Synthesis of Structurally Diversified Benzo[c]chromene Derivatives under (An)aerobic Conditions Catalyzed by CuI

Article abstract of DOI:10.1002/jhet.3666

2-Bromobenzoic acids underwent an α-arylation with cyclohexane-1,3-diones to give 1H-benzo[c]chromene-1,6(2H)-diones under Ar atmosphere catalyzed by CuI/l-proline in the presence of Cs₂CO₃. The subsequent regioselective oxidation took place under O₂ balloon automatically based on the substituents for the construction of structurally diversified benzo[c]coumarin derivatives.

Full text of DOI:10.1002/jhet.3666

Month 2019 Synthesis of Structurally Diversified Benzo[c]chromene Derivatives under
(An)aerobic Conditions Catalyzed by CuI
*
*
Fang Dong, Jian-Quan Liu, and Xiang-Shan Wang
School of Chemistry and Materials Science, Jiangsu Key Laboratory of Green Synthesis for Functional Materials, Jiangsu
Normal University, Xuzhou, Jiangsu 221116, People’s Republic of China
*E-mail: liujq316@jsnu.edu.cn; xswang1974@yahoo.com
Received January 9, 2019
DOI 10.1002/jhet.3666
Published online 00 Month 2019 in Wiley Online Library (wileyonlinelibrary.com).
2-Bromobenzoic acids underwent an α-arylation with cyclohexane-1,3-diones to give 1H-benzo[c]
chromene-1,6(2H)-diones under Ar atmosphere catalyzed by CuI/L-proline in the presence of Cs2CO3.
The subsequent regioselective oxidation took place under O2 balloon automatically based on the substituents
for the construction of structurally diversified benzo[c]coumarin derivatives.
J. Heterocyclic Chem., 00, 00 (2019).
INTRODUCTION
Fan’s group [15] utilized 2-bromobenzoate to react with
cyclohexane-1,3-dione catalyzed by CuI with benzo[c]
coumarins being obtained in moderate yields but losing a
molecule of alcohol in ester (Scheme 1, (3)). In fact,
using 2-halobenzoic acid as an easily available material
to react with cyclohexane-1,3-dione was a very efficient
and atomic economic method to synthesize 1H-benzo[c]
chromene-1,6(2H)-diones. Only losing a molecule of
water in the conversion, it concerns the concept of green
chemistry in organic synthesis accordingly. In 2012,
Liu’s group [16] realized this reaction under transition-
metal-free conditions. However, the valuable 2-
iodobenzoic acid was used as a reactant (Scheme 1, (4)).
As early as 1977, McKillop and Rao [17] also achieved a
copper-catalyzed arylation of dimedone with 2-
bromobenzoic acid, leading to 63% yield of 1H-benzo[c]
chromene-1,6(2H)-dione. Only an example was reported
but using the costly NaH as a base (Scheme 1, (4)).
Therefore, a simple method for synthesizing this type of
coumarins using easily available and cheap reactants is
very essential.
Coumarin is also named 2H-chromen-2-one, which is a
bicyclic oxygen-containing heterocycle. It is reported that
coumarin exists in numerous natural products [1], such as
tanizin [2], anisucoumaramide [3], and defucogilvocarcin
[4], and possesses good biological activities, for example,
antitumor [5], anti-Escherichia coli [6], anticoagulation
[7], and antifungal activities [8]. Acenocoumarol is a
noteworthy anticoagulant drug that functions as a vitamin
K antagonist [9]. In addition, dicoumarol [10] is a
naturally occurring anticoagulant medication, which
almost acts as the same function as acenocoumarol.
According to its remarkable anticoagulant effect, many
novel procedures for the synthesis of coumarins [11]
have been reported in the past few years.
Benzo[c]coumarin is an important member of this large
family whose derivatives also have the widespread
applications [12]. In very recent, Yang’s group [13]
reported that Rh(III)-catalyzed C─H activation of cyclic
2-diazo-1,3-diketones and benzoic acids was an efficient
method, leading to the functional benzo[c]coumarins in
2017 (Scheme 1, (1)). However, the cyclic 2-diazo-1,3-
diketone was not a class of available reactants. In 2018,
Cho’s group [14] realized the synthesis of 6H-benzo[c]
chromen-6-ones under metal–catalyst-free conditions
using aryl 2-bromobenzoate as a reactant promoted by
microwave in the presence of K2CO3 (Scheme 1, (2)).
In our lab, the same reaction of dimedone with 2-
bromobenzoic acid was charged with CuI/L-proline using
1.0 equiv of Cs2CO3 as the base under Ar atmosphere.
To our delight, the desired 1H-benzo[c]chromene-
1,6(2H)-dione was obtained in 76% yield. With the
deepening of our research, the methylene on 4-position
could be oxidized regioselectively under aerobic
© 2019 Wiley Periodicals, Inc.

F. Dong, J.-Q. Liu, and X.-S. Wang
Vol 000
Scheme 1. Approaches to benzo[c]coumarins.
conditions, leading to 1H-benzo[c]chromene-1,4,6-trione
in good yields. More interesting is that this oxidization
could be controlled step by step via regulating the
number of the substituents on cyclohexane-1,3-dione.
The final products were 1-hydroxy-6H-benzo[c]chromen-
6-ones through subsequent partial oxidation, dehydration,
and enolization. As our continuous study on the
construction of functionalized heterocycles catalyzed by
copper [18], herein, we would like to report the reaction
of 2-bromobenzoic acid and cyclohexane-1,3-dione
catalyzed by CuI under aerobic or anaerobic conditions,
leading to structurally diversified benzo[c]chromene
derivatives (Scheme 1, (5)).
