Regioselective palladium-catalyzed decarboxylative cross-coupling reaction of alkenyl acids with coumarins: Synthesis of 3-styrylcoumarin compounds

Article abstract of DOI:10.1021/jo502572j

A novel and efficient protocol for the regioselective synthesis of 3-styrylcoumarins from readily available cinnamic acids and coumarins is presented. The reaction proceeds via a decarboxylative cross-coupling mediated by a catalytic amount of Pd(OAc)₂, with Ag₂CO₃ as an oxidant, and with 1,10-phenanthroline as a ligand. A plausible reaction mechanism for this process is depicted, and the resulting 3-styrylcoumarins show excellent fluorescence quantum yields.

Full text of DOI:10.1021/jo502572j

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Note
Regioselective Palladium-Catalyzed Decarboxylative Cross-Coupling Reaction
of Alkenyl Acids with Coumarins: Synthesis of 3-Styrylcoumarin Compounds
Xu Wang, Shen-yan Li, Ying-Ming Pan, Heng-Shan Wang, Zhen-Feng Chen, and Ke-Bin Huang
J. Org. Chem., Just Accepted Manuscript • Publication Date (Web): 22 Jan 2015
Downloaded from http://pubs.acs.org on January 23, 2015
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Regioselective Palladium-Catalyzed Decarboxylative
Cross-Coupling Reaction of Alkenyl Acids with Coumarins:
Synthesis of 3-Styrylcoumarin Compounds
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Xu Wang, Shenꢀyan Li, Yingꢀming Pan*, Hengꢀshan Wang, Zhenꢀfeng Chen*, Keꢀbin Huang
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Key Laboratory for the Chemistry and Molecular Engineering of Medicinal Resources (Ministry of
Education of China), School of Chemistry & Pharmaceutical Sciences of Guangxi Normal University,
Guilin 541004, People’s Republic of China
panym2013@hotmail.com; chenzfubc@yahoo.com
ABSTRACT:
A novel and efficient protocol for the regioselective synthesis of 3ꢀstyrylcoumarins from
readily available cinnamic acids and coumarins is presented. The reaction proceeds via a decarboxylative
crossꢀcoupling mediated by catalytic amount of Pd(OAc)2, Ag2CO3 as an oxidant, and 1,10ꢀphenanthroline
as a ligand. A plausible reaction mechanism for this process is depicted, and the resulting 3ꢀstyrylcoumarins
show excellent fluorescence quantum yields.
Decarboxylative coupling reactions have become a powerful tool for regioselective
CꢀC and Cꢀheteroatom bonds formation,1 thus providing new protocols for Heckꢀtype
reactions,2 oxidative arylations,3 redoxꢀneutral crossꢀcoupling reactions,4 and
allylations.5 Among those, alkenyl acids act as crossꢀcoupling components by a
metalꢀpromoted decarboxylation process and are used in construction of CꢀC,6 CꢀN,7
CꢀS,8 and CꢀP9 bonds because of their stable, low cost, diversity, ready availability,
and the nontoxic byproduct (CO2). From environmental and economic perspectives,
the development of organic synthesis using inexpensive and stable material such as
alkenyl acids would be of significant importance.
Coumarins constitute a major class of naturally occurring compounds and
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privileged medicinal scaffolds, have been extensively investigated regard to their
pharmacological activity10 and outstanding optical properties11. Due to effective
fluorophores characterized by high fluorescence quantum yields,12 several coumarins
have been shown to exhibit their photophysical properties.13ꢀ18 The challenge is how
to effectively increase the spectroscopic bands intensity of coumarin derivatives. A
best solution is extending the conjugated πꢀelectron system, yielding coumarin
derivatives with greater intensity. Recently, various synthetic approaches have been
reported to synthesize 3ꢀstyrylcoumarins in the literature.19 For example, Heck
crossꢀcoupling reaction between 3ꢀbromocoumarin and olefins,19a 3ꢀvinyl coumarins
and aryl halides,19b coumarinꢀ3ꢀcarboxylic acid and olefins,19c coumarins and
alkenes,19d are a few prominent methods of synthesizing 3ꢀstyryl coumarins (Scheme
1). In light of the literature precedences1ꢀ19 and continuation of our efforts in the
development of transitionꢀmetalꢀcatalyzed CꢀH functionalization,20 we thought it
would be of interest to develop a method by a decarboxylative crossꢀcoupling reaction
of α,βꢀunsaturated carboxylic acids using coumarins. Herein, we disclose an efficient,
economic route for rapid synthesis of 3ꢀstyrylcoumarins via palladiumꢀcatalyzed
decarboxylative coupling of cinnamic acids employing coumarins.
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Scheme 1. Reported Methods for the Synthesis of 3-Styrylcoumarins
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Table 1. Reaction Conditions Optimizationa
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yield (%)b
entry
1
catalyst
Pd(OAc)2
Pd(OAc)2
PdCl2
ligand
–
additivec
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
Ag2CO3
Ag2O
solvent
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
PhCl
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10
40
36
30
22
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32
17
12
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11
15
34
41
14
31
0
2
Phen
Phen
Phen
Phen
Phen
Phen
Phen
L1
3
4
Pd(acac)2
Pd(dba)2
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6
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
7
8
AgOTf
9
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
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22d
23e
24f
L2
L3
L4
L5
L6
L7
L8
Phen
Phen
Phen
Phen
Phen
Phen
Phen
Phen
DMF
Dioxane
DCE
0
CH3CN
DMSO
DMSO
DMSO
0
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aAll reactions were carried out under the following conditions: coumarin 1a (0.3 mmol), 2a (0.2 mmol), Pd
catalyst (20 mol %), ligand (20 mol %) in different solvents (2 mL) at 130 oC for 72 h. bIsolated yield based on 2a.
c2.0 Equivalents. d Sealed tube . e140 oC. f The reaction was carried out using 15 mol % Pd(OAc)2.
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Our initial experiments showed that using Pd(OAc)2/AgOAc/DMSO as catalytic
system, the C3ꢀolefination of coumarin occurred with complete regioselectivity giving
a low isolated yield (10%) (Table 1, entry 1). Addition of 20 mol%
1,10ꢀphenanthroline increased the yield to 40% (Table 1, entry 2). In the presence of
1,10ꢀphenanthroline, a series of palladium catalysts were screened and did not display
better catalytic activity except PdCl2 showing the similar activity as that of Pd(OAc)2
(Table 1, entries 3, 4 and 5; Table S1, Supporting Information). Among the additives
examined, Ag2CO3 provided the best result (Table 1, entries 6ꢀ8; Table S1, Supporting
Information). Some other N,Nꢀligands L1-L8 were also evaluated, while these ligands
did produce active catalyst systems, the yields were inferior to that obtained with
1,10ꢀphenanthroline (Table 1, entries 9ꢀ16; Table S2, Supporting Information). The
solvent also affected the coupling reaction of coumarin and alkenyl acid. No product
was found with dioxane, DCE, or CH3CN as solvent, and only poor yields were
obtained when other solvents such as PhCl, DMF were employed (Table 1, entries
17−21), where DMSO turned out to be the most appropriate (Table S3, Supporting
Information). When in the sealed tube, the yield of 3a enhanced from 40% to 69%
(Table 1, entry 22), but no obvious improvement in the yield could be obtained as the
temperature was increased to 140 °C (Table 1, entry 22 vs. 23). A very slow reaction
rate and low yield were observed when the catalytic amount of Pd(OAc)2 decreased
from 20 to 15 mol % (Table 1, entry 22 vs. 24). The above investigations revealed that
the Pd(OAc)2/Ag2CO3/phen/DMSO system is the best combination for promoting the
olefination.
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With the optimized reaction conditions established, we started to investigate the
scope and limitation of this reaction, and the results are summarized in Table 2. It was
observed that a range of selected coumarin derivatives and cinnamic acids were
compatible with the reaction conditions, resulting in the formation of the desired
products in moderate to good yields with completely regioselectivity. Cinnamic acids
featuring electronꢀdonating or neutral groups at phenyl ring provided somewhat
higher yields of the olefination products than did those bearing electronꢀwithdrawing
groups (3a-b vs. 3cꢀd and 3e-g vs.3hꢀi). Gratifyingly, moderate to good reaction
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yields (55ꢀ78%) were obtained when courmarins were substituted by
electronꢀdonating groups such as ꢀMe, ꢀOMe, ꢀOEt at the Cꢀ6 or Cꢀ7 position even in
a shorter time (3eꢀo). The crystallization of compound 3g from ethanol gave a single
crystal suitable for Xꢀray analysis. It illustrates the molecular structure of the
substituted 3ꢀstyrylcoumarin 3g (see Suporting Information pp S29). Unfortunately,
coumarin possessing an electronꢀwithdrawing group such as ꢀNO2 at the Cꢀ6 position
gave the desired product 3p in poor yield. The electronꢀwithdrawing group
presumably is not conducive to the intermediate II formation (see Scheme 3). We
further investigated additional substrates and were pleased to observe that
quinolinones also worked well in the optimized system, leading to the formation of 3q
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and 3r.
Table 2. Direct C3-Olefination of the Coumarins with Various Cinnamic Acid Derivativesa,b
Pd(OAc)2 (20 mol%)
Ag2CO3 (2 equiv)
R2
COOH
R1
+
R1
1,10-phenanthroline (20 mol%)
R2
O
O
O
O
DMSO, 130 oC, 72 h
2
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3
aReaction conditions: 1 (0.3 mmol), 2 (0.2 mmol), Pd(OAc)2 (20 mol % to 2), Ag2CO3 (2 equiv to 2),
o
b
1,10ꢀphenanthroline (20 mol % to 2), DMSO (2 mL) , at 130 C, sealed tube, 72 h. Average isolated yield
based on 2.
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To investigate the reaction mechanism, control experiment was conducted (Scheme
2). A 67% yield of 3a was smoothly obtained in the presence of the radical scavenger
butyleret hydroxytoluen (BHT) (eq (1)), which could indicate that free radical
pathway is not involved. On the basis of these data, we proposed a mechanism for the
present reaction pathway (Scheme 3).21 Electrophilic palladation of coumarin at the
C3 position with the Pdꢀligand species was favorable due to the more nucleophilic
3ꢀposition, thereby affording the intermediate II. In parallel, the silver mediated
decarboxylation of cinnamic acid 1a affords alkenyl–silver specie. Alkenyl silver
would then transfer the alkenyl group to intermediate II under formation of silver
derivates by transmetallation to give the intermediate III. Finally, the desired product
3a would be released, regenerating the initial palladation species and resuming the
catalytic cycle.
