Visible-Light-Driven Enantioselective Aerobic Oxidation of β-Dicarbonyl Compounds Catalyzed by Cinchona-Derived Phase Transfer Catalysts in Batch and Semi-Flow

Article abstract of DOI:10.1002/adsc.201900777

The direct asymmetric α-hydroxylation of β-dicarbonyl compounds has been developed using cinchona-derived phase-transfer catalysts in batch and semi-flow processes. Using visible light as the driving force and air as oxidant, the corresponding products were obtained in excellent yields (up to 96%) and good enantioselectivities (up to 90% ee). The catalyst acts as a chiral center and a catalytic center and forms a chiral enolate complex with the substrate to act as a photosensitive center in the reaction. The use of semi-flow photochemical processes allowed a reduction in reaction time (24 h to 0.89 h) and good yields (up to 93%) and enantioselectivities (up to 88% ee) were obtained.

Full text of DOI:10.1002/adsc.201900777

UPDATES
DOI: 10.1002/adsc.201900777
Visible-Light-Driven Enantioselective Aerobic Oxidation of β-
Dicarbonyl Compounds Catalyzed by Cinchona-Derived Phase
Transfer Catalysts in Batch and Semi-Flow
Xiao-Fei Tang,a Jing-Nan Zhao,a Yu-Feng Wu,a Shi-Hao Feng,a Fan Yang,a
Zong-Yi Yu,a and Qing-Wei Menga,*
a
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024,
People’s Republic of China
Fax +86(0411)84986201
E-mail: mengqw@dlut.edu.cn
Manuscript received: June 25, 2019; Revised manuscript received: August 28, 2019;
Version of record online: ■■■, ■■■■
Supporting information for this article is available on the WWW under https://doi.org/10.1002/adsc.201900777
iridium(III) or rhodium(III) complex in the reaction
Abstract: The direct asymmetric α-hydroxylation
of β-dicarbonyl compounds has been developed
simultaneously acted as the catalytic center, chiral
center and photoredox center.[6] This type of bifunc-
using cinchona-derived phase-transfer catalysts in
tional or multifunctional catalyst that enables photo-
batch and semi-flow processes. Using visible light
reactions with both high yields and enantioselectivities
as the driving force and air as oxidant, the
has attracted considerable attention.[7]
corresponding products were obtained in excellent
yields (up to 96%) and good enantioselectivities (up
Oxygen is regarded as a widely accessible and
environmentally benign sustainable oxidant in nature.
to 90% ee). The catalyst acts as a chiral center and a
The best way of efficiently using photoactivated oxy-
catalytic center and forms a chiral enolate complex
gen to achieve asymmetric oxidations has become a
with the substrate to act as a photosensitive center
research hotspot.[8] To obtain bifunctional chiral cata-
in the reaction. The use of semi-flow photochemical
lysts that can activate oxygen, the Xiao group
processes allowed a reduction in reaction time (24 h
(Scheme 1a) and the Meng group (Scheme 1b) inde-
to 0.89 h) and good yields (up to 93%) and
pendently carried out research, mainly involving
enantioselectivities (up to 88% ee) were obtained.
combination
of
chiral
catalysts
with
a
photosensitizer.[9,10] However, the preparation of these
catalysts increases the number of synthetic steps,
especially the modification of tetraphenylporphyrin
(TPP) in our work, making the catalyst synthesis more
difficult. This prompted us to develop a new method to
use a cinchona-derived phase-transfer catalyst (PTC)
Keywords: aerobic oxidation; asymmetric catalysis;
phase-transfer catalyst; semi-flow; visible light catal-
ysis
Over recent years, as visible light has been increas- for the direct asymmetric α-hydroxylation of β-
ingly used in organic synthesis as a wide-ranging, dicarbonyl compounds by visible-light irradiation.
green and sustainable resource, interest in enantiose-
Microreactors have been widely used in the syn-
lective photochemical reactions has significantly thesis of fine chemicals and pharmaceuticals due to
grown.[1,2] In 2005, T. Bach embedded photochemical advantages in improving safety, efficient heat and mass
substrates into a rigid chiral catalyst to enable a transfer, and automation.[11] Photomicroreactors have
catalytic enantioselective cyclization driven by photo- been used to achieve various photocatalytic
induced electron transfer (λ>300 nm).[3] This strategy reactions.[12] In 2012, Kirsten Zeitler reported a photo-
was not explored further until the use of a chiral redox asymmetric α-alkylation of aldehydes, per-
thioxanthene catalyst was extended to a visible light- formed in a microreactor.[13] However, most reported
induced asymmetric cycloaddition in 2014.[4] The same reactions using photomicroreactors have been synthe-
year, Eric Meggers reported the use of a chiral sized of achiral compounds,[14] especially, aerobic
ruthenium complex as a catalyst to catalyze the oxidations.[15] Herein, we report a visible-light driven
asymmetric alkylation of 2-acylhydrazine.[5] The chiral heterogeneous gas-liquid-liquid asymmetric aerobic
Adv. Synth. Catal. 2019, 361, 1–9
1
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
��
These are not the final page numbers!

UPDATES
asc.wiley-vch.de
Figure 1. Schematic Representation of a Flow Photomicroreactor for the Asymmetric Photocatalytic Oxidation of β-Dicarbonyl
Compounds.
Scheme 1. Bifunctional Photocatalysts for Enantioselective Aerobic Oxidation of β-Dicarbonyl Compounds.
Adv. Synth. Catal. 2019, 361, 1–9
2
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
��
These are not the final page numbers!

UPDATES
asc.wiley-vch.de
Table 1. Screening of PTCs of the α-Hydroxylation of β-Keto Ester 1a[a]
Entry
Cat.
Light
Solvent
Yield[b]
(%)
ee[c]
(%)
1
2
3
4
5
6
7
8
9
10
11
12
1a
1a
1b
1c
1d
1e
1f
1 g
1 h
1i
white
Darkness
white
white
white
white
white
white
white
white
white
white
white
blue
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
m-xylene
p-xylene
m-xylene
m-xylene
m-xylene
75
NR
27
91
94
91
92
55
66
54
71
47
63
95
96
95
96
96
96
70
ND
74
76
58
77
74
62
64
67
59
50
51
77
80
70
82
85
90
1j
1k
1 l
1e
1e
1e
1e
1e
1e
13
14[d]
15[d]
16[d]
17[d,e]
18[d,e,f]
19[d,e,f,g]
blue
blue
blue
blue
blue
[a] Unless otherwise specified, the reaction was performed with β-keto ester 2a (31 mg, 0.1 mmol), 10 mol% catalyst, 4 mL solvent
and 2 mL 50% K2HPO4. The reaction was covered by a 3 W LEDs light at rt for 48 h.
[b] Isolated yield.
[c] Determined by HPLC analysis with hexane/2-propanol (80:20) as the eluent (Chiralcel ADÀ H).
[d] Reaction time 24 h.
[e] 2 equiv. Cs2CO3 in 2 mL H2O as a basic solution.
[f] 2a (31 mg, 0.1 mmol) in 16 mL m-xylene.
[g]
°
Reaction performed at À 5 C. NR=No reaction, ND=Not determined
oxidation catalyzed by cinchona-derived phase-transfer 3a was obtained in 75% yield with 70% ee after 48 h
catalysts in both batch and semi-flow processes (Table 1, entry 1). However, when the reaction was
(Scheme 1c).