optimize the reaction conditions (Table 1). Under argon
atmosphere, the various kinds of copper sources, such
as CuX (X = I, Br, Cl), CuOAc, Cu2O, CuBr2, and
copper powder, were screened in the presence of
K2CO3 (1.0 equiv) using DMF as a solvent at 100°C
for 20 h, and the effect of cuprous salts was obviously
better than that of Cu2O. To our delight, the CuI gave
the best result leading 3a in 56% yield. However, the
CuBr2 and Cu powder were unreactive to this reaction,
which no desired 3a was observed by thin-layer
chromatography (TLC). Then, organic bases, such as
Et3N and DBU, or inorganic bases including Na2CO3,
Cs2CO3, and NaH, were also tested using 10 mol%
CuI as the catalyst in DMF, and it was found that
strong base was beneficial to this conversion. Cs2CO3
(100 mol%) gave almost the same result (63% yield,
Table 1, entry 11) as that of NaH (64% yield), and
organic bases nearly conducted nonreactivity for this
reaction because only trace amount of 3a was observed
RESULTS AND DISCUSSION
In our initial study, the reaction of 2-bromobenzoic
acid (1a) and dimedone (2a) was used as the model to
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Synthesis of Structurally Diversified Benzo[c]chromene Derivatives
Table 1
Optimization of the reaction conditions.a
Entry
Catalyst
Ligand
Solvent
Base
Yields (%)a
1
2
3
4
5
6
7
8
CuI
—
—
—
—
—
—
—
—
—
—
—
—
L-Proline
o-Phen
PPh3
L-Proline
L-Proline
L-Proline
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
DME
DMA
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Et3N
56
36
21
38
12
0
CuBr
CuCl
CuOAc
Cu2O
CuBr2
Cu
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
0
Trace
Trace
48
63
64
76
72
68
72
62
75
9
DBU
10
11
12
13
14
15
16
17
18
Na2CO3
Cs2CO3
NaH
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Reaction conditions: 1a (101 mg, 0.5 mmol), 2a (70 mg, 0.5 mmol), catalyst (0.05 mmol), ligand (0.1 mmol), solvent (10.0 mL), and base (0.5 mmol),
100°C, 20 h.
aIsolated yields.
by TLC. Moreover, when the common ligands of metal
copper, such as L-proline, o-phen, and PPh3, were
added to the catalytic system, the coordinate CuI all
indicated higher catalytic activity comparing with
ligand-free conditions, and L-proline showed the highest
activity, leading 3a in 76% yield (Table 1, entry 13).
Table 2
Table 3
Synthetic results of 1H-benzo[c]chromene-1,6(2H)-dione.
Synthetic results of 1H-benzo[c]chromene-1,4,6-triones.
Reaction condition: 1 (0.5 mmol), 2 (0.5 mmol), Cs2CO3 (163 mg,
0.5 mmol), CuI (10 mg, 0.05 mmol), L-proline (12 mg, 0.1 mmol), and
DMF (10.0 mL), 20 h.
Reaction condition: 1 (0.5 mmol), 2 (0.5 mmol), Cs2CO3 (163 mg,
0.5 mmol), CuI (10 mg, 0.05 mmol), L-proline (12 mg, 0.1 mmol), and
DMF (10.0 mL), O2 balloon, 20 h.
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F. Dong, J.-Q. Liu, and X.-S. Wang
Vol 000
Finally, we tried to examine the use of a variety of
solvents (e.g. DMSO, DME, and DMA) in order to
further increase the reaction yield. However, they all
failed to provide better result than in the solvent of
DMF. After evaluating various conditions, we obtained
the optimum results using 10 mol% CuI accompanied
by 20 mol% L-porline, 1.0 equiv of Cs2CO3 in DMF
at 100°C.
Under the optimized reaction conditions, 2-
bromobenzoic acids bearing electron-donating groups,
such as methyl or methoxy, and electron-withdrawing
groups (e.g. Cl or F), all gave 3a–3i in the satisfied yields
(Table 2, 74–82%). Other dimedone analogues, for
example, cyclohexane-1,3-dione, 5-phenylcyclohexane-
1,3-dione, and 4,4-dimethylcyclohexane-1,3-dione, also
afforded the good results, leading to 3 in 72–80% yields
(Table 2, 3j–3l).
Table 4
Synthetic results of 1-hydroxy-6H-benzo[c]chromen-6-ones.
Surprisingly, the previously mentioned reaction also
could be proceeded smoothly under air keeping all
other reaction conditions as the same. However, a
byproduct was observed by TLC gradually as reaction
time was prolonged. Subsequently, it (R = 5-MeO,
R1 = R2 = Me) was isolated in 42% yield by column
chromatography. One of the methylene groups
disappeared in 1H-NMR. Instead, it changed to a new
carbonyl group which was found in its 13C-NMR. In
order to identify which methylene was oxidized in
the air? The X-ray diffraction analysis of product
4d was determined, and it was 8-methoxy-3,3-dimethyl-
2,3-dihydro-1H-benzo[c]chromene-1,4,6-trione. Table 3
Reaction condition: 1 (0.5 mmol), 2 (0.5 mmol), Cs2CO3 (163 mg,
0.5 mmol), CuI (10 mg, 0.05 mmol), L-proline (12 mg, 0.1 mmol), and
DMF (10.0 mL), O2 balloon, 20 h.
Scheme 2. The possible reaction mechanism.
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Month 2019
Synthesis of Structurally Diversified Benzo[c]chromene Derivatives
indicated that the methylene on 4-position was oxidized
If 3k was treated with CuI/L-proline in the presence of
Cs2CO3 under oxygen balloon at 100°C, product 5j was
obtained in 83% yield (Scheme 3). This controlled
reaction indicated that the first conversion is cyclization
to benzo[c]chromene analogue and then allylic oxidation.
selectively
to
corresponding
carbonyl
group
automatically.
Because the air functioned as a green oxidant in this
subsequent oxidation reaction, we repeated the same
reaction under the pure oxygen atmosphere. The yield of
4d could be improved observably from 42% to 86%.
Under O2 balloon, total of seven 1H-benzo[c]chromene-
1,4,6-triones were obtained in moderate yields with high
regioselectivity.
It was very interesting that the regioselective oxidation
reaction could be carried out step by step via group
controlling. If one of the substituent groups (R1 or R2)
was hydrogen atom, only one C─H bond was oxidized
to C─OH. The dehydration took place unexpectedly
followed by an enolization in cyclohexane-1,3-dione,
and phenol analogue was obtained finally. Table 4
CONCLUSION
In summary, the selective oxidation reaction of 2-
bromobenzoic acid and cyclohexane-1,3-dione catalyzed
by CuI/L-proline was found in the presence of Cs2CO3.
Under Ar atmosphere, it gave normal 1H-benzo[c]
chromene-1,6(2H)-dione derivatives in good yields. The
O2 as a greener oxidant could promote the subsequent
regioselective oxidation to provide 1H-benzo[c]chromene-
1,4,6-triones. It was controlled by substituents to undergo
a partial oxidation, leading to structurally diversified 1-
hydroxy-6H-benzo[c]chromen-6-one derivatives.
indicated
that
cyclohexane-1,3-dione,
5-
methylcyclohexane-1,3-dione, and 5-phenylcyclohexane-
1,3-dione, especially for 5-phenylcyclohexane-1,3-dione,
all gave partial oxidation products in good yields
(Table 4). The key step of this partial oxidation is
enolization. If there are two substituent groups on one
position in cyclohexane-1,3-dione, such as 5,5-
dimethylcyclohexane-1,3-dione, or 4,4-dimethylcyclo
hexane-1,3-dione (Table 3), the enolization was hold
back. Therefore, the second oxidation went on to give
ketone hydrate, which converted to corresponding
product 4 immediately.
According to the previously mentioned results, we think
that the first is α-arylation of carbonyl group catalyzed by
CuI/L-proline, which was well documented by Ma and
other groups [19]. And then, the carboxyl negative ion in
6 attacks the carbonyl followed by dehydration to give
product 3. Under aerobic conditions, the methylene on 4-
position is oxidized into two C─O─H bonds (8, the
similar allylic oxidations were realized by metal catalyst
of Rh2(esp)2[20]), and 8 loses a molecule of water to
afford product 4. When there is a hydrogen atom on 3-
position, the partial oxidation takes place first to lead
intermediate product 9. The dehydration preferentially
conducts to give ketone structure 10, and the final
product 5 is obtained via an enolization. The possible
reaction mechanism is outlined in Scheme 2.
EXPERIMENTAL
Melting points were determined in open capillaries and
are uncorrected. IR spectra were recorded on a TENSOR
27 spectrometer in KBr. NMR spectra were obtained
from solution in CDCl3 with Me4Si as internal standard
using a Bruker 400 spectrometer (Bruker Corp., Billerica,
MA). HRMS analyses were carried out using a Bruker
micrOTOF-Q MS analyzer (Bruker Corp.).
General procedure for the syntheses of 1H-benzo[c]
chromene-1,6(2H)-diones 3 (using 3a as a model).
2-
Bromobenzoic acid (101 mg, 0.5 mmol), dimetone
(70 mg, 0.5 mmol), CuI (10 mg, 0.05 mmol), L-proline
(12 mg, 0.1 mmol), and Cs2CO3 (163 mg, 0.5 mmol)
were added to a dry reaction flask with high vacuum
valve. After three times in vacuum and replacement of
argon, DMF (10.0 mL) was injected into the mixture.
Before reaching completion, the reaction mixture was
stirred and heated at 100°C under an Ar balloon. The
mixture was poured into 50-mL water, and the yellow
precipitate was formed and collected by filtration. The
crude product was purified by chromatography over silica
gel to give 3a using ethyl acetate and petroleum ether
(1:6) as an eluent.
3,3-Dimethyl-3,4-dihydro-1H-benzo[c]chromene-1,6(2H)-
dione (3a). Yield: 76% (92 mg); pale yellow solid; mp
127–128°C (lit. [13] mp 125–126°C); H-NMR (CDCl3,
Scheme 3. The controlled reaction.
1
400 MHz): δH 1.17 (s, 3H), 1.18 (s, 3H), 2.53 (d,
J = 3.2 Hz, 2H), 2.80 (d, J = 2.8 Hz, 2H), 7.52–7.56 (m,
1H), 7.78–7.82 (m, 1H), 8.29 (d, J = 7.6 Hz, 1H), 9.05
(dd, J = 8.0 Hz, J′ = 2.0 Hz, 1H); IR (KBr): ν 3117,
2966, 1736, 1668, 1618, 1482, 1372, 1335, 1323, 1248,
1195, 1155, 1061, 1035, 1022, 780 cmÀ1; HRMS (TOF,
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F. Dong, J.-Q. Liu, and X.-S. Wang
Vol 000
ESI, m/z): Calcd for C15H15O3 [M + H]+ 243.1016, found
243.1016.
3114, 2967, 2871, 1740, 1666, 1593, 1475, 1374, 1373,
1307, 1240, 1161, 1084, 1035, 998, 904, 781 cmÀ1
;
HRMS (TOF, ESI, m/z): Calcd for C15H14ClO3 [M + H]+
277.0626, found 277.0627.
9-Fluoro-3,3-dimethyl-3,4-dihydro-1H-benzo[c]chromene-
3,3,7-Trimethyl-3,4-dihydro-1H-benzo[c]chromene-1,6(2H)-
dione (3b). Yield: 78% (100 mg); pale yellow solid; mp
1
112–114°C (lit. [13] mp 109–110°C); H-NMR (CDCl3,
400 MHz): δH 1.17 (s, 6H, 2CH3), 2.51 (s, 2H), 2.77 (s,
2H), 2.80 (s, 3H), 7.33 (d, J = 7.6 Hz, 1H), 7.62–7.65
(m, 1H), 8.96 (d, J = 8.0 Hz, 1H); IR (KBr): ν 2961,
2929, 1744, 1674, 1621, 1473, 1426, 1383, 1363, 1328,
1295, 1240, 1163, 1065, 1012, 999, 768 cmÀ1; HRMS
(TOF, ESI, m/z): Calcd for C16H17O3 [M + H]+
1,6(2H)-dione (3g).
Yield: 75% (98 mg); pale yellow
1
solid; mp 171–172°C; H-NMR (CDCl3, 400 MHz): δH
1.19 (s, 6H, 2CH3), 2.53 (s, 2H), 2.81 (s, 2H), 7.20–7.25
(m, 1H), 8.31 (dd, J = 8.8 Hz, J′ = 5.6 Hz, 1H), 8.80 (dd,
J = 11.2 Hz, J′ = 2.8 Hz, 1H); 13C-NMR (CDCl3,
100 MHz): δC 28.1, 32.0, 42.6, 52.6, 110.0 (d, JF–
257.1172, found 257.1168.
= 3.0 Hz), 112.5 (d, JF–C = 26.0 Hz), 116.2 (d, JF–
C
8-Methoxy-3,3-dimethyl-3,4-dihydro-1H-benzo[c]chromene-
1,6(2H)-dione (3c). Yield: 82% (112 mg); pale yellow
= 2.2 Hz), 116.7 (d, JF–C = 23.3 Hz), 132.7 (d, JF–
= 10.5 Hz), 136.6 (d, JF–C = 12.3 Hz), 159.8, 167.3 (d,
C
C
solid; mp 141–142°C (lit. [15] mp 139–141°C);
1H-NMR (CDCl3, 400 MHz): δH 1.18 (s, 6H, 2CH3),
2.51 (s, 2H), 2.79 (s, 2H), 3.91 (s, 3H), 7.36 (dd,
J = 8.8 Hz, J′ = 2.8 Hz, 1H), 7.70 (d, J = 2.8 Hz, 1H),
8.98 (d, J = 9.2 Hz, 1H); IR (KBr): ν 2963, 2875, 1731,
1667, 1615, 1500, 1471, 1374, 1375, 1345, 1252, 1225,
1156, 1058, 1035, 884, 777 cmÀ1; HRMS (TOF, ESI,
m/z): Calcd for C16H16O4Na [M + Na]+ 295.0946, found
295.0952.
