Metal-free desulfonylation reaction through visible-light photoredox catalysis

Article abstract of DOI:10.1002/ejoc.201301105

The desulfonylation of β-arylketosulfones has been achieved in good to excellent yields by using 3-W blue LEDs light, 1 mol-% organic dye eosin Y bis(tetrabutylammonium salt) as photocatalyst, and diisopropylethylamine as reducing agent. Mechanistic studies demonstrate that oxidative quenching of the excited eosin Y by β-arylketosulfones plays a crucial role in the present photoredox catalytic cycle. Reductive desulfonylation is essential to enable to use of a sulfone as an auxiliary group. For reductive removal of sulfones, highly aggressive metal-containing reducing agents and harsh reaction conditions are often employed. In this paper, metal-free desulfonylation of β-arylketosulfones can be achieved efficiently at room temperature under visible-light irradiation.

Full text of DOI:10.1002/ejoc.201301105

FULL PAPER
DOI: 10.1002/ejoc.201301105
Metal-Free Desulfonylation Reaction Through Visible-Light Photoredox
Catalysis
Deng-Tao Yang,[a] Qing-Yuan Meng,[b] Jian-Ji Zhong,[b] Ming Xiang,[b] Qiang Liu,*[a,b] and
Li-Zhu Wu*[b]
Keywords: Photochemistry / Photocatalysis / Dyes/pigments / Synthetic methods / Sulfur
The desulfonylation of β-arylketosulfones has been achieved
in good to excellent yields by using 3-W blue LEDs light,
1 mol-% organic dye eosin Y bis(tetrabutylammonium salt)
as photocatalyst, and diisopropylethylamine as reducing
agent. Mechanistic studies demonstrate that oxidative
quenching of the excited eosin Y by β-arylketosulfones plays
a crucial role in the present photoredox catalytic cycle.
sulfonylated aryl ketone with excellent yields.[5] Despite the
advantage of its metal-free processes, the method was lim-
ited by the necessity of high-energy UV radiation. Recently,
visible-light photoredox catalysis[6] is continuing to emerge
as a powerful tool to develop more sustainable chemical
processes. We reported visible-light-induced aerobic cross-
dehydrogenative coupling (CDC) reaction by organic dye
eosin Y bis(tetrabutylammonium salt) (TBA-eosin Y), and
demonstrated that photoinduced electron transfer from N-
aryl tetrahydroisoquinolines to the exited TBA-eosin Y oc-
curred to generate eosin Y radical anions.[7] Given the
strong electron-donating ability of eosin Y and its applica-
tion in visible light photoredox catalysis,[8] one may expect
the electron transfer from excited eosin Y or eosin Y radical
anions to suitable sulfones for the desulfonylation. Herein,
we present the use of 1 mol-% TBA-eosin Y, as photocata-
lyst, and diisopropylethylamine (iPr2EtN), a simple amine
as reducing agent, to achieve efficiently the desulfonylation
of β-arylketosulfones under visible-light irradiation. More
importantly, the generation of eosin Y radical cations was
detected by flash photolysis, and a mechanistic study indi-
cates that oxidative quenching of the excited eosin Y by β-
arylketosulfones plays a vital role in the present photoredox
catalytic cycle.
Introduction
Use of a sulfone as an auxiliary group is still a significant
synthetic strategy to generate a range of useful products.
