Phenol Derivatives in Ruthenium-Catalyzed C–H Arylation: A General Synthetic Access to Azole-Based Congested Polyaromatics

Article abstract of DOI:10.1002/ejoc.201800312

Aryl triflates and related phenolates are suitable electrophile coupling partners for the ruthenium-catalyzed direct arylation of heteroaromatic substrates using azole N-directed C_sp2–H activation. We report herein convenient conditions for the efficient ortho-C–H functionalization of aryl-pyrazoles, thiazoles and pyridines in which [RuCl₂(p-Cym)]₂ precatalyst is employed with pivalic acid (PivOH) as co-catalyst. Different phenolate derivatives were successfully coupled, which tolerate a large scope of electron-rich substituents in para-, meta- and highly hindered ortho-position. Electron-withdrawing aryl triflates were found to be less reactive, making the general reactivity of these electrophiles complementary to those of aryl chlorides and deactivated bromides. This cost-effective ruthenium C–H activation/arylation synthesis of poly(hetero)aromatics was concurrently examined using triflates, mesylates, sulfonates, and carbonates, and was also successfully extended to the use of diethyl carbonate as an eco-friendly solvent.

Full text of DOI:10.1002/ejoc.201800312

https://doi.org/10.1002/ejoc.201800312
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C–H Arylation | Very Important Paper |
Phenol Derivatives in Ruthenium-Catalyzed C–H Arylation:
A General Synthetic Access to Azole-Based Congested
Polyaromatics
Julien Roger*[a] and Jean-Cyrille Hierso*[a,b]
Abstract: Aryl triflates and related phenolates are suitable elec- highly hindered ortho-position. Electron-withdrawing aryl tri-
trophile coupling partners for the ruthenium-catalyzed direct flates were found to be less reactive, making the general reac-
arylation of heteroaromatic substrates using azole N-directed tivity of these electrophiles complementary to those of aryl
Csp2–H activation. We report herein convenient conditions chlorides and deactivated bromides. This cost-effective ruth-
for the efficient ortho-C–H functionalization of aryl-pyrazoles, enium C–H activation/arylation synthesis of poly(hetero)aro-
thiazoles and pyridines in which [RuCl2(p-Cym)]2 precatalyst is matics was concurrently examined using triflates, mesylates,
employed with pivalic acid (PivOH) as co-catalyst. Different sulfonates, and carbonates, and was also successfully extended
phenolate derivatives were successfully coupled, which tolerate to the use of diethyl carbonate as an eco-friendly solvent.
a large scope of electron-rich substituents in para-, meta- and
Introduction
which are prepared from phenolic materials, thus providing
coupling reagents that are crystalline and fairly stable towards
Selective C–H activation/arylation reactions have resulted in the hydrolysis.[3] The use of aryl trifluoromethyl sulfonates in ruth-
development of valuable strategies to form aromatic molecules enium-based catalysis is limited to very few examples to date.
in straightforward and atom-economic protocols.[1] Further de- The relatively low cost of ruthenium as transition metal is yet
velopment of general synthetic conditions that are compatible very attractive for cost-efficient industrial applications.[4] Phenyl
with cost-efficiency and sustainable chemistry is highly de- triflate as electrophilic reagent was reported by Oi et al. in the
sirable. For instance, the use of more eco-friendly solvents at presence of [RuCl2(C6H6)]2 and PPh3 in NMP and led to a 61:7
lower temperatures is pertinent.[2] This approach may be advan- mixture of mono/diarylated phenyl pyridine.[4a] 5-Aryltetrazole
tageously combined with the exploitation of coupling partners was monoarylated with [RuCl2(p-Cym)]2 and MesCO2H or the
obtained from renewable resources. In this context, investiga- amino acid N-pivaloyl-L-valine (Piv-Val-OH) as co-catalyst in tolu-
tion on the use of electrophile alternatives to haloarenes, ob- ene in the presence of aryl bromides. Three examples of aryl
tained for instance from alcohols, is highly appropriate. Many triflates were reported under such conditions.[4b,4c] Weix and
alcohols are directly available from bio-resources, and the prep- co-workers reported the coupling of 2-methylbenzoic acid with
aration of reactive alcohol derivatives is generally easy to phenyl triflate using [RuCl2(p-Cym)]2 and 4,4′-di-tertbutyl-2,2′-
achieve. Accordingly, because of their wide availability, rather dipyridyl (dtbbpy) as ligand in NMP with a moderate 58 %
low cost and practical protection abilities, phenols are fre- yield.[4d] Similar yields for the same substrates were obtained in
quently used in total synthesis. The phenolic group can be used the presence of the cationic [Ru(tBuCN)6](BF4)2, with KOC(CF3)3,
to direct and introduce the desired functionality into aromatic in tBuCN at 140 °C.[4e] Clearly, general protocols for efficient N-
rings, and then can achieve carbon–carbon bond formation via ligand directed ortho-arylation of aromatics using sulfonates is
the corresponding sulfonate. In this regard, palladium-catalyzed still lacking. Based on our recent works in using azole ligands[5]
C–H functionalization has successfully exploited sulfonates, for palladium-catalyzed aromatic halogenation reactions,[6] we
devised conditions for the exploitation of aryl trifluoromethyl-
sulfonates as valuable electrophile coupling partners for aro-
[a] Institut de Chimie Moléculaire de l'Université de Bourgogne, UMR-CNRS
matic azoles by using ruthenium-catalyzed N-ligands directing
6302, Université de Bourgogne Franche-Comté (UBFC),
C–H activation/arylation. The catalytic system combining
9 avenue Alain Savary, 21078 Dijon, France
[RuCl2(p-Cym)]2 and pivalic acid promotes C–H functionalization
of a wide range of highly functionalized phenolate derivatives
using pyrazoles, benzothiazoles and pyridines as directing
groups. We introduced additionally an eco-friendly protocol
employing diethyl carbonate as solvent in ruthenium catalytic
arylation with triflates.
E-mail: julien.roger@u-bourgogne.fr
[b] Institut Universitaire de France (IUF)
103 Boulevard Saint Michel, 75005 Paris Cedex, France
E-mail: jean-cyrille.hierso@u-bourgogne.fr
http://www.icmub.fr/
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejoc.201800312.
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Results and Discussion
67 % of 1b (Table 1, entry 3). Using 1,4-dioxane did not improve
the conversion or the selectivity (entry 4). [Ru(OPiv)2(p-Cym)]
previously used for ortho-arylation of functionalized arenes with
aryl chlorides[9] essentially provided a much lower selectivity,
Aryl Triflates as Coupling Partners for Phenyl-1H-pyrazole
Poly(hetero)aromatic and biphenyl motifs are valuable synthetic
scaffolds in contemporary chemistry with regards to their wide
application as pharmaceuticals, agrochemicals, and in material
sciences.[7] Biphenyls bind to a wide range of proteins with high
levels of specificity with antihypertensive, antithrombotic anti-
rheumatic, anti-inflammatory and analgesic properties.[8] In the
convergent construction of these scaffolds the research focus
has shifted to direct C–H metal-catalyzed functionalization of
arenes. The development of methods using cost-effective ruth-
enium-catalyzed C–H arylation has provided attractive routes to
classical organometallic cross-coupling approaches.[1c,1d] Ac-
cordingly, our screening experiments started with the coupling
of phenyl-1H-pyrazole and phenyl triflate, both commercially
available (Table 1). We achieved coupling by using [RuCl2-
(p-Cym)]2 in toluene in the presence of KOAc. In the absence of
ruthenium, phenyl-1H-pyrazole was found to be unreactive in
refluxing toluene (entry 1). Conversely, in the presence of
2.5 mol-% [RuCl2(p-Cym)]2 (i.e. 5 mol-% [Ru]), a good conversion
of pyrazole starting material (87 %) yielded an unsatisfactory
mixture of 24 % of the biphenyl 1a and 63 % of diarylated 1b
(entry 2).
Table 2. Diarylation of phenyl-1H-pyrazole from functional aryl triflates.[a]
Table 1. Ruthenium-catalysed coupling of phenyl-1H-pyrazole with phenyl
triflate (Scheme 1).[a]
Entry
1[b]
Additive
[mol-%]
Solvent T [°C] Base
[equiv.]
Conv. 1a
1b
[%]
[%] [%]
tolu-
ene
tolu-
ene
PhCF3 110
diox-
–
110
110
KOAc (4)
0
0
0
2
3
4
–
–
–
KOAc (4) 87
KOAc (4) 96
KOAc (4) 90
24
29
26
63
67
64
110
ane
5[c]
6
7
–
–
PhCF3 110
PhCF3 110
KOAc (4) 90
K2CO3 (4) 75
K2CO3 (4) 94
42
33
20
48
42
74
Ac-Val-OH PhCF3 110
(30)
PivOH
(30)
PivOH
(30)
PivOH
(30)
8
PhCF3 110
PhCF3 110
PhCF3 80
K2CO3 (4) 99
K2CO3 (4) 64
K2CO3 (4) 77
0
99 (94)[d]
9[e]
10
37
29
27
48
[a] Conditions: phenyl-1H-pyrazole (1.0 equiv.), phenyl triflate (3.0 equiv.),
base (4.0 equiv.), [RuCl2(p-Cym)]2 (2.5 mol-%), additive (30 mol-%), solvent
[0.125
are determined by 1H NMR based on phenyl-1H-pyrazole. PhCF3: trifluoro-
methylbenzene; Ac-Val-OH: N-acetyl- -valine; PivOH: pivalic acid. [b] No ruth-
enium catalyst. [c] Pre-catalyst [Ru(OPiv)2(p-Cym)] (2.5 mol-%). [d] Isolated
yield. [e] Pre-catalyst [RuCl2(p-Cym)]2: 1.25 mol-%.
M based on phenyl-1H-pyrazole], 22 h, argon. Conversion and yields
L
[a] Conditions: phenyl-1H-pyrazole (1.0 equiv.), aryl triflate (3.0 equiv.),
[RuCl2(p-Cym)]2 (2.5 mol-%), PivOH (30 mol-%), K2CO3 (4.0 equiv.), PhCF3
(0.125
the phenyl-1H-pyrazole. [c] Isolated yield. [d] Pre-catalyst [RuCl2(p-Cym)]2
(5 mol-%), PivOH additive (60 mol-%).
M
), 110 °C, under argon, 22 h. [b] Determined by 1H NMR based on
Trifluoromethylbenzene, used as solvent, was found more ef-
fective, with 96 % conversion of pyrazole giving however only
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with a 42:48 mixture of 1a and 1b (entry 5). Changing the base
for K2CO3 did not improve this selectivity (42 % of 1a, entry 6).
Table 3. Ruthenium-catalyzed N-directing heteroaryl derivatives coupling to
2-naphthyl triflate.[a]
In the presence of N-acetyl-L-valine (Ac-Val-OH) amino acid, a
notable improvement was achieved, with 74 % yield obtained
for 1b (entry 7). Finally, high conversion and selectivity in diaryl-
ated 1b was achieved by using 30 mol-% PivOH as additive
(entry 8). A lower catalyst loading of 1.25 mol-% [RuCl2(p-Cym)]2
(2.5 mol-% [Ru]), or a lower temperature (80 °C) clearly limited
the efficiency of the catalyst in the ortho-directed diarylation
(entries 9 and 10, respectively). Interestingly, monoarylation was
preferentially achieved by tuning of the heteroaryl/triflate ratio
(2:1), thus yielding 70 % 1a (see the Supporting Information).
With the optimized conditions in hand, we investigated the
scope of functional aryl triflates tolerated in this coupling with
phenyl-1H-pyrazole (Table 2).
Electron-donating alkyl substituents placed in para-position
of the aryl triflate, such as methyl and isopropyl groups, gave
polyaromatic 2b (89 %) and 3b (72 %) in very good isolated
yields (Table 2, entries 1–2). 4-Acetylphenyl triflate was also eas-
ily coupled and 4b was obtained with a high isolated yield
of 96 % (entry 3). Electron-poor aryl triflates were found to be
significantly less reactive and 5 mol-% [RuCl2(p-Cym)]2 with
60 mol-% pivalic acid were necessary to isolate the monoaryl-
ated 5a from 2-pyridyl triflate in 25 % yield (entry 4). In the
same conditions, nitrophenyl triflate did not react with phenyl-
1H-pyrazole and was recovered unchanged after 22 h. On the
other hand, congested meta-substituted aryl triflates were effi-
ciently coupled, and 2-naphthyl triflate reacted with phenyl-1H-
pyrazole to give 6b in 90 % isolated yield (entry 5). 3,6-Di-
methoxyphenyl triflate was found to be more demanding and
by doubling the catalyst loading of [Ru]/PivOH catalyst, diaryl-
ated 7b was isolated in excellent 95 % yield (entry 6). ortho-
Substituted aryl triflates were also used for the formation of
highly congested (hetero)polyaromatic 8b–10b (entries 7–9). By
using 5 mol-% [RuCl2(p-Cym)]2 and 60 mol-% pivalic acid, the
ortho-methylated 8b was isolated in excellent 90 % yield (entry
7). The formation of ortho-methoxylated 9b was more difficult
(formed in 48 % together with the monoarylated 9a in 52 %)
and isolated yields of 9b and 9a were moderate (38 % and
42 %, respectively, entry 8). High conversion into the penta-
phenyl 1-[2,6-di(naphthalene-1-yl)phenyl]-1H-pyrazole 10b was
achieved with a high 85 % isolated yield (entry 9).
[a] Conditions: heteroaryl (1.0 equiv.), 2-naphthyl triflate (3.0 equiv.), [RuCl2(p-
Cym)]2 (2.5 mol-%), PivOH (30 mol-%), K2CO3 (4.0 equiv.), PhCF3 (0.125
M
N-Directing Heteroaryl Derivatives as Coupling Partners
for Aryl Triflates
based on phenyl-1H-pyrazole), 110 °C, under argon, 22 h. 1H NMR yield based
on the heteroaryl. [b] NMR yield. [c] Isolated yield. [d] Not determined since
several side-products co-exist. [e] 2-naphthyl triflate (1.5 equiv.), [RuCl2-
(p-Cym)]2 (5 mol-%), PivOH (60 mol-%), K2CO3 (2.0 equiv.). [f] [RuCl2(p-Cym)]2
(5 mol-%), PivOH (60 mol-%).
We further applied these general coupling conditions to other
heteroaryl substrates that incorporate functions at the aromatic
or heteroaromatic moieties. By using the bulky 2-naphthyl tri-
flate coupling partner, we investigated the direct arylation of
variously substituted arylpyrazoles, pyridines and thiazoles
(Table 3). Using 2.5 mol-% [RuCl2(p-Cym)]2 with 30 mol-%
PivOH, and K2CO3 in trifluoromethylbenzene at 110 °C, the 1-(4-
trifluoromethylphenyl)-1H-pyrazole gave diarylated 11b in 79 %
isolated yield with 87 % selectivity (entry 1).
(Table 3, entry 2). The lack of selectivity is possibly due to com-
petitive oxidative addition of chloride to ruthenium. From 3-
nitrophenyl pyrazole, arylation occurs selectively in the para-
position from nitro substituent, giving a modest 15 % yield of
monoarylated 13a (entry 3, see also Table S1 in the Supporting
The coupling of 4-chlorophenyl pyrazole was found to be Information). Conversely, 2-(4-chloro-1H-pyrazol-1-yl)-phenyl
more challenging, giving a moderate 43 % isolated yield of 12b coupled with 2-naphthyl triflate to give 14b in 55 % isolated
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yield (entry 4). Thus, a functional group on the N-directing pyr- cellent yield (49 %, 91 %, 92 % and 73 %, respectively). The cata-
azole unit was tolerated in ruthenium catalysis, while we have lytic system also achieved 4-tolyl triflate coupling with 1-(4-tri-
recently shown that similar palladium ortho-C–H functionaliza- fluoromethylphenyl)-1H-pyrazole to give 18b in 93 % yield, and
tion from substituted pyrazole directing groups is a very chal- the coupling with 2-phenylpyridine gave 19b in 55 % yield.
lenging issue.[9a] These coupling were successfully extended to
C–H ortho-functionalization of 2-phenylpyridine with 2-naphth-
General Reactivity of Phenolate Coupling Partners
yl triflate, which furnished 15b in 85 % isolated yield (entry 5),
and to 2-phenylbenzothiazole, which gave 16b in very good
83 % yield (40 % after workup, entry 6).
The general reactivity and comparative adequacy of various
phenolates in C–C coupling is a question that is generally
poorly addressed although it may be decisive in the efficiency
of catalytic processes. Herein, we compared different leaving
groups derived from 2-naphthol under our general conditions.
Phenol derivatization is easy to handle and we synthesized at
gram scale (up to 2 g) five sulfonate, carbonate and acetate
reagents. The introduction of trifluoromethane sulfonate group
was performed under anhydrous conditions using trifluoro-
methane sulfonic anhydride to give 20a in 91 % isolated yield
Coupling in Dichloroethane (DCE) Solvent of Aryl Triflates
and Heteroaryls
Ruthenium-catalyzed arylation using N-directing ligands have
mostly been performed in solvents such as NMP or 1,4-dioxane,
which are considered as poor eco-friendly solvents regarding
waste issues (incineration, recycling, bio-treatments and VOC
emissions) and toxicity (reprotoxicity, mutagenicity).[2b] Toluene
and its derivatives, such as xylene and trifluoromethylbenzene
are currently considered less harmful and might be recom-
mended as valuable media alternatives. Progress in ruthenium-
catalyzed C–H arylation has been achieved by using aryl chlor-
ide electrophile coupling partners in water,[10] and by the em-
ployment of tosylates first in NMP, then in water and solvent-
free conditions.[11] We envisioned that sustainable conditions
could also be reached by the employment of aryl triflate deriva-
tives in diethylcarbonate (DCE) as solvent.[12] We tested our
present catalytic protocol with this aim. By using DCE, further
optimization appeared to be necessary, and we satisfactorily
coupled aryl triflates with N-directing arylpyrazole and aryl-
pyridine after careful conditions screening (Table S2 in the Sup-
porting Information).
Table 4. Sulfonates and carbonates from 2-naphthol (20).
Entry
Reagent [equiv.]
Leaving group
Isolated yield [%]
1[a]
2[b]
3[c]
4[d]
5[e]
Tf2O (1.2)
–OSO2CF3
–OSO2Tolyl
–OSO2CH3
–OSO2C2H5
–OCOCH3
20a, 91
20b, 90
20c, 85
20d, 91
20e, 99
ClSO2Tolyl (3.0)
ClSO2CH3 (3.0)
ClCO2C2H5 (3.0)
ClCOCH3 (3.0)
[a] Conditions: 2-naphthol (20, 1 equiv.), NEt3 (1.5 equiv.), trifluoromethane
sulfonic anhydride (1.2 equiv.) in anhydrous CH2Cl2 at 0 °C. [b] 2-naphthol (20,
1 equiv.), NEt3 (3.0 equiv.), p-toluenesulfonyl chloride (3.0 equiv.) in CH3CN at
room temp. [c] 2-naphthol (20, 1 equiv.), NEt3 (3.0 equiv.), methanesulfonyl
chloride (3.0 equiv.) in CH3CN at r.t. [d] 2-Naphthol (20, 1 equiv.), NEt3
(3.0 equiv.), ethyl chloroformate (3.0 equiv.) in CH2Cl2 at r.t. [e] 2-naphthol
(20, 1 equiv.), NEt3 (3.0 equiv.), acetyl chloride (3.0 equiv.) in CH2Cl2 at room
temp.
In the presence of [RuCl2(p-Cym)]2 and KOAc in DCE at
120 °C, we obtained 1b in 60 % after 48 h (Scheme 1). The
coupling of aryl triflates with phenyl-1H-pyrazole was extended
to yield the polyaromatic methylated 2b, acetylated 4b,
naphthylated 6b and methoxylated 17b with fairly good to ex-
Scheme 1. Ruthenium-catalyzed triflate coupling in diethyl carbonate.[a]
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Scheme 2. Phenolate derivatives in Ru-catalyzed ortho-sp2 C–H arylation of arylpyrazole.
(Table 4, entry 1). Similarly, we achieved the synthesis of tosyl- N-directed C–H functionalization. Additionally, these valuable
ate 20b, mesylate 20c, carbonate 20d, and acetate 20e in 85 % alternative electrophile coupling partners could be used in
to 99 % yield (Table 4, entries 2–5). Naphthalen-2-yl 4-methyl- eco-friendly solvent diethyl carbonate without acidic additive.
benzenesulfonate 20b reacted with phenyl-1H-pyrazole to give Finally, these efficient coupling conditions were successfully ex-
diarylated 6b in high 93 % yield (Scheme 2, conditions A). Inter- tended to sulfonates such as tosylates and mesitylates. Further
estingly our protocol in PhCF3 was found to be very efficient studies will address metal-catalyzed reactions promoting the
since related studies using tosylates have been limited to single more reluctant phenolate derivatives we identified herein, such
arylation reactions.[11a,11b] The mesylate derivative was found to as carbonates and acetates.
be slightly less reactive but achieved a very good 87 % yield
(Scheme 2, conditions A). A limitation of our protocol was
reached with the coupling of carbonates since ethyl naphth-
alen-2-yl carbonate 20d achieved only a limited conversion into
a mixture of 6a and 6b (5 % and 10 %, respectively). Finally,
Experimental Section
General Procedure for Ruthenium-Catalyzed N-Directed ortho-
C–H Diarylation
naphthalen-2-yl acetate 20e did not react under these condi-
tions.
In DEC solvent slower reactions were achieved for naphth-
alen-2-yl sulfonate 20b and 20c (Scheme 2, conditions B) to
give a mixture of unreacted phenyl-1H-pyrazole reagent,
monoarylated 6a and diarylated 6b in 19:33:48 ratio after 48 h.
(i) In trifluoromethylbenzene: As a typical experiment, an oven-dried
20 mL Schlenk tube equipped with a magnetic stirring bar was
charged with phenyl-1H-pyrazole (66 μL, 0.5 mmol), phenyl triflate
(320 μL, 1.5 mmol), K2CO3 (276 mg, 2 mmol), [RuCl2(p-Cym)]2
(7.8 mg, 2.5 mol-%) and PivOH (15 mg, 30 mol-%) in trifluoromethyl-
benzene (4 mL). The mixture was stirred at 110 °C under argon for
22 h. After extraction (CH2Cl2/H2O), the organic layer was removed
in vacuo. The crude product was purified by column chromatogra-
phy on silica or recrystallization (heptane/ethyl acetate) to afford
the corresponding product.
Conclusions
We reported general conditions for selective ortho-diarylation
of various arylheteroaryl substrates by using N-ligand directed
ruthenium-catalyzed coupling of highly functionalized aryl
phenolate derivatives. The complex [RuCl2(p-Cym)]2 combined
with pivalic acid (PivOH), allows very efficient coupling in ortho
C–H functionalization of aryl triflates, which overcome the
chemoselectivity issues related to mixtures of mono and diaryl-
ation products. Our general protocol tolerated electron-donat-
ing substituents in para-, meta- and ortho-position of aryl tri-
flates, including significantly congested substituents. Function-
alized arylpyrazoles, pyridines and thiazoles were also tolerated,
(ii) In diethyl carbonate (DEC): As a typical experiment, an oven-dried
20 mL Schlenk tube equipped with a magnetic stirring bar was
charged with phenyl triflate (320 μL, 1.5 mmol), KOAc (196 mg,
2 mmol) and [RuCl2(p-Cym)]2 (7.8 mg, 2.5 mol-%) and placed under
vacuum for 20 min. Under argon, phenyl-1H-pyrazole (66 μL,
0.5 mmol) was added with diethyl carbonate (4 mL). The mixture
was stirred at 110 °C under argon for 22 h. After extraction (CH2Cl2/
H2O), the organic layer was removed in vacuo. The crude product
was purified by column chromatography on silica or recrystalliza-
while this is known to be rather difficult in related palladium tion (heptane/ethyl acetate) to afford the corresponding product.
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Acknowledgments
This work was supported by the Centre National de la Recher-
che Scientifique (CNRS), Université de Bourgogne, Conseil Ré-
gional de Bourgogne through the plan d'Actions Régional pour
l'Innovation (PARI, program CDEA, 3MIM) and the Fonds Euro-
péen de Dévelopement Régional (FEDER). Thanks are due to S.
Royer for some triflate reagent preparations.
Keywords: Biphenyl · C–H activation · Ruthenium ·
Arylation · Dichloroethane · Sulfonates · Triflates
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Received: February 21, 2018
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
C–H Arylation
J. Roger,* J.-C. Hierso* ...................... 1–7
Phenol Derivatives in Ruthenium-
Catalyzed C–H Arylation: A General
Synthetic Access to Azole-Based
Congested Polyaromatics
Aryl triflates are suitable electrophile directed sp2 C–H activation including
coupling partners for the ruthenium- diethyl carbonate as an eco-friendly
catalyzed direct diarylation of hetero- solvent.
aromatic substrates using azole N-
Ruthenium-Catalyzed @CHActivation of Phenol Derivatives towards Azole-Based Congested Polyaromatics by Roger
and Hierso @univbourgogne @ICMUB @Univ_BFC
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