Na 2 CO 3-Catalyzed O-Acylation of Phenols for the Synthesis of Aryl Carboxylates with Use of Alkenyl Carboxylates

Article abstract of DOI:10.1055/s-0037-1610265

Inorganic base-catalyzed O-acylation of phenol and its derivatives has been developed. The procedure provides an efficient catalysis system for the preparation of aryl carboxylates with alkenyl carboxylates as acyl reagents. The reaction proceeded smoothly by using ?-Na ₂ CO ₃ as the catalyst in MeCN to produce the corresponding aryl carboxylates in good to excellent yields.

Full text of DOI:10.1055/s-0037-1610265

SYNLETT
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3
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0
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©
Georg Thieme Verlag Stuttgart · New York
2018, 29, A–E
letter
A
en
Synlett
X.-Y. Zhou, X. Chen
Letter
Na CO -Catalyzed O-Acylation of Phenols for the Synthesis of Aryl
2
3
Carboxylates with Use of Alkenyl Carboxylates
R' = Alkyl
Xiao-Yu Zhou*
×
√
O
O
Xia Chen*
+
Ar OH
Inorganic Base
R' = Alkenyl
R'
Ar
R
O
R
O
School of Chemistry and Materials Engineering, Liupanshui
Normal University, Liupanshui, 553004, P. R. of China
zhouxiaoyu20062006@126.com
R = alkyl and alkenyl
R' = vinyl or prop-1-en-2-yl
yield: 27 to >99%
Received: 14.07.2018
Accepted after revision: 09.08.2018
Published online: 31.08.2018
iron-catalyzed transesterification for the acylation of pri-
6
mary and secondary alcohols and thiols. In 2002, Nolan’s
7
DOI: 10.1055/s-0037-1610265; Art ID: st-2018-w0443-l
group reported an NHC-catalyzed transesterification/acy-
lation reaction of alcohols. In this work, the NHC showed
excellent catalytic activity in the transesterification reac-
tion of vinyl acetate with alcohols. However, the acylation
of phenols was difficult for the synthesis of aryl carboxyl-
ates because of the low reactivity.
Abstract Inorganic base-catalyzed O-acylation of phenol and its deriv-
atives has been developed. The procedure provides an efficient catalysis
system for the preparation of aryl carboxylates with alkenyl carboxyl-
ates as acyl reagents. The reaction proceeded smoothly by using
Na CO as the catalyst in MeCN to produce the corresponding aryl car-
2
3
boxylates in good to excellent yields.
Synthesis of aryl carboxylates from phenols
Key words acylation, phenols, aryl carboxlates, alkenyl carboxylates,
O
O
catalysis
R
O
O
R
O
O
Acylation has been employed as one of the most ubiqui-
tous and significant technologies in organic synthesis,
which further have a great value for the preparation of nat-
ural products, pharmaceuticals, and other fine chemicals.
Equally important, it plays an important role in protecting
group chemistry, especially in terms of amino and hydroxyl
acylation
O
R
S
S
R
Ar OH
Ar
base or Lewis acid
catalytic system
R
O
R
X
X = Cl or Br
Synthesis of aryl carboxylates from acids
O
1
group protection. Therefore, the development of conve-
R
Y
nient and efficient methods for the selective acylation of
amines and alcohols has attracted considerable attention.
In the last decades, many efforts have been made in the
preparation of aryl carboxylates. The normal and direct
methods to obtain aryl carboxylates are acylations of phe-
nols using acyl halides, anhydrides, and carboxylic acids as
acyl reagents (Scheme 1). However, these methods have
many limitations, such as poor functional group compati-
bility, low regioselectivity, and harsh reaction conditions. In
O
O
Ar2IX, base
Ar
R
OH
R
O
X = OTs, OTf or BF4
Y = B(OH)2 or Si(OMe)3
ArM, [O], [Cu] cat.
