Cyclization of aryl 3-aryl propynoates into 4-arylcoumarins catalyzed by cyclometalated Platinum(II) complexes

Article abstract of DOI:10.1016/j.tet.2020.131029

Cyclometalated (ppy)Pt^II complexes (ppy = 2-phenylpyridinato-C²,N) catalyze the intramolecular cyclization of aryl propynoates to form coumarins and benzocoumarins. The complex [(ppy)PtCl(MeCN)] (5 mol %) was the most active and effi

Full text of DOI:10.1016/j.tet.2020.131029

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Cyclization of aryl 3-aryl propynoates into 4-arylcoumarins catalyzed by
cyclometalated Platinum(II) complexes
Olesia Zaitceva, Valérie Bénéteau, Dmitry S. Ryabukhin, Ivan I. Eliseev, Mikhal A.
Kinzhalov, Benoit Louis, Aleksander V. Vasilyev, Patrick Pale
PII:
S0040-4020(20)30136-8
https://doi.org/10.1016/j.tet.2020.131029
TET 131029
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 7 December 2019
Revised Date: 4 February 2020
Accepted Date: 6 February 2020
Please cite this article as: Zaitceva O, Bénéteau Valé, Ryabukhin DS, Eliseev II, Kinzhalov MA,
Louis B, Vasilyev AV, Pale P, Cyclization of aryl 3-aryl propynoates into 4-arylcoumarins catalyzed
by cyclometalated Platinum(II) complexes, Tetrahedron (2020), doi: https://doi.org/10.1016/
j.tet.2020.131029.
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Cyclization of Aryl 3-Aryl propynoates into
4-Arylcoumarins Catalyzed by
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Cyclometalated Platinum(II) Complexes
Olesia Zaitceva, Valérie Bénéteau, Dmitry S. Ryabukhin, Ivan I. Eliseev, Mikhal A. Kinzhalov, Benoit Louis,
Aleksander V. Vasilyev,* Patrick Pale*
Institut de Chimie, UMR 7177, CNRS and Université de Strasbourg,
Strasbourg, 4 rue B. Pascal, 67000 Strasbourg, France.
Saint Petersburg State University 7/9 Universitetskaya Nab., 199034 &
State Forest Technical University, 5 Institutskii per., 194021
Saint Petersburg, Russian Federation.
ICPEES, ECPM, Université de Strasbourg
25 rue Becquerel, 67087 Strasbourg cedex 2, France

1
Tetrahedron
journal homepage: www.elsevier.com
Cyclization of Aryl 3-Arylpropynoates into 4-Arylcoumarins Catalyzed by
Cyclometalated Platinum(II) Complexes
Olesia Zaitceva,a, c Valérie Bénéteau,a Dmitry S. Ryabukhin,c Ivan I. Eliseev,b Mikhal A. Kinzhalov,b
Benoit Louis,a, d Aleksander V. Vasilyevb, c * and Patrick Pale a *
a Institut de Chimie, UMR 7177, CNRS University of Strasbourg, 4 rue B. Pascal, 67000 Strasbourg, France
b Saint Petersburg State University, 7/9 Universitetskaya Nab., 199034 Saint Petersburg, Russian Federation
c Saint Petersburg State Forest Technical University, 5 Institutskii per., 194021 Saint Petersburg, Russian Federation
d Present address: Institut de Chimie et Procédés pour l'Energie, l'Environnement et la Santé, ECPM, Université de Strasbourg, 25 rue Becquerel, 67087
Strasbourg cedex 2, France
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Cyclometalated (ppy)PtII complexes (ppy
=
2-phenylpyridinato-C2,N) catalyze the
intramolecular cyclization of aryl propynoates to form coumarins and benzocoumarins. The
complex [(ppy)PtCl(MeCN)] (5 mol %) was the most active and efficient catalyst for such
reaction, especially in the presence of AgSbF6 (15 mol %) in 1,2-dichloroethane. With this
catalytic system, a wide range of substituents and functional groups proved compatible with the
cyclization process, leading to a large variety of substituted coumarins and benzocoumarins (22
Available online
Dedicated to Professor Léon Ghosez to examples, 77−99%)
acknowledge his many seminal research
achievements, his unique contribution to
Tetrahedron and his friendship.
2009 Elsevier Ltd. All rights reserved
.
Keywords:
coumarin
cyclization
platinacycle
platinum
catalysis
processes initiated by electron transfer from AgI, CuII, FeIII salts
or IrIII complex.9 Such cyclization required specific conditions,
while leading to side-products. In contrast, cyclization promoted
1. Introduction
Coumarins are natural products, isolated from a large range of
organisms (Figure 1).1 They exhibit a broad range of activity that
has made the coumarin core a privileged scaffold found
nowadays in numerous pharmaceutical, agrochemical and
cosmetic compounds.2 Due to their optical properties, coumarins
are also widely employed in biology as fluorophores, fluorescent
labels and probes for imaging,3 as well as in material sciences as
laser and as organic light-emitting diodes.4 They further gained
application as dyes and optical brighteners.5
As these various properties can be tuned by substituting the
coumarin core, numerous syntheses have been proposed since the
original Pechmann condensation,6 and among them,7 metal-
catalyzed routes emerged as mild alternatives to the traditional
methods requiring strongly acidic or basic conditions.8 In
particular, the metal-promoted cyclization of aryl propynoates
offers a simple, convergent and modular access to coumarin
derivatives. Within these methods, some of them relied on radical
Figure 1. Representative examples of bioactive natural and non-natural
coumarins

