Synergistic Ag(I)/nBu4NBr-catalyzed fixation of CO2 to β-oxopropyl carbonates via propargylic alcohols and monohydric alcohols

Article abstract of DOI:10.1016/j.tet.2019.03.006

Chemical fixation of carbon dioxide under mild reaction conditions e.g. atmospheric pressure and low temperature depends upon the ability of catalyst. Herein, a synergistic catalytic scheme of silver sulfadiazine/ⁿBu₄NBr was described for the three-component reaction of propargylic alcohols, CO₂, and monohydric alcohols. This catalytic system was demonstrated effectively to provide β-oxopropyl carbonates in excellent yields (up to 99% yield with 5 mol% catalyst). The method tolerated a wide scope of propargylic alcohols and monohydric alcohols under atmospheric CO₂ pressure and solvent-free conditions. The excellent catalytic performance was attributed to the synergistic catalysis confirmed by the careful experiments.

Full text of DOI:10.1016/j.tet.2019.03.006

Tetrahedron 75 (2019) 2343e2349
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
n
Synergistic Ag(I)/ Bu NBr-catalyzed fixation of CO to
b-oxopropyl
4
2
carbonates via propargylic alcohols and monohydric alcohols
a
b
,
*
c
b
b
Jingyuan Li , Qingwen Song , Hengxuan Zhang , Ping Liu , Kan Zhang ,
c
a, **
Junwen Wang , Dengsong Zhang
Department of Chemistry, College of Sciences, Shanghai University, Shanghai, 200444, PR China
State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, 030001, PR China
College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan, 030024, PR China
a
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 February 2019
Received in revised form
Chemical fixation of carbon dioxide under mild reaction conditions e.g. atmospheric pressure and low
temperature depends upon the ability of catalyst. Herein, a synergistic catalytic scheme of silver sulfa-
n
diazine/ Bu
4
NBr was described for the three-component reaction of propargylic alcohols, CO
-oxopropyl car-
bonates in excellent yields (up to 99% yield with 5 mol% catalyst). The method tolerated a wide scope of
propargylic alcohols and monohydric alcohols under atmospheric CO pressure and solvent-free con-
2
, and
4
March 2019
monohydric alcohols. This catalytic system was demonstrated effectively to provide
b
Accepted 5 March 2019
Available online 6 March 2019
2
ditions. The excellent catalytic performance was attributed to the synergistic catalysis confirmed by the
careful experiments.
Keywords:
Carbon dioxide utilization
©
2019 Elsevier Ltd. All rights reserved.
b
-Oxoalkyl carbonates
Cascade reaction
Synergistic catalysis
Synthetic methods
1
. Introduction
studied the three-component cascade reaction of propargylic al-
cohols, primary alcohols and CO in detail [15]. Using bicyclic
guanidines as catalysts, -oxoalkyl carbonates were obtained in up
to 87% yield under the supercritical CO conditions. In 2016, an
effective silver (Ag CO /PPh , 10 mol%) catalytic strategy for three-
component reaction of propargylic alcohols, CO , and monohydric
alcohols was developed by the He group. [16], and -oxoalkyl car-
2
Organic carbonates have wide applications in organic synthesis,
b
pharmaceutical chemistry and agriculture etc. [1,2]. Among them,
2
b
-oxoalkyl carbonates, a kind of asymmetrical carbonates, are used
2
3
3
as important intermediates and reagents especially in organic
synthesis [3,4]. Traditionally, they generally prepared through the
reactions of chloroformates with crotonaldehyde congeners [5] or
the oxygenation of allyl carbonates [6]. Over the last few decades,
increasing attention was paid to chemical fixation of CO
value chemicals due to its renewable, abundant and nontoxic ad-
vantages [7e12]. Therefore, CO utilization as C feedstock is
promising in place of traditional carboxylation reagent for
2
b
bonates was gained in excellent yield (up to 98%) and selectivity.
Subsequently, a AgCl/ionic liquid (i.e.1-butyl-3-methylimidazolium
acetate ([Bmim]OAc)) (1.0 equiv. ionic liquid) catalytic system was
demonstrated to be effective for the three-component reaction
2
into high-
ꢀ
2
1
under ambient conditions (30 C and 0.1 MPa) [17]. Recently, we
b
-
explored the early transition metal zinc(II) (ZnCl
[5.4.0]undec-7-ene (DBU)) system (50 mol% DBU), and high yields
(99%) of -oxopropyl carbonates could be obtained under 1 MPa
CO [18]. Though various methods were established, totally, some
2
/1,8-diazabicyclo
oxoalkyl carbonates synthesis from the viewpoint of green chem-
istry and sustainable development.
b
In the early years, the reaction of
-ACCs) and alcohols affording -oxopropyl carbonates was re-
ported by Dixneuf et al. [13,14]. Subsequently, the Costa group
a
-alkylidene cyclic carbonates
2
(a
b
drawbacks such as high pressure, insufficient catalytic ability, and
large amount of organic solvent etc. remained suffering. Therefore,
the design of robust catalysts could be of great significance and
urgently required. Moreover, to improve the catalytic efficiency
*
Corresponding author.
under milder conditions (e.g. atmospheric pressure of CO
also greatly accelerate the course of CO utilization.
According to the previous reports [15e18], two steps, namely
2
) could
** Corresponding author.
2
E-mail addresses: songqingwen@sxicc.ac.cn (Q. Song), dszhang@shu.edu.cn
(
D. Zhang).
https://doi.org/10.1016/j.tet.2019.03.006
040-4020/© 2019 Elsevier Ltd. All rights reserved.