Scheme 1 The synthesis of carboxylates
The development of acylation agents is of high interest
in the research on acylation reactions. Early studies on the
acylation reaction using vinyl and isopropenyl acetates as
2
addition, transition-metal-catalyzed C–O bond formation,
3
4
carbonylation, C–H bond activation, and esterification of
5
8a
arene carboxylic acids are relatively new methods for the
acyl agents were provided by Bram and his co-workers.
synthesis of esters. In contrast to those methods, the trans-
esterification is also a traditional method, in which an iron
catalyst and N-heterocyclic carbene (NHC) present the most
popular catalysis systems, such as neutral and nucleophilic
And Ishii’s group demonstrated that Cp* Sm(THF) -cata-
2
2
lyzed acylation of alcohols and amines could be achieved
under ambient conditions.8b Subsequently, isopropenyl ace-
tate was utilized as an efficient acyl agent in the acylation
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

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X.-Y. Zhou, X. Chen
Letter
of tertiary alcohols mediated by an oxime ester and
Na CO showed a higher catalytic activity than all the oth-
2
3
8c
Cp* Sm(THF) . In 2013, Toy and his colleagues developed a
ers. In order to improve the yields further, the amount of
Na CO was optimized (entries 5–9), and 20 mol% Na CO
2
2
reusable rasta resin-TBD catalyst for the transesterification
with alkenyl carboxylates as agents.8 In 2010, Grimme et al
developed an NHC-catalyzed approach for the chemoselec-
tive acylation of alcohols for the synthesis of esters involv-
2
3
2
3
d
was found optimal, leading to 99% yield (entry 7). The O-ac-
ylation of 2-naphthol can be performed under the base-cat-
alyzed reaction conditions; no target product was detected
without use of base (entry 9). In order to test whether the
use of 4.0 equivalents of 2a was necessary, 3.0 equivalents
of 2a were added and the yield decreased to 87% (entry 10).
This indicated that use of 4.0 equivalents of vinyl ester was
the better dosage. Subsequently, other solvents and the
temperature were evaluated. Toluene (entry 11), 1,4-diox-
ane (entry 12), ethanol (EtOH, entry 13), and tetrahydrofu-
ran (THF, entry 14) were chosen as solvents in the Na CO -
9
ing oxidations of aldehydes in the presence of amines. Be-
sides, diaryliodonium salts can be used for the synthesis of
carboxylates. In 2011, an efficient arylation of carboxylic
acids with diaryliodonium salts was provided by Olofsson’s
group and aryl carboxylates were obtained in high yields.10
In 2016, Tan and his co-workers reported a general and ex-
cellent acylation reagent, diacyl disulfide, for the synthesis
of esters catalyzed by DMAP [4-(N,N-dimethylamino)pyri-
dine]. This protocol offered a promising synthetic platform
on site-selective acylation of phenolic and primary aliphat-
ic hydroxyl groups, which greatly expanded the realm of
2
3
(20 mol%) catalyzed acylation of 1a at 120 °C, and the yields
decreased obviously (19, 45, 13, and 40%, respectively). The
poor reactivities were considered to be due to the low solu-
bility of Na CO in other solvents. At last, the results show
11
protecting group chemistry. Quite recently, Bode and his
2
3
12
co-workers reported the chemoselective acylation of pri-
mary amines and amides using potassium acyltrifluorobo-
rates as acyl agents under acidic conditions and medium to
high yields were obtained.
that the temperature has a significant effect on the O-acyla-
tion (entries 15 and 16) and 120 °C proved to be the best
choice. Therefore, the subsequent reactions of esters 2a–h
In our current work, we developed an efficient O-acyla-
tion of phenols using sodium carbonate (Na CO ) and alke-
Table 1 Conditions Optimization for Base-Catalyzed Synthesis of Aryl
Carboxylates
a
2
3
nyl carboxylates as catalyst and acyl source, respectively
OH
O
O
(Scheme 2). The results are presented herein.
cat. (y mol%)
+
O
solvent, 120 °C
O
Transesterification of hydroxyl compounds
1
a
2a
3aa
R2
O
O
OH
√
R2
Ar
R
R
O
Entry
2a (x equiv) Cat. (y mol%)
Solvent
Yield
(%)
O
b
transesterification
R1
base, acid, iron or
NHC catalysis system
R
O
1
2
3
4
5
6
7
8
9
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
3.0
4.0
4.0
4.0
4.0
4.0
4.0
HCO
2
Na∙2H
2
O (200)
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
toluene
1,4-dioxane
EtOH
76
75
64
74
78
88
99
82
n.a.
87
19
45
13
40
95
72
R1 = alkyl
×
Ar OH
HCO Na∙2H O (100)
2
2
O
O
NEt
3
(200)
This work
K
2
CO
3
(100)
OH
R'
O
2
Na CO3 (20 mol%)
Na
2
CO
3
3
(100)
(50)
R
+
R
MeCN, 120 °C
O
O
R'
Na
2
CO
Scheme 2 Na CO -catalyzed O-acylation of phenols
2
3
Na CO (20)
2
3
Na
–
2
CO
3
(10)
The initial experiment began with 2-naphthol (1a) and
vinyl acetate (2a) as the model starting materials and sodi-
um formate (HCO Na∙2H O) as the base in acetonitrile
1
0
1
Na
Na
Na
2
2
2
CO
CO
CO
3
3
3
(20)
(20)
(20)
2
2
1
(
(
MeCN) at 120 °C. The product naphthalen-2-yl acetate
3aa) was isolated in 76 and 75% yield (200 and 100 mol%
12
13
HCO Na∙2H O, Table 1, entries 1 and 2). This result encour-
2
2
Na CO (20)
2
2
2
2
3
3
3
3
aged us to adhere to our initial hypothesis that vinyl esters
could be utilized as acylation agents for the acylation of 2-
naphthol under basic conditions. Then, the catalyst, the
amount of acylation agent, solvent, and temperature were
evaluated to improve the yield of the product 3aa. The re-
14
Na
Na
Na
CO
CO
CO
(20)
(20)
(20)
THF
1
5c
6d
MeCN
MeCN
1
a
Reaction conditions: 1a (72 mg, 0.50 mmol), 2a (x equiv), cat. (y mol%),
solvent (3.0 mL), 120 °C, 24 h.
Isolated yields.
Carried out at 100 °C.
Carried out at 80 °C.
sults are shown in Table 1. Triethylamine (NEt , entry 3),
b
c
3
potassium carbonate (K CO , entry 4), and sodium carbon-
2
3
d
ate (Na CO , entry 5) were tested as the bases. Among them,
2
3
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X.-Y. Zhou, X. Chen
Letter
and phenols 1a–n were performed in the presence of Na2-
Subsequently, the O-acylations of phenols 1b–n with vi-
nyl acetate (2a) were conducted under the optimal reaction
conditions, as shown in Table 3, and the phenols 1b–k were
compatible with these reaction conditions for the prepara-
tion of aryl acetates (47–>99%, entries 1–10). In especial,
the optimal conditions can be applied to the O-acylation of
naphthalene-1,5-diol (1c, entry 2), pyrocatechol (1f, entry
5), hydroquinone (1i, entry 8), but with relatively lower
yields (47, 77, and 79%, respectively). In order to test
whether the O-acylation can be suitable for alcohols, 4-(hy-
droxymethyl)phenol (1l) and naphthalen-2-yl methanol
(1m) with alcohol hydroxyl groups were subjected to the
reaction conditions, and the products 3la and 3ma were
obtained in 27 and 63% yield, respectively (entries 11 and
CO (20 mol%) and vinyl ester (4.0 equiv) as the catalyst and
3
acylation agent, respectively, in MeCN at 120 °C.
The reactions of 2-naphthol (1a) and the esters 2a–h
(Table 2, entries 1–8) were conducted to screen the scope of
carboxylates 2 under the optimal conditions. The results
show that the alkenyl carboxylates 2a–g can react smooth-
ly, and moderate to high isolated yields (79–>99% yield, en-
tries 1–7) of products 3 were obtained. When ethyl acetate
was used as the acylation agent, there was no product de-
tected and the starting materials were recovered (entry 8).
The alkyl carboxylate was not applicable to the O-acylation
of phenols, which was considered to be due to the stability
of alkyl carboxylates.
1
2). The results indicate that the optimal conditions were
Table 2 Scope of Substrate 2a
not suitable enough for the O-acylation of alcohols.
OH
Na2CO3 (20 mol%)
R'
MeCN, 120 °C
O
R'
O
Table 3 Scope of Substrate 1a
+
O
O
OH
O
O
2 3
Na CO (20 mol%)
1a
2
3aa– ag
+
R
R
O
O
MeCN, 120 °C
Entry
1
2
3aa–ag
Yield
b
1
2a
3ba–ma
(
%)
O
Entry
1
3ba–ma
Yield (%)b
O
O
99
>99
82
O
O
O
O
O
2
2
2
a
b
c
OH
3
aa
1
90
2
3
3aa
1
b
3
ba
O
O
O
O
O
O
O
O
O
HO
O
3
3
3
3
3
ac
ad
ae
af
2c
47
OH
O
O
O
O
1
1
1
c
4
>99
>99
86
3
ca
2
d
OH
O
O
O
O
nPr
3
4
>99
>99
O
O
5
nPr
2
O
O
O
d
3da
e
OH
O
O
O
tBu
O
6
tBu
2
O
f
e
3ea
O
4
OH
7c
79
O
O
O
OH
OH
5c
O
77
76
2
2
g
h
ag
O
O
1
f
3
fa
8
3aa
n.a.
O
O
a
Reaction conditions: 1a (72 mg, 0.50 mmol), 2 (2.0 mmol, 4.0 equiv),
CO (10.6 mg, 0.10 mmol, 20 mol%), MeCN (3.0 mL), 120 °C, 24 h.
Isolated yields.
O
6
Na
2
3
b
c
1g
1
.1 equiv 2a was added.
3ga
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X.-Y. Zhou, X. Chen
Letter
Table 3 (continued)
was added to the reaction and 12.7 g of 3aa was obtained
with 97.7% yield (Scheme 4). The result indicates that the
Na CO -catalyzed O-acylation of phenols for the synthesis
of aryl carboxylates may be appropriate for scale-up and in-
dustrial production.
Yield (%)b
Entry
1
3ba–ma
2
3
OH
O
7
98
O
1
h
3ha
Na2CO3
(1.5 g, 20 mol%)
OH
O
OH
O
O
O
+
8c
79
98
81
27
O
O
MeCN (50 mL)
O
HO
O
120 °C
1
i
3ia
1a
10.0 g)
2a
3aa
(12.6 g, 97.7% yield)
(
(23.9 g, 4.0 equiv)
OH
OH
O
O
Scheme 4 The scale-up conditions for the synthesis of 3aa
O
O
9
O
O
3ja
1
j
In conclusion, by using alkenyl carboxylates as acylation
agents, the Na CO -catalyzed O-acylation of phenols was
2
3
successfully achieved for the selective synthesis of aryl car-
boxylates with up to >99% yield.13 The principle of these re-
actions provides a new strategy to develop other types of
acylation reactions under convenient reaction conditions.
To the best of our knowledge, this catalytic O-acylation of
phenols for the synthesis of aryl carboxylates by using alke-
nyl carboxylates as acyl sources is the first example report-
ed on such reactions.
10
O2N
O2N
1
k
3ka
O
O
OH
1c
O
O
1
HO
1
l
O
3
3
la
OH
O
12
63
Funding Information
1
m
ma
The work was supported by the Youth Science and Technology Talent
Development Project in the Education Department of Guizhou Prov-
ince (Grant No. qianjiaohe KY zi [2016] number 263) and Innovation
Team of Liupanshui Normal University (Grant No. LPSSYKJTD201601).)(
a
Reaction conditions: 1 (0.50 mmol), 2a (172 mg, 2.0 mmol, 4.0 equiv),
CO (10.6 mg, 0.10 mmol, 20 mol%), MeCN (3.0 mL), 120 °C, 24 h.
Isolated yields.
Na
2
3
b
c
8
.0 equiv 2a was added.
Supporting Information
Based on the above results, O-acylation of phenols can
Supporting information for this article is available online at
https://doi.org/10.1055/s-0037-1610265.
be achieved by using alkenyl carboxylates as acyl agents but
not alkyl carboxylates. The reason presumably is that the
formation of by-product acetaldehyde 5 by isomerization of
S
u
p
p
ortioIgnfrm oaitn
S
u
p
p
o
nrtogI
i
f
rm oaitn
4
is the driving force for the process with alkenyl carboxyl-
References and Notes
ates, as shown in Scheme 3. However, EtOH was produced
as a by-product in the case of alkyl carboxylates and the re-
versed reaction inhibited the formation of aryl carboxyl-
ates.
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O
O
R'
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(
(
(
O
OH
H
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3
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©
Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

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Synlett
X.-Y. Zhou, X. Chen
Letter
(
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(
(
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(
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1
190.
MHz, CDCl ): δ = 7.81–7.72 (m, 3 H), 7.50 (d, J = 2.2 Hz, 1 H),
3
(
(
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C
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3
127.8, 127.6, 126.6, 125.7, 121.1, 118.5, 21.2 ppm. HRMS: m/z
+
(
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2
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©
Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E