Thieme Chemistry Journals Awardees - Where Are They Now? Rhodium-Catalyzed Synthesis of Unsymmetric Di(heteroaryl) Ethers Using Heteroaryl Exchange Reaction

Article abstract of DOI:10.1055/s-0036-1588801

Unsymmetric di(heteroaryl) ethers were synthesized by the rhodium-catalyzed heteroaryl exchange reaction of heteroaryl aryl ethers and heteroaryl esters at equilibrium. Diverse unsymmetric di(heteroaryl) ethers containing five- and six-membered heteroaren

Full text of DOI:10.1055/s-0036-1588801

SYNLETT
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
© Georg Thieme Verlag Stuttgart · New York
2017, 28, A–G
letter
A
en
S. Tanii et al.
Letter
Synlett
Thieme Chemistry Journals Awardees – Where Are They Now?
Rhodium-Catalyzed Synthesis of Unsymmetric Di(heteroaryl)
Ethers Using Heteroaryl Exchange Reaction
Saori Tanii
RhH(PPh3)4 (5 mol%)
dppBz (10 mol%)
O
C
X'
X
Mieko Arisawa*
Takaya Tougo
OAr
+
Y'
PhCl, refl.
O
Ph
Y
3 equiv
Ar = p-ClC6H4
O
C
Kiyofumi Horiuchi
Masahiko Yamaguchi*
X'
X
+
Ph
OAr
Y
Y'
O
24 new compounds
Department of Organic Chemistry, Graduate School of
Pharmaceutical Sciences, Tohoku University, 6-3 Aoba,
Sendai, 980-8578, Japan
yama@m.tohoku.ac.jp
arisawa@m.tohoku.ac.jp
X
= Aryl, N-heteroaryl, 2-benzoazolyl, 2-oxazolyl, 2-furyl,
Y
X'
2-thienyl groups
= Aryl, 2-pyridyl, 3-pyridyl, 4-pyridyl, N-heteroaryl, 3-furyl,
3-thienyl groups
Y'
Received: 02.03.2017
Accepted after revision: 26.03.2017
Published online: 27.04.2017
DOI: 10.1055/s-0036-1588801; Art ID: st-2017-u0154-l
Abstract Unsymmetric di(heteroaryl) ethers were synthesized by the
rhodium-catalyzed heteroaryl exchange reaction of heteroaryl aryl
ethers and heteroaryl esters at equilibrium. Diverse unsymmetric di(he-
teroaryl) ethers containing five- and six-membered heteroarenes were
obtained. Di(heteroaryl) ethers can be synthesized starting from diaryl
ethers, because heteroaryl aryl ethers are obtained by the heteroaryl
exchange reaction of diaryl ethers.
Key words unsymmetric di(heteroaryl) ethers, rhodium, heteroaryl
exchange reaction, C–O bond cleavage, heteroaryl benzoates
Diaryl ethers are widely present in natural products and
functional materials, and substitution of the aryl groups
with heteroarenes is an attractive method to modify their
properties such as conformation, electron density, and lipo-
philicity.1 However, known unsymmetrical di(heteroaryl)
ethers, where two aryl groups in the diaryl ether are substi-
tuted by different heteroarenes, are limited.2 Several di(pyr-
idyl) ethers have been synthesized by the classical nucleop-
hilic aromatic substitution of halopyridines and hydroxy-
pyridines in the presence of stoichiometric amounts of
bases,3 which in some cases employ metal catalysis.4
Di(pyridyl) ethers have been synthesized by the reaction of
hydroxypyridine and pyridine-N-oxides.5 These aromatic
substitution reactions in most cases provide di(pyridyl)
ethers. The palladium-catalyzed substitution reaction of 2-
pyrimidyl or 4-quinazolyl derivatives with the pyridotri-
azol-1-yloxy leaving group and heteroarylboric acids has
been reported. It is noted that the heteroarylboric acids are
converted into hydroxyheteroarenes by palladium-cata-
lyzed oxidation, which nucleophilically substitute the pyri-
dotriazol-1-yloxy group.6 The reaction, however, is restrict-
ed to 2-pyrimidyl or 4-quinazolyl derivatives, and the use of
Mieko Arisawa was born in Yamagata, Japan, in 1974. She received
her B.Sc. (1996) and Ph.D. degrees (2001) from the Tohoku University.