0

2344
J. Li et al. / Tetrahedron 75 (2019) 2343e2349
n
the carboxylative cyclization of propargylic alcohols with CO
2
and
were examined respectively in combination with Bu
4
NBr (entries
transesterification of intermediate -ACCs with monohydric alco-
a
2e8). However, low catalytic activity was showed and low product
yields were acquired. Gratifyingly, silver sulfadiazine/ Bu NBr gave
4
n
hols, are comprised in the three-component reaction (Scheme 1a).
In addition, the activation of C^C bond and hydroxyl group was
considered as key procedures for high transformations [17,19e23].
Based on the theory, we speculated that the designed species
bearing with good ability for activating C^C bond in propargylic
alcohols and hydroxyl groups in propargylic alcohols/monohydric
alcohols could potentially possess the high catalytic activity even
under atmospheric pressure of CO .
2
Recently, sulfadiazine received considerable attention in the
preparation of metalloantibiotic due to its flexible coordination
a better result with 16% yield of 3a than that of other catalytic
systems (entry 9). Furthermore, the catalytic performance of
analogous species such as silver p-toluenesulfonate was also
examined and compared, but unsatisfactory result was given (entry
10).
Subsequently, to improve the efficiency, various quaternary
ammonium salts were also evaluated in the presence of silver
sulfadiazine. The quaternary ammonium salts with different cation
were effective to enhance the catalytic activity (entries 9 and
ability with metal species [24e26]. The eSO
2
NHe moiety could
11e13),
and
the
activity followed
the
order:
n
n
n
make the sulfadiazine molecule become a potential anionic donor.
Accordingly, hydrogen-bonding interaction between hydroxyl
group and sulfadiazine anion (proton acceptor) was envisioned
able to facilitate the activation of hydroxyl group (Scheme 1b)
Bu
4
NBr > Pr
4
NBr > (C
7
H
15
)
4
NBr > Et NBr. Presumably, with the
4
increase of carbon number of quaternary ammonium cation, the
weaker ion pair interaction was beneficial to enhance the nucleo-
philicity of carbonate intermediate and facilitate the coupling re-
[
23,27e29], which was confirmed in the recently reported trans-
2
action of propargylic alcohols and CO [34e36]. Nevertheless,
formation of vicinal diols [30]. In addition, silver species was one of
the most effective metal compounds for C^C bond activation in
alkyne or its derivatives involved reactions [31e33]. Based on those
considerations, we proposed that the combination of sulfadiazine
and silver i.e. silver sulfadiazine could also establish a bifunctional
catalyst which could be able to well catalyze the cascade reaction of
bulkier alkyl of n-heptyl displayed lower activity in the reaction due
to the steric effect. Furthermore, silver sulfadiazine/ Bu NCl used as
4
n
catalysts was also examined, but a reduced yield was acquired
(entry 14). This is probably attributed to the weaker dissociation
ꢁ
ꢁ
capacity of Cl than that of Br [37]. Meanwhile, no obvious dif-
n
4
ference was showed between silver sulfadiazine/ Bu NI and silver
sulfadiazine/ Bu
stronger dissociation capacity of I did not further boost the reac-
tion. Considering that the quaternary phosphonium salt cation has
n
propargylic alcohols, CO
2
, and monohydric alcohols under the mild
4
NBr (entry 15 vs. 9), which indicated that the
ꢁ
conditions (Scheme 1b). As a result, synergistic catalytic system of
n
silver sulfadiazine/ Bu
bonates synthesis in excellent yields under atmospheric pressure of
CO and neat conditions.
4
NBr was developed for b-oxopropyl car-
a great influence on the carboxylative cyclization of propargylic
n
2
alcohols with CO
2
[23], the activity of Bu
4
PBr was also examined,
but no good result was gained (entry 16). Moreover, the 3a yield
was remarkably improved to 61% without using any solvent in the
2
. Results and discussion
n
presence of silver sulfadiazine/ Bu
4
NBr (entry 17).
4
NBr catalytic system was
n
Then, silver sulfadiazine/ Bu
2.1. Optimization of the reaction conditions
employed to study the effect of temperature, and the results are
shown in Fig. 1. Notably, this catalytic system was active at room
temperature despite low yield, which implied the potential good
catalytic activity of the catalysts. Besides, the highest yield of
Initially, the reaction conditions were optimized by exploring
the model reaction of benzyl alcohol (1a), 2-methylbut-3-yn-2-ol
2a) and CO under 0.1 MPa (Table 1). Without any catalyst,
(
2
ꢀ
product was obtained at 80 C.
benzyl (2-methyl-3-oxobutan-2-yl) carbonate (3a) was not ob-
In addition, prolong the reaction time to 18 h or 24 h, the yield
was not significantly improved (entries 18 and 19 vs. 17). It sug-
gested that the reaction time was not a key factor to limit product
formation under the given conditions. By modulating the molar
ratio of 1a and 2a ranging from 1:1 to 1:1.5, almost quantitative 3a
tained (entry 1). Then, several basic silver salts or its oxide
including AgVO , Ag PO , Ag CO , Ag O, Ag SO , AgOAc and AgOBz
3 3 4 2 3 2 2 4
yields was obtained for 18 h (entries 17 and 20e22). Notably, the
n
individual catalyst silver sulfadiazine or Bu
4
NBr showed no ac-
tivity (entries 23 and 24).
Finally, the effect of catalyst loading on the reaction was also
investigated (Table S1, Supporting information), and the results
n
showed that 5 mol% silver sulfadiazine and 5 mol% Bu
4
NBr was
ꢀ
adaptive for the effective conversion under 0.1 MPa CO
2
at 80 C for
1
[
8 h. In contrast to the previously reported catalytic systems
15e18], this work bore more advantages such as lower catalyst
loadings, atmospheric pressure of CO and solvent-free condition.
2
2.2. Scope of substrates
With the optimized conditions (Table 1, entry 22) in hand, the
scope of monohydric alcohols was initially investigated (Table 2).
