One-pot preparation of 4-aryl-3-bromocoumarins from 4-aryl-2-propynoic acids with diaryliodonium salts, TBAB, and Na2S2O8

Article abstract of DOI:10.3762/bjoc.14.22

Various 4-aryl-3-bromocoumarins were smoothly obtained in moderate yields in one pot by treating 3-aryl-2-propynoic acids with diaryliodonium triflates and K₂CO₃ in the presence of CuCl, followed by the reaction with tetrabutylammoni

Full text of DOI:10.3762/bjoc.14.22

One-pot preparation of 4-aryl-3-bromocoumarins from
4-aryl-2-propynoic acids with diaryliodonium salts,
TBAB, and Na2S2O8
Teppei Sasaki1, Katsuhiko Moriyama1,2 and Hideo Togo*1
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2018, 14, 345–353.
1Department of Chemistry, Graduate School of Science, Chiba
University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522, Japan and
2Molecular Chirality Research Center, Chiba University, Yayoi-cho
1-33, Inage-ku, Chiba 263-8522, Japan
doi:10.3762/bjoc.14.22
Received: 11 December 2017
Accepted: 26 January 2018
Published: 05 February 2018
Email:
Hideo Togo* - togo@faculty.chiba-u.jp
This article is part of the Thematic Series "Hypervalent iodine chemistry in
organic synthesis".
* Corresponding author
Guest Editor: T. Wirth
Keywords:
3-aryl-2-propynoic acid; bromo-cyclization; coumarin; diaryliodonium
triflate; O-phenylation
© 2018 Sasaki et al.; licensee Beilstein-Institut.
License and terms: see end of document.
Abstract
Various 4-aryl-3-bromocoumarins were smoothly obtained in moderate yields in one pot by treating 3-aryl-2-propynoic acids with
diaryliodonium triflates and K2CO3 in the presence of CuCl, followed by the reaction with tetrabutylammonium bromide (TBAB)
and Na2S2O8. The obtained 3-bromo-4-phenylcoumarin was transformed into 4-phenylcoumarin derivatives bearing C–H, C–S,
C–N, and C–C bonds at 3-position.
Introduction
Coumarin is a benzo-α-pyrone and one of the typical hetero- Comprehensive synthetic studies of coumarins and their deriva-
cyclic compounds. The importance of coumarins arises from the tives have been carried out [15,16]. Typically, coumarins are
fact that the coumarin skeleton is present in many natural prod- prepared by the acid-catalyzed condensation of 2-alkynoic acids
ucts extracted from plants [1-3] and some of them show potent and phenols or the condensation of β-ketoesters and phenols
pharmacological activities, such as antidepressant [4], antimi- (the Pechmann condensation) [17]. Recent studies for the metal-
crobial [5,6], antioxidants [7,8], anti-inflammatory [9,10], catalyzed reactions for the synthesis of the coumarin skeleton
antinociceptive [11], antitumor [1], antiasthmatic [12], and are as follows: the Yb(OTf)3-catalyzed microwave irradiation
antiviral including anti-HIV [13,14].
of phenols and propynoic acids [18], the Pd(OAc)2-catalyzed
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Beilstein J. Org. Chem. 2018, 14, 345–353.
oxidative cyclocarbonylation of 2-vinylphenols at 110 °C [19], pounds [43-46], we would like to report an efficient one-pot
the FeCl3-catalyzed areneselenyl-cyclization of aryl 2-alkyn- preparation of 4-aryl-3-bromocoumarins by treatment of 3-aryl-
oates with ArSeSeAr at rt [20], and the Rh-catalyzed annula- 2-propynoic acids with diaryliodonium triflate in the presence
tion of arylthiocarbamates with alkynes/AgOTf/Cu(OAc)2 at of a base, followed by the reaction with tetrabutylammonium
120 °C [21]. As examples of the transition-metal-free construc- bromide (TBAB) and Na2S2O8 in a mixture of 1,2-dichloro-
tion of the coumarin skeleton, the Brønsted acid-catalyzed reac- ethane and water [31].