The synthetic applicability to obtain these products is at-
tributed to the facts: economical and stable functionality
(often crystalline) facilitates purification and the strong in-
ductive effect of a sulfone moiety stabilizes carbanions.[1]
To remove the sulfone moiety, further functional group
transformations are needed. One of the most widely used
methods is the replacement of sulfone group with hydrogen,
which is always achieved by reductive desulfonylation[2] by
using metal-containing reducing agents, such as Al (Hg),[3a]
Zn/HOAc,[3b] Bu3SnH,[3c] Bu3SnCl/NaBH3CN,[3d] Mg/
[3f]
MeOH,[3e] SmI2
and Sm/HgCl2.[3g] Recent efforts have
shown that reductive desulfonylation of sulfones can also
be accomplished by using a neutral organic electron donor
bisimidazolylidene.[3h]
In contrast to traditional thermal reactions, light can be
considered an ideal reagent for environmentally friendly,
“green” chemical synthesis. Early works of Ohno and co-
workers have demonstrated that the desulfonylation of β-
ketosulfones can be realized by a photochemical ap-
proach.[4] However, inclusion of precious-metal catalyst
ruthenium(II) complex and a stoichiometric Hantzsch ester
restricts their practical application. We have found that di-
rect irradiation of β-arylketosulfones with UV light in the
presence of ascorbic acid resulted in the formation of de-
Results and Discussion
Our preliminary studies focused on desulfonylation of 3-
methyl-3-(phenylsulfonyl) chroman-4-one (1a). To achieve
this desired transformation, we started with the reaction of
1a in the presence of TBA-eosin Y and iPr2EtN under ar-
gon by using a 3-W blue LED in acetonitrile. Interestingly,
desired product 1b was obtained in Ͼ 99% yield (Table 1,
Entry 1). The absence of TBA-eosin Y, however, resulted
in negligible conversion of 1a under the same conditions
(Table 1, Entry 2). According to the UV/Vis absorption that
[a] State Key Laboratory of Applied Organic Chemistry, College
of Chemistry and Chemical Engineering, Lanzhou University,
Lanzhou 730000, P. R. China
E-mail: liuqiang@lzu.edu.cn
[b] Key Laboratory of Photochemical Conversion and
Optoelectronic Materials, Technical Institute of Physics and
Chemistry, the Chinese Academy of Sciences,
Beijing 100190, P. R. China
E-mail: lzwu@ipc.ac.cn
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201301105.
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Metal-Free Desulfonylation Reaction
only TBA-eosin Y exhibits a broad absorption band at electron-withdrawing (Table 2, Entry 21) group were at-
wavelength longer than 400 nm,[9] no conversion was ob- tached to the phenyl group of the sulfones. The formic acid
served when the reaction was carried out in the dark substantially improved the performance of the reaction
(Table 1, Entry 3). The results suggest that both light and (Table 2, Entries 11, 17–19), which may reduce basicity of
eosin Y are essential for desulfonylation. When Hantzsch the reaction system, especially when acidity of α-carbon of
ester 1,4-dihydropyridine (HEH) was used instead of the substrates is relatively high. A variety of substituted
iPr2EtN, the reaction was also quantitative (Table 1, En- functional groups were tolerated: allyl (Table 2, Entries 2, 5,
try 4). The case employing Et3N as reducing agent showed 6, 7, 10, and 16), ester (Table 2, Entry 8), epoxide (Table 2,
decreased efficiency (Table 1, Entry 5). Formic acid, which Entry 9), tert-butyldimethylsilane (Table 2, Entry 13), and
was used as a hydrogen atom source in the photoredox- hydroxy (Table 2, Entry 14). There was no reaction of the
catalyzed dehalogenation reaction,[10] gave negligible prod- sulfonylated aliphatic ketone substrate (Table 2, Entry 22),
uct (Table 1, Entry 6). We also investigated the influence of possibly owing to the fact that the reduction potential of
solvents upon this reaction; neither protic solvents nor
aprotic solvents improved the product yield (Table 1, En-
tries 7–9) except acetonitrile. Considering iPr2EtN is much
cheaper and easier to obtain than HEH, and the aromatiza-
tion of the latter could influence the purification of prod-
ucts, we chose iPr2EtN as a reductant in the presence of
TBA-eosin Y in acetonitrile with irradiation by blue LEDs
as the standard conditions.
Table 2. Substrate scope studies of desulfonylation reaction.