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Scheme 2. Mechanistic Investigations for the Decarboxylative Cross-Coupling Reaction.
Scheme 3. Plausible Mechanism.
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Absorption and emission properties, as well as fluorescence quantum yields (ΦF) of
the synthesized coumarins derivatives 3 are summarized in Table 3. A change of less
than 8 nm for λmax was observed among 3e, 3f, 3g, 3h, 3i by simply modifying the
substituents at the benzene ring moiety position (Table 3, entries 5ꢀ9). In comparison
with 3a and 3b, a longer wavelength of the absorption maximum peak (λmax) was
obtained upon the introduction of electronꢀdonating groups such as ethoxy at the Cꢀ7
position (Table 3, entry 3 vs. 1; entry 4 vs. 2). All of these compounds exhibited
excellent fluorescence, regardless of the electronꢀdonating or withdrawing ability of
the substituents. The fluorescence quantum yield (ΦF) remained in the range of
0.39ꢀ0.92. Obviously, the introduction of electronꢀdonating groups into
3ꢀstyrylcoumarin derivatives showed a better fluorescence quantum yields than
electronꢀwithdrawing groups.
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Table 3. Photophysical Properties of 3-Styrylcoumarin Derivatives 3.
a
c
entry
1
compounds
λmax [nm]
λemb [nm]
ΦF
349
440
0.67
3a
2
3
354
358
365
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443
0.76
0.83
0.92
0.81
0.88
0.87
0.39
0.52
0.79
0.86
0.82
0.75
3b
3k
3l
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5
3e
3f
6
7
3g
3h
3i
8
9
10
11
12
13
3j
3m
3n
3o
aAbsorption maxima in acetonitrile (longest wavelength transition). bMaxima of the corrected emission
spectra in acetonitrile. cDetermined by quinine sulfate (ΦF = 0.55, excited at 347 nm) as a standard.
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In summary, we have successfully developed a flexible and rapid route to
synthesize series of 3ꢀstyryl coumarins from cinnamic acids and coumarins via a
palladium catalyzed decarboxylative crossꢀcoupling reaction. 3ꢀStyrylcoumarins were
obtained in moderate to good yields and showed good fluorescence quantums. The
current study provides a clue for the further development of new types fluorescent
materials.
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EXPERIMENTAL SECTION
The reaction mixture of coumarins 1 (0.3 mmol), alkenyl acid 2 (0.2 mmol), Pd(OAc)2 (20 mol %), Ag2CO3 (2
equiv), 1,10ꢀphenanthroline (20 mol %), DMSO (2 mL) was stirred at 130 oC for 72 h in sealed tube, and
monitored periodically by TLC. Upon completion, the reaction mixture was diluted with water (30 mL) and
extracted with ethyl acetate (3 × 30 mL). The combined organic layers were washed with water and brine, dried
over Na2SO4 and filtered. The solvent was removed under vacuum. The residue was purified by flash column
chromatography to afford 3.
3-Styryl-chromen-2-one (3a): Purified via flash column chromatography with 20% ethyl acetate/hexane,
yielding 69% (34.2 mg) as a yellow solid: 161ꢀ163 oC (162ꢀ164 oC)1; 1H NMR (500 MHz, CDCl3) δ 7.83 (s, 1H),
7.63 (d, J = 16.3 Hz, 1H), 7.58ꢀ7.50 (m, 4H), 7.41ꢀ7.30 (m, 5H), 7.16 (d, J = 16.3 Hz, 1H); 13C NMR (125 MHz,
CDCl3) δ 160.4, 152.8, 136.8, 133.6, 131.1, 128.7, 128.4, 127.6, 127.0, 124.9, 124.5, 122.0, 119.7, 116.4.
HRAPCIMS calcd for C17H12O2 (M + H)+ 249.0916; found 249.0908.
Reference1: Gordo, J.; Avo, J.; Parola, A. J.; Lima, J. C.; Pereira, A.; Branco, P. S. Org. Lett., 2011, 13, 5112.
3-(2-p-Tolyl-vinyl)-chromen-2-one (3b): Purified via flash column chromatography with 20% ethyl
acetate/hexane, yielding 72% (37.7 mg) as a yellow solid: 147ꢀ149 oC; 1H NMR (500 MHz, CDCl3) δ 7.71 (s, 1H),
7.49 (d, J = 16.3 Hz, 1H), 7.45ꢀ7.29 (m, 4H), 7.26ꢀ7.18 (m, 2H), 7.10 (d, J = 7.8 Hz, 2H), 7.02 (d, J = 16.3 Hz,
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1H), 2.29 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 160.4, 152.7, 138.5, 136.2, 134.0, 133.6, 130.9, 129.5, 127.5,
126.9, 125.1, 124.5, 121.0, 119.7, 116.4, 21.3. HRAPCIMS calcd for C18H14O2 (M + H)+ 263.1072; found
263.1067.