conducted in darkness, 3a was not detected (Table 1,
Inspired by Melchiorre’s work, we wondered entry 2). The C-2’ unmodified catalyst 1b was found
whether the cinchonine-derived PTCs or the complex to give product 3a in only 27% yield and 74% ee
formed by the PTCs and a β-keto ester could act as a (Table 1, entry 3). Furthermore, other C-2’ modified
photosensitive center to activate oxygen under visible catalysts were screened (Table 1, entries 4–7, 1c–
light.[7c] When we tried to use PTC 1a to catalyze the 1f).[7c,16] The phenyl-substituted catalyst 1c and 2-
enantioselective α-hydroxylation of β-keto ester 2a naphthalene-substituted catalyst 1d afforded product
with air under 3 W white LEDs light without a 3a with high yields and moderate enantioselectivities,
photosensitizer, we were surprised to find that product and catalyst 1e achieved a better enantioselectivity
Adv. Synth. Catal. 2019, 361, 1–9
3
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
��
These are not the final page numbers!

UPDATES
asc.wiley-vch.de
Table 2. Substrate Scope[a]
than the others (91% yield, 77% ee). A benzyl
substituent was then examined; 3,5-fluoro, 3,5-chloro
and 3,5-iodo groups in the benzylic position resulted in
an obvious decrease of enantioselectivity (Table 1,
entries 8–13, 1j–1l). The other reaction conditions
were then screened further. When the light source was
changed to blue light, the reaction time was shortened
to 24 h, and 3a was obtained in 95% yield with 77%
ee (Table 1, entry 14). When the solvent was changed
to m-xylene, 3a was obtained in 80% ee (Table 1,
entry 15). When the base solution was replaced with 2
equiv. Cs2CO3 in water, the enantioselectivity was
improved (Table 1, entry 17). Reducing the substrate
concentration to 6.25 mM resulted in a significant
increase of enantioselectivity (Table 1, entry 18). Fi-
nally, the enantioselectivity could be further improved
°
to 90% ee by lowering the temperature (À 5 C,
Table 1, entry 19).
Once the optimized conditions had been estab-
lished, the scope of substrates was examined. 1-
Indanone-derived 1-adamantyl β-keto esters substrates
were investigated initially (Table 2, 2b–2h). The 5- or
6-position halogen-substituted substrates (Table 2, 2b–
2d) were well tolerated in the reaction and the
corresponding products 3b–3d were obtained in
excellent yields (88–96%) with good enantioselectiv-
ities (84–90% ee). However, the enantioselectivity of
the 4-trifluoromethyl-substituted product 3e decreased
to 64% ee. Introducing electron-donating groups
(À CH3, À OCH3) into the 5- and 6-substituted of
indanone provided the corresponding products 3f–3h
in 87–92% yields and 79–83% ee. Next, the ester
groups of the substrates (Table 2, 2i–2m) were
investigated. It was found that the enantioselectivity
decreased with a decrease of steric hindrance in the
ester substituents. The 2-adamantyl ester product 3i
was obtained in 85% yield and 79% ee. Products 3j–
3m (Table 2) were produced in good yields (81–90%)
and moderate enantioselectivities (56–70% ee). Then,
the tetralone substrates (Table 2, 2n–2p) were also
examined, and were smoothly transformed into the
desired products 3n–3p in 72–89% yields and 67–
72% ee. Finally, the reaction was further extended to
[a] General conditions: substrate 2 (0.1 mmol), 1e (10 mol%),
m-xylene (16 mL) and 2 equiv. Cs2CO3 in 2 mL H2O at
°
À 5 C. The reaction was covered by a 3 W blue LEDs light
for 24 h. All yields are isolated yields and enantiomeric ratios
were determined by chiral HPLC.
β-ketone amide substrates (Table 2, 2q–2t) and pro- basic solution damages the glass, the reaction con-
vided products 3q–3t in acceptable yields. Of note, ditions in the flow photomicroreactor were not exactly
the product 3q achieved an impressive 83% ee. the same as those for the batch reactor. The residence
Products 3r–3t were obtained in 52–57% yield and time was shortened from 24 h in the batch reactor to
only 24–56% ee, probably due to steric hindrance. The 0.89 h in the flow photomicroreactor, and 3a was
steric hindrance effect was similar to that of the ester obtained in 95% yield and 87% ee (Table 3, entry 1).
substrates, where the enantioselectivity decreased with Then, different light sources were investigated (Ta-
decreasing steric hindrance in the ester substituents. In ble 3, entries 2–4). It was found that violet light could
addition, the reaction failed to occur for cyclopenta- further shorten the residence time to 0.14 h, but gave
none-derived β-keto ester substrate 2u.
the product 3a with only 84% ee (Table 3, entry 2).
Next, we attempted to transfer the photocatalytic The yield of 3a decreased significantly with red light
asymmetric oxidation reaction from a batch to a and white light (Table 3, entries 3–4). The enantiose-
continuous flow reactor. As the low temperature causes lectivity decreased slightly with higher reaction pres-
solidification and expansion of water, and the strong sure and temperature (Table 3, entries 5–6). The
Adv. Synth. Catal. 2019, 361, 1–9
4
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
��
These are not the final page numbers!

UPDATES
asc.wiley-vch.de
Table 3. Optimization of the Reaction Conditions for α-Hydroxylation of β-Keto Ester 1a in Semi-flow[a]
Entry
Light
Pressure
(bar)
Residence time
(h)
Yield[b]
(%)
ee[c]
(%)
1
2
3
4
blue
violet
red
white
blue
blue
blue
3
3
3
3
5
3
3
0.89
0.14
0.89
0.89
1.12
0.86
0.89
95
96
<10
47
96
87
84
ND
86
85
85
88
5
6d
7e
95
95
[a] General conditions: pump 1: substrate 2a (0.1 mmol), 10 mol% 1e in 16 mL m-xylene, 1.5 mL/min; pump 2: 1% Cs2CO3 aq.
1.5 mL/min. O2:10 mL/min. The reaction was covered by LEDs light. The reaction pressure was 3 bar and the reaction
°
temperature was 0 C in the flow photomicroreactor as shown in Figure 1.
[b] All Isolated yields.
[c] Determined by HPLC analysis with hexane/2-propanol (80:20) as the eluent (Chiralcel ADÀ H).
[d]
°
Reaction temperature 20 C.
[e] 20 mol% 1e.
Table 4. Substrate Scope in the Photomicroreactor[a]
[a] General conditions: pump 1: substrate 2 (0.1 mmol), 1e (20 mol%) in m-xylene (16 mL), 1.5 mL/min; pump 2: 1% Cs2CO3 aq.
°
1.5 mL/min. O2:10 mL/min. The reaction was covered by blue LEDs light. The reaction temperature was 0 C, and reaction
pressure was 3 bar. All yields are isolated yields and enantiomeric ratios were determined by chiral HPLC.
enantioselectivity could be improved to 88% ee by
To better understand the mechanism of the reaction,
increasing the catalyst 1e loading to 20 mol% (Table 3, control experiments were performed. When the radical
entry 7). The substrate scope was then expanded. quencher 2,2,6,6-tetramethylpiperidine-1-oxyl (TEM-
Substrates (2a–2d, 2f–2i and 2q) could be trans- PO) was added to the reaction,[5] product 3a was
formed into the corresponding products (3a–3d, 3f–3i obtained in 95% yield with 90% ee and no α-
and 3q) in good yields (54–95%) and enantioselectiv- oxyamination products 8a were detected from the
ities (78–88% ee).
reaction mixture (Scheme 2a). As 1,4-diazabicyclo-
Adv. Synth. Catal. 2019, 361, 1–9
5
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
��
These are not the final page numbers!

UPDATES
asc.wiley-vch.de
Scheme 2. Control Experiments.
Scheme 3. Postulated Mechanism.
[2,2,2]octane (DABCO) has good solubility in water, a solution formed after 10 min (See Supporting Informa-
control experiment without water was carried out. As a tion Figure S4). We also performed UV-vis and
result, the product 3a was obtained in 96% yield with fluorescence spectroscopy. The absorption of a solution
1
77% ee (Scheme 2b). The O2 inhibitor (DABCO) was of substrate 2a, PTC 1e and Cs2CO3 was higher than a
added to the reaction (Scheme 2c), and it was found solution of substrate 2a and PTC 1e, or a solution of
that the reaction rate decreased significantly. After PTC 1e at 330–365 nm, exhibiting an obvious bath-
48 h of reaction, only 18% yield and 47% ee were ochromic shift (See Supporting Information Figure S5
achieved. Therefore, it was confirmed that 1O2 is and S6). With the addition of PTC 1e, the emission
present in the oxidation reaction. The product 3a was intensity of substrate 2a dramatically decreased (See
obtained in higher yields with C-2’ modified catalysts Supporting Information Figure S7). Therefore, we
(1a, 1c–1f) than with unmodified catalyst 1b (Table 1, believe that substrate 2a and PTC 1e form a chiral
entries 1 and 3–7). The reaction also failed to occur for enolate complex under basic conditions, and that the
aliphatic cyclic β-keto ester substrate 2u. PTC 1e did complex acted as a photosensitive center in the
not completely dissolve in m-xylene and formed a reaction. According to these results and previous
turbid solution. However, when substrate 2a, PTC 1e studies,[9,10,17] we proposed a plausible mechanism
and Cs2CO3 were added to m-xylene and H2O, a clear (Scheme 3). The enol anion 5 forms from substrate 2
Adv. Synth. Catal. 2019, 361, 1–9
6
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
��
These are not the final page numbers!

UPDATES
asc.wiley-vch.de
the microreactors in the full process (without reuse). After
completion of the reaction (confirmed by TLC), the mixture
was diluted with EtOAc (50 mL), washed with water (3×
20 mL), dried over anhydrous Na2SO4, filtered, and concen-
trated in vacuo. The residue was purified by column chromatog-
raphy on silica gel (petroleum ether/ethyl acetate=10/1, 5/1) to
afford the product 3. The ee of the product was determined by
chiral HPLC.
under the action of base, and forms chiral enolate
complex 6 with PTC 1e. Under visible light, the
3
complex 6 acts as a photosensitizer to activate O2 into
1
1O2. The Re-face of complex 6 is shielded by the Ad
1
group, so the O2 or hydroperoxide 7 can only attack
the complex 6 from the Si-face, affording α-hydrox-
ylation product 3 with the S-configuration. Therefore,
the cinchona-derived phase-transfer catalyst simulta-
neously acts as a chiral center and a phase-transfer
catalytic center and forms a chiral enolate complex
with substrate to act as a photosensitive center in the
reaction.
In conclusion, a visible light-driven enantioselective
aerobic oxidation of β-dicarbonyl compounds cata-
lyzed by cinchona-derived PTCs in batch and semi-
flow is reported. The easily modified cinchona-derived
PTCs act as a chiral center and a phase-transfer
catalytic center and form a chiral enolate complex with
substrates to act as a photosensitive center in the
reaction. A flow photomicroreactor was used to
achieve a visible light-driven heterogeneous gas-
liquid-liquid asymmetric aerobic oxidation reaction.
Good yields and enantioselectivities were obtained and
the reaction residence time could be substantially
shortened by semi-flow processes. Further research on
extending the cinchona-derived PTCs to other asym-
metric reactions are currently underway in our labo-
ratory.
Acknowledgements
We would like to thank the National Natural Science
Foundation of China (Nos. 21476041, U1608224, 61633006)
and the State Key Laboratory of Fine Chemicals for their
support.
References
[1] For representative reviews, see: a) R. Brimioulle, D.
Lenhart, M. M. Maturi, T. Bach, Angew. Chem. Int. Ed.
2015, 54, 3872–3890; Angew. Chem. 2015, 127, 3944–
3963; b) E. Meggers, Chem. Commun. 2015, 51, 3290–
3301; c) J. T. Tellis, C. B. Kelly, D. N. Primmer, M.
Jouffroy, N. R. Patel, G. A. Molander, Acc. Chem. Res.
2016, 49, 1429–1439; d) K. L. Skubi, T. R. Blum, T. P.
Yoon, Chem. Rev. 2016, 116, 10035–10074; e) Q. Liu, L.
Wu, Natl. Sci. Rev. 2017, 4, 359–380; f) M. Silvi, P.
Melchiorre, Nature 2018, 554, 41–49.
[2] For representative reviews, see: a) J. M. R. Narayanam,
C. R. J. Stephenson, Chem. Soc. Rev. 2011, 40, 102–113;
b) J. Xuan, W. Xiao, Angew. Chem. Int. Ed. 2012, 51,
6828–6838; Angew. Chem. 2012, 124, 6934–6944;
c) C. K. Prier, D. A. Rankic, D. W. C. MacMillan, Chem.
Rev. 2013, 113, 5322–5363; d) X. Lang, X. Chen, J.
Zhao, Chem. Soc. Rev. 2014, 43, 473–486; e) D. P. Hari,
B. König, Chem. Commun. 2014, 50, 6688–6699;
f) D. M. Schultz, T. P. Yoon, Science 2014, 343, 985;
g) T. Bach, Angew. Chem. Int. Ed. 2015, 54, 11294–
11295; Angew. Chem. 2015, 127, 11448–11449; h) L.
Marzo, S. K. Pagire, O. Reiser, B. König, Angew. Chem.
Int. Ed. 2018, 57, 10034–10072; Angew. Chem. 2018,
130, 10188–10228.
Experimental Section
General Produce for Synthesis of 3in the Batch
Substrate 2 (0.1 mmol) and 1e (10 mol%) in m-xylene (16 mL),
and 2 equiv. Cs2CO3 aq (in 2 mL H2O) were added to a test tube
equipped with a stirring bar. The reaction was covered by a 3 W
°
LED blue light at À 5 C for 24 h. After completion of the
reaction (confirmed by TLC), the mixture was diluted with
EtOAc (50 mL), washed with water (3×20 mL), dried over
anhydrous Na2SO4, filtered, and concentrated in vacuo. The
residue was purified by column chromatography on silica gel
(petroleum ether/ethyl acetate=10/1, 5/1) to afford the product
3. The ee of the product was determined by chiral HPLC.
[3] A. Bauer, F. Westkamper, S. Grimme, T. Bach, Nature
2005, 436, 1139–1140.
[4] a) R. Alonso, T. Bach, Angew. Chem. Int. Ed. 2014, 53,
4368–4371; Angew. Chem. 2014, 126, 4457–4460; b) A.
Tröster, R. Alonso, A. Bauer, T. Bach, J. Am. Chem. Soc.
2016, 138, 7808–7811.
[5] H. Huo, X. Shen, C. Wang, L. Zhang, P. Röse, L. Chen,
K. Harms, M. Marsch, G. Hilt, E. Meggers, Nature 2014,
515, 100–103.
[6] a) Y. Tan, W. Yuan, L. Gong, E. Meggers, Angew. Chem.
Int. Ed. 2015, 54, 13045–13048; Angew. Chem. 2015,
127, 13237–13240; b) W. Xu, X. Shen, Q. Ma, L. Gong,
E. Meggers, ACS Catal. 2016, 6, 7641–7646; c) X.
Huang, T. R. Quinn, R. D. Webster, L. Zhang, O. Wiest,
E. Meggers, J. Am. Chem. Soc. 2017, 139, 9120–9123.
General Produce for Synthesis of 3in the flow
Photomicroreactor
The organic phase was prepared by dissolving substrates 2
(0.1 mmol) and 1e (20 mol%) in m-xylene (16 mL). The
aqueous phase was a Cs2CO3 solution (1% Cs2CO3). The
organic phase and aqueous phase were introduced through
pump 1 and pump 2 at a flow rate of 1.5 mL/min. Oxygen was
introduced through a mass flowmeter at a flow rate of 10 mL/
min. The reaction pressure was 3 bar and the reaction temper-
°
ature was 0 C in the flow photomicroreactor. The outlet of the
back pressure regulator was directly attached to the original
reaction tube (the reaction tube was connected to air with a pipe
to release the excess O2 and relieve pressure quickly), and the
reaction mixture was circulated. O2 was continuously inlet to
Adv. Synth. Catal. 2019, 361, 1–9
7
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
��
These are not the final page numbers!

UPDATES
asc.wiley-vch.de
[7] a) E. Arceo, I. D. Jurberg, A. Alvarez-Fernandez, P. [14] a) K. Sakeda, K. Wakabayashi, Y. Matsushita, T.
Melchiorre, Nat. Chem. 2013, 5, 750–756; b) E. Arceo,
A. Bahamonde, G. Bergonzini, P. Melchiorre, Chem. Sci.
2014, 5, 2438–2442; c) Ł. Woźniak, J. J. Murphy, P.
Melchiorre, J. Am. Chem. Soc. 2015, 137, 5678–5681.
[8] Selected reports: a) A. Córdova, H. Sundén, M. Engqv-
ist, I. Ibrahem, J. Casas, J. Am. Chem. Soc. 2004, 126,
8914–8915; b) H. Sundén, M. Engqvist, J. Casas, I.
Ibrahem, A. Córdova, Angew. Chem. Int. Ed. 2004, 43,
6532–6535; Angew. Chem. 2004, 116, 6694–6697; c) H.
Egami, T. Katsuki, J. Am. Chem. Soc. 2009, 131, 6082–
6083; d) H. Tanaka, H. Nishi-kawa, T. Uchida, T.
Katsuki, J. Am. Chem. Soc. 2010, 132, 34, 12034–12041;
e) X. Lu, T. E. Long, Tetrahedron Lett. 2011, 52, 5051–
5054; f) L. Bu, J. Li, Y. Yin, B. Qiao, G. Chai, X. Zhao,
Z. Jiang, Chem. Asian J. 2018, 13, 2382–2387.
Ichimura, T. Suzuki, T. Wada, Y. Inoue, J. Photochem.
Photobiol. A: Chem. 2007, 192, 166–171; b) X. Wang,
G. D. Cuny, T. Noël, Angew. Chem. Int. Ed. 2013, 52,
7860–864; Angew. Chem. 2013, 125, 8014–8018; c) P.
Schroll, B. König, Eur. J. Org. Chem. 2015, 2, 309–313;
d) N. J. W. Straathof, S. E. Cramer, V. Hessel, T. Noël,
Angew. Chem. Int. Ed. 2016, 55, 15549–15553; Angew.
Chem. 2016, 128, 15778–15782; e) D. Chandrasekhar, S.
Borra, J. B. Nanubolu, R. A. Maurya, Org. Lett. 2016,
18, 2974–2977; f) I. A. Yunus, C. Basheer, H. A. Al-
Muallem, J. Environ. Chem. Eng. 2016, 4, 2802–2806;
g) S. Borra, D. Chandrasekhar, S. Adhikary, S. Rasala, S.
Gokulnath, R. A. Maurya, J. Org. Chem. 2017, 82,
2249–2256.
[15] Selected reports: a) R. C. R. Wootton, R. Fortt, A. J.
de Mello, Org. Process Res. Dev. 2002, 6, 187–189;
b) K. Jähnisch, U. Dingerdissen, Chem. Eng. Technol.
2005, 28, 426–427; c) S. Meyer, D. Tietze, S. Raub, B.
Schäfer, G. Kreisel, J. Photochem. Photobiol. A: Chem.
2007, 186, 248–253; d) T. Carofiglio, P. Donnola, M.
Maggini, M. Rossetto, E. Rossi, Adv. Synth. Catal. 2008,
350, 2815–2822; e) F. Lévesque, P. H. Seeberger Org.
Lett. 2011, 13, 5008–5011; f) A. Yavorskyy, O. Shvyd-
kiv, K. Nolan, N. Hoffmann, M. Oelgemöller, Tetrahe-
dron Lett. 2011, 52, 278–280; g) D. Chandrasekhar, S.
