Ionic Liquids with Multi-Active Sites Synergistically Catalyzed Metal-Free Transformation of Alcohols Using Dimethyl Carbonate as an Environmental Solvent

Article abstract of DOI:10.1002/ejoc.202100564

One of the ultimate goals in organic synthesis is to develop metal-free, efficient and easily separable catalytic system for atom economic organic reactions in an environmental solvent. Direct substitution reaction of alcohols and hydrocarbon compounds is a significant and atom economic method for C?C bond formation. Herein, a metal-free and efficient catalytic system including recyclable pyridine-based ionic liquids with multiple active sites as the catalyst and dimethyl carbonate as the environmentally friendly solvent was developed for atom economic C3 substitution of 4-hydroxycoumarins with alcohols. Primary aromatic alcohols, secondary aliphatic and aromatic alcohols were suitable for the reaction, providing up to 99 % yield. The catalytic system could be easily scaled up to gram-scale with nearly quantitative yield. Coumatetralyl as commercial rodenticide could be prepared directly from commercially available 4-hydroxycoumarin and 1,2,3,4-tetrahydronaphthalen-1-ol. Racemic product derived from the reaction of (R)-1-phenylethanol and 4-hydroxycoumarin indicated the reaction was achieved through an S_N1 pathway. The comparison of the activities and acidities of the ionic liquids demonstrated that there was no directly relationship between them. Control experiments showed that the reaction probably proceeded via carbocation, ether intermediate and synergistically promoted effect of hydrogen bonding between the ionic liquid with multi-active sites and substrates.

Full text of DOI:10.1002/ejoc.202100564

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doi.org/10.1002/ejoc.202100564
Ionic Liquids with Multi-Active Sites Synergistically
Catalyzed Metal-Free Transformation of Alcohols Using
Dimethyl Carbonate as an Environmental Solvent
Zengmin Li+,[a] Yating Wen+,[a] Ning Wang,[a] Feng Han,*[a] Ying Li,[a] Hongfeng Zhuang,[a] and
Chengxia Miao*[a]
One of the ultimate goals in organic synthesis is to develop
metal-free, efficient and easily separable catalytic system for
atom economic organic reactions in an environmental solvent.
Direct substitution reaction of alcohols and hydrocarbon
compounds is a significant and atom economic method for CÀ C
bond formation. Herein, a metal-free and efficient catalytic
system including recyclable pyridine-based ionic liquids with
multiple active sites as the catalyst and dimethyl carbonate as
the environmentally friendly solvent was developed for atom
economic C3 substitution of 4-hydroxycoumarins with alcohols.
Primary aromatic alcohols, secondary aliphatic and aromatic
alcohols were suitable for the reaction, providing up to 99%
yield. The catalytic system could be easily scaled up to gram-
scale with nearly quantitative yield. Coumatetralyl as commer-
cial rodenticide could be prepared directly from commercially
available 4-hydroxycoumarin and 1,2,3,4-tetrahydronaphthalen-
1-ol. Racemic product derived from the reaction of (R)-1-
phenylethanol and 4-hydroxycoumarin indicated the reaction
was achieved through an SN1 pathway. The comparison of the
activities and acidities of the ionic liquids demonstrated that
there was no directly relationship between them. Control
experiments showed that the reaction probably proceeded via
carbocation, ether intermediate and synergistically promoted
effect of hydrogen bonding between the ionic liquid with
multi-active sites and substrates.
Introduction
oxidative Heck reactions via simultaneous CÀ H functionalization
at the C3 position of coumarins under aerobic conditions.[11–12]
Besides, Pd-catalyzed CÀ C bond formation reaction for the
synthesis of 4-hydroxycoumarins with C3-alkylation could be
realized with organic halides and boronic acid as the
substrates.[13] And the C3 substitution of 4-hydroxycoumarins
with alcohols catalyzed by Fe(ClO4)3 ·H2O,[14] Al(OTf)3,[15] Bi-
(NO3)3 ·5H2O in ionic liquid,[16] Yb(OTf)3,[17] I2,[18] TMSOTf (TMS,
trimethylsilyl),[19] Amberlite IR-120,[20] palladium complexes,[21]
Developing metal-free, efficient and easily separable catalytic
system for atom economic organic reactions in an environ-
mental solvent is one of the ultimate goals in organic synthesis
from the view-point of green chemistry. The direct substitution
reaction of alcohols is an attractive process for water as the sole
by-product, which is recognized as one of ten key Green
Chemistry research areas.[1–2] Direct substitution of hydrocarbon
compounds with alcohols is a significant CÀ C bond forming
method for petrochemical processing, the synthesis of pharma-
ceutical agents and so on.[3–5] 4-Hydroxycoumarins as important
precursors in the realm of organic synthesis can be transformed
by different methods into a series of 4-hydroxycoumarin
derivatives, especially 3-(benzyl)-substituted 4-hydroxycoumar-
ins, which exhibit a wide range of biological activities such as
anti-HIV, antimalarial, antibacterial, cytotoxic and so on.[6–10] At
present, there are several methods for the synthesis of 3-
substituted 4-hydroxycoumarin derivatives through C3 substitu-
tion. One strategy was achieved with olefins as the alkylation
reagent using FeCl3 ·6H2O as the catalyst or Pd-catalyzed
[22]
RuCl2[PPh3]3 or p-toluenesulfonic acid[23] was also reported.
However, metals were usually used as catalysts in the reported
methods. And carbocation was usually recognized as the key
intermediate derived from alcohols especially in Lewis or
Brønsted acid-catalyzed systems among the third developed
systems. Previously, we have developed several efficient and
mild systems catalyzed by acidic ionic liquids to generate
carbocations from alcohols, which can react with sulfonamide,
amide, carbamate, aromatic amine, olefins, thiols et al. to
produce corresponding products.[24–28] Ionic liquids exhibit high
thermal and chemical stability, negligible vapor pressure, easy
recyclability, tunable properties and could be used as environ-
mental catalysts for the reaction by introducing different
functionalized groups.[29–33] On the other hand, dimethyl
carbonate (DMC) is recognized as a green solvent for fast
biodegradability, low toxicity, mild odor, low evaporation rate,
low density and good environmental compatibility[34,35] and it
has been used in several reactions, such as rearrangement
reaction,[36] Diels-Alder reaction,[37] insertion reaction,[38] olefin
metathesis transformations,[39] asymmetric hydrogenation,[40]
oxidation.[41]
[a] Z. Li,+ Y. Wen,+ N. Wang, Prof. F. Han, Prof. Y. Li, H. Zhuang, Prof. C. Miao
College of Chemistry and Material Science
Shandong Agricultural University
Daizong Road No. 61, Tai’an 271018, China
E-mail: chxmiao@sdau.edu.cn
fenghan@sdau.edu.cn
[+] These authors contributed equally to this work.
