Photocatalytic Asymmetric Epoxidation of Terminal Olefins Using Water as an Oxygen Source in the Presence of a Mononuclear Non-Heme Chiral Manganese Complex

Article abstract of DOI:10.1021/jacs.6b10836

Photocatalytic enantioselective epoxidation of terminal olefins using a mononuclear non-heme chiral manganese catalyst, [(R,R-BQCN)Mn^II]²⁺, and water as an oxygen source yields epoxides with relatively high enantioselectivities (e.g., up to 60% enantiomeric excess). A synthetic mononuclear non-heme chiral Mn(IV)-oxo complex, [(R,R-BQCN)Mn^IV(O)]²⁺, affords similar enantioselectivities in the epoxidation of terminal olefins under stoichiometric reaction conditions. Mechanistic details of each individual step of the photoinduced catalysis, including formation of the Mn(IV)-oxo intermediate, are discussed on the basis of combined results of laser flash photolysis and other spectroscopic methods.

Full text of DOI:10.1021/jacs.6b10836

Subscriber access provided by United Arab Emirates University | Libraries Deanship
Communication
Photocatalytic Asymmetric Epoxidation of Terminal
Olefins Using Water as an Oxygen Source in the Presence
of a Mononuclear Nonheme Chiral Manganese Complex
Duyi Shen, Claudio Saracini, Yong-Min Lee, Wei Sun, Shunichi Fukuzumi, and Wonwoo Nam
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b10836 • Publication Date (Web): 23 Nov 2016
Downloaded from http://pubs.acs.org on November 25, 2016
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Journal of the American Chemical Society is published by the American Chemical
Society. 1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 5
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
Photocatalytic Asymmetric Epoxidation of Terminal Olefins Us-
ing Water as an Oxygen Source in the Presence of a Mononuclear
Nonheme Chiral Manganese Complex
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Duyi Shen,† Claudio Saracini,† Yong-Min Lee,† Wei Sun,*,‡ Shunichi Fukuzumi,*,†,¶ and Won-
woo Nam*,†,‡
†Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
‡State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese
Academy of Sciences, Lanzhou 730000, China
¶Faculty of Science and Engineering, Meijo University, SENTAN, Japan Science and Technology Agency (JST), Nagoya,
Aichi 468-8502, Japan
Supporting Information Placeholder
reactions using water as the environmentally benign oxy-
gen source have been attempted for the asymmetric
expoxidation of olefins. Further, although high-valent
manganese(V)-oxo species have been proposed as reactive
epoxidizing intermediates in the asymmetric epoxidation
of olefins invariably,4,5a direct evidence for the
intermediacy of such Mn(V)-oxo species under catalytic
and/or stoichiometric reaction conditions has yet to be
obtained. Thus, the nature of the asymmetric epoxidizing
intermediate(s) (e.g., Mn(V)-oxo, Mn(IV)-oxo, or Mn-OX (X
= OH or OR)) remains to be clarified.6 In addition, although
the formation of a nonheme Mn(IV)-oxo complex (and
nonheme Fe(IV)-oxo and Ru(IV)-oxo complexes) under
ABSTRACT: Photocatalytic enantioselective epoxidation of
terminal olefins using a mononuclear nonheme chiral
manganese catalyst, [(R,R-BQCN)MnII]2+, and water as an
oxygen source yields epoxides with relatively high enanti-
oselectivities (e.g., up to 60% enantiomeric excess). A syn-
thetic mononuclear nonheme chiral Mn(IV)-oxo complex,
[(R,R-BQCN)MnIV(O)]2+, affords similar enantioselectivities
in the epoxidation of terminal olefins under stoichiometric
reaction conditions. Mechanistic details of each individual
step of the photoinduced catalysis, including formation of
the Mn(IV)-oxo intermediate, are discussed from a com-
bined study of laser flash photolysis and other spectro-
scopic methods.
photocatalytic
oxidation
conditions
has
been
demonstrated recently,7-10 detailed mechanism(s) of the
photoinduced generation of the M(IV)-oxo complex has yet
to be addressed.
