Catalytic method for the synthesis of C-N-linked BI(HETEROARYL)S using heteroaryl ethers and N -Benzoyl heteroarenes

Article abstract of DOI:10.1021/acs.orglett.8b00245

C-N-linked bi(heteroaryl)s are synthesized by a rhodium-catalyzed N-heteroarylation reaction of N-benzoyl heteroarenes including azoles/azolones, pyridones, cyclic ureas, and cyclic imides using heteroaryl aryl ethers. The reaction involves the covalent bond-exchange reaction of N-CO and HetAr-O bonds without using metal bases and exhibits a broad applicability, giving diverse C-N-linked bi(heteroaryl)s containing five- and six-membered heteroarenes. The N-heteroarylation of N-H azoles/azolones and pyridone proceeds at higher reaction temperatures.

Full text of DOI:10.1021/acs.orglett.8b00245

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Catalytic Method for the Synthesis of C−N-Linked Bi(heteroaryl)s
Using Heteroaryl Ethers and N‑Benzoyl Heteroarenes
Saori Tanii, Mieko Arisawa,* Takaya Tougo, and Masahiko Yamaguchi*
Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Sendai 980-8578, Japan
S
* Supporting Information
ABSTRACT: C−N-linked bi(heteroaryl)s are synthesized by
a rhodium-catalyzed N-heteroarylation reaction of N-benzoyl
heteroarenes including azoles/azolones, pyridones, cyclic
ureas, and cyclic imides using heteroaryl aryl ethers. The
reaction involves the covalent bond-exchange reaction of N−
CO and HetAr−O bonds without using metal bases and
exhibits a broad applicability, giving diverse C−N-linked
bi(heteroaryl)s containing five- and six-membered heteroar-
enes. The N-heteroarylation of N−H azoles/azolones and
pyridone proceeds at higher reaction temperatures.
he diaryl is a privileged structure for drugs,1 and the
Tbi(heteroaryl) is an attractive structure because of
structural diversity involving various heteroaryls. Such com-
pounds contain several heteroatoms in the diaryl structure
capable of interacting with proteins and nucleic acids and likely
to exhibit biological activities. In such compounds, along with
the carbon−carbon (C−C) linked mode, the carbon−nitrogen
(C−N) linked mode is conceivable (Figure 1), which occurs in
drugs such as epirizole and zopiclone.2
amine for the reaction of benzimidazoles;9 1-methylimidazole
for the reaction of carbazoles;10 and trans-N,N′-dimethylcyclo-
hexane-1,2-diamine for the reaction of 2- and 4-pyridones.11
The limited scope was considered to be due to significant
differences in the reactivity of metalated N-heterocyclic
reagents depending on the heteroaryl structure. Heteroarenes
have N−H hydrogens with diverse acidities, as shown by
examples of N−H protons of triazole derivatives (pKa 14−15),
2,5-pyrrolidinedione (pKa 14.7), 4-pyridone (pKa 14.8), 2-
pyridone (pKa 17.0), 1,3-dihydro-2H-indol-2-one (pKa 18.5),
diazoles (pKa 18−20), indole (pKa 21.0), and pyrrole (pKa
23.0).13 The reactivity of the conjugate bases differs, and
controlling the reactivity by designing the metal complex and
ligands is necessary depending on the N-metalated substrates.
In addition, metalated N-heteroarenes are often not soluble in
organic solvents, and the resulting heterogeneous conditions
makes the reaction complex. It is desirable to develop a versatile
synthetic method for C−N-linked bi(heteroaryl)s.
Figure 1. C−C-linked mode and C−N-linked mode.