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3-[2-(4-Chloro-phenyl)-vinyl]-chromen-2-one (3c): Purified via flash column chromatography with 20% ethyl
acetate/hexane, yielding 59% (33.2 mg) as a yellow solid: 154ꢀ156 oC; 1H NMR (500 MHz, CDCl3) δ 7.82 (s, 1H),
7.61 (d, J = 16.5 Hz, 1H), 7.56ꢀ7.45 (m, 4H), 7.37ꢀ7.28 (m, 4H), 7.11 (d, J = 16.3 Hz, 1H); 13C NMR (125 MHz,
CDCl3) δ 160.2, 152.9, 137.3, 135.4, 134.1, 132.4, 131.3, 129.0, 128.1, 127.7, 124.7, 124.6, 122.7, 119.6, 116.5.
HRAPCIMS calcd for C17H11ClO2 (M + H)+ 283.0526; found 283.0523.
3-[2-(4-Fluoro-phenyl)-vinyl]-chromen-2-one (3d): Purified via flash column chromatography with 20% ethyl
acetate/hexane, yielding 53% (28.2 mg) as a yellow solid: 145ꢀ148 oC; 1H NMR (500 MHz, CDCl3) δ 7.86 (s, 1H),
7.70 (d, J = 16.5 Hz, 1H), 7.65ꢀ7.61 (m, 1H), 7.54ꢀ7.48 (m, 2H), 7.34 (d, J = 8.3 Hz, 1H), 7.31ꢀ7.26 (m, 2H),
7.25ꢀ7.19 (m, 1H), 7.15 (t, J = 7.6 Hz, 1H), 7.10ꢀ7.05 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 160.5 (d, J(CꢀF)
=
=
256.8 Hz), 160.4, 153.0, 137.1, 131.3, 129.8 (d, J(CꢀF) = 8.5 Hz), 127.7 (d, J(CꢀF) = 3.3 Hz), 127.5, 125.8 (d, J(CꢀF)
3.7 Hz), 125.0, 124.8 (d, J(CꢀF) = 11.7 Hz), 124.6, 124.4 (d, J = 3.5 Hz), 124.2 (d, J(CꢀF) = 5.3 Hz), 119.6, 116.5,
115.9 (d, J(CꢀF) = 22.0 Hz). HRAPCIMS calcd for C17H11FO2 (M + H)+ 267.0821; found 267.0813.
6-Methyl-3-styryl-chromen-2-one (3e): Purified via flash column chromatography with 20% ethyl
acetate/hexane, yielding 74% (38.7 mg) as a yellow solid: 140ꢀ142 oC; 1H NMR (500 MHz, CDCl3) δ 7.77 (s, 1H),
7.62 (d, J = 16.4 Hz, 1H), 7.59 ꢀ7.55 (m, 2H), 7.40 (t, J = 7.5 Hz, 2H), 7.33ꢀ7.24(m, 4H), 7.16 (d, J = 16.3 Hz, 1H),
2.44 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 160.6, 151.0, 136.9, 134.2, 133.5, 132.2, 130.3, 128.8, 128.4, 127.5,
127.0, 124.8, 122.2, 119.5, 116.2, 20.8. HRAPCIMS calcd for C18H14O2 (M + H)+ 263.1072; found 263.1067.
6-Methyl-3-(2-p-tolyl-vinyl)-chromen-2-one (3f): Purified via flash column chromatography with 20% ethyl
acetate/hexane, yielding 75% (41.4 mg) as a yellow solid: 172ꢀ174 oC; 1H NMR (500 MHz, CDCl3) δ 7.73 (s, 1H),
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7.57 (d, J = 16.4 Hz, 1H), 7.47 (d, J = 8.1 Hz, 2H), 7.31ꢀ7.28 (m, 2H), 7.24ꢀ7.19 (m, 3H), 7.11 (d, J = 16.3 Hz,
1H), 2.43 (s, 3H), 2.39 (s, 3H).; 13C NMR (125 MHz, CDCl3) δ 160.7, 1510, 138.5, 136.4, 134.2, 132,1, 133.4,
132.1, 129.5 127.4, 126.9, 125.0, 121.2, 119.5, 116.1, 21.4, 20.8. HRAPCIMS calcd for C19H16O2 (M + H)+
277.1229; found 277.1224.
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6-Methyl-3-(2-m-tolyl-vinyl)-chromen-2-one (3g): Purified via flash column chromatography with 20% ethyl
acetate/hexane, yielding 74% (41.4 mg) as a yellow solid: 144ꢀ145 oC; 1H NMR (500 MHz, CDCl3) δ 7.77 (s, 1H),
7.58 (d, J = 16.3 Hz, 1H), 7.41ꢀ7.36 (m, 2H), 7.32ꢀ7.25 (m, 4H), 7.18ꢀ7.13 (m, 2H), 2.44 (s, 3H), 2.41 (s, 3H); 13C
NMR (125 MHz, CDCl3) δ 160.7, 151.0, 138.3, 136.8, 136.6, 134.2, 133.5, 132.2, 129.3, 128.6, 127.6, 127.4,
124.9, 124.2, 121.9, 119.5, 116.1, 21.4, 20.8. HRAPCIMS calcd for C19H16O2 (M + H)+ 277.1229; found
277.1225.