Development of highly efficient and environmentally
benign catalytic oxidation reactions using bioinspired
metal complexes under mild conditions is of current
interest in the communities of synthetic organic, oxidation,
and bioinorganic chemistry.1 Recently, enantioselective
epoxidation of olefins using bioinspired metal catalysts has
attracted much attention,2 since the resulting epoxides are
important building blocks and intermediates that can be
used in fine chemical and pharmaceutical industries and
understanding mechanistic details of the biomimetic
catalysis may provide clues for the development of
biologically relevant and catalytically efficient and selec-
tive oxidation systems. Indeed, it has been shown recently
that nonheme manganese (and iron) complexes supported
by chiral tetradentate aminopyridine ligands are highly
promising catalysts in the enantioselective epoxidation of
Scheme 1. Enantioselective Epoxidation of Terminal
Olefins by a Mn(IV)-Oxo Complex under Photocatalytic
and Stoichiometric Reaction Conditions
electron-deficient
olefins,
affording
excellent
enantioselectivities up to 99% enantiomeric excess (ee)
values;2-5 it is notable that an environmentally benign
oxidant, hydrogen peroxide (H2O2), has been used in those
asymmetric olefin epoxidation reactions. However, to the
best of our knowledge, no photocatalytic oxidation
1
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 5
Herein, we report the photocatalytic enantioselective
epoxidation of terminal olefins using a chiral manganese
catalyst, [(R,R-BQCN)MnII(OTf)2] (1; BQCN
N,N'-
Table 1. Photocatalytic Enantioselective Epoxidation of
Terminal Olefins by 1a
1
2
3
4
=
yield
(%)b
ee
(%)b
dimethyl-N,N'-bis(8-quinolyl)cyclohexanediamine, OTf =
entry
substrate
product
–
CF3SO3 ),11 [RuII(bpy)3]2+ (bpy = 2,2’-bipyridine) as a pho-
5
6
7
8
tocatalyst, [CoIII(NH3)5Cl]2+ as a one-electron oxidant, and
water as an oxygen source (Scheme 1); it should be noted
that terminal olefins are challenging substrates in
(asymmetric) epoxidation reactions.12 We also report the
first direct evidence for the involvement of a high-valent
Mn(IV)-oxo complex as an epoxidizing intermediate in the
1
59 ± 4
68 ± 5
24 ± 3
26 ± 3
35 ± 4
65 ± 5
53
50
57
60
56
43
2
3
4
5
6
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
asymmetric epoxidation of olefins;
a
mononuclear
nonheme Mn(IV)-oxo complex, [(R,R-BQCN)MnIV(O)]2+ (2),
synthesized using cerium(IV) ammonium nitrate (CAN) as
an oxidant,11 afforded moderately high ee values in the
asymmetric epoxidation of olefins (Scheme 1). The
photocatalytic formation mechanism and kinetics of the
Mn(IV)-oxo complex were elucidated using a combination
of nanosecond laser flash photolysis and other
spectroscopic measurements.
The chiral Mn(II) complex, [(R,R-BQCN)MnII(OTf)2] (1),
was synthesized by reacting Mn(OTf)2 with a chiral R,R-
BQCN ligand (Supporting Information (SI), Experimental
Section). Photoirradiation (λ > 420 nm) of a solvent mix-
ture of CH3CN and H2O (v/v = 1:24) containing vinylcyclo-
hexane (0.030 mmol), 1 (2.0 mol%), [RuII(bpy)3]2+ (10
mol%), [CoIII(NH3)5Cl]2+ (8 equiv to substrate), and acetic
acid (40 equiv to substrate) yielded the epoxide product,
2-cyclohexyloxirane (59 ± 4% yield, TON = 30 ± 2) with a
moderately high enantioselectivity (>50% ee) (eq 1) (Ta-
ble 1, entry 1; SI, Table S1 for the optimization of reaction
a
A solvent mixture of CH3CN and H2O (v/v = 1:24) con-
taining substrate (0.030 mmol),
[RuII(bpy)3]2+ (10 mol%), [CoIII(NH3)5Cl]2+ (8 equiv), and
acetic acid (40 equiv) was photoirradiated at 20 oC for 4 h.
The ee values were determined by GC with chirasil-Dex
CB column.
1
(2.0 mol%),
b
sible intermediate generated in the photocatalytic oxida-
tion reactions. A Mn(IV)-oxo species is also a viable inter-
mediate; however, such a Mn(IV)-oxo complex has been
rarely suggested as an epoxidizing intermediate in the
catalytic asymmetric epoxidation reactions. Since it has
been shown recently that mononuclear nonheme Mn(IV)-
oxo complexes are capable of epoxidizing olefins,14 we syn-
thesized a Mn(IV)-oxo complex bearing the R,R-BQCN
ligand, [(R,R-BQCN)MnIV(O)]2+ (2), according to the pub-
lished procedues,11 and investigated its reactivity in
asymmetric epoxidation of terminal olefins (Figure 1; SI,
Figure S2). Upon addition of vinylcyclohexane to a solution
of 2, the absorption band at 640 nm due to 2 disappeared
and the decay rate obeyed first-order kinetics (Figure 1,
inset). The pseudo-first-order rate constant increased
linearly with the increase of vinylcyclohexane
concentration (SI, Figure S3), giving a second-order rate
conditions; see also Table S2). When the photocatalytic
epoxidation of vinylcyclohexane was performed using
H218O (97% 18O-enriched) instead of H216O, the epoxide
product contained 94 ± 2% 18O (SI, Figure S1) in the ab-
sence and presence of air, indicating that the oxygen in the
epoxide product was derived from water. Other terminal
olefins were also oxidized to the corresponding epoxides
with moderate yields and enantioselectivities (Table 1; SI,
Table S2); the highest yield (68 ± 5%) was obtained for
vinylpentane with 50 ± 2% ee (Table 1, entry 2), whereas
the highest ee (60 ± 2% ee) but with a lower yield (26 ±
3%) was obtained for 1-heptene (Table 1, entry 4). No or
negligible amounts of epoxides were formed when the
photocatalytic oxidation reactions were performed in the
absence of 1, [RuII(bpy)3]2+, [CoIII(NH3)5Cl]2+, or acetic
acid,13 indicating that all these components are required
for the formation of the epoxide products.
constant of 1.1(1) M–1 s–1 at 20 C. Importantly, analysis of
o
the reaction solution revealed the formation of epoxide
product, 2-cyclohexyloxirane (70 ± 4% yield based on the
amount of 2 and 62 ± 2% ee). Similarly, a second-order
rate constant of 2.6(2) × 10–1 M–1 s–1 at 20 oC was obtained
in the reaction of 2 with 1-heptene, which yielded 1,2-
epoxyheptane as the product (80 ± 4% yield based on the
amount of 2) with an ee value of 63 ± 2% (SI, Figure S4; see
also Table S3). In these reactions, Mn(II) species was
formed as the decay product of 2 (SI, Figure S5). Thus, the
present results demonstrate that a chiral Mn(IV)-oxo
complex indeed epoxidizes terminal olefins to give the
Then, what is the nature of the intermediate responsi-
ble for the asymmetric epoxidation of olefins? As proposed
in most of the catalytic asymmetric epoxidation reac-
tions,4,5a a Mn(V)-oxo species can be considered as a plau-
corresponding
epoxides
with
moderately
high
2
ACS Paragon Plus Environment

Page 3 of 5
Journal of the American Chemical Society
netics and the pseudo-first-order rate constant increased
linearly with increasing the concentration of
1
2
3
4
5
6
7
8
[CoIII(NH3)5Cl]2+ (SI, Figure S8). The second-order rate con-
stant (ka in Scheme 2) was determined to be 6.2(5) × 107
M–1 s–1. The intercept was 1.1 × 106 s–1, which agrees well
with the decay rate constant of [Ru(bpy)3]2+* in the ab-
sence of [CoIII(NH3)5Cl]2+ (kT = 1.2(1) × 106 s–1) (vide infra).
The fast dynamics of the first ET of MnII to give MnIII
was also examined with laser flash-photolysis (Scheme 2,
reaction b). In contrast to the case without 1, complete
recovery of the bleaching at 450 nm was observed within
180 µs after nanosecond laser excitation of a CH3CN/H2O
(v/v = 1:1) solution of [RuII(bpy)3]2+ and [CoIII(NH3)5Cl]2+
with 1 due to the full regeneration of [RuII(bpy)3]2+ (Figure
2; SI, Figure S7, blue line). The recovery rate obeyed first-
order kinetics and the rate constant of ET from 1 to
[RuIII(bpy)3]3+ (kb in Scheme 2) was determined to be 3.7(3)
× 107 M–1 s–1 at 20 oC from the slope of the linear plot of the
pseudo-first-order rate constant vs concentration of 1 (SI,
Figures S9).