Borra, J. S. Kapure, G. S. Shivaji, G. Srinivasulub, R. A.
Maurya, Org. Chem. Front. 2015, 2, 1308–1312; h) Y.
Nagasawa, K. Tanba, N. Tada, E. Yamaguchi, A. Itoh,
Synlett 2015, 26, 412–415; i) N. J. W. Straathof, Y. Su,
V. Hessel, T. Noël, Nat. Protoc. 2016, 11, 10–21; j) Y.
Wu, G. Zhou, Q. Meng, X. Tang, G. Liu, H. Yin, J.
Zhao, F. Yang, Z. Yu, Y. Luo, J. Org. Chem. 2018, 83,
13051–13062.
[9] W. Ding, L. Lu, Q. Zhou, Y. Wei, J. Chen, W. Xiao, J.
Am. Chem. Soc. 2017, 139, 63–66.
[10] X. Tang, S. Feng, Y. Wang, Y. Yang, Z. Zheng, J. Zhao,
Y. Wu, H. Yin, G. Liu, Q. Meng, Tetrahedron 2018, 74,
3624–3633.
[11] For representative reviews, see: a) T. Fukuyama, M. T.
Rahman, M. Sato, I. Ryu, Synlett 2008, 2, 151–163;
b) C. Wiles, P. Watts, Future Med. Chem. 2009, 1, 1593–
1612; c) R. L. Hartman, J. P. McMullen, K. F. Jensen,
Angew. Chem. Int. Ed. 2011, 50, 7502–7519; Angew.
Chem. 2011, 123, 7642–7661; d) L. Malet-Sanz, F.
Susanne, J. Med. Chem. 2012, 55, 4062–4098; e) R. L.
Hartman, Org. Process Res. Dev. 2012, 16, 870–887;
f) B. Gutmann, D. Cantillo, C. O. Kappe, Angew. Chem.
Int. Ed. 2015, 54, 6688–6728; Angew. Chem. 2015, 127,
6788–6832; g) R. Munirathinam, J. Huskens, W. Ver-
boom, Adv. Synth. Catal. 2015, 357, 1093–1123;
h) H. P. L. Gemoets, Y. Su, M. Shang, V. Hessel, R.
Luque, T. Noël, Chem. Soc. Rev. 2016, 45, 83–117; i) M. [16] L. Hintermann, M. Schmitz, U. Englert, Angew. Chem.
Atobe, H. Tateno, Y. Matsumura, Chem. Rev. 2018, 118,
Int. Ed. 2007, 46, 5164–5167; Angew. Chem. 2007, 119,
4541–4572.
5256–5259.
[12] a) D. Zhao, K. Ding, ACS Catal. 2013, 3, 928–944; [17] a) M. Lian, Z. Li, Y. Cai, Q. Meng, Z. Gao, Chem. Asian
b) D. Cambié, C. Bottecchia, N. J. W. Straathof, V.
Hessel, T. Noël, Chem. Rev. 2016, 116, 10276–10341.
J. 2012, 7, 2019–2023; b) J. Liu, W. Ding, Q. Zhou, D.
Liu, L. Lu, W. Xiao, Org. Lett. 2018, 20, 461–464.
[13] M. Neumann, K. Zeitler, Org. Lett. 2012, 14, 2658–2661.
Adv. Synth. Catal. 2019, 361, 1–9
8
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
��
These are not the final page numbers!

UPDATES
Visible-Light-Driven Enantioselective Aerobic Oxidation of
β-Dicarbonyl Compounds Catalyzed by Cinchona-Derived
Phase Transfer Catalysts in Batch and Semi-Flow
Adv. Synth. Catal. 2019, 361, 1–9
X.-F. Tang, J.-N. Zhao, Y.-F. Wu, S.-H. Feng, F. Yang, Z.-Y.
Yu, Q.-W. Meng*