With regard to the synthesis of C−N-linked bi(heteroaryl)s,
a substitution reaction of the N−H-hydrogen of azoles/
azolones, pyridones, cyclic ureas, and cyclic imides with
halogenated heteroarenes is generally employed in the presence
of a metal base or a metal reagent.3 Catalysis by copper,4,7−11
palladium,5 and nickel6 complexes is also used. Recently, the
synthesis of C−N-linked bi(heteroaryl)s by oxidative coupling
between the N−H nitrogen in azoles and the C−H carbon in
heteroarenes has also been developed in the presence of
oxidants.12 The scope of these conventional syntheses of C−N-
linked bi(heteroaryl)s, however, is rather limited, and it is
necessary to employ different catalysts, ligands, bases, and
reaction conditions depending on the substrates. For example,
copper complexes such as CuI, CuCl, Cu2), and CuO were
employed in copper-catalyzed reactions in the presence of
stoichiometric amounts of different bases such as K2CO3,
CsCO3, K3PO4, Et3N, and NaOMe. With regard to the ligand
effect, N,N′-(phenylmethylene)bisacetamide was used for the
N-heteroarylation reaction of benzotriazoles;7 salicylaldoxime
(salox) for the reaction of pyrazoles;8 (1R,2R)-cyclohexanedi-
Recently, we have reported a synthetic method for
unsymmetric bi(heteroaryl) compounds, HetAr-O-HetAr′,14
HetAr-S-HetAr′,15 and HetAr-CH2-HetAr′16 using a rhodium-
catalyzed heteroaryl-exchange reaction between heteroaryl aryl
ethers and heteroaryl benzoates/heteroaryl thioesters/hetero-
arylmethylene ketones.17 Metalated heteroaryl alcohols and
heteroaryl thiols are not used in rhodium-catalyzed reactions,
and neutral organic substrates are used such as esters and
thioesters. These reactions have a broad applicability and
provide various novel bi(heteroaryl) compounds because of the
use of bond exchange reactions between C−O bonds and C−
S/C−O/C−C bonds in neutral organic substrates.
Described here is the rhodium-catalyzed synthesis of C−N-
linked bi(heteroaryl)s by an N-heteroarylation reaction using
Received: January 23, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b00245
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
heteroaryl aryl ethers and N-benzoyl heteroarenes (Scheme 1).
Various N-benzoyl azoles containing benzotriazolyl, benzimi-
chlorophenyl ethers containing five- and six-membered
heteroaryls, such as 1,3-benzothiazolyl, 1,3-benzoxazolyl, 1,3-
oxazolyl, 2-furyl, and 4-quinazolinyl groups, reacted with 1-
benzoyl-1H-benzotriazole 1a, and the corresponding 1-
heteroaryl-1H-benzotriazoles 3a−f were obtained. The reaction
of N-benzoyl 1H-benzimidazole, 1H-indole, 9H-carbazole, and
pyrrole provided C−N-linked bi(heteroaryl)s 3g−n. This
reaction is a novel catalytic method for synthesizing diverse
C−N-linked bi(heteroaryl)s from heteroaryl aryl ethers and N-
benzoyl azoles. Conventional methods for N-heteroarylation of
azoles employed different catalysts, ligands, and bases depend-
ing on substrates. The reaction of 1a and 3-trifluoromethyl-4-
(4-chlorophenoxy)benzonitrile (1 equiv) gave N-arylated
product 3o (73%). The ester 4 was isolated as coproducts in
all cases.
The rhodium-catalyzed heteroaryl exchange reaction was
applied to the N-heteroarylation of N-benzoyl lactams. When 2-
(4-chlorophenoxy)quinazoline was reacted with 3-benzoyl-3H-
benzoxazol-2-one 5a (1 equiv) in the presence of RhH(PPh3)4
(5 mol %) and dppBz (10 mol %) in refluxing chlorobenzene
(bp 132 °C) for 2 h, 3-(4-quinazolinyl)-3H-benzoxazol-2-one
6a (97%) and 4-chlorophenyl benzoate 4 (98%) were obtained
(Table 2, 6a). The yield of 6a at 100 °C decreased to 41%
Scheme 1. Rh-Catalyzed N-Heteroarylation Reaction
dazolyl, indolyl, carbazolyl, and pyrrolyl groups, and N-benzoyl
cyclic amides containing 2-pyridonyl, 4-pyridonyl, 1,3-benzo-
thiazolonyl, 1,3-benzoxazolonyl, imidazolonyl, imidathiazolonyl,
1H-isoindole-1,3(2H)-dionyl, and 2,5-pyrrolidinedionyl groups
were efficiently reacted. In addition, a wide range of electron-
deficient/electron-rich five/six-membered heteroaryl aryl ethers
such as 2-benzoxazolyl, 2-benzothiazolyl, 2-oxazolyl, 2-furyl, 2-
pyridyl, 2-quinazolinyl, and 2-triazyl derivatives were employed.
The rhodium-catalyzed N-heteroarylation of N-benzoyl hetero-
arenes proceeds without using metal bases, unlike conventional
methods, and exhibits a broad scope to provide various C−N-
linked bi(heteroaryl)s. N-Heteroarylation of N-benzoyl hetero-
arenes by heteroaryl aryl ethers provided various C−N-linked
bi(heteroaryl)s with concomitant C−N and C−O bond
cleavage and exchange.18 The N-heteroarylation of N−H
azoles/azolones and pyridone proceeded at a high reaction
temperature and also showed broad applicability.
Table 2. Rh-Catalyzed N-Heteroarylation of N-Benzoyl
Lactams
When 1-benzoyl-1H-benzotriazole 1a was reacted with 2-(4-
chlorophenoxy)benzoxazole 2a (1 equiv) in the presence of
RhH(PPh3)4 (5 mol %) and dppBz (10 mol %) in
chlorobenzene at 100 °C for 2 h, 1-(2-benzoxazolyl)-1H-
benzotriazole 3a (94%), and 4-chlorophenyl benzoate 4 (99%)
were obtained (Table 1, 3a). No reaction occurred in the
absence of RhH(PPh3)4 or dppBz. Various N-heteroaryl azoles
were synthesized by the heteroaryl exchange reaction of
heteroaryl aryl ethers and N-benzoyl azoles. Heteroaryl 4-
Table 1. Rh-Catalyzed N-Heteroarylation of N-Benzoyl
Azoles
a
Under PhCl at 100 °C.
yield. No reaction occurred in the absence of RhH(PPh3)4 or
dppBz. Various N-heteroaryl azolones, cyclic ureas, and cyclic
imides were synthesized by the heteroaryl exchange reaction of
heteroaryl aryl ethers and N-benzoyl lactams (Table 2). Five-
and six-membered heteroaryl 4-chlorophenyl ethers with 1,3-
benzothiazolyl, 1,3-benzoxazolyl, 1,3-oxazolyl, and 4-quinazo-
linyl groups were reacted with 5a, and the corresponding N-
heteroaryl benzoxazolones 6a−d were obtained. The reaction
of 1-benzoyl-1,3-dihydro-3-phenyl-2H-imidazol-2-one provided
N-heteroaryl ureas 6e−g. This reaction was also applied to N-
heteroarylation of thioamides giving N-heteroaryl thiamides 6h
and 6i. N-Heteroarylation of N-benzoyl phthalimide and
succinimide gave the corresponding N-benzoxazolyl com-
pounds 6j, 6k, and 6l. N-Heteroarylation of phthalimide and
succinimide derivatives has not been reported before. The
a
Under refluxing PhCl.
B
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Letter
resulting N-heteroaryl cyclic ureas and imides except for 6b, 6c,
6h, and 6j are new compounds.
Table 3. Rh-Catalyzed N-Heteroarylation of N-Heteroarenes
The above experiments were conducted using N-benzoyl
azolones, and it was found that O-benzoyl derivatives also
underwent N-heteroarylation. 2-Benzothiazolyl benzoate 5c′,
which was obtained from 2-benzothiazolone and benzoyl
chloride using triethylamine at room temperature, was reacted
with 2-(4-chlorophenoxy)benzoxazole to give 6c in 78% yield
(Scheme 2). Then both 5c and 5c′ undergo N-heteroarylation
Scheme 2. Rh-catalyzed N-Heteroarylation of 5c′
reaction. It is noted that 2-benzothiazolyl benzoate 5c′
quantitatively rearranged to N-benzoyl benzothiazolone 5c in
refluxing chlorobenzene for 2 h without the rhodium catalyst.
Pyridyl benzoates were also N-heteroarylated. When 2-(4-
chlorophenoxyl)benzothiazole was reacted with 2- pyridyl
benzoate 7 (1 equiv) in the presence of RhH(PPh3)4 (5 mol
%) and dppBz (10 mol %) in chlorobenzene at 100 °C for 5 h,
1-(2-benzothiazolyl)-1H-pyridin-2-one 9a (100%) and 4-
chlorophenyl benzoate 4 (95%) were obtained (Scheme 3).
a
Under PhCl at 100 °C.
containing five- and six-membered heteroarenes giving the
corresponding products 3a, 3c, and 3f. N-Benzoxazolylation of
benzimidazole, indole, and pyrrole provided 3g, 3j, and 3n. N-
Heteroarylation of azolones and pyridine gave the correspond-
ing N-benzoxazolyl/N-benzothiazolyl products 6b, 6c, 6h, and
9a. N-Heteroarylation of N−H azoles/azolones and pyridone
showed a broad applicability, although the yields decreased for
the N-benzoyl deriveatives.
Scheme 3. Rh-Catalyzed N-Heteroarylation of 2- and 4-
Pyridones
A possible mechanism of the reaction is shown in Scheme 4.
The phosphine ligand in RhH(PPh3)4 is exchanged with dppBz,
Scheme 4. Proposed Reaction Mechanism
Several heteroaryl (4-chlorophenyl) ethers were reacted with 2-
and 4-pyridyl benzoates to give N-heteroaryl 2-pyridones and 4-
pyridone. It was determined that 2-pyridyl and 4-pyridyl
benzoates did not isomerize to 1-benzoyl-1H-pyridin-2-one and
pyridine-4-one in refluxing chlorobenzene for 2 h in the
presence of RhH(PPh3)4 (5 mol %) and dppBz (10 mol %),
which indicated N-benzoyl pyridone not being the intermediate
of this reaction.
Rhodium-catalyzed N-heteroarylation can be applied to N−
H azoles/azolones and pyridone at a higher temperature
without employing N-benzoyl heteroarenes (Table 3). When 2-
(4-chlorophenyloxy)benzoxazole was reacted with benzotria-
zole (1 equiv) in the presence of RhH(PPh3)4 (5 mol %) and
dppBz (10 mol %) in refluxing chlorobenzene for 5 h, 1-(2-
benzoxazolyl)-1H-benzotriazole 3a (99%) and 4-chlorophenol
(96%) were obtained. It is necessary to elevate the reaction
temperature to that of refluxing chlorobenzene. For example,
the yields of 3a and 3g at 100 °C decreased to 56% and 25%
from 99% and 90% in refluxing chlorobenzene, respectively.
The benzotriazole reacted efficiently with heteroaryl aryl ethers
and the oxidative addition of a N-benzoyl heteroarene provides
the benzoylrhodium intermediate A. The intermediate A then
undergoes heteroaryl exchange reaction with a heteroaryl aryl
ether probably via σ-bond metathesis to form HetAr′−
Rh(III)−NHetAr complex B and a benzoate ester, and C−N-
linked bi(heteroaryl) is liberated by reductive elimination with
the regeneration of rhodium catalyst. It is considered that the
C−N bond cleavage precedes the C−O bond cleavage. It is
because N-heteroarylation of N-heteroarenes requires more
severe reaction conditions than that of N-benzoyl heterearenes,
and the initial formation of a benzoylrhodium intermediate A is
C
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Organic Letters
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(4) For example, N-heteroarylation of azoles: (a) Jerome, P.;
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In summary, N-heteroaryl azoles/azolones, pyridones, cyclic
ureas, and cyclic imides were synthesized from heteroaryl (4-
chlorophenyl) ethers and N-benzoyl heteroarenes including
azoles/azolones, pyridones, cyclic ureas, and cyclic imides using
a rhodium-catalyzed heteroaryl exchange reaction. This is a
novel method to form the C−N bonds of C−N-linked
bi(heteroaryl)s. Rhodium-catalyzed N-heteroarylation was also
applied to N-heteroarylation of N−H azoles/azolones and
pyridone. The N-heteroarylation reactions have broad applic-
ability and are insensitive to the structures of substrates. It is
also worth noting that the byproducts of the reactions, aryl
benzoates and phenols, are readily separated and recycled.
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b00245.
■
S
Experimental procedure, characterization data, and NMR
spectra for all products (PDF)
(7) Wan, J.-P.; Chai, Y.-F.; Wu, J.-M.; Pan, Y.-J. Synlett 2008, 3068.
(8) Cristau, H.-J.; Cellier, P. P.; Spindler, J.-F.; Taillefer, M. Eur. J.
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AUTHOR INFORMATION
Corresponding Authors
■
(9) Huang, A.; Jayaraman, L.; Fura, A.; Vite, G. D.; Trainor, G. L.;
Gottardis, M. M.; Spires, T. E.; Spires, V. M.; Rizzo, C. A.; Obermeier,
M. T.; Elzinga, P. A.; Todderud, G.; Fan, Y.; Newitt, J. A.; Beyer, S. M.;
Zhu, Y.; Warrack, B. M.; Goodenough, A. K.; Tebben, A. J.; Doweyko,
A. M.; Gold, D. L.; Balog, A. ACS Med. Chem. Lett. 2016, 7, 40.
(10) Zhao, X.; She, Y.; Fang, K.; Li, G. J. Org. Chem. 2017, 82, 1024.
(11) (a) Siddle, J. S.; Batsanov, A. S.; Caldwell, S. T.; Cooke, G.;
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S.; Leung, M.-k. Tetrahedron 2009, 65, 1679. (c) Li, C. S.; Dixon, D. D.
Tetrahedron Lett. 2004, 45, 4257.
*E-mail: arisawa@m.tohoku.ac.jp.
*E-mail: yama@m.tohoku.ac.jp.
ORCID
Mieko Arisawa: 0000-0002-9561-2653
Masahiko Yamaguchi: 0000-0003-3965-7598
Notes
(12) Copper-catalyzed reaction of benzotriazole and quinolone/
thiophene derivatives using Selectfluor: (a) Sun, K.; Zhu, Z.; Sun, J.;
Liu, L.; Wang, X. J. Org. Chem. 2016, 81, 1476. (b) Sun, K.; Wang, X.;
Liu, L.; Sun, J.; Liu, X.; Li, Z.; Zhang, Z.; Zhang, G. ACS Catal. 2015,
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(13) (a) Bordwell, F. G.; Fried, H. E. J. Org. Chem. 1991, 56, 4218.
(b) Taft, R. W.; Bordwell, F. G. Acc. Chem. Res. 1988, 21, 463.
(c) Bordwell, F. G.; Drucker, G. E.; Fried, H. E. J. Org. Chem. 1981, 46,
632.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was supported by the Platform Project for
Supporting Drug Discovery and Life Science Research funded
by Japan Agency for Medical Research and Development
(AMED), JSPS KAKENHI Grant Nos. 17K19112 and
15H00911, and Tohoku University Center for Gender Equality
Promotion (TUMUG).
(14) Tanii, S.; Arisawa, M.; Tougo, T.; Horiuchi, K.; Yamaguchi, M.
Synlett 2017, 28, 1601.
(15) Arisawa, M.; Tazawa, T.; Tanii, S.; Horiuchi, K.; Yamaguchi, M.
J. Org. Chem. 2017, 82, 804.
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(18) For example, imide C−N bond cleavage reactions: (a) Dander,
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