Aerobic oxidation of aldehydes by visible light photocatalysis

Article abstract of DOI:10.1016/j.tetlet.2013.09.005

An efficient and environmentally benign method for the oxidation of aldehydes to carboxylic acids has been developed. Singlet oxygen, generated by visible light in the presence of a Ru or Ir photocatalyst, reacted with aldehydes to give the corresponding carboxylic acids in excellent yields. The reaction is highly chemo-selective, in which only an aldehyde moiety is reactive even in the presence of other photo-oxidation active sites. This method is an example of an ideal green chemical reaction in the sense that molecular oxygen and visible light are key sources for the transformation.

Full text of DOI:10.1016/j.tetlet.2013.09.005

Tetrahedron Letters 54 (2013) 6222–6225
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Aerobic oxidation of aldehydes by visible light photocatalysis
Naeem Iqbal , Sungkyu Choi , Youngmin You , Eun Jin Cho a,b,
a
b
c,
⇑
⇑
a
Department of Chemistry and Applied Chemistry, Hanyang University, 55 Hanyangdaehak-ro, Sangnok-gu, Ansan, Kyeonggi-do 426-791, Republic of Korea
Department of Bionanotechnology, Hanyang University, 55 Hanyangdaehak-ro, Sangnok-gu, Ansan, Kyeonggi-do 426-791, Republic of Korea
Department of Advanced Materials Engineering for Information and Electronics, Kyung Hee University, Yongin-si, Kyeonggi-do 446-701, Republic of Korea
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 July 2013
Revised 29 August 2013
Accepted 4 September 2013
Available online 10 September 2013
An efficient and environmentally benign method for the oxidation of aldehydes to carboxylic acids has
been developed. Singlet oxygen, generated by visible light in the presence of a Ru or Ir photocatalyst,
reacted with aldehydes to give the corresponding carboxylic acids in excellent yields. The reaction is
highly chemo-selective, in which only an aldehyde moiety is reactive even in the presence of other
photo-oxidation active sites. This method is an example of an ideal green chemical reaction in the sense
that molecular oxygen and visible light are key sources for the transformation.
Keywords:
Photocatalyst
Oxygen
Ó 2013 Elsevier Ltd. All rights reserved.
Visible light
Aldehyde
Carboxylic acid
Oxidation is one of the fundamental reactions in nature, and the
oxidation of aldehydes to carboxylic acids has been of great inter-
est in synthetic organic chemistry. A variety of synthetic methods
widely used
oxidants
1
O
O
oxidant
CrO , NaClO ,
3
2
(1)
for the transformation of aldehydes including transition metal cat-
alyzed reactions have been reported, which use a range of oxidants
R
H
R
OH
KMnO
4
, KHSO5,
t
BuO H, H O , O
2
2
2
2
2
,3
(
Fig. 1(1)). However, many of these methods suffer from harsh
reaction conditions, limited substrate scope, or the need for stoi-
chiometric amounts of costly or hazardous oxidizing agents. Thus,
the development of more efficient and convenient methods is still
desired. Herein, we present an environmentally benign method for
the oxidation of aldehydes to carboxylic acids, which utilizes ideal
O
O
photocatalyst, O2
visible light
(
2)
R
H
R
OH
Figure 1. Oxidations of aldehydes using various oxidants.
4
green natural resources: molecular oxygen as oxidant and visible
5
–7
light
as an energy source (Fig. 2(1)).
e- transfer
1
The photosensitized production of singlet oxygen ( O
2
) plays a
RuL32+ + O
3
[ RuL33+..... O2
]
RuL32+ + 1O2 (1)
*
*
2
crucial role in a range of areas from polymer science to cancer ther-
8
apy. In addition, singlet oxygen is an important intermediate in
energy transfer
RuL 2+ + 3O2
RuL32+
+
1O2
3
(2)
organic reactions involving photo-oxidation. Cyclometalated Ru/Ir
photocatalysts have proven to be highly efficient singlet oxygen
generators under visible light irradiation either by single electron
Figure 2. Two possible pathways for generation of singlet oxygen using a Ru
photocatalyst.
9
transfer (Fig. 2(1)) or by energy transfer (Fig. 2(2)). Figure 3 shows
examples of photocatalysts which are used in visible light-induced
5
radical reactions. We envisioned that singlet oxygen generation
converted to carboxylic acid 2a in the presence of molecular
by Ru/Ir catalysts could accelerate the aerobic oxidation of
aldehydes.