Benzyl alcohols bearing electron-donation group at the para-
position on the aryl ring could be effectively converted into the
corresponding
b-oxopropyl carbonates 3aed in good yields (entries
1e4). While (3-methoxyphenyl)methanol provided the target
product 3e in a slightly lower yield (entry 5), which might result
from low reactivity of substrate brought by meta-substituted
electron-donation group. The benzyl alcohols with electron-
2
Scheme 1. Synthesis of b-oxoalkyl carbonates through CO fixation.

J. Li et al. / Tetrahedron 75 (2019) 2343e2349
2345
Table 1
Optimization of the reaction conditions .
a
Entry
Catalyst
Co-catalyst
Conv.(%) of 1ab
a
-ACC Yield (%)b
3a Yield (%)b
1
2
3
4
5
6
7
8
9
e
e
0
4
5
5
5
6
7
9
19
3
4
14
10
3
13
7
63
70
71
69
89
99
0
0
3
2
2
<1
1
19
23
56
2
0
2
2
4
3
2
5
6
16
2
2
13
7
2
n
AgVO
3
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
4
4
4
4
4
4
4
4
4
NBr
NBr
NBr
NBr
NBr
NBr
NBr
NBr
NBr
NBr
NBr
15 4
H ) NBr
NCl
NI
PBr
NBr
NBr
NBr
NBr
NBr
NBr
n
n
n
n
n
n
n
n
Ag
Ag
Ag
Ag
AgOAc
AgOBz
3
2
2
2
PO
4
CO
O
3
SO
4
Silver sulfadiazine
Silver p-toluenesulfonate
Silver sulfadiazine
Silver sulfadiazine
Silver sulfadiazine
Silver sulfadiazine
Silver sulfadiazine
Silver sulfadiazine
Silver sulfadiazine
Silver sulfadiazine
Silver sulfadiazine
Silver sulfadiazine
Silver sulfadiazine
Silver sulfadiazine
Silver sulfadiazine
e
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Et
4
3
n
Pr
(C
4
52
62
25
58
32
18
14
16
22
32
25
0
n
n
n
n
n
n
n
n
n
n
7
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
4
4
4
4
4
4
4
4
4
13
4
c
61
66
68
66
89
98
0
c,d
c,e
c,f
c,g
c,d,g
c,d,g
c,d,g
e
n
Bu
4
NBr
0
0
0
a
ꢀ
3 2
Reaction conditions: 1a (108.1 mg, 1.0 mmol), 2a (84.1 mg, 1.0 mmol), catalyst (0.05 mmol, 5.0 mol%), co-catalyst (0.05 mmol, 5.0 mol%), CH CN (2 mL), CO balloon, 80 C,
1
0 h.
b
Determined by Gas chromatography (GC) using biphenyl as the internal standard.
Neat.
c
d
e
f
1
2
1
1
8 h.
4 h.
a (108.1 mg, 1.0 mmol), 2a (109.3 mg, 1.3 mmol).
a (108.1 mg, 1.0 mmol), 2a (126.2 mg, 1.5 mmol).
g
conditions (entry 12) probably due to its weak nucleophilicity.
As well, a variety of propargylic alcohols were also verified
suitable to the catalytic protocols. Both alkyl-substituted and vinyl-
substituted propargylic alcohols afforded
b-oxopropyl carbonates
(3meo) in moderate to excellent yields (entries 13e15). Generally,
a lower reactivity of 1-octyn-3-ol (2p) was displayed than that of
tertiary alcohols ascribing to the absence of gem-dialkyl effect
(entry 16) [29,38,39]. Cyclohexyl-substituted propargylic alcohol
also exhibited high reactivity in 97% 3q yield (entry 17). Conspic-
n
4
uously, high efficiency of silver sulfadiazine/ Bu NBr system was
showed for a wide range of alcohol substrates under atmospheric
pressure and solvent-free conditions with low catalyst loadings.
2.3. Mechanism study
Fig. 1. Temperature effect. Reaction conditions: 1a (108.1 mg, 1.0 mmol), 2a (84.1 mg,
.0 mmol), silver sulfadiazine (17.9 mg, 5.0 mol%), nBu
NBr (16.1 mg, 5.0 mol%), CO
balloon, 10 h. The data were determined by GC using biphenyl as the internal standard.
1
4
2
See Scheme 1a, the three-component cascade reaction includes
two reaction steps namely the carboxylative cyclization of prop-
argylic alcohols with CO and transesterification of intermediate
2
a-
ACCs with monohydric alcohols [16e18]. Here, the reaction
mechanism was also confirmed through the “one-pot” process as
seen from the time profiles in Fig. 2. In the beginning, the two steps
reacted quickly. After several hours, the rate of transesterification
slowed down, e.g. the 2a conversion reached 94% within 6 h while
the 1a conversion and 3a yield were 82% and 80%, respectively.
withdrawing groups at the para- and ortho-positions (3f and 3g)
also showed good compatibility (entries 6 and 7). Additionally, with
the increase of alkyl chain length, primary alcohols proceeded
smoothly and gave the desired products 3hej in excellent yields
(
entries 8e10) [17]. Meanwhile, cyclohexanol resulted in a
decreased yield of 3k (entry 11), which may be attributed to the
steric effect in the alcoholysis of -ACC intermediate. Notably,
phenol (1l) was demonstrated ineffective under the same reaction
Later, full conversion of 2a into intermediate
monitored, and the accumulated -ACC was mostly consumed after
8 h. These results revealed that the transesterification of the
a-ACC for 9 h was
a
a
1

2346
J. Li et al. / Tetrahedron 75 (2019) 2343e2349
Table 2
Scope of the propargylic alcohols and primary alcohols .
a
Entry
1
Product
Yield (%)b
95 (98)c
Entry
10
Product
Yield (%)b
99
c
2
3
89
91
11
12
45 (67)d
0
4
5
6
7
92
64
80
88
13
14
15
16
98
96
81
48 (85)d
8
9
93
85
17
97
a
b
c
Reaction conditions: 1 (1.0 mmol), 2 (1.5 mmol), silver sulfadiazine (17.9 mg, 5.0 mol%), nBu
Isolated yield.