Table 1. Optimization of reaction conditions.[a]
Entry Conditions
Time [h]
Yield [%]
1
2
3
4
5
6
7
8
9
standard conditions
no TBA-eosin Y
no light
13
13
13
12
20
20
20
20
20
Ͼ 99
trace
0
Ͼ 99
68
0
69
HEH[b] instead of iPr2EtN
Et3N instead of iPr2EtN
HCOOH instead of iPr2EtN
DMF instead of CH3CN
CH2Cl2 instead of CH3CN
MeOH instead of CH3CN
52
61
[a] Standard conditions as described: TBA-eosin Y(1 mol-%), iP-
r2EtN (10 equiv.), CH3CN, room temp., 3-W 450 nm LED.
[b] HEH: Hantzsch ester 1,4-dihydropyridine.
The scope of the desulfonylation process was further il-
lustrated by the examples detailed in Table 2. Variation of
β-arylketosulfones revealed that a range of skeletons and
functional groups participated in this desulfonylation reac-
tion. We found chroman-4-one-containing substrates also
afforded corresponding products in good to excellent yields
(Table 2, Entries 1–3). Similarly, reactions of sulfonylated
acylbenzenes (Table 2, Entries 4–9), 1-tetralones (Table 2,
Entries 10–14) and 2-acylpyridine (Table 2, Entry 20) were
successful. To explore the influence of electronic effects, we
examined both electron-withdrawing and electron-donating
aryl substituents; both proved to be efficient (Table 2, En-
tries 15–19). Moreover, the chemistry was also successful
[a] Isolated yield, yields in brackets performed with 10 equiv. for-
mic acid. [b] Yield determined by GC. [c] Yields based on the con-
version of starting materials [conversion of 13a: 61%, conversion
when the electron-donating group (Table 2, Entry 12), and of 14a: 67%].
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22a [–1.94 V versus saturated calomel electrode (SCE)] is tron transfer from eosin Y radical anion to β-arylketosul-
much lower than that of 1a (–1.51 V versus SCE).[9]
fone 1a is unfavorable. This conclusion was further sup-
The photocatalytic desulfonylation was investigated in a ported by electrochemical studies.[9]
degassed CH3CN solution at room temperature by means
In light of the results presented above, we propose the
of laser-flash photolysis. Figure 1 (a) shows the transient following mechanism for the desulfonylation reaction
absorption spectra of TBA-eosin Y obtained through (Scheme 1). Visible-light irradiation of TBA-eosin Y gener-
532 nm-laser irradiation. Immediately after a laser pulse, a ates the excited TBA-eosin Y. Oxidative quenching of the
strong negative bleach of the ground-state absorption of excited TBA-eosin Y by β-arylketosulfones 1a results in the
TBA-eosin Y at approximately 530 nm and characteristic formation of the TBA-eosin Y radical cation (EY+·) and
absorption of the triplet state of TBA-eosin Y at 580 nm 1a–· radical anion. Subsequent electron transfer from iP-
were observed. When β-arylketosulfone 1a was introduced r2EtN to EY+· radical cation regenerates TBA-eosin Y and
into the solution of TBA-eosin Y (Figure 1, c), a new ab- completes the catalytic cycle. Finally, 1a–· radical anion un-
sorption band develops at 460 nm, which is in line with that dergoes desulfonylation to populate 1b· ketone radical,
of reported eosin Y radical cation.[11,12] From the kinetics which can abstract a hydrogen atom from iPr2EtN or
probed at 460 nm, the rise grows quickly with an electron iPr2EtN radical cation to afford corresponding ketone 1b.
transfer (ET) rate constant (kET) of 1.1ϫ105 s–1 (9.4 μs),
and the back charge recombination (kCR) derived from the
decay phase was determined to 4.0ϫ103 s–1 (253 μs). With
progressive addition of iPr2EtN into the solution, the life-
time of the eosin Y radical cation gradually decreased (Fig-
ure 1, c). The quenching can be attributed to further elec-
tron transfer from iPr2EtN to the eosin Y radical cation,
which, once consumed, produced the eosin Y radical cation
and regenerated eosin Y. Although we also observed the
signal of radical anion of TBA-eosin Y at 420 nm[12] by
laser-flash photolysis of TBA-eosin Y in the presence of a
high concentration of iPr2EtN, no quenching was found
when β-arylketosulfone 1a was subsequently added to the
Scheme 1. Mechanistic proposal for the visible-light-catalyzed de-
solution (Figure 1, b). The results indicated that the elec- sulfonylation process.
Figure 1. (a) Transient absorption difference spectra of TBA-eosin Y (1.0ϫ10–5 molL–1) in CH3CN at room temperature. (b) Transient
absorption difference spectra of TBA-eosin Y (1.0ϫ10–5 molL–1) with iPr2EtN (2ϫ10–2 molL–1) in CH3CN at room temperature.
(c) Transient absorption difference spectra of TBA-eosin Y (1.0ϫ10–5 molL–1) with 1a (2ϫ10–3 molL–1) in CH3CN at room temperature,
and the kinetic decay of eosin Y radical cation recorded at 410 nm by progressive addition of iPr2EtN.
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Metal-Free Desulfonylation Reaction
8.4 Hz, 1 H), 4.48 (dd, J = 11, 4.8 Hz, 1 H), 4.13 (t, J = 11 Hz, 1 H),
2.85 (m, 1 H), 1.20 (d, J = 6.9 Hz, 3 H) ppm. 13C NMR (100 MHz,
Conclusions
In conclusion, we have developed a visible-light-driven CDCl3): δ = 194.7, 161.7, 135.6, 127.3, 121.3, 120.5, 117.7, 72.2,
40.7, 10.6 ppm.
method for desulfonylation of β-arylketosulfones. By com-
bining cheap, readily available TBA-eosin Y and iPr2EtN,
the photoredox catalytic system can afford desired desulf-
Product of 2a: 16.4 mg, yield 87%. Yellow oil. 1H NMR (400 MHz,
CDCl3): δ = 7.89 (d, J = 7.8 Hz, 1 H), 7.46 (dd, J = 7.5, 8.1 Hz, 1
onylated products with high efficiency and excellent func- H), 7.01 (dd, J = 7.5, 7.8 Hz, 1 H), 6.95 (d, J = 8.1 Hz, 1 H), 5.83
(m, 1 H), 5.14 (d, J = 16.8 Hz, 1 H), 5.11 (d, J = 10.2 Hz, 1 H),
4.50 (dd, J = 4.5, 11.4 Hz, 1 H), 4.24 (dd, J = 9.3, 11.4 Hz, 1 H),
2.71 (m, 2 H), 2.26 (ddd, J = 7.8, 9.0, 15.6 Hz) ppm. 13C NMR
(100 MHz, CDCl3): δ = 193.6, 161.6, 135.8, 134.6, 127.4, 121.3,
120.6, 117.8, 117.7, 69.9, 45.2, 30.5 ppm.
tional group tolerance. Flash photolysis and electrochemi-
cal studies reveal that oxidative quenching (electron transfer
from the excited TBA-eosin Y to β-arylketosulfones) domi-
nates the catalytic cycle.
Product of 3a: 20.0 mg, yield 84%. Yellow oil. 1H NMR (400 MHz,
CDCl3): δ = 7.93 (d, J = 8.4 Hz, 1 H), 7.47 (dd, J = 8.4, 8.7 Hz, 1
H), 7.29 (m, 5 H), 7.02 (dd, J = 7.2, 7.5 Hz, 1 H), 6.96 (d, J =
8.1 Hz, 1 H), 4.36 (dd, J = 4.8, 11.7 Hz, 1 H), 4.16 (dd, J = 9.0,
11.7 Hz, 1 H), 3.29 (dd, J = 4.5, 14.1 Hz, 1 H), 2.92 (m, 1 H), 2.70
(dd, J = 10.8, 14.1 Hz, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ
= 193.7, 161.5, 138.2, 135.8, 129.0, 128.6, 127.4, 126.6, 121.4, 120.5,
117.7, 69.4, 47.6, 32.3 ppm.
Experimental Section
General Information: Unless otherwise noted, all commercially
available compounds were used as received without further purifi-
cation. Silica gel (200–300 meshes) was used for column
chromatography, and the distillation range of petroleum was 60–
1
90 °C. H and 13C NMR spectra were recorded with Bruker AM-
400 MHz instruments, and spectroscopic data are reported in ppm
relative to tetramethylsilane (TMS) as internal standard. HRMS
data were determined with a Bruker Daltonics APEXII 47e FT-
ICR spectrometer. GC yields were measured with a Varian CP-
3380 instrument. Voltammetric experiments were manipulated on
a Princeton Applied Research Potentiostat/Galvanostat model 283.
The UV/Vis absorption spectra were recorded with a Shimadzu
1601 PC spectrophotometer. Time-resolved emission and transient
absorption spectroscopy were carried out on an Edinburgh LP 920
instrument.
Product of 4a and 21a: GC yield 90% and 99%, respectively. Yellow
oil. 1H NMR (400 MHz, CDCl3): δ = 7.94 (m, 2 H), 7.54 (m, 1 H),
7.44 (m, 2 H), 2.58 (s, 3 H) ppm.
Product of 5a: 14.4 mg, yield 90%. Yellow oil. 1H NMR (300 MHz,
CDCl3): δ = 7.97 (d, J = 7.2 Hz, 2 H), 7.56 (t, J = 7.5 Hz, 2 H),
7.46 (dd, J = 7.2, 7.5 Hz), 5.90 (m, 1 H), 5.10 (d, J = 17.1 Hz, 1
H), 5.01 (d, J = 9.8 Hz, 1 H), 3.08 (t, J = 7.8 Hz, 2 H), 2.50 (q, J
= 7.8, 7.2 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 199.4,
137.3, 136.9, 133.0, 128.5, 128.0, 115.2, 37.7, 28.1 ppm.
Product of 6a: 18.4 mg, yield 98%. Yellow oil. 1H NMR (300 MHz,
CDCl3): δ = 7.95 (d, J = 8.4 Hz, 2 H), 7.55 (t, J = 7.5 Hz, 1 H),
7.45 (dd, J = 8.4, 7.5 Hz, 2 H), 5.17 (t, J = 7.8 Hz, 1 H), 2.99 (t, J
= 7.5 Hz, 2 H), 2.42 (q, J = 7.5, 7.8 Hz, 2 H), 1.69 (s, 3 H), 1.63
(s, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 200.1, 137.0, 132.9,
132.7, 128.5, 128.0, 122.9, 38.7, 25.7, 22.9, 17.6 ppm.
Product of 7a: 20.0 mg, yield Ͼ 99%. Yellow oil. 1H NMR
(400 MHz, CDCl3): δ = 7.97 (m, 2 H), 7.57 (m, 1 H), 7.46 (m, 2
H), 5.73 (m, 1 H), 5.59 (m, 1 H), 2.95 (m, 2 H), 2.83 (m, 1 H), 2.03
(m, 2 H), 1.86 (m, 1 H), 1.74 (m, 1 H), 1.61 (m, 1 H), 1.32 (m, 1
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 199.6, 137.3, 132.9,
130.8, 128.6, 128.1, 127.9, 44.8, 31.6, 29.1, 25.1, 21.1 ppm.
General Method of Substrate Preparation: To a solution of the sub-
strate ketone (1 mmol) in absolute ethyl ether (5 mL) was added
AlCl3 (0.01 mmol) under argon at 0 °C, and then liquid bromine
was added dropwise. The mixture was stirred vigorously at room
temperature. After complete consumption of the substrate, satu-
rated NaHCO3 was used to neutralize HBr and Br2 in the mixture.