In 1998, she was appointed as a research associate at Tohoku Universi-
ty, and was promoted to an assistant professor in 2001 and a lecturer in
2010. Since 2013, she is an associate professor at Tohoku University.
She received the Sankyo Chemical Co., LTD. Award in Synthetic Organic
Chemistry, Japan, in 2001, the Banyu Young Chemist Award in 2002,
the Incentive Award in Synthetic Organic Chemistry Japan in 2010, and
the Thieme Chemistry Journals Award in 2011. Her research interests
are the development of transition-metal-catalyzed efficient synthetic
methodologies/reactions of organoheteroatom compounds.
hydroxyheteroarenes instead of heteroarylboric acids is
preferable because of their availability. It should also be
noted that all these substitution reactions employ stoichio-
metric amounts of bases.
Recently, we have reported the rhodium-catalyzed syn-
thesis of di(heteroaryl) sulfides and di(heteroaryl)meth-
anes from heteroaryl ethers by heteroaryl exchange reac-
tion.7a,b The synthesis provided di(heteroaryl) compounds
connected by a one-atom of sulfur and carbon, using the C–
O bond cleavage of heteroaryl aryl ethers. It was then con-
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–G

B
S. Tanii et al.
Letter
Synlett
sidered that various di(heteroaryl) ethers could be obtained
from heteroaryl ethers by a heteroaryl exchange reaction,
although such a method had not yet been developed.
Described here is the rhodium-catalyzed synthesis of
unsymmetric di(heteroaryl) ethers by heteroaryl exchange
(Scheme 1, B). Under rhodium-catalyzed conditions, the re-
action of heteroaryl aryl ethers and heteroaryl benzoates
provided di(heteroaryl) ethers. The C–O bond cleavage and
heteroaryl exchange of heteroaryl aryl ethers provided un-
symmetric di(heteroaryl) ethers containing multiple het-
eroatoms. The advantages of this method are as follows: 1)
diverse unsymmetrical di(heteroaryl) ethers containing
various five- and six-membered heteroarenes can be syn-
thesized; 2) substrates are stable and readily available; 3)
the rhodium-catalyzed reaction does not employ metal
bases. It should also be noted that unsymmetric di(het-
eroaryl) ethers can, in principle, be synthesized from diaryl
ethers by subsequent rhodium-catalyzed heteroaryl ex-
change reactions (Schemes 1, A and B).
It was initially confirmed that the HetAr–O bonds of he-
teroaryl aryl ethers can be cleaved and exchanged by rhodi-
um catalysis. When 2-(4-chlorophenoxy)-6-chlorobenzox-
azole (1) was reacted with 2-phenoxybenzothiazole (2a, 3
equiv) in the presence of RhH(PPh3)4 (5 mol%) and dppBz
(10 mol%, dppBz = 1,2-bis(diphenylphosphino)benzene) in
refluxing chlorobenzene for five hours, 2-phenoxy-6-chlo-
robenzoxazole (3a, 72%), and 2-(4-chlorophenoxy)benzo-
thiazole (4, 62%) were obtained with recovery of 1 (18%)
and 2a (74%, Scheme 2). No reaction occurred in the ab-
sence of the RhH(PPh3)4 or dppBz. The use of several biden-
tate ligands revealed a high efficiency of dppBz for this re-
action: 1,2-bis(diphenylphosphino)ethane (yields of 3a and
4: 52% and 79%), cis-1,2-bis(diphenylphosphino)ethylene
(59% and 78%), 1,3-bis(diphenylphosphino)propane (15%
and 29%), and 1,4-bis(diphenylphosphino)butane (not de-
tected). Monodentate ligands tris(4-methoxyphenyl)phos-
phine and tris(4-chlorophenyl)phosphine were ineffective.
These results show that the bidentate phosphine ligands
A. Formation of heteroaryl aryl ethers
X
X
Rh cat.
Ar OAr'
OPh
+
OAr'
Ar OPh
+
Y
Y
B. Formation of di(heteroaryl) ethers
O
X'
O
X'
X
X
Rh cat.