GC yield.
ꢀ
2
NBr (16.1 mg, 5.0 mol%), CO balloon, 80 C, 18 h.
4
d
2
CO 1.0 MPa.
intermediate
a-ACCs with monohydric alcohols was the rate-
determining step in the whole process. Also, the accumulated a-
ACC in Table 1 supported the conclusion.
To further explore the reaction mechanism of the silver sulfa-
n
diazine/ Bu
4
NBr catalytic system, stepwise experiments were also
performed. As seen from the results (Table 3, entries 2 and 3), silver
n
sulfadiazine and Bu
first step. However, employing silver sulfadiazine/ Bu
alysts, the quantitative yield of intermediate -ACC was obtained
Table 3, entry 4). The results suggested that silver sulfadiazine and
4
NBr alone showed no catalytic activity for the
n
4
NBr as cat-
a
(
n
Bu
4
NBr synergistically catalyzed the carboxylative cyclization of
. In the second step, the reaction did not
NBr (Table 4, entry 3). On the contrary, silver sul-
propargylic alcohol and CO
2
n
occur with Bu
4
fadiazine could catalyze the reaction and 3a yield was 25% (Table 4,
entry 2). Moreover, with the co-existence of silver sulfadiazine and
Fig. 2. Reaction monitoring profile. Reaction conditions: 1a (108.1 mg, 1.0 mmol), 2a
n
n
4
Bu NBr, 3a yield was improved to 70% (Table 4, entry 4). Therefore,
(
%
126.2 mg, 1.5 mmol), silver sulfadiazine (17.9 mg, 5.0 mol%), Bu
4
NBr (16.1 mg, 5.0 mol
n
ꢀ
silver sulfadiazine/ Bu
fect in the reaction of 1a and intermediate
30] and Fourier transform infrared (FTIR) measurements (Sup-
porting Information, Fig. S1) confirmed that hydroxyl group of
4
NBr also probably exhibited synergistic ef-
), CO balloon, 80 C. The data were determined by GC using biphenyl as the internal
2
standard.
a-ACC. NMR spectrum
[

J. Li et al. / Tetrahedron 75 (2019) 2343e2349
2347
Table 3
The reaction of CO
2
and 2-methyl-3-butyn-2-ol (2a)a.
Entry
Catalyst
Co-catalyst
a
-ACC Yield (%)b
1
2
3
4
e
e
0
0
0
Scheme 3. Carboxylation process investigation. Reaction conditions: silver sulfadia-
4 2
zine (17.9 mg, 5.0 mol%), Bu NBr (16.1 mg, 5.0 mol%), CO balloon, 80 C, 18 h.
n
ꢀ
Silver sulfadiazine
e
e
n
Bu
Bu
4
NBr
NBr
n
Silver sulfadiazine
4
>99
a
Reaction conditions: 2a (84.1 mg, 1.0 mmol), silver sulfadiazine (17.9 mg,
n
ꢀ
5
.0 mol%), Bu
4
NBr (16.1 mg, 5.0 mol%), CO
2
balloon, 80 C, 18 h.
b
Determined by GC using biphenyl as the internal standard.
Table 4
The reaction of benzyl alcohol (1a) and a
-ACCa.
Entry
Catalyst
Co-catalyst
Conv.(%) of 1ab
3a Yield (%)b
1
2
3
4
e
e
0
26
0
0
25
0
Silver sulfadiazine
e
e
n
Bu
Bu
4
NBr
NBr
n
Silver sulfadiazine
4
72
70
a
Reaction conditions: 1a (108.1 mg, 1.0 mmol),
a
-ACC (128.1 mg, 1.0 mmol),
n
ꢀ
silver sulfadiazine (17.9 mg, 5.0 mol%), Bu
4
NBr (16.1 mg, 5.0 mol%), 80 C, 18 h.
b
Determined by GC using biphenyl as the internal standard.
Scheme 4. Plausible reaction mechanism.
propargylic alcohol could be activated by silver sulfadiazine.
On the basis of the experimental results and previous studies
Moreover, silver sulfadiazine was also verified to activate the hy-
n
[
16e18], a possible mechanism for silver sulfadiazine/ Bu
4
NBr-
1
droxyl group of monohydric alcohols by H NMR analysis and FTIR
catalyzed reaction of propargylic alcohols, monohydric alcohols
and CO was proposed (Scheme 4). Firstly, the intermediate A is
obtained from the reaction of propargylic alcohols and CO
spectrum (see Figs. S2 and S3 in Supporting Information). The
simultaneous activation of the substrates contributed to the
enhanced efficiency.
2
2
.
n
þ
Attributing to the presence of Bu
philic cyclization of A further leads to intermediate
ondly, a nucleophilic attack of monohydric alcohol at the carbonyl
group of -ACCs generates the intermediate B, which subsequently
undergoes tautomerization and affords the target product.
4
N , the intramolecular nucleo-
In addition, to avoid the interference from the ion exchange
a
-ACCs. Sec-
n
between silver sulfadiazine and Bu
4
NBr, the blank experiments
were carefully performed (Scheme 2). As a result, AgBr, AgBr/sul-
a
n
fadiazine and AgBr/sulfadiazine/ Bu
4
NBr were demonstrated
inactive for the three-component reaction. Therefore, the syner-
n
gistic effect of silver sulfadiazine and Bu
promote the cascade reaction under atmospheric CO
As shown in Scheme 3a, BnOC(¼O)OBn was not detected in the
reaction of 1a and CO . Meanwhile, -oxopropyl carbonate 3h was
also not obtained in the three-component reaction of dimethyl
carbonate, 2a and CO (Scheme 3b). Therefore, the results indicated
4
NBr was confirmed to
3
. Conclusion
2
pressure.