3-[2-(4-Chloro-phenyl)-vinyl]-6-methyl-chromen-2-one (3h): Purified via flash column chromatography with
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20% ethyl acetate/hexane, yielding 62% (36.7 mg) as a yellow solid: 164ꢀ166 C; H NMR (500 MHz, CDCl3) δ
7.75 (s, 1H), 7.59 (d, J = 16.3 Hz, 1H), 7.48 (d, J = 8.1 Hz, 2H), 7.32 (dd, J = 24.8, 9.4 Hz, 4H), 7.24 (d, J = 8.3
Hz, 1H), 7.09 (d, J = 16.3 Hz, 1H), 2.44 (s, 3H);13C NMR (125 MHz, CDCl3) δ 160.5, 151.0, 137.4, 135.4, 134.3,
134.0, 132.4, 132.2, 128.9, 128.1, 127.5, 124.5,122.9,119.3, 116.2, 20.8. HRAPCIMS calcd for C18H13ClO2 (M +
H)+ 297.0682; found 297.0680.
3-[2-(4-Fluoro-phenyl)-vinyl]-6-methyl-chromen-2-one (3i): Purified via flash column chromatography with
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20% ethyl acetate/hexane, yielding 55% (30.8 mg) as a yellow solid: 144ꢀ145 C; H NMR (500 MHz, CDCl3) δ
7.72 (s, 1H), 7.57 (d, J = 16.3 Hz, 1H), 7.51 (dd, J = 8.1, 5.6 Hz, 2H), 7.30 (d, J = 8.7 Hz, 2H), 7.22 (d, J = 8.2 Hz,
1H), 7.05 (dd, J = 10.9, 6.1 Hz, 3H), 2.41 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 162.8 (d, J(CꢀF) = 247.0 Hz),
160.6, 151.0, 137.0, 134.2, 133.1 (d, J(CꢀF) = 3.7 Hz), 132.3, 131.4, 128.6 (d, J(CꢀF) = 8.0 Hz), 127.4, 124.6, 122.1,
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119.4, 116.2, 115.8 (d, J(CꢀF) = 21.6 Hz), 20.8. HRAPCIMS calcd for C18H13FO2 (M + H)+ 281.0978; found
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3-[2-(4-Chloro-phenyl)-vinyl]-7-methoxy-chromen-2-one (3j): Purified via flash column chromatography with
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20% ethyl acetate/hexane, yielding 64% (39.9 mg) as a yellow solid: 179ꢀ181 C; H NMR (500 MHz, CDCl3) δ
7.74 (s, 1H), 7.52 (d, J = 16.4 Hz, 1H), 7.44ꢀ7.40 (m, 3H), 7.32 (d, J = 8.5 Hz, 2H), 7.05 (d, J = 16.3 Hz, 1H),
6.88ꢀ6.82 (m, 2H), 3.88 (s, 3H);13C NMR (125 MHz, CDCl3) δ 162.7, 160.5,154.7,137.8, 135.7,133.8,131.1, 128.9,
128.7, 128.0, 123.0, 121.3,113.3,113.1, 100.5, 55.8. HRAPCIMS calcd for C18H13ClO3 (M + H)+ 313.0631; found
313.0627.
7-Ethoxy-3-styryl-chromen-2-one (3k): Purified via flash column chromatography with 20% ethyl
acetate/hexane, yielding 75% (43.8 mg) as a yellow solid: 147ꢀ148 oC; 1H NMR (500 MHz, CDCl3) δ 7.75 (s, 1H),
7.56ꢀ7.53 (m, 3H), 7.42ꢀ7.29 (m, 3H), 7.30 (d, J = 7.4 Hz, 1H), 7.11 (d, J = 16.4 Hz, 1H), 6.86 (dd, J = 8.6, 2.3 Hz,
1H), 6.82 (d, J = 2.1 Hz, 1H), 4.10 (q, J = 7.0 Hz, 2H), 1.47 (t, J = 7.0 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ
161.9, 160.7, 154.7, 137.3, 137.1, 132.2, 128. 7, 128.6, 128.1, 126.8, 122.4,121.4, 113.3, 113.2, 100.9, 64.2, 14.6.
HRAPCIMS calcd for C19H16O3 (M + H)+ 293.1178; found 293.1171.
7-Ethoxy-3-styryl-chromen-2-one (3l): Purified via flash column chromatography with 20% ethyl
acetate/hexane, yielding 78% (47.8 mg) as a yellow solid: 148ꢀ150 oC; 1H NMR (500 MHz, CDCl3) δ 7.73 (s, 1H),
7.49 (d, J = 16.3 Hz, 1H), 7.43 (d, J = 8.1 Hz, 2H), 7.39 (d, J = 8.6 Hz, 1H), 7.17 (d, J = 7.9 Hz, 2H), 7.06 (d, J =
16.3 Hz, 1H), 6.84 (dd, J = 8.6, 2.4 Hz, 1H), 6.81 (d, J = 2.4 Hz, 1H), 4.09 (q, J = 7.0 Hz, 2H), 2.36 (s, 3H), 1.46 (t,
J = 7.0 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 161.8, 160.8, 154.6, 138.2, 136.8, 134.3, 132.2, 129.5, 128.5,
126.8, 121.6, 121.3, 113.3,113.2, 100.9, 64.2, 21.3, 14.6. HRAPCIMS calcd for C20H18O3 (M + H)+ 307.1334;
found 307.1332.
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7-Ethoxy-3-(2-m-tolyl-vinyl)-chromen-2-one (3m): Purified via flash column chromatography with 20% ethyl
acetate/hexane, yielding 74% (45.2 mg) as a yellow solid: 138ꢀ140 oC; 1H NMR (500 MHz, CDCl3) δ 7.77 (s, 1H),
7.51 (d, J = 16.3 Hz, 1H), 7.44ꢀ7.33 (m, 3H), 7.28 (d, J = 6.0 Hz, 1H), 7.12 (dd, J = 12.2, 4.0 Hz, 2H), 6.90ꢀ6.81
(m, 2H), 4.12 (q, J = 6.9 Hz, 2H), 2.40 (s, 3H), 1.49 (t, J = 7.0 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 161.8,
160.8, 154.6, 138.3, 137.0, 132.3, 129.0, 128.6, 128.5, 127.5, 124.1, 122.1, 121.5, 113.3, 113.2, 100.9, 64.2, 21.4,
14.6. HRAPCIMS calcd for C20H18O3 (M + H)+ 307.1334; found 307.1331.
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7-Ethoxy-3-[2-(4-fluoro-phenyl)-vinyl]-chromen-2-one (3n): Purified via flash column chromatography with
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20% ethyl acetate/hexane, yielding 61% (37.8 mg) as a yellow solid: 118ꢀ120 C; H NMR (500 MHz, CDCl3) δ
7.74 (s, 1H), 7.52ꢀ7.49 (m, 2H), 7.41 (d, J = 8.5 Hz, 1H), 7.08ꢀ6.99 (m, 3H), 6.91ꢀ6.77 (m, 3H), 4.11 (q, 6.9 Hz,
2H), 1.47 (t, J = 7.0 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 162.6 (d, J(CꢀF) = 246.6 Hz), 161.9, 154.6, 137.4,
133.3 (d, J(CꢀF) = 3.3 Hz), 131.0, 128.6, 128.3 (d, J(CꢀF) = 8.0 Hz), 122.2, 121.2, 115.7 (d, J(CꢀF) = 21.6 Hz), 113.3,
113.2, 108.9, 100.9, 64.2, 14.5. HRAPCIMS calcd for C19H15FO3 (M + H)+ 311.1083; found 311.1067.
3-[2-(4-Chloro-phenyl)-vinyl]-7-ethoxy-chromen-2-one (3o): Purified via flash column chromatography with
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20% ethyl acetate/hexane, yielding 60% (39.1 mg) as a yellow solid: 118ꢀ120 C; H NMR (500 MHz, CDCl3) δ
7.73 (s, 1H), 7.50 (d, J = 16.4 Hz, 1H), 7.44 (d, J = 8.5 Hz, 2H), 7.39 (d, J = 8.6 Hz, 1H), 7.31 (d, J = 8.5 Hz, 2H),
7.03 (d, J = 16.3 Hz, 1H), 6.84 (dd, J = 8.6, 2.3 Hz, 1H), 6.80 (d, J = 2.3 Hz, 1H), 4.09 (q, J = 7.0 Hz, 2H), 1.45 (t,
J = 7.0 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 162.1, 160.6, 154.7, 137.8, 135.7, 133.7, 130.9, 128.9, 128.7,
127.9, 123.1, 121.1, 113.4, 113.1, 100.9, 64.2, 14.6. HRAPCIMS calcd for C19H15ClO3 (M + H)+ 327.0788; found
327.0782.
6-Nitro-3-(2-p-tolyl-vinyl)-chromen-2-one (3p): HRAPCIMS calcd for C18H13NO4 (M + Na)+ 330.0742; found
330.0739.
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1-Methyl-3-(2-p-tolyl-vinyl)-1H-quinolin-2-one (3q): Purified via flash column chromatography with 20%
ethyl acetate/hexane, yielding 42% (24.7 mg) as a yellow oil; 1H NMR (500 MHz, CDCl3) δ 7.88 (s, 1H), 7.60 (d,
J = 7.7 Hz, 1H), 7.56ꢀ7.45 (m, 4H), 7.40 ꢀ7.34 (m, 2H), 7.23 (d, J = 7.6 Hz, 1H), 7.17 (d, J = 7.8 Hz, 2H), 3.79 (s,
3H), 2.36 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 161.7, 139.0, 137.9, 134.8, 132.9, 131.7, 129.9, 129.4, 128.6,
128.2, 126.8, 122.5, 122.3, 120.9, 114.0, 29.9, 21.3. HRAPCIMS calcd for C19H17NO (M + H)+ 276.1388; found
276.1380.
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3-[2-(4-Chloro-phenyl)-vinyl]-1-methyl-1H-quinolin-2-one (3r): Purified via flash column chromatography
with 20% ethyl acetate/hexane, yielding 40% (23.6 mg) as a yellow oil; 1H NMR (500 MHz, CDCl3) δ 7.88 (s, 1H),
7.60 (d, J = 7.8 Hz, 1H), 7.55ꢀ7.48 (m, 4H), 7.39ꢀ7.29 (m, 5H), 3.79 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 161.6,
139.1, 136.0, 133.8, 133.5, 130.5, 130.3, 128.8, 128.,7, 128.4, 128.0, 124.3, 122.4, 120,7, 114.0, 29.7. HRAPCIMS
calcd for C18H15ClNO (M + H)+ 296.0842; found 296.0834.