We commenced our investigation of the oxidation of aldehydes
by employing p-anisaldehyde 1a as a model substrate. 1a was
3 2
oxygen and 1 mol % [Ru(bpy) Cl ] as the photocatalyst under
photo-irradiation by blue LEDs at room temperature (Table 1, entry
1). In order to maximize the yield of product 2a, we screened a
variety of Ru and Ir photocatalysts. Ir complexes were observed
to possess a higher reactivity than Ru catalysts in general (entries
1
–5), probably due to higher quantum efficiencies of Ir(III)
⇑
Corresponding authors. Tel.: +82 31 400 5496; fax: +82 31 400 5457 (E.J.C.).
E-mail addresses: odds2@khu.ac.kr (Y. You), echo@hanyang.ac.kr (E.J. Cho).
complexes than Ru(II) complexes and efficient intersystem cross-
0
040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.09.005

N. Iqbal et al. / Tetrahedron Letters 54 (2013) 6222–6225
6223
Table 2
Substrate scope
F
F
a,b
N
N
N
Ir
0
.5-1.0 mol % [Ir(dFppy) ], O2
N
N
N
N
N
N
O
3
O
F
F
Ru2+
N
Ir+
R
H
O
MeCN (0.25M), r.t.
blue LEDs, 3-12 h
R
OH
N
[
N
F
1
2
N
F
O
O
[
Ru(bpy)3]2+
[Ir(dtb-bpy)(ppy)2]+
Ir(dFppy)3]
OH
OH
OH
Figure 3. Representative visible light photocatalysts.
MeO
2
2
a, 99%
2b, 99%
2c, 95%
Table 1
a
O
O
Catalyst screening and control experiments
O
O
O
OH
OH
OH
OH
H
1 mol % photocatalyst, O2
MeCN, blue LEDs, r.t.
OH
F
Br
d, 90%
2e, 93%
2f, 95%
MeO
MeO
1
a
2a
O
CF3
O
O
Entry
Photocatalyst
Product yieldb (%)
F3C
OH
OH
1
2
3
4
5
6
7
Ru(bpy)Cl
Ru(phen)Cl
2
49
31
92
86
2
Ir(ppy)
Ir(ppy)
2
(dtb-bpy)PF
6
2g, 94%
2h, 92%
2i, 97%
3
Ir(dFppy)
No photocatalyst
3
99
O
Trace
Trace
Trace
99
O
O
Ir(dFppy)
Ir(dFppy)
Ir(dFppy)
Ir(dFppy)
3
3
3
3
(no light)
(no O
(0.5 mol %)
(0.1 mol %)
OH
c
OH
8
2
)
OH
6
9
1
0d
2j, 96%
2k, 99%
2l, 90%
90
a
Reaction conditions: Compound 1a (0.2 mmol), photocatalyst (1 mol %), CH
0.8 mL), O bubbling and O balloon, Blue LEDs, room temperature, 12 h.
Isolated yields.
Reaction was done under Ar atmosphere.
Reaction took more than 24 h.
3
CN
O
O
H
(
2
2
b
from
OH
c
HO
O
H
d
2m, 95%
O
1m
a
Reaction conditions: 1(1 mmol), Ir(dFppy)
3
(0.5–1.0 mol %), MeCN (4 mL), O
2
bubling and balloon, Blue LEDs, room temperature, 3–12 h.
over between the singlet and triplet excited states of Ir(III)
b
9
c,d
10
Isolated yields based on an average of two runs.
complexes.
Among these catalysts, Ir(dFppy)
3
(entry 5) was
found to be the best photocatalyst for the transformation. Control
experiments showed that the transformation required a photocat-
alyst, visible light irradiation, and molecular oxygen (entries 6–8).
Although the catalyst loading could be lowered to 0.1 mol %, at
Next, we performed reactions to confirm that singlet oxygen
was the key reactive species for this transformation. Reaction of
1
b was carried out in DMSO, DMF, and water, solvents that are
3
least 0.5 mol % Ir(dFppy) was required for reproducible results
1
5
known to be singlet oxygen quenchers (Table 3). The fact that
the reactions did not proceed in these solvents supports our
hypothesis that the oxidation is accelerated by the generation of
singlet oxygen under visible light-photosensitized conditions.
