Regioselective Bismuth-Catalyzed Synthesis of Pyranocoumarins and Furocoumarins from 4-Hydroxycoumarins and Propargyl Alcohols

Article abstract of DOI:10.1002/bkcs.12058

An efficient method for the bismuth-catalyzed regioselective synthesis of pyranocoumarins and furocoumarins has been developed from the reaction of 4-hydroxycoumarins with propargyl alcohols. The reaction proceeds through sequential propargylation and int

Full text of DOI:10.1002/bkcs.12058

Article
DOI: 10.1002/bkcs.12058
BULLETIN OF THE
J. Kim et al.
KOREAN CHEMICAL SOCIETY
Regioselective Bismuth-Catalyzed Synthesis of Pyranocoumarins and
Furocoumarins from 4-Hydroxycoumarins and Propargyl Alcohols
‡,
Jaehyun Kim,† Kooyeon Lee,†, and Phil Ho Lee
*
*
†Department of Bio-Health Technology, Kangwon National University, Chuncheon 24341, Republic of
Korea
‡Department of Chemistry, Kangwon National University, Chuncheon 24341, Republic of Korea.
*E-mails: lky@kangwon.ac.kr, phlee@kangwon.ac.kr
Received April 15, 2020, Accepted May 6, 2020
An efficient method for the bismuth-catalyzed regioselective synthesis of pyranocoumarins and fur-
ocoumarins has been developed from the reaction of 4-hydroxycoumarins with propargyl alcohols. The
reaction proceeds through sequential propargylation and intramolecular cyclization reactions catalyzed by
bismuth(III) triflate.
Keywords: Bismuth, Catalysis, Pyranocoumarin, Furocoumarin, Regioselectivity
Introduction
reactions occasionally suffer from introduction of the same
aryl group on the substrate and formation of a mixture of
pyranocoumarins and furocoumarins. Thus, the develop-
ment of new and convenient methods to regioselectively
prepare pyranocoumarins and furocoumarins is continu-
ously required.
Pyranocoumarins and furocoumarins are important
privileged scaffolds among naturally occurring oxygen-con-
taining cyclic compounds and have been shown to have a
wide range of bioactivities such as antifungal, anticancer,
anti-HIV, anti-inflammatory, antioxidant, antiproliferative,
antibacterial, and insecticidal activities.1 Recently, these
compounds have received considerable attention in medici-
nal chemistry for the treatment of skin disorders.2 For
example, neo-tanshinlactone is a kind of furocoumarin that
was isolated from the rhizome of Salvia miltiorrhiza Bunge.
The agent has shown potent and selective activity against
breast cancer.3 For this reason, many chemists are inter-
ested in the development of synthetic methods for
pyranocoumarins and furocoumarins (Scheme 1).4,5 Typi-
cally, pyranocoumarins are prepared from the reaction of 4-
hydroxycoumarins with various electrophiles including 1,3-
diarylallylic compounds (a),6a propargyl alcohols (b),6b and
α,β-unsaturated aldehydes or ketones (c),6c as well as mul-
ticomponent reactions.7 Additionally, Ru-catalyzed reaction
of 4-hydroxycoumarins with propargyl alcohols has been
shown to produce pyranocoumarins (d).6d In 2015,
Bezuidenhoudt and co-workers reported a catalytic system
involving Al(OTf)3 and organocatalysts (DBU, NMM) that
could promote coupling of 4-hydroxycoumarins with acti-
vated propargyl alcohols for the synthesis of either
pyranocoumarins or furocoumarins (e).6e Recently,
Yaragorla and co-workers reported an efficient
regioselective synthesis of fused and substituted furans
using Ca(OTf)2 as the catalyst (f).6f More recently, Ren and
Wang developed regioselective access to structurally
diverse coumarin derivatives through iron-catalyzed annula-
tion reactions (g).6g Although the previously reported
methods are effective and have many advantages, these
Bismuth catalysts have received considerable attention
due to their low toxicity and cost, ease of handling, high
catalytic efficiency, and stability.8 Moreover, bismuth is a
well-known catalyst for the dual activation of alkynes and
hydroxyl groups through σ,π-chelation, as reported by
Shibasaki et al.9 Because of these characteristics, bismuth
is an efficient catalyst for propargylation through σ,π-dual
activation of propargyl alcohols. In addition, sequential pro-
cesses that involve multiple chemical transformations in
one-pot, with minimal work-up steps and less waste genera-
tion, have improved synthetic chemistry in recent years.
In continuation with our investigations directed toward
the synthesis of coumarin, phosphacoumarin, and
phosphaisocoumarin derivatives,10 we report herein a
regioselective Bi-catalyzed synthesis of pyranocoumarins
and furocoumarins through sequential propargylation and
cyclization reactions (Scheme 2).
Results and Discussion
The initial cyclization was carried out with 4-
hydroxycoumarin (1a) and 1,3-diphenylprop-2-yn-1-ol (2a)
in the presence of a variety of metal triflates in chloroben-
zene (Table 1). When Yb(OTf)3 (10 mol %) was used as a
catalyst, a propargylated coumarin 3a was selectively pro-
duced in 59% yield (entry 1). Although In(OTf)3 and Fe
(OTf)3 gave 3a as the major product, Cu(OTf)2 and AgOTf
selectively provided the desired pyranocoumarin 4a even at
low yields (entries 4 and 5). Gratifyingly, Bi(OTf)3
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(a)
(b)
(c)
(d)
(e)
(f)
(g)
Scheme 1. Previously reported synthetic methods of pyranocoumarins and furocoumarins.
increased the yield of 3a up to 56%, maintaining high
selectivity (entry 6). These results indicate that Bi(OTf)3
efficiently catalyzes propargylation followed by cyclization
in one-pot. Next, a wide range of solvents, including chlo-
robenzene, dichloroethane, tetrahydrofuran, diglyme, tolu-
ene, and nitromethane (CH3NO2), were screened, and
CH3NO2 gave the best result (entry 11). When the amount
of Bi(OTf)3 was decreased to 5 mol%, the yield of 4a
decreased to 65%, maintaining the selectivity (entry 12).