In summary, a highly efficient strategy was developed for the
2
b
synthesis of
2
b-oxopropyl carbonates by incorporating CO with
propargylic alcohols and monohydric alcohols. Through synergistic
2
n
silver sulfadiazine and Bu
4
NBr catalysis, the three-component
pressure and
that ROC(¼O)OR was not the intermediate in this catalytic system.
reaction was performed under atmospheric CO
2
neat conditions. In addition, the protocol tolerating a wide scope of
propargylic alcohols and monohydric alcohols was well demon-
strated, and the yields of
synergistic strategy provides new insights into chemical fixation of
CO under atmospheric pressure and mild conditions.
b-oxopropyl carbonates reached 99%. This
2
4. Experimental section
4.1. General information
Scheme 2. Control experiments.
Carbon dioxide with a purity of 99.999% was commercially

2348
J. Li et al. / Tetrahedron 75 (2019) 2343e2349
available. All reagents and solvents were purchased from com-
mercial suppliers (Aladdin, Macklin) and used without further
purification. All reactions were carried out without any special
precautions against air and moisture. Nuclear magnetic resonance
301.1426.
4
(
.3.3. 2-Methyl-3-oxobutan-2-yl (4-(methylthio)benzyl) carbonate
3d) [18]
Colorless liquid. Yield: 92% (260 mg). R
(
NMR) spectra were recorded on a Bruker AVANCE III 400 MHz
f
¼ 0.39 (petroleum
):
7.31e7.29 (d, J ¼ 8.0 Hz, 2H), 7.25e7.23 (d, J ¼ 7.6 Hz, 2H), 5.10 (s,
H), 2.48 (d, J ¼ 0.8 Hz, 3H), 2.13 (d, J ¼ 1.2 Hz, 3H),1.51 (d, J ¼ 1.2 Hz,
1
13
spectrometer (400 MHz for H and 100.6 MHz for C) using CDCl
as solvent. GC analyses were performed through using BEIFEN
420A equipped with a flame-ionization detector and a capillary
m). High-resolution
3
1
ether/ethyl acetate (v/v) ¼ 10:1). H NMR (400 MHz, CDCl
3
d
3
2
6
column (122-7032UI, 30 m ꢂ 0.25 mm ꢂ 0.25
m
13
3
H) ppm; C NMR (100.6 MHz, CDCl ): d 206.5, 153.8, 139.4, 131.5,
mass spectra (HRMS) were recorded on a Bruker micrOTOF-Q III
by ESI technique. Melting point (mp) was measured on a X4
apparatus and was uncorrected.
129.1, 126.3, 85.7, 69.4, 23.5, 23.2, 15.5 ppm; HRMS (ESI):
þ
þ
C
14
H
18
O
4
SNa for [MþNa] calculated 305.0818, found 305.0817.
4
(
.3.4. 3-Methoxybenzyl (2-methyl-3-oxobutan-2-yl) carbonate
3e) [16]
Colorless liquid. Yield: 64% (170 mg). R
4
.2. General procedure for the synthesis of benzyl (2-methyl-3-
oxobutan-2-yl) carbonate (3a)
f
¼ 0.39 (petroleum ether/
): 7.22e7.17
m, 1H), 6.89e6.78 (m, 3H), 5.06 (d, J ¼ 7.7 Hz, 2H), 3.73 (s, 3H), 2.06
1
ethyl acetate (v/v) ¼ 10:1). H NMR (400 MHz, CDCl
3
d
The catalyst (0.05 mmol, 5.0 mol%), co-catalyst (0.05 mmol,
(
(
5
2
.0 mol%), benzyl alcohol (108.1 mg, 1.0 mmol), 2-methylbut-3-yn-
-ol (84.1 mg, 1.0 mmol), and CH CN (2 mL) were added to a 10 mL
13
3
s, 3H),1.43 (s, 6H) ppm. C NMR (100.6 MHz, CDCl ): d 206.5,159.7,
3
153.7, 136.4, 129.6, 120.3, 114.2, 113.4, 85.7, 69.6, 55.1 ppm. HRMS
Schlenk tube equipped with magnetic stirring. Then, the Schlenk
tube connecting a balloon filled with CO
8
Na for [MþNa]þ calculated 289.1046, found
þ
(ESI): C14
18
H O
5
2
(ca. 3.5 L) was stirred at
0 C for the given time. After the reaction, the mixture was flushed
2
89.1022.
ꢀ
with EtOAc and concentrated under vacuum. At last, the residue
was purified by column chromatography (silica gel) to provide
products 3a.
4
.3.5. 4-Chlorobenzyl (2-methyl-3-oxobutan-2-yl) carbonate (3f)
[18]
Colorless liquid. Yield: 80% (217 mg). R
Benzyl (2-methyl-3-oxobutan-2-yl) carbonate (3a) [16] Color-
f
¼ 0.49 (petroleum ether/
ethyl acetate (v/v) ¼ 10:1). H NMR (400 MHz, CDCl ): 7.36e7.31
m, 4H), 5.11 (s, 2H), 2.13 (s, 3H), 1.51 (s, 6H) ppm; C NMR
1
less liquid. Yield: 95% (224 mg). R
f
¼ 0.25 (petroleum ether/ethyl
acetate (v/v) ¼ 30:1). H NMR (400 MHz, CDCl ): 7.39e7.34 (m,
H), 5.15 (s, 2H), 2.13 (s, 3H), 1.51 (s, 6H) ppm; C NMR (100.6 MHz,
3
d
1
13
(
3
d
13
5
(100.6 MHz, CDCl
6
calculated 293.0551, found 293.0551.