Based on the results, we propose a plausible mechanism16 for
the oxidation of aldehydes by visible light photocatalysis (Fig. 4).
The activated catalyst with visible light generates singlet oxygen.
Singlet oxygen reacts with an aldehyde to generate peroxy acid 3
and completion of the reaction in a reasonable time (entries 9
and 10). We also examined the effect of other parameters, such
as solvents and reaction concentration, and the reaction worked
best in MeCN with a 0.25 M concentration.
With optimized conditions in hand, oxidations of a wide range
of aldehydes were explored in the presence of Ir(dFppy)
3
catalyst
1
1
(Table 2). Both aromatic and aliphatic aldehydes were converted
into the corresponding carboxylic acids, showing the efficiency of
the new synthetic method. Reactions of both electron-poor and
electron-rich aromatic aldehydes gave excellent yields of products.
Notably, this reaction showed high chemo-selectivity under the
conditions. Benzylic systems, which could undergo aerobic photo-
oxidation, appeared to be inactive under the reaction conditions
1
7
through acyl radical and hydroperoxyl radical (HOOÁ) as interme-
Table 3
Solvent ( O
1
2
quencher) effect on aerobic oxidation of 1b
1
2
O
O
(2c, 2i).
In addition, undecenal was smoothly converted to
0
.5mol% [Ru(bpy) Cl ], O
3 2 2
undecylenic acid 2l although its alkene moiety could have been
H
OH
solvent (0.25 M), r.t.
blue LEDs, 4 h
13,14
reactive to oxidation with singlet oxygen.
1m containing two
1b
2b
aldehyde moieties underwent oxidations to give 2m with a longer
reaction time (24 h). It was found that the transformation of highly
Entry
Solvent
Yield (%)
reactive aldehydes was just as efficient as using [Ru(bpy)
which was less reactive than Ir(dFppy) in the optimization study
of 1a. For instance, benzaldehyde was converted to 2b in the pres-
ence of only 0.1 mol % [Ru(bpy) Cl ].
3 2
Cl ],
1
2
3
4
MeCN
DMSO
DMF
99
0
0
3
3
2
H
2
O
Trace

6
224
N. Iqbal et al. / Tetrahedron Letters 54 (2013) 6222–6225
was removed under vacuum, and the corresponding carboxylic
acid was purified by flash silica gel chromatography.
H
O
18
O
O
H
R
454 nm
O
O
2
X
R
OH
R
4
Acknowledgment
2
Ir(dFppy)3 *Ir(dFppy)3
O
This work was supported by the research fund of the Hanyang
University (HY-2011-G).
1
1O
3O
H
R
2
2
O
O
O
Supplementary data
O
+
O
H
O
R
O
H
R
H
R
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.
09.005.
1
3
Figure 4. Proposed mechanism for the oxidation.
References and notes
1.
(a) McNesby, J. R.; Heller, C. A. Chem. Rev. 1954, 54, 325; (b) Maslov, S. S.;
Blyumberg, E. A. Russ. Chem. Rev. 1976, 45, 155; (c) Sajus, L.; De Roch, I. S. In
Comprehensive Chemical Kinetics; Bamford, C. H., Tipper, C. F. H., Eds., 1980; p
8
9. Vol. 16; (d) Hudlicky, M. Oxidations in Organic Chemistry. In ACS
Monograph Series 186; American Chemical Society: Washington, DC, 1990; p
74.
1
2.
Some examples of oxidations of aldehydes using various oxidants, see: (a)
Bowden, K.; Heilbron, I. M.; Jones, E. R. H.; Weedon, B. C. L. J. Chem. Soc. 1946,
39; (b) Ganem, B.; Heggs, R. P.; Biloski, A. J.; Schwartz, D. R. Tetrahedron Lett.
1980, 21, 685; (c) Nwaukwa, S. O.; Keehn, P. M. Tetrahedron Lett. 1982, 23,
3135; (d) Webb, K. S.; Ruszkay, S. J. Tetrahedron 1998, 54, 401; (e) Benjamin, R.
T.; Sivakumar, M.; Hollist, G. O.; Borhan, B. Org. Lett. 2003, 5, 1031; (f) Grill, J.
M.; Ogle, J. W.; Miller, S. A. J. Org. Chem. 2006, 71, 9291; (g) Tandon, P. K.;
Gayatri, ; Sahgal, S.; Srivastava, M.; Singh, S. B. Appl. Organomet. Chem. 2007, 21,
1
1
2
35; (h) Sedelmeier, J.; Ley, S. V.; Baxendale, I. R.; Baumann, M. Org. Lett. 2010,
2, 3618; (i) Chakraborty, D.; Majumder, C.; Malik, P. Appl. Organomet. Chem.
011, 25, 487; (j) Murray, A. T.; Matton, P.; Fairhurst, N. W. G.; John, M. P.;
Figure 5. Photoluminescence spectra of 10
l
M
Ir(dFppy)
3
(a) and 10 lM
2+
[
3
Ru(bpy) ]
(b) in Ar-saturated MeCN solutions in the absence (solid line) and
Carbery, D. R. Org. Lett. 2012, 14, 3656; (k) Zhao, J.; Mück-Lichtenfeld, C.;
Studer, A. Adv. Synth. Catal. 2013, 355, 1098.
presence (dotted line) of 10 equiv of m-CPBA.
3.
Some transition metal-catalyzed oxidations, see: (a) Yamada, T.; Rhode, O.;
Takai, T.; Mukaiyama, T. Chem. Lett. 1991, 5; (b) Bhatia, B.; Punniyamurthy, T.;
Iqbal, J. J. Org. Chem. 1993, 58, 5518; (c) Sato, K.; Hyodo, M.; Takagi, J.; Aoki, M.;
Noyori, R. Tetrahedron Lett. 2000, 41, 1439; (d) Lim, M.; Yoon, C. M.; An, G.;
Rhee, H. Tetrahedron Lett. 2007, 48, 3835; (e) Sodhi, R. K.; Paul, S.; Clark, J. H.
Green Chem. 2012, 14, 1649.
diates. The peroxy acid 3 subsequently undergoes reaction with
another aldehyde to form complex 4, followed by Bayer–Villiger
type rearrangement to generate two molecules of carboxylic acid
2
. We additionally performed bimolecular photoluminescence
4. Some Reviews on reactions using molecular oxygen, see: (a) Maldotti, A.;
Molinari, A.; Amadelli, R. Chem. Rev. 2002, 102, 3811; (b) Punniyamurthy, T.;
Velusamy, S.; Iqbal, J. Chem. Rev. 2005, 105, 2329; (c) Gligorich, K. M.; Sigman,
M. S. Chem. Commun. 2009, 3854; (d) Suzuki, T. Chem. Rev. 1825, 2011, 111.
5. Some recent reviews on visible light-induced photocatalysis, see: (a) Yoon, T.
P.; Ischay, M. A.; Du, J. Nat. Chem. 2010, 2, 527; (b) Narayanam, J. M. R.;
Stephenson, C. R. J. Chem. Soc. Rev. 2011, 40, 102; (c) Xuan, J.; Xiao, W.-J. Angew.
Chem., Int. Ed. 2012, 51, 6828; (d) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C.
Chem. Rev. 2013, 113, 5322.
6. Some examples of photoredox catalysis including our previous works, see: (a)
Nicewicz, D. A.; MacMillan, D. W. C. Science 2008, 322, 77; (b) Ischay, M. A.;
Anzovino, M. E.; Du, J.; Yoon, T. P. J. Am. Chem. Soc. 2008, 130, 12886; (c)
Narayanam, J. M. R.; Tucker, J. W.; Stephenson, C. R. J. J. Am. Chem. Soc. 2009,
131, 8756; (d) Lin, S.; Ischay, M. A.; Fry, C. G.; Yoon, T. P. J. Am. Chem. Soc. 2011,
quenching experiments using peroxy acid 3, m-chloroperbenzoic
acid (m-CPBA) to check the possibility of 3 to undergo a photore-
dox reaction under our conditions (Fig. 5). It was found that the
presence of 3 exerted negligible influences on the phosphorescence
2+
3 3
emission of Ir(dFppy) and [Ru(bpy) ] . The results indicated lack
of any oxidative interactions between 3 and the photocatalysts
under photoexcitation, because oxidation of the catalysts should
lead to phosphorescence changes. Thus, the pathway involving
the oxidation of the photocatalyst by 3 could be safely excluded.