ASSOCIATED CONTENT
Supporting Information
Detailed experimental procedures and characterization of new compounds. This material is available free of charge
via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
panym2013@hotmail.com; chenzfubc@yahoo.com
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
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We thank Ministry of Education of China (IRT1225), the National Natural Science Foundation of China
(21362002, 41465009 and 81260472), Guangxi Natural Science Foundation of China (2012GXNSFAA053027
and 2014GXNSFDA118007), State Key Laboratory Cultivation Base for the Chemistry and Molecular
Engineering of Medicinal Resources, Ministry of Science and Technology of China (CMEMR2014ꢀA02,
CMEMR2014ꢀA04 and CMEMR2013ꢀC01), and Bagui Scholar Program.
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REFERENCES
(1) (a) Li, C.; Breit, B. J. Am. Chem. Soc. 2014, 136, 862. (b) Neely, J. M.; Rovis, T. J. Am. Chem. Soc. 2014, 136,
2735. (c) Gooßen, L. J.; Rodríguez, N.; Lange, P. P. Angew. Chem., Int. Ed. 2010, 49, 1111. (d) Weaver, J. D.; Recio, A.;
Grenning, A. J.; Tunge, J. A. Chem. Rev. 2011, 111, 1846. (e) Shang, R.; Liu, L. Sci. Chin. Chem. 2011, 54, 1670. (f)
Rodríguez, N.; Gooßen, L. J. Chem. Soc. Rev. 2011, 40, 5030. (g) Dzik, W. I.; Lange, P. P.; Goossen, L. J. Chem. Sci.
2012, 3, 2671. (h) Song, B.; Knauber, T.; Gooßen, L, J. Angew. Chem., Int. Ed. 2013, 52, 2954. (i) Zhang, M.; Zhou, J.;
Kan, J.; Wang, M.; Su, W.; Hong, M. Chem. Commun. 2010, 46, 5455. (j) Zhou, J.; Wu, G.; Zhang, M.; Jie, X.; Su, W.
Chem. Eur. J. 2012, 18, 8032. (k) Xiang, S. H.; Cai, S. T.; Zeng, J.; Liu, X. W. Org. Lett. 2011, 13, 4608.
(2) (a) Huang, L.; Qi, J.; Wu, X.; Huang, K.; Jiang, H. Org. Lett. 2013, 15. 2330. (b) Myers, A. G.; Tanaka, D.;
Mannion, M. R. J. Am. Chem. Soc. 2002, 124, 11250. (c) Forgione, P.; Brochu, M. C.; Stonge, M.; Thesen, K. H.; Bailey,
M. D.; Bilodeau, F. J. Am. Chem. Soc. 2006, 128, 11350. (d) Maehara, A.; Tsurugi, H.; Satoh, T.; Miura, M. Org. Lett.
2008, 10, 1159. (e) Hu, P.; Kan, J.; Su, W.; Hong, M. Org. Lett. 2009, 11, 2341. (f) Myers, A. G.; Tanaka, D.; Mannion,
M. R. J. Am. Chem. Soc. 2002, 124, 11250. (g) Tanaka, D.; Romeril, S. P.; Myers, A. G. J. Am. Chem. Soc. 2005, 127,
10323. (h) Tanaka, D.; Myers, A. G. Org. Lett. 2004, 6, 433. (i) Fu, Z.; Huang, S.; Su, W.; Hong, M. Org. Lett. 2010, 12,
4992.
(3) (a) Voutchkova, A.; Coplin, A.; Leadbeater, N. E.; Crabtree, R. H. Chem. Commun. 2008, 6312. (b) Wang, C.; Piel,
I.; Glorius, F. J. Am. Chem. Soc. 2009, 131, 4194.
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4
5
6
(4) (a) Gooßen, L. J.; Deng, G.; Levy, L. M. Science. 2006, 313, 662. (b) Gooßen, L. J.; Rodríguez, N.; Melzer, B.;
Linder, C.; Deng, G.; Levy, L. M. J. Am. Chem. Soc. 2007, 129, 4824.
7
8
9
(5) Rayabarapu, D. K.; Tunge, J. A. J. Am. Chem. Soc. 2005, 127, 13510.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
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41
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43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(6) Gooßen, L. J.; Gooßen, K. Top. Organomet. Chem. 2013, 44, 121.
(7) Rokade, B. V.; Prabhu, K. R. Org. Biomol. Chem. 2013, 11, 6713.
(8) Xu, Y. L.; Tang, X. D.; Hu, W. G.; Wu, W. Q.; Jiang, H. F. Green Chem. 2014. 16, 3720.
(9) Hu, J.; Zhao, N.; Yang, B.; Wang, G.; Guo, L. N.; Liang, Y. M.; Yang, S. D. Chem.-Eur. J. 2011, 17, 5516.
(10) (a) Kostova, I.; Nikolov, N.; Chipilska, L. J. Ethnopharmacol. 1993, 39, 205. (b) Hoult, J. R. S.; Paya, M. Gen.
Pharmac. 1996, 27, 713. (c) Eckardt, T.; Hagen, V.; Schade, B.; Schmidt, R.; Schweitzer, C.; Bendig, J. J. Org. Chem.
2002, 67, 703. (d) Wang, C. J.; Hsieh, Y. J.; Chu, C. Y.; Lin, Y. Y.; Tseng, T. H. Cancer Lett. 2002, 183, 163. (e) Zhao,
Y.; Zheng, Q.; Dakin, K.; Xu, K.; Martinez, M. L.; Li, W. H. J. Am. Chem. Soc. 2004, 126, 4653. (f) Komatsu, K.; Urano,
Y.; Kojima, H.; Nagano, T. J. Am. Chem. Soc. 2007, 129, 13447. (g) Signore, G.; Nifosi, R.; Albertazzi, L.; Storti, B.;
Bizzarri, R. J. Am. Chem. Soc. 2010, 132, 1276. (h) Wang, C.; Wu, C.; Zhu, J.; Miller, R. H.; Wang, Y. J. Med. Chem.
2011, 54, 2331. (i) Devji, T.; Reddy, C.; Woo, C.; Awale, S.; Kadota, S.; CarricoꢀMoniz, D. Bioorg. Med. Chem. Lett.
2011, 21, 5770. (j) Matos, M. J.; VazquezꢀRodriguez, S.; Santana, L.; Uriarte, E.; FuentesꢀEdfuf, C.; Santos, Y.;
MunozꢀCrego, A. Molecules. 2013, 18, 1394.
(11) (a) Christie, R. M.; Lui, C. H. Dyes Pigm. 2000, 47, 79. (b) Schiedel, M. S.; Briehn, C. A.; Bäuerle, P. Angew.
Chem. Int., Ed. 2001, 40, 4677. (c) Elangovan, A.; Lin, J. H.; Yang, S. W.; Hsu, H. Y.; Ho, T. I. J. Org. Chem. 2004, 69,
8086. (d) Turki, H.; Abid, S.; El Gharbi, R.; FeryꢀForgues, S. C. R. Chimie. 2006, 9, 1252. (e) Uchiyama, S.; Takehira, K.;
Yoshihara, T.; Tobita, S.; Ohwada, T. Org. Lett. 2006, 8, 5869. (f) Hirano, T.; Hiromoto, K.; Kagechika, H. Org. Lett.
2007, 9, 1315.
(12) (a) Gordo, J.; Avo, J.; Parola, A. J.; Lima, J. C.; Pereira, A.; Branco, P. S. Org. lett. 2011, 13, 5112. (b)
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Kuznetsova, N. A.; Kaliya, O. L. Usp. Khimii. 1992, 61, 1243.
5
6
7
8
9
(13) (a) Chang, C. H.; Cheng, H. C.; Lu, Y. J.; Tien, K. C.; Lin, H. W.; Lin, C. L.; Yang, C. J.; Wu, C. C. Org.
Electron. 2010, 11, 247. (b) Yu, T. Z.; Zhang, P.; Zhao, Y. L.; Zhang, H.; Meng, J.; Fan, D. W. Org. Electron. 2009, 10,
653.
10
11
12
13
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17
18
19
20
21
22
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26
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49
50
51
52
53
54
55
56
57
58
59
60
(14) (a) Dorlars, A.; Schellhammer, C. W.; Schroeder, J. Angew. Chem., Int. Ed. Engl. 1975, 14, 665. (b) Kido, J.;
Iizumi, Y. Appl. Phys. Lett. 1998, 73, 2721.
(15) Painelli, A.; Terenziani, F. Synth. Met. 2001, 124, 171.
(16) Rrajitha, B.; Naveen, V.; Someshwar, P.; Narsimha, P.; Thirupathi,Y. Arkivoc. 2006, 12, 23.
(17) (a) Jung, H. S.; Kwon, P. S.; Lee, J. W.; Kim, J. I.; Hong, C. S.; Kim, J. W.; Yan, S. H.; Lee, J. Y.; Lee, J. H.; Joo,
T.; Kim, J. S. J. Am. Chem. Soc. 2009, 131, 2008. (b) Sheng, R. L.; Wang, P. F.; Gao, Y. H.; Wu, Y.; Liu, W. M.; Ma, J.
J.; Li, H. P.; Wu, S. K. Org. Lett. 2008, 10, 5015.
(18) Carter, K. P., Young, A. M., Palmer, A. E. Chem. Rev. 2014, 114, 4564.
(19) (a) Schiedel, M. S.; Briehn, C. A.; Bäuerle, P. Angew. Chem., Int. Ed. 2001, 40, 4677. (b) Gordo, J.; Avo, J.;
Parola, A. J.; Lima, J. C.; Pereira, A.; Branco, P. S. Org. Lett. 2011, 13, 5112. (c) Jafarpour, F.; Zarei, S.; Olia, M. B. A.;
Jalalimanesh, N.; Rahiminejadan, S. J. Org. Chem. 2013, 78, 2957. (d) Min, M.; Kim, Y.; Hong, S. Chem. Commun.
2013, 49, 196.
(20) (a) Wang, X.; Li, S. Y.; Pan, Y. M.; Wang, H. S.; Liang, H.; Chen, Z. F.; Qin, X. H. Org. Lett. 2014, 16, 580.
(21) (a) Mi, X.; Huang, M. M.; Zhang, J. Y.; Wang, C. Y.; Wu, Y. J. Org. Lett. 2013, 15, 6266. (b) Hu, J., Zhao, N.,
Yang, B., Wang, G., Guo, L. N., Liang, Y. M., Yang, S. D. Chem.-Eur. J. 2011, 17, 5516.
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