tion of phenols and propynoic acids [22] and the (−)-riboflavin-
catalyzed photochemical reaction of cinnamic acids [23] were Results and Discussion
reported recently. Moreover, the use of radical cyclization for First, treatment of 3-phenyl-2-propynoic acid (1a, 0.5 mmol)
the construction of the coumarin skeleton has become wide- with diphenyliodonium triflate (A, 1.0 equiv) in the presence of
spread. Examples include the radical addition–cyclization reac- CuCl (5 mol %) and K2CO3 (1.0 equiv) in dichloromethane
tions of aryl 2-alkynoates with RC(=O)CO2H/AgNO3(cat.)/ (3.0 mL) at 40 °C based on a previous report [46] gave phenyl
K2S2O8 at 60 °C [24], with Cu(OAc)2/1-trifluoromethyl-3,3- 3-phenyl-2-propynoate (2Aa) in 46% yield, as shown in
dimethyl-1,2-benziodoxole (Togni reagent) at 60 °C [25], with Table 1, entry 1. When the amount of the solvent was increased
R2P(=O)H/Ag2CO3(cat.)/Mg(NO3)2 at 100 °C [26], with to 7.5 mL under the same conditions, the yield of phenyl ester
BrCF2CO2Et/fac-Ir(ppy)3(cat.) under irradiation at rt [27], with 2Aa was increased to 74% (Table 1, entry 2). Under the same
R-CH=O/(n-Bu)4NBr (TBAB, cat.)/K2S2O8 at 90 °C [28], with conditions, the base was changed to NaH, Cs2CO3, t-BuOK,
ArSO2H/Eosin Y(cat.)/tert-butyl hydrogen peroxide (TBHP) at NaNH2, and K3PO4 instead of K2CO3. However, the yield of
rt [29], and with ArSO2NHNH2/n-Bu4NI(cat.)/TBHP at 80 °C phenyl ester 2Aa was moderate to low (Table 1, entries 3–7).
[30].
When the amount of K2CO3 was reduced to 0.5 equiv under the
same conditions as those in entry 2, the yield of phenyl ester
In addition, the formation of coumarins via the bromine-radical- 2Aa was increased to 80% (Table 1, entry 8). When CuCl was
mediated reaction of aryl 2-alkynoates with TBAB/K2S2O8 at changed to CuI and CuBr, the difference of the yield of phenyl
90 °C [31], the cyanomethyl-radical-mediated reaction of aryl ester 2Aa was small, but CuCl gave the highest yield (Table 1,
2-alkynoates with tert-butyl peroxybenzoate (TBPB)/aceto- entries 8–10). Then, the reaction temperature was changed to
nitrile at 130 °C [32], the sunlight-promoted reaction of aryl 0 °C, rt, 50 °C, and 60 °C under the same conditions as those in
2-alkynoates with N-iodosuccinimide (NIS) at rt [33], and the entry 8, and phenyl ester 2Aa was obtained in 83% yield at
visible-light-mediated reaction of aryl 2-alkynoates with 50 °C (Table 1, entries 11–14). On the other hand, when the
N-bromosuccinimide (NBS) at rt [34], where those reactions present reaction was carried out without CuCl under the same
proceed via radical spiro-cyclization and then radical 1,2- conditions, phenyl ester 2Aa was not obtained at all (Table 1,
carboxyl group migration, were reported.
entry 15).
On the other hand, diaryliodonium salts are very useful for the Then, the iodocyclization of phenyl ester 2Aa to 3-iodo-4-
C-arylation of active CH groups, the O-arylation of OH groups, phenylcoumarin (3Aa’) with N-iodosuccinimide (NIS,
and the N-arylation of NH groups under metal-free conditions 2.0 equiv)/BF3·Et2O (2.0 or 1.1 equiv) was studied based on the
[35-39]. For example, treatment of arenecarboxylic acids and previous reports [45,46], as shown in Table 2. However, 3-iodo-
alkanecarboxylic acids with diaryliodonium salts and t-BuOK 4-phenylcoumarin (3Aa’) was obtained in low to moderate
under toluene refluxing conditions provides the corresponding yields (Table 2, entries 1 and 2). To improve the yield of
aryl carboxylates in good yields [40,41]. However, the O-aryl- 3-halo-4-phenylcoumarins 3Aa or 3Aa’, the halocyclization of
ation of 2-alkynoic acids, which are much more acidic than 2Aa with N-bromosuccinimide (NBS, 2.0 equiv)/BF3·Et2O
arenecarboxylic acids and alkanecarboxylic acids, and there- (1.1 equiv), with 1,3-diiodo-5,5-dimethylhydantoin (DIH,
fore, the conjugate bases of 2-alkynoic acids are much less 2.0 equiv)/BF3·Et2O (1.1 equiv), and with 1,3-dibromo-5,5-
nucleophilic than those of arenecarboxylic acids and alkanecar- dimethylhydantoin (DBH, 2.0 equiv)/BF3·Et2O (1.1 equiv) was
boxylic acids, was not studied. On the other hand, it is known carried out to form 3-bromo-4-phenylcoumarin (3Aa), 3-iodo-
that 4-arylcoumarins have antitumor activity [42]. Therefore, 4-phenylcoumarin (3Aa’), and 3-bromo-4-phenylcoumarin
the one-pot preparation of 4-arylcoumarins from 3-aryl-2- (3Aa) in 28, 49 and 46% yields, respectively (Table 2, entries
alkynoic acids via aryl esters and cyclization is attractive and 3–5). The treatment of phenyl ester 2Aa with molecular iodine
important.