The organic layer was dried with Na2SO4. The residue bromo-
ketone was obtained after evaporation, which was used as the sub-
strate for the next reaction directly without further purification.
The bromoketone obtained was dissolved in dimethylformamide
(DMF) under argon at 0 °C, then PhSO2Na was added. The mix-
ture was stirred vigorously at room temperature until complete con-
sumption of the substrate. The mixture was quenched with H2O
and extracted with EtOAc. The organic layer was washed with
H2O, evaporated and purified by flash chromatography on silica
gel to give β-arylketosulfones.
Product of 8a: 14.8 mg, yield 77%. Yellow oil. 1H NMR (400 MHz,
CDCl3): enol isomer: product of 8a = 0.29. δ = 7.91 (m, 2 H), 7.55
(m, 1 H), 7.42 (m, 2 H), 4.12 (m, 2 H), 3.96 (d, J = 1.2 Hz), 1.21
(m, 3 H) ppm.
Product of 9a: 13.2 mg, yield 75%. Yellow oil. 1H NMR (400 MHz,
CDCl3): δ = 7.79 (m, 2 H), 7.56–7.60 (m, 1 H), 7.46–7.50 (m, 2 H),
3.20 (t, J = 7.2 Hz, 2 H), 3.10–3.17 (m, 1 H), 2.81 (t, J = 4.4 Hz,
1 H), 2.55–2.58 (m, 1 H), 2.16–2.24 (m, 1 H), 1.80–1.89 (m, 1
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 199.0, 136.8, 133.2,
128.6, 128.1, 51.6, 47.4, 34.5, 26.7 ppm.
Product of 10a: 18.3 mg, yield 98%. Yellow oil. 1H NMR
(400 MHz, CDCl3): δ = 8.03 (d, J = 7.2 Hz, 1 H), 7.45 (m, 1 H),
7.29 (t, J = 7.2 Hz, 1 H), 7.23 (d, J = 7.2 Hz, 1 H), 5.85 (m, 1 H),
5.09 (m, 2 H), 2.99 (m, 2 H), 2.27 (m, 1 H), 2.55 (m, 1 H), 2.24
(m, 2 H), 1.86 (m, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
199.4, 144.0, 136.2, 133.2, 132.5, 128.7, 127.4, 126.5, 116.8, 47.1,
34.0, 28.6, 27.9 ppm.
General Procedure: In a 10 mL snap-cap vial equipped with a mag-
netic stirring bar and fitted with a septum, the β-ketosulfone
(1 equiv.), diisopropylethylamine (iPr2EtN; 10 equiv.), eosin Y bis-
(tetrabutylammonium salt) (TBA-eosin Y; 0.01 equiv.) were dis-
solved in CH3CN (0.1 mmol/mL). The mixture was bubbled with
a stream of argon for 20 min through a syringe needle. The vial
was then irradiated by using a single 450 nm LED. The progress of
the reaction was monitored by thin-layer chromatography at regu-
lar intervals. Generally, conversion was close to 100% after 12 h of
irradiation. Upon removal of solvent under vacuum, the residue
was purified by flash chromatography on silica gel to afford the
corresponding products.
Product of 1a: 16.2 mg, yield Ͼ 99%. Yellow oil. 1H NMR
(400 MHz, CDCl3): δ = 7.88 (d, J = 8.1 Hz, 1 H), 7.45 (dd, J =
7.5, 8.4 Hz, 1 H), 6.99 (dd, J = 7.5, 8.1 Hz, 1 H), 6.94 (d, J =
Product of 11a and 12a: 14.3 mg, yield 98%, and 13.3 mg, yield
1
91%, respectively. White solid. H NMR (400 MHz, CDCl3): δ =
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Q. Liu, L.-Z. Wu et al.
FULL PAPER
8.03 (dd, J = 0.8, 7.6 Hz, 1 H), 7.46 (td, J = 1.2, 7.6 Hz), 7.30 (t,
J = 7.6 Hz, 1 H), 7.26 (t, J = 7.6 Hz, 1 H), 2.96 (t, J = 6.0 Hz, 2
H), 2.65 (t, J = 6.0 Hz, 2 H), 2.13 (m, 2 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 198.3, 144.4, 133.3, 132.6, 128.7, 127.1,
126.6, 39.1, 29.6, 23.2 ppm.
Acknowledgments
Financial support from the National Natural Science Foundation
of China (NSFC) (grant numbers 21172102 and 21090343), the
Ministry of Science and Technology of China (grant number
2013CB834804), and the Fundamental Research Funds for the
Central Universities is gratefully acknowledged.
Product of 13a: 15.4 mg, conversion 61%, yield 70%. Yellow oil.
1H NMR (400 MHz, CDCl3): δ = 8.03 (dd, J = 1.2, 7.6 Hz, 1 H),
7.46 (m, 1 H), 7.30 (t, J = 7.6 Hz, 1 H), 7.23 (d, J = 7.6 Hz, 1 H),
3.61 (t, J = 6.7 Hz, 2 H), 2.99 (m, 2 H), 2.48 (m, 1 H), 2.22 (m, 1
H), 1.91 (m, 2 H), 1.26–1.53 (m, 9 H), 0.90 (s, 9 H), 0.05 (s, 6
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 200.4, 143.9, 133.0,
132.6, 128.6, 127.5, 126.5, 63.3, 47.5, 32.84, 29.6, 29.4, 28.3, 28.2,
27.0, 26.0, 25.7, 18.4, –5.3 ppm. HRMS (ESI): calcd. for
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527–532; e) J. M. R. Narayanam, C. R. J. Stephenson, Chem.
Soc. Rev. 2011, 40, 102–113; f) J. W. Tucker, C. R. J. Stephen-
son, J. Org. Chem. 2012, 77, 1617–1622; g) C. K. Prier, D. A.
Rankic, D. W. C. Macmillian, Chem. Rev. 2013, DOI: 10.1021/
cr300503r.
C22H36NaO2Si [M + Na]+ 383.2377; found 383.2378. IR (film): ν =
˜
2930.5, 2857.2, 1685.5, 1601.5, 1460.0, 1252.8, 1099.3, 837.1, 776.2,
739.8 cm–1.
Product of 14a: 11.7 mg, conversion 67%, yield 71%. Yellow oil.
1H NMR (400 MHz, CDCl3): δ = 8.02 (d, J = 7.6 Hz, 1 H), 7.45
(m, 1 H), 7.29 (t, J = 7.6 Hz, 1 H), 7.22 (d, J = Hz7.6 H, 1 H),
3.64 (t, J = 6.4 Hz, 2 H), 3.00 (m, 2 H), 2.48 (m, 1 H), 2.21 (m, 1
H), 1.85 (m, 2 H), 1.38–1.85 (m, 10 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 200.4, 143.9, 133.1, 132.6, 128.6, 127.5, 126.5, 63.0,
47.5, 32.7, 29.5, 29.3, 28.3, 28.2, 26.9, 25.6 ppm. HRMS (ESI):
calcd. for C16H22NaO2 [M + Na]+ 269.1512; found 269.1511. IR
(film): ν = 3397.2, 2930.6, 2857.5, 1680.6, 1600.5, 1455.5, 1224.6,
˜
742.5 cm–1.
Product of 15a: 10.7 mg, yield 71%. White solid. 1H NMR
(300 MHz, CDCl3): δ = 7.95 (dd, J = 1.8, 6.6 Hz, 2 H), 6.94 (dd,
J = 1.8, 6.6 Hz, 2 H), 3.88 (s, 3 H), 2.56 (s, 3 H) ppm.
Product of 16a: 16.0 mg, yield 82%. Yellow oil. 1H NMR
(400 MHz, CDCl3): δ = 7.95 (dd, J = 2.0, 7.2 Hz, 2 H), 6.94 (dd,
J = 2.0, 7.2 Hz, 2 H), 5.89 (m, 1 H), 5.10 (m, 2 H), 3.88 (s, 3 H),
3.03 (t, J = 7.2 Hz, 2 H), 2.49 (m, 2 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 198.0, 163.4, 137.5, 130.3, 129.8, 115.4, 113.7, 55.4,
37.4, 28.4 ppm.
Product of 17a: 11.0 mg, yield 71%. White solid. 1H NMR
(300 MHz, CDCl3): δ = 7.86 (dd, J = 3.0, 9.0 Hz, 2 H), 7.40 (dd,
J = 3.0, 9.0 Hz, 2 H), 2.56 (d, J = 3.0 Hz, 3 H) ppm.
Product of 18a: 19.1 mg, yield 96%. Yellow solid. 1H NMR
(400 MHz, CDCl3): δ = 7.80 (dt, J = 2.4, 8.4 Hz, 2 H), 7.59 (dt, J
= 2.4, 8.4 Hz, 2 H), 2.58 (s, 3 H) ppm.
[7] Q. Liu, Y.-N. Li, H.-H. Zhang, B. Chen, C.-H. Tung, L.-Z.
Wu, Chem. Eur. J. 2012, 18, 620–627.
[8] a) D. Ravelli, M. Fagnoni, A. Albini, Chem. Soc. Rev. 2013,
42, 97–113; b) D. Ravelli, M. Fagnoni, ChemCatChem 2012, 4,
169–171; c) Y. C. Teo, Y. Pan, C. H. Tan, ChemCatChem 2013,
5, 235–240; d) D. P. Hari, P. Schroll, B. König, J. Am. Chem.
Soc. 2012, 134, 2958–2961; e) D. P. Hari, T. Hering, B. König,
Org. Lett. 2012, 14, 5334–5337; f) M. Neumann, S. Füldner, B.
König, K. Zeitler, Angew. Chem. 2011, 123, 981–985; Angew.
Chem. Int. Ed. 2011, 50, 951–954; g) D. P. Hari, B. König, Org.
Lett. 2011, 13, 3852–3855.
Product of 19a: 18.8 mg, yield 79%. Yellow oil. 1H NMR
(400 MHz, CDCl3): δ = 7.83 (dd, J = 2, 6.8 Hz, 2 H), 7.61 (dd, J
= 2, 6.8 Hz, 2 H), 5.90 (m, 1 H), 5.06 (m, 2 H), 3.04 (m, 2 H), 2.50
(m, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 198.3, 137.0,
135.6, 131.9, 129.5, 128.1, 115.5, 37.7, 28.0 ppm.
[9] The detailed information is provided in the Supporting Infor-
mation.
Product of 20a: 9.6 mg, yield 79%. Yellow oil. 1H NMR (300 MHz,
CDCl3): δ = 8.63 (m, 1 H), 7.98 (m, 1 H), 7.77 (m, 1 H), 7.41 (m, [10] J. M. R. Narayanam, J. W. Tucker, C. R. J. Stephenson, J. Am.
Chem. Soc. 2009, 131, 8756–8757.
1 H), 2.67 (m, 3 H) ppm.
[11] E. Joselevich, I. Willner, J. Phys. Chem. 1995, 99, 6903–6912.
[12] S. D.-M. Islam, T. Konishi, M. Fujitsuka, O. Ito, Y. Nakamura,
Y. Usui, Photochem. Photobiol. 2000, 71, 675–680.
Received: July 24, 2013
Supporting Information (see footnote on the first page of this arti-
cle): UV/Vis absorption of the system, data of electrochemistry,
and calculation of the free Gibbs energy changes for the electron-
transfer processes.
Published Online: October 2, 2013
7532
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 7528–7532