In conclusion, we have developed a highly efficient visible light-
induced oxidation method for the conversion of aldehydes to car-
boxylic acids. It is noteworthy that the reaction proceeds by
employing ideal natural sources, molecular oxygen, and visible
light, as essential ingredients for the transformation. The reaction
is highly chemo-selective, in which only the aldehyde moiety is
reactive even in the presence of other photo-oxidative active sites.
We present our protocol as an eco-friendly and efficient alternative
to current oxidation methods of aldehydes.
1
5
33, 19350; (e) Iqbal, N.; Choi, S.; Ko, E.; Cho, E. J. Tetrahedron Lett. 2005, 2012,
3; (f) Kim, H.; Lee, C. Angew. Chem., Int. Ed. 2012, 51, 12303; (g) Nguyen, J. D.;
D’Amato, E. M.; Narayanam, J. M. R.; Stephenson, C. R. J. Nature Chem. 2012, 4,
854; (h) Iqbal, N.; Choi, S.; Kim, E.; Cho, E. J. J. Org. Chem. 2012, 77, 11383; (i)
Pirnot, M. T.; Rankic, D. A.; Martin, D. B. C.; MacMillan, D. W. C. Science 2013,
3
39, 1593; (j) Kim, E.; Choi, S.; Kim, H.; Cho, E. J. Chem. Eur. J. 2013, 19, 6209; (k)
Yu, C.; Lee, K.; You, Y.; Cho, E. J. Adv. Synth. Catal. 2013, 355, 1471.
7. Previous reports on visible light-induced oxidations of aldehydes, see: (a)
Hajimohammadi, M.; Safari, N.; Mofakham, H.; Shaabani, A. Tetrahedron Lett.
2010, 51, 4061; (b) Hajimohammadi, M.; Mofakham, H.; Safari, N.; Manesh, A.
M. J. Porphyrins Phthalocyanines 2012, 16, 94.
8.
(a)Singlet Oxygen: Reactions with Organic Compounds and Polymers; Ranby, B.,
Rabek, J. F., Eds.; John Wiley and Sons: New York, 1978; (b)Singlet Oxygen;
Wasserman, H. H., Murray, R. W., Eds.; Academic Press: New York, 1979. Vol.
Experimental procedure
40; (c) Derosa, M. C.; Crutchley, R. J. Coord. Chem. Rev. 2002, 233, 351; (d)
An oven-dried resealable test tube equipped with a magnetic
Snyder, J. W.; Zebger, I.; Gao, Z.; Poulsen, L. S.; Frederiksen, P. K.; Skovsen, E.;
Mcilroy, S. P.; Klinger, M.; Andersen, L. K.; Ogilby, P. R. Acc. Chem. Res. 2004, 37,
stir bar was charged with aldehyde (1.0 mmol), Ir(dFppy)
0.005–0.01 mmol) and MeCN (4.0 mL, 0.25 M). Oxygen was then
3
894; (e) Greer, A. Acc. Chem. Res. 2006, 39, 797.
(
9.
(a) Demas, J. N.; Harris, E. W.; McBride, R. P. J. Am. Chem. Soc. 1977, 99, 3547; (b)
Mulazzani, Q. G.; Sun, H.; Hoffman, M. Z.; Ford, W. E.; Rodgers, M. A. J. J. Phys.
Chem. 1994, 98, 1145; (c) Tamayo, A. B.; Alleyne, B. D.; Djurovich, P. I.;
Lamansky, S.; Tsyba, I.; Ho, N. N.; Bau, R.; Thompson, M. E. J. Am. Chem. Soc.
bubbled through the reaction mixture, and the vessel was sealed
with a silicone septa screw-cap. A balloon filled with oxygen was
attached to the tube, and the test tube was placed under blue LEDs
at room temperature. The reaction was allowed to proceed for
2003, 125, 7377; (d) Djurovich, P. I.; Murphy, D.; Thompson, M. E.; Hernandez,
B.; Gao, R.; Hunt, P. L.; Selke, M. Dalton Trans. 2007, 3763; (e) Ulbricht, C.; Beyer,
B.; Friebe, C.; Winter, A.; Schubert, U. S. Adv. Mater. 2009, 21, 4418; (f)
Takizawa, S.; Aboshi, R.; Murata, S. Photochem. Photobiol. Sci. 2011, 10, 895.
3
–12 h, and reaction progress was checked by TLC. The solvent

N. Iqbal et al. / Tetrahedron Letters 54 (2013) 6222–6225
0. (a) Xu, C.; Mochizuki, D.; Hashimoto, Y.; Honda, T.; Tsukahara, Y.; Yamauchi, T.;
6225
) d
1
1
1
2H), 7.61 (t, J = 7.6 Hz, 1H), 7.49 (t, J = 7.6 Hz, 2H); 13C NMR (101 MHz, CDCl
167.39, 132.90, 130.81, 129.31, 128.61. 2c: white solid; 1H NMR (400 MHz,
CDCl ) d 12.81 (br s, 1H), 7.86 (d, J = 8.0 Hz, 2H), 7.35 (d, J = 8.0 Hz, 2H), 2.94
(septet, J = 7.0 Hz, 1H), 1.20 (d, J = 7.0 Hz, 6H); C NMR (101 MHz, CDCl
167.31, 153.64, 129.49, 128.45, 126.53, 33.50, 23.57. 2d: white solid; 1H NMR
(400 MHz, CDCl ) d 12.98 (b s, 1H), 6.87 (s, 2H), 2.23 (s, 6H), 2.22 (s, 3H). 2e:
white solid; 1H NMR (400 MHz, CDCl
) d 13.07 (br s, 1H), 8.00 (dd, J = 8.8,
6.0 Hz, 2H), 7.31 (dd, J = 8.8, 8.8 Hz, 2H); C NMR (101 MHz, CDCl
164.94 (d, J = 251.3 Hz), 132.13 (d, J = 9.6 Hz), 127.40 (d, J = 2.8 Hz), 115.64 (d,
J = 22.0 Hz). 2f: white solid; 1H NMR (400 MHz, CDCl
) d 12.98 (br s, 1H), 7.86
(d, J = 8.6 Hz, 2H), 7.70 (d, J = 8.6 Hz, 2H); C NMR (101 MHz, CDCl ) d 166.72,
131.67, 131.31, 130.34, 126.75. 2g: white solid; 1H NMR (400 MHz, CDCl
) d
12.77 (br s, 1H), 8.20 (d, J = 7.6 Hz, 1H), 8.14 (s, 1H), 7.92 (d, J = 7.6 Hz, 1H), 7.71
(t, J = 7.6 Hz, 1H); 13C NMR (101 MHz, CDCl
) d 166.18, 133.25, 132.14, 130.02,
129.56 (q, J = 32.4 Hz), 129.30 (q, J = 3.5 Hz), 125.63 (q, J = 3.7 Hz), 123.89 (q,
3
Wada, Y. Eur. J. Inorg. Chem. 2012, 3113; (b) Morimoto, K.; Nakae, T.; Ohara, K.;
Tamura, K.; Nagaokaa, S.; Sato, H. New J. Chem. 2012, 36, 2467.
3
13
1. The quantum yield for the photocatalytic oxidation of p-anisaldehyde to p-
anisic acid (2a) has been directly determined to be 2.6% by employing the
standard ferrioxalate actinometry. See the Supplementary data.
3
) d
3
2. (a) Sereda, G.; Rajpara, V. Tetrahedron Lett. 2007, 48, 3417; (b) Lechner, R.;
Kummel, S.; Konig, B. Photochem. Photobiol. Sci. 2010, 9, 1367; (c) Mori, K.;
Kawashima, M.; Che, M.; Yamashita, H. Angew. Chem., Int. Ed. 2010, 49, 8598;
3
1
3
3
) d 166.42,
(
d) Mori, K.; Tottori, M.; Watanabe, K.; Che, M.; Yamashita, H. J. Phys. Chem. C.
3
1
3
2
011, 115, 21358; (e) Pandey, G.; Pal, S.; Laha, R. Angew. Chem., Int. Ed. 2013, 52,
3
5
146.