(2.0 equiv)/K2CO3 (2.0 equiv) did not generate 3-iodo-4-
phenylcoumarin (3Aa’) at all (Table 2, entry 6). Thus, the iodo-
Here, as part of our ongoing investigation of the synthetic use of nium-based or bromonium-based electrophilic cyclization of
diaryliodonium salts for the preparation of heterocyclic com- phenyl 3-phenyl-2-propynoate (2Aa) does not proceed effi-
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Table 1: O-Phenylation of 3-phenyl-2-propynoic acid (1a) with diphenyliodonium triflate (A).
entry
base
solvent (mL)
additive (mol %)
temp. (°C)
yield (%)
1
K2CO3 (1.0)
K2CO3 (1.0)
NaH (1.0)
CH2Cl2 (3.0)
CH2Cl2 (7.5)
CH2Cl2 (7.5)
CH2Cl2 (7.5)
CH2Cl2 (7.5)
CH2Cl2 (7.5)
CH2Cl2 (7.5)
CH2Cl2 (7.5)
CH2Cl2 (7.5)
CH2Cl2 (7.5)
CH2Cl2 (7.5)
CH2Cl2 (7.5)
DCE (7.5)
CuCl (5)
CuCl (5)
CuCl (5)
CuCl (5)
CuCl (5)
CuCl (5)
CuCl (5)
CuCl (5)
CuI (5)
40
40
40
40
40
40
40
40
40
40
0
46
74
24
17
48
9
2
3
4
Cs2CO3 (0.5)
t-BuOK (1.0)
NaNH2 (1.0)
K3PO4 (1.0)
K2CO3 (0.5)
K2CO3 (0.5)
K2CO3 (0.5)
K2CO3 (0.5)
K2CO3 (0.5)
K2CO3 (0.5)
K2CO3 (0.5)
K2CO3 (0.5)
5
6
7
30
80
78
77
11
71
83
75
0
8
9
10
11
12
13
14
15
CuBr (5)
CuCl (5)
CuCl (5)
CuCl (5)
CuCl (5)
–
rt
50
60
50
DCE (7.5)
DCE (7.5)
Table 2: Halocyclization of phenyl 3-phenyl-2-propynoate (2Aa) to 3-halo-4-phenylcoumarins 3Aa and 3Aa’.