9
10
11
12
Figure 1. Absorption spectral changes observed in the reac-
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
tion of 2 with vinylcyclohexane (50 mM) in CH3CN/H2O (v/v =
o
9:1) at 20 C. 2 was prepared by reacting 1 (0.50 mM) with
CAN (3.0 mM).
enantioselectivities (Scheme 1). Further, based on the
present results, we suggest that Mn(IV)-oxo species should
be considered as active oxidants responsible for the
asymmetric epoxidation of olefins reported in previous
studies.2-5
We then investigated each individual step of the photo-
catalytic oxidation of 1 carried out in the presence of
[RuII(bpy)3]2+ and [CoIII(NH3)5Cl]2+. The initial steps of the
photocatalytic cycle were too fast to be followed using a
photodiode array spectrophotometer. Thus, nanosecond
laser flash photolysis was used to examine the kinetics and
the reaction mechanism (see Scheme 2). Laser excitation
(λex = 430 nm) of a CH3CN/H2O (v/v = 1:1) solution of
[RuII(bpy)3]2+ resulted in the formation of the triplet ex-
cited state species, [Ru(bpy)3]2+*, which decayed back to
the starting [RuII(bpy)3]2+ complex with the rate constant
of kT = 1.2(1) × 106 s–1 (lifetime = 830(40) µs)7a,9a at 20 oC,
as indicated by the full recovery of the bleaching at 450 nm
(SI, Figure S6; see also Figure S7, black line). In the pres-
ence of [CoIII(NH3)5Cl]2+, the recovery was faster but not
complete (SI, Figure S7, red line), indicating that electron
transfer (ET) from [Ru(bpy)3]2+* to [CoIII(NH3)5Cl]2+ oc-
curred to give [RuIII(bpy)3]3+ and [CoII(NH3)5Cl]+ (Scheme 2,
reaction a); the latter is known to decompose irreversibly
to release NH3.9a The rate of the ET, monitored by the re-
covery of the bleaching at 450 nm, obeyed first-order ki-
Figure 2. Representative transient absorption spectra ob-
served at 6.4, 20, 60, and 177 µs after nanosecond laser pulse
excitation (λex = 430 nm) of a CH3CN/H2O (v/v = 1:1) solution
of [RuII(bpy)3]2+ (40 µM), [CoIII(NH3)5Cl]2+ (4.0 mM), and 1
(0.80 mM) at 20 oC.
The second ET from 3 to [RuIII(bpy)3]3+ was slow
(Scheme 2, reaction c); therefore, the reaction was fol-
lowed using a photodiode array spectrophotometer. As
reported previously,8 3 was produced in the one-electron
oxidation of
1
with 1.1 equiv of [RuIII(bpy)3]3+ in
Scheme 2. Mechanistic Details for the Photoinduced
Generation of 2 and Its Reaction with Olefin
CH3CN/H2O (v/v = 1:1). Further addition of 1.1 equiv of
[RuIII(bpy)3]3+ to the solution of 3 resulted in ET from 3 to
[RuIII(bpy)3]3+, yielding 2 and [RuII(bpy)3]2+ after deproto-
nation (SI, Figures S10 and S11). The second-order rate
constant of the second ET (kc in Scheme 2) was then de-
termined under second-order kinetics conditions to be
o
1.6(1) × 103 M–1 s–1 in CH3CN/H2O (v/v = 1:1) at 20 C (SI,
Figure S10), where the same kc value was obtained using
different concentrations of 3 and [RuIII(bpy)3]3+ (1:1). In
the final step of the reaction cycle (Scheme 2, reaction d),
[(R,R-BQCN)MnIV(O)]2+ (2) oxygenated vinylcyclohexane to
give the epoxide product with the rate constant of 1.1(1) M–
1 s–1 at 20 oC (kd in Scheme 2) (SI, Figure S3).
In conclusion, photocatalytic enantioselective epoxida-
tion of terminal olefins with a chiral manganese complex
has been achieved using H2O as an oxygen source,
3
ACS Paragon Plus Environment

Journal of the American Chemical Society
[RuII(bpy)3]2+ as a photocatalyst, and [CoIII(NH3)5Cl]2+ as a
Page 4 of 5
Inorg. Chem. 2014, 59, 447. (f) Cussó, O.; Garcia-Bosch, I.; Ribas,
1
2
3
4
5
6
7
8
weak one-electron oxidant. The present study has paved a
new way to use water as the most environmentally benign
oxygen source in asymmetric epoxidation reactions. We
have also provided the first example of using a synthetic
chiral Mn(IV)-oxo complex in the asymmetric epoxidation
of olefins. We are currently synthesizing more chiral Mn-
oxo complexes with different ligands and will investigate
their reactivities in various asymmetric oxidation reactions
to understand the detailed mechanisms as well as the
ligand effect on the enantioselectivity in the asymmetric
epoxidation of olefins.
X.; Lloret-Fillol, J.; Costas, M. J. Am. Chem. Soc. 2013, 135, 14871.
(4) (a) Talsi, E. P.; Bryliakov, K. P. Coord. Chem. Rev. 2012, 256,
1418. (b) Bryliakov, K. P.; Talsi, E. P. Coord. Chem. Rev. 2014, 276,
73. (c) Ottenbacher, R. V.; Samsonenko, D. G.; Talsi, E. P.; Bryliakov,
K. P. ACS Catal. 2014, 4, 1599. (d) Lyakin, O. Y.; Zima, A. M.;
Samsonenko, D. G.; Bryliakov, K. P.; Talsi, E. P. ACS Catal. 2015, 5,
2702. (e) Ottenbacher, R. V.; Talsi, E. P.; Bryliakov, K. P. Catal.
Today 2016, 278, 30. (f) Zima, A. M.; Lyakin, O. Y.; Ottenbacher, R.
V.; Bryliakov, K. P.; Talsi, E. P. ACS Catal. 2016, 6, 5399.
(5) (a) Miao, C.; Wang, B.; Wang, Y.; Xia, C.; Lee, Y.-M.; Nam, W.;
Sun, W. J. Am. Chem. Soc. 2016, 138, 936. (b) Shen, D.; Qiu, B.; Xu,
D.; Miao, C.; Xia, C.; Sun, W. Org. Lett. 2016, 18, 372. (c) Wang, X.;
Miao, C.; Wang, S.; Xia, C.; Sun, W. ChemCatChem 2013, 5, 2489.
(6) (a) Wang, B.; Lee, Y.-M.; Seo, M. S.; Nam, W. Angew. Chem.,
Int. Ed. 2015, 54, 11740. (b) Wang, B.; Lee, Y.-M.; Clémancey, M.;
Seo, M. S.; Sarangi, R.; Latour, J.-M.; Nam, W. J. Am. Chem. Soc.
2016, 138, 2426.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ASSOCIATED CONTENT
Supporting Information.
Experimental details, Figures S1 – S11, Tables S1 – S4, and
GC chromatograms. This material is available free of
charge via the Internet at http://pubs.acs.org.
(7) (a) Kotani, H.; Suenobu, T.; Lee, Y.-M.; Nam, W.; Fukuzumi, S.
J. Am. Chem. Soc. 2011, 133, 3249. (b) Company, A.; Sabenya, G.;
González-Béjar, M.; Gómez, L.; Clémancey, M.; Blondin, G.; Jas-
niewski, A. J.; Puri, M.; Browne, W. R.; Latour, J.-M.; Que, L., Jr.;
Costas, M.; Pérez-Prieto, J.; Lloret-Fillol, J. J. Am. Chem. Soc. 2014,
136, 4624.
AUTHOR INFORMATION
Corresponding Author
wwnam@ewha.ac.kr
fukuzumi@chem.eng.osaka-u.ac.jp
wsun@licp.cas.cn
(8) Wu, X.; Yang, X.; Lee, Y.-M.; Nam, W.; Sun, L. Chem. Commun.
2015, 51, 4013.
Notes
(9) (a) Fukuzumi, S.; Kishi, T.; Kotani, H.; Lee, Y.-M.; Nam, W.
Nat. Chem. 2011, 3, 38. (b) Fukuzumi, S.; Mizuno, T.; Ojiri, T.
Chem.–Eur. J. 2012, 18, 15794. (c) Herrero, C.; Quaranta, A.; Ri-
coux, R.; Trehoux, A.; Mahammed, A.; Gross, Z.; Banse, F.; Mahy, J.-
P. Dalton Trans. 2016, 45, 706.
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was supported by NRF of Korea through the CRI
(NRF-2012R1A3A2048842 to W.N.) and GRL (NRF-2010-
00353 to W.N.) programs, JSPS KAKENHI (No. 16H02268
to S.F.), and NSFC (National Natural Science Foundation of
China, 21473226 to W.S.).
(10) (a) Ohzu, S.; Ishizuka, T.; Hirai, Y.; Fukuzumi, S.; Kojima, T.
Chem.–Eur. J. 2013, 19, 1563. (b) Farràs, P.; Di Giovanni, C.; Clif-
ford, J. N.; Garrido-Barros, P.; Palomares, E.; Llobet, A. Green Chem.
2016, 18, 255.
(11) Sawant, S. C.; Wu, X.; Cho, J.; Cho, K.-B.; Kim, S. H.; Seo, M. S.;
Lee, Y.-M.; Kubo, M.; Ogura, T.; Shaik, S.; Nam, W. Angew. Chem.,
Int. Ed. 2010, 49, 8190.
REFERENCES
(1) (a) Que, L., Jr.; Tolman, W. B. Nature 2008, 455, 333. (b)
Chen, Z.; Yin, G. Chem. Soc. Rev. 2015, 44, 1083. (c) Engelmann, X.;
Monte-Pérez, I.; Ray, K. Angew. Chem., Int. Ed. 2016, 55, 7632.
(2) (a) Saisaha, P.; de Boer, J. W.; Browne, W. R. Chem. Soc. Rev.
2013, 42, 2059. (b) Gopalaiah, K. Chem. Rev. 2013, 113, 3248. (c)
Gelalcha, F. G. Adv. Synth. Catal. 2014, 356, 261. (d) Wang, C.; Ya-
mamoto, H. Chem.-Asian J. 2015, 10, 2056. (e) Fingerhut, A.;
Serdyuk, O. V.; Tsogoeva, S. B. Green Chem. 2015, 17, 2042. (f)
Oloo, W. N.; Que, L., Jr. Acc. Chem. Res. 2015, 48, 2612. (g) Krish-
nan, K. K.; Thomas, A. M.; Sindhu, K. S.; Anilkumar, G. Tetrahedron
2016, 72, 1.
(12) (a) Coombs, J. R.; Morken, J. P. Angew. Chem., Int. Ed. 2016,
55, 2636. (b) Moretti, R. A.; Du Bois, J.; Stack, T. D. P. Org. Lett.
2016, 18, 2528. (c) Sawada, Y.; Matsumoto, K.; Katsuki, T. Angew.
Chem., Int. Ed. 2007, 46, 4559. (d) Murphy, A.; Dubois, G.; Stack, T.
D. P. J. Am. Chem. Soc. 2003, 125, 5250.
(13) Replacement of acetic acid by other acids (e.g., HOTf, HClO4,
trifluoroacetic acid, and 2-ethylhexanoic acid) and acetate anions
(e.g., CH3CO2Na) has failed to yield epoxide in the photocatalytic
oxidation of vinylcyclohexane (SI, Table S4). However, using
propionic acid instead of acetic acid afforded the same amount of
epoxide product (e.g., 59 ± 4%) but with a low enantioselectivity
(e.g., 25 ± 2% ee; SI, Table S4). Thus, acetic acid plays an impor-
tant role in the photocatalytic enantioselective epoxidation of
terminal olefins. However, the exact role of acetic acid has yet to
be clarified.
(3) (a) Cussó, O.; Cianfanelli, M.; Ribas, X.; Gebbink, R. J. M. K.;
Costas, M. J. Am. Chem. Soc. 2016, 138, 2732. (b) Serrano-Plana, J.;
Aguinaco, A.; Belda, R.; Garciá-España, E.; Basallote, M. G.; Com-
pany, A.; Costas, M. Angew. Chem., Int. Ed. 2016, 55, 6310. (c)
Cussó, O.; Ribas, X.; Lloret-Fillol, J.; Costas, M. Angew. Chem., Int. Ed.
2015, 54, 2729. (d) Cussó, O.; Ribas, X.; Costas, M. Chem. Commun.
2015, 51, 14285. (e) Codola, Z.; Lloret-Fillol, J.; Costas, M. Prog.
(14) Kim, S.; Cho, K.-B.; Lee, Y.-M.; Chen, J.; Fukuzumi, S.; Nam, W.
J. Am. Chem. Soc. 2016, 138, 10654.
4
ACS Paragon Plus Environment

Page 5 of 5
Journal of the American Chemical Society
1
2
TOC Graphic
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
5
ACS Paragon Plus Environment