3
):
d
206.4, 153.7, 134.6, 133.4, 129.8, 128.8, 85.9,
þ
8.9, 23.6, 23.2 ppm; HRMS (ESI): C13
H15ClO
4
Na for [MþNa]þ
CDCl
3
):
d
206.6, 153.8, 134.9, 128.64, 128.60, 128.34, 85.7, 69.8, 23.5,
þ
23.2 ppm; HRMS (ESI): C13
59.0941, found 259.0962.
16
H O
4
Na for [MþNa]þ calculated
2
4
.3.6. 2-Chlorobenzyl (2-methyl-3-oxobutan-2-yl) carbonate (3g)
4
.3. General procedure for the synthesis of various
b
-oxopropyl
Colorless liquid. Yield: 88% (238 mg). R ¼ 0.46 (petroleum
f
1
carbonates (3beq)
ether/ethyl acetate (v/v) ¼ 10:1). H NMR (400 MHz, CDCl
3
): d 7.33
(
3
dtd, J ¼ 10.0, 5.2, 3.0 Hz, 2H), 7.24e7.16 (m, 2H), 5.19 (s, 2H), 2.08 (s,
This silver sulfadiazine (17.9 mg, 5.0 mol%), nBu
.0 mol%), monohydric alcohol (1.0 mmol) and propargylic alcohol
1.5 mmol) were introduced into a 10 mL Schlenk tube equipped
with magnetic stirring. Next, the Schlenk tube was connected with
NBr (16.1 mg,
13
4
3
H), 1.45 (s, 6H) ppm; C NMR (100.6 MHz, CDCl ): d 206.3, 153.6,
5
(
133.6, 132.6, 129.8, 129.5, 126.9, 85.8, 66.8, 23.4, 23.1 ppm. HRMS
(ESI): C13
293.0558.
þ
H15ClO
4
Na for [MþNa]þ calculated 293.0551, found
a CO
8
2
balloon (ca. 3.5 L), and the reaction mixture was stirred at
0 C for 18 h. After the reaction, it was flushed with EtOAc and
ꢀ
4.3.7. Methyl (2-methyl-3-oxobutan-2-yl) carbonate (3h) [17]
concentrated under vacuum. Finally, the residue was purified by
column chromatography (silica gel) using petroleum ether/EtOAc
as eluent to give the products.
Colorless liquid. Yield: 93% (149 mg). Petroleum ether/ethyl
1
acetate (v/v) ¼ 20:1. H NMR (400 MHz, CDCl
3
): d 3.74 (s, 3H), 2.13 (s,
13
3
8
3
H), 1.47 (s, 6H) ppm; C NMR (100.6 MHz, CDCl ): d 206.5, 154.4,
5.5, 54.8, 23.5, 23.1 ppm; HRMS (ESI): C H O
7 12 4
Na for [MþNa]þ
þ
4
[
.3.1. 4-Methylbenzyl (2-methyl-3-oxobutan-2-yl) carbonate (3b)
18]
Colorless liquid. Yield: 89% (223 mg). R
calculated 183.0628, found 183.0603.
f
¼ 0.49 (petroleum
):
7.28e7.26 (d, J ¼ 8.0 Hz, 2H), 7.18e7.16 (d, J ¼ 7.6 Hz, 2H), 5.12 (s,
1
4.3.8. 2-Methyl-3-oxobutan-2-yl propyl carbonate (3i) [18]
ether/ethyl acetate (v/v) ¼ 10:1). H NMR (400 MHz, CDCl
3
Colorless liquid. Yield: 85% (160 mg). Petroleum ether/ethyl
d
1
13
acetate (v/v) ¼ 20:1. H NMR (400 MHz, CDCl ):
d
3.95 (t, J ¼ 6.8 Hz,
3
2
CDCl
H), 2.35 (s, 3H), 2.13 (s, 3H), 1.51 (s, 6H) ppm; C NMR (100.6 MHz,
2
H), 2.02 (s, 3H), 1.60e1.51 (m, 2H), 1.36 (s, 6H), 0.82 (t, J ¼ 7.6 Hz,
3
):
d
206.7,153.8,138.6,131.9,129.3,128.5, 85.7, 69.8, 23.5, 23.2,
13
Na for [MþNa]þ calculated
þ
3H) ppm; C NMR (100.6 MHz, CDCl ):
2
calculated 211.0941, found 211.0917.
d
206.1, 153.7, 84.9, 69.4,
3
18 4
21.2 ppm; HRMS (ESI): C14H O
þ
3.1, 22.9, 21.7, 9.8 ppm; HRMS (ESI): C
9
H
16
O
4
Na for [MþNa]þ
273.1097, found 273.1106.
4.3.2. 4-Isopropylbenzyl (2-methyl-3-oxobutan-2-yl) carbonate
(3c) [18]
4.3.9. 2-Methyl-3-oxobutan-2-yl octyl carbonate (3j)
Colorless liquid. Yield: 91% (253 mg). R
ether/ethyl acetate (v/v) ¼ 10:1). H NMR (400 MHz, CDCl
f
¼ 0.54 (petroleum
):
7.32e7.30 (d, J ¼ 8.0 Hz, 2H), 7.24e7.22 (d, J ¼ 8.0 Hz, 2H), 5.12 (s,
H), 2.96e2.86 (m, 1H), 2.13 (s, 3H), 1.51 (s, 6H), 1.25e1.23 (d,
Colorless liquid. Yield: 99% (256 mg). Petroleum ether/ethyl
1
1
3
acetate (v/v) ¼ 20:1. H NMR (400 MHz, CDCl
3
):
d
4.07 (t, J ¼ 6.7 Hz,
d
2H), 2.11 (s, 3H), 1.65e1.55 (m, 2H), 1.45 (s, 6H), 1.32e1.17 (m, 10H),
13
2
0.82 (t, J ¼ 6.8 Hz, 3H) ppm; C NMR (100.6 MHz, CDCl
3
): d 206.5,
13
J ¼ 6.8 Hz, 6H) ppm; C NMR (100.6 MHz, CDCl
3
):
d
206.7, 153.8,
153.9, 85.2, 68.3, 31.6, 29.0, 28.5, 25.5, 23.3, 23.1, 22.5, 13.9 ppm.
1
49.6, 132.3, 128.6, 126.7, 85.7, 69.8, 33.9, 23.9, 23.5, 23.2 ppm;
HRMS (ESI): C14
281.1759.
H
26
O
4
Na for [MþNa]þ calculated 281.1723, found
þ
þ
HRMS (ESI): C16
H
22
O
4
Na for [MþNa]þ calculated 301.1410, found

J. Li et al. / Tetrahedron 75 (2019) 2343e2349
2349
4
.3.10. Cyclohexyl (2-methyl-3-oxobutan-2-yl) carbonate (3k) [18]
Foundation of China (21602232) and the Natural Science Founda-
tion of Shanxi Province (201701D221057).
ꢀ
White solid. mp: 35e36 C. Yield: 67% (153 mg). Petroleum
1
ether/ethyl acetate (v/v) ¼ 20:1.
3
H NMR (400 MHz, CDCl ):
d
4.60e4.56 (m, 1H), 2.16 (s, 3H), 1.95e1.91 (m, 2H), 1.78e1.73 (m,
Appendix A. Supplementary data
13
2
H), 1.50 (s, 6H), 1.55e1.21 (m, 6H) ppm; C NMR (100.6 MHz,
CDCl
3
):
d
206.9, 153.4, 85.2, 31.5, 25.1, 23.7, 23.4, 23.2 ppm; HRMS
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2019.03.006.
Na for [MþNa]þ calculated 251.1254, found
þ
(
ESI): C12
H
20
O
4
2
51.1271.
References
4
.3.11. Benzyl (3-methyl-2-oxopentan-3-yl) carbonate (3m) [18]
Colorless liquid. Yield: 98% (245 mg). R
¼ 0.51 (petroleum ether/
ethyl acetate (v/v) ¼ 10:1). H NMR (400 MHz, CDCl ): 7.40e7.34
m, 5H), 5.15 (d, J ¼ 1.6 Hz, 2H), 2.11 (s, 3H), 1.97e1.88 (m, 1H),
.81e1.72 (m, 1H), 1.52 (d, J ¼ 1.2 Hz, 3H), 0.89 (t, J ¼ 7.6 Hz, 3H)
f
[1] A.-A.G. Shaikh, S. Sivaram, Chem. Rev. 96 (1996) 951e976.
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1
3
d
4
554e4581.
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0 (2009) 741e743.
(
1
[
13
2
3
ppm; C NMR (100.6 MHz, CDCl ): d 206.7, 153.8, 135.0, 128.62,
[
[
5] P.F. De Cusati, R.A. Olofson, Tetrahedron Lett. 31 (1990) 1405e1408.
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128.60, 128.34, 88.5, 69.7, 29.5, 24.2, 19.5, 7.5 ppm; HRMS (ESI):
Na for [MþNa]þ calculated 273.1097, found 273.1118.
þ
C
H
14 18
O
4
[
7] P. Markewitz, W. Kuckshinrichs, W. Leitner, J. Linssen, P. Zapp, R. Bongartz,
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4
.3.12. Benzyl (3,5-dimethyl-2-oxohexan-3-yl) carbonate (3n) [18]
Colorless liquid. Yield: 96% (267 mg). R
¼ 0.59 (petroleum
ether/ethyl acetate (v/v) ¼ 10:1). H NMR (400 MHz, CDCl ):
7.40e7.34 (m, 5H), 5.15 (d, J ¼ 2.0 Hz, 2H), 2.13 (s, 3H), 1.83e1.71
[
[
f
1
[10] M. Cokoja, C. Bruckmeier, B. Rieger, W.A. Herrmann, F.E. Kühn, Angew. Chem.
3
Int. Ed. 50 (2011) 8510e8537.
d
[
[
11] Q. Liu, L. Wu, R. Jackstell, M. Beller, Nat. Commun. 6 (2015) 5933e5948.
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13
(
(
m, 3H), 1.55 (s, 3H), 0.91 (t, J ¼ 6.0 Hz, 6H) ppm; C NMR
ꢀ
100.6 MHz, CDCl
3
):
d
206.9, 153.7, 135.1, 128.6, 128.3, 88.6, 69.6,
M. Makkee, J. Gascon, F. Kapteijn, Chem. Rev. 117 (2017) 9804e9838.
þ
[13] J.M. Joumier, J. Fournier, C. Bruneau, P.H. Dixneuf, J. Chem. Soc. Perkin Trans. 1
1991) 3271e3274.
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749e1751.
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53 (2011) 133e146.
4
4.2, 24.3, 24.2, 23.8, 23.7, 20.6 ppm; HRMS (ESI): C16
22
H O
4
Na for
(
þ
[MþNa] calculated 301.1410, found 301.1436.
[
[
[
[
[
1
4
.3.13. Benzyl (3-methyl-4-oxopent-1-en-3-yl) carbonate (3o) [16]
Colorless liquid. Yield: 81% (201 mg). R
¼ 0.57 (petroleum
):
7.41e7.34 (m, 5H), 6.01e5.96 (q, J ¼ 10.8 Hz, J ¼ 17.6 Hz, 1H),
.46e5.41 (d, J ¼ 17.2 Hz, 1H), 5.32e5.29 (d, J ¼ 10.8 Hz, 1H),
3
f
16] Z.-H. Zhou, Q.-W. Song, J.-N. Xie, R. Ma, L.-N. He, Chem. Asian J. 11 (2016)
2065e2071.