2
Tetrahedron
by π-electrophilic cations (PdII, PtIV and AuIII salts or AuI
the cyclization of aryl propynoates. Such ligand usually exhibits
strong trans-influence, while increasing metal electrophilicity,16
and both effects are required to allow coordination and activation
of the propynoate substrate. Furthermore, platinacycles exhibit a
remarkable stability of the Pt-C bond,17 and they thus should
give stable catalysts. In this context, one of the simplest
cyclometalating ligand, i.e. 2-phenylpyridine (ppy), was initially
selected. The corresponding platinacycles, (2- phenylpyridinato-
C2,N)Pt(II) complexes, have been reported,18-19 but they were
never used in catalysis. It was thus worth investigating them as
catalysts. Such complexes could be obtained from 2-
phenylpyridine and potassium tetrachloroplatinate, but their
synthesis seems not so obvious.18 Here, the chloro-bridged dimer
[{(ppy)PtCl}2] 1a was readily produced in warm aqueous
ethoxyethanol (Scheme 2). The mild heating of this dimer in
acetonitrile afforded the analytically pure monomeric complex
[(ppy)PtCl(MeCN)] 1b, that was isolated in 91% yield. This
complex 1b was fully characterized by ESI-HRMS, FTIR, 1H and
13C NMR, and by single-crystal X-ray diffraction. Similarly, the
monomeric complex 1c19 was obtained by dissociation of the
dimeric 1a in DMSO.
complexes) provided reliable results.10 Among the most efficient,
Pd catalysts required trifluoroacetic acid as solvent, which could
be deleterious for sensitive compounds.10a-d Au catalysts are also
10e-j
quite efficient,
but they required Ag salts as cocatalyst,
especially AuCl3, which needs 3 equivalents of AgOTf. Au-
catalyzed reactions are also sensitive to moisture, since water
induces the formation of spiro compounds in competition with
the expected coumarins.10g Despite solubility problem due to its
polymeric structure, PtCl4 is also known as catalyst for such
cyclization, although modest to good yields have been observed
depending on the substituents (Scheme 1).10k-m Although PtCl2
has also been screened for this cyclization, it always gave lower
yields (13-28 vs 73-78%).10h, 10k-l However, PtCl2 usually exhibits
similar and even better reactivity compared to that of PtCl4,
despite its lower electrophilicity.11 It should thus compete with
Au(I) and PtCl4 catalysts in the cyclization of aryl propynoates.
We thus investigated Pt(II) derivatives, reasoning that Pt(II)
reactivity and solubility could be tuned by using specific ligand.
We showed here that cyclometalated platinum(II) complexes
[(ppy)PtLCl, ppy = (2-phenylpyridinato-C2,N)] offer an enhanced
reactivity, providing various coumarins in good to high yields.
Radical-mediated routes
Electrophilic metal-mediated routes
O
O
O
Pd(OAc)2
R1
TFA, DCM
+ isom.
R2
O
O
BrCF2COOEt
R1
50-91 %
ref. 10a-d
O
Ir(bpy)3
K2CO3, DMF
F2C
R2
O
O
EtOOC
ref. 9a
(tBu2BiPhP)Au(NCMe)
hν
67-85 %
O
DCM
72 %
OMe
OMe
O
O
R3
COOH
R1
ref. 10e-f
R3
AgNO3, K2S2O5
MeCN, H2O
O
O
O
O
O
O
R2
PPh3AuCl
NR2
R1
AgOTf or AgSbF6
DCE
ref. 9b
O
22-51 %
CF3
ref. 10g-h
I
80-95 %
R2
O
O
O
AuCl3, EtOH
O
R1
NR2
or
Cu(OAc)2
K2CO3, MeCN
AuCl3/3 AgOTf
DCE
F3C
ref. 10i-j
R2
Ph
ref. 9c
44-99 %
26-70 %
O
O
O
O
PtCl4
R1
R3SeSeR3
R1
DCE or diox
FeCl3
DCM or MeNO2
R3Se
Scheme 2. Synthesis of 2-(pyridin-2-yl)phenyl Pt(II) complexes, and a XRD
view of crystal of 1b (Thermal ellipsoids drawn with 50% probability;
hydrogen labels omitted for simplicity)
R2
ref. 10k-m
31-88 %
R2
41-94 %
ref. 9d-e
This work
NCMe
O
O
Pt
Cl
O
O
N
Complex 1b is a stable solid in air at room temperature, but in
CH2Cl2, CHCl3 or MeOH solutions, 1b is slowly transformed to
the starting chloro-bridged dimer 1a (the transformation was
complete after 48 hours as showed by 1H NMR monitoring). The
presence of [M−Сl]+ peaks in ESI-HRMS indicates the existence
of small amount of the corresponding dechlorinated complex in
equilibrium with the chloro-bridged dimer 1a and acetonitrile in
MeOH solutions. In contrast, the monomeric [(ppy)PtCl(DMSO)]
complex 1c is stable in solutions and does not evolve back to
dimer 1a. The large stability difference for these monomeric
complexes in solution is clearly indicative of a weak coordinating
bond between the nitrile ligand and the platinum center, which
could be of interest in catalysis.
R1
R1
20 exemples
50-99 %
DCE
R2
R2
Scheme 1. Known metal-promoted cyclizations of aryl propynoates and the
proposed new catalyzed version.
2. Results and discussion
2.1. Catalyst synthesis & study.
As a matter of fact, not many Pt(II) complexes have been
developed for catalytic purposes in organic synthesis.11-13
Nevertheless, numerous Pt(II) derivatives have been prepared as
analogs to the well-known ‘cisplatin’ drug since the discovery of
its anticancer property.14 More recently, the increasing
development of luminescent systems (sensors, switches,
bioprobes, imaging tools and OLED) has also promoted the
synthesis of Pt(II) derivatives.15 Among the latter, platinacycles
have often been employed due to the ease with which their
photophysical properties could be modulated. Their electronic
properties, as well as the control of the cis/trans complex
geometry, can indeed easily be tuned.
2.2. Catalysis set up
The simple phenyl 3-phenylpropynoate 2a was first selected
as model to study the catalytic ability of the above-mentioned Pt
complexes. Unfortunately, almost no reaction could be detected
with this substrate. Its dimethylated analog 2b proved more
reactive and although it gave a mixture of regioisomeric
coumarins (3b and 3b’ in a 5:1 ratio), compound 2b was used to
screen Pt catalysts (Table 1).
Expecting similar tuning of catalytic properties, we explored
the behavior of Pt(II) derivatives with cyclometalated ligands in

3
While the absence of metal catalyst led to the recovery of the
starting material 2b (entry 1), simple platinum di- or tetrachloride
salts provided the expected cyclized products, i.e. the coumarins
3b and 3b’, in non-coordinating solvent, but with low conversion
reactive, giving coumarins in almost quantitative yield within a
day (entry 7). However, its DMSO form 1c only induced very
slow reaction, leading to only 37% after 3 days (entry 8). Such a
large reactivity difference between these two monomeric
(ppy)Pt(II) complexes clearly reflects the leaving ability of the
ligand (see their respective stability, section 2.1).
and thus in low yields (entries 2 and 3), in agreement with some
10k-l
reports.10h,
More soluble complexes tended to slightly
improve conversions and yields, but to the detriment of reaction
time (entries 4 and 5). In sharp contrast, the (ppy)Pt(II) dimer 1a
provided coumarins in high yield after full conversion, but still
after long reaction time (entry 6). As expected, the monomeric
(ppy)Pt(II) complex in its acetonitrile form 1b proved much more
It is worth noticing here that the cyclometalated platinum
complexes 1a-b efficiently provided the cyclized coumarinic
product in high yields, while simple platinum chloride salts could
only promote this cyclization with low yields (87-95% vs 14-
20% respectively).
Table 1. Catalyst screening for the Pt-catalyzed cyclization of 3,4-dimethylphenyl 3-phenylpropynoate 2b.
Entry
Catalyst
Time (h)
24
Overall yield of 3b and 3b’ (%)a, b
1
2
3
4
5
6
7
8
none
0
PtCl2
24
20 (16c)
14 (7c)
20
PtCl4
24
cis-[PtCl2(MeCN)2]
cis-[PtCl2(DMSO)2]
[{(ppy)PtCl}2] 1a
[(ppy)PtCl(MeCN)] 1b
[(ppy)PtCl(DMSO)] 1c
76
75
19
56
87
24
95
75
37
a 1H NMR yields.
presence of silver tetrafluoroborate, the same slow transformation
b The 3b:3b’ ratios were always at 5:1 within experimental errors.
was observed (entry 3), but silver hexafluoroantimonate
drastically increased it (~10 times; entry 4 vs 3). Increasing the
amount of silver salt rewardingly increased further the
c Isolated yields.
conversion (entries 5
−7), with an optimum observed around
To go further, we optimized the required amount of complex
1b, while increasing the cationic nature of the metallic center by
the addition of silver salts (Table 2). Silver salts are well known
to abstract halide from metal halide complexes, thus liberating a
coordination site on the metal and rendering the metal ion more
electrophilic. This set up was performed on the cyclization of the
more challenging ortho-substituted ester 2c.
15 20%, which led to complete conversion and high yields
−
(entries 6 and 7). Control experiments revealed that silver salts
alone were not efficient enough to drive the cyclization to
completion within reasonable times (entry 8 vs 6−7).
These results clearly confirmed the requirement of at least one
free coordination site on platinum, and probably two (after
exchanging MeCN and removing Cl), to induce the expected
cyclization (see the Mechanism section below).
Without silver salt, the (ppy)Pt(II)-catalyzed cyclization of the
relatively hindered 2-methylphenyl phenylpropynoate 2c proved
to be slow and only low conversion could be achieved within one
hour, regardless the catalyst loading (entries 1 and 2). In the
.
Table 2. Optimization of the catalyst loading and additive for the cyclization of 2-methylphenyl 3-phenylpropynoate 2c.
Entry
Catalyst (mol%)
Additive (mol%)
-
Yield (%)a
1
2
3
4
5
6
7
8
[(ppy)PtCl(MeCN)] 1b (5)
8
1b (15)
1b (5)
1b (5)
1b (5)
1b (5)
1b (5)
-
-
11
4
AgBF4 (5%)
AgSbF6 (5%)
AgSbF6 (10%)
AgSbF6 (15%)
AgSbF6 (20%)
AgSbF6 (20%)
42
91
97
100
11
a Determined by1H NMR; the remaining part was the starting material.

4
Tetrahedron
2.3. Synthesis of coumarins: Scope and limitation
Methoxylated or phenoxylated esters 2g-j were as well
efficiently cyclized with yields ranging from 82 to 94% (entries
10), with even faster reactions again for the meta-substituted
isomers (entries 9-10 vs 7 8). In contrast, the electrodeficient
bromo ester 2k led to lower conversion and yield (entry 11 vs 1).
For the methoxylated as well as for the bromo derivatives, the
Au-catalyzed method provided similar or slightly higher
yields,10e, 10j while simple Pt salts led to lower yields.10k
With a catalyst and conditions in hands, the influence of steric
and electronic effects on the reaction course was examined with
appropriately substituted aryl propynoates. The latter were
prepared through classical esterification methods (See S. I.).
7
−
−
In a first set of experiments, aryl propynoates substituted at
the ester moiety were investigated (Table 3). Reactions were
monitored by TLC and stopped when full conversion of the
starting material was reached, or after maximum 24h for slower
cases. Esters carrying electron-rich substituents at the O-aryl
residue gave higher conversions and yields of coumarins than
It is worth mentioning that the position of the substituent in
the major products produced from meta-substituted aryl
propynoates has been ascertained by establishing the structure of
3j by XRD and NMR spectra comparison (See S. I.).
those of the unsubstituted 2a (entries 2−10 vs 1). Some variations
These results support the classically proposed mechanism
based on nucleophilic addition of the aryl ester moiety to the
metal-π-coordinated alkyne, for which the more electron rich the
ester moiety, the more nucleophilic they are, inducing a more
efficient cyclization (see the Mechanism section 2.5 below).
nevertheless occurred depending on the nature of the substituent
and on its position. A single methyl group induced a sharp
increase in yield (entries 3-5 vs 1). Interestingly, the position of
this group seems to play a role in the reaction time. The ortho
isomer 2c did not seem suffering much from steric hindrance, as
similar conversion and yield were observed with its para isomer
(entry 3 vs 4). As expected from mechanistic hypothesis (see
section 2.5), the meta isomer 2e gave a slightly faster reaction.
The latter provided two regioisomeric coumarins, with the less
hindered being the most abundant (~4:1 ratio; entry 5). It is worth
noticing that the Pd(OAc)2/TFA method10a-c provided lower
selectivity (2:1), as well as lower yields in this series (75, 50, 78
vs 85, 89, 87 % for respectively the formation of 3c, 3d, 3e-e’).
To confirm that hypothesis, the electronic density of the
ynoate moiety was modulated by specific substituents. The fluoro
derivative 2l gave almost the same yield that the unsubstituted 2a
(entry 12 vs 1), while its methylated analog 2m led to a slightly
improved yield (entry 13 vs 1 vs 12). These results again support
the proposed mechanism, but ynoate electronic effects seem to
less affect the cyclization ability as compared to those observed
with ester substituents (e.g. entry 13 vs 4). To check this aspect,
compounds 2n−o were prepared and submitted to cyclization.
The dimethylated analog 2b behave analogously in terms of
Acting on both sides also affected conversion and yield but the
results showed that the substituent on the ester moiety indeed
mostly drove the reaction efficacy (entry 15 vs 14).
efficacy and regioselectivity (entries 2 vs 4−5), but 2b provided
two isomers 3b and 3b' with a slightly better selectivity
compared to 2e (entry 2 vs 5). In contrast, the dimethylated 2f
proved more reactive than 2b furnishing 3f in only two hours
(entry 6 vs 2). Here again the the Pd(OAc)2/TFA method10a-c
provided lower yields for similar compounds (75 vs 88 %).
.

5
Table 3. [(ppy)PtCl(MeCN)]-catalyzed cyclization of aryl propynoates to coumarins.
O
O
O
O
1b (5 mol%)
R1
R1
AgSbF6 (15 mol%)
DCE, 85 °C
R2
R2
2
3
O
Entry
Ynoate 2
Coumarin 3
Time (h)
24
Yield (%)a
54
Literature Yield (%)
O
O
O
1
2
3
3a
Ph
2a
Ph
O
O
O
O
O
O
24
24
88 (5:1)
85
3b'
Ph 3b
Ph
2b
Ph
O
7510a
O
O
O
3c
Ph
Ph
O
2c
2d
2e
O
O
O
O
4
5
6
24
20
2
89
5010a
Ph
O
3d
Ph
Ph
75 (2:1) 10a
O
O
O
O
87 (4.3:1)
88
3e'
3e
Ph
Ph
75b, 10a
9810j
O
O
O
O
O
7
8
24
24
84
86
MeO
MeO
MeO
3g
Ph
O
2g
Ph
MeO
O
O
3h
Ph
2h
Ph
MeO
O
O
O
MeO
PhO
O
O
O
O
9
1
94 (3.2:1)
82 (4:1)
25
5010k
3i'
3i
Ph
O
MeO
PhO
Ph
2i
Ph
Ph
O
PhO
O
O
O
10
11
12
2
3j'
3j
Ph
Ph
2j
24
10
4410j
O
O
O
50
3l
O
O
O
O
F
2l
F
O
13
14
24
24
59
3m
2m
60 (3.8:1)
O
O
15
24
50
3o
O
O
OMe
OMe
2o
Cl
Cl
a Isolated yields.
2.4. Synthesis of benzocoumarins

6
Tetrahedron
Besides the biological activities associated to coumarins,
cyclization at the more nucleophilic α position in naphtyl
derivatives. The structures of the products produced from the β-
naphtyl propynoates have been ascertained by establishing the
structure of 3r and 3t by XRD and NMR spectra comparison
(See S. I.).
benzocoumarins also constitute a promising family of photonic
materials due to the extended nature of their π-electron system.20
As only a limited number of such benzocoumarins have so far
been reported,21 we extended our strategy to the synthesis of a
few benzocoumarins. A simple way to do so is to start from
naphthyl ester derivatives.
When substituents of different electron density were
introduced on the phenyl propiolic moiety (2r-t), only variations
Rewardingly, naphtyl esters 2p
the set-up conditions. Full conversion and high yields were
achieved within minutes (5 45 min; Table 4). The α isomer 2p
very rapidly gave the expected benzocoumarin 3p in quantitative
yield (entry 1). Interestingly, the β-naphtyl isomer required even
shorter time and quantitatively provided a single regioisomer 3q
(entry 2 vs 1). Although the latter corresponds to the more
hindered isomer among the two possible, it also corresponds to
-
t proved very reactive under
of the reaction time were observed (entries 3−5 vs 2). No
variations occurred regarding conversion and yields, except for
the methyl substituted derivative 2r (entry 3 vs 2). Surprisingly,
the fluoro analog 2t reacted as fast and as efficiently than the
reference compound 2q (entry 5 vs 2). These results, and
especially the latter, confirm the prominent role of the ester
moiety in such Pt(II)-catalyzed cyclization.
−
.
Table 4. [(ppy)PtCl(MeCN)]-catalyzed cyclization of naphtyl propynoates to benzocoumarins.
O
O
O
O
1b (5 mol%)
AgSbF6 (15 mol%)
DCE, 85 °C
R2
R2
3
2
Entry
1
Ynoate 2
Coumarin 3
Time (mn)
15
Yield (%)a
99
O
O
O
O
3p
Ph
O
2p
Ph
O
O
O
O
2
3
5
99
74
Ph
2q
Ph
3q
O
30
O
O
3r
2r
O
O
4
5
45
99
99
O
O
MeO
3s
2s
OMe
O
O
5
O
O
F
3t
2t
F
a Isolated yields.
(B in Sch. 3). Once activated, the alkynyl moiety could suffer
from intramolecular nucleophilic addition of the phenolic ester
moiety.
2.5. Mechanism
As described above (see Section 2.2 and Table 1), a large
reactivity difference was observed with (ppy)Pt(II) complexes
compared to other Pt species. Among the former, the two
monomeric (ppy)Pt(II) complexes 1b and 1c also exhibited a net
activity difference as catalyst. These results as well as their
respective stability (see section 2.1) clearly reflects the leaving
ability of the ligand and the requirement for a free coordination
site to induce the expected cyclization. The strong requirement
for a free coordination site on platinum was further supported by
the enhanced catalytic activity upon addition of silver salt (see
Table 2).
During our preliminary investigations, we observed in the
presence of complex 1b without additive a strong reactivity
enhancement when an electrodonating substituent was located at
the meta-position of the phenolic moiety of 2 (Sch. 4, top), and
the more electrodonating this substituent, the more efficient and
rapid was the cyclization (Sch. 4, bottom). Similar trend was also
observed in the presence of silver additive (See Table 3, entry 9
vs 7-8). These results showed that the more nucleophilic is the
ortho position in the phenolic moiety of 2, the more efficient is
the cyclization reaction. These results strongly suggest that the
cyclization process is based on the nucleophilic addition of the
phenolic moiety to the Pt-activated propynoate moiety.
Under the latter conditions, strongly electrophilic Pt(II)
species (A in Sch. 3) would be in situ produced and π-
coordination to the propynoate esters 2 would thus be facilitated

7
Scheme 4. Cyclization of aryl propynoates, carrying electrodonating group
(EDG) at the O-aryl residue, catalyzed by the monomeric catalyst 1b.
4. Experimental section
NMR spectra were recorded on Bruker Avance 300, 400, or
500 instruments. Spectra were recorded in CDCl3 solutions
referenced to TMS or the solvent residual peak. IR spectra were
recorded neat on Bruker Alpha ATR instrument. High-resolution
mass spectra (HRMS) data were recorded on a microTOF
spectrometer equipped with orthogonal electrospray interface
(ESI). Chromatography was carried out using silica gel 60 (40–
63 ꢀm). Reagents and solvents were purified using standard
methods. Anhydrous CH2Cl2, DCE, THF, and MeOH were dried
by passing through activated alumina under a positive pressure of
argon using GlassTechnology GTS100 devices. All other
chemicals were used as received. All spectroscopies and analyses
were performed at the Fédération de Chimie Le Bel, CNRS and
University of Strasbourg.
Scheme 3. Proposed mechanism for the cyclisation of aryl propynoates to
coumarins catalyzed by the (ppy)Pt(II) complex 1b.
Although more Lewis acidic than gold,22 platinum can easily
form π-complexes (e.g.
B
in Sch. 3) and even
platinacyclopropene-type complex (e.g. C), in agreement with
the well-known strong back-donation of Pt(II) complexes.12b,
23
The alkyne deformation induced by Pt(II) coordination24 in B (or
C) exposes the more nucleophilic ortho position of the phenolic
moiety next to the more electrophilic carbon of the propynoate
moiety and thus favors the 6-endo-dig cyclization. The latter
should thus produce a cationic organoplatinum intermediate (D),
which could then evolve through elimination of a proton to
restore aromaticity. The so-liberated proton then allowed
protodemetalation, which regenerates the catalyst and liberates
the so-formed coumarin.
4.1. Synthesis of platinum complexes
4.1.1. Chlorido[2-(pyridin-2-yl)phenyl] Pt(II
(1a)1 8
:
To a degassed water-ethoxyethanol (1:3) solution was added
0.58 g (3.7 mmol) of 2-phenylpyridine and 1.55 g (3.7 mmol) of
dipotassium tetrachloroplatinate(II). The reaction mixture was
heated at 75 °C for 24h. After cooling to room temperature, the
reaction mixture was poured into 40 ml of distilled water. The
resulting precipitate was filtered, washed with 10 ml of water and
5 ml of acetone, twice with 5 ml of dichloromethane and dried in
air at room temperature. As a result, 1a was obtained as a pale-
3. Conclusion
1
yellow powder. Yield: 44%. H NMR (300 MHz, DMSO-d6): δ=
In this work, an efficient and mild access to coumarins has
been developed, using monomeric or dimeric platinacycles as
catalyst. Various substituents and functional groups proved
compatible with the cyclization process, leading to a large variety
of substituted coumarins. Benzocoumarins were also accessible
in very high yields via the same platinacycle-catalyzed process.
7.15 (t, 1H, J =7.2 Hz, Harom.), 7.19 (t, 1H, J =7.2 Hz, Harom.), 7.51
(t, 1H, J =7.2 Hz, Harom.), 7.78 (d, 1H, J =6.0 Hz, Harom.), 8.13-
8.16 (m, 2H, Harom.), 8.22 (d, 1H, J =6.1 Hz, Harom.), 9.49 (d, 1H, J
=6.1 Hz, Harom.). Elemental analyses (C, H, N): calcd for
C22H16Cl2N2Pt2 34.34%, 2.10%, 3.64%; found: 34.21%, 2.06%,
3.58%.
Among the screened Pt(II) catalysts, the 2-(pyridin-2-
yl)phenylPt(II)(acetonitrile) chloride complex 1b was the most
active and efficient. With this readily accessible complex,
quantitative yields of benzocoumarins could be achieved and up
to 94 % yield of coumarins was isolated. This platinacycle
catalyst is thus highly competitive compared to other known
catalysts, including the simple platinum chlorides.
4.1.2. (acetonitrile)chlorido[2-(pyridin-2-
yl)phenyl]Pt(II) (1b)
The dimeric complex [{(ppy)PtCl}]2 1a (60 mg; 0.078 mmol)
was stirred in acetonitrile (0.5 ml) at 45 °C for 16h. The resulting
precipitate was filtered and dried in air at room temperature. 1b
was obtained as a yellow powder. Yield: 91%. IR (neat): 413,
480, 556, 628, 725, 743, 857, 1030, 1068, 1124, 1158, 1237,
The reactivity of the (ppy)Pt complexes reported here will be
further explored and developed as a useful tool in organic
synthesis.
1276, 1318, 1425, 1440, 1485, 1584, 1609, 2090, 3045 cm-1. H
1
NMR (300 MHz, CDCl3): δ= 2.57 (s + 195Pt satellites 4JPt-H = 6.2
Hz, 3H, CH3), 7.09-7.17 (m, 3H, Harom.), 7.30 (dd, J = 6.3, 2.2, +
3
195Pt satellites JPt-H = 21.4 Hz, 1H, Harom.), 7.43-7.46 (m, 1H,
Harom.), 7.60 (brd, J = 7.8 Hz, 1H, Harom.), 7.82 (td, 1Harom., J =
8.0, 1.5 Hz, Harom.), 9.55-9.72 (dd, J = 5.8, 1.5 Hz + 195Pt
3
satellites JPt-H = 22.7 Hz, 1H, Harom.). 13С NMR (125MHz,
CDCl3): δ = 4.6, 116.5, 118.4, 122.0, 123.8, 124.3, 130.5, 132.0,

8
Tetrahedron
139.5, 139.6, 144.0, 151.0, 167.8. HRMS (ESI-µTOF): m/z [M–
Cl+MeCN]+ calcd for C15H14N3Pt: 431.0831; found: 431.0841.
Single crystal XRD structure (see S. I. and CCDC n° 1894192).
(300 MHz, CDCl3): δ= 3.85 (s, 3H, CH3), 6.91 (d, 2H, J =6.8 Hz,
arom.), 7.32 (dd, 1H, J = 8.8, 2.3 Hz, Harom.), 7.45-7.54 (m, 2H,
H
Harom.), 7.59 (d, 2H, J =8.9 Hz, Harom.), 7.66 (d, 1H, J =2.3 Hz,
Harom.), 7.81-7.90 (m, 3H, Harom.). 13С NMR (125MHz, CDCl3): δ
= 55.6, 80.0, 90.0, 111.1, 114.5, 118.8, 120.9, 126.1, 126.8,
127.91, 127.94, 129.7, 131.7, 133.8, 135.4, 147.9, 152.8, 162.0.
HRMS (ESI): m/z [M+H]+ calcd for C20H15O3: 303.1016; found:
303.0995.
4.2. General procedure for the synthesis of aryl propynoates (2a-
2t).
To a solution of propiolic acid derivative (6.8 mmol, 1eq) and
phenol derivative (6.8 mmol, 1eq) in 10 mL of CH2Cl2 was added
DCC (7.53 mmol, 1.1eq) and 10 drops of pyridine. The reaction
4.2.5. Naphthalen-2-yl 3-(4-
fluorophenyl)propynoate (2t)
°
mixture was stirred for 5-12 hours at 0 С or rt. Upon reaction
completion, the mixture was treated with water (50 ml), extracted
with chloroform (3 × 50 ml). The combined organic phases were
washed with 0.2 N NaOH (2 × 50 ml), water (2 × 50 ml) and
dried over Na2SO4. After filtration, the solvent was removed
under reduced pressure. The crude product was then purified by
column chromatography on silica gel (eluent pentane : diethyl
ether 95:5).
Yield: 59%. Pale yellow solid; m.p =103–105.9 °C; Rf = 0.5
(10% diethyl ether/pentane). IR (neat): 470, 536, 573, 731, 762,
776, 821, 839, 865, 896, 938, 962, 1153, 1174, 1204, 1227, 1291,
1
1502, 1597, 1708, 2215, 3066, 3408 cm-1. H NMR (500 MHz,
CDCl3): δ= 7.09 - 7.14 (m, 2H, Harom.), 7.32 (dd, 1H, J = 8.8, 2.3
Hz, Harom.), 7.48 - 7.53 (m, 2H, Harom.), 7.63 - 7.67 (m, 3H, Harom.),
7.82 - 7.90 (m, 3H, Harom.). 13С NMR (125MHz, CDCl3): δ =
80.3, 87.9, 115.50, 115.53, 116.3, 116.5, 118.7, 120.8, 126.2,
126.9, 127.92, 127.96, 129.8, 131.8, 133.7, 135.6, 135.7, 147.8,
152.5, 163.3, 165.3. HRMS (ESI): m/z [M+H]+ calcd for
C19H12FO2: 291.0816; found: 291.0810.
4.2.1. 2,5-Dimethylphenyl 3-phenyl
propynoate (2f)
Yield: 74%. White solid; m.p =74.5–76 °C; Rf = 0.57 (10%
diethyl ether/pentane). IR (neat): 451, 534, 557, 602, 689, 737,
758, 816, 904, 998, 1149, 1182, 1238, 1280, 1440, 1487, 1572,
4.3. General procedure for the Pt-catalyzed cyclization (3a – 3t).
1
1623, 1718, 2215, 2920 cm-1. H NMR (300 MHz, CDCl3): δ=
2.21 (s, 3H, CH3), 2.34 (s, 3H, CH3), 6.92 (s, 1H, Harom.), 6.99 (d,
1H, J = 7.7 Hz, Harom.), 7.14 (d, 1H, J = 7.7 Hz, Harom.), 7.41 (t,
2H, J = 7.2 Hz, Harom.), 7.49 (t, 1H, J = 7.4 Hz, Harom.), 7.63 (d,
2H, J = 6.8 Hz, Harom.). 13С NMR (125MHz, CDCl3): δ = 15.9,
21.0, 80.3, 88.5, 119.4, 122.3, 127.0, 127.5, 128.8, 131.1, 133.3,
137.2, 148.6, 152.4. HRMS (ESI): m/z [M+H]+ calcd for
C17H15O2: 251.1067; found: 251.1068.
In a sealed tube (with a screw cap) filled with 2 ml of 1,2-
DCE was added (ppy)PtCl(MeCN) (0.05 eq) and AgSbF6 (0.15
eq), and after 5 min of mixing, was added O-aryl esters of 3-
arylpropynoic acid (30 mg, 1eq). The reaction was performed at
85 °C with stirring, during 5 min - 24 h. At the end of the
reaction, the mixture was filtered and the solvent was removed
under reduced pressure. The resulting reaction product was
purified by column chromatography on silica gel (eluents
cyclohexane : diethyl ether 80:20).
4.2.2. 3,4-Dimethylphenyl 3-(4-
methylphenyl)propynoate (2n)
4.3.1. 5,8-dimethyl-4-phenyl-2H-chromen-2-
one (3f)
Yield: 53%. White solid; m.p =100.3–101.8°C; Rf = 0.6 (10%
diethyl ether/pentane). IR (neat): 428, 536, 578, 710, 734, 819,
1
916, 1155, 1185, 1236, 1288, 1495, 1717, 2220, 2915 cm-1. H
Yield: 88%. White solid; m.p =97.4–99.4 °C; Rf = 0.25 (20%
diethyl ether /pentane). 1H NMR (300 MHz, CDCl3): δ = 2.39 (s,
3H, CH3), 2.42 (s, 3H, CH3), 6.30 (s, 1H, =CH-), 7.03 (d, 1H, J =
8.2 Hz, Harom), 7.20 (d, 1H, J = 8.2 Hz, Harom.), 7.41 – 7.45 (m,
2H, Harom), 7.48 – 7.52 (m, 3H, Harom). 13С NMR (125MHz,
CDCl3): δ = 11.8, 20.6, 113.8, 116.9, 124.0, 125.1, 125.7, 128.6,
128.9, 129.6, 135.9, 141.8, 152.5, 156.3, 161.4. IR (neat): 424,
497, 570, 619, 638, 699, 712, 757, 778, 817, 890, 953, 1090,
1176, 1258, 1370, 1448, 1597, 1707, 2853, 2921, 2973, 3059 cm-
1. HRMS (ESI- µTOF): m/z [M+K]+ calcd for C17H14KO2:
289.0625; found: 289.0588.
NMR (500 MHz, CDCl3): δ = 2.25 (s, 3H, CH3), 2.27 (s, 3H,
CH3), 2.40 (s, 3H, CH3), 6.91 (dd, 1H, J = 8.2, 2.5 Hz, Harom.),
6.96 (d, 1H, J = 2.3 Hz, Harom.), 7.15 (d, 1H, J = 8.2 Hz, Harom.),
7.21 (d, 2H, J = 8.0 Hz, Harom.), 7.52 (d, 2H, J = 8.1 Hz, Harom.).
13С NMR (125MHz, CDCl3): δ = 19.3, 20.0, 21.8, 80.2, 89.1,
116.3, 118.6, 122.4, 129.5, 130.5, 133.3, 134.8, 138.2, 141.8,
148.1, 152.9. HRMS (ESI): m/z [M+K]+ calcd for C18H16KO2:
303.0782; found: 303.0789.
4.2.3. Naphthalen-2-yl 3-(4-
methylphenyl)propynoate (2r)
4.3.2. 7-Phenoxy-4-phenyl-2H-chromen-2-one
(3j)
Yield: 53%. Pale yellow solid; m.p = 104.5–106.9 °С; Rf = 0.5
(10% diethyl ether/pentane). IR (neat): 404, 481, 533, 570, 733,
761, 814, 896, 960, 1141, 1184, 1206, 1238, 1288, 1355, 1506,
Yield: 82%. Rf = 0.3 (20% diethyl ether / cyclohexane). IR
(neat): 404, 429, 466, 496, 570, 614, 644, 689, 731, 771, 797,
818, 836, 850, 868, 936, 999, 1049, 1072, 1113, 1147, 1182,
1241, 1271, 1339, 1374, 1449, 1484, 1550, 1586, 1712, 2853,
2923, 3051, 3088 cm-1. 1H NMR (300 MHz, CDCl3): δ = 6.23 (s,
0.25H, =CH-), 6.26 (s, 1H, =CH-), 6.42 – 6.45 (m, 0.5H, Harom.),
6.77 (dd, 0.26H, J = 8.2, 1.1 Hz Harom.), 6.87 (dd, 1H, J = 8.8, 2.5
Hz, Harom.), 6.92 (d, 1H, J = 2.4 Hz, Harom.), 6.96 – 6.99 (m,
0.26H, Harom.), 7.07 – 7.15 (m, 2.54H, Harom.), 7.20 – 7.25 (m,
2.26H, Harom.), 7.38 – 7.48 m (5.22H, Harom.), 7.50 – 7.54 (m, 3H,
Harom.). HRMS (ESI-µTOF): m/z [M+H]+ calcd for C21H15O3:
315.1016; found: 315.1001. Single crystal XRD structure (see S.
I. and CCDC n° 1970640).
1
1600, 1715, 2209, 2913 cm-1. H NMR (300 MHz, CDCl3): δ=
2.40 (s, 3H, CH3), 7.21 (d, 2H, J =7.9 Hz, Harom.), 7.32 (dd,
1Harom., J = 8.9, 2.4 Hz, Harom.), 7.48-7.55 (m, 4H, Harom.), 7.66 (d,
1H, J =2.5 Hz, Harom.), 7.82-7.90 (m, 3H, Harom.). 13С NMR
(125MHz, CDCl3): δ = 21.9, 80.1, 89.6, 116.2, 118.7, 120.9,
126.1, 126.8, 127.9, 129.6, 129.7, 131.8, 133.3, 133.8, 142.0,
147.9, 152.7. HRMS (ESI): m/z [M+H]+ calcd for C20H15O2:
287.1067; found: 287.1074.
4.2.4. Naphthalen-2-yl 3-(4-
methoxyphenyl)propynoate (2s)
Yield: 48%. Pale beige solid; m.p=91–93°C; Rf = 0.2 (10%
diethyl ether/pentane). IR (neat): 468, 536, 577, 729, 759, 800,
827, 853, 889, 965, 1024, 1138, 1185, 1211, 1257, 1289, 1509,
4.3.3. 6,7-Dimethyl-4-(p-tolyl)-2H-chromen-
2-one (3n)
1
1603, 1710, 2204, 2847, 2928, 3008, 3063, 3283 cm-1. H NMR

9
Sabnis, R. W. Handbook of Fluorescent Dyes and Probes,
Wiley: Hoboken 2015.
Trenor, S. R.; Shultz, A. R.; Love, B. J.; Long, T. E. Chem. Rev.,
2004, 104, 3059.
Zabradnik. M. Production and Application of Fluorescent
Brightening Agents, Wiley: New York, 1992.
Yield: 60%. White solid; Rf = 0.2(20% diethyl ether /pentane).
1H NMR (400 MHz, CDCl3): δ = 2.23 (s, 3H, CH3), 2.35 (s, 3H,
CH3), 2.46 (s, 3H, CH3), 6.27 (s, 1H, =CH-), 7.19 (s, 1H, Harom.),
7.23 (s, 1H, Harom.), 7.31-7.37 (m, 4H, Harom.). 13С NMR
(125MHz, CDCl3): δ = 19.5, 20.3, 21.5, 114.0, 116.8, 118.0,
127.1, 128.5, 129.6, 132.8, 133.0, 139.8, 142.1, 152.7, 155.9,
161.6. HRMS (ESI-µTOF): m/z [M+H]+ calcd for C18H17O2:
265.1223; found: 265.1219.
4.
5.
6. von Pechmann, H. Ber. Deutsch. Chem. Ges. 1884, 17, 929.
7. For recent reviews, see: a) Vekariya, R. J;. Patel, H. D. Synth.
Comm. 2014, 44, 2756; b) Zambare, A. S.; Kalam Khan, F. A.;
Zambare, S. P.; Shinde, S. D.; Sangshetti, J. N. Curr. Org.
Chem. 2016, 20, 798; c) Medina, F. G., Marrero, J. C.; Macias-
Alonso, M.; Gonzales, M. C.; Cordova-Guerrero, I.; Teissier
Garcia, A. G. Osegueda-Robles, S. Nat. Prod. Rep. 2015, 32,
1472; d) Ryabukhin, D. S.; Vasilyev, A. V. Russ. Chem. Rev.
2016, 85, 637.
4.3.4. 4-(4-Methylphenyl)-2H-
benzo[f]chromen-2-one (3r).
Yield: 74%. White solid; m.p=124.8–126.6°C. Rf=0.19 (20%
diethyl ether /pentane). IR (neat): 408, 459, 566, 603, 747, 811,
933, 996, 1055, 1454, 1509, 1546, 1622, 1721, 2852, 2921 cm-1.
1H NMR (300 MHz, CDCl3): δ = 2.50 (s, 3H, CH3), 6.37 (s, 3H,
=CH-), 7.17 – 7.22 (m, 1H, Harom), 7.25 (d, 2H, J = 8.2 Hz, H),
7.31 – 7.37 (m, 3H, H), 7.40 – 7.45 (m, 1H, H), 7.51 (d, 1H, J =
8.9 Hz, H), 7.85 (dd, 1H, J = 8.1, 1.3 Hz H), 7.99 (d, 1H, J = 8.9
Hz, H). 13С NMR (125MHz, CDCl3): δ = 21.6, 113.3, 116.8,
117.6, 125.4, 126.2, 126.8, 127.5, 129.1, 129.6, 129.9, 131.4,
134.0, 136.8, 139.4, 154.9, 156.8, 160.6. HRMS (ESI-µTOF):
m/z [M+H]+ calcd for C20H15O2: 287.1067; found: 287.1093.
Single crystal XRD structure (see S. I. and CCDC).
8. For reviews on metal-catalyzed synthesis of coumarins, see: a)
Priyanka; Sharma, R. K.; Katiyar, D. Synthesis 2016, 48, 2303;
b) Bhatia, R.; Pathania, S.; Singh, V.; Rawal, R. K. Chem.
Heterocycl. Compds 2018, 54, 280.
9. IrIII: a) Fu, W.; Zhu, M.; Zou, G.; Xu, C.; Wang, Z.; Ji, B. J.
Org. Chem. 2015, 80, 4766; AgI: b) Yan, K.; Yang, D.; Wei,
W.; Wang, F.; Shuai, Y.; Li Q., Wang, H. J. Org. Chem. 2015,
80, 1550; CuII: c) Li, Y.; Lu, Y.; Qiu G.; Ding, Q. Org. Lett.
2014, 16, 4240; FeIII: d) Mantovani, A. C.; Goulart, T. A. C.;
Back, D. F.; Menezes, P. H.; Zeni, G. J. Org. Chem. 2014, 79,
10526 ; e) Li, R. Wang, S. R.; Lu, W. Org. Lett. 2007, 9, 2219;
10. PdII: a) Jia, C.; Piao, D.; Oymada, J.; Kitamura, T.; Fujiwara, Y.
J. Org. Chem. 2000, 65, 7516; b) Kitamura, T.; Otsubo, K. J.
Org. Chem. 2012, 77, 2978; c) Kitamura, T.; Otsubo, K.
Heterocycles 2012, 86, 759; d) Li, K.; Zeng, Y.; Neuenswander,
B. Tunge, J. A. J. Org. Chem. 2005, 70, 6515; AuI, AuIII e)
Menon, R. J. ; Findlay, A. D;. Bissember, A. C. Banwell, M. G.
J. Org. Chem., 2009, 74, 8901; f) Cervi, A.; Aillard, P.; Hazer,
N.; Petit, L.; Chai, C. L. L.; Willis, A. C. Banwell, M. G. J. Org.
Chem. 2013, 78 9876; g) Aparece, M. D.; Vadola, P. A. Org.
Lett. 2014, 16, 6008; h) Vadola, P. A.; Sames, D. J. Org. Chem.
2012, 77, 7804; i) Do, J. H.; Kim, H. N.; Yoon, J.; Kim, J. S.;
Kim, H.-J. Org. Lett. 2010, 12, 932; j) Shi, Z.; He, C. J. Org.
Chem. 2004, 69, 3669; PtIV k) Pastine, S. J.; Youn, S. W.;
Sames, D. Tetrahedron 2003, 59, 8859; l) Pastine, S. J.; Youn,
S. W.; Sames, D. Org. Lett. 2003, 5, 1055; m) Wang, T.; Wang,
C.; Zhang, J. He, H. J. Heterocyclic Chem. 2015, 52, 1406.
11. a) Fürstner, A.; Stelzer, F. Szillat, H. J. Am. Chem. Soc. 2001,
123, 11863; (b) Méndez, M.; Paz Munoz, M.; Nevado, C.;
Cardenas, D. J.; Echavarren, A. M. J. Am. Chem. Soc. 2001,
123, 10511
4.3.5. 1-(4-Fluorophenyl)-2H-
benzo[f] chromen-2-one (3t)
Yield: 99%. White solid; m.p=116.5–121.4°C; Rf=0.15 (20%
diethyl ether /pentane). IR (neat): 402, 503, 532, 565, 600, 685,
698, 723, 750, 817, 848, 893, 933, 996, 1074, 1092, 1154, 1182,
1214, 1267, 1319, 1394, 1430, 1454, 1503, 1546, 1599, 1622,
1
1717, 2849, 2920, 3069 cm-1. H NMR (300 MHz, CDCl3): δ =
6.37 (s, 1H, =CH-), 7.17 – 7.28 (m, 4H, Harom.), 7.33 – 7.39 (m,
2H, Harom.), 7.40 – 7.46 (m, 1H, Harom.), 7.54 (d, 1H, J = 9.0 Hz,
Harom.), 7.87 (dd, 1H, J = 8.1, 1.2 Hz Harom.), 8.02 (d, 1H, J = 8.9
Hz, Harom.). 13С NMR (125MHz, CDCl3): δ = 113.0, 116.4, 116.6,
117.2, 117.7, 125.6, 125.9, 127.0, 129.3, 129.4, 129.5, 129.6,
131.5, 134.3, 135.6, 135.7, 155.0, 155.6, 160.4, 162.4, 164.4.
HRMS (ESI-µTOF): m/z [M+H]+ calcd for C19H12FO2: 291.0816;
found: 291.0817. Single crystal XRD structure (see S. I. and
CCDC).
12. For reviews, see : a) Clarke, M. L. Polyhedron 2001, 20, 151; b)
Chianese, A. R.; Lee, S. J.; Gagné, M. Angew. Chem. Int. Ed.
2007, 46, 4042.
Acknowledgments
13. Pt(II) derivatives have been mostly used for :
- enyne cycloisomerization; see e.g. : 11a-b, c) Aubert, C.;
Buisine, O.; Malacria, M. Chem. Rev. 2002, 102, 813: d)
Nelsen, D. L.; Organometallics 2009, 28, 950; e) Brissy, D.;
Skander, M.; Jullien, H.; Retailleau, P.; Marinetti, A. Org.
Lett. 2009, 11, 2137; f) Zhang, Y.; Jullien, H.; Brissy, D.;
Retailleau, P.; Voituriez, A.; Marinetti, A. ChemCatChem
2013, 5, 2051
The authors thank the CNRS, the French Ministry of Research
and the Russian Science Foundation (grant no. 17-73-10087).
References and notes
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Advances in Structure Activity Relatioships of Coumarin
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250.
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3.

10
Tetrahedron
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Supplementary Material
Experimental details for the synthesis of Pt(II) complexes, for
all starting aryl propynoates and coumarin products, as well as
copy of 1H, 13C and 19F NMR spectra and XRD data and
structures for some compounds, are provided.
i.
a
m
a
m
o

Highlights
- The synthesis of dimeric and monomeric cyclometalated Platinum(II) complexes is
reported.
- The cyclization of aryl propynoates to coumarins and benzocoumarins is reported
- 2- phenylpyridinato-C2,N)Pt(II) complexe is a very efficient catalyst for these
cyclizations

Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests: