Synthesis of 2,4-Diaryl-4H-Chromenes via Decarboxylative Alkylation of β-Keto Acids to ortho-Quinone Methides as Reactive Intermediates

Full text of DOI:10.1002/bkcs.11534

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DOI: 10.1002/bkcs.11534
BULLETIN OF THE
J. H. Kim and D. Y. Kim
KOREAN CHEMICAL SOCIETY
Synthesis of 2,4-Diaryl-4H-Chromenes via Decarboxylative Alkylation
of β-Keto Acids to ortho-Quinone Methides as Reactive Intermediates
*
Joo Hee Kim and Dae Young Kim
Department of Chemistry, Soonchunhyang University, Chungnam 31538, South Korea.
*E-mail: dyoung@sch.ac.kr
Received March 7, 2018, Accepted June 15, 2018
Keywords: 4H-Chromenes, ortho-Quinone methides, Decarboxyaltive alkylation, β-Keto acids
4H-Chromenes are ubiquitous in natural products and phar-
maceuticals with a variety of physiological and biological
activities.1 In particular, 2,4-diaryl-4H-chromene moiety
forms the core structure of biologically active compounds
such as enzyme inhibitors against a variety of targets.2
Consequently, the construction of 2,4-diaryl-4H-chromene
skeletons is of great significance. In recent years, several
groups reported the synthesis of 2,4-diaryl-4H-chromene
derivatives based on the 1,4-reduction of the pyrylium ions3
or the addition of phenol nucleophiles to benzopyrylium
salts.4 Although these are to some extent satisfied as syn-
thetic process, a new and efficient synthetic route for the
synthesis of 2,4-diaryl-4H-chromenes is highly desired.
ortho-Quinone methides (o-QMs) are versatile intermedi-
ates in organic synthesis and materials chemistry as well as
biological processes.5 A number of progress has been made
in the addition of a wide range of nucleophiles to o-QMs
under transition metal catalysis6 or organocatalysis.7
Recently, o-QMs have successfully been applied to a cata-
lytic enantioselective reactions with various nucleophiles.
However, to the best of our knowledge, the decarboxylative
alkylation reaction between β-keto acids and o-QMs has
not been reported yet. The decarboxylative reactions of
β-keto acids as of ketone enolate equivalents have received
much attention due to their higher reactivity and regioselec-
tivity.8 Therefore, it is seen that in situ generated o-QMs
could probably react with β-keto acids via decarboxylative
alkylation to produce Michael adduct, followed by sequen-
tial formation of the hemiketals and dehydration to give
2,4-diaryl-4H-chromenes.
presence of 10 mol % of p-TsOH in dichloromethane at room
temperature. The desired product 3a was obtained with trace
amount (Table 1, entry 1). Then, we tested the decarboxyal-
tive alkylation benzoylacetic acid (2a) with 10 mol % of p-
TsOH at high temperature (40 ꢀC). The reaction gave a mod-
erate yield (31%) of 3a (Table 1, entry 2). By screening
Brønsted acids including 2,4-dinitrobenzensulfonic acid
(DNBS), methasulfonic acid (MsOH), TFA, and diphenyl-
phophoric acid (DPP) (Table 1, entries 2–7), it was found out
that MsOH was the best acid catalyst for this reaction, result-
ing into the 3a in 47% yield (Table 1, entry 5). In order to
improve the yield, various solvents were then tested in the
presence of 10 mol % of MsOH together with benzoylacetic
Table 1. Optimization of the reaction conditions.a,b
Temp.
(ꢀC)
Time
(h)
Yieldb
(%)
Entry Cat.
Solvent
1
2
3
4
5
6
7
8
TsOH
TsOH
TfOH
DNBS CH2Cl2
MsOH CH2Cl2
TFA
DPP
MsOH CHCl3
MsOH DCE
MsOH THF
MsOH Benzene 80
MsOH Toluene 110
MsOH Toluene 110
CH2Cl2
CH2Cl2
CH2Cl2
rt
12
12
12
12
12
24
24
12
12
12
12
12
8
Trace
31
28
33
47
31
35
61
65
50
63
75
85
40
40
40
40
40
40
61
83
65
CH2Cl2
CH2Cl2
As part of a research program related to the development
of synthetic methods for the C C bond formations,9 we
reported decarboxylative aldol and Michael reactions of
β-keto acids.8 Herein, we report a new and facile synthesis
of 2,4-diaryl-4H-chromenes via decarboxyaltive alkylation
of β-keto acids to o-QM intermediates, followed by sequen-
tial cyclization and dehydration.
To determine suitable reaction conditions for the decarbox-
yaltive alkylation of β-keto acids to o-QM intermediates, we
first examined the decarboxyaltive alkylation of benzoylace-
tic acid (2a) with o-hydroxy benzylic alcohol 1a in the
9
10
11
12
13c
a
Reactions were carried out with 1a (0.1 mmol), 2a (0.3 mmol),
catalyst (0.01 mmol) in solvent (2 mL).
Isolated yield.
b
c
30 mol% of MsOH loading.
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To examine the generality of the catalytic decarboxyla-
tive alkylation reaction of the β-keto acid derivatives 2 to
o-hydroxy benzylic alcohol 1a, the study was done on the
decarboxylative alkylation of various β-keto acids 2 with o-
hydroxy benzylic alcohol 1a in the presence of 30 mol %
of MsOH in toluene at reflux. A range of electron-donating
and electron-withdrawing substitutions on the β-aryl group
of the β-keto acids 2 provided the desired products 3a–3g
in high yields (77–90%, Scheme 1). The heteroaryl- and
naphthyl-substituted β-keto acids 2 provided the products
3h–3i with high yields (71–78%, Scheme 1). The research
on the possibility of decarboxylative alkylation using a
wide range of o-hydroxy benzylic alcohols 1 with benzoy-
lacetic acid (2a) under optimized conditions was carried
out. A range of ortho-, meta-, para-substitutions on the
benzylic aryl group of o-hydroxy benzylic alcohols 1 gave
out the corresponding products 3j–3o in high yields
(71–91%, Scheme 1).
Based on the experimental results, a plausible reaction
pathway and activation mode was proposed (Scheme 2).
The o-QM intermediates A were generated in situ from o-
hydroxy benzyl alcohol 1 in the presence of Brønsted acid.
Then, the alkylation reaction between o-QM intermediates
A and enol intermediate derived from β-keto acids 2, gives
Michael products B, followed by sequential formation of
the hemiketals C and dehydration to give 2,4-diaryl-4H-
chromenes 3.
In conclusion, we have present a new and efficient syn-
thesis of 2,4-diaryl-4H-chromenes via decarboxyaltive
alkylation of β-keto acids to o-QM intermediates, followed
by sequential cyclization and dehydration. The synthetically
useful 2,4-diaryl-4H-chromene derivatives were obtained in
high yields. Current studies are aimed at developing a cata-
lytic enenatioselective alkylation of β-keto acids to o-QM
intermediates.
Experimental
General Procedure for the Synthesis of 2,4-Diaryl-4H-
Chromenes 3. To a stirred solution of o-hydroxy benzylic
Scheme 1. Synthesis of 2,4-diaryl-4H-chromenes.a,b
aReactions were carried out with o-hydroxy benzylic alcohol
1 (0.1 mmol), β-keto acid 2 (0.3 mmol), MsOH (0.03 mmol) in
toluene (2 mL) at reflux for 8 h. bIsolated yield.
acid (2a) and o-hydroxy benzylic alcohol 1a at reflux condi-
tion. The commonly used solvents, such as dichloromethane,
chloroform, 1,2-dichloroethanes (DCE), THF, benzene, and
toluene were tolerated well in this reaction (47–75% yields,
Table 1, entries 5 and 8–12). Among the solvents probed, the
best results (75% yield) were achieved when the reaction was
carried out in toluene (Table 1, entry 12). At high loading to
30 mol % of MsOH, the yield can be elevated to 85%
(entry 13).
Scheme 2. Proposed reaction pathway.
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alcohol 1 (0.1 mmol) and β-keto acid 2 (0.3 mmol) in tolu-
ene (2 mL) was added MsOH (2.9 mg, 0.03 mmol) at room
temperature. The reaction mixture was stirred for 8 h at
reflux. After completion of the reaction, the resulting solu-
tion was diluted with saturated NaHCO3 solution (10 mL),
and extracted with ethyl acetate (2 × 15 mL). The com-
bined organic layers were dried over MgSO4, filtered, con-
centrated, and purified by flash chromatography (EtOAc/
hexane = 1:10) to afford 2,4-diaryl-4H-chromenes 3.
