Sunlight-Driven Synthesis of Triarylethylenes (TAEs) via Metal-Free Mizoroki–Heck-Type Coupling

Article abstract of DOI:10.1002/ejoc.201800883

A protocol for the preparation of substituted triarylethylenes (TAEs) was developed by using arylazo sulfones as substrates in the presence of 1,1-diarylethylenes. The process took place efficiently in the absence of any (photo)catalyst upon exposure of the reaction mixture to (simulated) sunlight.

Full text of DOI:10.1002/ejoc.201800883

A Journal of
Accepted Article
Title: Sunlight-driven synthesis of triarylethylenes (TAEs) via metal-free
Mizoroki-Heck-type coupling
Authors: Stefano Protti, Carlotta Raviola, Maurizio Fagnoni, Louis
Onuigbo, and Andrea Di Fonzo
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10.1002/ejoc.201800883
European Journal of Organic Chemistry
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Sunlight-driven synthesis of triarylethylenes (TAEs) via metal-free
Mizoroki–Heck-type coupling
Louis Onuigbo,[a] § Carlotta Raviola,[a] § Andrea Di Fonzo,[b] Stefao Protti[a]* and Maurizio Fagnoni[a]
Abstract: A protocol for the preparation of substituted triarylethylenes
(TAEs) was developed by using arylazo sulfones as substrates in the
presence of 1,1-diarylethylenes. The process took place efficiently in
the absence of any (photo)catalyst upon exposure of the reaction
mixture to (simulated) sunlight .
Recently several efforts have been devoted to improve the Heck
reaction in terms of sustainability and safety[16,17] but only little
attention has been given to the development of metal-free
protocols,[18] most of them exploiting photochemical conditions.[19-
21]
However, despite the formation of a triarylethylene from 1,1-
diphenylethylene and aryl halides (iodides, chlorides) has been
described to occur via the photogeneration of a triplet aryl cation
(path e)[20] or an aryl radical[21] (path f), the scope of such
proposals is rather limited, and, a high energy demanding UV-
light source is required to activate the aromatic substrates.[20,21]
Thus, currently, to the best of our knowledge, a versatile metal-
free Heck protocol for the preparation of TAEs is still lacking.
Introduction
Compounds bearing the triarylethylene (TAE) core mimic the
effect of natural estrogen by binding to the Estrogen Receptor
(ER) and produce either an agonist or an antagonist effect. These
so-called selective estrogen receptor modulators (SERM) find
application in the treatment of estrogen-dependent disorders,[1]
namely breast cancer (tamoxifen[2] and its analogue toremifene[3]),
osteoporosis (raloxifene)[4] and cyclical mastalgia (afimoxifene).[5]
Other bioactive TAEs are clomifene, that is currently employed
for fertility induction,[6] and ormeloxifene (also known as
centchroman) a non-hormonal, nonsteroidal oral contraceptive.[7]
Furthermore, substituted triarylethylenes exhibiting aggregation-
induced emission (AIE) have been recently considered for the
preparation of Organic Light Emitting Diodes (OLEDs).[8] For this
aim, a large number of protocols having the TAE moiety as
synthetic target have been reported in the literature, including,
among others, the McMurry coupling between two ketones
occurring in the presence of a low-valent titanium salt,[9] (Scheme
1,
path
a)
and
the
transition-metal
catalyzed
hydro(hetero)arylation of diarylalkynes (path b).[10] On the other
hand, the poor regioselectivity of such processes, along with the
formation in the former example of homocoupling products,
limited seriously their synthetic application.[9] Another strategy
relies on the formation of an Aryl-Csp2 bond and, among the
different approaches proposed,[11-13] the Mizoroki–Heck reaction
involving the coupling of a 1,2- (path c)[14,15a,b] or a 1,1- (path
d)[15a,c] disubstituted alkene with an aryl halide is the most
attractive since no previous activation of the olefin is needed.
Scheme 1. Synthetic approaches to the triarylethylene core proposed in the
literature.
We recently exploited the peculiar photochemical properties of
arylazo sulfones I in organic synthesis.[22-25] Such bench-stable
derivatives of anilines bear a -N2SO2CH3 moiety[22] that imparts
both color and photoreactivity to the molecule and for this reason,
has been dubbed as dyedauxiliary group.[24] Indeed, aryl radicals
(Ar•, obtained via homolysis of the N-S bond occurring from the
1n* state and loss of a N2 molecule) and triplet aryl cations (3Ar+,
in turn generated upon heterolysis from the 3* state and loss of
N2) were smoothly generated from I in a wavelength-selective
fashion by irradiation with visible and UV-light sources,
respectively.[22] Obviously, upon solar light exposition both
[a]
[b]
L. Onuigbo, C. Raviola, Dr., S. Protti, Dr., M. Fagnoni, Prof.
PhotoGreen Lab, Department of Chemistry
University of Pavia
V.Le Taramelli 12, 27100 Pavia
E-mail: stefano.protti@unipv.it
http://www-2.unipv.it/photogreenlab/index.php
A. Di Fonzo, Dr.
Laboratorio Biochimica, Biotecnologie e Diagnostica Avanzata.
Fondazione IRCCS Policlinico San Matteo
Supporting information and th ORCID identification number(s) for
tha author(s) of this article can be found under ((Please delete this
text if not appropriate))
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10.1002/ejoc.201800883
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species were released.[22] These substrates have been employed
in different photocatalyst- and metal-free arylation protocols, for
the preparation of (hetero)biaryls,[22] allyl arenes[23] and aromatic
amides.24
whereas in acetone the efficiency of the arylation increased, and
a 5:1 mixture of 2a and 3a was obtained (entry 3). Notably, when
moving to dry acetonitrile, 2a was the only product observed (80%,
entry 4). Arylation remained the exclusive path also in the
presence of a halved concentration of DPE, but the efficiency of
the reaction significantly dropped. Replacing part of the organic
solvent with water resulted in a decrease of the amount of 2a
along with the formation of carbinol 4a (entry 5).
Table 1. Optimization of the reaction protocol. [a]
Entry
Conditions
Light source,
tirr (h)
Products
(% yield)
1
2
dry CH2Cl2
dry CH3COOEt
dry Acetone
Solarbox,[b] 4h
Solarbox,[b] 4h
Solarbox,[b] 4h
Solarbox,[b] 4h
Solarbox,[b] 4h
Solarbox,[b] 4h
366 nm,[d] 4h
2a, 65; 3a, 7
2a, 50; 3a, 7
2a, 81; 3a, 16
2a, 80, (55)[c]
2a, 46; 4a, 6
2a, 69; 4a, 6
2a, 22
3
4
dry MeCN
5
MeCN-H2O (9:1)
K2S2O8 (1 equiv.),
MeCN/H2O (9:1)
6
7
dry MeCN
dry MeCN
dry MeCN
dry MeCN
dry MeCN
8
410 nm,[e] 16 h
450 nm,[f] 16 h
2a, 82
Scheme 2. Wavelength-selective generation of aryl radicals and aryl cations
from arylazo sulfones (I).
9
2a, 80
Natural Sunlight,
2 days [g]
10
11[h]
2a, 83
In the aim of investigating the scope of arylazo sulfones as
photoactivated substrates in metal-free arylation procedures we
thus decided to explore the reactivity of such compounds in the
presence of 1,1-diarylethylenes, being capable to trap various
chemical intermediates.[20,21]
[i]
-
-
[a] The reaction mixture was deareated by means of three freeze-pump-thaw
cycles. Irradiations have been carried out until the complete consumption of
1a. [b] A solar simulator equipped with a 1500 W Xe lamp (500 W/m2). [c]
0.1 M DPE used. [d] 10 x 15 W Phosphor coated Hg lamp. [e] 1 W LED
(410 nm). [f] 1 W LED (450 nm). [g] The reaction vessel was exposed to
sunlight for 2 days (6 h per day). [h] Blank experiment carried out in the
absence of light. [i] No arylation observed.
Results and Discussion
At the beginning, we investigated the photolysis of 4-
cyanophenylazo sulfone 1a (0.05 M) in the presence of 1,1-
diphenylethylene (DPE, 0.2 M) as the coupling partner (Table 1).
Reactions were performed by means of a solar simulator
equipped with a 1500 W Xenon lamp. The reaction mixture was
deareated by means of three freeze pump thaw cycles.
Gratifyingly, irradiation in dichloromethane resulted in the
formation of triarylethylene 2a in 65% yield, along with a low
amount of 1,1,2-triarylethane 3a (7%, entry 1). The use of ethyl
acetate as the solvent was detrimental for the process (entry 2),
External oxidants such as K2S2O8 did not alter improve
significantly the selectivity of the process (entry 6). We finally
investigated the role of different light sources, finding that the
reaction was inefficient under UV-light irradiation (366 nm, 22%
yield of 2a, entry 7). On the other hand, visible LEDs (entries 8,9)
gave results comparable to that observed in entry 4. To our delight,
a 83% yield of 2a was also obtained when exposing the reaction
vessel to natural sunlight for two sunny days in Pavia, September
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10.1002/ejoc.201800883
European Journal of Organic Chemistry
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2017 (6 h of exposition per day, entry 10, see also ESI). Finally,
no reaction took place when storing the reaction vessel covered
by an aluminium foil in the solar simulator (entry 11).
sulfone 1j and 1k afforded the corresponding 1,2,2-
triarylethylenes 2j,k in 58 and 89% yield, respectively. The results
were not satisfactory starting from 2l (40% of the 4-tbutyl-
substituted product isolated), whereas with 1m the reaction failed,
since a mixture of 2m and 3m was formed in a very low overall
yield. The process was applied also to nitrogen-containing
heterocycles, and 3-pyridyl derivative 2n was obtained in a
moderate yield (49%). Furthermore, in selected case we
demonstrated that the excess of the employed diphenylethylene
can be recovered almost quantitatively (ca. 90%).
The developed protocol worked to some extent also in the case
of substituted diphenylethylenes, as depicted in Scheme 3. Thus,
arylated 5a and 5c were obtained from 1-methyl-4-(1-
phenylvinyl)benzene as a mixture of diasteroisomers, in discrete
yields (up to 60%), whereas in the case of 1,1'-(ethenylidene)-
bis(4-chlorobenzene),
trapping
of
the
photogenerated
intermediates took place unsatisfactorily and only a 28% yield of
6a was formed under simulated sunlight exposition (32% yield
when a 450 nm LED was employed).
Scheme 3. Synthesis of substituted triarylethylenes 5 and 6.
As hinted above, the photoreactivity of arylazo sulfones 1 has
been the subject of a detailed investigation by our research group.
Thus, a triplet aryl cation (Scheme 4, path a) and an aryl
Scheme 2. Preparation of triarylethylenes 2a-n
•
radical/CH3SO2 pair (path a') are both generated upon solar
exposition. According to the reported literature[19,20] such
intermediates can be easily trapped by diarylethylenes to afford
the cation II+ and the radical adduct II•, respectively. Whereas
With these preliminary results in hand, we thus adopted the
reaction conditions described in entry 4 in order to extend the
scope of such arylation protocol.
-
As depicted in Scheme 2, the reaction took place efficiently with
substrates bearing electron-withdrawing substituents in para-
position and compounds 2a-f were isolated in up to 85% yield
(see the case of p-bromoderivative 2d). Good yields (around
55%) were also obtained in the synthesis of 3- and 2-
vinylbenzonitriles 2g and 2h as well as in the preparation of the
2- chloroderivative 2i. Interestingly, in the case of 2g the yield was
strongly improved when carrying out the reaction in MeCN-H2O
5:1 mixture. Analogously, irradiation of phenylazo- and p-tolylazo
deprotonation by the methanesulfinate anion (CH3SO2 ) is the
most feasible pathway occurring to II+ (path d), the
•
methanesulfonyl radical (CH3SO2 ) was found able to act as a
monoelectronic oxidant for different radical intermediates
including imidoyl radicals.[24] Thus, oxidation of II• to II+ (path c)
and ensuing deprotonation (path d) afforded the desired products
•
2, 5-6. However, a hydrogen atom abstraction from II• by CH3SO2
to give directly the triarylethylene can not be so far excluded. With
the aim of further investigating the mechanism of the reaction, and
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confirming the intermediacy of an aryl radical, we carried out the
irradiation at 450 nm of 1a in dry acetonitrile in the presence of
DPE and of the radical trap 2,2,6,6-tetramethylpiperidin-1-yl)oxyl
(TEMPO).[26] In this case, arylation of DPE was almost
suppressed (5% yield of 2a) and we isolated only a small amount
of adduct 7a (23% yield). On the other hand, the formation of 2a
observed also during the irradiation at 366 nm (where, according
to literature, a triplet aryl cation is exclusively generated)[22]
confirmed likewise the capability of the diarylethylene to act as a
phenyl cation trap. Finally, the formation of a reactive Electron
Donor-Acceptor complex between the arylazo sulfones and the
diarylethylenes was excluded on the basis of spectroscopic
analyses (see ESI files for further details).
heteroaromatics), with the only exception of compounds bearing
strong electron-donating substituents such as 2m (which already
gave unsatisfactory results in previous investigations). [23]
The obtained results pointed out the potentialities of our approach
as a sustainable and versatile route to TAE derivatives.
This metal- and (photo)catalyst-free arylation procedure
combines the peculiar photoreactivity of arylazo sulfones and the
impressive reactivity of the 1,1-diarylethylene moiety towards
photogenerated intermediates such as aryl radicals and triplet aryl
cations. The process occurs under mild conditions, since
simulated or natural sunlight are exclusively employed to activate
the substrates, and the reaction was applied, to some extent, also
to substituted diarylethylenes. Finally, a large part of the
unreacted diphenylethylene employed can be easily recovered
during the purification step.
Experimental Section
Experimental
General. 1H and 13C NMR spectra were recorded on a 300 MHz
spectrometer, chemical shifts were reported in ppm downfield
from TMS, and the attributions were made on the basis of 1H and
13C signals, as well as DEPT-135 experiments; chemical shifts are
reported in ppm downfield from TMS. GC-MS analyses were
carried out by using a GC-DSQ single quadrupole GC/MS system.
A Rtx-5MS (30 m × 0.25 mm × 0.25 μm) capillary column was
used for analytes separation with helium as carrier gas at 1 mL
min-1. The injection in the GC system was performed in split mode
and the injector temperature was 250 °C. The GC oven
temperature was held at 80°C for 5 min, increased to 250 °C by a
temperature ramp of 10 °C min-1 and held for five min. The
transfer line temperature was 250 °C and the ion source
temperature 250 °C. Mass spectral analyses were carried out in
full scan mode. The reaction course was followed by GC and TLC
analyses. Solvent of HPLC purity were employed in the
photochemical reactions. 1,1-diphenylethylene is commercially
available and was purified by column chromatography before
using. Arylazo sulfones 1a-n were previously synthesized and
fully characterized in our lab.[24]
Scheme 4. Proposed mechanism for the photoinduced synthesis of
triarylethylenes
As concerning the influence of the aromatic substituent of arylazo
sulfones 1 on the efficiency of the arylation, and in particular, on
the unsatisfactory results obtained in the case of substrates
bearing electron-donating groups (see for instance compounds.
2l,m) it should be noticed that a similar behaviour have been
already observed in our previous works[22,24] and in recent
arylation procedures where an aryl radical is involved.[27]
Photochemical synthesis of triarylethylenes 2, 5-6.
A solution (8 mL) of arylazo sulfone 1a-n (0.05 M, 0.4 mmol,
except where otherwise reported), the chosen diarylethylene (0.2
M, 1.6 mmol, except where otherwise reported) in dry acetonitrile
was divided in four portions and poured into four Pyrex vials (2
mL each one). The vials were sealed with a septum, degassed
three times by “pump-freeze-thaw” cycles (×3) via a syringe
needle and the reaction mixture was irradiated in a solar simulator
equipped with a 1.5 kW Xenon lamp (conditions: 500W with
outdoor + IR filter) for 4 h. The photolyzed solution was then
concentrated under vacuo and purified by flash chromatography
(eluant: petroleum ether:AcOEt mixture).
Conclusions
As hinted above, the development of a metal-free Mirozoki-Heck
coupling has been documented in literature[18-21] and such
protocols were sometimes applied to the building of
a
4-(2,2-diphenylvinyl)benzonitrile (2a). From 84 mg of 4-
((methylsulfonyl)diazenyl)benzonitrile (1a, 0.05 M, 0.4 mmol) and
282 L (0.2 M, 1.6 mmol) of 1,1-diphenylethylene (DPE) in 8 mL
triarylethylene core.[19,20] However, whereas the previous
examples showed a limited scope, the present proposal can be
efficiently applied to a wide range of substrates (including
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10.1002/ejoc.201800883
European Journal of Organic Chemistry
FULL PAPER
of dry MeCN, irradiated for
4
h. Purification by flash
Purification by flash chromatography afforded 99 mg of 2f (white
solid, mp: 121-123°C, lit.[34] 125°C), 83% yield). Spectroscopic
data of 2f were in accordance with the literature.35 IR (NaCl, /cm-
1): 2935, 2846, 17501, 956, 894. Furthermore, 90% of the the
unreacted DPE was recovered during the isolation step.
chromatography afforded 90 mg of 2a (white solid, mp: 104-
105°C, lit.[27a] 110°C, 80% yield). Spectroscopic data of 2a were
in accordance with the literature.[28] The same process was
carried out by exposing the reaction mixture to natural sunlight for
2 days (6 hours/day). Under these conditions, 2a was isolated in
83% yield. When the reaction was carried out in acetone, the GC-
MS analysis pointed out the presence of 3a (81%) along with
minor amounts of 4-(2,2-diphenylethyl)benzonitrile[29] (3a, 16%
yield, m/z: 167 (M+, 100)). On contrast, when a MeCN-H2O 5:1
mixture was used as the solvent, 4-(1-hydroxy-2,2-
diphenylethyl)benzonitrile[30] (4a, 6% yield, m/z:183 (100), 116
(5)) was obtained as the byproduct.
1-(2-(4-nitrophenyl)-1-phenylvinyl)benzene (2b). From 92 mg
of 1-(methylsulfonyl)-2-(4-nitrophenyl)diazene (1b, 0.05 M, 0.4
mmol) and 282 L (0.2 M, 1.6 mmol) of DPE in 8 mL of dry MeCN.
Purification by flash chromatography afforded 68 mg of 2b (yellow
solid, mp: 146-148°C, lit.[31a] 148-150°C), 56% yield).
Spectroscopic data of 2b were in accordance with the
literature.[31a,b]
3-(2,2-diphenylethenil)benzonitrile (2g). From 84 mg of 2-
((methylsulfonyl)diazenyl)benzonitrile (1h, 0.05 M, 0.4 mmol) and
282 L (0.2 M, 1.6 mmol) of DPE in 8 mL of dry MeCN. Purification
by flash chromatography afforded 28 mg of 2h (colorless oil, 25%
yield). Spectroscopic data of 2h were in accordance with the
literature[36] IR (NaCl, /cm-1) 3059, 2923, 2853, 2116, 1491,1027,
942, 885. When the same reaction is carried out in MeCN-H2O 9-
1 mixture instead of dry MeCN, 2h was isolated in 55% yield.
2-(2,2-diphenylvinyl)benzonitrile (2h). From 84 mg of 3-
((methylsulfonyl)diazenyl)benzonitrile (1g, 0.05 M, 0.4 mmol) and
282 L (0.2 M, 1.6 mmol) of DPE in 8 mL of dry MeCN. Purification
by flash chromatography afforded 61 mg of 2g (colorless solid,
mp: 120-121°C, lit 124-125°C,37 54% yield). Spectroscopic data
of 2g were in accordance with the literature.[37]
2-(2-chlorophenyl)-1,1-diphenylethylene (2i). From 88 mg of 1-
(methylsulfonyl)-2-(2-chlorophenyl)diazene (1i, 0.05 M, 0.4 mmol)
and 282 L (0.2 M, 1.6 mmol) of DPE in 8 mL of dry MeCN.
Purification by flash chromatography afforded 65 mg of 2i
(colorless solid, 56% yield, mp: 110-111°C). Spectroscopic data
of 2i were in accordance with the literature.[38] A 90% of the the
unreacted DPE was recovered during the isolation step.
2-(4-chlorophenyl)-1,1-diphenylethylene (2c). From 88 mg of
1-(methylsulfonyl)-2-(4-chlorophenyl)diazene (1c, 0.05 M, 0.4
mmol) and 282 L (0.2 M, 1.6 mmol) of DPE in 8 mL of dry MeCN.
Purification by flash chromatography afforded 62 mg of 2c
(colorless oil, 53% yield). Spectroscopic data of 2c were in
accordance with the literature.[32]
2-(4-bromophenyl)-1,1-diphenylethylene (2d). From 105 mg of
1-(methylsulfonyl)-2-(4-bromophenyl)diazene (1d, 0.05 M, 0.4
mmol) and 282 L (0.2 M, 1.6 mmol) of DPE in 8 mL of dry MeCN.
Purification by flash chromatography afforded 114 mg of 2d
(colorless solid, 85% yield, mp: 72.9-74°C, lit[33a] 77°C).
Spectroscopic data of 2d were in accordance with the
literature.[33b] Furthermore, 90% of the the unreacted DPE was
recovered during the isolation step.
1,1,2-Triphenylethylene (2j). From 74 mg of 1-(methylsulfonyl)-
2-phenyldiazene (1j, 0.05 M, 0.4 mmol) and 282 L (0.2 M, 1.6
mmol) of DPE in 8 mL of dry MeCN. Purification by flash
chromatography afforded 59 mg of 2j (colourless solid, mp: 70-
72°C, lit.[39] 71-73°C, 58% yield). Spectroscopic data of 2j were in
accordance with the literature.[39]
1,1-diphenyl-2-(4-methylphenyl)ethylene (2k). From 79 mg of
1-(methylsulfonyl)-2-(4-methylphenyl)diazene (1k, 0.05 M, 0.4
mmol) 282 L (0.2 M, 1.6 mmol) of DPE in 8 mL of dry MeCN.
Purification by flash chromatography afforded 96 mg of 2k.
(colourless oil, 89% yield). Spectroscopic data of 2k were in
accordance with the literature.[31]
1,1-Diphenyl-2-(4-tert-butylphenyl)ethylene (2l). From 96 mg
of 1-(methylsulfonyl)-2-(4-tert-butylphenyl)diazene (1l, 0.05 M,
0.4 mmol) and 282 L (0.2 M, 1.6 mmol) of DPE in 8 mL of dry
MeCN. Purification by flash chromatography afforded 50 mg of 2l
(white solid, mp: 71-73°C, lit.[40] 74-76°C, 40% yield). 1H NMR
data of 2l were in accordance with the literature.[36] 13C NMR
(CDCl3) 31.1 (CH3), 34.4, 124,8 (CH), 127.2 (CH), 127.3 (CH),
127.9 (CH), 128.0(CH), 128.1 (CH), 128.6 (CH), 129.12 (CH),
Methyl 4-(2,2-diphenylvinyl)benzoate (2e). From 98 mg of
methyl 4-((methylsulfonyl)diazenyl)benzoate (1d, 0.05 M, 0.4
mmol) and 282 L (0.2 M, 1.6 mmol) of DPE in 8 mL of dry MeCN.
Purification by flash chromatography afforded 70 mg of 2e
(colourless oil, 56% yield) along with a minor amount of methyl 4-
(2-hydroxy-2,2-diphenylethyl)benzoate (4e, 20 mg, 15%
colourless solid, mp: 147-150°C).
1
2e: H NMR (CDCl3),  3.90 (s, 3H), 7.00 (s, 1H), 7.10-7.15 (d,
2H, J = 8.3 Hz), 7.20-7.25 (m, 2H), 7.36 (s, 1H), 7.80-7.85 (d, 2H,
J = 8.3 Hz). 13C NMR (CDCl3) 51.9 (CH3), 127 (CH), 127.6,
127.7 (CH), 127.9 (CH), 128.2 (CH), 128.6 (CH), 129.1 (CH),
129.3 (CH), 129.9, 130.2 (CH), 132.3 (CH), 139.7, 142.1, 142.8,
144.9, 166.8. IR (NaCl, /cm-1) 2926, 2844, 1706, 1212, 755. Anal. 130.1 (CH), 134.3, 140.5, 141.5, 143.5, 149.8. Anal. Calcd for
Calcd for C22H18O2: C, 84.05; H, 5.77. Found: C,84.1; H, 5.8.
4e: 1H NMR (CDCl3), 3.70 (s, 2H), 3.90 (s, 3H), 6.95-7.00 (m,
2H), 7.25-7.40 (m, 10 H), 7.80-7.85 (m, 2H). 13C NMR (CDCl3)
48.1 (CH2), 52 (CH3),78.1, 126.1 (CH), 127.1 (CH), 127.8 (CH),
128.4, 129 (CH), 130, 130.8 (CH), 141.8, 146.1, 166.6. IR (NaCl,
/cm-1) 2954, 1706, 1120, 755. Anal. Calcd for C22H20O3: C, 79.50;
H, 6.06. Found: C,79.5; H, 6.1.
1-(4-acetyl)phenyl-2,2-diphenylethylene (2f). From 91 mg of 1-
(4-((methylsulfonyl)diazenyl)phenyl)ethanone (1f, 0.05 M, 0.4
mmol) and 282 L (0.2 M, 1.6 mmol) of DPE in 8 mL of dry MeCN.
C24H14: C, 92.26; H, 7.74. Found: C, 92.3; H, 7.7.
Irradiation of 1m in MeCN in the presence of DPE. A solution
of 86 mg of 1-(methylsulfonyl)-2-(4-methoxyphenyl)diazene (1m,
0.05 M, 0.4 mmol) and 282 L (0.2 M, 1.6 mmol) of DPE in dry
MeCN (8 mL) was irradiated in a Solarbox for 4 hours. GC -MS
analyses of the photolysed pointed out the presence of low
amount
(<10%
overall)
of
1,1-diphenyl-2-(4-
methoxyphenyl)ethylene[41a] (2m, m/z: 286 (M+, 100), 165 (40))
and 1,1-diphenyl-2-(4-methoxyphenyl)ethane[41b] (3m, m/z: 167
(30), 120 (100)).
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1,1-diphenyl-2-(3-pyridyl)ethylene (2n). From 74 mg of 3-
((methylsulfonyl)diazenyl)pyridine (1n, 0.05 M, 0.4 mmol) and 282
L (0.2 M, 1.6 mmol) of DPE in 8 mL of dry MeCN. Purification by
flash chromatography afforded 50 mg of 2n (oil, 49% yield).
Spectroscopic data of 2n were in accordance with the
literature..[16d]
4-(2-phenyl-2-(p-tolyl)vinyl)benzonitrile (5a). From 84 mg
(0.05 M, 0.4 mmol) of 1a and 317 L (0.2 M, 1.6 mmol) of 1-
methyl-4-(1-phenylvinyl)benzene in dry MeCN (8 mL). Purification
by flash chromatography afforded 74 mg of 5a (colouless oil, 63%,
dr 53:47).
5a:1H NMR (CDCl3)  2.40 (s, 3H), 2.45 (s, 3H), 6.90-6.95 (m,
2H), 7.05-7.10 (m, 5H), 7.15-7.20 (m, 7H), 7.25-7.30 (m, 2H),
7.35-7.45 (m, 12H); 13C NMR (CDCl3) 21.1 (CH3), 21.2
(CH3),109.4, 109.5, 118.9, 119, 125.2 (CH), 125.7 (CH), 127.5
(CH), 127.8 (CH), 127.9 (CH), 128.1 (CH), 128.2 (CH), 128.7 (CH),
128.8 (CH), 129 (CH), 129.5 (CH), 129.7 (CH), 129.8 (CH), 129.9
(CH), 130 CH), 131.5 (CH), 131.6 (CH), 136.2, 137.9, 138.2,
139.4, 139.6, 142.2, 142.3, 142.7, 146.1, 146.2. IR (NaCl, /cm-1)
3020, 2220, 1595, 1070, 890. Anal. Calcd for C22H17N: C, 89.46;
H, 5.80; N, 4.74. Found: C, 88.5; H, 5.9; N, 4.6.
1-chloro-4-(2-phenyl-2-(p-tolyl)vinyl)benzene (5c). From 88
mg (0.05 M, 0.4 mmol) of 1c and 317 L (0.2 M, 1.6 mmol) of 1-
methyl-4-(1-phenylvinyl)benzene in dry MeCN (8 mL). Purification
by flash chromatography afforded 48 mg of 5c (colouless oil, 40%
yield, dr 53:47).
References
§
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Acknowledgements
The work has been funded by Cariplo Foundation and Lombardy
Region, Italy, Project 2015-0756 “Visible Light Generation of
Reactive Intermediates from Azosulfones”. We are grateful to D.
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Keywords: Metal-free Arylation • Photogenerated intermediates
• Triarylethylenes • Sunlight-driven processes • Photochemistry.
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Entry for the Table of Contents
FULL PAPER
The
preparation
of
substituted
L. Onuigbo, C. Raviola, A. Di Fonzo, S.
Protti* and M. Fagnoni
triarylethylenes (TAEs) was achieved
under metal- and (photo)catalyst-free
conditions,
starting
from
Page No. – Page No.
photoactivated arylazo sulfones.
Sunlight-driven
synthesis
of
triarylethylenes (TAEs) via metal-free
Mizoroki–Heck-type coupling
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