8.2, 1.2 Hz, 4H), 7.59 (dd, J¼10.6, 4.3 Hz, 2H), 7.48 (dd, J¼10.8,
13
4
.8 Hz, 4H); C NMR (126 MHz, CDCl
3
) d 196.9, 137.7 (2C), 132.5
(2C), 130.2 (4C), 128.4 (4C).
Other benzaldehydes 4 were prepared in a similar manner.
3
. Experimental section
1
3
d
.1.1. p-Anisaldehyde (4b). Colorless oil; H NMR (500 MHz, CDCl
3
)
9.88 (s, 1H), 7.84 (d, J¼8.9 Hz, 2H), 7.00 (d, J¼8.8 Hz, 2H), 3.89 (s,
Caution: The present conditions may have a risk of fire although
13
3
H); C NMR (126 MHz, CDCl
3
)
d
191.0, 164.7, 132.1 (2C), 130.0,
it has never happened in our whole experimental works.
114.4 (2C), 55.7.
1
3
.1. Oxidation of benzhydrol 1a in the presence of sub-
3.1.2. m-Anisaldehyde (4c). Colorless oil; H NMR (500 MHz, CDCl
3
)
stoichiometric amounts of activated MnO : preparation of
benzophenone 2 (Table 1, entry 6). General procedure
2
d
9.98 (s, 1H), 7.48e7.41 (m, 2H), 7.39 (d, J¼2.4 Hz, 1H), 7.18 (dt,
13
J¼6.6, 2.6 Hz, 1H), 3.87 (s, 3H); C NMR (126 MHz, CDCl
60.2, 137.9, 130.2, 123.8, 121.7, 112.0, 55.6.
3
)
d
192.4,
1
Benzhydrol 1 (0.3831 g, 2.08 mmol) was dissolved in toluene
ꢀ
ꢀ
(
1
15 mL) and activated MnO
2
(purchased from Aldrich, 0.106 g,
3.1.3. Piperonal (4d). White solid; mp 34.5e35 C (lit. 35e39 C);
1
.92 mmol, 50 mg/mmol) was added to the solution. The reaction
H NMR (500 MHz, CDCl
3
)
d
9.81 (s, 1H), 7.41 (dd, J¼7.9, 1.6 Hz, 1H),
ꢀ
mixture was heated at 110 C under oxygen atmosphere for 4 h.
7.33 (d, J¼1.5 Hz,1H), 6.93 (d, J¼7.9 Hz,1H), 6.07 (s, 2H), 1.57 (s, 2H);

A. Kamimura et al. / Tetrahedron 69 (2013) 5968e5972
5971
13C NMR (126 MHz, CDCl
)
d
190.5, 153.2, 148.8, 132.0, 128.9, 108.5,
13C NMR (126 MHz, CDCl
126.4, 19.7.
)
d
193.0, 140.7, 134.2, 133.8, 132.2, 131.9,
3
3
107.0, 102.2.
1
3
.1.4. 3,4-Dimethoxybenzaldehyde
(4e). White
solid;
mp
9.85 (s,
3.1.16. 4-Methylacetophenone (6). Colorless oil; H NMR (500 MHz,
ꢀ
ꢀ
1
41.5e42.5 C (lit. 40e43 C); H NMR (500 MHz, CDCl
3
)
d
CDCl
3
)
d
7.85 (d, J¼8.2 Hz, 2H), 7.25 (d, J¼8.6 Hz, 2H), 2.57 (s, 3H),
13
1
H), 7.46 (dd, J¼8.2, 1.9 Hz, 1H), 7.41 (d, J¼1.8 Hz, 1H), 6.98 (d,
2.41 (s, 3H); C NMR (126 MHz, CDCl
(2C), 128.5 (2C), 26.6, 21.7.
3
) d 198.0, 144.0, 134.8, 129.3
13
J¼8.2 Hz, 1H), 3.97 (s, 3H), 3.94 (s, 3H); C NMR (126 MHz, CDCl
3
)
d
191.1, 154.6, 149.7, 130.2, 127.1, 110.4, 108.9, 56.3, 56.1.
3
.1.17. Cinnamaldehyde (8a). Colorless oil; 1H NMR (500 MHz,
CDCl
9.69 (d, J¼8.1 Hz, 1H), 7.62e7.51 (m, 2H), 7.47 (dd, J¼16.1,
ꢀ
3.1.5. 2-Naphthaldehyde (4f). White solid; mp 58e59 C (lit.
3
) d
ꢀ
1
13
5
8e61 C); H NMR (500 MHz, CDCl
3
)
d
10.16 (s, 1H), 8.35 (d,
1.5 Hz,1H), 7.47e7.34 (m, 3H), 6.71 (ddd, J¼15.8, 7.6, 0.7 Hz,1H);
C
J¼0.5 Hz, 1H), 8.01 (dd, J¼8.2, 0.5 Hz, 1H), 7.96 (dd, J¼8.5, 1.5 Hz,
NMR (126 MHz, CDCl
128.6.
3
) d 193.9, 153.0, 134.1, 131.4, 129.2, 128.7,
1
6
CDCl
H), 7.94 (d, J¼8.5 Hz, 1H), 7.91 (d, J¼8.3 Hz, 1H), 7.65 (ddd, J¼8.2,
13
.9, 1.3 Hz, 1H), 7.59 (ddd, J¼8.1, 6.9, 1.3 Hz, 1H); C NMR (126 MHz,
192.5, 136.6, 134.8, 134.2, 132.7, 129.6, 129.3, 129.2, 128.2,
3
)
d
3.1.18. Citroneral (8b). Colorless oil; 1H NMR (500 MHz, CDCl
)
3
1
27.2, 122.9.
d
9.98 (d, J¼8.2 Hz, 1H), 5.87 (d, J¼8.1 Hz, 1H), 5.11e5.01 (m, 1H),
13
2
.25e2.17 (m, 4H), 2.16 (s, 3H), 1.67 (s, 3H), 1.60 (s, 3H); C NMR
3
d
.1.6. 2-Furfural (4g). Colorless oil; 1H NMR (500 MHz, CDCl
9.66 (s,1H), 7.90e7.55 (m, 1H), 7.25 (dd, J¼3.6,1.4 Hz,1H), 6.60 (dt,
3
)
(126 MHz, CDCl
17.9, 17.7.
3
)
d
191.5, 164.1, 133.1, 127.5, 122.6, 40.7, 25.8, 25.7,
1
3
J¼3.4, 1.3 Hz, 1H); C NMR (126 MHz, CDCl
21.2, 112.7.
3
) d 178.0, 153.0, 148.2,
ꢀ
1
3.1.19. Terephthalaldehyde (10a). White solid; mp 112e113 C (lit.
ꢀ
1
1
14e116 C); H NMR (500 MHz, CDCl
3
)
d
10.13 (s, 2H), 8.05 (s, 4H);
1
3
3.1.7. 4-Nitrobenzaldehyde
(4h). Pale
yellow
solid;
mp
10.16 (s,
C NMR (126 MHz, CDCl ) d 191.6 (2C), 140.1 (2C), 130.3 (2C).
3
ꢀ
ꢀ
1
102.5e103 C (lit.103e106 C); H NMR (500 MHz, CDCl
3
)
d
1
3
1
H), 8.40 (d, J¼8.5 Hz, 2H), 8.07 (d, J¼8.2 Hz, 2H); C NMR
3.2. Procedure for leaching test (Scheme 3)
(
126 MHz, CDCl 190.4, 151.2, 140.1, 130.6 (2C), 124.4 (2C).
3
) d
A mixture of benzyl alcohol 3a (0.1195 g, 1.105 mmol), tridecane
ꢀ
3
4
.1.8. 2-Nitrobenzaldehyde (4i). Pale yellow solid; mp 41e42 C (lit.
(internal standard, 0.1971 g, 1.069 mmol) and MnO (59.8 mg,
2
ꢀ
1
ꢀ
2e44 C); H NMR (500 MHz, CDCl
3
)
d
10.43 (s, 1H), 8.12 (d,
0.68 mmol) in toluene (10 mL) was heated at 110 C under oxygen
J¼7.9 Hz, 1H), 7.96 (d, J¼7.4 Hz, 1H), 7.80 (t, J¼7.4 Hz, 1H), 7.76 (t,
atmosphere for 10 min. GC analysis revealed the yield of benzalde-
hyde 4a was 7%. The reaction mixture was divided into two, one was
13
J¼7.4 Hz, 1H); C NMR (126 MHz, CDCl
3
)
d
188.3, 134.2, 133.8, 131.5,
129.8, 124.6.
supernatant, and the other was the reaction mixture containing
ꢀ
MnO
2
. The two reaction mixture were heated at 110 C under oxygen
ꢀ
3
4
.1.9. 4-Chlorobenzaldehyde (4j). White solid; mp 44.5e45 C (lit.
atmosphere for additional 5 h. GC analyses indicated the yields of 4a
were 7% for the former solution and 100% for the latter mixture.
ꢀ
1
5e50 C); H NMR (500 MHz, CDCl
3
)
d
9.98 (s, 1H), 7.82 (d,
J¼8.3 Hz, 2H), 7.52 (d, J¼8.5 Hz, 2H); C NMR (126 MHz, CDCl
1
3
3
)
d
191.1, 141.1, 134.8, 131.0 (2C), 129.6 (2C).
3.3. Recycling use of MnO (Scheme 4), second time and later
2
ꢀ
3
5
.1.10. 4-Bromobenzaldehyde (4k). White solid; mp 55e56 C (lit.
A mixture of 1 (0.365 g, 1.98 mmol) and MnO (recovered from
the reaction of 1, see above) in toluene (10 mL) was heated at 110 C
under oxygen atmosphere for 6 h. Supernatant of the reaction
2
ꢀ
1
ꢀ
5e58 C); H NMR (500 MHz, CDCl
3
)
d
9.97 (s, 1H), 7.75 (d,
J¼8.3 Hz, 2H), 7.69 (d, J¼8.4 Hz, 3H); C NMR (126 MHz, CDCl
1
3
3
)
d
191.2, 135.1, 132.6 (2C), 131.1 (2C), 129.9.
mixture was separated and MnO residue was washed with toluene
2
for three times. The supernatant and the wash solution were
ꢀ
3
.1.11. 2,6-Dichlorobenzaldehyde (4l). White solid; mp 67e68
C
combined and evaporated. Crude product was purified through
flash chromatography (silica gel/hexaneeEtOAc 3:1) to give 2 in
42% yield (0.150 g, 0.82 mmol). The third time use was examined
from 1 (0.343 g, 1.876 mmol) and 2 was isolated in 24% yield
ꢀ
1
(
lit. 69e71 C); H NMR (500 MHz, CDCl
H), 7.21 (s, 1H); 13C NMR (126 MHz, CDCl
2C), 130.5, 129.9 (2C).
3
)
d
10.44 (s, 1H), 7.34 (s,
) d 188.9, 137.0, 133.7
2
(
3
(
0.080 g, 0.44 mmol). The fourth time use was examined from 1
3
.1.12. 3-Bromobenzaldehyde (4m). Colorless oil; 1H NMR
9.96 (s, 1H), 8.01 (s, 1H), 7.81 (d, J¼7.6 Hz, 1H),
(0.311 g, 1.69 mmol) and 2 was isolated in 16% yield (0.048 g,
0.263 mmol).
(
500 MHz, CDCl
3
)
d
13
7
.75 (ddt, J¼8.0, 1.8, 0.8 Hz, 1H), 7.42 (t, J¼7.8 Hz, 1H); C NMR
(
126 MHz, CDCl
3
)
d
190.9, 138.1, 137.4, 132.5, 130.7, 128.5, 123.5.
Supplementary data
1
3
CDCl
.1.13. 4-Tolualdehyde (4n). Colorless oil; H NMR (500 MHz,
Spectroscopic charts for compounds 2, 4, 6, 8, and 10. Supple-
mentary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2013.04.109.
13
3
)
d
9.95 (s,1H), 7.77 (d, J¼7.9 Hz, 2H), 7.32 (d, J¼7.9 Hz, 2H);
C
3
NMR (126 MHz, CDCl ) d
2
192.1, 145.7, 134.3, 130.0 (2C), 129.8 (2C),
2.0.
References and notes
3
.1.14. 3-Tolualdehyde (4o). Colorless oil; 1H NMR (500 MHz,
CDCl
3
)
d
9.98 (s, 1H), 7.72e7.61 (m, 2H), 7.47e7.33 (m, 2H), 2.43 (s,
1. Handbook of Reagents for Organic Synthesis, Oxidizing and Reducing Agents;
Burke, S. D., Danheiser, R. L., Eds.; John Wiley and Sons: Chichester, UK, 1999.
1
3
3
3
H); C NMR (126 MHz, CDCl ) d 192.8, 139.0, 136.5, 135.4, 130.1,
2. (a) Corey, E. J.; Suggs, J. W. Tetrahedron Lett. 1975, 16, 2647; (b) Corey, E. J.;
Schmidt, G. Tetrahedron Lett. 1979, 20, 399.
129.0, 127.3, 21.3.
3
. Mancuso, A. J.; Swern, D. Synthesis 1981, 165.
.1.15. 2-Tolualdehyde (4p). Colorless oil; 1H NMR (500 MHz,
4. (a) Griffith, W. P.; Ley, S. V. Aldrichimica Acta 1990, 23, 13; (b) Ley, S. V.; Norman,
3
J.; Griffith, W. P.; Marsden, S. P. Synthesis 1994, 639.
. (a) Dess, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4155; (b) Boeckman, R. K., Jr.;
Shao, P.; Mullins, J. J. Org. Synth. 2000, 77, 141.
CDCl
3
)
d
10.27 (s, 1H), 7.80 (dd, J¼7.6, 1.3 Hz, 1H), 7.47 (td, J¼7.5,
5
1.4 Hz, 1H), 7.36 (t, J¼7.5 Hz, 1H), 7.26 (d, J¼7.0 Hz, 1H), 2.67 (s, 3H);

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7
1
2
(
2
9. Activated MnO is available from SigmaeAldrich.
10. (a) Luo, J.; Huang, A.; Park, S. H.; Suib, S. L.; Young, C.-L. O. Chem. Mater. 1998, 10,
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1977, 40; (f) Harfenist, M.; Bavley, A.; Lazier, W. A. J. Org. Chem. 1954, 19, 1608;
(
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