JF–C = 254.6 Hz), 169.2, 196.8; IR (KBr): ν 3082, 2960,
2925, 1744, 1678, 1621, 1497, 1430, 1397, 1318, 1249,
1208, 1152, 1144, 1055, 1037, 947, 833, 781 cmÀ1
;
HRMS (TOF, ESI, m/z): Calcd for C15H14FO3 [M + H]+
261.0921, found 261.0935.
3,3,9-Trimethyl-3,4-dihydro-1H-benzo[c]chromene-1,6(2H)-
dione (3h). Yield: 80% (102 mg); pale yellow solid; mp
1
147–148°C (lit. [13] mp 143–145°C); H-NMR (CDCl3,
400 MHz): δH 1.18 (s, 6H, 2CH3), 2.51 (s, 3H), 2.52 (s,
2H), 2.79 (s, 2H), 7.35 (dd, J = 8.0 Hz, J′ = 1.2 Hz, 1H),
8.18 (d, J = 8.0 Hz, 1H), 8.87 (s, 1H); IR (KBr): ν 2965,
2929, 1744, 1675, 1621, 1566, 1488, 1368, 1314, 1249,
1159, 1149, 1033, 904, 830, 776 cmÀ1; HRMS (TOF,
ESI, m/z): Calcd for C16H17O3 [M + H]+ 257.1172,
found 257.1170.
8-Fluoro-3,3-dimethyl-3,4-dihydro-1H-benzo[c]chromene-
1,6(2H)-dione (3d).
Yield: 75% (98 mg); pale yellow
1
solid; mp 147–148°C; H-NMR (CDCl3, 400 MHz): δH
1.19 (s, 6H, 2CH3), 2.53 (s, 2H), 2.81 (s, 2H), 7.48–7.53
(m, 1H), 7.91–7.94 (m, 1H), 9.10 (dd, J = 9.2 Hz, J
′ = 5.2 Hz, 1H); 13C-NMR (CDCl3, 100 MHz): δC 28.1,
32.0, 42.4, 52.7, 110.2, 115.0 (d, JF–C = 23.1 Hz), 121.8
(d, JF–C = 7.9 Hz), 123.6 (d, JF–C = 21.7 Hz), 128.7 (d,
JF–C = 7.4 Hz), 130.4 (d, JF–C = 2.9 Hz), 159.9 (d, JF–
8,9-Dimethoxy-3,3-dimethyl-3,4-dihydro-1H-benzo[c]
chromene-1,6(2H)-dione (3i). Yield: 82% (124 mg); pale
yellow solid; mp 155–156°C; 1H-NMR (CDCl3,
400 MHz): δH 1.18 (s, 6H, 2CH3), 2.52 (s, 2H), 2.80 (s,
2H), 3.99 (s, 3H), 4.05 (s, 3H), 7.64 (s, 1H), 8.65 (s,
1H); 13C-NMR (CDCl3, 100 MHz): δC 28.1, 32.0, 42.5,
52.9, 56.2, 56.4, 107.0, 109.4, 110.3, 113.0, 129.7,
149.4, 155.5, 160.6, 167.3, 197.4; IR (KBr): ν 3125,
3034, 1717, 1686, 1621, 1598, 1575, 1450, 1374, 1396,
= 3.3 Hz), 161.8 (d, JF–C = 249.5 Hz), 167.3, 196.8; IR
C
(KBr): ν 3082, 2960, 2925, 1744, 1678, 1621, 1497,
1430, 1397, 1318, 1249, 1208, 1152, 1144, 1055, 1037,
947, 833, 781 cmÀ1; HRMS (TOF, ESI, m/z): Calcd for
C15H14FO3 [M + H]+ 261.0921, found 261.0911.
3,3,8-Trimethyl-3,4-dihydro-1H-benzo[c]chromene-1,6(2H)-
dione (3e). Yield: 81% (104 mg); pale yellow solid; mp
1299, 1202, 1096, 1048, 988, 900, 845, 778 cmÀ1
;
1
153–155°C (lit. [13] mp 151–152°C); H-NMR (CDCl3,
HRMS (TOF, ESI, m/z): Calcd for C17H18NaO5
[M + Na]+ 325.1052, found 325.1052.
400 MHz): δH 1.18 (s, 6H, 2CH3), 2.46 (s, 3H), 2.51
(s, 2H), 2.79 (s, 2H), 7.60 (dd, J = 8.8 Hz, J′ = 2.0 Hz,
1H), 8.08 (s, 1H), 8.92 (d, J = 8.4 Hz, 1H); IR (KBr):
ν 2966, 2921, 1731, 1673, 1619, 1504, 1467, 1365,
1331, 1254, 1157, 1065, 1041, 877, 784 cmÀ1; HRMS
9-Methyl-3,4-dihydro-1H-benzo[c]chromene-1,6(2H)-dione
(3j). Yield: 73% (83 mg); pale yellow solid; mp 127–
128°C (lit. [13] mp 129–130°C); 1H-NMR (CDCl3,
400 MHz): δH 2.15–2.19 (m, 2H), 2.52 (s, 3H), 2.66 (t,
J = 6.8 Hz, 2H), 2.93 (t, J = 6.8 Hz, 2H), 7.35 (d,
J = 8.0 Hz, 1H), 8.17 (d, J = 8.4 Hz, 1H), 8.87 (s, 1H);
IR (KBr): ν 2965, 2941, 1746, 1717, 1686, 1634, 1606,
1492, 1463, 1321, 1284, 1195, 1155, 1061, 1035, 1022,
(TOF, ESI, m/z): Calcd for C16H17O3 [M + H]+
257.1172, found 257.1177.
9-Chloro-3,3-dimethyl-3,4-dihydro-1H-benzo[c]chromene-
1,6(2H)-dione (3f).
Yield: 74% (102 mg); pale yellow
1
780 cmÀ1
; HRMS (TOF, APCI, m/z): Calcd for
solid; mp 157–159°C; H-NMR (CDCl3, 400 MHz): δH
1.18 (s, 6H, 2CH3), 2.53 (s, 2H), 2.81 (s, 2H), 7.49 (dd,
J = 8.4 Hz, J′ = 2.0 Hz, 1H), 8.20 (d, J = 8.4 Hz, 1H),
9.11 (d, J = 2.0 Hz, 1H); 13C-NMR (CDCl3, 100 MHz):
δC 28.1, 31.9, 42.6, 52.7, 109.8, 118.1, 125.8, 129.0,
131.1, 135.1, 142.8, 160.0, 169.1, 196.5; IR (KBr): ν
C14H13O3 [M + H]+ 229.0859, found 229.0860.
9-Methyl-3-phenyl-3,4-dihydro-1H-benzo[c]chromene-
1,6(2H)-dione (3k).
Yield: 72% (109 mg); pale yellow
solid; mp 170–171°C (lit. [13] mp 168–169°C); 1H-
NMR (CDCl3, 400 MHz): δH 2.53 (s, 3H), 2.85–2.98
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2019
Synthesis of Structurally Diversified Benzo[c]chromene Derivatives
(m, 2H), 3.15–3.17 (m, 2H), 3.52–3.59 (m, 1H),
7.29–7.33 (m, 3H), 7.35–7.41 (m, 3H), 8.18
(d, J = 8.0 Hz, 1H), 8.90 (s, 1H); IR (KBr): ν 3163,
3125, 3033, 1717, 1687, 1621, 1598, 1419, 1397, 1299,
8-Methoxy-3,3-dimethyl-2,3-dihydro-1H-benzo[c]chromene-
1,4,6-trione (4d). Yield: 86% (123 mg); pale yellow solid;
1
mp 173–175°C; H-NMR (CDCl3, 400 MHz): δH 1.38 (s,
6H, 2CH3), 2.98 (s, 2H), 3.96 (s, 3H), 7.43 (dd,
J = 9.2 Hz, J′ = 2.8 Hz, 1H), 7.80 (d, J = 2.8 Hz, 1H),
7.86 (d, J = 9.2 Hz, 1H); 13C-NMR (CDCl3, 100 MHz):
δC 25.9, 44.9, 53.6, 55.9, 111.5, 119.4, 124.3, 124.6,
129.9, 148.9, 159.1, 162.0, 193.7, 195.4; IR (KBr): ν
3020, 2982, 2969, 2931, 1750, 1710, 1671, 1610, 1407,
1360, 1312, 1258, 1199, 1074, 1032, 918, 840,
1202, 1096, 1048, 1013, 988, 970, 845, 777 cmÀ1
;
HRMS (TOF, APCI, m/z): Calcd for C20H17O3
[M + H]+ 305.1172, found 305.1160.
2,2-Dimethyl-3,4-dihydro-1H-benzo[c]chromene-1,6(2H)-
dione (3l). Yield: 80% (97 mg); pale yellow solid; mp
1
111–112°C (lit. [15] mp 109–110°C); H-NMR (CDCl3,
774 cmÀ1
;
HRMS (TOF, ESI, m/z): Calcd for
400 MHz): δH 1.25 (s, 6H, 2CH3), 2.01 (t, J = 6.4 Hz,
2H), 2.95 (d, J = 6.4 Hz, 2H), 7.50–7.55 (m, 1H), 7.76–
7.81 (m, 1H), 8.29 (dd, J = 8.0 Hz, J′ = 1.2 Hz, 1H),
9.04 (d, J = 8.4 Hz, 1H); IR (KBr): ν 2969, 2633, 1766,
1736, 1666, 1617, 1563, 1480, 1450, 1375, 1366, 1317,
1246, 1185, 1156, 1018, 984, 840, 785 cmÀ1; HRMS
(TOF, ESI, m/z): Calcd for C15H15O3 [M + H]+
243.1016, found 243.1000.
C16H14NaO5 [M + Na]+ 309.0739, found 309.0741.
3,3,9-Trimethyl-2,3-dihydro-1H-benzo[c]chromene-1,4,6-
trione (4e). Yield: 55% (74 mg); pale yellow solid; mp
165–166°C; 1H-NMR (CDCl3, 400 MHz): δH 1.39 (s,
6H, 2CH3), 2.56 (s, 3H), 2.90 (s, 2H), 7.54 (d,
J = 8.0 Hz, 1H), 8.28 (d, J = 8.0 Hz, 1H), 8.74 (s, 1H);
13C-NMR (CDCl3, 100 MHz): δC 22.4, 25.8, 45.0, 53.6,
119.1, 120.2, 128.1, 130.3, 131.3, 132.7, 147.3, 150.8,
159.0, 193.9, 195.3; IR (KBr): ν 3030, 2961, 2930, 1755,
1663, 1618, 1606, 1560, 1484, 1460, 1420, 1362, 1309,
General procedure for the syntheses of 1H-benzo[c]
chromene-1,4,6-triones 4 (using 4a as a model).
This
procedure is almost the same as that of 3a, except for
replacement with oxygen and being controlled in an O2
balloon until all 2a was consumed.
3,3-Dimethyl-2,3-dihydro-1H-benzo[c]chromene-1,4,6-trione
(4a). Yield: 79% (101 mg); pale yellow solid; mp 124–
1250, 1187, 1131, 1052, 1017, 987, 842, 773 cmÀ1
;
HRMS (TOF, ESI, m/z): Calcd for C16H15O4 [M + H]+
271.0965, found 271.0956.
8,9-Dimethoxy-3,3-dimethyl-2,3-dihydro-1H-benzo[c]
125°C; 1H-NMR (CDCl3, 400 MHz): δH 1.40 (s, 6H,
2CH3), 3.00 (s, 2H), 7.72–7.76 (m, 1H), 7.88–7.92 (m,
1H), 8.41 (d, J = 7.6 Hz, 1H), 8.95 (d, J = 8.4 Hz, 1H);
13C-NMR (CDCl3, 100 MHz): δC 25.8, 45.4, 53.5, 119.0,
122.7, 128.0, 130.3, 131.4, 131.5, 135.8, 150.6, 159.0,
193.8, 195.1.
chromene-1,4,6-trione (4f).
