Construction of Multifunctionalized Azopyrazoles by Silver- Catalyzed Cascade Reaction of Diazo Compounds

Article abstract of DOI:10.1002/adsc.201500197

A variety of multisubstituted azopyrazoles were synthesized in good yield from an efficient one-pot silver trifluoromethanesulfonate (AgOTf)-catalyzed cascade reaction of α-diazo-β-keto esters with two arylhydrazines or two arylhydrazine hydrochlorides. This cascade reaction included pyrazolone formation, NH insertion, and oxidation. For the synthesis of more diverse azopyrazoles bearing two different aromatic rings, the silver(I)-catalyzed cascade reaction of 4-diazopyrazol-3-one with arylhydrazine hydrochlorides was also developed. The advantages of these methodologies are easy handling, mild reaction conditions, and an effective and non-toxic catalyst usage.

Full text of DOI:10.1002/adsc.201500197

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DOI: 10.1002/adsc.201500197
Very Important Publication
Construction of Multifunctionalized Azopyrazoles by Silver-
Catalyzed Cascade Reaction of Diazo Compounds
Rameshwar Prasad Pandita and Yong Rok Leea,*
a
School of Chemical Engineering, Yeungnam University, 214-1 Dae-Dong, Gyeongsan 712-749, Republic of Korea
Fax: +(82)-53-810-4631; phone: (+82)-53-810-2529; e-mail: yrlee@yu.ac.kr
Received: February 25, 2015; Revised: April 23, 2015; Published online: July 14, 2015
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201500197.
Abstract: A variety of multisubstituted azopyrazoles reaction of 4-diazopyrazol-3-one with arylhydrazine
were synthesized in good yield from an efficient one- hydrochlorides was also developed. The advantages
pot silver trifluoromethanesulfonate (AgOTf)-cata- of these methodologies are easy handling, mild reac-
lyzed cascade reaction of a-diazo-b-keto esters with tion conditions, and an effective and non-toxic cata-
two arylhydrazines or two arylhydrazine hydrochlor- lyst usage.
ides. This cascade reaction included pyrazolone for-
À
mation, N H insertion, and oxidation. For the syn-
thesis of more diverse azopyrazoles bearing two dif- Keywords: activation; coupling; ethers; multifunc-
ferent aromatic rings, the silver(I)-catalyzed cascade tionalized azopyrazoles; palladium; radicals
Introduction
medicines.[9] Among these, rimonabant (1), celecoxib
(2), and fipronil (3) have been commercialized as
Pyrazoles belong to one of the most important classes medicines or insecticides (Figure 1). Owing to their
of heteroaromatic compounds and have been report- importance and usefulness, a number of methods for
ed to possess a wide range of biological properties, the preparation of pyrazoles have been developed.[10]
such as anti-inflammatory,[1] antibacterial,[2] analge-
Pyrazoles bearing an azo group (azopyrazoles) are
sic,[3] antifungal,[4] antipyretic,[5] plant growth regulat- also found as the core structure in many food color-
ing properties,[6] protein kinase inhibitors,[7] and anti- ings,[11] dyestuffs,[12] and bioactive molecules
viral[8] activities. They have been also used as an im- (Figure 2).[13] They exhibited a broad spectrum of bio-
portant building blocks and structural motifs in the logical properties such as antibacterial,[14] antifungal[15]
synthesis of natural products, agrochemicals, and and HIV-1 inhibitory activities.[16] In addition to pyra-
zoles, several methods for the synthesis of azopyra-
Figure 1. Selected examples of commercialized materials
bearing a pyrazole scaffold.
Figure 2. Examples of food coloring and bioactive materials
bearing azopyrazole skeleton.
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Rameshwar Prasad Pandit and Yong Rok Lee
Scheme 1. Silver-catalyzed synthesis of diverse azopyrazoles.
zoles have been reported.[17] Most of these methods
involve harsh operations and multistep procedures
through reactions of aryldiazonium salts with b-keto
esters followed by pyrazole formation using hydra-
zines.[17]
Table 1. Reaction of diazodicarbonyl (7a) and phenylhydra-
zine (8a) under different metal catalysts and conditions.[a]
Although several approaches to the synthesis of
azopyrazoles have been reported, they are limited by
harsh reaction conditions, low yields, raw material
availability, and required multiple synthetic steps. Ac-
cordingly, there is a demand for a facile one-step ap-
proach for the synthesis of azopyrazoles. To the best
of the authorsꢁ knowledge, there is a paucity of re-
ports on one-step procedures for the synthesis of azo-
pyrazole derivatives from readily available starting
materials, which prompted us to develop a novel one-
pot reaction relying on the characteristic reactivity of
diazo compounds.[18] The present study has estab-
lished the decomposition of diazo compounds as an
effective means of synthesizing various heterocycles
and new molecules.[19] As a part of an ongoing study
in this area, this paper reports a silver(I)-catalyzed re-
action for the synthesis of a variety of multifunction-
[a]
The reaction was carried out with 7a (0.5 mmol) and 8a
(1.2 mmol).
Isolated yields were calculated from 7a.
[b]
À
alized azopyrazoles by pyrazole formation, N H in-
sertion, and oxidation through a cascade reaction
from readily available diazodicarbonyl compounds
and two arylhydrazines (Scheme 1).
With other catalysts, such as Cu(OTf)2 (20 mol%),
Ru(PPh3)3Cl2 (5 mol%), and Rh2(OAc)4 (2 mol%),
the yield of 9a was not improved (entries 12–14). The
structure of 9a was determined by analysis of its spec-
tral data. The 1H NMR spectrum of 9a showed
Results and Discussion
To approach azopyrazoles, our investigation first com- a methyl signal on the pyrazole ring as a singlet at d=
menced with the reaction of ethyl 2-diazo-3-oxobuta- 2.35 ppm and a hydroxy peak at 13.57 ppm as a singlet.
noate[18j] (7a, 0.5 mmol) and phenylhydrazine (8a, The structure of 9a was further confirmed by X-ray
1.2 mmol) with different catalysts and solvents crystallographic analysis of the closely related com-
(Table 1). Treatment of 7a with 8a in the presence of pound 9m[20] (see the Supporting Information for de-
20 mol% of Ag2O, AgNO3, AgOAc or AgSbF6, as tails).
catalysts at 708C for 24 h in acetonitrile provided the
Further reactions of a-diazo-b-keto esters 7b–7f
product 9a in 17, 42, 45, and 52% yields, respectively with alkyl substituents (R), such as ethyl, n-propyl,
(entries 1–4). Using 20 mol% of AgOTf at 708C for isopropyl, n-pentyl, and benzyl groups with phenylhy-
24 h in acetonitrile, 9a was produced in 72% yield drazine (8a) for 24 h afforded the desired products
(entry 5). Decreasing (10 mol%) or increasing 9b–9f in 88–95% yield. In addition, reactions of a-
(40 mol%) the AgOTf loading did not improve the diazo-b-keto esters 7g–7j with phenyl or aryl rings
yield (entries 6 and 7). With other non-polar and containing electron-donating or electron-withdrawing
polar solvents, such as dichloroethane, toluene, diox- groups afforded the desired products 9g–9j in 85–93%
ane, and ethanol, the yield of 9a was not increased yield. To demonstrate the versatility of this methodol-
(entries 8–11).
ogy, reactions with substituted phenylhydrazine hy-
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Construction of Multifunctionalized Azopyrazoles by Silver-Catalyzed Cascade
Table 2. Formation of azopyrazoles 9b–9q from diazo compounds 7a–7j and arylhydrazines 8a–8h.
drochlorides were examined further. For example, the lead to the formation of other azopyrazole derivatives
reaction of 7a with 2,4-dimethyl-, 2,5-dimethyl-, 2- bearing two different aromatic rings (Table 3). The re-
ethyl-, 4-isopropyl-, or 4-methoxyphenylhydrazine hy- actions of 10 with 2-ethyl-, 4-isopropyl- or 4-methoxy-
drochloride bearing electron-donating groups on the phenylhydrazine hydrochloride bearing an electron-
benzene ring afforded the expected products 9k–9o in donating group on the benzene ring provided the ex-
87–94% yield, and that with 4-fluoro- or 4-chlorophe- pected products 11a–11c in 91, 93, and 80% yield, re-
nylhydrazine hydrochloride bearing an electron-with- spectively. A combination of 10 with 4-fluoro-, or 4-
drawing group provided products 9p (80%) and 9q chlorophenylhydrazine hydrochloride bearing an elec-
(77%) in slightly lower yields (Table 2).
tron-withdrawing group afforded products 11d (95%)
Considering the general applicability of the reac- and 11e (95%), whereas that with 1-naphthalenylhy-
tion using a-diazo-b-keto esters 7a–7i as starting ma- drazine hydrochloride gave the desired product 11f
terials, we examined the possibility of using 4-diazo- (85%).
pyrazol-3-one as a starting material, which should
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Table 3. Formation of azopyrazoles (11a–11 f) from reaction of 4-diazopyrazol-3-one (10) and arylhydrazines (8d–8i).
Scheme 2. Proposed mechanism for the formation of 9a.
The mechanism for the formation of the observed Conclusions
product 9a can be explained, as shown Scheme 2. The
diazo compound 7a first reacts with phenylhydrazine In summary, diverse and multifunctionalized azopyra-
(8a) to give 4-diazopyrazol-3-one 10. To gain evidence zole derivatives were synthesized in a one-pot proce-
of the formation of intermediate 10 in the absence of dure by the silver(I)-catalyzed reaction of a-diazo-b-
Ag(I) catalyst, we carried out the reaction of 7a and keto esters with arylhydrazines or arylhydrazine hy-
8a in acetonitrile at 708C for 24 h without any cata- drochlorides. This protocol includes cascade pyrazo-
À
lyst. In this case, compound 10 was produced in 61% lone formation, N H insertion, and oxidation. In ad-
yield, together with recovery of the starting material dition, Ag(I)-catalyzed reactions of 4-diazopyrazol-3-
7a (20%). The decomposition of diazo intermediate one with arylhydrazine hydrochlorides for the synthe-
10 is initiated by the Ag(I) catalyst to give a metal sis of various other azopyrazoles bearing two different
carbenoid 12 via the loss of N2.[21] The nucleophilic aromatic rings are described. This cascade reaction
attack of phenylhydrazine (8a) to an electrophic silver allows the synthesis of highly functionalized azopyra-
carbenoid 12 gives another ylide intermediate 13, zole derivatives, which may find a wide range of ap-
which undergoes the removal of a catalyst and proton plications in the synthesis of natural products, phar-
transfer, leading to the formation of intermediate 14 maceuticals or coloring industry.
À
as an N H insertion product. The oxidation of 14 in
the presence Ag(I) catalyst finally leads to 9a.
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Construction of Multifunctionalized Azopyrazoles by Silver-Catalyzed Cascade
(300 MHz, CDCl3): d=13.59 (1H, s, OH), 7.95 (2H, d, J=
8.1 Hz), 7.43–7.39 (6H, m), 7.21–7.16 (2H, m), 2.71 (2H, t,
J=7.8 Hz), 1.90–1.78 (2H, m), 1.05 (3H, t, J=7.2 Hz);
13C NMR (75 MHz, CDCl3): d=157.8, 151.9, 141.1, 138.0,
129.6, 129.6, 128.8, 128.8, 128.1, 125.7, 125.1, 118.6, 118.6,
115.7 115.7, 28.6, 20.9, 14.0; IR (KBr): n=2950, 1656, 1551,
1490, 1152, 1260, 1154, 1056, 752 cmÀ1; HR-MS (EI): m/z=
306.1479 (M+), calcd. for C18H18N4O: 306.1481.
Experimental Section
General Remarks
All experiments were carried out under a nitrogen atmos-
phere. Merck precoated silica gel plates (Art. 5554) with flu-
orescent indicator were used for analytical TLC. Flash
column chromatography was performed using silica gel 9385
1
(Merck). H NMR and 13C NMR spectra were recorded on
3-Isopropyl-1-phenyl-4-(phenyldiazenyl)-1H-pyrazol-5-ol
(9d): Prepared from methyl 2-diazo-4-methyl-3-oxopenta-
noate 7d (85 mg, 0.5 mmol) with phenylhydrazine 8a
(130 mg, 1.2 mmol) according to general procedure in 24 h
as an orange solid; yield: 140 mg (92%); mp 145–1478C;
1H NMR (300 MHz, CDCl3): d=13.61 (1H, s, OH), 7.98
(2H, d, J=8.1 Hz), 7.50–7.39 (6H, m), 7.21–7.14 (2H, m),
3.23–3.13 (1H, m), 1.43 (6H, d, J=6.9 Hz); 13C NMR
(75 MHz, CDCl3): d=157.9, 155.9, 141.2, 138.1, 129.6, 129.6,
128.8, 128.8, 127.4, 125.5, 124.9, 118.5, 118.5, 115.6 115.6,
27.6, 20.7, 20.7; IR (KBr): n=2963, 1656, 1548, 1486, 1344,
1259, 1150, 1009, 740 cmÀ1; HR-MS (EI): m/z=306.1480
(M+), calcd. for C18H18N4O: 306.1481.
a Varian VNS (300 and 75 MHz, respectively) spectrometer
in CDCl3 using d=7.24 and 77.23 ppm as solvent chemical
shifts. Multiplicities are abbreviated as follows; s=singlet,
d=doublet, t=triplet, q=quartet, m=multiplet and dd=
doublet of doublets. IR spectra were recorded on an FT-IR
(BIO-RAD), and HR-MS was carried out at the Korean
Basic Science Institute. Structural measurements for the
complexes were performed at Jeonju center of Korea Basic
Science Institute.
General Experimental Procedure for the Synthesis of
Azopyrazoles and Characterization Data for All New
Compounds (9a–9q)
3-Pentyl-1-phenyl-4-(phenyldiazenyl)-1H-pyrazol-5-ol
(9e): Prepared from ethyl 2-diazo-3-oxooctanoate 7e
(106 mg, 0.5 mmol) with phenylhydrazine 8a (130 mg,
1.2 mmol) according to general procedure in 24 h as an
To a solution of a-diazo b-keto ester (0.5 mmol) and arylhy-
drazine or arylhydrazine hydrochloride (1.2 mmol) in aceto-
nitrile (5.0 mL) was added AgOTf (26 mg, 20 mol%) and
the mixture heated at 708C under a nitrogen atmosphere
until completion of reaction as indicated by TLC. The vola-
tiles were removed under vacuum and the residue was puri-
fied by silica gel column chromatography (hexane: ethyl
acetate=30:1) to give desired product as solid (see the Sup-
porting Information for details).
1
orange solid; yield: 158 mg (95%); mp 95–978C; H NMR
(300 MHz, CDCl3): d=13.61 (1H, s, OH), 7.95 (2H, d, J=
8.1 Hz), 7.43–7.39 (6H, m), 7.21–7.16 (2H, m), 2.72 (2H, t,
J=7.5 Hz), 1.83–1.78 (2H, m), 1.41–1.36 (4H, m), 0.92 (3H,
t, J=6.9 Hz); 13C NMR (75 MHz, CDCl3): d=157.8, 152.1,
141.1, 138.0, 129.6, 129.6, 128.8, 128.8, 128.1, 125.6, 125.0,
118.6, 118.6, 115.7 115.7, 31.5, 27.1, 26.6, 22.3, 13.9; IR
(KBr): n=2927, 1654, 1550, 1485, 1351, 1254, 1152, 1064,
745 cmÀ1; HR-MS (EI): m/z=334.1792 (M+), calcd. for
C20H22N4O: 334.1794.
3-Benzyl-1-phenyl-4-(phenyldiazenyl)-1H-pyrazol-5-ol
(9f): Prepared from methyl 2-diazo-3-oxo-4-phenylbuta-
noate 7f (109 mg, 0.5 mmol) with phenylhydrazine 8a
(130 mg, 1.2 mmol) according to general procedure in 24 h
as an orange solid; yield: 159 mg (90%); mp 150–1528C;
1H NMR (300 MHz, CDCl3): d=13.44 (1H, s, OH), 7.87
(2H, d, J=7.8 Hz), 7.37–7.21 (10H, m), 7.14–7.07 (3H, m),
3.98 (2H, s); 13C NMR (75 MHz, CDCl3): d=157.7, 150.2,
141.0, 138.0, 137.0, 129.6, 129.6, 129.1, 129.1, 128.8, 128.8,
128.5, 128.5, 127.5, 126.7, 125.8, 125.1, 118.6, 118.6, 115.8,
115.8; 33.2 IR (KBr): n=3054, 1661, 1546, 1494, 1339, 1260,
1143, 1055, 749 cmÀ1; HR-MS (EI): m/z=354.1478 (M+),
calcd. for C22H18N4O: 354.1481.
3-Phenyl-1-phenyl-4-(phenyldiazenyl)-1H-pyrazol-5-ol
(9g): Prepared from ethyl 2-diazo-3-oxo-3-phenylpropanoate
7g (109 mg, 0.5 mmol) with phenylhydrazine 8a (130 mg,
1.2 mmol) according to general procedure in 24 h as an
orange red solid; yield: 153 mg (90%); mp 157–1598C;
1H NMR (300 MHz, CDCl3): d=13.92 (1H, s, OH), 8.16–
8.13 (2H, m), 8.00–7.97 (2H, m), 7.43–7.31 (9H, m), 7.17–
7.13 (2H, m); 13C NMR (75 MHz, CDCl3): d=158.0, 146.4,
141.1, 138.0, 130.3, 129.7, 129.7, 129.7, 128.9, 128.9, 128.5,
128.5, 127.4, 127.4, 127.2, 126.0, 125.4, 118.8, 118.8, 116.0,
116.0; IR (KBr): n=3051, 1655, 1486, 1486, 1330, 1262,
1160, 955, 748 cmÀ1; HR-MS (EI): m/z=340.1323 (M+),
calcd. for C21H16N4O: 340.1324.
3-Methyl-1-phenyl-4-(phenyldiazenyl)-1H-pyrazol-5-ol
(9a): Prepared from ethyl 2-diazo-3-oxobutanoate 7a
(78 mg, 0.5 mmol) with phenylhydrazine (8a, 130 mg,
1.2 mmol) according to general procedure in 24 h as an
1
orange solid; yield: 100 mg (72%); mp 130–1328C; H NMR
(300 MHz, CDCl3): d=13.57 (1H, s, OH), 7.94 (2H, d, J=
8.4 Hz), 7.45–7.38 (6H, m), 7.18 (2H, t, J=7.5 Hz), 2.35
(3H, s); 13C NMR (75 MHz, CDCl3): d=157.7, 148.5, 141.1,
138.0, 129.6, 129.6, 129.0, 128.9, 125.7, 125.1, 121.7, 118.5,
118.5, 115.8, 115.8, 11.7; IR (KBr): n=1657, 1555, 1493,
1342, 1263, 1157, 751 cmÀ1; HR-MS (EI) m/z=278.1166
(M+), calcd. for C16H14N4O: 278.1168.
3-Ethyl-1-phenyl-4-(phenyldiazenyl)-1H-pyrazol-5-ol (9b):
Prepared from ethyl 2-diazo-3-oxopentanoate 7b (85 mg,
0.5 mmol) with phenylhydrazine 8a (130 mg, 1.2 mmol) ac-
cording to general procedure in 24 h as an orange solid;
yield: 128 mg (88%); mp 109–1118C; 1H NMR (300 MHz,
CDCl3): d=13.57 (1H, s, OH), 7.95 (2H, d, J=7.8 Hz),
7.43–7.40 (6H, m), 7.21–7.16 (2H, m), 2.76 (2H, q, J=
7.5 Hz), 1.37 (3H, t, J=7.5 Hz); 13C NMR (75 MHz,
CDCl3): d=157.9, 152.9, 141.1, 138.0, 129.6, 129.6, 128.8,
128.8, 127.9, 125.7, 125.1, 118.6, 118.6, 115.7, 115.7, 20.2,
11.7; IR (KBr): n=2967, 1656, 1550, 1488, 1342, 1261, 1153,
1049, 747 cmÀ1; HR-MS (EI): m/z=292.1322 (M+), calcd.
for C17H16N4O: 292.1324.
3-Propyl-1-phenyl-4-(phenyldiazenyl)-1H-pyrazol-5-ol
(9c): Prepared from ethyl 2-diazo-3-oxohexanoate 7c
(92 mg, 0.5 mmol) with phenylhydrazine 8a (130 mg,
1.2 mmol) according to general procedure in 24 h as an
1
orange solid; yield: 139 mg (91%); mp 120–1228C; H NMR
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1-Phenyl-4-(phenyldiazenyl)-3-(p-tolyl)-1H-pyrazol-5-ol
(9h): Prepared from methyl 2-diazo-3-oxo-3-(p-tolyl)propa-
noate 7h (109 mg, 0.5 mmol) with phenylhydrazine 8a
(130 mg, 1.2 mmol) according to general procedure in 24 h
as a red solid; yield: 177 mg (92%); mp 150–1528C;
1H NMR (300 MHz, CDCl3): d=13.86 (1H, s, OH), 8.03
(2H, d, J=8.1 Hz), 7.97 (2H, d, J=7.8 Hz), 7.38–7.32 (6H,
m), 7.20–7.11 (4H, m), 2.31 (3H, s); 13C NMR (75 MHz,
CDCl3): d=158.0, 146.5, 141.1, 139.8, 138.0, 129.6, 129.6,
129.2, 129.2, 128.8, 128.8, 127.5, 127.4, 127.3, 127.3, 125.8,
125.2, 118.7, 118.7, 115.9, 115.9, 21.4; IR (KBr): n=3050,
1661, 1480, 1484, 1332, 1266, 1167, 957 cmÀ1; HR-MS (EI):
m/z=354.1482 (M+), calcd. for C22H18N4O: 354.1481.
7.05 (2H, m), 6.90 (1H, d, J=7.5 Hz), 2.37 (6H, s), 2.32
(6H, s), 2.25 (3H, s); 13C NMR (75 MHz, CDCl3): d=158.1,
147.9, 139.0, 137.3, 136.3, 135.3, 132.0, 130.8, 130.8, 129.3,
128.3, 127.1, 126.3, 122.3, 114.7, 21.2, 20.7, 17.9, 16.2, 11.8;
IR (KBr): n=1646, 1565, 1451, 1270, 1139, 1048, 791 cmÀ1
;
HR-MS (EI): m/z=334.1792 (M+), calcd. for C20H22N4O:
334.1794.
1-(2-Ethylphenyl)-4-[(2-ethylphenyl)diazenyl]-3-methyl-
1H-pyrazol-5-ol (9m): Prepared from ethyl 2-diazo-3-oxobu-
tanoate 7a (78 mg, 0.5 mmol) with 2-ethylphenylhydrazine
hydrochloride 8d (206 mg, 1.2 mmol) according to general
procedure in 24 h as an orange solid; yield: 150 mg (90%);
1
mp 90–928C; H NMR (300 MHz, CDCl3): d=13.79 (1H, s,
3-(4-Methoxyphenyl)-1-phenyl-4-(phenyldiazenyl)-1H-pyr-
azol-5-ol (9i): Prepared from methyl 2-diazo-3-(4-methoxy-
phenyl)-3-oxopropanoate 7i (117 mg, 0.5 mmol) with phe-
nylhydrazine 8a (130 mg, 1.2 mmol) according to general
procedure in 24 h as a red solid; yield: 172 mg (93%); mp
172–1748C; 1H NMR (300 MHz, CDCl3): d=14.02 (1H, s,
OH), 8.23 (2H, d, J=8.4 Hz), 8.09 (2H, d, J=8.1 Hz), 7.50–
7.48 (6H, m), 7.28–7.24 (2H, m); 7.05 (2H, d, J=8.4 Hz);
3.910 (3H, s); 13C NMR (75 MHz, CDCl3): d=160.9, 158.0,
146.3, 141.1, 138.0, 129.7, 129.7, 128.8, 128.8, 128.8, 128.8,
127.4, 125.9, 125.3, 122.9, 118.8, 118.8, 115.9, 115.9, 114.0,
114.0, 55.3; IR (KBr): n=3048,1654, 1544, 1485, 1336, 1253,
1161, 1027, 957, 744 cmÀ1; HR-MS (EI): m/z=370.1430
(M+), calcd. for C22H18N4O2: 370.1430.
OH), 7.73 (1H, d, J=8.0 Hz), 7.26–7.12 (6H, m), 7.08–7.03
(1H, m), 2.69–2.55 (4H, m), 2.28 (3H, s), 1.21 (3H, t, J=
7.5 Hz), 1.10 (3H, t, J=7.5 Hz); 13C NMR (75 MHz,
CDCl3): d=158.4, 147.9, 141.3, 138.6, 134.9, 131.2, 129.2,
129.0, 128.9, 128.3, 127.3, 127.3, 126.5, 125.6, 114.5, 24.6,
23.5, 14.3, 13.7, 11.7; IR (KBr): n=2966, 1648, 1548, 1454,
1339,1255, 1162, 1047, 751 cmÀ1
; HR-MS (EI): m/z=
334.1791 (M+), calcd. for C20H22N4O: 334.1794.
1-(4-Isopropylphenyl)-4-[(4-isopropylphenyl)diazenyl]-3-
methyl-1H-pyrazol-5-ol (9n): Prepared from ethyl 2-diazo-3-
oxobutanoate 7a (78 mg, 0.5 mmol) with 4-isopropylphenyl-
hydrazine hydrochloride 8e (223 mg, 1.2 mmol) according to
general procedure in 24 h as an orange solid; yield: 170 mg
1
(94%); mp 80–828C; H NMR (300 MHz, CDCl3): d=13.52
3-(4-Nitrophenyl)-1-phenyl-4-(phenyldiazenyl)-1H-pyra-
zol-5-ol (9j): Prepared from methyl 2-diazo-3-(4-nitrophen-
yl)-3-oxopropanoate 7j (124 mg, 0.5 mmol) with phenylhy-
drazine 8a (120 mg, 1.2 mmol) according to general proce-
dure in 24 h as a yellow solid; yield: 163 mg (85%); mp 240–
(1H, s, OH), 7.75 (2H, d, J=8.7 Hz), 7.26–7.14 (6H, m),
2.86–2.77 (2H, m), 2.23 (3H, s), 1.17 (6H, d, J=6.9 Hz),
1.15 (6H, d, J=6.6 Hz); 13C NMR (75 MHz, CDCl3): d=
157.5, 148.1, 146.7, 145.6, 139.0, 135.8, 127.9, 127.5, 127.5,
126.7, 126.7, 118.6, 118.6, 115.7, 115.7, 33.6, 33.6, 23.9, 23.9,
23.8, 23.8, 11.6; IR (KBr): n=2951, 1650, 1538, 1345, 1265,
1152, 1046, 816 cmÀ1; HR-MS (EI): m/z=362.2107 (M+),
calcd. for C22H26N4O: 362.2107.
1
2428C; H NMR (300 MHz, CDCl3): d=14.11 (1H, s, OH),
8.43 (2H, d, J=9.0 Hz), 8.34 (2H, d, J=8.7 Hz), 8.04 (2H,
d, J=7.8 Hz), 7.48–7.44 (6H, m), 7.28 (2H, d, J=6.9 Hz);
13C NMR (150 MHz, CDCl3): d=158.0, 148.1, 143.9, 140.7,
137.7, 136.4, 129.9, 129.9, 129.0, 129.0, 127.8, 127.8, 126.8,
126.6, 126.0, 123.8, 123.8, 119.0, 119.0, 116.3, 116.3; IR
(KBr): n=3045,1652, 1545, 1487, 1335, 1250, 1160, 1022,
955, 741 cmÀ1; HR-MS (EI): m/z=385.1173 (M+), calcd. for
C21H15N5O3: 385.1175.
1-(4-Methoxyphenyl)-4-[(4-methoxyphenyl)diazenyl]-3-
methyl-1H-pyrazol-5-ol (9o): Prepared from ethyl 2-diazo-3-
oxobutanoate 7a (78 mg, 0.5 mmol) with 4-methoxyphenyl-
hydrazine hydrochloride 8f (208 mg, 1.2 mmol) according to
general procedure in 24 h as an orange red solid; yield:
1
147 mg (87%); mp 127–1298C; H NMR (300 MHz, CDCl3):
1-(2,4-Dimethylphenyl)-4-[(2,4-dimethylphenyl)diazenyl]-
3-methyl-1H-pyrazol-5-ol (9k): Prepared from ethyl 2-diazo-
3-oxobutanoate 7a (78 mg, 0.5 mmol) with 2,4-dimethylphe-
nylhydrazine hydrochloride 8b (206 mg, 1.2 mmol) according
to general procedure in 24 h as an orange solid; yield:
d=13.69 (1H, s, OH), 7.80 (2H, d, J=9.0 Hz), 7.35 (2H, d,
J=9.0 Hz), 6.94–6.90 (4H, m), 3.80 (6H, s), 2.32 (3H, s);
13C NMR (75 MHz, CDCl3): d=157.9, 157.4, 157.0, 148.0,
134.7, 131.5, 127.5, 120.3, 120.3, 117.1, 117.1, 114.9, 114.9,
114.0, 114.0, 55.5, 55.4, 11.7; IR (KBr): n=2950, 1545, 1490,
1101, 1030, 811, 525 cmÀ1; HR-MS (EI): m/z=338.1376
(M+), calcd. for C18H18N4O3: 338.1379.
1
150 mg (90%); mp 130–1328C; H NMR (300 MHz, CDCl3):
d=13.79 (1H, s, OH), 7.67 (1H, d, J=8.4 Hz), 7.19 (1H, d,
J=7.8 Hz), 7.09–7.04 (3H, m), 6.99 (1H, s), 2.34 (3H, s),
2.32 (9H, s), 2.24 (3H, s); 13C NMR (75 MHz, CDCl3): d=
158.3, 147.7, 138.3, 137.0, 135.3, 134.9, 133.0, 131.6, 131.6,
128.0, 128.0, 127.2, 126.6, 125.2, 114.4, 21.1, 20.9, 18.2, 16.6,
11.8; IR (KBr): n=2917, 1650, 1554, 1270, 1176, 1038,
797 cmÀ1; HR-MS (EI): m/z=334.1790 (M+), calcd. for
C20H22N4O: 334.1794.
1-(4-Fluorophenyl)-4-[(4-fluorophenyl)diazenyl]-3-
methyl-1H-pyrazol-5-ol (9p): Prepared from ethyl 2-diazo-3-
oxobutanoate 7a (78 mg, 0.5 mmol) with 4-fluorophenylhy-
drazine hydrochloride 8g (194 mg, 1.2 mmol) according to
general procedure in 24 h as an orange solid; yield: 125 mg
(80%); mp 192–1948C; 1H NMR (300 MHz, CDCl3): d=
13.53 (1H, s, OH), 7.89–7.86 (2H, m), 7.37–7.34 (2H, m),
7.16–7.04 (4H, m), 2.31 (3H, s); 13C NMR (75 MHz,
CDCl3): d=162.2, 161.6, 158.9, 157.4, 148.4, 137.3, 128.3,
120.2, 120.1, 117.2, 117.1, 116.7, 116.4, 115.7, 115.4, 11.7; IR
(KBr): n=1654, 1554, 1498, 1278, 1216, 1154, 820 cmÀ1; HR-
MS (EI): m/z=314.0977 (M+), calcd. for C16H12F2N4O:
314.0979.
1-(2,5-Dimethylphenyl)-4-[(2,5-dimethylphenyl)diazenyl]-
3-methyl-1H-pyrazol-5-ol (9l): Prepared from ethyl 2-diazo-
3-oxobutanoate 7a (78 mg, 0.5 mmol) with 2,5-dimethylphe-
nylhydrazine hydrochloride 8c (206 mg, 1.2 mmol) according
to general procedure in 24 h as an orange solid; yield:
1
151 mg (91%); mp 100–1028C; H NMR (300 MHz, CDCl3):
d=13.75 (1H, s, OH), 7.60 (1H, s), 7.18–7.14 (2H, m), 7.09–
2662
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FULL PAPERS
Construction of Multifunctionalized Azopyrazoles by Silver-Catalyzed Cascade
1-(4-Chlorophenyl)-4-[(4-chlorophenyl)diazenyl]-3-
(2H, d, J=8.1 Hz), 7.42–7.35 (4H, m), 7.17 (1H, t, J=
7.5 Hz), 6.93 (2H, d, J=9.0 Hz), 3.81 (3H, s), 2.34 (3H, s);
13C NMR (75 MHz, CDCl3): d=158.0, 148.3, 138.2, 134.7,
128.8, 128.8, 126.1, 125.0, 118.5, 118.5 117.2, 115.2, 114.9,
114.8, 114.3, 55.5, 11.7; IR (KBr) 1545, 1491, 1236, 1153,
1031, 814, 530 cmÀ1; HR-MS (EI): m/z=308.1271 (M+),
calcd. for C17H16N4O2: 308.1273.
4-[(4-Fluorophenyl)diazenyl]-3-methyl-1-phenyl-1H-pyra-
zol-5-ol (11d): Prepared from 4-diazo-5-methyl-2-phenyl-2,4-
dihydro-3H-pyrazol-3-one 10 (100 mg, 0.5 mmol) with 4-flu-
orophenylhydrazine hydrochloride 8g (97 mg, 0.6 mmol) ac-
cording to general procedure in 12 h as an orange solid;
yield: 140 mg (95%); mp 103–1058C; 1H NMR (300 MHz,
CDCl3): d=13.58 (1H, s, OH), 7.92 (2H, d, J=8.4 Hz),
7.42–7.35 (4H, m), 7.20–7.06 (3H, m), 2.33 (3H, s);
13C NMR (75 MHz, CDCl3): d=157.7, 148.4, 138.0, 137.4,
128.8, 128.8, 128.8, 128.5, 125.1, 118.5, 118.5, 117.2, 117.1,
116.7, 116.4, 11.7; IR (KBr): n=3054, 1653, 1549, 1496,
1214, 1155, 828, 762, 516 cmÀ1; HR-MS (EI): m/z=296.1074
(M+), calcd. for C16H13FN4O: 296.1073.
4-[(4-Chlorophenyl)diazenyl]-3-methyl-1-phenyl-1H-pyra-
zol-5-ol (11e): Prepared from 4-diazo-5-methyl-2-phenyl-2,4-
dihydro-3H-pyrazol-3-one 10 (200 mg, 1.0 mmol) with 4-
chlorophenylhydrazine hydrochloride 8h (107 mg, 0.6 mmol)
according to general procedure in 12 h as an orange solid;
yield: 100 mg (95%); mp 132–1348C; 1H NMR (300 MHz,
CDCl3): d=13.52 (1H, s, OH), 7.92 (2H, d, J=8.1 Hz),
7.42–7.30 (6H, m), 7.18 (1H, t, J=7.5 Hz), 2.32 (3H, s);
13C NMR (75 MHz, CDCl3): d=157.6, 148.4, 139.7, 137.9,
130.8, 129.7, 129.7, 129.0, 128.8, 128.8, 125.2, 118.4, 118.4,
116.8, 116.8, 11.7; IR (KBr): n=3062, 1654, 1553, 1490,
1263, 1089, 767 cmÀ1; HR-MS (EI): m/z=312.0776 (M+),
calcd. for C16H13ClN4O: 312.0778.
3-Methyl-4-(naphthalen-1-yldiazenyl)-1-phenyl-1H-pyra-
zol-5-ol (11f): Prepared from 4-diazo-5-methyl-2-phenyl-2,4-
dihydro-3H-pyrazol-3-one 10 (100 mg, 1.0 mmol) with 1-
naphthalenylhydrazine hydrochloride 8i (116 mg, 0.6 mmol)
according to general procedure in 12 h as an orange red
solid; yield: 140 mg (85%); mp 198–2008C; 1H NMR
(300 MHz, CDCl3): d=14.52 (1H, s, OH), 8.06 (1H, d, J=
8.1 Hz), 7.99–7.86 (4H, m), 7.70 (1H, d, J=8.1 Hz), 7.65–
7.41(5H, m), 7.24–7.18 (1H, m), 2.40 (3H, s); 13C NMR
(75 MHz, CDCl3): d=158.0, 148.5, 138.0, 136.0, 134.0, 129.9,
128.9, 128.9, 128.8, 127.0, 126.5, 126.0, 125.9, 125.2, 123.1,
119.3, 118.8, 118.8, 111.3, 11.8; IR (KBr): n=3060, 1652,
1558, 1497, 1258, 1161, 775 cmÀ1; HR-MS (EI): m/z=
328.1322 (M+), calcd. for C20H16N4O: 328.1324.
methyl-1H-pyrazol-5-ol (9q): Prepared from ethyl 2-diazo-3-
oxobutanoate 7a (78 mg, 0.5 mmol) with 4-chlorophenylhy-
drazine hydrochloride 8h (213 mg, 1.2 mmol) according to
general procedure in 24 h as an orange solid; yield: 233 mg
(77%); mp 217–2198C; 1H NMR (300 MHz, CDCl3): d=
13.48 (1H, s, OH), 7.89 (2H, d, J=9.0 Hz), 7.37–7.35 (6H,
m), 2.33 (3H, s); 13C NMR (150 MHz, CDCl3 +DMSO-d6):
d=157.4, 148.6, 139.5, 136.4, 130.9, 130.1, 129.6, 129.6, 128.8,
128.8, 128.5, 119.4, 119.4, 116.8, 116.8, 11.6; IR (KBr): n=
1650, 1555, 1490, 1275, 1214, 1157, 825 cmÀ1; HR-MS (EI):
m/z=346.0391 (M+), calcd. for C16H12Cl2N4O: 346.0388.
General Experimental Procedure for the Synthesis of
Azopyrazoles and Characterization Data for New
Compounds (11a–11f)
To a solution of 4-diazo-5-methyl-2-phenyl-2,4-dihydro-3H-
pyrazol-3-one 10 (100 mg, 0.5 mmol) and arylhydrazine hy-
drochloride (0.6 mmol) in acetonitrile (5.0 mL) was added
AgOTf (26 mg, 20 mol%) and the mixture heated at 708C
under a nitrogen atmosphere until completion of reaction as
indicated by TLC. The volatiles were removed under
vacuum and the residue was purified by silica gel column
chromatography (hexane: ethylacetate=30:1) to give de-
sired products as solid.
4-[(2-Ethylphenyl)diazenyl]-3-methyl-1-phenyl-1H-pyra-
zol-5-ol (11a): Prepared from 4-diazo-5-methyl-2-phenyl-2,4-
dihydro-3H-pyrazol-3-one 10 (100 mg, 0.5 mmol) with 2-eth-
ylphenylhydrazine hydrochloride 8d (103 mg, 0.6 mmol) ac-
cording to general procedure in 12 h as an orange solid;
yield: 139 mg (91%); mp 107–1098C; 1H NMR (300 MHz,
CDCl3): d=13.77 (1H, s, OH), 7.87 (2H, d, J=7.8 Hz), 7.72
(1H, d, J=8.4 Hz), 7.34 (2H, t, J=7.5 Hz), 7.22 (1H, d, J=
7.2 Hz), 7.17–7.05 (3H, m), 2.70 (2H, q, J=7.2 Hz), 2.30
(3H, s), 1.27 (3H, t, J=7.5 Hz); 13C NMR (75 MHz,
CDCl3): d=157.9, 148.4, 138.6, 137.9, 131.3, 129.1, 129.0,
128.9, 128.9, 127.3, 125.8, 125.1, 118.7, 118.7, 114.7, 23.6,
13.7, 11.7; IR (KBr): n=1653, 1546, 1484, 1328, 1249, 1152,
749 cmÀ1; HR-MS (EI): m/z=306.1478 (M+). calcd. for
C18H18N4O: 306.1481.
4-[(4-Isopropylphenyl)diazenyl]-3-methyl-1-phenyl-1H-
pyrazol-5-ol (11b): Prepared from 4-diazo-5-methyl-2-
phenyl-2,4-dihydro-3H-pyrazol-3-one 10 (100 mg, 0.5 mmol)
with 4-isopropylphenylhydrazine hydrochloride 8e (112 mg,
0.6 mmol) according to general procedure in 12 h as an
1
orange solid; yield: 148 mg (93%); mp 80–828C; H NMR
(300 MHz, CDCl3): d=13.56 (1H, s, OH), 7.88 (2H, d, J=
7.8 Hz), 7.37–7.28 (4H, m), 7.21–7.10 (3H, m), 2.88-.2.81
(1H, m), 2.29 (3H, s), 1.19 (6H, d, J=6.6 Hz); 13C NMR
(75 MHz, CDCl3): d=157.8, 148.4, 146.9, 139.0, 128.8, 128.8,
127.6, 127.6, 127.0, 125.0, 122.7, 118.5, 118.5, 115.8, 115.8,
33.7, 23.9, 23.8, 11.7; IR (KBr): n=1656, 1546, 1495, 1266,
1154, 828 cmÀ1; HR-MS (EI): m/z=320.1638 (M+), calcd.
for C19H20N4O: 320.1637.
4-[(4-Methoxyphenyl)diazenyl]-3-methyl-1-phenyl-1H-
pyrazol-5-ol (11c): Prepared from 4-diazo-5-methyl-2-
phenyl-2,4-dihydro-3H-pyrazol-3-one 10 (200 mg, 1.0 mmol)
with 4-methoxyphenylhydrazine hydrochloride 8f (104 mg,
0.6 mmol) according to general procedure in 12 h as an
orange red solid; yield: 123 mg (80%); mp 105–1078C;
1H NMR (300 MHz, CDCl3): d=13.70 (1H, s, OH), 7.94
Crystal Refinement Data for Compound 9m
C20H22N4O, M =334.42, orthorhombic, space group Pbca,
a=7.2201(7) Š, b=14.7712(13) Š, c=33.119(3) Š, V=
3532.1(6) Š3, Z=8, T=200 (2) K, 1calcd.=1.258 mgmÀ3,
2qmax=28.36, refinement of 230 parameters on 4409 inde-
pendent reflections out of 24596 collected reflections (Rint
=
0.0887) led to R1=0.0539 [I>2s(I)], wR2=0.1813 (all data)
and S=0.922 with the largest difference peak and hole of
0.543 and À0.424 eŠÀ3 respectively.
Adv. Synth. Catal. 2015, 357, 2657 – 2664
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asc.wiley-vch.de
2663

FULL PAPERS
Rameshwar Prasad Pandit and Yong Rok Lee
[12] M. A. Metwally, E. Abdel-Galil, A. Metwally, F. A.
Amer, Dyes Pigm. 2012, 92, 902–908.
Acknowledgements
[13] a) V. Kumar, K. Kaur, G. K. Gupta, A. K. Sharma, Eur.
J. Med. Chem. 2013, 69, 735–753; b) S. Trofimenko,
Chem. Rev. 1972, 72, 497–509.
This research was supported by the National Research Foun-
dation of Korea (NRF) grant funded by the Korea Govern-
ment (MSIP) (NRF-2014R1A2A1A11052391).
[14] P. D. Kale, J. Chem. Pharm. Res. 2013, 5, 130–133.
[15] V. Sareen, V. Khatri, D. Shinde, S. Sareen, Indian J.
Chem. 2011, 50B, 937–940.
[16] P. C. Lyer, J. Zhao, L. A. Emert-Sedlak, K. K. Moore,
T. E. Smithgall, B. W. Day, Bioorg. Med. Chem. Lett.
2014, 24, 1702–1706.
[17] a) B. F. Abdel-Wahab, A.-A. S. El-Ahl, F. A. Badria,
Chem. Pharm. Bull. 2009, 57, 1348–1351; b) S. El-Met-
wally, A. K. Khalil, Acta. Chim. Slov. 2010, 57, 941–947;
References
[1] A. A. Bekhit, T. Abdel-Aziem, Bioorg. Med. Chem.
2004, 12, 1935–1945.
[2] A. Mohammed, S. M. Hassan, A. Wadood, Orient. J.
Chem. 2002, 18, 351–353.
[3] Z. Tabarelli, M. A. Rubin, D. B. Berlese, P. D. Sauzem,
T. P. Missio, M. V. Teixeira, A. P. Sinhorin, M. A. P.
Martins, N. Zanatta, H. G. Bonacorso, C. F. Mello,
Brag. J. Med. Biol. Res. 2004, 37, 1531–1540.
[4] S. K. Sahu, M. Banerjee, A. Samantray, C. Behara,
M. A. Azam, Trop. J. Pharm. Res. 2008, 7, 961–968.
[5] F. R. Souza, V. T. Souza, V. Ratzlaff, L. P. Borges, M. R.
Olivera, H. G. Bonacorso, N. Zanatta, M. A. P. Martins,
C. F. Mello, Eur. J. Pharmacol. 2002, 451, 141–147.
[6] S. Joerg, G. Reinhold, S. Otto, S. H. Joachim, S. Robert,
L. Klaus, Ger. Offen. 04 Feb. 1988.
[7] R. Tripathy, A. Ghose, J. Singh, E. R. Bacon, T. S. An-
geles, S. X. Yang, M. S. Albom, L. D. Aimone, J. L.
Herman, J. P. Mallamo, Bioorg. Med. Chem. Lett. 2007,
17, 1793–1798.
[8] A. E. Rashad, M. I. Hegab, R. E. Abdel-Megeid, J. A.
Micky, F. M. E. Abdel-Megeid, Bioorg. Med. Chem.
2008, 16, 7102–7106.
˘
c) N. ErgeÅ, S. Rollas, Y. Topaloglu, Arch. Pharm. 1986,
319, 545–549.
[18] a) E. C. Lee, G. C. Fu, J. Am. Chem. Soc. 2007, 129,
12066–12067; b) Q.-H. Deng, H.-W. Xu, A. W.-H.
Yuen, Z.-J. Xu, C.-M. Che, Org. Lett. 2008, 10, 1529–
1532; c) T. J. Auvil, S. S. So, A. E. Mattson, Angew.
Chem. 2013, 125, 11527–11530; Angew. Chem. Int. Ed.
2013, 52, 11317–11320; d) T. Curtius, J. Prakt. Chem.
1888, 38, 396–440; e) P. Yates, J. Am. Chem. Soc. 1952,
74, 5376–5381; f) C. F. García, M. McKervey, T. Ye,
Chem. Commun. 1996, 1465–1466; g) P. Rodríguez, A.
Caballero, M. M. Díaz-Requejo, M. C. Nicasio, P. J.
PØrez, Org. Lett. 2006, 8, 557–560; h) B. Liu, S.-F. Zhu,
W. Zhang, C. Chen, Q.-L. Zhou, J. Am. Chem. Soc.
2007, 129, 5834–5835; i) L. K. Baumann, H. M. Mbuvi,
G. Du, L. K. Woo, Organometallics 2007, 26, 3995–
4002; j) R. P. Pandit, Y. R. Lee, Org. Biomol. Chem.
2014, 12, 4407–4411; k) C. Qin, H. M. L. Davies, J. Am.
Chem. Soc. 2014, 136, 9792–9796; l) H. M. L. Davies,
J. S. Alford, Chem. Soc. Rev. 2014, 43, 5151–5162;
m) Z. Yu, B. Ma, M. Chen, H. H. Wu, L. Liu, J. Zhang,
J. Am. Chem. Soc. 2014, 136, 6904–6907.
[19] a) Y. R. Lee, J. Y. Suk, B. S. Kim, Tetrahedron Lett.
1999, 40, 6603–6607; b) Y. R. Lee, J. Y. Suk, Tetrahe-
dron 2002, 58, 2359–2367; c) Y. R. Lee, J. Y. Suk,
Chem. Commun. 1998, 2621–2622; d) P. Neupane, X.
Li, J. H. Jung, Y. R. Lee, Tetrahedron 2012, 68, 2496–
2508; e) K. B. Somai Magar, Y. R. Lee, Org. Lett. 2013,
15, 4288–4291; f) L. Xia, Y. R. Lee, Adv. Synth. Catal.
2013, 355, 2361–2374.
[9] L. Le Corre, L. Tak-Tak, A. Guillard, G. Prestat, C.
Gravier-Pelletier, P. Busca, Org. Biomol. Chem. 2015,
13, 409–423.
[10] a) S. Fustero, M. Sµnchez-Roselló, P. Barrio, A. Simón-
Fuentes, Chem. Rev. 2011, 111, 6984–7034; b) J.-Y.
Yoon, S.-G. Lee, H. Shin, Curr. Org. Chem. 2011, 15,
657–674; c) A. Schmidt, A. Dreger, Curr. Org. Chem.
2011, 15, 1423–1463; d) X. Yu, J. Zhang, Chem. Eur. J.
2012, 18, 12945–12949; e) X. Qi, J. M. Ready, Angew.
Chem. 2007, 119, 3306–3308; Angew. Chem. Int. Ed.
2007, 46, 3242–3244; f) G. Zhang, Y. Zhao, H. Ge,
Angew. Chem. 2013, 125, 2619–2623; Angew. Chem.
Int. Ed. 2013, 52, 2559–2563; g) F. Li, J. Nie, L. Sun, Y.
Zheng, J.-A. Ma, Angew. Chem. 2013, 125, 6375–6378;
Angew. Chem. Int. Ed. 2013, 52, 6255–6258; h) J. J.
Neumann, M. Suri, F. Glorius, Angew. Chem. 2010, 122,
7957–7961; Angew. Chem. Int. Ed. 2010, 49, 7790–7794;
[20] The structure of 9m (CCDC 1044982) was confirmed
by X-ray diffraction analysis. These data can be ob-
tained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
[21] a) S. Bachmann, D. Fielenbach, K. A. Jørgensen, Org.
Biomol. Chem. 2004, 2, 3044–3049; b) H. V. R. Dias,
R. G. Browning, S. A. Polach, H. V. K. Diyabalanage,
C. J. Lovely, J. Am. Chem. Soc. 2003, 125, 9270–9271.
´
´
i) V. Markovic, M. D. Joksovic, Green Chem. 2015, 17,
842–847; j) M. Kissane, S. E. Lawrence, A. R. Maguire,
Org. Biomol. Chem. 2010, 8, 2735–2748.
[11] Y. Deng, B. Tang, H. Zhao, J. Xu, J. Xiao, X. Zhang, H.
Xu, S. Zhang, Color. Technol. 2012, 129, 144–149.
2664
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ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2015, 357, 2657 – 2664