entry
additive (equiv)
solvent (mL)
temp. (°C)
time (h)
yield (%)
1
NIS (2.0), BF3·Et2O (2.0)
NIS (2.0), BF3·Et2O (1.1)
NBS (2.0), BF3·Et2O (1.1)
DIH (2.0), BF3·Et2O (1.1)
DBH (2.0), BF3·Et2O (1.1)
I2 (2.0), K2CO3 (2.0)
CH2Cl2 (3.0)
40
40
40
40
40
40
90
90
90
90
90
90
90
90
1
36 (3Aa’)
45 (3Aa’)
28 (3Aa)
49 (3Aa’)
46 (3Aa)
0
2
CH2Cl2 (3.0)
1
3
CH2Cl2 (3.0)
1
4
CH2Cl2 (3.0)
1
5
CH2Cl2 (3.0)
1
6
CH3CN (3.0)
1
7
TBAB (2.0), Na2S2O8 (1.5)
TBAI (2.0), Na2S2O8 (1.5)
TBAB (2.0), Na2S2O8 (1.0)
TBAB (2.0), Na2S2O8 (2.0)
TBAB (2.5), Na2S2O8 (1.0)
TBAB (2.0), K2S2O8 (1.0)
TBAB (2.0), (NH4)2S2O8 (1.0)
TBAB (2.0), Oxone® (1.0)
DCE:H2O (1:1, 5.0)
DCE:H2O (1:1, 5.0)
DCE:H2O (1:1, 5.0)
DCE:H2O (1:1, 5.0)
DCE:H2O (1:1, 5.0)
DCE:H2O (1:1, 5.0)
DCE:H2O (1:1, 5.0)
DCE:H2O (1:1, 5.0)
19
19
19
19
19
19
19
19
68 (3Aa)
45 (3Aa’)
79 (3Aa)
51 (3Aa)
69 (3Aa)
71 (3Aa)
69 (3Aa)
37 (3Aa)
8
9
10
11
12
13
14
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ciently. Then, the bromo-radical-based cyclization of phenyl 3-aryl-2-propynoic acids bearing heteroaromatic groups, treat-
3-phenyl-2-propynoate (2Aa) with tetrabutylammonium bro- ment of 3-(benzothiophen-2’-yl)-2-propynoic acid (1n) and
mide (TBAB, 2.0 equiv)/Na2S2O8 (1.5 equiv) [31] in a mixture 3-(benzofuran-2’-yl)-2-propynoic acid (1o) under the same pro-
of 1,2-dichloroethane (DCE) and water at 90 °C was carried out cedure and conditions gave the corresponding coumarins 3An
to give 3-bromo-4-phenylcoumarin (3Aa) in 68% yield and 3Ao in moderate yields, respectively. Under the present
(Table 2, entry 7). When the iodocyclization of phenyl ester procedure and conditions, use of 2-hexynoic acid (1p), a
2Aa with tetrabutylammonium iodide (TBAI, 2.0 equiv)/ 3-alkyl-2-propynoic acid, provided 3-bromo-4-propylcoumarin
Na2S2O8 (1.5 equiv) was carried out, the yield of iodocycliza- (3Ap) in 42% yield, as shown in Scheme 1.
tion product 3Aa’ was decreased to 45% (Table 2, entry 8).
When the bromocyclization of phenyl ester 2Aa with TBAB Then, other diaryliodonium triflates were used instead of
(2.0 equiv)/Na2S2O8 (1.0 equiv) in a mixture of DCE and water diphenyliodonium triflate (A). Treatment of 3-phenyl-2-propy-
at 90 °C was carried out, 3-bromo-4-phenylcoumarin (3Aa) was noic acid (1a) with diaryliodonium triflates (1.0 equiv), such as
obtained in 79% yield (Table 2, entry 9). When Na2S2O8 was di(p-methylphenyl)iodonium triflate (B), di(tert-butylphenyl)io-
increased to 2.0 equivalents or TBAB was increased to donium triflate (C), di(p-chlorophenyl)iodonium triflate (D),
2.5 equivalents under the same conditions, the yields of and di(p-bromophenyl)iodonium triflate (E), in the presence of
3-bromo-4-phenylcoumarin (3Aa) were decreased to 51 and CuCl and K2CO3 in CH2Cl2 for 3 h under refluxing conditions,
69%, respectively (Table 2, entries 10 and 11). Moreover, when followed by removal of the solvent and the reaction with TBAB
Na2S2O8 was changed to K2S2O8, (NH4)2S2O8, and Oxone® (2.0 equiv) and Na2S2O8 (2.0 equiv) in a mixture of DCE and
(2KHSO5·KHSO4·K2SO4), the yields of 3-bromo-4-phenyl- water at 90 °C for 19 h gave 3-bromo-4-phenylcoumarin deriva-
coumarin (3Aa) were decreased to 71, 69 and 37%, respective- tives 3Ba–3Ea bearing methyl, tert-butyl, chloro, and bromo
ly (Table 2, entries 12–14). Thus, it was confirmed that the groups at 7-position in good to moderate yields, respectively, as
treatment of phenyl ester 2Aa with TBAB (2.0 equiv)/Na2S2O8 shown in Scheme 2.
(1.0 equiv) in a mixture of DCE and water at 90 °C for 19 h was
the most efficient, giving 3-bromo-4-phenylcoumarin (3Aa) in As regards the synthetic utilization of the products in the
good yield (Table 2, entry 9).
present one-pot reaction, treatment of 3-bromo-4-phenyl-
coumarin (3Aa) with Zn in ethanol under refluxing conditions
Finally, based on the results in Table 1 and Table 2, the one-pot gave 4-phenylcoumarin (4Aa) in 81% yield. Treatment of
preparation of 4-aryl-3-bromocoumarins 3 from 3-aryl-2-propy- 3-bromo-4-phenylcoumarin (3Aa) with p-toluenethiol/N,N’-
noic acids 1 was carried out. 3-Aryl-2-propynoic acids 1, such dimethylethylenediamine (DMEDA)/K2CO3 in the presence of
as 3-phenyl-2-propynoic acid (1a), 3-(o-methylphenyl)-2- CuI in toluene at refluxing temperature and with p-methoxy-
propynoic acid (1b), 3-(m-methylphenyl)-2-propynoic acid (1c), benzamide/DMEDA/K2CO3 in the presence of CuI in toluene at
3-(p-methylphenyl)-2-propynoic acid (1d), 3-(p-methoxy- refluxing temperature generated 3-(4-methylbenzenesulfenyl)-
phenyl)-2-propynoic acid (1e), 3-(p-fluorophenyl)-2-propynoic 4-phenylcoumarin (5Aa) and 3-(4-methoxylbenzoylamino)-4-
acid (1f), 3-(p-chlorophenyl)-2-propynoic acid (1g), 3-(o- phenylcoumarin (6Aa) in 62 and 51% yields, respectively. The
chlorophenyl)-2-propynoic acid (1h), 3-(m-chlorophenyl)-2- Pd-catalyzed coupling reactions of 3-bromo-4-phenylcoumarin
propynoic acid (1i), 3-(p-bromophenyl)-2-propynoic acid (1j), (3Aa) with 4-methylstyrene/K2CO3/PdCl2(Ph3P)2, with phenyl-
3-(p-biphenyl)-2-propynoic acid (1k), 3-(naphthalen-2’-yl)-2- acetylene/PdCl2(Ph3P)2/Et3N and with PhB(OH)2/K2CO3/
propynoic acid (1l), and 3-(naphthalen-1’-yl)-2-propynoic acid PdCl2(Ph3P)2 provided the corresponding C–C bonded
(1m), were treated with diphenyliodonium triflate (A, coumarin derivatives 7Aa, 8Aa, and 9Aa in 79, 60 and 76%
1.0 equiv) in the presence of CuCl and K2CO3 in CH2Cl2 for yields, respectively (Scheme 3).
3 h under refluxing conditions. After removal of the solvent, the
second-step treatment of the reaction mixture with TBAB To support the present bromocyclization reaction to form
(2.0 equiv) and Na2S2O8 (2.0 equiv) in a mixture of DCE and 4-aryl-3-bromocoumarins with TBAB and Na2S2O8 at the
water at 90 °C for 19 h gave 4-aryl-3-bromocoumarins second step, the present one-pot preparation of 3-bromo-4-
3Aa–3Am in moderate yields, respectively, as shown in phenylcoumarin (3Aa) from 3-phenyl-2-propynoic acid (1a)
Scheme 1. As a gram-scale experiment, treatment of 3-phenyl- was carried out in the presence of 2,2,6,6-tetramethylpiperidine
2-propynoic acid (1a, 8 mmol) with diphenyliodonium triflate 1-oxyl radical (TEMPO, 2.0 equiv) or 2,6-di(tert-butyl-p-cresol
A in the presence of CuCl and K2CO3 in CH2Cl2 for 3 h, fol- (BHT, 3.0 equiv) at the second step under the same procedure
lowed by removal of the solvent and the reaction with TBAB and conditions, but 3-bromo-4-phenylcoumarin (3Aa) was not
and Na2S2O8 in a mixture of DCE and water at 90 °C for 19 h obtained at all in both reactions. Thus, the present bromo-
gave 3-bromo-4-phenylcoumarin (3Aa) in 52% yield. For cyclization of the formed phenyl 3-phenyl-2-propynoate (2Aa)
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Beilstein J. Org. Chem. 2018, 14, 345–353.
Scheme 1: One-pot preparation of 4-aryl-3-bromocoumarins 3 from 3-aryl-2-propynoic acids 1 with diphenyliodonium triflate (A).
a3-Phenyl-2-propynoic acid (1a, 8.0 mmol) was used. bThe first reaction step was conducted with K2CO3 (1.0 equiv) under refluxing conditions.
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Beilstein J. Org. Chem. 2018, 14, 345–353.
Scheme 2: One-pot preparation of 3-bromo-4-phenylcoumarins 3a from 3-phenyl-2-propynoic acid (1a) with daryliodonium triflates B–E.
Scheme 3: Derivatization of 3-bromo-4-phenylcoumarin.
with TBAB and Na2S2O8 in a mixture of DCE and water is a propynoic acid (1a) with di(p-chlorophenyl)iodonium triflate
radical-mediated bromocyclization reaction. X-ray crystallo- (D) and then with TBAB and Na2S2O8, was carried out, as
graphic analysis of 3-bromo-7-chloro-4-phenylcoumarin (3Da), shown in Figure 1. Based on those results, the possible reaction
which was formed by the subsequent treatment of 3-phenyl-2- pathway is shown in Scheme 4.
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Beilstein J. Org. Chem. 2018, 14, 345–353.
tive vinyl radical I [47]. Ipso-cyclization of the vinyl radical I
occurs to form spiro radical intermediate II. Then, β-cleavage
of the spiro radical intermediate II proceeds to form carboxyl
radical III. 6-Exo-trig cyclization of the carboxyl radical III
onto the aromatic ring takes place to form adduct radical IV,
which would be rapidly oxidized by Na2S2O8 to form cation
intermediate V. Smooth deprotonation of cation intermediate V
occurs to generate 4-aryl-3-bromocoumarin 3 (2nd step). The
radical ipso-cyclization of the formed vinyl radical and its 1,2-
carboxyl group migration agree with previously reported results
[31-34].
Conclusion
The successive treatment of 3-aryl-2-propynoic acids with
diaryliodonium triflates in the presence of K2CO3 and CuCl,
and then with tetrabutylammonium bromide (TBAB) and
Na2S2O8 gave 4-aryl-3-bromocoumarins bearing hydrogen,
methyl, tert-butyl, chloro, and bromo groups at 7-position in
moderate yields, respectively. In one of the obtained 4-aryl-3-
bromocoumarins, the C–Br bond of 3-bromo-4-phenyl-
coumarin was smoothly converted into 4-phenylcoumarins
bearing C–H, C–S, C–N, and C–C bonds at 3-position. We
believe the present method will be useful for the preparation of
various 4-arylcoumarin derivatives due to its simple one-pot
synthesis.
Figure 1: ORTEP of 3-bromo-7-chloro-4-phenylcoumarin (3Da).
The O-arylation of 3-aryl-2-propynoic acid 1 with diaryliodo-
nium triflate in the presence of K2CO3 and CuCl occurs to form
aryl 3-aryl-2-propynoate 2 (1st step). The bromocyclization of
aryl 3-aryl-2-propynoate 2 with TBAB and Na2S2O8 proceeds
via a bromoradical addition to the triple bond to form very reac-
Scheme 4: Possible reaction pathway.
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14.Ong, E. B. B.; Watanabe, N.; Saito, A.; Futamura, Y.; El Galil, K. H. A.;
Koito, A.; Najimudin, N.; Osada, H. J. Biol. Chem. 2011, 286,
14049–14056. doi:10.1074/jbc.M110.185397
Supporting Information
Supporting Information File 1
15.Vekariya, R. H.; Patel, H. D. Synth. Commun. 2014, 44, 2756–2788.
doi:10.1080/00397911.2014.926374
NMR charts of all coumarin derivatives 3Aa–3Ap,
3Ba–3Ea, and 4Aa–9Aa, and X-ray analytical data of 3Da.
[https://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-14-22-S1.pdf]
16.Žalubovskis, R. Chem. Heterocycl. Compd. (Engl. Transl.) 2015, 51,
607–612. doi:10.1007/s10593-015-1748-8
17.Sethna, S.; Phadke, R. Org. React. 2011, 7, 1–58.
doi:10.1002/0471264180.or007.01
18.Fiorito, S.; Epifano, F.; Taddeo, V. A.; Genovese, S. Tetrahedron Lett.
2016, 57, 2939–2942. doi:10.1016/j.tetlet.2016.05.087
19.Ferguson, J.; Zeng, F.; Alper, H. Org. Lett. 2012, 14, 5602–5605.
doi:10.1021/ol302725x
Acknowledgements
Financial support in the form of a Grant-in–Aid for Scientific
Research (No. 15K05418) from the Ministry of Education, Cul-
ture, Sports, Science, and Technology in Japan is gratefully ac-
knowledged.
20.Mantovani, A. C.; Goulart, T. A. C.; Back, D. F.; Menezes, P. H.;
Zeni, G. J. Org. Chem. 2014, 79, 10526–10536.
doi:10.1021/jo502199q
21.Zhao, Y.; Han, F.; Yang, L.; Xia, C. Org. Lett. 2015, 17, 1477–1480.
doi:10.1021/acs.orglett.5b00364
ORCID® iDs
Hideo Togo - https://orcid.org/0000-0002-3633-7292
22.Choi, H.; Kim, J.; Lee, K. Tetrahedron Lett. 2016, 57, 3600–3603.
doi:10.1016/j.tetlet.2016.06.039
23.Metternich, J. B.; Gilmour, R. J. Am. Chem. Soc. 2016, 138,
1040–1045. doi:10.1021/jacs.5b12081
References
24.Yan, K.; Yang, D.; Wei, W.; Wang, F.; Shuai, Y.; Li, Q.; Wang, H.
J. Org. Chem. 2015, 80, 1550–1556. doi:10.1021/jo502474z
25.Li, Y.; Lu, Y.; Qiu, G.; Ding, Q. Org. Lett. 2014, 16, 4240–4243.
doi:10.1021/ol501939m
1. Lacy, A. Curr. Pharm. Des. 2004, 10, 3797–3811.
doi:10.2174/1381612043382693
2. Musa, M. A.; Badisa, V. L. D.; Latinwo, L. M.; Waryoba, C.;
Ugochukwu, N. Anticancer Res. 2010, 30, 4613–4617.
3. Medina, F. G.; Marrero, J. G.; Macías-Alonso, M.; González, M. C.;
Córdova-Guerrero, I.; García, A. G. T.; Osegueda-Robles, S.
Nat. Prod. Rep. 2015, 32, 1472–1507. doi:10.1039/C4NP00162A
4. Sashidhara, K. V.; Kumar, A.; Chatterjee, M.; Rao, K. B.; Singh, S.;
Verma, A. K.; Palit, G. Bioorg. Med. Chem. Lett. 2011, 21, 1937–1941.
doi:10.1016/j.bmcl.2011.02.040
26.Mi, X.; Wang, C.; Huang, M.; Zhang, J.; Wu, Y.; Wu, Y. Org. Lett. 2014,
16, 3356–3359. doi:10.1021/ol5013839
27.Fu, W.; Zhu, M.; Zou, G.; Xu, C.; Wang, Z.; Ji, B. J. Org. Chem. 2015,
80, 4766–4770. doi:10.1021/acs.joc.5b00305
28.Mi, X.; Wang, C.; Huang, M.; Wu, Y.; Wu, Y. J. Org. Chem. 2015, 80,
148–155. doi:10.1021/jo502220b
29.Yang, W.; Yang, S.; Li, P.; Wang, L. Chem. Commun. 2015, 51,
7520–7523. doi:10.1039/C5CC00878F
5. Ostrov, D. A.; Hernández-Prada, J. A.; Corsino, P. E.; Finton, K. A.;
Le, N.; Rowe, T. C. Antimicrob. Agents Chemother. 2007, 51,
3688–3698. doi:10.1128/AAC.00392-07
30.Wei, W.; Wen, J.; Yang, D.; Guo, M.; Wang, Y.; You, J.; Wang, H.
Chem. Commun. 2015, 51, 768–771. doi:10.1039/C4CC08117J
31.Qiu, G.; Liu, T.; Ding, Q. Org. Chem. Front. 2016, 3, 510–515.
doi:10.1039/C6QO00041J
6. Chimenti, F.; Bizzarri, B.; Bolasco, A.; Secci, D.; Chimenti, P.;
Granese, A.; Carradori, S.; Rivanera, D.; Zicari, A.; Scaltrito, M. M.;
Sisto, F. Bioorg. Med. Chem. Lett. 2010, 20, 4922–4926.
doi:10.1016/j.bmcl.2010.06.048
32.Yu, Y.; Zhuang, S.; Liu, P.; Sun, P. J. Org. Chem. 2016, 81,
11489–11495. doi:10.1021/acs.joc.6b02155
7. Kostova, I.; Bhatia, S.; Grigorov, P.; Balkansky, S.; Parmar, V. S.;
Prasad, A. K.; Saso, L. Curr. Med. Chem. 2011, 18, 3929–3951.
doi:10.2174/092986711803414395
33.Ni, S.; Cao, J.; Mei, H.; Han, J.; Li, S.; Pan, Y. Green Chem. 2016, 18,
3935–3939. doi:10.1039/C6GC01027J
34.Feng, S.; Li, J.; Li, Z.; Sun, H.; Shi, H.; Wang, X.; Xie, X.; She, X.
Org. Biomol. Chem. 2017, 15, 8820–8826. doi:10.1039/C7OB02199B
35.Aradi, K.; Tóth, B. L.; Tolnai, G. L.; Novák, Z. Synlett 2016, 27,
1456–1485. doi:10.1055/s-0035-1561369
8. Xi, G.-L.; Liu, Z.-Q. J. Agric. Food Chem. 2015, 63, 3516–3523.
doi:10.1021/acs.jafc.5b00399
9. Bansal, Y.; Sethi, P.; Bansal, G. Med. Chem. Res. 2013, 22,
3049–3060. doi:10.1007/s00044-012-0321-6
36.Olofsson, B. Top. Curr. Chem. 2015, 373, 135–166.
doi:10.1007/128_2015_661
10.Fylaktakidou, K. C.; Hadjipavlou-Litina, D. J.; Litinas, K. E.;
Nicolaides, D. N. Curr. Pharm. Des. 2004, 10, 3813–3833.
doi:10.2174/1381612043382710
37.Fañanás-Mastral, M. Synthesis 2017, 49, 1905–1930.
doi:10.1055/s-0036-1589483
11.De Almeida Barros, T. A.; De Freitas, L. A. R.; Filho, J. M. B.;
Nunes, X. P.; Giulietti, A. M.; De Souza, G. E.; Dos Santos, R. R.;
Soares, M. B. P.; Villarreal, C. F. J. Pharm. Pharmacol. 2010, 62,
205–213. doi:10.1211/jpp.62.02.0008
38.Stuart, D. R. Chem. – Eur. J. 2017, 23, 15852–15863.
doi:10.1002/chem.201702732
39.Cao, C. K.; Sheng, J.; Chen, C. Synthesis 2017, 49, 5081–5092.
doi:10.1055/s-0036-1589515
12.Sánchez-Recillas, A.; Navarrete-Vázquez, G.; Hidalgo-Figueroa, S.;
Rios, M. Y.; Ibarra-Barajas, M.; Estrada-Soto, S. Eur. J. Med. Chem.
2014, 77, 400–408. doi:10.1016/j.ejmech.2014.03.029
13.Hwu, J. R.; Lin, S.-Y.; Tsay, S.-C.; De Clercq, E.; Leyssen, P.; Neyts, J.
J. Med. Chem. 2011, 54, 2114–2126. doi:10.1021/jm101337v
40.Petersen, T. B.; Khan, R.; Olofsson, B. Org. Lett. 2011, 13, 3462–3465.
doi:10.1021/ol2012082
41.Jalalian, N.; Petersen, T. B.; Olofsson, B. Chem. – Eur. J. 2012, 18,
14140–14149. doi:10.1002/chem.201201645
352

Beilstein J. Org. Chem. 2018, 14, 345–353.
42.Mutai, P.; Breuzard, G.; Pagano, A.; Allegro, D.; Peyrot, V.; Chibale, K.
Bioorg. Med. Chem. 2017, 25, 1652–1665.
doi:10.1016/j.bmc.2017.01.035
43.Kakinuma, Y.; Moriyama, K.; Togo, H. Synthesis 2013, 45, 183–188.
doi:10.1055/s-0032-1316824
44.Miyagi, K.; Moriyama, K.; Togo, H. Heterocycles 2014, 89, 2122–2136.
doi:10.3987/COM-14-13071
45.Sasaki, T.; Miyagi, K.; Moriyama, K.; Togo, H. Org. Lett. 2016, 18,
944–947. doi:10.1021/acs.orglett.5b03651
46.Sasaki, T.; Moriyama, K.; Togo, H. J. Org. Chem. 2017, 82,
11727–11734. doi:10.1021/acs.joc.7b01433
47.Togo, H. Advanced Free Radicals for Organic Synthesis; Chapter 3;
Elsevier: Oxford, 2004; pp 75–94.
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