3
1
3. (a) Tung, C. H.; Guan, J. Q. J. Am. Chem. Soc. 1998, 120, 11874; (b) Stratakis, M.;
Orfanopoulos, M. Tetrahedron 2000, 56, 1595; (c) Clennan, E. L. Tetrahedron
3
2
000, 56, 9151; (d) Zhang, D.; Wu, L. Z.; Yang, Q. Z.; Li, X. H.; Zhang, L. P.; Tung,
C. H. Org. Lett. 2003, 5, 3221; (e) Rajeev, R.; Sunoj, R. B. J. Org. Chem. 2012, 77,
474.
1
J = 273.4 Hz). 2h: white solid; H NMR (400 MHz, CDCl
7.86–7.65 (m, 4H); 13C NMR (101 MHz, CDCl
) d 167.90, 132.69, 132.43 (q,
J = 2.0 Hz), 131.22, 129.71, 126.56 (q, J = 22.2 Hz), 126.53 (q, J = 5.3 Hz), 123.60
(q, J = 274.3 Hz). 2i: yellow oil; 1H NMR (400 MHz, CDCl
) d 12.17 (br s, 1H),
7.23–7.15 (m, 5H), 2.81 (t, J = 7.6 Hz, 2H), 2.52 (t, J = 7.6 Hz, 2H); C NMR
(101 MHz, CDCl ) d 173.80, 140.90, 128.32, 128.26, 126.00, 35.25, 30.36. 2j:
colorless oil; 1H NMR (400 MHz, CDCl
) d 12.02 (br s, 1H), 2.17 (tt, J = 10.8,
3.6 Hz, 1H), 1.84–1.73 (m, 2H), 1.69–1.60 (m, 2H), 1.58–1.10 (m, 6H); C NMR
3
) d 13.58 (br s, 1H),
2
3
1
1
4. Formation of epoxides from reaction with the alkene moiety was observed
upon longer reaction time (>5 h).
3
13
5. (a) Bonnett, R.; Martinez, G. Tetrahedron 2001, 57(9513), 513; (b) Ogunsipe, A.;
Chen, J. Y.; Nyokong, T. New J. Chem. 2004, 28, 822; (c) Kruk, I.; Hassan, A. E.;
Michalska, T.; Ichszteld, K.; Kubasik-Kladna, K.; Olgen, S. Luminescence 2007,
3
3
13
22, 379.
1
6. Some reviews on mechanistic details of aerobic oxidation of aldehydes, see: (a)
(101 MHz, CDCl
NMR (400 MHz, CDCl
2H), 1.31–1.19 (m, 8H), 0.85 (t, J = 6.8 Hz, 3H); C NMR (101 MHz, CDCl
3
) d 176.77, 42.25, 28.71, 25.48, 24.98. 2k: colorless oil; 1
H
Wan, P.; Muralidharaina, S.; Cauley, I.; Babbage, C. A. Can. J. Chem. 1987, 65,
3
) d 11.98 (br s, 1H), 2.17 (t, J = 7.2 Hz, 2H), 1.53–1.43 (m,
13
1
775; (b) Lehtinen, C.; Nevalainen, V.; Brunow, G. Tetrahedron 2000, 56, 9375.
3
) d
1
1
7. Chatgilialoglu, C.; Crich, D.; Komatsu, M.; Ryu, I. Chem. Rev. 1991, 1999, 99.
174.53, 33.71, 31.22, 28.59, 28.49, 24.56, 22.12, 13.95. 2l: colorless oil; 1H NMR
1
8. Analytical data of compounds: 2a: white solid; H NMR (400 MHz, CDCl
3
) d
C
3
(400 MHz, CDCl ) d 11.97 (br s, 1H), 5.78 (ddt, J = 17.2, 10.2, 5.6 Hz, 1H), 4.99
(ddt, J = 17.2, 1.8, 1.6 Hz, 1H), 4.22 (ddt, J = 10.2, 1.6, 1.2 Hz, 1H), 2.18 (t,
J = 7.2 Hz, 2H), 2.04–1.95 (m, 2H), 1.54–1.18 (m, 12H).
1
3
1
2.64 (br s, 1H), 7.89 (d, J = 9.2 Hz, 2H), 7.01 (d, J = 9.2 Hz, 2H), 3.82(s, 3H);
NMR (101 MHz, CDCl
3
) d 167.05, 162.85, 131.37, 123.00, 113.83, 55.45. 2b:
) d 12.97 (br s, 1H), 7.95 (d, J = 7.6 Hz,
white solid; 1H NMR (400 MHz, CDCl
3