Next, BiCl3 and Bi(NO3)3ꢀ5H2O were examined to deter-
mine the optimum catalyst. In contrast to Bi(OTf)3, BiCl3
afforded propargylated coumarin 3a as the major product
(entry 13). However, Bi(NO3)3ꢀ5H2O was inefficient as a
catalyst (entry 14). When AgOTf (30 mol%) was used in
the presence of BiCl3 (10 mol%), 4a was obtained in 61%
yield (entry 15). To check the possibility of catalysis by a
protic acid, we attempted the sequential propargylation and
cyclization
reaction
in
the
presence
of
trifluoromethanesulfonic acid (10 mol%) in CH3NO2 at 100
ꢁC, which produced 3a in 13% yield (entry 16). These
results indicate that Bi(OTf)3 is essential for the selective
synthesis of pyranocoumarin 4a. The optimum conditions
were obtained from the reaction of 1a (1.2 equiv) with 2a
(0.2 mmol, 1.0 equiv) using Bi(OTf)3 (10 mol%) in
CH3NO2 at 100 ꢁC for 8 h, providing 4a in 83% yield
(entry 11).
Stimulated by these results, the scope of propargyl alco-
hols and coumarins was examined (Table 2). First, many
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Regioselective Bismuth-Catalyzed Synthesis of Pyranocoumarins
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substituents were examined as the R2 group on the aryl ring
of the propargyl alcohol (2). Substrates bearing electron-
donating 2-methyl and 3-methoxy groups were cyclized to
afford 4b and 4c in 53% and 40%, respectively. Moreover,
3-Cl- and 2-Br-substituted propargyl alcohols provided the
desired pyranocoumarins 4d (79%) and 4e (70%). Electron-
withdrawing groups including 4-CF3 and 3-NO2 gave the
corresponding pyranocoumarins (4f and 4g) in 90% and
66% yields, respectively. As a result, it was determined that
substrates with electron-withdrawing groups were more
reactive than those with electron-donating groups, and the
positional characteristics were not significant in these reac-
tions. We also investigated the effects of substituents at the
R3 position. Propargyl alcohols substituted with 2-methyl-
and 3-chlorophenyl groups on R3 gave the desired
pyranocoumarins 4h and 4j in 77% and 65% yields, respec-
tively. However, the propargyl alcohol substituted with the
strong electron-donating 3-methoxyphenyl group was less
reactive. Next, some substituents such as methyl, tert-butyl,
methoxy, and benzo groups were introduced into the R1
position of 4-hydroxycoumarin to investigate the reactivity
of the substrate. When the 4-hydroxycoumarins bore
methyl groups at positions
6 and 8, the desired
pyranocoumarins 4k and 4l were produced in 65% and
72% yields, respectively. In the case of 6,8-di(tert-butyl)-
and 7-methoxy-substituted 4-hydroxycoumarins, the
corresponding pyranocoumarins (4m and 4n) were obtained
in moderate yields. When 4-hydroxy-2H-benzo[h]chromen-
2-one was used, pyranocoumarin 4o was produced in 30%
yield. Unfortunately, the reaction did not proceed when R2
was replaced with aliphatic groups.
To broaden the scope of the reaction, we applied 1-
phenylprop-2-yn-1-ol (5a), which is a terminal propargyl
alcohol, in the reaction with 4-hydroxycoumarin 1a under
the optimum reaction conditions (Table 3). Surprisingly,
furocoumarin (6a) and furochromone (7a) instead of
pyranocoumarin were obtained in 51% and 27% yields,
Scheme 2. Selective Bi-catalyzed synthesis of pyranocoumarins
and furocoumarins.
Table 1. Reaction optimization for the regioselective synthesis of pyranocoumarins.a
Entry
Cat (mol %)
Solvent
Temp (ꢁC)
Time (h)
Yield (%)b (3a:4a)
1
2
3
4
5
6
7
8
Yb(OTf)3 (10)
In(OTf)3 (10)
Fe(OTf)3 (10)
Cu(OTf)2 (10)
AgOTf (10)
Bi(OTf)3 (10)
Bi(OTf)3 (10)
Bi(OTf)3 (10)
Bi(OTf)3 (10)
Bi(OTf)3 (10)
Bi(OTf)3 (10)
Bi(OTf)3 (5)
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
DCE
THF
diglyme
toluene
CH3NO2
CH3NO2
CH3NO2
CH3NO2
CH3NO2
CH3NO2
100
100
100
100
100
100
84
24
24
24
24
10
24
24
24
24
24
8
59:0
43:16
43:16
0:28
0:32
0:56 (51)c
23:25
42:25
3:52
66
9
100
100
100
100
100
100
100
100
10
11
12
13
14
15
16
0:65
0:83 (79)c
0:65
8
BiCl3 (10)
24
24
24
8
64:4
0:0
0:61
0:13
Bi(NO3)3ꢀ5H2O
BiCl3 (10)/AgOTf (30)
TfOH (10)
a Reaction conditions: 4-Hydroxycoumarin (1a, 1.2 equiv) and 1,3-diphenylprop-2-yn-1-ol (2a, 0.2 mmol, 1 equiv) were used in solvent (1.0 mL)
under air.
b NMR yields using dibromomethane as the internal standard.
c Isolated yield.
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Regioselective Bismuth-Catalyzed Synthesis of Pyranocoumarins
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Table 2. Regioselective synthesis of pyranocoumarins.a
Table 3. Reaction optimization for the synthesis of
furocoumarins.a
Entry Solvent
Temp (ꢁC) Time (h) Yield (%)b (6a:7a)
1
2
3
CH3NO2
PhCl
DCE
100
100
84
3.5 51:27
3.5 34:22
3.5 42:39
4
5
6c
1,4-dioxane
diglyme
diglyme
100
100
100
3
3
14
63:10
71:5
10:70
a Reaction conditions: 4-Hydroxycoumarin (1a, 1.2 equiv) and 1,3-
diphenylprop-2-yn-1-ol (5a, 0.2 mmol, 1 equiv) were used in solvent
(1.0 mL) under air.
b NMR yields using dibromomethane as an internal standard.
c TfOH (10 mol %) was used instead of Bi(OTf)3.
With these results in hand, a wide range of substrates
were applied in the regioselective synthesis of fur-
ocoumarins (6) (Table 4). When R2 was 2- and 3-tolyl
groups, 6b and 6c were obtained in 68% and 57% yields,
respectively. In the case of a propargyl alcohol with a 4-
methoxyphenyl group, the corresponding furocoumarin 6d
was produced in 63% yield. The reactivity of 4-
chlorophenyl-substituted propargyl alcohol was poor. 1-
Naphthyl-substituted propargyl alcohol was applied to the
present transformation, providing the corresponding
furocoumarin 6f in 65% yield. When a propargyl alcohol
bearing a thiophen-2-yl group was used, 6g was produced
in 42% yield. Methyl and chloro-substituted 4-
hydroxycoumarins were converted to furocoumarins 6h, 6i,
and 6j, respectively, in acceptable yields. Additionally, ben-
zene-ring-fused 4-hydroxycoumarin was subjected to
sequential propargylation and cyclization, producing the
desired furocoumarin 6k in 40% yield. It is noteworthy that
6k is the skeleton of neotanshinlactone, which is an impor-
tant natural product.3 In all cases, a trace amount (5% <) of
the furochromone derivatives 7 was detected.
Although the detailed mechanism remains to be clarified,
a plausible reaction mechanism is shown in Scheme 3. Bi
(OTf)3 is a particularly interesting Lewis acid, with both
oxophilic and carbophilic character, thus presenting broad
catalytic activity and activating carbonyl and hydroxyl
groups as well as isolated C─C multiple bonds.8d,11 Thus,
the proposed mechanism of the present reaction involves
activation of the propargyl alcohol (2 and 5) through
σ,π-dual activation by the bismuth catalyst, which shows
hard/soft borderline characteristics, and the formation of a
propargylation intermediate 3 through attack of the 4-
hydroxycoumarin (1). The resulting intermediate (3) is
a Reaction was carried out with 4-hydroxycoumarin (1, 1.2 equiv),
propargyl alcohol (2, 0.3 mmol, 1.0 equiv), and Bi(OTf)3 (10 mol %)
in CH3NO2 (1.5 mL) at 100 ꢁC for 8–12 h under air.
respectively (entry 1). Regarding the synthesis of fur-
ocoumarins (6a), the selectivity depended on the solvent.
High selectivity was not observed with PhCl and DCE
(entries 2 and 3). In the case of 1,4-dioxane, the ratio of
6a and 7a increased to 63:10 (entry 4). When diglyme
was used as a solvent, the highest selectivity was
obtained in 76% yield (6a:7a = 14.2:1) (entry 5). To
check the possibility of catalysis by a protic acid, we
attempted the sequential propargylation and cyclization
reaction in the presence of trifluoromethanesulfonic acid
(10 mol %) in diglyme at 100 ꢁC, which produced fur-
ochromone (7a) in 70% yield (entry 6). These results
indicate that Bi(OTf)3 is essential for the selective syn-
thesis of furocoumarin 6a.
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Scheme 3. A proposed mechanism.
again σ,π-dual activated by the bismuth catalyst, and when
an aryl group is present in the R2 position,
pyranocoumarins (4) are obtained through 6-endo-dig cycli-
zation. When no substituents are present in the R2 position,
furocoumarins (6) are obtained through 5-exo-dig cycliza-
tion. The isomerization of the propargylation intermediate
(30) to 300 followed by 5-exo-dig cyclization provides
furochromones (7). Notably, Bi(OTf)3 acts as a bifunctional
catalyst and efficiently catalyzes propargylation as well as
cyclization in one-pot.
Table 4. Regioselective synthesis of furocoumarins.a
Conclusion
In conclusion, a regioselective Bi-catalyzed synthetic
method for pyranocoumarin derivatives has been developed
through sequential propargylation and cyclization reactions
(6-endo mode) of 4-hydroxycoumarins with propargyl alco-
hols. When terminal propargyl alcohols were used, fur-
ocoumarins and furochromones were obtained through the
5-exo mode, and the best selectivity for furocoumarins was
observed with diglyme as the solvent. Elucidation of the
exact reason behind the observed regioselectivity is under-
way in our laboratory.
Experimental
General. The starting 1,3-diphenylprop-2-yn-1-ol12 and 1-
phenylprop-2-yn-1-ol13
derivatives
were
prepared
a Reactions were carried out with 1 (1.2 equiv), 5 (0.3 mmol, 1 equiv),
and Bi(OTf)3 (10 mol %) in diglyme (1.5 mL) at 100 ꢁC for 3 h
under air.
according to the reported literature procedure. Commercial
available reagents were used without purification. All reac-
tion mixtures were stirred magnetically and were monitored
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by thin-layer chromatography using silica gel precoated
glass plates, which were visualized with UV light and then,
developed using either iodine or a solution of anisaldehyde.
Flash column chromatography was carried out using silica
122.7, 120.8, 116.8, 114.6, 114.5, 112.3, 103.7, 103.5,
55.2, 36.6.6
4-(3-Chlorophenyl)-2-phenylpyrano[3,2-c]chromen-5
(4H)-one (4d). Yield: 91 mg (79%); Rf = 0.3 (EtOAc:Hex-
1
1
gel (230–400 mesh). H NMR (400 MHz) and 13C NMR
ane = 1:10); White solid; Melting point: 132–133 C; H
ꢁ
(100 MHz) spectra were recorded on NMR spectrometer.
Deuterated chloroform was used as the solvents, and chem-
ical shift values (δ) are reported in parts per million relative
to the residual signals of these solvent [7.26 for 1H
(chloroform‑d) and δ 77.16 for 13C (chloroform‑d)]. Infra-
red spectra were recorded on FTIR spectrometer. High-res-
olution mass spectra (HRMS) were obtained electron
impact (EI) ionization technique (magnetic sector—electric
sector double focusing mass analyzer) from the Kangwon
National University Central Laboratory and KBSI (Korea
Basic Science Institute Daegu Center). Melting points were
determined in open capillary tube.
NMR (400 MHz, CDCl3, 293 K, TMS) δ 8.03 (dd,
J1 = 1.52 Hz, J2 = 7.92 Hz, 1H), 7.74–7.72 (m, 2H), 7.60–
7.56 (m, 1H), 7.48–7.31 (m, 7H), 7.25–7.19 (m, 2H), 5.79
(d, J = 4.84 Hz, 1H), 4.69 (d, J = 4.84 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ 161.4, 156.0, 152.8, 147.2, 145.6,
134.6, 132.4, 132.3, 129.9, 129.5, 128.8, 128.6, 127.5,
124.7, 124.3, 122.8, 116.9, 114.4, 103.1, 103.0, 36.5.1h
4-(2-Bromophenyl)-2-phenylpyrano[3,2-c]chromen-5
(4H)-one (4e). Yield: 90 mg (70%); Rf = 0.3 (EtOAc:Hex-
ane = 1:10); White power; Melting point: 238–239 C; H
NMR (400 MHz, CDCl3, 293 K, TMS) δ 8.05–8.03 (m,
1H), 7.71–7.68 (m, 2H), 7.63–7.58 (m, 2H), 7.45–7.38 (m,
5H), 7.25–7.17 (m, 2H), 7.11–7.06 (m, 1H), 5.89 (d,
J = 4.64 Hz, 1H), 5.22 (d, J = 4.60 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ 161.1, 157.2, 152.9, 146.7, 142.4,
133.2, 132.5, 132.3, 129.6, 129.3, 128.7, 128.6, 128.1,
124.7, 124.3, 123.3, 122.8, 116.9, 114.3, 102.2, 102.1,
36.4.14
1
ꢁ
General Procedure for Pyrano[3,2-c]coumarins. To a
test tube were added 4-hydroxycoumarin (1, 0.36 mmol),
internal propargyl alcohol (2, 0.3 mmol), and Bi(OTf)3
(10 mol %) in nitromethane (1.5 mL). The resulting mix-
ꢁ
ture was stirred at 100 C for 8–12 h. After completion of
the reaction, the mixture was concentrated and directly
purified by column chromatography on silica gel using
EtOAc:hexane = 1:10.
4-(4-(Trifluoromethyl)phenyl)-2-phenylpyrano[3,2-c]
chromen-5(4H)-one (4f). Yield: 113 mg (90%); Rf = 0.3
(EtOAc:Hexane = 1:10); Light yellow solid; Melting point:
2,4-Diphenyl-4H-pyrano[3,2-c]chromen-5-one
(4a).
1
ꢁ
Yield: 83 mg (79%); Rf = 0.3 (EtOAc:Hexane = 1:10);
White solid; Melting point: 176–178 ꢁC; 1H NMR
(400 MHz, CDCl3, 293 K, TMS) δ 8.02 (dd, J1 = 1.52 Hz,
J2 = 7.92 Hz, 1H), 7.74–7.71 (m, 2H), 7.59–7.54 (m, 1H),
7.47–7.29 (m, 9H), 7.25–7.21 (m, 1H), 5.85–5.84 (d,
J = 4.92 Hz, 1H), 4.72–4.70 (d, J = 4.92 Hz, 1H); 13C
NMR (100 MHz, CDCl3) δ 161.5, 155.8, 152.8, 146.9,
143.6, 132.6, 132.0, 129.3, 128.7, 127.3, 124.7, 124.2,
122.7, 116.9, 114.6, 103.8, 103.7, 36.6.6c
180–182 C; H NMR (400 MHz, CDCl3, 293 K, TMS) δ
8.04 (dd, J1 = 1.52 Hz, J2 = 7.92 Hz, 1H), 7.75–7.72 (m,
2H), 7.62–7.53 (m, 5H), 7.49–7.35 (m, 5H), 5.81 (d,
J = 4.84 Hz, 1H), 4.80 (d, J = 4.84 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ 161.4, 156.1, 152.8, 147.4, 132.4,
132.3, 129.6, 129.3, 128.9, 128.8, 125.7, 125.6, 125.6,
124.7, 124.4, 122.7, 116.9, 114.3, 102.9, 102.8, 36.6; FTIR
(ATR): 3056, 2924, 1928, 1720, 1610, 1322, 1159, 1010,
853, 840, 761, 639, 527, 425 cm−1; HRMS (EI) m/z: M+
Calcd. for C25H15F3O3 420.0973; found 420.0975.15
2-Phenyl-4-o-tolylpyrano[3,2-c]chromen-5(4H)-one (4b).
Yield: 58 mg (53%); Rf = 0.3 (EtOAc: Hexane = 1:10);
4-(3-Nitrophenyl)-2-phenylpyrano[3,2-c]chromen-5(4H)-
one (4g). Yield: 78 mg (66%); Rf = 0.3 (EtOAc:Hex-
ane = 1:10); Light yellow solid; Melting point: 185–186
1
ꢁ
Pale yellow powder; Melting point: 184–186 C; H NMR
(400 MHz, CDCl3, 293 K, TMS) δ 8.04 (dd, J1 = 1.50 Hz,
J2 = 7.90 Hz, 1H), 7.72–7.69 (m, 2H), 7.61–7.57 (m, 1H),
7.46–7.35 (m, 5H), 7.20–7.16 (m, 2H), 7.13–7.10 (m,,2H),
5.78 (d, J = 4.68 Hz, 1H), 4.95 (d, J = 4.68 Hz, 1H); 13C
NMR (100 MHz, CDCl3) δ 161.4, 156.2, 152.7, 146.4,
142.3, 135.6, 132.7, 132.0, 130.6, 129.2, 128.8, 128.6,
126.9, 126.6, 124.6, 124.2, 122.6, 116.8, 114.5, 103.7,
103.4, 32.6, 19.6.6e
1
ꢁC; H NMR (400 MHz, CDCl3, 293 K, TMS) δ 8.25 (t,
J
= 2.0 Hz, 1H), 8.12–8.09 (m, 1H), 8.05 (dd,
J1 = 1.52 Hz, J2 = 7.92 Hz, 1H), 7.81–7.79 (m, 1H), 7.76–
7.73 (m, 2H), 7.63–7.59 (m, 1H), 7.52–7.40 (m,5H), 7.37–
7.35 (m, 1H), 5.80 (d, J = 4.72 Hz, 1H), 4.86 (d,
J = 4.72 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 161.3,
156.3, 152.8, 148.6, 147.7, 145.6, 134.8, 132.5, 132.1,
129.7, 129.5, 128.8, 124.8, 124.4, 123.4, 122.9, 122.4,
116.9, 114.2, 102.4, 102.3, 36.6.15
4-(3-Methoxyphenyl)-2-phenylpyrano[3,2-c]chromen-5
(4H)-one (4c). Yield: 46 mg (40%); Rf = 0.15 (EtOAc:
ꢁ
Hexane = 1:10); White solid; Melting point: 144–146 C;
4-Phenyl-2-(o-tolyl)pyrano[3,2-c]chromen-5(4H)-one
(4h). Yield: 85 mg (77%); Rf = 0.3 (EtOAc: Hex-
1H NMR (400 MHz, CDCl3, 293 K, TMS) δ 8.01 (dd,
J1 = 1.46 Hz, J2 = 7.90 Hz, 1H), 7.74–7.59 (m, 2H), 7.57–
7.55 (m, 1H), 7.47–7.33 (m, 5H), 7.25–7.22 (m, 1H), 7.02–
6.96 (m, 2H), 6.79–6.76 (m, 1H), 5.84 (d, J = 4.96 Hz,
1H), 4.70 (d, J = 4.92 Hz, 1H), 3.78 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 161.5, 159.8, 155.8, 152.7, 146.9,
145.2, 132.6, 132.0, 129.6, 129.2, 128.7, 124.7, 124.2,
1
ꢁ
ane = 1:10); White powder; Melting point: 128–130 C; H
NMR (400 MHz, CDCl3, 293 K, TMS) δ 7.87–7.85 (m,
1H), 7.53–7.41 (m, 4H), 7.35–7.21 (m, 8H), 5.44 (d,
J = 4.92 Hz, 1H), 4.71 (d, J = 4.92 Hz, 1H), 2.47 (s, 3H);
13C NMR (100 MHz, CDCl3) δ 161.6, 155.9, 152.7, 148.6,
143.7, 136.8, 133.4, 131.9, 130.7, 129.5, 129.3, 128.7,
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ꢁ
128.5, 127.2, 126.0, 124.1, 122.7, 116.8, 114.5, 107.7,
103.5, 36.8, 20.5; FTIR (ATR): 3026, 1714, 1628, 1454,
1385, 1243, 1009, 752, 696, 666, 459 cm−1; HRMS (EI)
m/z: M+ Calcd. for C25H18O3 366.1256; found 366.1258.
2-(3-Methoxyphenyl)-4-phenylpyrano[3,2-c]chromen-5
(4H)-one (4i). Yield: 23 mg (20%); Rf = 0.2 (EtOAc:Hꢁex-
ane = 1:10); Pale red powder; Melting point: 141–143 C;
1H NMR (400 MHz, CDCl3, 293 K, TMS) δ 8.01 (dd,
J1 = 1.44 Hz, J2 = 7.92 Hz, 1H), 7.59–7.55 (m, 1H), 7.43–
7.21 (m, 10H), 6.97–6.94 (m, 1H), 5.84 (d, J = 4.92 Hz,
1H), 4.71 (d, J = 4.92 Hz, 1H), 3.87 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 161.5, 159.8, 155.7, 152.7, 146.7,
143.5, 134.92, 132.0, 129.7, 128.6, 128.5, 127.2, 124.2,
122.7, 117.2, 116.0, 114.5, 114.4, 110.7, 104.92, 103.6,
55.4, 36.6; FT-IR (ATR): 3081, 3028, 1712, 1627, 1490,
1392, 1305, 1046, 752, 701, 663, 551, 440 cm−1; HRMS
(EI) m/z: M+ Calcd. for C25H18O4 382.1205; found
382.1205.
2-(3-Chlorophenyl)-4-phenylpyrano[3,2-c]chromen-5
(4H)-one (4j). Yield: 75 mg (65%); Rf = 0.3 (EtOAc:Hꢁex-
ane = 1:10); Pale yellow solid; Melting point: 200–202 C;
1H NMR (400 MHz, CDCl3, 293 K, TMS) δ 8.00 (dd,
J1 = 1.44 Hz, J2 = 7.92 Hz, 1H), 7.71–7.70 (m, 1H), 7.62–
7.56 (m, 2H), 7.41–7.31 (m, 8H), 7.25–7.22 (m, 1H), 5.86
(d, J = 4.92 Hz, 1H), 4.71 (d, J = 4.92 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ 161.3, 155.6, 152.7, 145.7, 143.2,
134.8, 134.4, 132.1, 129.9, 129.2, 128.7, 128.4, 127.4,
124.8, 124.3, 122.8, 122.6, 116.9, 114.3, 104.9, 103.6,
36.6; FT-IR (ATR): 3083, 3027, 1711, 1628, 1391, 1270,
1022, 759, 747, 680, 549, 421 cm−1; HRMS (EI) m/z: M+
Calcd. for C24H15ClO3 386.0710; found 386.0713.
Hexane = 1:10); Yellow solid; Melting point: 116–118 C;
1H NMR (400 MHz, CDCl3, 293 K, TMS) δ 7.89 (d,
J = 2.32 Hz, 1H), 7.75–7.72 (m, 2H), 7.61 (d, J = 2.36 Hz,
1H), 7.49–7.40 (m, 5H), 7.34–7.29 (m, 2H), 7.25–7.20 (m,
1H), 5.84 (d, J = 4.96 Hz, 1H), 4.71 (d, J = 4.96 Hz, 1H),
1.49 (s, 9H), 1.42 (s, 9H); 13C NMR (100 MHz, CDCl3) δ
161.3, 156.4, 149.6, 147.1, 146.3, 143.8, 137.4, 133.0,
129.2, 128.7, 128.6, 128.5, 127.2, 124.7, 116.7, 114.2,
103.8, 102.9, 36.56, 35.2, 34.9, 31.5, 29.9, 29.7; FT-IR
(ATR): 2964, 1708, 1611, 1364, 1264, 1045, 732, 699,
609, 509 cm−1; HRMS (EI) m/z: M+ Calcd. for C32H32O3
464.2351; found 464.2353.
8-Methoxy-2,4-diphenylpyrano[3,2-c]chromen-5(4H)-
one (4n). Yield: 61 mg (53%); Rf = 0.2 (EtOAc: Hꢁex-
ane = 1:10); Pale yellow solid; Melting point: 205–207 C;
1H NMR (400 MHz, CDCl3, 293 K, TMS) δ 7.89 (d,
J = 8.84 Hz, 1H), 7.72–7.70 (m, 2H), 7.46–7.40 (m, 5H),
7.33–7.29 (m, 2H), 7.25–7.20 (m, 1H), 6.94–6.92 (m, 1H),
6.80 (d, J = 2.36 Hz, 1H), 5.83 (d, J = 4.92 Hz, 1H), 4.66
(d, J = 4.92 Hz, 1H), 3.86 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 162.9, 161.9, 156.1, 154.5, 146.7, 143.8, 132.7,
129.2, 128.6, 128.5, 128.4, 127.1, 124.6, 123.7, 112.6,
107.7, 103.8, 100.9, 100.5, 55.8, 36.5; FT-IR (ATR): 3074,
3025, 2851, 1711, 1616, 1398, 1254, 1174, 1029, 694,
553, 459 cm−1; HRMS (EI) m/z: M+ Calcd. for C25H18O4
382.1205; found 382.1206.
General Procedure for Furo[3,2-c]coumarins. To a test
tube were added 4-hydroxycoumarin (1, 0.36 mmol), termi-
nal propargyl alcohol (5, 0.3 mmol), and Bi(OTf)3 (10 mol
%) in diglyme (1.5 mL). The resulting mixture was stirred
at 100 C for 3 h. After completion of the reaction, the
mixture was concentrated and directly purified by column
ꢁ
9-Methyl-2,4-diphenylpyrano[3,2-c]chromen-5(4H)-one
(4k). Yield: 71 mg (65%); Rf = 0.3 (EtOAc: Hex-
chromatography on silica gel using EtOAc:hexane = 1:7.
1
ꢁ
ane = 1:10); White solid; Melting point: 216–218 C; H
NMR (400 MHz, CDCl3, 293 K, TMS) δ 7.77–7.73 (m,
3H), 7.47–7.30 (m, 8H), 7.25–7.22 (m, 2H), 5.84 (d,
J = 4.96 Hz, 1H), 4.71 (d, J = 4.92 Hz, 1H), 2.50 (s, 3H);
13C NMR (100 MHz, CDCl3) δ 161.7, 155.8, 151.0, 146.9,
143.7, 134.92, 133.1, 132.7, 129.3, 128.9, 128.7, 128.5,
127.2, 124.7, 122.3, 116.6, 114.2, 103.8, 103.6, 103.4,
36.6, 21.1.6c
1,3-Diphenylbenzo[h]pyrano[3,2-c]chromen-12(1H)-one
(4o). Yield: 36 mg (30%); Rf = 0.3 (EtOAc: Hꢁex-
ane = 1:10); Yellow powder; Melting point: 222–224 C;
1H NMR (400 MHz, CDCl3, 293 K, TMS) δ 8.51–8.49 (m,
1H), 8.00 (d, J = 8.72 Hz, 1H), 7.91–7.88 (m, 1H), 7.78–
7.76 (m, 3H), 7.64–7.61 (m, 2H), 7.49–7.42 (m, 5H), 7.34–
7.31 (m, 2H), 7.25–7.23 (m, 1H), 5.88 (d, J = 4.92 Hz,
1H), 4.76 (d, J = 4.92 Hz, 1H); 13C NMR (100 MHz,
CDCl3) δ 161.9, 157.1, 150.6, 147.4, 144.1, 135.3, 133.2,
129.7, 129.5, 129.4, 129.2, 128.7, 128.3, 127.7, 127.6,
125.2, 124.7, 123.4, 123.0, 118.7, 110.2, 104.2, 103.6,
37.1; FT-IR (ATR): 3058, 3024, 2921, 1710, 1617, 1376,
1021, 811, 756, 695, 567, 422 cm−1; HRMS (EI) m/z: M+
Calcd. for C28H18O3 402.1256; found 402.1254.
7-Methyl-2,4-diphenylpyrano[3,2-c]chromen-5(4H)-one
(4l). Yield: 79 mg (72%); Rf = 0.3 (EtOAc: Hexane = 1:10);
Yellow powder; Melting point: 162–163 ꢁC; 1H NMR
(400 MHz, CDCl3, 293 K, TMS) δ 7.86 (dd, J1 = 1.0 Hz,
J2 = 7.92 Hz, 1H),), 7.74–7.71 (m, 2H), 7.46–7.37 (m, 6H),
7.34–7.19 (m, 4H), 5.84 (d, J = 4.92 Hz, 1H), 4.71 (d,
J = 4.96 Hz, 1H), 2.42 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 162.6, 161.5, 155.9, 151.1, 147.0, 143.7, 133.2,
132.7, 129.2, 128.7, 128.6, 128.5, 127.2, 126.3, 124.7,
123.7, 120.3, 114.3, 103.7, 103.4, 36.6, 15.7; FT-IR
(ATR): 3062, 3026, 1713, 1630, 1467, 1386, 1216, 1012,
757, 701, 606, 548, 447 cm−1; HRMS (EI) m/z: M+ Calcd.
for C25H18O3 366.1256; found 366.1254.
2-Methyl-3-phenyl-4H-furo[3,2-c]chromen-4-one
(6a).
Yield: 59 mg (71%); Rf = 0.3 (EtOAc:Hexane = 1:7); Pale
yellow powder; Melting point: 195–197 ꢁC; 1H NMR
(400 MHz, CDCl3, 293 K, TMS)
δ 7.84 (dd, 1H,
J1 = 1.36 Hz, J2 = 7.8 Hz), 7.52–7.30 (m, 8H), 2.51 (s,
3H); 13C NMR (100 MHz, CDCl3) δ 157.7, 156.3, 152.3,
151.7, 130.3, 130.0, 129.9, 128.2, 127.8, 124.3, 120.6,
120.5, 117.1, 112.8, 109.6, 12.6; FTIR (ATR): 3069, 2918,
7,9-Di-tert-butyl-2,4-diphenylpyrano[3,2-c]chromen-5
(4H)-one (4m). Yield: 67 mg (48%); Rf = 0.6 (EtOAc:
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KOREAN CHEMICAL SOCIETY
1722, 1628, 1591, 1083, 747, 692, 514 cm−1; HRMS (EI)
m/z: M+ Calcd. for C18H12O3 276.0786; found 276.0786.16
2-Methyl-3-(o-tolyl)-4H-furo[3,2-c]chromen-4-one (6b).
Yield: 59 mg (68%); Rf = 0.3 (EtOAc:Hexane = 1:7); Pale
yellow solid; Melting point: 146–147 ꢁC; 1H NMR
133.7, 132.3, 130.3, 128.9, 128.6, 128.5, 127.7, 126.3,
125.9, 125.5, 125.3, 124.4, 120.7, 118.3, 117.2, 113.0,
111.4, 12.6; FT-IR (ATR) 3050, 2927, 1736, 1660, 1065,
959, 775, 754, 424 cm−1; HRMS (EI) m/z: M+ Calcd. for
C22H14O3 326.0943; found 326.0943.16
(400 MHz, CDCl3, 293 K, TMS)
δ
7.88 (dd, 1H,
2-Methyl-3-(thiophen-2-yl)-4H-furo[3,2-c]chromen-4-one
(6g). Yield: 35 mg (42%); Rf = 0.3 (EtOAc: Hexane = 1:7);
Brown solid; Melting point: 137–138 ꢁC; 1H NMR
J1 = 1.5 Hz, J2 = 7.8 Hz), 7.49–7.46 (m, 1H), 7.43–7.40
(m, 1H), 7.36–7.31 (m, 3H), 7.25–7.22 (m, 2H), 2.35 (s,
3H), 2.24 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 157.7,
156.1, 152.4, 151.9, 137.8, 130.5, 130.2, 130.1, 129.7,
128.4, 125.7, 124.3, 120.6, 119.5, 117.2, 112.9, 111.0,
19.9, 12.2; FT-IR (ATR): 2923, 1726, 1629, 1500, 1074,
943, 897, 746, 735, 446 cm−1; HRMS (EI) m/z: M+ Calcd.
for C19H14O3 290.0943; found 290.0943.
(400 MHz, CDCl3, 293 K, TMS)
δ 7.82 (dd, 1H,
J1 = 1.4 Hz, J2 = 7.8 Hz), 7.59–7.58 (m, 1H), 7.49–7.46
(m, 1H), 7.39–7.38 (m, 2H), 7.32–7.30 (m, 1H), 7.16–7.13
(m, 1H), 2.54 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
157.6, 156.3, 152.4, 152.0, 130.5, 129.1, 127.4, 125.8,
124.4, 120.7, 117.0, 114.4, 112.5, 109.3, 13.4; FT-IR
(ATR): 3104, 3062, 2921, 1724, 1627, 1072, 751, 718,
695, 455 cm−1; HRMS (EI) m/z: M+ Calcd. for C16H10O3S
282.0351; found 282.0351.5f
2-Methyl-3-(m-tolyl)-4H-furo[3,2-c]chromen-4-one (6c).
Yield: 50 mg (57%); Rf = 0.3 (EtOAc: Hexane = 1:7); Pale
yellow solid; Melting point: 128–130 ꢁC; 1H NMR
(400 MHz, CDCl3, 293 K, TMS)
δ
7.83 (dd, 1H,
2,8-Dimethyl-3-phenyl-4H-furo[3,2-c]chromen-4-one
(6h). Yield: 37 mg (43%); Rf = 0.3 (EtOAc: Hexane = 1:7);
J1 = 1.3 Hz, J2 = 7.8 Hz), 7.48–7.44 (m, 1H), 7.40–7.24
(m, 5H), 7.19–7.17 (m, 1H), 2.50 (s, 3H), 2.41 (s, 3H); 13C
NMR (100 MHz, CDCl3) δ 157.7, 156.2, 152.3, 151.7,
137.7, 130.6, 130.2, 129.9, 128.6, 128.1, 127.0, 124.3,
120.6, 117.1, 112.8, 109.7, 21.5, 12.6; FT-IR (ATR): 3043,
2920, 1722, 1680, 1500, 1063, 953, 749, 703, 697,
434 cm−1; HRMS (EI) m/z: M+ Calcd. for for C19H14O3
290.0943; found 290.0943.5f
3-(4-Methoxyphenyl)-2-methyl-4H-furo[3,2-c]chromen-
4-one (6d). Yield: 58 mg (63%); Rf = 0.2 (EtOAc:Hꢁex-
ane = 1:7); Pale brown solid; Melting point: 165–167 C;
1H NMR (400 MHz, CDCl3, 293 K, TMS) δ 7.83 (dd, 1H,
J1 = 1.4 Hz, J2 = 7.8 Hz), 7.49–7.39 (m, 4H), 7.33–7.29
(m, 1H), 7.01–6.97 (m, 2H), 3.85 (s, 1H), 2.50 (s, 3H); 13C
NMR (100 MHz, CDCl3) δ 159.2, 157.8, 156.1, 152.2,
151.2, 131.1, 130.2, 124.3, 122.2, 120.5, 120.1, 117.0,
113.7, 112.8, 109.7, 55.3, 12.6; FT-IR (ATR): 2922, 2843,
1737, 1596, 1515, 1251, 945, 837, 753, 548 cm−1; HRMS
(EI) m/z: M+ Calcd. for C19H14O4 306.0892; found
306.0892.5f
3-(4-Chlorophenyl)-2-methyl-4H-furo[3,2-c]chromen-4-
one (6e). Yield: 33 mg (35%); Rf = 0.3 (EtOAc:Hꢁex-
ane = 1:7); Pale yellow solid; Melting point: 176–177 C;
1H NMR (400 MHz, CDCl3, 293 K, TMS) δ 7.86 (dd, 1H,
J1 = 1.4 Hz, J2 = 7.8 Hz), 7.50–7.48 (m, 1H), 7.43–7.41
(m, 5H), 7.29–7.25 (m, 1H), 2.51 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 157.7, 156.5, 152.4, 151.8, 131.8,
131.2, 130.5, 129.2, 128.5, 124.4, 120.7, 119.5, 117.1,
112.7, 109.4, 12.6; FT-IR (ATR): 3076, 2919, 1743, 1631,
1492, 1382, 1069, 966, 748, 692, 528 cm−1; HRMS (EI)
m/z: M+ Calcd. for C18H11ClO3 310.0397; found 310.0397.
2-Methyl-3-(naphthalen-1-yl)-4H-furo[3,2-c]chromen-4-
one (6f). Yield: 64 mg (65%); Rf = 0.3 (EtOAc:Hꢁex-
ane = 1:7); Pale yellow solid; Melting point: 140–141 C;
1H NMR (400 MHz, CDCl3, 293 K, TMS) δ 7.94–7.90 (m,
3H), 7.69–7.67 (m, 1H), 7.57–7.53 (m, 1H), 7.50–7.47 (m,
3H), 7.45–7.41 (m, 2H), 7.35–7.33 (m, 1H), 2.33 (s, 3H);
13C NMR (100 MHz, CDCl3) δ 157.4, 156.4, 152.9, 152.5,
1
Pale yellow solid; Melting point: 128–130 ꢁC; H NMR
(400 MHz, CDCl3, 293 K, TMS) δ 7.61 (s, 1H), 7.51–7.42
(m, 4H), 7.38–7.34 (m, 1H), 7.29–7.24 (m, 2H), 2.49 (s,
3H), 2.43 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 157.9,
156.4, 151.5, 150.5, 134.1, 131.3, 130.1, 129.9, 128.2,
127.7, 120.5, 120.3, 116.8, 112.4, 109.5, 20.9, 12.6; FT-IR
(ATR): 3051, 2924, 1727, 1568, 1381, 1062, 753, 705,
543, 508 cm−1; HRMS (EI) m/z: M+ Calcd. for C19H14O3
290.0943; found 290.0943.16
2,6-Dimethyl-3-phenyl-4H-furo[3,2-c]chromen-4-one
(6i). Yield: 40 mg (46%); Rf = 0.3 (EtOAc: Hexane = 1:7);
1
Pale yellow solid; Melting point: 142–144 ꢁC; H NMR
(400 MHz, CDCl3, 293 K, TMS)
δ 7.68 (dd, 1H,
J1 = 0.9 Hz, J2 = 7.7 Hz), 7.50–7.43 (m, 4H), 7.38–7.36
(m, 1H), 7.31–7.29 (m, 1H), 7.21–7.19 (m, 1H), 2.50 (s,
3H), 2.47 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 157.7,
156.7, 151.5, 150.8, 131.6, 130.2, 129.9, 128.2, 127.7,
126.6, 123.8, 120.4, 118.2, 112.4, 109.4, 16.1, 12.7; FT-IR
(ATR): 3047, 2921, 1739, 1566, 1021, 766, 747, 696,
505 cm−1; HRMS (EI) m/z: M+ Calcd. for C19H14O3
290.0943; found 290.0943.
8-Chloro-2-methyl-3-phenyl-4H-furo[3,2-c]chromen-4-
one (6j). Yield: 37 mg (40%); Rf = 0.3 (EtOAc:Hꢁex-
ane = 1:7); Pale yellow solid; Melting point: 149–150 C;
1H NMR (400 MHz, CDCl3, 293 K, TMS) δ 7.80 (d, 1H,
J = 2.4 Hz), 7.50–7.32 (m, 8H), 2.51 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 157.1, 154.9, 152.5, 150.6, 130.2,
129.9, 129.8, 129.7, 128.3, 128.0, 120.7, 120.1, 118.5,
113.8, 110.4, 12.7; FT-IR (ATR): 3082, 2916, 1744, 1502,
1055, 966, 943, 757, 697, 559, 504 cm−1; HRMS (EI) m/z:
M+ Calcd. for C18H11ClO3 310.0397; found 310.0397.16
2-Methyl-1-phenyl-11H-benzo[h]furo[3,2-c]chromen-11-
one (6k). Yield: 39 mg (40%); Rf = 0.3 (EtOAc:Hꢁex-
ane = 1:7); Pale yellow solid; Melting point: 212–214 C;
1H NMR (400 MHz, CDCl3, 293 K, TMS) δ 8.58–8.55 (m,
1H), 7.86–7.83 (m, 2H), 7.73–7.71 (m, 1H), 7.64–7.54 (m,
4H), 7.50–7.46 (m, 2H), 7.41–7.37 (m, 1H) 2.54 (s, 3H);
Bull. Korean Chem. Soc. 2020, Vol. 41, 709–718
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KOREAN CHEMICAL SOCIETY
13C NMR (100 MHz, CDCl3) δ 157.6, 157.3, 151.5, 149.0,
134.0, 130.1, 129.9, 128.2, 128.0, 127.9, 127.7, 127.2,
124.5, 123.3, 122.6, 120.4, 116.9, 109.2, 107.9, 12.7; FTIR
(ATR): 2920, 1724, 1485, 1095, 1002, 808, 700, 563,
421 cm−1; HRMS (EI) m/z: M+ Calcd. for C22H14O3
326.0943; found 326.0943.16
(d) W. Lin, J. Huang, X. Liao, Z. Yuan, S. Feng, Y. Xie, W.
Ma, Pharmacol. Res. 2016, 111, 849.
4. For pyranocoumarins(a)G. Appendino, G. Cravotto, S.
Tagliapietra, G. M. Nano, G. Palmisano, Helv. Chim. Acta
1993, 76, 1194. (a) G. Appendino, G. Gravotto, L. Toma, R.
Annunziata, G. J. Palmisano, Org. Chem. 1994, 59, 5556. b
Y. Jacquot, B. Refouvelet, L. Bermont, G. L. Adessi, G.
Leclercq, A. Xicluna, Pharmazie 2002, 57, 233. c J. Moreau,
C. Hubert, J. Batany, L. Toupet, T. Roisnel, J.-P. Hurvois, J.-
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(7a).
Yield: 22 mg (27%); Rf = 0.27 (EtOAc: Hexane = 1:7);
1
Pale yellow solid; Melting point: 164–166 ꢁC; H NMR
(400 MHz, CDCl3, 293 K, TMS)
δ 8.30 (dd, 1H,
J1 = 1.3 Hz, J2 = 7.9 Hz), 7.69–7.64 (m, 1H), 7.59–7.53
(m, 3H), 7.47–7.42 (m, 3H), 7.38–7.34 (m, 1H), 2.46 (s,
3H), 13C NMR (100 MHz, CDCl3) δ 173.4, 161.8, 152.7,
142.9, 133.1, 130.6, 129.9, 128.1, 127.6, 126.7, 125.2,
124.0, 119.2, 117.5, 102.4, 12.1; FT-IR (ATR): 3054,
2921, 1655, 1606, 1475, 1175, 871, 754, 732, 524 cm−1
;
HRMS (EI) m/z: M+ Calcd. for C18H12O3 276.0786; found
276.0786.
Acknowledgments. This work was supported by the
National Research Foundation of Korea (NRF) grant
funded by the Korea Government (MISP) (2011-0018355)
and 2017 Research Grant from Kangwon National Univer-
sity (No. 520170418).
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Supporting Information. Additional supporting informa-
tion (1H and 13C NMR spectra for new compounds) is
available in the online version of this article.
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Regioselective Bismuth-Catalyzed Synthesis of Pyranocoumarins
KOREAN CHEMICAL SOCIETY
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