17] J. Hu, J. Ma, L. Lu, Q. Qian, Z. Zhang, C. Xie, B. Han, ChemSusChem 10 (2017)
1
ether/ethyl acetate (v/v) ¼ 10:1). H NMR (400 MHz, CDCl
3
d
1292e1297.
5
5
18] Q.-W. Song, Q.-N. Zhao, J.-Y. Li, K. Zhang, P. Liu, Synthesis 51 (2019) 739e746.
13
.18e5.17 (d, J ¼ 1.6 Hz, 2H), 2.10 (s, 3H), 1.62 (s, 3H) ppm; C NMR
[19] Z. Zhou, C. He, L. Yang, Y. Wang, T. Liu, C. Duan, ACS Catal. 7 (2017)
248e2256.
[20] K. Chen, G. Shi, R. Dao, K. Mei, X. Zhou, H. Li, C. Wang, Chem. Commun. 52
2016) 7830e7833.
[21] J. Ma, L. Lu, Q. Mei, Q. Zhu, J. Hu, B. Han, ChemCatChem 9 (2017) 4090e4097.
2
(
100.6 MHz, CDCl
3
):
d
204.0, 153.7, 135.6, 134.8, 128.7, 128.6, 128.4,
þ
117.0, 87.7, 70.0, 23.6, 21.1 ppm; HRMS (ESI): C14
H
16
O
4
Na for
(
þ
[MþNa] calculated 271.0941, found 271.0955.
[
[
22] S. Xia, Y. Song, X. Li, H. Li, L.N. He, Molecules 23 (2018) 3033e3044.
23] Y. Wu, Y. Zhao, R. Li, B. Yu, Y. Chen, X. Liu, C. Wu, X. Luo, Z. Liu, ACS Catal. 7
4
.3.14. Benzyl (2-oxooctan-3-yl) carbonate (3p) [16]
(2017) 6251e6255.
Colorless liquid. Yield: 85% (237 mg). R ¼ 0.51 (petroleum ether/
f
[24] F.A. Saad, A.M. Khedr, J. Mol. Liq. 231 (2017) 572e579.
1
ethyl acetate (v/v) ¼ 10:1). H NMR (400 MHz, CDCl
3
): d 7.40e7.34
[25] A. Boughougal, F.Z. Cherchali, A. Messai, N. Attik, D. Decoret, M. Hologne,
C. Sanglar, G. Pilet, J.B. Tommasino, D. Luneau, New J. Chem. 42 (2018)
(
2
m, 5H), 5.18 (s, 2H), 5.02e4.97 (q, J ¼ 6.8 Hz, J ¼ 14 Hz, 1H),
15346e15352.
.53e2.36 (m, 2H), 1.62e1.54 (m, 2H), 1.43e1.41 (d, J ¼ 6.8 Hz, 3H),
13
[
[
[
[
[
26] M. Rocha, O.E. Piro, G.A. Echeverría, A.C. Pastoriza, M.A. Sgariglia, J.R. Sober oꢀ n,
D.M. Gil, J. Mol. Struct. 1176 (2019) 605e613.
27] Q.-W. Song, W.-Q. Chen, R. Ma, A. Yu, Q.-Y. Li, Y. Chang, L.-N. He, Chem-
SusChem 8 (2015) 821e827.
28] Y. Yuan, Y. Xie, C. Zeng, D. Song, S. Chaemchuen, C. Chen, F. Verpoort, Green
Chem. 19 (2017) 2936e2940.
29] Y. Yuan, Y. Xie, C. Zeng, D. Song, S. Chaemchuen, C. Chen, F. Verpoort, Catal.
Sci. Technol. 7 (2017), 2935e293.
1
.32e1.24 (m, 4H), 0.88 (t, J ¼ 6.8 Hz, 3H) ppm;
C NMR
(
100.6 MHz, CDCl
3
):
d
207.6, 154.5, 134.9, 128.8, 128.6, 128.3, 77.9,
þ
7
0.0, 37.9, 31.2, 22.7, 22.4, 16.3, 13.9 ppm; HRMS (ESI): C16
22
H O
4
Na
þ
for [MþNa] calculated 301.1410, found 301.1438.
4
.3.15. 1-Acetylcyclohexyl benzyl carbonate (3q) [18]
Pale yellow liquid. Yield: 97% (268 mg). R
¼ 0.57 (petroleum
ether/ethyl acetate (v/v) ¼ 10:1). H NMR (400 MHz, CDCl ):
7.40e7.34 (m, 5H), 5.17 (s, 2H), 2.09 (s, 3H), 2.08e2.02 (m, 1H),
30] J.-Y. Li, L.-H. Han, Q.-C. Xu, Q.-W. Song, P. Liu, K. Zhang, ACS Sustain. Chem.
Eng. 7 (2019) 3378e3388.
f
1
[31] S.H. Kim, K.H. Kim, S.H. Hong, Angew. Chem. Int. Ed. 53 (2014) 771e774.
3
[
[
32] R. Karmakar, D. Lee, Chem. Soc. Rev. 45 (2016) 4459e4470.
33] K. Sekine, T. Yamada, Chem. Soc. Rev. 45 (2016) 4524e4532.
d
13
1.72e1.54 (m, 8H), 1.31e1.21 (m, 1H) ppm; C NMR (100.6 MHz,
[34] Q.-W. Song, L.-N. He, Adv. Synth. Catal. 358 (2015) 1251e1258.
[35] B. Grignard, C. Ngassamtounzoua, S. Gennen, B. Gilbert, R. M
eꢀ reau, C. Jerome,
CDCl
2
3
):
d
207.0, 153.8, 135.0, 128.61, 128.60, 128.3, 87.2, 69.8, 30.7,
Na for [MþNa]þ
þ
T. Tassaing, C. