Custom-Made Pyrene Photocatalyst-Promoted Desulfonylation of Arylethenyl Sulfones Using Green-Light-Emitting Diodes

Article abstract of DOI:10.1055/s-0040-1706025

The Sonogashira coupling of 1,3,6,8-tetrabromopyrene with 4-[(-)-β-citronellyloxy]phenylethyne was employed to synthesize 1,3,6,8-tetra[4-(citronellyloxy)phenylethynyl]pyrene. The pyrene derivative catalyzed the reductive desulfonylation of ethenyl sulfones via visible-light irradiation (514 nm green light-emitting diodes) in the presence of i -Pr ₂NEt. The β-citronellyloxy groups provided the sufficient solubility to the highly π-expanded pyrene catalyst, and their polar oxygen functionalities enabled the easy separation of the catalyst from the products via column chromatography.

Full text of DOI:10.1055/s-0040-1706025

SYNTHESIS
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart
2021, 53, A–K
special topic
A
Bond Activation – in Honor of Prof. Shinji
H. Watanabe et al.
Special Topic
Synthesis
Custom-Made Pyrene Photocatalyst-Promoted Desulfonylation of
Arylethenyl Sulfones Using Green-Light-Emitting Diodes
Hikaru Watanabea
Kazuki Nakajimaa
Kento Ekunia
Ryota Edagawaa
Yuta Akagia
Yasuhiro Okudaa
Kan Wakamatsub
OR
RO
pyrene catalyst
green LED (30 W)
i-Pr2NEt
PhSO2
Ph
H
Ph
Ph
MeCN–THF
50 °C, 9 h
88%
catalyst
Ph
0
0
0
0
-0
0
0
2
-
1
3
9
6
-
5
8
5
1
0
0
0
0-0
0
0
2
-7
4
6
7
-
1
0
0
5
Akihiro Orita*a
0
0
0
0
-0
0
0
1
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8
6
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5
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# Easily separable pyrene catalyst
# Alternative Julia olefination
RO
OR
a Department of Applied Chemistry and Biotechnology,
Okayama University of Science, 1-1, Ridai-cho, Kita-ku,
Okayama 700-0005, Japan
# Green LED-driven C–SO2 bond activation
CH2
R:
orita@dac.ous.ac.jp
b Department of Chemistry, Okayama University of Science,
1-1, Ridai-cho, Kita-ku, Okayama 700-0005, Japan
Published as part of the Special Topic
Bond Activation – in Honor of Prof. Shinji Murai
Corresponding Author
Received: 06.01.2021
Accepted after revision: 25.01.2021
Published online: 22.02.2021
tant. In 1995, Keck developed an alternative to Julia olefina-
tion using SmI2 rather than amalgam and demonstrated the
usability of the former (equation 1 in Scheme 1).8 However,
the precious rare-earth metal reagent (SmI2) was still re-
quired as a reductant, and high E-selectivity of the olefinic
product was not achieved. To achieve operational compac-
tion of this process, modified Julia olefinations were devel-
oped using heteroaromatic sulfones, which are widely uti-
lized in organic syntheses (equation 2 in Scheme 1).9,10
DOI: 10.1055/s-0040-1706025; Art ID: ss-2021-f0005-st
Abstract The Sonogashira coupling of 1,3,6,8-tetrabromopyrene
with 4-[(–)--citronellyloxy]phenylethyne was employed to synthesize
1,3,6,8-tetra[4-(citronellyloxy)phenylethynyl]pyrene. The pyrene deriv-
ative catalyzed the reductive desulfonylation of ethenyl sulfones via vis-
ible-light irradiation (514 nm green light-emitting diodes) in the pres-
ence of i-Pr2NEt. The -citronellyloxy groups provided the sufficient
solubility to the highly -expanded pyrene catalyst, and their polar oxy-
gen functionalities enabled the easy separation of the catalyst from the
products via column chromatography.
Conventional and modified Julia olefinations
1) BuLi
PhSO2
2) PhCHO
PhSO2
Ph
3) Ac2O
Na(Hg)
or SmI2
Ph
Ph
Keywords desulfonylation, photocatalyst, pyrene, ethenyl sulfones,
ethenes, green LED
Ph
(1)
(2)
Ph
Ph
THF
OAc
Ar'SO2
(1995 Keck)
1) BuLi
Ar'SO2
Ph
2) PhCHO
+ Ar'O– + SO2
Aryl sulfones have attracted considerable attention ow-
ing to their ability to exhibit potent biological activities1
and to act as easily accessible air-stable reagents in organic
syntheses.2 The C–SO2 bonds of sulfones can be activated
using various methods,3 and these protocols are used in the
carbon–carbon (C–C) bond formations and/or the transfor-
mation of functional groups.2,4,5 Recently, photoredox C–SO2
bond activation has been extensively developed and uti-
lized in organic syntheses.6 In 1973, Julia reported the
transformation of sulfones to olefins.7 This olefination pro-
tocol comprised two types of transformation: (i) base-pro-
moted C–C bond formation between sulfones and alde-
hydes followed by acetylation using Ac2O and (ii) simulta-
neous reductive desulfonylation and deacetoxylation from
the resulting -acetoxysulfones (equation 1 in Scheme 1).
Although Julia olefination was synthetically useful, it re-
quired the use of hazardous sodium amalgam as a reduc-
Ph
Ph
Ph
O–
THF
Ar': heteroaromatic
Light-driven Julia olefination
PhSO2
Ph
1) BuLi
2) 3-BrC6H4CHO
H
PhSO2
blue LED
(3)
(4)
3) Ac2O
4) t-BuOK
i-Pr2NEt
MeCN–THF
Ph
Br
Ph
Br
This work
1, green LED
RO
OR
R:
CH2
1
RO
OR
Scheme 1 Conventional and light-driven Julia olefinations
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–K
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
H. Watanabe et al.
Special Topic
Synthesis
To avoid the use of hazardous and/or precious metal re-
agents for the reductive desulfonylation,11 we developed a
new technology by exploiting perylene/blue light-emitting
diodes (LEDs) as a photocatalyst system (equation 3 in
Scheme 1).6c This protocol worked well in the transforma-
tion of functionalized ethenyl sulfones to the corresponding
ethenes with high E-selectivity. For example, in the desulfo-
nylation of bromo-/chloro-substituted ethenyl sulfones, the
desired halo-substituted stilbenes were obtained, whereas
the halo groups remained untouched. Although this proto-
col is versatile in synthetic chemistry owing to its environ-
mentally benign and mild reaction conditions, it was diffi-
cult or practically impossible to separate the perylene pho-
tocatalyst from less-polar ethene products, which had no
polar functional groups due to a small difference in polari-
ties. To solve this problem, we have developed pyrene cata-
lyst 1 as a next-generation photocatalyst for reductive de-
sulfonylation (equation 4 in Scheme 1). Catalyst 1 compris-
es a -extended pyrene substituted at the 1, 3, 6, and 8
positions by four phenylethynes bearing long branched
alkoxy groups.12 Herein, we report that 1 promotes C–SO2
bond cleavage via visible-light (green LEDs) irradiation. Fur-
thermore, 1 was easily separated from the ethene products
via column chromatography.
of 1 (1.0 x 10–7 M), the acetylenic pyrene 1 emitted strong
fluorescence (Emax 499 nm, ΦF 0.98), and the intersection of
the normalized absorption and emission spectra indicated
the energy of the lowest excited singlet state (E00) at 491
nm. Due to its low-energy absorption band, we anticipated
that 1 would be able to undergo photo-excitation via irradi-
ation of visible light from green LEDs (514 nm) and drive
the following photoreactions.
Figure 1 Spectral profiles of UV/Vis absorption of 1 (CHCl3, 1.0 × 10–5
M) and the emission of green LEDs (arbitrary unit)
First, we designed the ‘custom-made’ pyrene photocata-
lyst 1, which was featured in three contexts: (i) a visible-
light-driven system; (ii) sufficient solubility; and (iii) polari-
ty-assisted easy separation from the products (Scheme 2).
Catalyst 1 bore an expanded -system and long branched
alkyl chains and possessed oxygen functionality; we ex-
pected these characters to satisfy all the requirements. The
pyrene core of 1 is a thermally and photochemically stable
polycyclic aromatic unit and has been widely used as a fluo-
rescent optical material for organic LEDs (OLEDs), organic
field-effect transistors (OFETs), organic photovoltaics
(OPVs), and sensing.13 Photocatalyst 1 was easily prepared
by the consecutive bromination of commercially available
pyrene and Sonogashira coupling of the resulting 1,3,6,8-
tetrabromide with 4-[(S)--citronellyloxy]phenylethyne
(Scheme 2).14
We estimated the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO)
levels of 1 using the density functional theory (DFT) calcu-
lations at the B3LYP/6-31G(d) level of theory. The DFT
simulations demonstrated HOMO and LUMO at –4.60 and
–2.13 eV, respectively, as presented in Figure 2.15 To evalu-
ate the reduction potential of 1 in the photo-promoted de-
sulfonylation, we also simulated the singly occupied molec-
ular orbital (SOMO) level of radical anion 1.–, which formed
through a single-electron transfer (SET) from a sacrificing
reagent, i-Pr2NEt, to photo-excited pyrene 1*. The DFT cal-
culations indicated that radical anion 1.– bore the SOMO
level at –0.44 eV, which enabled a single-electron transfer to
ethenyl sulfone 2a with –1.65 eV of LUMO under irradiation
of green LEDs (Figure 2). Since the SOMO level of 1.– (–0.44
eV) was significantly lower compared with that of perylene
radical anion (+0.83 eV), which was used as a photocatalyst
in the existing research,16 we anticipated that pyrene 1
would serve as a somewhat mild photo-driven reductant. In
parallel with these DFT calculations, we also investigated
electrochemical reduction of 1 and 2a using the cyclic vol-
tammetry swept in CH2Cl2 (1.0 mM) by using Ag/AgNO3 as a
reference electrode. In the reduction process, 1 demonstrat-
ed a finely reversible profile diagnosing its electrochemical
stability, while 2a did quasi-reversible. Their half-wave re-
duction potentials E1/2red (in CH2Cl2) were observed at –1.40
V and –1.81 V (Fc+/Fc), and the LUMO energy levels of 1 and
2a was estimated as –3.40 eV and –2.99 eV, respectively.17
The (S)--citronellyloxy groups attached to the four termi-
nus points of phenylethynyl moieties improved the solubili-
ty of the -system expanded pyrene 1 to implement a
O
Br
Br
(5.0 equiv)
PdCl2(PPh3)2 (20 mol%)
CuI (40 mol%)
Br2
pyrene
1 70%
MeNO2
toluene, NEt3
80 °C, 20 h
Br
Br
Scheme 2 Synthesis of photocatalyst 1
When the ultraviolet/visible (UV/Vis) absorption of 1
was recorded in CHCl3 (1.0 × 10–5 M), a broad absorption
band was observed at 387–530 nm, and the longest-wave-
length absorption maximum (max) was at 478 nm ( 70 300
L/mol·cm), indicating the highly expanded -system of 1
(Figure 1). When UV light was irradiated to a CHCl3 solution
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–K