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejoc.202100564
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As a continuation of our efforts to develop reactions
wanted to exploit more efficient, mild and environmental
system to catalyze the atom economic C3 substitution of 4-
hydroxycoumarins with carbocations derived from alcohols. The
reaction was synergistically catalyzed by metal-free pyridine-
based ionic liquids with multiple active sites using DMC as the
green solvent, providing up to 99% yield (Scheme 1 and
Figure 1). The developed catalytic system could be easily
separated from the product and be suitable for one-step
synthesis of coumatetralyl as commercial rodenticide. And a
mechanism involving the synergistically promoted effect of
hydrogen bonding, carbocation and ether intermediate was
proposed.
involving generated carbocation as the intermediate,[24–28] we
Scheme 1. C3 substitution of 4-hydroxycoumarins with alcohols catalyzed by
[BsPy][OTf].
Results and Discussion
The initial examination was performed by using 4-hydroxycou-
marin and phenyl(p-tolyl)methanol as the substrates (Table 1).
Obviously, the reaction did not occur without any catalyst
(Table 1, entry 1). Interestingly, 52% yield could be provided
with 1 mol% of [BsPy][OTf] as the catalyst and CH3CN as the
°
solvent at 80 C (Table 1, entry 2). Using 5 mol% of [BsPy][OTf]
Figure 1. Ionic liquids used in the work.
as the catalyst for the transformation led to 94% yield, and
there was no significant change by further increasing the
catalyst loading to 10 mol% (Table 1, entries 3–5). Then we
examined the influence of solvents on the reaction. Most
solvents gave moderate to excellent yields, except DMF (N,N-
dimethylformamide), DMSO (dimethyl sulfoxide) and H2O
(Table 1, entries 4, 6–15). DMC was chosen as the best solvent
for availability in large amounts and at low prices, providing a
suitable liquid temperature range, low (eco)toxicity, and
complete biodegradability (Table 1, entry 12).[34,35,42] Besides, the
reaction was sensitive to the temperature and would become
Table 1. Screening the reaction conditions for the substitution of 4-
hydroxycoumarin with phenyl(p-tolyl)methanol catalyzed by ionic liquids.a
Yield [%]b
°
Entry
Cat. [mol%]
Solvent
T [ C]
1
2
3
4
5
6
7
8
–
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
DMF
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
60
40
25
60
60
60
60
60
60
60
60
60
60
NRc
52
84
[BsPy][OTf] (1)
[BsPy][OTf] (2)
[BsPy][OTf] (5)
[BsPy][OTf] (10)
[BsPy][OTf] (5)
[BsPy][OTf] (5)
[BsPy][OTf] (5)
[BsPy][OTf] (5)
[BsPy][OTf] (5)
[BsPy][OTf] (5)
[BsPy][OTf] (5)
[BsPy][OTf] (5)
[BsPy][OTf] (5)
[BsPy][OTf] (5)
[BsPy][OTf] (5)
[BsPy][OTf] (5)
[BsPy][OTf] (5)
[BsPy][OTf] (5)
[BsMim][OTf] (5)
[BsMPr][OTf] (5)
[BsMPip][OTf] (5)
[BsMMo][OTf] (5)
[BsM(dio)TMP][OTf] (5)
[BuPy][OTf] (5)
[BsPy][HSO4] (5)
[BsPy][OTs] (5)
[BsPy][CH3SO3] (5)
°
poorer when the temperature was lower than 60 C (Table 1,
94
entries 12 and 16–18). Moreover, shorten the reaction time
would also decrease the yield (Table 1, entry 16 vs 19).
Subsequently, the effects of the cations derived from pyridine,
imidazole, pyrrolidine, piperidine, morpholine and thiomorpho-
line 1,1-dioxide were investigated (Figure 1 and Table 1, en-
tries 16 and 20–25). The results indicated that the cation had
significant influence on the reaction. Excellent yield could be
obtained only by employing pyridine-based ionic liquids as the
catalyst (Table 1, entry 16). Moreover, the sulfonic acid in the
side chain of ionic liquids was also necessary for the reaction
96
NRc
NRc
NRc
86
DMSO
H2O
9
THFd
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
n-hexane
1,4-dioxane
DMC
79
99
98
98
96
96
96
27
DCEd
toluene
CYHd
DMC
DMC
DMC
DMC
DMC
DMC
DMC
DMC
DMC
DMC
DMC
DMC
À
(Table 1, entry 16 vs 25). Utilizing other anions such as HSO4 ,
trace
47e
32
OTsÀ or CH3SO3 instead of OTfÀ also resulted in lower yields
À
(Table 1, entries 16 vs 26–28). The phenomena indicated that
the reaction needed the synergistic action of multiple active
sites belonging to pyridine-based ionic liquids to display
excellent activity. Additionally, the optimum ratios of 4-
hydroxycoumarin and phenyl(p-tolyl)methanol were compared
and 1:1.2 gave the best result (Table S1). Also, the recyclability
of [BsPy][OTf] was tested. The results indicated that the ionic
liquids could be recycled and reused, and there was some
change in yield after the fourth run under the optimized
reaction conditions, providing yield from 96% to 86% (Table 1,
entry 16 and Figure S1).
11
47
NRc
16
NRc
trace
31
DMC
33
[a] Reaction conditions: 4-hydroxycoumarin 1a (0.5 mmol), phenyl(p-tolyl)
methanol 2a (0.6 mmol), catalyst (catalytic amount refers to 4-hydrox-
ycoumarin), solvent (2 mL), at a certain temperature for 2 h. [b] Isolated
yield. [c] NR=no reaction. [d] THF: tetrahydrofuran; DCE: dichloroethane;
CYH: cyclohexane; [e] t=1 h.
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The generality of the reaction was studied under the
either electron-donating or electron-withdrawing substituents
on the phenyl ring proved reactive with certain variation in the
isolated yields (Table 2, entries 1–12). Diphenylmethanol with-
out any substituent just gave 64% yield under optimized
reaction conditions (Table 2, entry 5). However, 96% yield could
be obtained by prolonging the reaction time to 8 h (Table 2,
entry 6). In order to prove the structure of the desired products,
the x-ray structure of 3e was obtained from n-hexane/ethyl
acetate (Figure 2 and Table S2). An electron-donating substitu-
ent in the 4-position of the phenyl ring was well tolerated,
generating 96% or 98% yield for Me or OMe respectively
(Table 2, entries 1 and 3). Substrate with two electron-donating
substituents in 4, 4’-position on the phenyl ring exhibited better
activity, furnishing 99% yield of 3d with 2 h (Table 2, entry 4).
There is some relationship between the activity and the steric
hindrance and moving the Me to the 2-position of the phenyl
ring was detrimental for the transformation (Table 2, entry 1 vs
2). Besides, substrates with halogen substituents in the 4-
position on the phenyl group were also tolerated by prolonging
the reaction time (Table 2, entries 7–11). The more the electron-
withdrawing substituents had, the poorer the activity was
(Table 2, entry 11). And 81% yield could be obtained with
phenyl as the substituent to disperse the positive charge and
make it more stable (Table 2, entry 12). Other activated
secondary aromatic alcohol such as 1,3-diphenylprop-2-en-1-ol
also exhibited a good yield under optimized reaction conditions
(Table 2, entry 13). 1-Phenylethan-1-ol and primary aromatic
alcohols such as (4-methoxyphenyl)methanol could provide
moderate yields when the reaction time was extended to 8 or
24 h (Table 2, entries 14 and 15). In addition, the reaction of
secondary aliphatic alcohols such as 2-cyclohexen-1-ol and
cyclohexanol could also occur, providing 45% and 35% yield
respectively by prolong the reaction time to 24 h (Table 2,
entries 16 and 17).
optimized reaction conditions (Table 2). The activities of a series
of secondary aromatic alcohols were tested. The results
demonstrated that most secondary aromatic alcohols bearing
Table 2. Substrate scope of C3 substitution of 4-hydroxycoumarin with
different alcohols catalyzed by [BsPy][OTf].a
Entry
Product
Yield [%]b
1
2
3
4
5
6
7
8
3a, R1=Ph, R2=4-MeÀ Ph
3b, R1=Ph, R2=2-MeÀ Ph
3c, R1=Ph, R2=4-OMeÀ Ph
3d, R1=R2=4-OMeÀ Ph
3e, R1=R2=Ph
96
78c
98
99
64
96c
92d
81d
66d
81e
62d
81
3f, R1=Ph, R2À 4-FÀ Ph
3g, R1=Ph, R2=4-ClÀ Ph
3h, R1=Ph, R2=4-BrÀ Ph
3i, R1=Ph, R2=4-CF3À Ph
3j, R1=R2=4-ClÀ Ph
9
10
11
12
3k, R1=Ph, R2=4-PhÀ Ph
13
90
14
15
3m, R1=Me, R2=Ph
68c
67f
3n, R1=H, R2 =4-OMeÀ Ph
16
45g
Additionally, application of the catalytic system to 4-
hydroxycoumarin derivatives showed that excellent yields could
be obtained with substrates bearing both electron-withdrawing
and electron-donating groups in the 6 or 7-position (Table 3). 4-
Hydroxycoumarins with electron-donating groups such as Me,
17
35f
[a] Reaction conditions: 4-hydroxycoumarin 1a (0.5 mmol), alcohol 2
(0.6 mmol), [BsPy][OTf] (5 mol% refers to 4-hydroxycoumarin), DMC (2 mL),
°
°
Table 3. C3 substitution of 4-hydroxycoumarins with phenyl(p-tolyl)
at 60 C for 2 h. [b] Isolated yield. [c] t=8 h. [d] t=12 h. [e] 80 C, 4 h. [f]
methanol catalyzed by [BsPy][OTf].a
°
[BsPy][OTf] (10 mol%), at 80 C for 24 h. [g] t=24 h.
Entry
Product
Yield [%]b
1
2
3
4
5
6
7
3a, R=H
96
96
99
3q, R=7-Me
3r, R=7-OMe
3s, R=6-Me
3t, R=6-F
3u, R=6-Cl
3v, R=6-Br
97
63c
92c
92c
[a] Reaction conditions: 4-hydroxycoumarin derivative
1 (0.5 mmol),
phenyl(p-tolyl)methanol 2a (0.6 mmol), [BsPy][OTf] (5 mol% refers to 4-
°
Figure 2. X-ray structure of 3e (hydrogen atoms linked to carbons are
omitted for clarity, CCDC-2092740).
hydroxycoumarin derivative), DMC (2 mL) at 60 C for 2 h. [b] Isolated
yield. [c] 12 h.
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OMe in the 6 or 7-position displayed good activities, giving
order to test the reaction mechanism. (R)-1-phenylethanol was
tested to react with 4-hydroxycoumarin under the optimized
reaction conditions for 8 h, providing racemic product 3m
(Scheme 4). The result indicated that the reaction was achieved
through an SN1 pathway and not an SN2 pathway.
nearly quantitative yields (Table 3, entries 2–4). Good yields
were also observed by employing halogen-substituted sub-
strates by prolonging the reaction time to 12 h, except 6-fluoro-
4-hydroxycoumarin (Table 3, entries 4, 6, 7 vs 5).
After demonstrating the substrate scope of the catalytic
system, we examined the scalability of our catalytic system for
the C3 substitution of 4-hydroxycoumarin with phenyl(p-tolyl)
methanol (Scheme 2). Delightedly, the reaction could be carried
out smoothly to provide 87% yield of the desired product
under the optimized reaction conditions, and up to 98% yield
could be acquired by prolonging the reaction time from 2 to
3 h.
Ethers also usually recognized as the reaction intermediates
could be detected by GC-MS compared with the standard
sample during the reactions. And the corresponding ethers
could be isolated under the optimized reaction conditions
when 4-hydroxycoumarin was not added into the catalytic
system (Scheme 5, (1)). Nearly quantitative yield could be
obtained when 0.5 mmol 4-hydroxycoumarin was reacted with
0.3 mmol
4,4’-(oxybis(phenylmethylene))bis(methylbenzene)
Coumatetralyl (3w) is a common agricultural chemical and
the first anticoagulant rodenticides since mid-1950s. Now it is
still widely used for pest control in many aeras.[43] As a further
demonstration of the utility of our developed system, the C3
substitution of 4-hydroxycoumarin with 1,2,3,4-tetrahydronaph-
thalen-1-ol to generate coumatetralyl was performed under
certain reaction conditions with [BsPy][OTf] as the catalyst
(Scheme 3). Interestingly, 71% yield could be provided without
any by-product under optimized reaction conditions by
prolonging the reaction time to 24 h. And 69% yield could be
under optimized reaction conditions (Scheme 5, (2)). The
phenomena demonstrated that aromatic ether may be involved
in the reaction.
According to our results and the previous report,[24–28,44] we
proposed a possible mechanism involving carbocation and
ethers as the intermediates and synergistically promoted effect
of hydrogen bonding (Scheme 6). Initially, we thought that the
activities may be significantly influenced by the acidities of the
ionic liquids. So, the acidities of the ionic liquids were tested in
order to demonstrate the effect of the ionic liquids
(Table S3),[45–48] which indicated that the order of the acidities
was as follows: [BsPy][CH3SO3]>[BsPy][OTf]>[BuPy][OTf]>
[BsPy][OTs]>[BsPy][HSO4]. Compared with the data in Table 1
(entries 16, 25–28), the results showed that there was no
obvious relationship between the activity and acidity. Also, the
screening of the cations and the side chain in Table 1
(entries 16, 20–25) indicated that both cations and the sulfonic
acid group were important for the reaction. And trifluorometh-
ylsulfonate was also essential for the reaction after testing
several anions. Moreover, Liu et al. proved the hydrogen
bonding effect between ionic liquids and ethers using NMR
analysis and DFT calculation.[44] Therefore, we proposed cation
and anion of the ionic liquids would synergistically catalyze the
reaction in our developed system through the effect of hydro-
gen bonding based on the phenomena. Sulfonic acid group of
the cation and trifluoromethanesulfonate as the anion would
activate the hydrogen of alcohols and the hydrogen of 4-
hydroxycoumarin respectively under the effect of hydrogen
bonding. Electron-donating group in the phenyl ring of
aromatic alcohols was beneficial for the reaction, possibly
advantageous to stabilization of the carbocation (Table 2,
°
obtained with 20 mol% [BsPy][OTf] as the catalyst at 80 C for
2 h. That’s to say, the catalytic system was available for one step
synthesis of coumatetralyl.
According to the previous reports, the reaction in our
developed acidic system seems to proceed by a carbocation
intermediate,[14] which was attacked by 4-hydroxycoumarin as
the nucleophile. Some control experiment was performed in
Scheme 2. Scale-up experiments.
Scheme 3. Application of the catalytic system for one step synthesis of
coumatetralyl.
Scheme 5. Control experiments for the substitution of 4-hydroxycoumarin
with phenyl(p-tolyl)methanol.
Scheme 4. The reaction of 4-hydroxycoumarin with (R)-1-phenylethanol.
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Scheme 6. Proposed mechanism for the substitution under the reaction conditions.
Experimental Section
entries 1, 3 and 4). 4-(Pyridin-1-ium-1-yl)butane-1-sulfonate and
trifluoromethanesulfonic acid would be formed during the
reaction (I), which could be in-situ transformed to [BsPy][OTf]
acting as the catalyst again (II). On the other hand, formed
carbocation would be attacked by carbanion 5 derived from 1
through SN1 pathway to generate compound 3’, which could
exist in tautomeric keto-enol forms with desired product 3.
Meanwhile, carbocation 7 would react with another alcohol
immediately to providing intermediate 8, which would generate
9 by losing the proton. Intermediates 7, 8 and 9 could exist in
balance.
General
NMR spectra were recorded on BRUKER AVANCETM III 400, BRUKER
1
AVANCE III HD 600 spectrometers. H NMR (400 or 600 MHz) and
13C NMR (101 or 151 MHz) spectra were obtained as solutions in
CDCl3 or (CD3)2SO. Chemical shifts were reported in parts per million
(ppm, δ) and referenced to TMS (trimethylsilane). The high-
resolution mass spectra (HRMS) were recorded on an Agilent
Technologies 1260-G6530B LC-MS. Optical rotation was recorded
with a WZZ-3 automatic polarimeter (sodium lamp, 1-dm cuvette, c
°
in g/100 mL, 20 C). All reagents and solvents were obtained from
commercial suppliers without further purification unless noted
otherwise. All reactions were monitored by TLC (Thin Layer
Chromatography) with silica gel coated plates. Silica gel (200–300
microns) was used for all chromatographic separations, providing
isolated yields.
Conclusion
We have developed an efficient, economic and environmental
system for C3 substitution of 4-hydroxycoumarin with alcohols.
The system was catalyzed by pyridine-based ionic liquids with
multi-active sites in dimethyl carbonate as the environmental
solvent, providing a series of 4-hydroxycoumarin derivatives
with up to 99% yield. Nearly quantitively yield could be
obtained when the scalability of our catalytic system was
applied for the C3 substitution of 4-hydroxycoumarin with
phenyl(p-tolyl)methanol. Interestingly, coumatetralyl as com-
mercial rodenticide could be smoothly synthesized in one step
with the developed system. An SN1 pathway was deduced from
the racemic product derived from the reaction of (R)-1-phenyl-
ethanol and 4-hydroxycoumarin. The comparison between the
activities and acidities of the ionic liquids demonstrated that
there was no directly relationship for them. And a mechanism
involving effects of hydrogen bonding between the ionic
liquids and substrates, carbocation and ether was proposed.
Developing new strategies for the transformation of alcohols
are in progress in our lab.
Representative experimental procedure for the substitution
of 4-hydroxycoumarin with alcohols
To a mixture of 4-hydroxycoumarin (81 mg, 0.5 mmol) and phenyl
(p-tolyl)methanol (118.9 mg, 0.6 mmol) in DMC (2 mL), a certain
amount of catalyst was added, and the reaction mixture was stirred
for several hours at a definite temperature. The progress of the
reaction mixture was monitored by TLC. After completion of the
reaction, the mixture was extracted with ethyl acetate and
concentrated under vacuum. The crude product was purified by
silica gel column (200–300 mesh) with petroleum ether/ethyl
acetate (6:1) as eluent to afford the corresponding product. Finally,
the pure product can be obtained after vacuum drying and oil
pump to remove the remaining solvent.
The procedure for the reuse of [BsPy][OTf] in the substitution
of 4-hydroxycoumarin with phenyl(p-tolyl)methanol
To test the catalyst reusability, the reaction was carried out in the
presence of [BsPy][OTf] under the optimal reaction conditions with
4-hydroxycoumarin and phenyl(p-tolyl)methanol as the substrates
for 2 h detected by TLC. After each cycle, DMC was removed with
oil pump, and the residue was dissolved with petroleum ether:eth-
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°
hyl acetate (3:1, 10 mL) and heated under 60 C, so the product
3-((4-Fluorophenyl)(phenyl)
methyl)-4-hydroxy-2H-chromen-2-one (3f)
and ionic liquids were extracted and separated. The Schlenk tube
containing ionic liquids was then dried and used directly for the
next cycle.
White solid, 159.8 mg, 92% yield; Melting point: 164–165 C; 1H
NMR (600 MHz, CDCl3) δ 7.73 (dd, J=7.9, 1.3 Hz, 1H), 7.57–7.52 (m,
1H), 7.40 (t, J=7.4 Hz, 2H), 7.34 (dd, J=13.1, 7.6 Hz, 2H), 7.25 (s,
5H), 7.07 (t, J=8.6 Hz, 2H), 6.19 (s, 1H), 5.95 (s, 1H). 13C NMR
(151 MHz, CDCl3) δ 163.1, 161.3, 160.6, 152.7, 140.0, 135.3, 132.3,
130.5, 130.4, 129.7, 128.6, 128.1, 124.0, 123.2, 116.3 (t, J=21.2 Hz),
115.8, 107.6, 46.6. HRMS-ESI: Calcd. For C22H16O3: 346.1005, Found
[M+Na]+: 369.0893.
°
Characterization of the products[14–22]
4-Hydroxy-3-(phenyl(p-tolyl)methyl)-2H-chromen-2-one (3a)
White solid, 164.3 mg, 96% yield; Melting point: 146–147 C; 1H
°
NMR (400 MHz, CDCl3) δ 7.76–7.69 (m, 1H), 7.53 (ddd, J=8.7, 7.4,
1.6 Hz, 1H), 7.41–7.34 (m, 2H), 7.33–7.23 (m, 5H), 7.17 (q, J=8.2 Hz,
4H), 6.33 (dd, J=7.4, 2.8 Hz, 1H), 5.93 (s, 1H), 2.35 (s, 3H). 13C NMR
(101 MHz, CDCl3) δ 163.2, 160.7, 152.8, 140.1, 137.7, 137.0, 132.1,
130.3, 129.4, 128.8, 128.7, 127.7, 123.9, 123.2, 116.5, 116.0, 107.9,
47.0, 21.1. HRMS-ESI: Calcd. For C23H18O3: 342.1256. Found
[M+Na]+: 365.1148.
3-((4-Chlorophenyl)(phenyl)
methyl)-4-hydroxy-2H-chromen-2-one (3g)
White solid, 147.1 mg, 81% yield; Melting point: 151–152 C; 1H
NMR (400 MHz, CDCl3) δ 7.74 (d, J=7.9 Hz, 1H), 7.55 (t, J=7.8 Hz,
1H), 7.36 (dt, J=15.5, 7.4 Hz, 6H), 7.28–7.20 (m, 5H), 6.30 (s, 1H),
5.94 (s, 1H). 13C NMR (101 MHz, CDCl3) δ 163.1, 160.8, 152.7, 139.8,
138.2, 133.5, 132.3, 130.2, 129.7, 129.4, 128.6, 128.2, 124.0, 123.2,
116.5, 115.8, 107.3, 46.7. HRMS-ESI: Calcd. For C22H15ClO3: 362.0710,
Found [M+Na]+: 385.0598.
°
4-Hydroxy-3-(phenyl(o-tolyl)methyl)-2H-chromen-2-one (3b)
White solid, 133.5 mg, 78% yield; Melting point: 161–162 C; 1H
°
NMR (400 MHz, CDCl3) δ 7.72 (d, J=7.9 Hz, 1H), 7.54 (dd, J=11.4,
4.2 Hz, 1H), 7.34 (ddd, J=21.2, 15.9, 7.0 Hz, 6H), 7.20 (dd, J=17.4,
9.5 Hz, 3H), 7.02 (d, J=7.6 Hz, 1H), 6.37 (s, 1H), 6.01 (s, 1H), 2.32 (s,
3H). 13C NMR (101 MHz, CDCl3) δ 163.0, 161.0, 152.7, 139.8, 138.6,
138.1, 132.1, 131.7, 129.5, 128.8, 128.0, 127.8, 127.4, 127.0, 123.9,
123.2, 116.5, 115.8, 106.5, 45.2, 19.7. HRMS-ESI: Calcd. For C23H18O3:
342.1244. Found [M+Na]+: 365.1136.
3-((4-Bromophenyl)(phenyl)
methyl)-4-hydroxy-2H-chromen-2-one (3h)
White solid, 135.2 mg, 66% yield; Melting point: 176–177 C; 1H
NMR (400 MHz, CDCl3) δ 7.73 (d, J=7.9 Hz, 1H), 7.58–7.47 (m, 3H),
7.37 (dt, J=19.2, 7.9 Hz, 4H), 7.25 (d, J=8.7 Hz, 3H), 7.17 (d, J=
7.6 Hz, 2H), 6.19 (s, 1H), 5.93 (s, 1H). 13C NMR (101 MHz, CDCl3) δ
163.1, 160.7, 152.7, 139.7, 138.7, 132.4, 132.3, 130.5, 129.8, 128.6,
128.2, 124.0, 123.2, 121.7, 116.5, 115.8, 107.3, 46.8. HRMS-ESI: Calcd.
For C22H15BrO3: 406.0205, Found [M+Na]+: 429.0088.
°
4-Hydroxy-3-((4-methoxyphenyl)(phenyl)
methyl)-2H-chromen-2-one (3c)
1
°
Orange solid, 175.3 mg, 98% yield; Melting point: 87–88 C; H NMR
(600 MHz, CDCl3) δ 7.73 (d, J=7.9 Hz, 1H), 7.53 (t, J=7.8 Hz, 1H),
7.38 (t, J=7.4 Hz, 2H), 7.34–7.30 (m, 2H), 7.28 (d, J=8.1 Hz, 3H), 7.18
(d, J=8.5 Hz, 2H), 6.91 (d, J=8.7 Hz, 2H), 6.31 (s, 1H), 5.91 (s, 1H),
3.81 (s, 3H). 13C NMR (151 MHz, CDCl3) δ 163.3, 160.6, 159.2, 152.7,
140.2, 132.1, 131.7, 129.9, 129.4, 128.7, 127.7, 123.9, 123.2, 116.5,
116.0, 114.9, 107.9, 55.3, 46.6. HRMS-ESI: Calcd. For C23H18O4:
358.1205. Found [M+Na]+: 381.1099.
4-Hydroxy-3-(phenyl(4-(trifluoromethyl)phenyl)
methyl)-2H-chromen-2-one (3i)
White solid, 159.6 mg, 81% yield; Melting point: 158–159 C; 1H
NMR (400 MHz, CDCl3) δ 7.75 (d, J=7.9 Hz, 1H), 7.63 (d, J=7.9 Hz,
2H), 7.56 (t, J=7.8 Hz, 1H), 7.37 (ddd, J=27.9, 16.9, 8.8 Hz, 6H),
7.27–7.21 (m, 3H), 6.30 (s, 1H), 6.03 (s, 1H). 13C NMR (101 MHz,
CDCl3) δ 163.1, 161.0, 152.7, 143.8, 139.5, 132.5, 129.9, 129.3, 128.7,
128.4, 126.1 (q, J=7.41 Hz), 125.4, 124.1, 123.2, 122.7, 116.6, 115.7,
107.0, 47.2. HRMS-ESI: Calcd. For C23H15F3O3: 396.0973, Found [M+
Na]+: 419.0861.
°
3-(Bis(4-methoxyphenyl)methyl)-4-hydroxy-2H-chromen-2-one
(3d)
Reddish orange solid, 191.5 mg, 99% yield; Melting point: 148–
1
°
149 C; H NMR (400 MHz, CDCl3) δ 7.73 (d, J=7.8 Hz, 1H), 7.53 (t,
3-(Bis(4-chlorophenyl)methyl)-4-hydroxy-2H-chromen-2-one (3j)
J=7.7 Hz, 1H), 7.33–7.15 (m, 6H), 6.90 (d, J=8.5 Hz, 4H), 6.39 (s, 1H),
5.84 (s, 1H), 3.81 (s, 6H). 13C NMR (101 MHz, CDCl3) δ 163.2, 160.5,
159.1, 152.7, 132.01, 132.0, 129.8, 123.9, 123.1, 116.4, 116.0, 114.8,
113.4, 108.0, 55.3, 45.8. HRMS-ESI: Calcd. For C24H20O5: 388.1311,
Found [M+Na]+: 411.1200.
White solid, 123.5 mg, 62% yield; Melting point: 177–178 C; 1H
°
NMR (600 MHz, CDCl3) δ 7.73 (dd, J=7.9, 1.1 Hz, 1H), 7.58–7.52 (m,
1H), 7.40 (t, J=7.4 Hz, 2H), 7.34 (dt, J=16.5, 5.9 Hz, 4H), 7.26–7.19
(m, 4H), 6.21 (s, 1H), 5.94 (s, 1H). 13C NMR (151 MHz, CDCl3) δ 163.1,
160.7, 152.7, 139.80, 138.2, 133.6, 132.3, 130.2, 129.8, 129.5, 128.7,
128.2, 124.0, 123.2, 116.5, 115.8, 107.4, 46.8. HRMS-ESI: Calcd. For
C22H14Cl2O3: 396.0320, Found [M+Na]+: 419.0208.
3-Benzhydryl-4-hydroxy-2H-chromen-2-one (3e)
White solid, 157.8 mg, 96% yield; Melting point: 154–156 C; 1H
NMR (400 MHz, CDCl3) δ 7.73 (dd, J=8.0, 1.5 Hz, 1H), 7.54 (ddd, J=
8.8, 7.4, 1.6 Hz, 1H), 7.42–7.36 (m, 4H), 7.36–7.30 (m, 3H), 7.30–7.26
(m, 5H), 6.22 (s, 1H), 5.99 (s, 1H). 13C NMR (101 MHz, CDCl3) δ 163.2,
152.7, 139.9, 132.2, 129.5, 128.8, 127.9, 123.9, 123.2, 116.5, 115.9,
107.7, 107.1, 47.4. HRMS-ESI: Calcd. For C22H15FO3: 328.1099, Found
[M+Na]+: 351.0994.
°
3-([1,1’-Biphenyl]-4-yl(phenyl)
methyl)-4-hydroxy-2H-chromen-2-one (3k)
White solid, 163.2 mg, 81% yield; Melting point: 181–182 C; 1H
°
NMR (400 MHz, CDCl3) δ 7.75 (d, J=7.9 Hz, 1H), 7.66–7.51 (m, 5H),
7.47–7.25 (m, 12H), 6.35 (s, 1H), 6.02 (s, 1H). 13C NMR (101 MHz,
CDCl3) δ 163.2, 160.7, 152.7, 140.7, 140.3, 140.0, 138.8, 132.2, 129.5,
129.2, 128.83, 128.77, 128.1, 127.9, 127.5, 127.0, 124.0, 123.2, 116.5,
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115.9, 107.7, 47.0. HRMS-ESI: Calcd. For C28H20O3: 404.1412, Found
106.9, 47.0, 21.8, 21.1. HRMS-ESI: Calcd. For C24H20O3: 356.1412,
[M+Na]+: 427.1301.
Found [M+Na]+: 379.1306.
3-(1,3-Diphenylallyl)-4-hydroxy-2H-chromen-2-one (3l)
4-Hydroxy-7-methoxy-3-(phenyl(p-tolyl)
methyl)-2H-chromen-2-one (3r)
White solid, 183.6 mg, 99% yield; Melting point: 133–135 C; 1H
NMR (400 MHz, CDCl3) δ 7.51 (s, 1H), 7.40–7.26 (m, 6H), 7.18 (dt, J=
24.8, 8.3 Hz, 5H), 6.26 (s, 1H), 5.93 (s, 1H), 2.36 (d, J=9.5 Hz, 6H). 13C
NMR (101 MHz, CDCl3) δ 163.4, 160.7, 150.9, 140.1, 137.7, 137.0,
133.6, 133.1, 130.2, 129.3, 128.8, 128.6, 127.7, 122.8, 116.2, 115.6,
107.8, 47.0, 21.1, 20.9. HRMS-ESI: Calcd. For C24H20O3: 356.1412,
Found [M+Na]+: 379.1303.
1
°
White solid, 161.3 mg, 90% yield; Melting point: 85–86 C; H NMR
(600 MHz, CDCl3) δ 7.78 (d, J=7.9 Hz, 1H), 7.55 (t, J=7.2 Hz, 1H),
7.41 (dd, J=17.2, 9.0 Hz, 6H), 7.36–7.31 (m, 4H), 7.29 (d, J=8.0 Hz,
2H), 6.85 (s, 1H), 6.74 (dd, J=16.1, 6.1 Hz, 1H), 6.52 (d, J=16.0 Hz,
1H), 5.48 (d, J=5.9 Hz, 1H). 13C NMR (151 MHz, CDCl3) δ 163.1,
162.4, 160.9, 152.8, 139.4, 136.0, 134.1, 132.2, 129.5, 128.7, 128.2,
128.1, 127.9, 126.6, 124.0, 123.1, 116.5, 115.9, 106.3, 44.0. HRMS-ESI:
Calcd. For C24H18O3: 354.1256, Found [M+Na]+: 377.1146.
°
4-Hydroxy-3-(1-phenylethyl)-2H-chromen-2-one (3m)
4-Hydroxy-6-methyl-3-(phenyl(p-tolyl)
methyl)-2H-chromen-2-one (3s)
White solid, 172.7 mg, 97% yield; Melting point: 128–129 C; 1H
NMR (400 MHz, CDCl3) δ 7.61 (d, J=8.6 Hz, 1H), 7.42–7.23 (m, 5H),
7.16 (q, J=8.0 Hz, 4H), 6.81 (d, J=10.6 Hz, 2H), 6.25 (s, 1H), 5.90 (s,
1H), 3.86 (s, 3H), 2.35 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 163.7,
163.0, 161.1, 154.5, 140.3, 137.6, 137.2, 130.2, 129.3, 128.8, 128.6,
127.6, 124.2, 112.2, 109.1, 105.2, 100.2, 55.8, 46.9, 21.1. HRMS-ESI:
Calcd. For C24H20O4: 372.1362, Found [M+Na]+: 395.1252.
1
°
White solid, 91.1 mg, 68% yield; Melting point: 159–161 C; H NMR
(400 MHz, CDCl3) δ 7.66 (d, J=7.8 Hz, 1H), 7.48 (dt, J=14.9, 7.2 Hz,
4H), 7.34 (dd, J=19.9, 7.7 Hz, 2H), 7.23 (dd, J=15.0, 7.5 Hz, 1H), 6.10
(s, 1H), 4.74 (q, J=7.0 Hz, 1H), 1.67 (d, J=7.2 Hz, 3H). 13C NMR
(101 MHz, CDCl3) δ 163.5, 159.7, 152.5, 141.5, 131.9, 129.8, 127.9,
127.3, 123.9, 122.9, 116.4, 116.1, 110.1, 34.5, 16.5. HRMS-ESI: Calcd.
For C17H14O3: 266.0943, Found [M+Na]+: 289.0837.
°
4-Hydroxy-3-(4-methoxybenzyl)-2H-chromen-2-one (3n)
6-Fluoro-4-hydroxy-3-(phenyl(p-tolyl)
methyl)-2H-chromen-2-one (3t)
White solid, 113.9 mg, 63% yield; Melting point: 167–168 C; 1H
NMR (400 MHz, CDCl3) δ 7.42–7.34 (m, 3H), 7.34–7.21 (m, 5H), 7.21–
7.11 (m, 4H), 6.40 (s, 1H), 5.91 (s, 1H), 2.35 (s, 3H). 13C NMR
(101 MHz, CDCl3) δ 162.9, 159.8 (t, J=2.5 Hz), 157.5, 148.8 (d, J=
1.5 Hz), 139.8, 137.8, 136.7, 130.3, 129.4, 128.0 (d, J=10.9 Hz), 127.8,
119.6, 119.5, 118.0 (d, J=8.1 Hz), 117.0 (d, J=8.8 Hz), 109.1, 108.7
(d, J=18.2 Hz), 47.1, 21.1. HRMS-ESI: Calcd. For C23H17FO3: 360.1162,
Found [M+Na]+: 383.1053.
1
°
White solid, 94.9 mg, 67% yield; Melting point: 128–129 C; H NMR
(400 MHz, CDCl3) δ 7.76 (d, J=7.9 Hz, 1H), 7.53 (t, J=7.7 Hz, 1H),
7.30 (dd, J=19.2, 8.7 Hz, 4H), 6.87 (d, J=8.3 Hz, 2H), 6.52 (s, 1H),
3.98 (s, 2H), 3.78 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 163.9, 160.4,
158.9, 152.5, 131.9, 129.6, 129.0, 124.0, 122.8, 116.6, 115.7, 114.8,
104.5, 55.3, 29.3. HRMS-ESI: Calcd. For C17H14O4: 282.0892, Found [M
+Na]+: 305.0783.
°
3-(Cyclohex-2-en-1-yl)-4-hydroxy-2H-chromen-2-one (3o)
1
°
White solid, 54.5 mg, 45% yield; Melting point: 115–116 C; H NMR
(400 MHz, CDCl3) δ 7.78 (d, J=10.2 Hz, 2H), 7.52 (t, J=7.7 Hz, 1H),
7.30 (d, J=7.5 Hz, 1H), 6.32 (d, J=9.7 Hz, 1H), 6.06 (d, J=9.9 Hz,
1H), 3.87 (s, 1H), 2.22 (s, 2H), 2.17–2.00 (m, 1H), 1.90–1.56 (m, 3H).
13C NMR (101 MHz, CDCl3) δ 163.3, 161.0, 152.4, 135.0, 131.7, 128.8,
123.8, 122.8, 116.3, 116.0, 107.4, 77.3, 77.0, 76.7, 33.0, 28.1, 25.2,
21.0. HRMS-ESI: Calcd. For C15H14O3: 242.0943, Found [M+H]+:
243.0885.
6-Chloro-4-hydroxy-3-(phenyl(p-tolyl)
methyl)-2H-chromen-2-one (3u)
White solid, 173.5 mg, 92% yield; Melting point: 157–158 C; 1H
°
NMR (400 MHz, CDCl3) δ 7.70 (s, 1H), 7.47 (d, J=8.7 Hz, 1H), 7.36 (dt,
J=22.4, 7.2 Hz, 3H), 7.26 (s, 3H), 7.16 (dd, J=25.7, 7.8 Hz, 4H), 6.31
(s, 1H), 5.90 (s, 1H), 2.36 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 162.7,
159.5, 151.0, 139.7, 137.9, 136.6, 132.0, 130.3, 129.5, 128.7, 128.6,
127.9, 122.8, 117.9, 117.2, 108.7, 47.1, 21.1. HRMS-ESI: Calcd. For
C23H17ClO3: 376.0866, Found [M+Na]+: 399.0754.
3-Cyclohexyl-4-hydroxy-2H-chromen-2-one (3p)
1
°
White solid, 42.7 mg, 35% yield; Melting point: 108–110 C; H NMR
(400 MHz, CDCl3) δ 7.85 (d, J=7.5 Hz, 1H), 7.54 (t, J=7.3 Hz, 1H),
7.36–7.26 (m, 2H), 5.67 (s, 1H), 4.48 (s, 1H), 2.07–1.34 (m, 10H). 13C
NMR (101 MHz, CDCl3) δ 164.4, 163.4, 153.5, 132.3, 123.8, 123.2,
116.7, 116.3, 90.7, 77.4, 77.1, 76.8, 30.9, 25.3, 23.3. HRMS-ESI: Calcd.
For C15H16O3: 244.1099, Found [M+Na]+: 267.0997.
6-Bromo-4-hydroxy-3-(phenyl(p-tolyl)
methyl)-2H-chromen-2-one (3v)
White solid, 194.2 mg, 92% yield; Melting point: 148–149 C; 1H
°
NMR (400 MHz, CDCl3) δ 7.85 (s, 1H), 7.61 (d, J=8.8 Hz, 1H), 7.43–
7.30 (m, 3H), 7.26–7.25 (m, 2H), 7.20 (d, J=8.8 Hz, 3H), 7.13 (d, J=
7.6 Hz, 2H), 6.31 (s, 1H), 5.90 (s, 1H), 2.36 (s, 3H). 13C NMR (101 MHz,
CDCl3) δ 162.6, 159.4, 151.5, 139.7, 137.9, 136.6, 134.8, 130.3, 129.5,
128.7, 128.6, 127.9, 125.9, 118.2, 117.6, 116.7, 108.7, 47.1, 21.1.
HRMS-ESI: Calcd. For C23H17BrO3: 420.0361, Found [M+H]+:
421.0433.
4-Hydroxy-7-methyl-3-(phenyl(p-tolyl)
methyl)-2H-chromen-2-one (3q)
White solid, 171.1 mg, 96% yield; Melting point: 139–140 C; 1H
NMR (400 MHz, CDCl3) δ 7.59 (d, J=8.1 Hz, 1H), 7.44–7.22 (m, 5H),
7.19–7.03 (m, 6H), 6.30 (s, 1H), 5.92 (s, 1H), 2.43 (s, 3H), 2.34 (s, 3H).
13C NMR (101 MHz, CDCl3) δ 163.5, 161.0, 152.9, 143.3, 140.2, 137.6,
137.2, 130.2, 129.3, 128.8, 128.7, 127.6, 125.2, 122.9, 116.6, 113.5,
°
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°
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NMR (400 MHz, (CD3)2SO) δ 11.47 (s, 1H), 8.00 (d, J=7.6 Hz, 1H),
7.60 (t, J=7.7 Hz, 1H), 7.48–7.28 (m, 2H), 7.20–6.65 (m, 4H), 4.49 (dd,
J=10.5, 5.8 Hz, 1H), 2.82 (ddd, J=32.0, 22.0, 9.8 Hz, 2H), 2.26–1.56
(m, 4H). 13C NMR (101 MHz, DMSO) δ 160.7, 152.2, 138.7, 136.8,
131.7, 128.7, 126.4, 125.7, 125.1, 123.8, 123.4, 116.3, 116.1, 109.0,
35.3, 29.5, 27.1, 23.1. HRMS-ESI: Calcd. For C19H16O3: 292.1099,
Found [M+Na]+: 315.0991.
Deposition Number 2092740 (for 3e) contains the supplementary
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We are grateful to the National Natural Science Foundation of
China (No. 21972079 and 21702127), Natural Science Foundation
of Shandong Province (No. ZR2019MB002), Incubation Program of
Youth Innovation in Shandong Province and Fluorosilicone
Materials Joint Funds of Shandong Provincial Natural Science
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Conflict of Interest
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The authors declare no conflict of interest.
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Manuscript received: May 7, 2021
Revised manuscript received: July 2, 2021
Accepted manuscript online: July 8, 2021
Eur. J. Org. Chem. 2021, 3819–3826
www.eurjoc.org
3826
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