OAr'
+
+
OAr'
Ph
Ph
O
Y'
Y'
Y
O
Y
Ar' = 4-ClC6H4
X, Y, X', Y' = C, N, O, S
Scheme 1 Rhodium-catalyzed heteroaryl exchange reactions
RhH(PPh3)4 (5 mol%)
dppBz (10 mol%)
N
N
O
Cl
+
O
X
PhCl, reflux, 5 h
O
Cl
S
1
2a–d (3 equiv)
N
O
O
N
X
O
Cl
+
S
Cl
4
X = Ha
H
46% (3a)
72% (3a)
74% (3b)
71% (3c)
75% (3d)
48%
62%
70%
74%
68%
MeO
Me
CN
N
N
S
Rh cat.
O
O
Cl
+
PhCl, reflux, 5 h
O
Cl
4 (1 equiv)
3a
N
O
O
N
S
Cl
+
O
Cl
1 41%
2a 45%
Rh cat.
HetAr
OAr
+
HetAr'
OAr'
HetAr
OAr'
+
HetAr'
OAr
Scheme 2 Rhodium-catalyzed exchange reaction of heteroaryl aryl ethers. a 2a (1 equiv) was used.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–G

C
S. Tanii et al.
Letter
Synlett
with phosphino groups separated by two carbon atoms are
essential. Previously, we reported that the HetAr–O bond
was selectively cleaved over the Ar–O bond in the rhodium-
catalyzed fluorination, sulfidation, and methylation reac-
tions of heteroaryl aryl ethers (HetAr–O–Ar).7a–c It was then
considered that the 1,3-benzoxazolyl–O bonds of 1 and 2a
were selectively cleaved and exchanged. When the molar
ratio 2a/1 was changed from 3 to 1, the yields of 3a and 4
decreased to 46% and 48%, respectively. The reverse reac-
tion of 3a and 4 under the same reaction conditions gave 1
and 2a in 41% and 45% yields, respectively, which naturally
indicated the equilibrium nature of the reaction. Electron-
donating and electron-withdrawing groups at the aryl 4-
substituents exerted a small effect. The rhodium catalyst
can cleave the HetAr–O bond without using the added bases
and exchanged the heteroaryl groups.
The heteroaryl aryl ethers, which are the substrates in
the reactions in Scheme 2, can be synthesized from activat-
ed diaryl ethers (Scheme 3).8 Heteroaryl aryl ethers con-
taining five- and six-membered heteroarenes 7a–d were
synthesized from 4-(4-chlorophenoxy)-3-trifluoromethyl-
benzonitrile (5) under rhodium-catalyzed conditions. The
rhodium complex catalyzes the aryl–O bond cleavage and
heteroaryl exchange of the activated diaryl ether as well as
the heteroaryl aryl ethers.
group with HetArO–C bond cleavage. It was considered that
the unsymmetric di(heteroaryl) ethers could be formed us-
ing heteroaryl esters, in which HetArO–COPh bond cleavage
occurred because this bond is likely weaker than the HetAr–
O bond (red line, reaction mode II).
The use of heteroaryl benzoate, as expected, formed un-
symmetric di(heteroaryl) ethers from heteroaryl (4-chloro-
phenyl) ethers. When 2-phenoxybenzothiazole (2a,
3
equiv) was reacted with pyridine-3-yl benzoate (9) in the
presence of RhH(PPh3)4 (5 mol%) and dppBz (10 mol%) in
refluxing chlorobenzene for five hours, 2-(3-pyridinyl-
oxy)benzothiazole (10, 69%) and phenyl benzoate (11, 70%)
were obtained with recovery of 2a (73%) and 9 (25%,
Scheme 5).9 No reaction occurred in the absence of
RhH(PPh3)4 or dppBz. When the molar ratio 2a/9 was
changed from 3 to 1, the yields of 10 and 11 decreased to
37% and 39%, respectively. The reverse reaction of 10 and 11
under the same reaction conditions gave 2a and 9 in 39%
and 40% yields, respectively, which indicated the equilibri-
um nature of the reaction. The heteroaryloxy group of het-
eroaryl benzoate was transferred to the heteroaryl aryl
ethers by rhodium catalysis via HetArO–COPh bond cleav-
age.
Various unsymmetric di(heteroaryl) ethers were syn-
thesized by the heteroaryl exchange reaction of heteroaryl
aryl ethers and heteroaryl benzoates (Table 1). The het-
eroaryl 4-chlorophenyl ethers containing five-membered
heteroarenes such as 1,3-benzothiazolyl, 1,3-benzoxazolyl,
1,3-oxazolyl, 2-furyl, and 2-thienyl groups reacted with
pyridine-3-yl benzoate (9), and the corresponding het-
eroaryl 3-pyridyl ethers 10, 14a–k were obtained. The six-
The heteroaryl aryl ethers are obtained by the het-
eroaryl exchange of diaryl ethers via HetAr–OAr bond cleav-
age (Scheme 4, blue line, reaction mode I). It was noted,
however, that the di(heteroaryl) ethers cannot be obtained
by this method because the HetAr–OAr bond is preferential-
ly cleaved, and it is necessary to transfer the heteroaryloxy
RhH(PPh3)4 (5 mol%)
dppBz (10 mol%)
Y
OPh
NC
O
Cl
+
PhCl, reflux, 5 h
X
CF3
6 (3 equiv)
5
Y
O
Cl
+
CN
PhO
F3C
X
X
Y
7
8
=
benzothiazolyl (a)
74%
74%
72%
66%
74%
71%
69%
70%
6-Cl-benzoxazolyl (b)
6,7-(MeO)2-2-quinazolyl (c)
4-CN-2-pyridyl (d)
Scheme 3 Rhodium-catalyzed exchange reaction using diaryl ethers
Reaction mode I
Rh cat.
HetAr
OAr
+
HetAr
OPh
HetAr
OPh
HetAr
OAr
+
Reaction mode II
O
C
O
C
Rh cat.
+
HetAr
O
HetAr
Ph
OAr
HetAr
OAr
+
HetAr
O
Ph
Scheme 4 Reactions using heteroaryl aryl ethers and heteroaryl benzoate
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–G

D
S. Tanii et al.
Letter
Synlett
RhH(PPh3)4 (5 mol%)
dppBz (10 mol%)
O
N
+
O
N
PhCl, reflux, 5 h
Ph
O
S
2a (X equiv)
9
N
O
O
+
O
Ph
S
N
10
37%
69%
11
39%
70%
X = 1
X = 3
2a (73%) and 9 (25%) were recovered
O
N
O
S
Rh cat.
+
PhCl, reflux, 5 h
O
Ph
N
10 (1 equiv)
N
11
O
O
+
N
+
S
O
Ph
2a 39%
9 40%
O
C
O
Rh cat.
HetAr
OAr
HetAr'O
Ph
HetAr
OHetAr'
Ph
ArO
C
+
Scheme 5 Rhodium-catalyzed exchange reaction of 2-phenoxybenzothiazole and pyridine-3yl benzoate
membered heteroaryl 4-chlorophenyl ethers with 2-triazyl,
4-quinazolinyl, and 3-quinolinyl groups were also convert-
ed into the di(heteroaryl) ethers 14l–o. The reaction of 3-
quinolinyl, 5-quinolinyl, and 8-quinolinyl benzoates with 2-
(4-chlorophenoxy)benzothiazole gave the corresponding
benzothiazolyl quinolinyl ethers 14p–r in good yield. Note
that the use of 4-pyridyl and 2-pyridyl benzoate derivatives
formed unsymmetric benzothiazolyl 2- and 4-pyridyl
ethers 14s–u without isomerization to N-heteroaryl pyri-
dones.10 The structure of 14u was confirmed by X-ray crys-
tal structure analysis (Figure 1).11 The unsymmetric five-
membered di(heteroaryl) ethers containing furyl and thie-
nyl groups 14v–y were also obtained. The resulting unsym-
metric di(heteroaryl) ethers are new compounds, except for
14l. This reaction is a novel catalytic method for synthesiz-
ing diverse unsymmetric di(heteroaryl) ethers from het-
eroaryl aryl ethers and heteroaryl benzoates, which are sta-
ble and readily available.
6). 1-Chloro-4-(4-nitrophenoxy)benzene also reacted. The
heteroaryl aryl ethers can be obtained from diaryl ethers
and heteroaryl esters.
A possible mechanism of the reaction is shown in
Scheme 7. The phosphine ligand in RhH(PPh3)4 is exchanged
with dppBz, and the oxidative addition of O-(heteroaryl) es-
ter provides the benzoylrhodium intermediate A. The inter-
mediate A then undergoes a heteroaryl exchange reaction
with heteroaryl aryl ether forming HetAr′–Rh(III)–OHetAr
complex B and benzoate ester, and the unsymmetrical
di(heteroaryl) ethers are liberated by reductive elimination
with the regeneration of the rhodium catalyst. In this reac-
tion, the HetAr–O bond in the ethers and HetArO–COPh
bond in the esters are regioselectively cleaved, and the oth-
er C–O bond does not react. It is considered that the het-
eroaryl groups and aryl groups with electron-withdrawing
substituent weaken the C–O bond.7c,12
In summary, unsymmetric di(heteroaryl) ethers were
synthesized from heteroaryl aryl ethers and heteroaryl
benzoates by a heteroaryl exchange reaction. Diverse un-
symmetric di(heteroaryl) ethers containing five- and six-
membered heteroarenes were obtained in high yields.
Di(heteroaryl) ethers can be synthesized starting from acti-
vated diaryl ethers using the rhodium-catalyzed heteroaryl
exchanged reaction.
The reaction of diaryl ethers and a heteroaryl ester was
also examined. The reaction of 4-(4-chlorophenoxy)-3-tri-
fluoromethylbenzonitrile (5a) and pyridine-3-yl benzoate
(9) gave 3-trifluoromethyl-4-(3-pyridinyloxy)benzonitrile
(16a) and 15 in 72% and 69% yields, respectively (Scheme
Acknowledgment
This research was supported by the Platform Project for Supporting
Drug Discovery and Life Science Research (Platform for Drug Discov-
ery, Informatics, and Structural Life Science) from the Japan Agency
for Medical Research and Development (AMED) and JSPS KAKENHI
Grant Number JP15H00911.
Figure 1 ORTEP view of 14u
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–G

E
S. Tanii et al.
Letter
Synlett
Table 1 Rhodium-Catalyzed Synthesis of Unsymmetric Di(heteroaryl) Ethers.
X
O
O
X
Rh cat.
HetAr
HetAr
+
OAr
+
Y
O
OAr
O
Ph
Ph
Y
13
14
15
12 (3 equiv)
Ar = 4-ClC6H4
X, Y = C, N, O, S
R'
Ph
R
R
N
N
N
R
N
N
N
O
S
O
O
O
O
X
14a R = MeO, R′ = X = H, 60%
14b R = R′ = MeO, X = H, 64%
14c R = R′ = H, X = Cl, 21%
14d R = H, 47%
14e R = Cl, 70%
14f R = Me, 53%
14g R = Ph, 75%
14h R = H, 52%
Ph
N
N
R
R
N
N
O
S
O
O
N
Ph
N
O
14i R = CN, 58%
14j R = MeCO, 73%
14k R = PhCO, 50%
14l 54%b
R
R
CN
N
S
N
O
N
N
O
N
N
N
O
14m R = H, 68%
14n R = MeO, 78%
14o 72%b
14p 69%
N
N
N
N
S
O
N
N
S
O
S
O
O
14q 66%
14r 63%
14s 75%
Me
S
O
O
N
R
O
Ph
X
R
O
S
O
N
R
14t R = Ph, 77%
14u R = Cl, 6%, 23%c
14v R = MeCO, 72%
14w R = CN, 52%
14x R = Me, X = O, 49%
14y R = Ph, X = S, 43%
a The C–O bonds formed by the reaction are shown in red.
b 12 (1 equiv) and 13 (3 equiv) were reacted.
c RhH(PPh3)4 (20 mol%) and dppBz (40 mol%) were used.
Cl
RhH(PPh3)4 (5 mol%)
dppBz (10 mol%)
O
O
O
+
N
O
Cl
+
N
O
Ph
O
Ph
R
PhCl, reflux, 5 h
R
16
15
69%
61%
9 (3 equiv)
5
R = 2-CF3-4-CN (a) 72%
R = 4-NO2 (b)
56%
Scheme 6 Rhodium-catalyzed synthesis of heteroaryl aryl ethers from diaryl ethers
Supporting Information
References and Notes
Supporting information for this article is available online at
(1) Tynebor, R. M.; Chen, M.-H.; Natarajan, S. R.; O’Neill, E. A.;
Thompson, J. E.; Fitzgerald, C. E.; O’Keefe, S. J.; Doherty, J. B.
Bioorg. Med. Chem. Lett. 2011, 21, 411.
https://doi.org/10.1055/s-0036-1588801.
S
u
p
p
ortioInfgrmoaitn
S
u
p
p
ortiInfogrmoaitn
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–G

F
S. Tanii et al.
Letter
Synlett
RhH(PPh3)4
dppBz
PPh3
Y'
O
Y'
X
H
Ph2P
(s)
(s)
X'
Ph
O
X'
Y
O
Rh
Ph2P
(s) = solvent
Y'
Y
Y'
X
X
X'
Ph2P
Ph2P
X'
Ph2P
Ph2P
O
O
O
Rh
Rh
Ph
A
X
B
O
X
OAr
Ph
OAr
Y
Scheme 7 Proposed reaction mechanism
(2) (a) AMG 458: Liu, L.; Siegmund, A.; Xi, N.; Kaplan-Lefko, P.; Rex,
K.; Chen, A.; Lin, J.; Moriguchi, J.; Berry, L.; Huang, L.; Teffera, Y.;
Yang, Y.; Zhang, Y.; Bellon, S. F.; Lee, M.; Shimanovich, R.; Bak,
A.; Dominguez, C.; Norman, M. H.; Harmange, J.-C.; Dussault, I.;
Kim, T.-S. J. Med. Chem. 2008, 51, 3688. (b) Peace, S.; Philp, J.;
Brooks, C.; Piercy, V.; Moores, K.; Smethurst, C.; Watson, S.;
Gaines, S.; Zippoli, M.; Mookherjee, C.; Ife, R. Bioorg. Med. Chem.
Lett. 2010, 20, 3961.
(3) (a) Che, Y. L.; Braselton, J.; Forman, J.; Gallaschun, R. J.;
Mansbach, R.; Schmidt, A. W.; Seeger, T. F.; Sprouse, J. S.;
Tingley, F. D. III; Winston, E.; Schulz, D. W. J. Med. Chem. 2008,
51, 1377. (b) Voisin, A. S.; Bouillon, A.; Lancelot, J.-C.; Lesnard,
A.; Rault, S. Tetrahedron 2006, 62, 6000. Exceptionally, substitu-
tion reaction of 2,5-dinitrofuran and 3-hydroxypyridine was
reported: (c) Gavade, S.; Padiya, K.; Bajare, S.; Balaskar, R.;
Mane, D. J. Heterocycl. Chem. 2011, 48, 458. Reaction of 2-
chloro-1,3-oxazolyl compound and 3-hydroxypyridine: (d) Oka,
Y.; Yabuuchi, T.; Fujii, Y.; Ohtake, H.; Wakahara, S.; Matsumoto,
K.; Endo, M.; Tamura, Y.; Sekiguchi, Y. Bioorg. Med. Chem. Lett.
2012, 22, 7534.
(4) Copper-catalyzed reaction: (a) Reddy, K. U. M.; Kumar, K. S.;
Reddy, A. P. Asian J. Chem. 2014, 26, 4747. (b) Maiti, D.;
Buchwald, S. L. J. Org. Chem. 2010, 75, 1791. (c) Altman, R. A.;
Buchwald, S. L. Org. Lett. 2007, 9, 643. (d) Barker, D. J.; Summers,
L. A. J. Heterocycl. Chem. 1983, 20, 1411. Reaction of 2-bro-
mopyridine and water: (e) Tlili, A.; Monnier, F.; Taillefer, M.
Chem. Eur. J. 2010, 16, 12299. Cobalt-catalyzed reaction:
(f) Kundu, D.; Tripathy, M.; Maity, P.; Ranu, B. C. Chem. Eur. J.
2015, 21, 8727. Palladium-catalyzed reaction: (g) Zhang, T.;
Tudge, M. T. Tetrahedron Lett. 2015, 56, 2329. (h) Platon, M.; Cui,
L.; Mom, S.; Richard, P.; Saeys, M.; Hierso, J.-C. Adv. Synth. Catal.
2011, 353, 3403.
(5) (a) Rodrigues, N.; Boiaryna, L.; Vercouillie, J.; Guilloteau, D.;
Suzenet, F.; Buron, F.; Routier, S. Eur. J. Org. Chem. 2016, 5024.
(b) Londregan, A. T.; Jennings, S.; Wei, L. Org. Lett. 2011, 13,
1840.
(6) (a) Wacharasindhu, S.; Bardhan, S.; Wan, Z.-K.; Tabei, K.;
Mansour, T. S. J. Am. Chem. Soc. 2009, 131, 4174. (b) Bardhan, S.;
Wacharasindhu, S.; Wan, Z.-K.; Mansour, T. S. Org. Lett. 2009,
11, 2511. (c) Bardhan, S.; Tabei, K.; Wan, Z.-K.; Mansour, T. S.
Tetrahedron Lett. 2009, 50, 5733.
(7) (a) Arisawa, M.; Tazawa, T.; Tanii, S.; Horiuchi, K.; Yamaguchi, M.
J. Org. Chem. 2017, 82, 804. (b) Li, G.; Arisawa, M.; Yamaguchi,
M. Chem. Commun. 2014, 50, 4328. (c) Arisawa, M.; Tanii, S.;
Tazawa, T.; Yamaguchi, M. Chem. Commun. 2016, 52, 11390.
(8) It was reported that diphenyl ether can be synthesized by dehy-
dration of phenol, and heteroaryl aryl ethers and di(heteroaryl)
ethers can, in principle, be obtained from phenols without
using a base: (a) Zsolczai, D.; Németh, J.; Hell, Z. Tetrahedron
Lett. 2015, 56, 6389. (b) Buske, G. R.; Garces, J. M.; Dianis, W. P.
US 5288922, 1994. (c) Karuppannasamy, S.; Narayanan, K.;
Pillai, C. N. J. Catal. 1980, 66, 281.
(9) General Procedure for the Synthesis of Unsymmetric Di(het-
eroaryl) Ethers
In a two-necked flask equipped with a magnetic stirrer bar and
a reflux condenser were placed RhH(PPh3)4 (5 mol%, 14.4 mg),
dppBz (10 mol%, 11.1 mg), 2-phenoxy-1,3-benzothiazole (2a,
0.75 mmol, 170.5 mg), and pyridine-3-yl benzoate (9, 0.25
mmol, 49.8 mg) in chlorobenzene (0.5 mL) under an argon
atmosphere, and the solution was stirred and heated at reflux
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–G

G
S. Tanii et al.
Letter
Synlett
for 5 h. The solvent was removed under reduced pressure, and
the residue was purified by flush column chromatography on
silica gel giving 2-(3-pyridinyloxy)-1,3-benzothiazole (10, 69%,
39.4 mg) and phenylbenzoate (11, 70%, 34.7 mg) with recovery
of 2a (73%, 124.4 mg) and 9 (25%, 12.5 mg).
1428, 1256, 1235, 1021 cm–1. MS (EI): m/z (%) = 228 (100) [M+],
200 (50) [M+ – CN]. HRMS: m/z calcd for C12H8N2OS: 228.0357;
found: 228.0343.
(10) You, F.; Twieg, R. J. Tetrahedron Lett. 1999, 40, 8759.
(11) Crystallographic data including structure factors have been
deposited with the Cambridge Crystallographic Data Centre as
supplementary publication number CCDC 1534272 for com-
pound 14u. The data can be obtained free of charge from The
Analytical Data of Compound 10
Colorless solid; mp 63.0–64.0 °C (hexane). 1H NMR (400 MHz,
CDCl3): δ = 7.31 (1 H, td, J = 1.2, 8.0 Hz), 7.41 (2 H, t, J = 8.0 Hz),
7.72 (2 H, m), 7.82 (1 H, ddd, J = 1.6, 3.2, 8.4 Hz), 8.56 (1 H, dd,
J = 1.2, 4.8 Hz), 8.73 (1 H, d, J = 2.8 Hz). 13C NMR (100 MHz,
CDCl3): δ = 121.4, 121.9, 124.2, 124.5, 126.4, 128.0, 132.3, 142.7,
147.0, 148.7, 151.2, 170.8. IR (KBr) 3060, 1527, 1475, 1440,
Cambridge
Crystallographic
Data
Centre
via
www.ccdc.cam.ac.uk/getstructures.
(12) For a related observation see: Sawatlon, B.; Wititsuwannakul,
T.; Tantirungrotechai, Y.; Surawatanawong, P. Dalton Trans.
2014, 43, 18123.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–G