C
H. Watanabe et al.
Special Topic
Synthesis
practical solubility at room temperature (20 °C) in common
organic solvents such as EtOAc, CHCl3, toluene, THF, and ac-
etone. However, in hexane, MeCN, MeOH, and EtOH, 1 was
insoluble at room temperature and even at 50 °C. When lin-
ear alkyl chains were attached instead of (S)--citronelly-
loxy groups, insoluble or sparingly soluble pyrenes were
synthesized. The oxygen functionality of the (S)--citronel-
lyloxy group plays a significant role in the tuning of the po-
larity of 1 to enable its easy separation from olefinic prod-
ucts via column chromatography on silica gel; for example,
the retardation factor (Rf) values developed by 20% CH2Cl2/
hexane was 0.17 for 1 and 0.70 for trans-stilbene (0.57 for
perylene).
PhSO2
PhCHO
(1.2 equiv)
LiHMDS
(1.2 equiv)
ClP(O)(OEt)2
(1.2 equiv)
LiHMDS
(1.05 equiv)
PhSO2
(5)
Ph
–78 °C, 1 h;
rt, 1 h
THF
–78 °C, 10 min
–78 °C, 1 h
–78 °C, 0.5 h
Ph
Ph
2a 82%
R1
R2
yield
77
PhSO2
Ph
PhSO2
R1
2b
2c
H
H
4-Me
3-MeO 57
2d 4-MeO
2e 4-CF3
H
H
2-Cl
3-Br
4-Br
H
H
3-Br
H
82
75
59
83
71
86
85
76
49
55
O
2f
2g
2h
H
H
H
2n 67%
R2
2i 3-Br
2j 4-Br
2k 3-Br
2l 4-I
2m
H
3-I
PhSO2
1) BuLi
t-BuOK
(1.2 equiv)
PhSO2
2) PhCH=CHCHO
3) Ac2O
Ph
PhSO2
PhSO2
Ph
(6)
Ph
Ph
THF
LUMO
+1.35
–0.44
THF
Ph
OAc
83% (1.0:0.11)
–78 °C, 1 h;
0 °C, 2 h
2o 72%
(1.0:0.22)
R3N
2a
–1.65
Ph
Ph
hν
–2.13
–4.60
1*
1•–
SOMO
HOMO
1
1
R3N•+
2a•–
Scheme 3 One-pot synthesis of ethenyl sulfones from benzyl sulfones
–6.21
2a
1
1•–
and aldehydes
products
Figure 2 The calculated potentials of 1, radical anion 1.–, and 2a at the
B3LYP/6-31G(d) level of theory and a partial mechanism of reductive
desulfonylation
tion in the presence of four equivalents of i-Pr2NEt, 3a was
provided in an 83% yield, and a 13% of 2a was recovered. In
the presence of an equimolar amount of i-Pr2NEt, the de-
sired desulfonylation proceeded only sluggishly to result in
a 90% recovery of 2a. Although this reaction proceeded in
mixed solvents MeCN/THF,19 no 3a formation was observed
in other solvents, such as THF, DMF, DMSO, and toluene/
THF.
The ethenyl sulfones subjected to reductive desulfonyla-
tion were prepared from the corresponding benzyl sulfones
and arylaldehydes in the lithium hexamethyldisilazide
(LiHMDS)-promoted one-pot synthesis (Scheme 3). When a
THF solution of benzyl sulfone was successively treated
with LiHMDS (1.05 equiv), benzaldehyde, ClP(O)(OEt)2, and
LiHMDS (1.2 equiv), ethenyl sulfone 2a was obtained in an
82% yield with high geometrical selectivity (equation 5 in
Scheme 3). Although the E/Z geometry of 2a was not deter-
mined, we assumed it would be an E-isomer.18 The one-pot
process was useful for the syntheses of other functionalized
ethenyl sulfones 2. The substituted sulfones bearing methyl
2b, methoxy 2c and 2d, and trifluoromethyl 2e were pro-
duced via this synthetic process. Halogen-substituted deriv-
atives chloride 2f; bromides 2g, 2h, 2i, 2j, and 2k; and io-
dides 2l and 2m were also successfully synthesized in a
range of 49–86% yields, without a loss of halo groups.
The 2-furylethenyl 2n and dienyl sulfones 2o were also
synthesized from furfural and cinnamaldehyde, respective-
ly (equation 6 in Scheme 3).
1 (2.5 mol%), green LEDs (30 W)
i-Pr2NEt (8.0 equiv)
H
R1
(7)
2a
0.25
mmol
R2
MeCN (2.5 mL), THF (0.5 mL)
50 °C, 9 h
3a 88% (R1 = R2 = H)
from 2 to 3
R1
R2
yield (%)
81
3-MeO 66
2b 3b
2c 3c
H
H
4-Me
H
2d 3d 4-MeO
2e 3e 4-CF3
H
H
2-Cl
3-Br
4-Br
H
H
3-Br
H
52
86
75
86
34
80
80
96
9
O
Ph
3l 91% (from 2n)
2f 3f
2g 3g
2h 3h
H
H
H
H
Ph
Ph
2i 3g 3-Br
2j 3h 4-Br
2k 3i 3-Br
2l 3j 4-I
3m 68% (from 2o)
2m 3k
H
3-I
12
Scheme 4 Photocatalyst 1-promoted reductive desulfonylation of 2
using green LEDs
Since a variety of ethenyl sulfones 2 were obtained in
the one-pot process, we performed reductive desulfonyla-
tion of 2 using pyrene 1 as a photocatalyst. When the green
LED light (514 nm, 30 W) was irradiated in a THF/MeCN
solution of 2a in the presence of 2.5 mol% 1 and eight
equivalents of i-Pr2NEt at 50 °C for 9 hours, the desired de-
sulfonylation smoothly proceeded to provide trans-stilbene
(3a) in an 88% yield (equation 7 in Scheme 4). It is noted
that 3a could be easily purified via column chromatography
on silica gel without any contamination of 1 as was expect-
ed. When 2a was subjected to the 1-catalyzed desulfonyla-
When this reaction was conducted using perylene rath-
er than 1, desulfonylation did not occur due to the small
overlap between its absorption band and the emission band
of the green LEDs.20 In the desulfonylation of 4-methylsul-
fone 2b, the desired methylstilbene 3b was produced in an
81% yield via the green LED irradiation for 9 hours. The re-
ductive desulfonylation of methoxy-substituted sulfones 2c
and 2d successfully proceeded, and the corresponding me-
thoxyethenes 3c and 3d were obtained in 66% and 52%
yields, respectively. The 4-CF3-substituted sulfone 2e un-
derwent a somewhat more rapid desulfonylation compared
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–K

D
H. Watanabe et al.
Special Topic
Synthesis
with the corresponding 4-MeO derivative 2d, likely due to
an electron-withdrawing effect on the part of the CF3
group. In the competitive desulfonylation between 2d and
2e assisted by the green LED irradiation, 3e was selectively
present in a 46% yield, whereas 95% of 2d was recovered in-
tact (Scheme 5).21
with phenylethyne was consecutively performed, enyne 3n
was obtained in a 61% yield (86% × 71%; route 1 in Scheme
6). In similar two-step reactions, 2i was transformed into
3n in a 64% yield (route 2 in Scheme 6).22 In this process, 2i
was converted into 3g by reductive desulfonylation in a 97%
NMR yield, and the crude bromostilbene 3g was used in the
subsequent Sonogashira coupling without any purification.
Alternatively, the consecutive Sonogashira coupling–reduc-
tive desulfonylation protocol also functioned well, and 2i
was transformed into 3n through 2p in a stepwise manner
(62% yield, 80% × 78%; route 3 in Scheme 6).23
1 (2.5 mol%)
green LED
i-Pr2NEt
3d (2%) + 2d (95% recovery)
+ 3e (46%) + 2e (46% recovery)
2d
+ 2e
MeCN, THF
50 °C, 4 h
0.25 mmol
each
Scheme 5 Competitive photo-catalyzed desulfonylation between 2d
and 2e
Desulfonylation/Sonogashira coupling route
1 (2.5 mol%)
Ph
green LED
Pd(PPh3)4
i-Pr2NEt
In the 1-catalyzed photo-desulfonylation of halo-substi-
tuted ethenyl sulfones 2f–m, the significant effects of halo-
gens and/or their substitution positions were observed in
the chemical yields and chemoselectivities. Chloro-substi-
tuted ethenyl sulfone 2f provided the desired chloroethene
3f in a 75% yield. Ethenyl sulfones bearing the bromo group
at 3-positions of benzene rings 2g and 2i underwent desul-
fonylation to provide 3g in 86% and 80% yield, respectively.
In the desulfonylation of 4-bromide 2h, the desire product
3h (34%), as well as debrominated compounds 2a (25%) and
3a (2%), were produced alongside the recovery of 2h (44%).
In contrast, 4-bromo sulfone 2j underwent reductive desul-
fonylation to provide 3h in an 80% yield, despite the use of 5
mL of MeCN and 2 mL of THF being required because of
poor solubility. In 2.5 mL of MeCN and 2 mL of THF, the
chemical yield of 3h was significantly decreased to a 30%
yield. In the reductive desulfonylation of dibromoethenyl
sulfone 2k, the desired 3,3′-dibromo-substituted stilbene 3i
was obtained in a 96% yield, and no loss of bromo function-
ality was observed. In this reduction, iodine functionality
was labile. Iodo sulfones 2l and 2m yielded only small
amounts of the desired ethenes 3j (9%) and 3k (12%), and in
both reactions, the formation of deiodinated ethenyl sul-
fone 2a (27% and 35%, respectively) and the recovery of
staring sulfones 2l (57%) and 2m (31%) were observed. The
1/green LED-promoted desulfonylation occurred in het-
eroaromatic ethenyl sulfone 2n to provide 3l in a 91% yield.
In the reductive desulfonylation of dienyl sulfone 2o, the
desired diene 3m was successfully obtained in 68% yield. In
sharp contrast, when the desulfonylation of 2o was per-
formed using perylene/blue LED light, a complicated mix-
ture was obtained, and 3m was not synthesized. Although
1,2-diarylethenyl sulfones successfully underwent 1-cata-
lyzed reductive desulfonylation, 2-alkyl-1-phenylethenyl
sulfones did not due to their higher LUMO levels.
CuI
71%
2g
2i
3g
route 1
86%
Ph
Ph
Ph
[Pd, Cu]
1, green LED
[3g]
3n
64% (2 steps)
97% (NMR)
route 2
78%
1, green LED
Ph
[Pd, Cu]
Ph
PhSO2
route 3
80%
2p
Ph
Sonogashira coupling/desulfonylation route
Scheme 6 Two alternative syntheses of expanded -system enyne 3n
We applied this consecutive coupling–desulfonylation
protocol to the -system expansion using photo-labile ha-
loethenyl sulfones such as 2h and 2l (Scheme 7). In this
route, the direct photoreduction of 2h and 2l was avoided;
as such, we expect that the photochemically labile ethenyl
sulfones can also be used as stilbene equivalents for new -
systems. When bromo- 2h and iodoethenyl sulfones 2l
were treated with 4-MeO- and 4-Ph2N-substituted phenyl-
ethynes in the presence of Pd(PPh3)4 and CuI, the desired
ethyne adducts 2q and 2r were obtained in 48% and 66%
yield, respectively, via successive column chromatography
and recrystallization. The consecutive desulfonylation of 2q
and 2r using the 1/green LED protocol smoothly proceeded
to afford MeO- and Ph2N-substituted enynes 3o and 3p in
75% and 77% yield, respectively. During their purification,
pyrene photocatalyst 1 could be easily separated from
enyne products 3o and 3p via column chromatography on
silica gel, where the Rf values (CH2Cl2/hexane 1:4 as eluent)
were 0.23 for 3o, 0.26 for 3p, and 0.17 for 1. Figure 3 pres-
ents the UV/Vis absorption and fluorescence spectra of 3o
and 3p, and their optical properties are summarized in Ta-
ble 1. The amino-substituted enyne 3p demonstrated 29–
48 nm longer wavelengths than methoxy derivative 3o in
the UV-Vis absorption and photoluminescence spectra. In
photoluminescence, 3p exhibited a larger emission quan-
tum yield than 3o in CHCl3, but 3o did the larger than 3p in
a powdery state (Figure 3, inset), that is, ΦF 3o 0.74 vs 3p
0.87 in CHCl3 and ΦF 3o 0.40 versus 3p 0.08 in powdery
states. Interestingly, 3p indicated an emission profile at
We found that consecutive process, which comprised
1/green LED light-promoted desulfonylation and Sonogas-
hira coupling of the resulting bromostilbene was versatile
to synthesize additionally expanded -system. For instance,
when 2g was subjected to reductive desulfonylation, and
Sonogashira coupling of the resulting 3-bromostilbene (3g)
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–K

E
H. Watanabe et al.
Special Topic
Synthesis
OMe
OMe
Ph
Pd(PPh3)4
1
green LED
CuI
Ph
H
2h
2l
2q
PhSO2
3o
48%
75%
PhSO2
Ph
H
Ph
Ph
[Pd, Cu]
1
Ph
green LED
66%
77%
3p
2r
Ph2N
Ph2N
Ph2N
4
Scheme 7 The Sonogashira coupling/desulfonylation protocol using photo-labile halo-substituted ethenyl sulfones
Table 1 Optical Properties of 3o and 3p in CHCl3 and as a Powdery State
Ultraviolet/visible absorption
Photoluminescence
(1.0 × 10–5 M) [nm] [ (104) L/mol·cm]
In CHCl3 (1.0 × 10–7 M) [nm] (ΦF)a
Powdery state [nm] (ΦF)a
3o
3p
343 (5.1)
372 (4.8)
404 (0.74)
452 (0.87)
419 (0.40)
448 (0.08)
a Absolute fluorescence quantum yield measured by integrated sphere system (Hamamatsu photonics C9920-02).
approximately 450 nm in both the CHCl3 solution and the
powdery state. In sharp contrast, aminodiyne 4 demon-
strated a 20 nm difference of emission wavelengths be-
tween in CHCl3 solution and powdery state and a moderate
fluorescence quantum yield in the powdery state: fluores-
cence, 442 nm in CHCl3 (ΦF 0.92) and 462 nm (0.53).24
1
.– and –1.65 eV for the LUMO of ethenyl sulfone 2. Radical
anion 2.– underwent protonation by cationic radical 5.+, and
the resulting radical 7. consecutively effected SET from 6. to
provide anion 7–. The subsequent elimination of the PhSO2
anion consequently furnished stilbene (3a).
2a
1
hν
1*
PhSO2
PhSO2
PhSO2
Ph
Ph
Ph
3a
Ph
Ph
Ph
1
–
H
7
e–
– e–
H
– PhSO2
7–
2a•–
H+
– H+
N(i-Pr)Et
5
N(i-Pr)Et
5•+
N(i-Pr)Et
N(i-Pr)Et
6+
6•
N(i-Pr)Et
N(i-Pr)Et
N(i-Pr)2
N(i-Pr)2
8•
8+
N(i-Pr)2
N(i-Pr)2
Scheme 8 A plausible mechanism of 1/green-LED-promoted reductive
desulfonylation of 2a
Figure 3 The UV/Vis absorption of 3o (thick, black) and 3p (thick, red)
(CHCl3, 1.0 × 10–5 M) and photoluminescence spectra of 3o (thin, black)
and 3p (thin, red) [CHCl3, 1.0 × 10–7 M, powdery state (inset)].
In Table 2 are summarized the heats of formation, which
were simulated for all the intermediates derived from 2a at
the B3LYP/6-31G(d) level of theory. Based on the simula-
tion, an energy diagram for the transformation of 2a.– to 3a
was depicted in Figure 4, and the substantially downhill re-
action pathway would consistently support the reaction
mechanism proposed in Scheme 8. Although, in this reac-
tion, an -proton of ethyl group in cationic radical 5.+ could
be alternatively transferred to 2a.– to produce radical 8. and
Finally, a plausible mechanism for 1-catalyzed reductive
desulfonylation is presented in Scheme 8.6c Pyrene catalyst
1 was photochemically excited by irradiation of green LEDs
and transformed to anionic radical 1.– via SET from i-Pr2NEt
(5). Highly reactive anionic radical 1.– converted ethenyl
sulfone 2 into anionic radical 2.– through SET, with 1.– being
converted into 1: –0.44 eV for the SOMO of anionic radical
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–K

F
H. Watanabe et al.
Special Topic
Synthesis
subsequently cation 8+, we tentatively employed 6. and 6+
because they were thermodynamically more stable than 8.
and 8+.25
GF254, 0.25 mm) were used throughout this work. Silica gel column
chromatography was performed using DAISOGEL. All NMR spectra
were recorded on JEOL ECS400 and ECZ400S spectrometers and refer-
enced to the internal standard TMS ( = 0.0) for 1H NMR, CDCl3 ( =
77.16) for 13C NMR. Matrix-assisted laser desorption ionization time-
of-flight mass spectrometry (MALDI-TOF MS) was recorded on a
Bruker Autoflex Speed instrument. UV/Vis absorption and fluores-
cence spectra were recorded using JASCO V-650 and FP-6500, respec-
tively. The reduction and oxidation potentials (vs Fc/Fc+) were mea-
sured in CH2Cl2 (1.0 × 10–4 M, 100 mV/s scan rate, 0.1 M Bu4NPF6) us-
ing a glassy carbon as the working electrode, a platinum (Pt) counter
electrode, and a silver/silver ion (Ag/Ag+) reference electrode (0.01 M
AgNO3 and 0.1 M tetrabutylammonium perchlorate in MeCN) in 0.1 M
LiClO4/MeCN.
Table 2 The Heats of Formation (HOFs) Simulated for 2.–, 7., 7–, 3a,
and PhSO2– at the B3LYP/6-31G(d) Level of Theory
Stage
Chemical species HOF [kcal/mol]
Δ(ΣHOF) [kcal/mol]a
2.–
1
2
3
4
–828523.2
0.0
–356.5
–381.2
7.
–828879.7
–828904.4
7–
–
3a, PhSO2
–339300.6, –489627.7 –405.1
a Δ(ΣHOF) was calculated by the following equation:
Δ(ΣHOF) = ΣHOF(stage x) – HOF(stage 1).
(E)-1,2-Diphenyl-1-phenylsulfonylethene (2a);18a Typical Proce-
dure
To benzyl sulfone (232 mg, 1.0 mmol) in THF (8.0 mL) was added
LiHMDS (1.3 M in THF, 0.81 mL, 1.05 mmol) at –78 °C, and the mix-
ture was stirred for 10 min. To the solution was added benzaldehyde
(127 mg, 1.2 mmol), and the mixture was stirred for 30 min. Diethyl
chlorophosphate (207 mg, 1.2 mmol) was added, and the mixture was
stirred for 1 h. Then, LiHMDS (1.3 M in THF, 0.92 mL, 1.2 mmol) was
added at –78 °C, and the mixture was stirred at r.t. for 1 h. To this
mixture were added EtOAc (20 mL) and sat. aq NH4Cl (20 mL), and the
organic and aqueous layers were separated. The aqueous layer was
extracted with EtOAc, and the combined organic layers were washed
with H2O and brine. The organic layer was dried (MgSO4) and evapo-
rated. The crude product was subjected to column chromatography
on silica gel (hexane/EtOAc 8:2) and to recrystallization (MeOH) to af-
ford 2a as a white solid; yield: 263 mg (82%); mp 191–192 °C.
Figure 4 An energy diagram in the transformation of 2a.– to 3a
1H NMR (CDCl3, 400 MHz):  = 7.01–7.09 (m, 4 H), 7.17 (t, J = 7.4 Hz, 2
H), 7.23–7.32 (m, 3 H), 7.34–7.41 (m, 3 H), 7.53 (t, J = 7.4 Hz, 1 H),
7.62–7.64 (m, 2 H), 7.97 (s, 1 H).
In summary, a new photocatalyst 1 was developed. An
expanded -system of pyrene catalyst 1 triggered the de-
sired photoreaction, even by low-energy green light irradi-
ation, which resulted in carbon–sulfur (C–SO2) bond cleav-
age in ethenyl sulfones. Due to the long branched alkoxy
groups attached to the -system, 1 demonstrated sufficient
solubility in common organic solvents, and the proper po-
larity of oxygen functionalities enabled the easy separation
of ethene products from 1 via column chromatography. This
desulfonylation protocol worked well in halo-substituted
ethenyl sulfones and, in combination with the Sonogashira
coupling, achieved the syntheses of -expanded enynes.
Further application of the reductive desulfonylation using
1/green LEDs and other pyrene derivatives/visible light to
synthesize functionalized expanded -systems is in prog-
ress.
13C{1H} NMR (CDCl3, 101 MHz):  = 128.6, 128.77, 128.82, 129.0,
129.3, 130.2, 130.7, 130.9, 131.4, 132.9, 133.3, 137.8, 138.8, 141.4.
Other ethenyl sulfones 2b–n were synthesized according to the same
procedure. A synthetic procedure for 2o is described in the Support-
ing Information.
(E)-2-(4-Methylphenyl)-1-phenyl-1-phenylsulfonylethene (2b)18a
Isolated by column chromatography (hexane/EtOAc 8:2); yield: 515
mg (77%, 2.0 mmol scale); white solid; mp 209–210 °C.
1H NMR (CDCl3, 400 MHz):  = 2.27 (s, 3 H), 6.94–7.03 (m, 6 H), 7.26–
7.30 (m, 2 H), 7.34–7.41 (m, 3 H), 7.53 (t, J = 7.2 Hz, 1 H), 7.62 (d, J =
7.2 Hz, 2 H), 7.94 (s, 1 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 21.5, 128.7, 128.8, 128.9, 129.2,
129.4, 130.1, 130.7, 130.9, 131.6, 133.2, 137.8, 138.9, 140.2, 140.7.
(E)-2-(3-Methoxyphenyl)-1-phenyl-1-phenylsulfonylethene (2c)
Isolated by column chromatography (hexane/EtOAc 8:2); yield: 200
mg (57%, 1.0 mmol scale); white solid; mp 152–153 °C.
1H NMR (CDCl3, 400 MHz):  = 3.45 (s, 3 H), 6.50–6.51 (m, 1 H), 6.76–
6.82 (m, 2 H), 7.03 (d, J = 8.0 Hz, 2 H), 7.12 (t, J = 8.0 Hz, 1 H), 7.27–
7.42 (m, 5 H), 7.54 (t, J = 7.2 Hz, 1 H), 7.64 (d, J = 6.8 Hz, 2 H), 7.94 (s, 1
H).
13C{1H} NMR (CDCl3, 101 MHz):  = 54.9, 114.2, 117.1, 123.9, 128.7,
128.8, 129.0, 129.3, 129.6, 130.9, 131.5, 133.3, 134.0, 137.7, 138.7,
141.5, 159.3.
Unless otherwise stated, all the reactions were carried out under a N2
atmosphere. Glassware were oven-dried (70 °C) and heated under re-
duced pressure before use. Solvents were employed as eluents for all
other routine operations. Anhydrous solvents (THF, DMF, and DMSO)
were purchased from commercial suppliers and used without any
further purification. Toluene and MeCN were distilled from CaH2 be-
fore use. For TLC analyses, Merck precoated TLC plates (silica gel 60
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–K

G
H. Watanabe et al.
Special Topic
Synthesis
HRMS (MALDI-TOF): m/z [M + Na]+ calcd for C21H18O3SNa: 373.0874;
(E)-1-(3-Bromophenyl)-2-phenyl-1-phenylsulfonylethene (2i)6c
found: 373.0901.
Isolated by flash chromatography (hexane/EtOAc 8:2); yield: 344 mg
(86%, 1.0 mmol scale); white solid; mp 147.5–148.0 °C.
1H NMR (CDCl3, 400 MHz):  = 6.95–6.97 (m, 1 H), 7.08 (d, J = 7.2 Hz, 2
H), 7.15–7.23 (m, 4 H), 7.29 (t, J = 7.2 Hz, 1 H), 7.44 (t, J = 7.8 Hz, 2 H),
7.49–7.52 (m, 1 H), 7.57 (t, J = 7.4 Hz, 1 H), 7.63–7.66 (m, 2 H), 7.97 (s,
1 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 122.7, 128.7, 128.8, 129.0, 129.6,
130.45, 130.52, 130.7, 132.40, 132.43, 133.5, 133.6, 138.36, 138.40,
140.0. One carbon signal is missing due to overlapping.
(E)-1-(4-Methoxyphenyl)-2-phenyl-1-phenylsulfonylethene
(2d)18a
Isolated by flash chromatography (hexane/EtOAc 8:2); yield: 573 mg
(82%, 2.0 mmol scale); white solid; mp 150.5–151.0 °C.
1H NMR (CDCl3, 400 MHz):  = 3.82 (s, 3 H), 6.81 (d, J = 8.6 Hz, 2 H),
6.95 (d, J = 8.6 Hz, 2 H), 7.11 (d, J = 7.6 Hz, 2 H), 7.18 (t, J = 7.6 Hz, 2 H),
7.26 (t, J = 7.6 Hz, 2 H), 7.40 (t, J = 7.5 Hz, 2 H), 7.53 (t, J = 7.5 Hz, 1 H),
7.64 (d, J = 7.5 Hz, 2 H), 7.94 (s, 1 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 55.3, 114.4, 123.0, 128.5, 128.6,
128.7, 130.0, 130.6, 132.1, 133.0, 133.2, 137.7, 138.9, 141.1, 160.3.
(E)-1-(4-Bromophenyl)-2-phenyl-1-phenylsulfonylethene (2j)18a
Isolated by flash chromatography (hexane/EtOAc 8:2); yield: 339 mg
(85%, 1.0 mmol scale); white solid; mp 180–181 °C.
1H NMR (CDCl3, 400 MHz):  = 6.91 (d, J = 8.6 Hz, 2 H), 7.08 (d, J = 7.3
Hz, 2 H), 7.21 (t, J = 7.3 Hz, 2 H), 7.28 (t, J = 7.3 Hz, 1 H), 7.41–7.44 (m,
4 H), 7.56 (t, J = 7.5 Hz, 1 H), 7.64 (d, J = 7.5 Hz, 2 H), 7.98 (s, 1 H).
(E)-2-Phenyl-1-(4-trifluoromethyphenyl)-1-phenylsulfonyl-
ethene (2e)18a
Isolated by flash chromatography (hexane/EtOAc 8:2); yield: 583 mg
(75%, 2.0 mmol scale); white solid; mp 174–175 °C.
13C{1H} NMR (CDCl3, 101 MHz):  = 124.0, 128.7, 128.8, 129.0, 130.4,
130.5, 130.7, 132.3, 132.52, 132.55, 133.5, 138.4, 138.6, 140.2.
1H NMR (CDCl3, 400 MHz):  = 7.05 (d, J = 7.6 Hz, 2 H), 7.17–7.22 (m, 4
H), 7.27–7.31 (m, 1 H), 7.42 (t, J = 7.8 Hz, 2 H), 7.54–7.59 (m, 3 H), 7.63
(d, J = 7.2 Hz, 2 H), 8.03 (s, 1 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 123.9 (q, 1JC,F = 272.3 Hz), 125.9 (q,
3JC,F = 3.9 Hz), 128.7, 128.8, 129.1, 130.59, 130.63, 131.36 (q, 2JC,F = 32.8
Hz), 131.41, 132.3, 133.6, 135.5, 138.5, 138.8, 140.1.
(E)-1,2-Bis(3-bromophenyl)-1-phenylsulfonylethene (2k)
Isolated by flash chromatography (hexane/EtOAc 8:2); yield: 727 mg
(76%, 2.0 mmol scale); white solid; mp 123–124 °C.
19F{1H} NMR (CDCl3, 376 MHz):  = –63.2.
1H NMR (CDCl3, 400 MHz):  = 6.95 (d, J = 8.0 Hz, 2 H), 7.05 (t, J = 8.0
Hz, 1 H), 7.14–7.19 (m, 2 H), 7.25 (s, 1 H), 7.39–7.48 (m, 3 H), 7.50–
7.53 (m, 1 H), 7.58 (t, J = 7.6 Hz, 1 H), 7.63 (d, J = 7.2 Hz, 2 H), 7.88 (s, 1
H).
13C{1H} NMR (CDCl3, 101 MHz):  = 122.8, 122.9, 128.7, 128.8, 129.1,
129.4, 130.2, 130.6, 132.7, 132.9, 133.3, 133.4, 133.6, 133.8, 134.5,
136.6, 138.1, 141.7.
(E)-2-(2-Chlorophenyl)-1-phenyl-1-phenylsulfonylethene (2f)18a
Isolated by flash chromatography (hexane/EtOAc 8:2); yield: 419 mg
(59%, 2.0 mmol scale); white solid; mp 159–160 °C.
1H NMR (CDCl3, 400 MHz):  = 6.77 (d, J = 8.0 Hz, 1 H), 6.88 (t, J = 7.6
Hz, 1 H), 7.04–7.06 (m, 2 H), 7.15 (t, J = 7.8 Hz, 1 H), 7.21 (t, J = 7.6 Hz,
2 H), 7.29 (t, J = 7.6 Hz, 1 H), 7.37–7.42 (m, 3 H), 7.53 (t, J = 7.6 Hz, 1
H), 7.66–7.68 (m, 2 H), 8.29 (s, 1 H).
HRMS (MALDI-TOF): m/z [M
+
Na]+ calcd for C20H14Br2O2SNa:
498.8979; found: 498.8937.
13C{1H} NMR (CDCl3, 101 MHz):  = 126.5, 128.7, 128.9, 129.3, 129.8,
130.56, 130.60, 130.9, 131.6, 133.4, 134.9, 135.5, 138.6, 144.0. Two
carbon signals are missing probably due to overlapping.
(E)-1-(4-Iodophenyl)-2-phenyl-1-phenylsulfonylethene (2l)
Isolated by flash chromatography (hexane/EtOAc 8:2); yield: 656 mg
(49%, 3.0 mmol scale); white solid; mp 199–200 °C.
(E)-2-(3-Bromophenyl)-1-phenyl-1-phenylsulfonylethene (2g)6c
1H NMR (CDCl3, 400 MHz):  = 6.77 (d, J = 8.4 Hz, 2 H), 7.08 (d, J = 7.2
Hz, 2 H), 7.21 (t, J = 7.4 Hz, 2 H), 7.29 (t, J = 7.4 Hz, 1 H), 7.43 (t, J = 7.8
Hz, 2 H), 7.56 (t, J = 7.4 Hz, 1 H), 7.61–7.65 (m, 4 H), 7.97 (s, 1 H).
Isolated by flash chromatography (hexane/EtOAc 8:2); yield: 663 mg
(83%, 2.0 mmol scale); white solid; mp 117–118 °C.
13C{1H} NMR (CDCl3, 101 MHz):  = 95.9, 128.7, 128.8, 129.0, 130.4,
130.6, 131.0, 132.5, 132.6, 133.5, 138.2, 138.3, 138.6, 140.3.
HRMS (MALDI-TOF): m/z [M + Na]+ calcd for C20H15IO2SNa: 468.9735;
1H NMR (CDCl3, 400 MHz):  = 6.95–7.05 (m, 4 H), 7.20–7.21 (m, 1 H),
7.30 (t, J = 7.2 Hz, 2 H), 7.35–7.42 (m, 4 H), 7.54 (t, J = 7.6 Hz, 1 H),
7.61–7.64 (m, 2 H), 7.88 (s, 1 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 122.5, 128.7, 128.8, 129.0, 129.5,
130.0, 130.6, 130.7, 132.9, 133.35, 133.45, 134.87, 135.90, 138.3,
143.0. One carbon signal is missing due to overlapping.
found: 468.9766.
(E)-2-(3-Iodophenyl)-1-phenyl-1-phenylsulfonylethene (2m)18a
Isolated by flash chromatography (hexane/EtOAc 8:2); yield: 491 mg
(55%, 2.0 mmol scale); white solid; mp 140.0–140.5 °C.
(E)-2-(4-Bromophenyl)-1-phenyl-1-phenylsulfonylethene (2h)18a
1H NMR (CDCl3, 400 MHz):  = 6.88 (t, J = 7.8 Hz, 1 H), 6.98–7.01 (m, 3
H), 7.30 (t, J = 7.6 Hz, 2 H), 7.36–7.42 (m, 4 H), 7.54 (t, J = 7.6 Hz, 1 H),
7.63 (d, J = 6.8 Hz, 2 H), 7.85 (s, 1 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 94.2, 128.8, 128.9, 129.0, 129.3,
129.5, 130.1, 130.6, 130.8, 133.5, 135.0, 135.9, 138.4, 138.8, 139.5,
142.9.
Isolated by flash chromatography (hexane/EtOAc 8:2); yield: 567 mg
(71%, 2.0 mmol scale); white solid; mp 245–246 °C
1H NMR (CDCl3, 400 MHz):  = 6.92 (d, J = 8.8 Hz, 2 H), 7.00 (d, J = 6.8
Hz, 2 H), 7.27–7.31 (m, 4 H), 7.35–7.42 (m, 3 H), 7.52–7.56 (m, 1 H),
7.60–7.63 (m, 2 H), 7.89 (s, 1 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 124.7, 128.8, 128.9, 129.1, 129.5,
130.7, 131.0, 131.8, 131.9, 132.0, 133.4, 136.3, 138.5, 142.3.
(E)-2-(2-Furyl)-1-phenyl-1-phenylsulfonylethene (2n)18a
Isolated by flash chromatography (hexane/EtOAc 8:2); yield: 208 mg
(67%, 1.0 mmol scale); white solid mp 134.5–135.0 °C.
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–K

H
H. Watanabe et al.
Special Topic
Synthesis
1H NMR(CDCl3, 400 MHz):  = 5.89 (d, J = 3.4 Hz, 1 H), 6.27 (dd, J = 3.4,
1.8 Hz, 1 H), 7.02 (d, J = 7.6 Hz, 2 H), 7.31 (t, J = 7.2 Hz, 2 H), 7.35–7.42
(m, 4 H), 7.54 (t, J = 7.4 Hz, 1 H), 7.63 (d, J = 6.8 Hz, 2 H), 7.83 (s, 1 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 112.4, 115.5, 126.1, 128.6, 128.77,
128.83, 129.3, 130.5, 131.4, 133.3, 138.1, 138.9, 145.2, 149.3.
trans-4-Methoxystilbene (3d)27
Isolated by flash chromatography (hexane); yield: 27 mg (52%); white
solid.
1H NMR (CDCl3, 400 MHz):  = 3.83 (s, 3 H), 6.90 (d, J = 8.8 Hz, 2 H),
6.97 (d, J = 16.4 Hz, 1 H), 7.07 (d, J = 16.4 Hz, 1 H), 7.23 (t, J = 7.5 Hz, 1
H), 7.35 (t, J = 7.5 Hz, 2 H), 7.46 (d, J = 8.8 Hz, 2 H), 7.49 (d, J = 7.5 Hz, 2
H).
(1E,3E)-1,4-Diphenyl-1-phenylsulfonyl-1,3-butadiene (2o)
13C{1H} NMR (CDCl3, 101 MHz):  55.5, 114.3, 126.4, 126.8, 127.3,
Isolated by column chromatography (hexane/EtOAc 8:2) and then re-
crystallization (MeOH); yield: 62 mg [60% (83%
×
72%)]
127.9, 128.4, 128.8, 130.3, 137.8, 159.4.
[(1E,3E)/(1Z,3E) = 1.0:0.22]; white solid; mp 115–116 °C.
1H NMR (CDCl3, 400 MHz):  = 6.54–8.34 (dd, J = 15.6, 15.5, 10.8, 11.5
Hz, 1 H), 7.06–6.85 (d, J = 15.6, 15.5 Hz, 1 H), 7.13–7.58 (d, J = 6.8, 7.4
Hz, 2 H), 7.27–7.42 (m, 10 H), 7.49–7.54 (m, 1 H), 7.62–7.70 (d, J = 7.6,
7.4 Hz, 2 H), 7.74–6.77 (d, J = 10.8, 11.5 Hz, 1 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 122.8, 123.2, 127.5, 127.7, 127.9,
128.2, 128.4, 128.5, 128.78, 128.85, 128.87, 128.92, 129.0, 129.2,
129.48, 129.55, 130.2, 130.8, 131.1, 133.2, 135.76, 135.82, 136.2,
138.6, 139.5, 141.0, 141.1, 142.1, 142.9, 143.4.
trans-4-Trifluoromethylstilbene (3e)27
Isolated by flash chromatography (hexane); yield: 54 mg (86%); white
solid.
1H NMR (CDCl3, 400 MHz):  = 7.12 (d, J = 16.6 Hz, 1 H), 7.20 (d, J =
16.6 Hz, 1 H), 7.30 (t, J = 7.5 Hz, 1 H), 7.39 (t, J = 7.5 Hz, 2 H), 7.54 (d, J
= 7.5 Hz, 2 H), 7.61 (s, 4 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 123.9 (q, J = 240.3 Hz), 125.8 (q, J =
3.8 Hz), 126.7, 126.9, 127.3, 128.4, 128.9, 129.4 (q, J = 32.8 Hz), 131.4,
136.8, 141.0.
HRMS (MALDI-TOF): m/z [M + Na]+ calcd for C22H18O2SNa: 369.0925;
found: 369.0918.
19F{1H} NMR (CDCl3, 376 MHz):  = –62.9 (s, 3 F).
Stilbene (3a)26 by Reductive Desulfonylation of Ethenyl Sulfone 2a
Using 1/Green LED; Typical Procedure
trans-2-Chlorostilbene (3f)28
Isolated by flash chromatography (hexane); yield: 40 mg (75%); white
solid.
1H NMR (CDCl3, 400 MHz):  = 7.08 (d, J = 18.0 Hz, 1 H), 7.17–7.22 (m,
1 H), 7.25–7.31 (m, 2 H), 7.38 (t, J = 7.6 Hz, 3 H), 7.52 (d, J = 18.0 Hz, 1
H), 7.55 (d, J = 7.6 Hz, 2 H), 7.69 (d, J = 7.8 Hz, 1 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 124.9, 126.6, 127.0, 128.2, 128.6,
128.8, 129.9, 131.4, 133.6, 135.5, 137.2. One carbon signal is missing
due to overlapping.
To a round-bottomed flask were added 2a (80 mg, 0.25 mmol), photo-
catalyst 1 (7.6 mg, 6.3 mol), i-Pr2NEt (2.0 mmol, 0.35 mL), MeCN (2.5
mL), and THF (0.5 mL). The flask was placed in a glass water-bath sur-
rounded by a green LED strip lighting, and the green light was irradi-
ated at the mixture for 9 h. During the photoreaction, the bath tem-
perature was maintained at 50–60 °C due to heat radiation from the
photoreactor. The solvents were evaporated, and the crude product
was subjected to column chromatography on silica gel (hexane) to
give 3a as a white solid; yield: 40 mg (88%); mp 129–130 °C.
1H NMR (CDCl3, 400 MHz):  = 7.11 (s, 2 H), 7.26 (t, J = 7.4 Hz, 2 H),
7.36 (t, J = 7.4 Hz, 4 H), 7.52 (d, J = 7.4 Hz, 4 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 126.6, 127.7, 128.8, 137.4. One
trans-3-Bromostilbene (3g)6c
Isolated by flash chromatography (hexane); yield: 56 mg, from 2g
(86%), 52 mg, from 2i (80%); white solid.
1H NMR (CDCl3, 400 MHz):  = 7.02 (d, J = 16.6 Hz, 1 H), 7.11 (d, J =
16.6 Hz, 1 H), 7.22 (t, J = 7.9 Hz, 1 H), 7.28 (t, J = 8.0 Hz, 1 H), 7.35–7.39
(m, 3 H), 7.42 (d, J = 7.9 Hz, 1 H), 7.51 (d, J = 8.8 Hz, 2 H), 7.66–7.67 (m,
1 H).
carbon signal is missing due to overlapping).
Other stilbenes 3b–m were synthesized according to the same proce-
dure.
trans-4-Methylstilbene (3b)26
13C{1H} NMR (CDCl3, 101 MHz):  = 123.0, 125.3, 126.8, 127.2, 128.1,
128.8, 129.3, 130.2, 130.5, 136.9, 139.6. One carbon signal is missing
due to overlapping.
Isolated by flash chromatography (hexane); yield: 39 mg (81%); white
solid.
1H NMR (CDCl3, 400 MHz):  = 2.36 (s, 3 H), 7.05 (d, J = 16.4 Hz, 1 H),
7.10 (d, J = 16.4 Hz, 1 H), 7.17 (d, J = 7.6 Hz, 2 H), 7.22–7.27 (m, 1 H),
7.35 (t, J = 7.3 Hz, 2 H), 7.42 (d, J = 7.6 Hz, 2 H), 7.50 (d, J = 7.3 Hz, 2 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 21.4, 126.5, 126.6, 127.5, 127.8,
128.8, 129.5, 134.7, 137.6. Two carbon signals are missing due to
overlapping.
trans-4-Bromostilbene (3h)6c
Isolated by flash chromatography (hexane); yield: 22 mg, from 2h
(34%), 52 mg, from 2j (80%); white solid.
1H NMR (CDCl3, 400 MHz):  = 7.03 (d, J = 16.2 Hz, 1 H), 7.10 (d, J =
16.2 Hz, 1 H), 7.27–7.30 (m, 1 H), 7.34–7.39 (m, 4 H), 7.46–7.52 (m, 4
H).
trans-3-Methoxystilbene (3c)27
13C{1H} NMR (CDCl3, 101 MHz):  = 121.4, 126.7, 127.5, 128.0, 128.1,
128.9, 129.5, 131.9, 136.4, 137.1.
Isolated by flash chromatography (hexane); yield: 35 mg (66%); white
solid.
1H NMR (CDCl3, 400 MHz):  = 3.85 (s, 3 H), 6.81–6.84 (m, 1 H), 7.05–
7.13 (m, 4 H), 7.24–7.29 (m, 2 H), 7.36 (t, J = 7.6 Hz, 2 H), 7.51 (d, J =
7.6 Hz, 2 H).
trans-3,3′-Dibromostilbene (3i)29
Isolated by flash chromatography (hexane); yield: 81 mg (96%); white
solid.
1H NMR (CDCl3, 400 MHz):  = 7.02 (s, 2 H), 7.23 (t, J = 7.8 Hz, 2 H),
7.39–7.42 (m, 4 H), 7.66 (t, J = 1.8 Hz, 2 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 55.3, 111.9, 113.4, 119.3, 126.7,
127.8, 128.7, 128.8, 129.1, 129.7, 137.3, 138.9, 160.0.
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–K

I
H. Watanabe et al.
Special Topic
Synthesis
13C{1H} NMR (CDCl3, 101 MHz):  = 123.0, 125.4, 128.6, 129.5, 130.3,
130.9, 139.0.
Stepwise Sonogashira Coupling/Desulfonylation; Typical Proce-
dure (Scheme 6, route 3)
trans-4-Iodostilbene (3j)26
(i) (E)-2-Phenyl-1-(3-phenylethynyl)phenyl-1-phenylsulfonyl-
ethene (2p)
NMR yield by using CH2Br2 as an internal standard: 9%.
To a round-bottomed flask were added 2i (799 mg, 2.0 mmol),
Pd(PPh3)4 (116 mg, 0.1 mmol), CuI (19 mg, 0.1 mmol), ethynylben-
zene (245 mg, 2.4 mmol), i-Pr2NH (2.0 mL, 14 mmol), and toluene (20
mL), and the mixture was stirred at 80 °C for 24 h. The reaction was
quenched with sat. aq NH4Cl, and the organic and aqueous layers
were separated. The aqueous layer was extracted with EtOAc, and
combined organic layers were washed with H2O and brine. The or-
ganic layer was dried (MgSO4) and evaporated. The crude product was
subjected to flash chromatography (hexane/EtOAc 8:2) and recrystal-
lized from MeOH to afford 2p; yield: 673 mg (80%); white solid; mp
191–192 °C.
1H NMR (CDCl3, 400 MHz):  = 6.92 (dt, J = 8.0, 1.4 Hz, 1 H), 7.11 (d, J =
7.2 Hz, 2 H), 7.18–7.25 (m, 3 H), 7.27–7.29 (m, 2 H), 7.32–7.36 (m, 3
H), 7.43 (t, J = 7.8 Hz, 2 H), 7.46–7.58 (m, 4 H), 7.66 (d, J = 8.4 Hz, 2 H),
7.99 (s, 1 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 88.6, 90.5, 123.0, 124.3, 128.5,
128.6, 128.76, 128.81, 129.0, 129.1, 130.4, 130.7, 130.8, 131.7, 131.8,
132.4, 132.6, 133.5, 133.8, 138.1, 138.6, 140.6.
1H NMR (CDCl3, 400 MHz):  = 7.01 (d, J = 16.2 Hz, 1 H), 7.11 (d, J =
16.2 Hz, 1 H), 7.24–7.30 (m, 3 H), 7.36 (t, J = 7.4 Hz, 2 H), 7.50 (d, J =
7.2 Hz, 2 H), 7.68 (d, J = 8.8 Hz, 2 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 92.9, 126.7, 127.6, 128.1, 128.4,
128.9, 129.6, 136.99, 137.04, 137.9.
trans-3-Iodostilbene (3k)6c
NMR yield by using 1,4-dioxane as an internal standard: 12%.
1H NMR (CDCl3, 400 MHz):  = 6.98 (d, J = 16.0 Hz, 1 H), 7.07–7.11 (m,
2 H), 7.26–7.30 (m, 1 H), 7.37 (t, J = 7.6 Hz, 2 H), 7.45 (d, J = 8.0 Hz, 1
H), 7.50 (d, J = 7.2 Hz, 2 H), 7.58 (d, J = 7.2 Hz, 1 H), 7.87 (t, J = 1.6 Hz, 1
H).
13C{1H} NMR (CDCl3, 101 MHz):  = 94.9, 125.9, 126.8, 127.1, 128.1,
128.8, 130.1, 130.4, 135.4, 136.4, 136.9, 139.7.
trans-1-(2-Furyl)-2-phenylethene (3l)6c
Isolated by flash chromatography (hexane); yield: 39 mg (91%); white
solid.
HRMS (MALDI-TOF): m/z [M + Na]+ calcd for C28H20O2SNa: 443.1082;
found: 443.1045.
1H NMR (CDCl3, 400 MHz):  = 6.35 (d, J = 3.2 Hz, 1 H), 6.42 (dd, J = 3.2,
1.8 Hz, 1 H), 6.89 (d, J = 16.2 Hz, 1 H), 7.04 (d, J = 16.2 Hz, 1 H), 7.22–
7.24 (m, 1 H), 7.34 (t, J = 7.6 Hz, 2 H), 7.40 (d, J = 1.8 Hz, 1 H), 7.46 (d,
J = 7.2 Hz, 2 H).
Other -expanded ethenyl sulfones 2q and 2r were synthesized ac-
cording to the same procedure.
13C{1H} NMR (CDCl3, 101 MHz):  = 108.7, 111.7, 116.6, 126.4, 127.2,
127.7, 128.8, 137.1, 142.2, 153.4.
(E)-2-[4-(4-Methyoxyphenylethynyl)phenyl]-1-phenyl-1-phenyl-
sulfonylethene (2q)
Isolated by flash chromatography (hexane/EtOAc 8:2) and recrystal-
lized from EtOH; yield: 216 mg (48%); white solid; mp 225–226 °C.
trans,trans-1,4-Diphenyl-1,3-butadiene (3m)6c
1H NMR (CDCl3, 400 MHz):  = 3.82 (s, 3 H), 6.86 (d, J = 8.8 Hz, 2 H),
7.03 (d, J = 7.6 Hz, 4 H), 7.27–7.31 (m, 4 H), 7.35–7.43 (m, 5 H), 7.54 (t,
J = 7.6 Hz, 1 H), 7.63 (d, J = 8.0 Hz, 2 H), 7.94 (s, 1 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 55.4, 87.8, 92.0, 114.2, 115.0,
125.5, 128.7, 128.8, 129.0, 129.4, 130.5, 130.8, 131.2, 131.5, 132.3,
133.3, 133.4, 136.9, 138.7, 141.8, 160.0.
Isolated by flash chromatography (hexane); yield: 35 mg (68%); white
solid.
1H NMR (CDCl3, 400 MHz):  = 6.64–6.71 (m, 2 H), 6.93–7.00 (m, 2 H),
7.23 (t, J = 7.6 Hz, 2 H), 7.34 (t, J = 7.6 Hz, 4 H), 7.45 (d, J = 7.6 Hz, 4 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 126.5, 127.7, 128.8, 129.4, 133.0,
137.5.
HRMS (MALDI-TOF): m/z [M + Na]+ calcd for C29H22O3SNa: 473.1187;
found: 473.1221.
trans-3-(Phenylethynyl)stilbene (3n);30 Stepwise Desulfonylation/
Sonogashira Coupling (Scheme 6, route 1)
(E)-1-[4-(4-Diphenylaminophenylethynyl)phenyl]-2-phenyl-1-
phenylsulfonylethene (2r)
3-Bromostilbene (3g) was prepared from 2g by 1/green LED-assisted
reductive desulfonylation. To a round-bottomed flask were added 3g
(259 mg, 1.0 mmol), Pd(PPh3)4 (58 mg, 0.05 mmol), CuI (9.5 mg, 0.05
mmol), ethynylbenzene (123 mg, 1.2 mmol), i-Pr2NH (1.0 mL, 7.1
mmol), and toluene (10 mL), and the mixture was stirred at 80 °C for
24 h. The reaction was quenched with sat. aq NH4Cl, and the organic
and aqueous layers were separated. The aqueous layer was extracted
with EtOAc, and the combined organic layers were washed with H2O
and brine. The organic layer was dried (MgSO4) and evaporated. The
crude product was subjected to flash chromatography on silica gel
(hexane/CH2Cl2 9:1) to afford 3n; yield: 199 mg (71%); white solid.
Isolated by flash chromatography (hexane/EtOAc 8:2) and recrystal-
lized from EtOH; yield: 194 mg (66%); yellow solid; mp 168–169 °C.
1H NMR (CDCl3, 400 MHz):  = 6.99–7.03 (m, 4 H), 7.05–7.13 (m, 8 H),
7.19 (t, J = 7.6 Hz, 2 H), 7.29 (t, J = 8.0 Hz, 5 H), 7.36 (d, J = 8.4 Hz, 2 H),
7.39–7.43 (m, 4 H), 7.54 (t, J = 7.4 Hz, 1 H), 7.64 (d, J = 6.8 Hz, 2 H),
7.97 (s, 1 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 88.1, 91.6, 115.4, 122.1, 123.8,
124.7, 125.2, 128.7, 128.9, 129.5, 130.3, 130.7, 130.9, 132.0, 132.7,
133.4, 138.0, 138.7, 140.9, 147.2, 148.3. Three carbon signals are
missing probably due to overlapping.
1H NMR (CDCl3, 400 MHz):  = 7.08 (d, J = 16.4 Hz, 1 H), 7.16 (d, J =
16.4 Hz, 1 H), 7.28–7.30 (m, 1 H), 7.33–7.39 (m, 6 H), 7.43 (d, J = 7.6
Hz, 1 H), 7.48 (d, J = 7.6 Hz, 1 H), 7.52–7.57 (m, 4 H), 7.71 (t, J = 1.6 Hz,
1 H).
HRMS (MALDI-TOF): m/z [M + Na]+ calcd for C29H22O3SNa: 610.1817;
found: 610.1847.
13C{1H} NMR (CDCl3, 101 MHz):  = 89.4, 89.6, 123.3, 123.8, 126.6,
126.7, 127.9, 128.0, 128.4, 128.5, 128.8, 129.6, 130.7, 131.8, 137.2,
137. Two carbon signals are missing due to overlapping.
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–K

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H. Watanabe et al.
Special Topic
Synthesis
(ii) trans-3-(Phenylethynyl)stilbene (3n); Typical Procedure
References
To a round-bottomed flask were added 2p (105 mg, 0.25 mmol), 1
(7.6 mg, 6.3 mol), i-Pr2NEt (0.35 mL, 2.0 mmol), MeCN (2.5 mL), and
THF (0.5 mL). The flask was placed in a glass water-bath surrounded
by green LED strip lighting, and green light was irradiated at the mix-
ture for 9 h. During the photoreaction, the bath temperature was
maintained at 50–60 °C due to heat radiation from the photoreactor.
After the solvents were evaporated, the crude product was subject to
column chromatography on silica gel (hexane/CH2Cl2 9:1) to afford
3n; yield: 55 mg (78%).
(1) For selected reviews of bioactive sulfones, see: (a) Liu, J.; Zheng,
L. Adv. Synth. Catal. 2019, 361, 1710. (b) Devendar, P.; Yang, G.-F.
Top. Curr. Chem. 2017, 375, 1. (c) Ahmad, I.; Shagufta Int. J.
Pharm. 2015, 7, 19. (d) Chen, X.; Hussain, S.; Parveen, S.; Zhang,
S.; Yang, Y.; Zhu, C. Curr. Med. Chem. 2012, 19, 3578.
(2) For selected reviews, see: (a) Review of sulfones: Simpkins, N. S.
Sulfones in Organic Synthesis; Oxford: Pergamon Press, 1993.
(b) Qiu, D.; Lian, C.; Mao, J.; Fagnoni, M.; Protti, S. J. Org. Chem.
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Rivera, E. M.; Alvarado, C. ChemistrySelect 2019, 4, 13698.
(e) Yadav, D.; Menon, R. S. Org. Biomol. Chem. 2020, 18, 365.
(f) Li, Y.; Fan, Y. Synth. Commun. 2019, 49, 3227. (g) Trost, B. M.;
Kalnmals, C. A. Chem. Eur. J. 2019, 25, 11193. (h) Marcantoni, E.;
Palmieri, A.; Petrini, M. Org. Chem. Front. 2019, 6, 2142.
(i) Takahashi, F.; Nogi, K.; Yorimitsu, H. Phosphorus, Sulfur
Silicon Relat. Elem. 2019, 194, 742. (j) Guo, W.; Tao, K.; Tan, W.;
Zhao, M.; Zheng, L.; Fan, X. Org. Chem. Front. 2019, 6, 2048.
(3) It is reported that the bond dissociation energies of C–SO2 are
54–83 kcal/mol: Benson, S. W. Chem. Rev. 1978, 78, 23.
(4) Selected recent reviews and papers on C–C bond formations:
(a) Crespi, S.; Fagnoni, M. Chem. Rev. 2020, 120, 9790.
(b) Chatelain, P.; Sau, A.; Rowley, C. N.; Moran, J. Angew. Chem.
Int. Ed. 2019, 58, 14959. (c) Millius, N.; Lapointe, G.; Renaud, P.
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Front. 2018, 5, 3443. (e) Nambo, M.; Yim, J. C.-H.; Freitas, L. B.
O.; Tahara, Y.; Ariki, Z. T.; Maekawa, Y.; Yokogawa, D.; Crudden,
C. M. Nat. Commun. 2019, 10, 4528. (f) Merchant, R. R.; Edwards,
J. T.; Qin, T.; Kruszyk, M. M.; Bi, C.; Che, G.; Bao, D-H.; Qiao, W.;
Sun, L.; Collins, M. R.; Fadeyi, O. O.; Gallego, G. M.; Mousseau, J.
J.; Nuhant, P.; Baran, P. S. Science 2018, 360, 75.
Other ethynyl-substituted stilbenes 3o and 3p were synthesized ac-
cording to the same procedure.
trans-4-(4-Methoxyphenylethynyl)stilbene (3o)
Isolated by column chromatography on silica gel (hexane/CH2Cl2 9:1);
yield: 58 mg (75%); white solid; mp 224–225 °C.
1H NMR (CDCl3, 400 MHz):  = 3.83 (s, 3 H), 6.89 (d, J = 8.8 Hz, 2 H),
7.09 (d, J = 16.4 Hz, 1 H), 7.14 (d, J = 16.4 Hz, 1 H), 7.25–7.29 (m, 1 H),
7.37 (t, J = 7.4 Hz, 2 H), 7.47–7.53 (m, 8 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 55.5, 88.4, 90.5, 114.2, 115.5,
122.8, 126.5, 126.7, 128.0, 128.2, 128.9, 129.5, 131.9, 133.2, 137.1,
137.3, 159.8.
HRMS (MALDI-TOF): m/z [M]+ calcd for C23H18O: 310.1358; found:
310.1310.
trans-4-(4-Diphenylaminophenylethynyl)stilbene (3p)
Isolated by column chromatography on silica gel (hexane/CH2Cl2 8:2);
yield: 34 mg (77%); yellow solid; mp 200–201 °C.
1H NMR (CDCl3, 400 MHz):  = 7.01 (d, J = 8.4 Hz, 2 H), 7.06 (t, J = 7.6
Hz, 2 H), 7.10–7.16 (m, 6 H), 7.26–7.30 (m, 5 H), 7.35–7.40 (m, 4 H),
7.49–7.53 (m, 6 H).
13C{1H} NMR (CDCl3, 101 MHz):  = 89.0, 90.8, 116.2, 122.4, 122.7,
123.7, 125.1, 126.5, 126.7, 127.9, 128.1, 128.8, 129.48, 129.52, 131.9,
132.6, 137.0, 137.2, 147.3, 148.0.
(5) We also developed one-pot and one-shot syntheses of diary-
lethynes by using benzyl sulfones and aldehydes as starting
compounds: (a) Xu, F.; Peng, L.; Shinohara, K.; Morita, T.;
Yoshida, S.; Hosoya, T.; Orita, A.; Otera, J. J. Org. Chem. 2014, 79,
11592. (b) Orita, A.; Taniguchi, H.; Otera, J. Chem. Asian J. 2006,
1, 430. (c) Orita, A.; Miyamoto, K.; Nakashima, M.; Ye, F.; Otera,
J. Adv. Synth. Catal. 2004, 346, 767.
HRMS (MALDI-TOF): m/z [M]+ calcd for C34H25N: 447.1987; found:
447.2032.
(6) (a) Whalley, D. M.; Duon, H. A.; Greaney, M. F. Chem. Commun.
2020, 56, 11493. (b) Chen, Y.; McNamara, N.; May, O.; Pillaiyar,
T.; Blakemore, D. C.; Ley, S. V. Org. Lett. 2020, 22, 5746.
(c) Watanabe, H.; Takemoto, M.; Adachi, K.; Okuda, Y.; Dakegata,
A.; Fukuyama, T.; Ryu, I.; Wakamatsu, K.; Orita, A. Chem. Lett.
2020, 49, 409. (d) Wang, Z.-J.; Zheng, S.; Matsui, J. K.; Lu, Z.;
Molander, G. A. Chem. Sci. 2019, 10, 4389.
Funding Information
A. Orita thanks JSPS (JP18K05134), JSPS Innovative Areas
(JP18H04430), Okayama Prefecture Industrial Promotion Foundation,
and OUS Research Project (OUS-RP-29-1 and OUS-RP-19-4). Y. Okuda
thanks to JSPS (JP19K15574), Wesco Scientific Promotion Foundation,
and OUS Research Project (OUS-RP-29-1 and OUS-RP-20-6) for finan-
(7) Julia, M.; Paris, J. M. Tetrahedron Lett. 1973, 4833.
(8) (a) Keck, G. E.; Savin, K. A.; Weglarz, M. A. J. Org. Chem. 1995, 60,
3194. For Julia–Lythgoe olefination using sulfoxides, see:
(b) Pospíšil, J.; Pospíšil, T.; Markó, I. E. Org. Lett. 2005, 7, 2373.
For catalytic HgCl2/Mg-promoted Julia olefination, see: (c) Lee,
G. H.; Lee, H. K.; Choi, E. B.; Kim, B. T.; Pak, C. S. Tetrahedron Lett.
1995, 36, 5607.
(9) For selected reviews, see: (a) Chatterjee, B.; Bera, S.; Mondal, D.
Tetrahedron: Asymmetry 2014, 25, 1. (b) Zajc, B.; Kumar, R. Syn-
thesis 2010, 1822. (c) Aïssa, C. Eur. J. Org. Chem. 2009, 1831.
(d) Blakemore, P. R. J. Chem. Soc., Perkin Trans. 1 2002, 2563.
(10) More recently a practical direct olefination protocol of sulfones
with alcohols using nickel catalyst was successfully reported
(see also references cited therein): Waiba, S.; Das, A.; Barman,
M. K.; Maji, B. ACS Omega 2019, 4, 708.
cial support.JapanSocietyforth
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Acknowledgment
The authors thank Okayama University of Science Research Instru-
ments Center for the measurements of 400 MHz NMR (JNM-ECS400
and JNM-ECZ400S) and MALDI-TOF MS (autoflex speed).
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0040-1706025.
S
u
p
p
ortingInformati
o
nS
u
p
p
ortingInformati
o
n
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–K

K
H. Watanabe et al.
Special Topic
Synthesis
(11) Other reductive desulfonylations were also reported:
(a) Electrochemical desulfonylation: Botrel, A.; Furet, E.;
Fourets, O.; Pilard, J-F. New J. Chem. 2000, 24, 815.
(b) Transition-metal-catalyzed desulfonylation: Clayden, J.;
Cooney, J. J. A.; Julia, M. J. Chem. Soc., Perkin Trans. 1 1995, 7.
(c) Clayden, J.; Julia, M. J. Chem. Soc., Chem. Commun. 1993,
1682.
(20) An absorption terminus of perylene was observed at 460 nm.
See also the Supporting Information for details.
(21) DFT calculations (B3LYP/6-31G(d)) indicated the LUMO levels of
2d and 2e at –1.57 and –1.87 eV, respectively. The lower LUMO
level of 2e could explain its more rapid desulfonylation in the
competitive reaction. See also the Supporting Information for
details.
(12) We already reported the synthesis of 1,3,6,8-tetrakis((trimeth-
ylsilyl)ethynyl)pyrene and its optical properties: Xu, F.; Nishida,
T.; Shinohara, K.; Peng, L.; Takezaki, M.; Kamada, T.; Akashi, H.;
Nakamura, H.; Sugiyama, K.; Ohta, K.; Orita, A.; Otera, J. Organo-
metallics 2017, 36, 556.
(13) For selected reviews, see: (a) Möller, M. N.; Denicola, A. Free
Radic. Biol. Med. 2018, 128, 137. (b) Feng, X.; Hu, J-Y.; Redshaw,
C.; Yamato, T. Chem. Eur. J. 2016, 22, 11898. (c) Mauritz, K. A.
Mater. Sci. Eng. C 1998, C6, 121.
(14) (a) Diring, S.; Camerel, F.; Donnio, B.; Dintzer, T.; Toffanin, S.;
Capelli, R.; Muccini, M.; Ziessel, R. J. Am. Chem. Soc. 2009, 131,
18177. (b) Maeda, H.; Maeda, T.; Mizuno, K.; Fujimoto, K.;
Shimizu, H.; Inouye, M. Chem. Eur. J. 2006, 12, 824.
(15) For simplicity, the calculations were performed by using
1,3,6,8-tetra(4-methoxyphenylethynyl)pyrene.
(16) (a) Okamoto, S.; Tsujioka, H.; Sudo, A. Chem. Lett. 2018, 47, 369.
(b) Okamoto, S.; Ariki, R.; Tsujioka, H.; Sudo, A. J. Org. Chem.
2017, 82, 9731. (c) Okamoto, S.; Kojiyama, K.; Tsujioka, H.; Sudo,
A. Chem. Commun. 2016, 52, 11339. (d) See also ref. 6c.
(17) (a) The LUMO energy levels were calculated using the following
equation: ELUMO = –4.80–E1/2red [eV]: Liu, S-Y.; Shi, M-M.; Huang,
J-C.; Jin, Z-N.; Hu, X-L.; Pan, J-Y.; Li, H-Y.; Jen, A. K.-Y.; Chen, H-Z.
J. Mater. Chem. A 2013, 1, 2795. (b) See also the Supporting
Information for details.
(22) (a) We also attempted a three-step integration in the transfor-
mations of benzyl sulfone to 3n, namely, in the synthesis of
2g/desulfonylation/Sonogashira coupling. Unfortunately, the
desired enyne 3n was contaminated with a trace amount of 1,3-
di(phenylethynyl)benzene, which was produced at the synthe-
sis of 2g by the unexpected further elimination of sulfinic acid.
(b) See ref. 5c.
(23) When the crude product 2p was subjected to the 1/green LED
protocol, the expected desulfonylation did not emerge with 2p
remaining untouched.
(24) (a) Fang, J-K.; An, D-L.; Wakamatsu, K.; Ishikawa, T.; Iwanaga, T.;
Toyota, S.; Matsuo, D.; Orita, A.; Otera, J. Tetrahedron Lett. 2010,
51, 917. (b) See also the Supporting Information for details.
(25) (a) Although 6. and 6+ were more stable than 8. and 8+ by 2.2
kcal/mol and 5.7 kcal/mol, respectively, both 6. and 8. could be
formed in the protonation stage of 2a.– because a difference of
their HOFs (2.2 kcal/mol) was comparatively small and also
because the formation of 8. might be kinetically favored than 6..
In fact, both 6. and 8. were described in the existing research.
For instance, see ref. 16 and also the following paper:
Chatterjee, A.; König, B. Angew. Chem. Int. Ed. 2019, 58, 14289.
(b) See also the Supporting Information for the DFT calculations
of their HOFs.
(26) Huo, C.; He, X.; Chan, T. H. J. Org. Chem. 2008, 73, 8583.
(27) Xu, H. J.; Zhao, Y. Q.; Zhou, X. F. J. Org. Chem. 2011, 76, 8036.
(28) Kumar, S.; Pandey, A. K.; Singh, R.; Singh, K. N. Eur. J. Org. Chem.
2018, 5942.
(18) (a) Waiba, S.; Barman, M. K.; Maji, B. J. Org. Chem. 2019, 84, 973.
(b) Julia, M.; Launay, M.; Stacino, J-P.; Verpeaux, J-N. Tetrahe-
dron Lett. 1982, 23, 2465. (c) See also ref. 8a.
(19) Because of the poor solubility of 1 in MeCN, the addition of a
small amount of THF was crucial. See the Supporting Informa-
tion for more detail of the solubility of 1.
(29) Hang, T.; Chen, T.; Han, L. B. J. Org. Chem. 2018, 83, 2959.
(30) Zhang, X.; Liu, A.; Chen, W. Org. Lett. 2008, 10, 3849.
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