2,4-Diphenyl-4H-chromene (3a): 1H NMR (400 MHz,
CDCl3) δ 7.72 (d, J = 6.8 Hz, 2H), 7.41–7.28 (m, 7H),
7.24–7.16 (m, 2H), 7.12 (d, J = 8.0 Hz, 1H), 6.98–6.93 (m,
2H), 5.59 (d, J = 4.0 Hz, 1H), 4.85 (d, J = 4.0 Hz, 1H);
13C NMR (100 MHz, CDCl3) δ 150.95, 147.79, 146.65,
134.21, 129.73, 128.69, 128.51, 128.36, 128.33, 127.70,
126.70, 124.73, 123.50, 123.22, 116.69, 100.89, 41.13; EI-
MS: m/z = 284.1 [M+].
CDCl3) δ 151.03, 147.93, 146.78, 137.98, 134.20, 129.78,
129.34, 128.74, 128.43, 128.30, 127.73, 126.73, 125.44,
123.51, 123.30, 121.96, 116.75, 100.82, 41.20, 21.58; EI-
MS: m/z = 298.1 [M+].
2-(3-Fluorophenyl)-4-phenyl-4H-chromene (3g): 1H
NMR (400 MHz, CDCl3) δ 7.48 (d, J = 8.4 Hz, 1H),
7.45–7.41 (m, 1H), 7.36–7.17 (m, 7H), 7.12 (d, J = 8.0 Hz,
1H), 7.03 (td, J = 8.0 Hz, J = 2.4 Hz, 1H), 6.97 (d,
J = 3.6 Hz, 2H), 5.61 (d, J = 4.4 Hz, 1H), 4.84 (d,
J = 4.4 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 164.21,
161.77, 150.79, 146.1, 146.38, 136.55, 136.47, 129.88,
129.79, 128.79, 128.39, 127.86, 126.85, 123.75, 123.05,
120.33, 120.31, 116.71, 115.42, 115.21, 111.97, 111.73,
101.96, 41.11; 19F NMR (376 MHz, CDCl3): δ −114.67;
EI-MS: m/z = 302.1 [M+].
1
4-Phenyl-2-(thiophen-2-yl)-4H-chromene (3h): H NMR
(400 MHz, CDCl3)
δ 7.36–7.13 (m, 8H), 7.10 (d,
2-(4-Methoxyphenyl)-4-phenyl-4H-chromene (3b): 1H
NMR (400 MHz, CDCl3) δ 7.65 (d, J = 9.2Hz, 2 H),
7.33–7.27 (m, 4H), 7.24–7.16 (m, 2H), 7.11 (d,
J = 8.0 Hz, 1H), 6.98–6.90 (m, 4H), 5.47 (d,
J = 4.0 Hz, 1H), 4.83 (d, J = 4.4 Hz, 1H), 3.84 (s, 3H);
13C NMR (100 MHz, CDCl3) δ 159.89, 151.00, 147.60,
146.87, 129.72, 128.66, 128.36, 127.62, 126.92, 126.64,
126.10, 123.40, 123.34, 116.66, 113.69, 99.25, 55.35,
41.12; EI-MS: m/z = 314.1 [M+].
J = 8.4 Hz, 1H), 7.03 (dd, J = 5.2 Hz, J = 3.6 Hz, 1H),
6.95 (d, J = 3.6 Hz, 2H), 5.51 (d, J = 4.4 Hz, 1H), 4.81 (d,
J = 4.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 150.5,
146.33, 143.88, 137.98, 129.71, 128.66, 128.34, 127.69,
127.28, 126.72, 124.92, 123.63, 123.59, 123.05, 116.62,
100.16, 40.91; EI-MS: m/z = 290.1 [M+].
2-(Naphthalen-2-yl)-4-phenyl-4H-chromene (3i): 1H
NMR (400 MHz, CDCl3) δ 8.25 (s, 1H), 7.91–7.74 (m,
4H), 7.51–7.45 (m, 2H), 7.32 (d, J = 4.8 Hz, 4H),
7.25–7.20 (m, 3H), 7.00–6.96 (m, 2H), 5.74 (d, J = 4.8 Hz,
1H), 4.89 (d, J = 4.4 Hz, 1H); 13C NMR (100 MHz,
CDCl3) δ 151.10, 147.81, 146.73, 133.41, 133.31, 131.43,
129.85, 128.82, 128.58, 128.51, 128.03, 127.85, 127.71,
126.84, 126.43, 126.38, 123.91, 123.66, 123.33, 122.63,
116.83, 101.72, 41.34; EI-MS: m/z = 334.1 [M+].
4-Phenyl-2-(p-tolyl)-4H-chromene (3c): 1H NMR
(400 MHz, CDCl3) δ 7.61 (d, J = 8.4 Hz, 2H), 7.31–7.27
(m, 4H), 7.23–7.15 (m, 4H), 7.11 (d, J = 7.6 Hz, 1H),
6.97–6.92 (m, 2H), 5.53 (d, J = 4.4 Hz, 1H), 4.82 (d,
J = 4.0 Hz, 1H), 2.36 (s, 3H); 13C NMR (100 MHz, CDCl3)
δ 151.05, 147.89, 146.83, 138.45, 131.48, 129.77, 129.06,
128.71, 128.42, 127.69, 126.70, 124.69, 123.46, 123.35,
116.74, 100.11, 41.17, 21.31; EI-MS: m/z = 298.1 [M+].
2-(4-Fluorophenyl)-4-phenyl-4H-chromene (3d): 1H
NMR (400 MHz, CDCl3) δ 7.69 (dd, J = 9.0 Hz, 5.4 Hz,
2H), 7.34–7.16 (m, 6H), 7.12–7.05 (m, 3H), 6.96 (d,
J = 4.4 Hz, 2H), 5.52 (d, J = 4.4 Hz, 1H), 4.83 (d,
J = 4.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 164.19,
161.72, 150.87, 147.03, 146.59, 130.43, 130.40, 129.79,
128.76, 128.37, 127.78, 126.79, 126.65, 126.57, 123.65,
123.14, 116.67, 115.40, 115.19, 100.70, 41.10; 19F NMR
(376 MHz, CDCl3): δ −113.94; EI-MS: m/z = 302.1 [M+].
2-(4-Bromophenyl)-4-phenyl-4H-chromene (3e): 1H
NMR (400 MHz, CDCl3) δ 7.57 (d, J = 8.0 Hz, 2H), 7.49
(d, J = 8.8 Hz, 2H), 7.33–7.16 (m, 6H), 7.10 (d,
J = 8.4 Hz, 1H), 6.96 (d, J = 4.0 Hz, 2H), 5.57 (d,
J = 4.4 Hz, 1H), 4.81 (d, J = 4.0 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ 150.64, 146.77, 146.27, 132.99,
131.34, 129.65, 128.64, 128.24, 127.69, 126.69, 126.18,
123.59, 122.89, 122.40, 116.54, 101.30, 40.96; EI-MS: m/
z = 362.0 [M+].
4-(4-Methoxyphenyl)-2-phenyl-4H-chromene (3j): 1H
NMR (400 MHz, CDCl3) δ 7.75–7.70 (m, 2H), 7.40–7.33
(m, 3H), 7.22–7.10 (m, 4H), 6.96–6.95 (m, 2H), 6.86–6.83
(m, 2H), 5.57 (d, J = 4.0 Hz, 1H), 4.79 (d, J = 4.0 Hz,
1H), 3.77 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 158.45,
150.95, 147.67, 139.14, 134.31, 129.76, 129.36, 128.53,
128.38, 127.66, 124.76, 123.62, 123.54, 116.72, 114.11,
101.21, 55.32, 40.30; EI-MS: m/z = 314.1 [M+].
2-Phenyl-4-(p-tolyl)-4H-chromene (3k): 1H NMR
(400 MHz, CDCl3) δ 7.72–7.70 (m, 2H), 7.39–7.30 (m,
3H), 7.21–7.08 (m, 6H), 6.98–6.91 (m, 2H), 5.57 (d,
J = 4.4 Hz, 1H), 4.79 (d, J = 4.0 Hz, 1H), 2.30 (s, 3H);
13C NMR (100 MHz, CDCl3) δ 150.98, 147.70, 143.87,
136.34, 134.30, 129.75, 129.42, 128.50, 128.36, 128.29,
127.66, 124.75, 123.54, 123.47, 116.70, 101.11, 40.74,
21.09; EI-MS: m/z = 298.1 [M+].
4-(3-Methoxyphenyl)-2-phenyl-4H-chromene (3l): 1H
NMR (400 MHz, CDCl3) δ 7.72 (d, J = 7.6 Hz, 2H),
7.41–7.33 (m, 3H), 7.25–7.10 (m, 3H), 7.00–6.94 (m, 2H),
6.89 (d, J = 7.6 Hz, 1H), 6.83 (t, J = 2.0 Hz, 1H),
6.77–6.75 (m, 1H), 5.58 (d, J = 4.0 Hz, 1H), 4.81 (d,
J = 4.0 Hz, 1H), 3.76 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 159.93, 150.94, 148.27, 147.87, 134.23, 129.68,
128.55, 128.36, 127.76, 127.65, 124.77, 123.54, 123.04,
4-Phenyl-2-(m-tolyl)-4H-chromene (3f): 1H NMR
(400 MHz, CDCl3) δ 7.51 (d, J = 9.2 Hz, 2H), 7.32–7.11
(m, 9H), 6.95–6.94 (m, 2H), 5.56 (d, J = 4.0 Hz, 1H), 4.83
(d, J = 4.4 Hz, 1H), 2.38 (s, 3H); 13C NMR (100 MHz,
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3629. (c) L. Caruana, M. Fochi, L. Bernardi, Molecules 2015,
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120.85, 116.73, 114.35, 111.85, 110.75, 55.23, 41.15; EI-
MS: m/z = 314.1 [M+].
2-Phenyl-4-(m-tolyl)-4H-chromene (3m): 1H NMR
(400 MHz, CDCl3) δ 7.74–7.71 (m, 2H), 7.41–7.34 (m,
3H), 7.22–6.88 (m, 8H), 5.58 (d, J = 4.0 Hz, 1H), 4.81 (d,
J = 4.0 Hz, 1H), 2.31 (s, 3H); 13C NMR (100 MHz, CDCl3)
δ 150.90, 147.64, 146.58, 138.35, 134.22, 129.72, 129.09,
128.52, 128.46, 128.31, 127.62, 127.49, 125.47, 124.69,
123.46, 123.28, 116.65, 100.96, 41.03, 21.44; EI-MS: m/
z = 298.1 [M+].
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4-(2-Methoxyphenyl)-2-phenyl-4H-chromene (3n): 1H
NMR (400 MHz, CDCl3) δ 7.72–7.69 (m, 2H), 7.39–7.29
(m, 3H), 7.20–7.15 (m, 2H), 7.11–7.06 (m, 3H), 6.97–6.85
(m, 3H), 5.59 (d, J = 4.0 Hz, 1H), 5.39 (d, J = 4.4 Hz,
1H), 3.91 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 156.34,
151.64, 148.18, 135.03, 134.50, 130.17, 129.66, 128.31,
127.59, 127.53, 124.67, 123.48, 121.12, 116.52, 110.53,
100.63, 55.59, 33.29; EI-MS: m/z = 314.1 [M+].
2-Phenyl-4-(o-tolyl)-4H-chromene (3o): 1H NMR
(400 MHz, CDCl3) δ 7.70 (d, J = 7.2 Hz, 2H), 7.39–7.30
(m, 3H), 7.23–7.10 (m, 6H), 6.94 (t, J = 6.8 Hz, 1H), 6.85
(d, J = 7.6 Hz, 1H), 5.52 (d, J = 4.0 Hz, 1H), 5.13 (d,
J = 3.6 Hz, 1H), 2.43 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 151.43, 147.81, 144.39, 135.38, 134.27, 130.74,
130.13, 129.47, 128.50, 128.37, 127.76, 126.66, 124.70,
123.62, 123.24, 116.60, 100.44, 37.81, 19.77; EI-MS: m/
z = 298.1 [M+].
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Acknowledgments. This research was supported by Soon-
chunhyang University Research Fund.
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