Yield: 80% (126 mg); pale
yellow solid; mp 197–198°C; 1H-NMR (CDCl3,
400 MHz): δH 1.39 (s, 6H, 2CH3), 3.00 (s, 2H), 4.03 (s,
3H), 4.07 (s, 3H), 7.73 (s, 1H), 8.47 (s, 1H); 13C-NMR
(CDCl3, 100 MHz): δC 25.8, 44.9, 53.5, 56.4, 56.5,
108.6, 110.1, 116.7, 118.7, 126.4, 149.9, 151.9, 155.4,
158.9, 193.6, 195.9; IR (KBr): ν 3023, 2974, 2948, 1746,
1717, 1696, 1594, 1523, 1463, 1394, 1354, 1284, 1237,
1072, 1043, 878, 767 cmÀ1; HRMS (TOF, ESI, m/z):
Calcd for C17H16NaO6 [M + Na]+ 339.0845, found
339.0844.
3,3,7-Trimethyl-2,3-dihydro-1H-benzo[c]chromene-1,4,6-
trione (4b). Yield: 84% (113 mg); pale yellow solid; mp
167–168°C; 1H-NMR (CDCl3, 400 MHz): δH 1.38 (s,
6H, 2CH3), 2.85 (s, 3H), 2.90 (s, 2H), 7.53 (d,
J = 7.6 Hz, 1H), 7.77–7.75 (m, 1H), 8.80 (d, J = 8.0 Hz,
1H); 13C-NMR (CDCl3, 100 MHz): δC 23.7, 25.7, 29.7,
45.0, 53.9, 119.3, 120.9, 125.9, 132.6, 134.9, 144.3,
150.5, 158.1, 193.9, 195.2; IR (KBr): ν 3002, 2961,
2930, 1755, 1663, 1618, 1606, 1560, 1484, 1460, 1420,
1362, 1309, 1250, 1187, 1131, 1052, 1017, 987, 842,
773 cmÀ1; HRMS (TOF, ESI, m/z): Calcd for C16H15O4
[M + H]+ 271.0965, found 271.0955.
2,2-Dimethyl-2,3-dihydro-1H-benzo[c]chromene-1,4,6-trione
(4g). Yield: 84% (107 mg); pale yellow solid; mp 188–
189°C; 1H-NMR (CDCl3, 400 MHz): δH 1.47 (s, 6H,
2CH3), 2.69–2.73 (m, 2H), 7.52–7.56 (m, 1H), 7.77–7.81
(m, 1H), 8.29 (dd, J = 8.0 Hz, J′ = 1.2 Hz, 1H), 9.07 (dd,
J = 8.4 Hz, J′ = 0.4 Hz, 1H); 13C-NMR (CDCl3,
100 MHz): δC 26.3, 34.8, 35.8, 110.1, 119.8, 126.4,
128.4, 129.4, 134.2, 135.5, 160.7, 174.3, 197.0; IR
(KBr): ν 3021, 2961, 2930, 1755, 1663, 1618, 1606,
1560, 1484, 1460, 1420, 1362, 1309, 1250, 1187, 1131,
1052, 1017, 987, 842, 773 cmÀ1; HRMS (TOF, APCI,
m/z): Calcd for C15H13O4 [M + H]+ 257.0808, found
257.0807.
3,3,8-Trimethyl-2,3-dihydro-1H-benzo[c]chromene-1,4,6-
trione (4c). Yield: 89% (120 mg); pale yellow solid; mp
177–179°C; 1H-NMR (CDCl3, 400 MHz): δH 1.39 (s,
6H, 2CH3), 2.53 (s, 3H), 2.99 (s, 2H), 7.69–7.72 (m,
1H), 8.21 (s, 1H), 8.82 (d, J = 8.4 Hz, 1H); 13C-NMR
(CDCl3, 100 MHz): δC 22.4, 25.7, 45.0, 53.6, 119.1,
120.2, 128.1, 130.3, 131.3, 132.7, 147.3, 150.8, 159.0,
193.9, 195.9; IR (KBr): ν 3011, 2982, 2969, 2931, 1749,
1709, 1670, 1609, 1560, 1360, 1291, 1258, 1198, 1074,
1032, 918, 785 cmÀ1; HRMS (TOF, ESI, m/z): Calcd for
C16H15O4 [M + H]+ 271.0965, found 271.0954.
General procedure for the syntheses of 1-hydroxy-6H-
benzo[c]chromen-6-ones 5 (using 5a as a model).
This
procedure is almost the same as that of 4a, except for
using a mixture of ethyl acetate and petroleum ether (1:4)
as an eluant in the purification.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

F. Dong, J.-Q. Liu, and X.-S. Wang
Vol 000
1-Hydroxy-6H-benzo[c]chromen-6-one (5a). Yield: 76%
(81 mg); pale yellow solid; mp 231–233°C (lit. [15] mp
227–229°C); H-NMR (DMSO-d6, 400 MHz): δH 6.87–
J = 7.6 Hz, 1H), 11.26 (brs, 1H); 13C-NMR (DMSO-d6,
100 MHz): δC 105.8, 106.3, 110.4, 120.5, 127.1, 127.5,
128.5, 128.9, 129.6, 130.0, 134.8, 135.6, 138.9, 142.2,
153.1, 157.4, 161.0; IR (KBr): ν 3241, 2917, 1690, 1628,
1606, 1480, 1412, 1325, 1304, 1280, 1224, 1105, 1065,
822, 724 cmÀ1; HRMS (TOF, ESI, m/z): Calcd for
C19H11O3 [M À H]À 287.0708, found 287.0699.
1
6.93 (m, 2H), 7.33–7.37 (m, 1H), 7.61–7.65 (m, 1H),
7.90–7.94 (m, 1H), 8.28 (dd, J = 8.0 Hz, J′ = 1.2 Hz,
1H), 9.15 (d, J = 8.4 Hz, 1H), 11.09 (brs, 1H); 13C-NMR
(DMSO-d6, 100 MHz): δC 106.5, 108.2, 112.5, 120.5,
127.6, 128.5, 129.9, 130.7, 135.1, 135.5, 152.6, 157.2,
160.9; IR (KBr): ν 3250, 3130, 2917, 1704, 1616, 1604,
1486, 1434, 1356, 1320, 1262, 1219, 1103, 1052, 1021,
789 cmÀ1; HRMS (TOF, ESI, m/z): Calcd for C13H7O3
[M À H]À 211.0395, found 211.0392.
8-Fluoro-1-hydroxy-3-phenyl-6H-benzo[c]chromen-6-one
(5f). Yield: 74% (113 mg); pale yellow solid; mp 190–
191°C; 1H-NMR (DMSO-d6, 400 MHz): δH 7.20 (d,
J = 1.2 Hz, 1H), 7.22 (d, J = 1.2 Hz, 1H), 7.41–7.45 (m,
1H), 7.49–7.53 (m, 2H), 7.69–7.71 (m, 2H), 7.79–7.84 (m,
1H), 7.97 (dd, J = 8.8 Hz, J′ = 2.8 Hz, 1H), 9.19 (d,
J = 9.2 Hz, J′ = 5.2 Hz, 1H), 11.33 (brs, 1H); 13C-NMR
(DMSO-d6, 100 MHz): δC 105.1 (d, JF–C = 2.6 Hz), 106.3,
110.3, 113.4 (d, JF–C = 26.0 Hz), 116.2 (d, JF–C = 23.1 Hz),
117.3 (d, JF–C = 2.0 Hz), 127.1, 129.0, 129.6, 133.4 (d, JF–
1-Hydroxy-3-methyl-6H-benzo[c]chromen-6-one (5b).
Yield: 78% (88 mg); pale yellow solid; mp 216–217°C
(lit. [15] mp 215–217°C); 1H-NMR (DMSO-d6,
400 MHz): δH 2.31 (s, 3H), 6.72 (s, 2H), 7.57–7.61 (m,
1H), 7.87–7.91 (m, 1H), 8.24 (dd, J = 7.6 Hz, J
′ = 1.2 Hz, 1H), 9.07 (d, J = 8.4 Hz, 1H), 10.95 (s, 1H);
13C-NMR (DMSO-d6, 100 MHz): δC 21.4, 104.1, 108.7,
113.2, 120.1, 127.2, 128.0, 129.9, 135.2, 135.5, 141.0,
152.5, 156.8, 161.0; IR (KBr): ν 3347, 3030, 2924, 1701,
1617, 1608, 1405, 1314, 1269, 1112, 1059, 1029,
774 cmÀ1; HRMS (TOF, ESI, m/z): Calcd for C14H9O3
[M À H]À 225.0552, found 225.0564.
= 10.6 Hz), 137.5 (d, JF–C = 11.7 Hz), 138.7, 143.0,
C
153.3, 157.4, 160.1, 166.3 (d, JF–C = 249.5 Hz); IR (KBr):
ν 3365, 3034, 1705, 1616, 1604, 1600, 1512, 1471, 1322,
1196, 1103, 1036, 834, 789 cmÀ1; HRMS (TOF, ESI, m/z):
Calcd for C19H10FO3 [M À H]À 305.0614, found 305.0629.
1-Hydroxy-8-methyl-3-phenyl-6H-benzo[c]chromen-6-one
(5g). Yield: 75% (113 mg); pale yellow solid; mp 198–
1
199°C; H-NMR (DMSO-d6, 400 MHz): δH 2.47 (s, 3H),
1-Hydroxy-8-methoxy-3-methyl-6H-benzo[c]chromen-6-one
(5c). Yield: 75% (96 mg); pale yellow solid; mp 191–
7.17 (s, 1H), 7.18 (s, 1H), 7.40–7.44 (m, 1H), 7.49–7.52
(m, 2H), 7.69 (d, J = 8.0 Hz, 2H), 7.74 (d, J = 8.4 Hz, 1H),
8.09 (s, 1H), 9.02 (d, J = 8.8 Hz, 1H), 11.04 (brs, 1H);
13C-NMR (DMSO-d6, 100 MHz): δC 21.1, 106.0, 106.2,
110.4, 120.4, 127.0, 127.5, 128.7, 129.5, 129.7, 132.3,
136.5, 138.2, 139.1, 141.2, 152.9, 157.1, 161.0; IR (KBr):
ν 3289, 3059, 3033, 1705, 1684, 1657, 1487, 1398, 1285,
1104, 1055, 834, 740 cmÀ1; HRMS (TOF, ESI, m/z):
Calcd for C20H13O3 [M À H]À 301.0865, found 301.0881.
1
192°C; H-NMR (DMSO-d6, 400 MHz): δH 2.30 (s, 3H),
3.89 (s, 3H), 6.71 (s, 2H), 7.50 (dd, J = 9.2 Hz, J′ = 3.2 Hz,
1H), 7.68 (d, J = 2.8 Hz, 1H), 9.01 (d, J = 8.8 Hz, 1H),
10.84 (brs, 1H); 13C-NMR (DMSO-d6, 100 MHz): δC
21.4, 56.0, 104.1, 108.6, 111.6, 113.0, 121.5, 123.6, 128.5,
129.1, 139.8, 151.7, 156.0, 158.6, 160.9; IR (KBr): ν
3285, 3059, 1706, 1684, 1657, 1620, 1487, 1398, 1285,
1199, 1055, 833, 740 cmÀ1; HRMS (TOF, ESI, m/z):
Calcd for C15H11O4 [M À H]À 255.0651, found 255.0671.
1-Hydroxy-3,9-dimethyl-6H-benzo[c]chromen-6-one (5d).
Yield: 81% (97 mg); pale yellow solid; mp 187–189°C;
1H-NMR (DMSO-d6, 400 MHz): δH 2.30 (s, 3H), 2.49 (s,
3H), 6.69 (s, 1H), 6.71 (s, 1H), 7.40 (dd, J = 8.0 Hz, J
′ = 0.8 Hz, 1H), 8.13 (d, J = 8.0 Hz, 1H), 8.89 (s, 1H),
10.89 (brs, 1H); 13C-NMR (DMSO-d6, 100 MHz): δC
21.4, 22.6, 104.0, 108.7, 113.1, 117.7, 127.3, 129.0,
129.9, 135.2, 140.9, 145.9, 152.7, 156.8, 161.0; IR
(KBr): ν 3376, 3140, 1700, 1619, 1564, 1524, 1492,
1459, 1397, 1333, 1322, 1273, 1094, 929, 852,
1-Hydroxy-8-methoxy-3-phenyl-6H-benzo[c]chromen-6-one
(5h). Yield: 80% (127 mg); pale yellow solid; mp 210–
211°C (lit. [15] mp 242–244°C); 1H-NMR (DMSO-d6,
400 MHz): δH 3.90 (s, 3H), 7.16 (d, J = 1.2 Hz, 1H),
7.18 (d, J = 1.2 Hz, 1H), 7.40–7.43 (m, 1H), 7.48–7.54
(m, 3H), 7.68–7.70 (m, 3H), 9.06 (d, J = 9.2 Hz, 1H),
11.12 (brs, 1H); 13C-NMR (DMSO-d6, 100 MHz): δC
56.0, 105.9, 106.2, 110.3, 111.7, 121.9, 123.5, 127.0,
128.1, 128.7, 129.4, 129.6, 139.0, 141.1, 152.5, 156.5,
158.9, 160.8; IR (KBr): ν 3302, 3060, 1706, 1684, 1658,
1620, 1398, 1285, 1104, 1055, 857, 833, 789 cmÀ1
;
741 cmÀ1
; HRMS (TOF, APCI, m/z): Calcd for
HRMS (TOF, ESI, m/z): Calcd for C20H14NaO4
C15H13O3 [M + H]+ 241.0859, found 241.0860.
[M + Na]+ 341.0784, found 341.0780.
1-Hydroxy-3-phenyl-6H-benzo[c]chromen-6-one (5e).
9-Fluoro-1-hydroxy-3-phenyl-6H-benzo[c]chromen-6-one
Yield: 82% (118 mg); pale yellow solid; mp 273–275°C
(lit. [15] mp 270–272°C); 1H-NMR (DMSO-d6,
400 MHz): δH 7.20 (d, J = 1.2 Hz, 1H), 7.21 (d,
J = 1.2 Hz, 1H), 7.41–7.45 (m, 1H), 7.50–7.53 (m, 2H),
7.62–7.66 (m, 1H), 7.70–7.72 (m, 2H), 7.91–7.96 (m,
1H), 8.29 (dd, J = 8.0 Hz, J′ = 1.2 Hz, 1H), 9.15 (d,
(5i). Yield: 73% (112 mg); pale yellow solid; mp 193–
195°C; H-NMR (DMSO-d6, 400 MHz): δH 7.17 (s, 2H),
7.43–7.48 (m, 2H), 7.48–7.52 (m, 2H), 7.69–7.70 (m,
2H), 8.32 (dd, J = 8.8 Hz, J′ = 6.4 Hz, 1H), 8.78 (dd,
J = 12.0 Hz, J′ = 2.4 Hz, 1H), 11.42 (s, 1H); 13C-NMR
(DMSO-d6, 100 MHz): δC 105.0 (d, JF–C = 2.6 Hz),
1
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2019
Synthesis of Structurally Diversified Benzo[c]chromene Derivatives
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D. W.; Geng, Q.; Zhang, H.; Jiang, Y. W. Angew Chem Int Ed 2010, 49,
1291; (c) Yang, T.; Lin, C.; Fu, H.; Jiang, Y.; Zhao, Y. Org Lett 2005, 7,
4781.
106.3, 110.3, 113.4 (d, JF–C = 26.0 Hz), 116.2 (d, JF–
= 23.1 Hz), 117.3 (d, JF–C = 2.0 Hz), 127.1, 128.9,
C
129.6, 133.4 (d, JF–C = 10.6 Hz), 137.5 (d, JF–
C = 11.7 Hz), 138.7, 142.9, 153.3, 157.4, 160.0, 166.3 (d,
JF–C = 249.5 Hz); IR (KBr): ν 3291, 3058, 3033, 1705,
1684, 1657, 1621, 1487, 1420, 1398, 1286, 1199, 1104,
1055, 834, 740 cmÀ1; HRMS (TOF, ESI, m/z): Calcd for
C19H10FO3 [M À H]À 305.0614, found 305.0632.
1-Hydroxy-9-methyl-3-phenyl-6H-benzo[c]chromen-6-one
(5j). Yield: 72% (109 mg); pale yellow solid; mp 185–
1
187°C; H-NMR (DMSO-d6, 400 MHz): δH 2.51 (s, 3H),
7.17 (s, 1H), 7.18 (s, 1H), 7.38–7.43 (m, 2H), 7.50–7.53
(m, 2H), 7.70–7.72 (m, 2H), 8.16 (d, J = 8.0 Hz, 1H),
8.95 (s, 1H), 11.18 (brs, 1H); 13C-NMR (DMSO-d6,
100 MHz): δC 21.2, 105.9, 106.3, 110.3, 120.3, 127.0,
127.5, 128.8, 129.6, 129.7, 132.3, 136.6, 138.2, 139.0,
141.7, 152.8, 157.1, 161.0; IR (KBr): ν 3275, 1706,
1684, 1619, 1576, 1398, 1285, 1200, 1104, 1055, 833,
763, 740 cmÀ1; HRMS (TOF, ESI, m/z): Calcd for
C20H13O3 [M À H]À 301.0865, found 301.0866.
1-Hydroxy-10-methyl-3-phenyl-6H-benzo[c]chromen-6-one
(5k). Yield: 80% (121 mg); pale yellow solid; mp 197–
1
198°C; H-NMR (CDCl3, 400 MHz): δH 2.59 (s, 3H),
5.59 (s, 1H), 7.01 (d, J = 1.2 Hz, 1H), 7.25 (d,
J = 1.2 Hz, 1H), 7.42 (d, J = 7.6 Hz, 1H), 7.46–7.52 (m,
3H), 7.63–7.65 (m, 2H), 7.69 (d, J = 7.6 Hz, 1H), 8.24
(d, J = 8.0 Hz, 1H); 13C-NMR (CDCl3, 100 MHz): δC
23.1, 107.7, 110.5, 123.5, 126.9, 127.2, 127.7, 127.8,
128.4, 129.0, 132.5, 136.1, 137.8, 139.0, 143.1, 152.9,
158.5, 162.0; IR (KBr): ν 3273, 3061, 2916, 1706, 1659,
1591, 1506, 1482, 1377, 1340, 1246, 1034, 900,
778 cmÀ1; HRMS (TOF, ESI, m/z): Calcd for C20H13O3
[M À H]À 301.0865, found 301.0875.
Acknowledgments. This work was financially supported by the
National Natural Science Foundation of China (no. 21702078)
and Major Basic Research Project of the Natural Science Founda-
tion of the Jiangsu Higher Education Institutions (17KJA150003).
[20] Wang, Y.; Kuang, Y.; Wang, Y. Chem Commun 2015, 51,
5852.
REFERENCES AND NOTES
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SUPPORTING INFORMATION
Additional supporting information may be found online
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article.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet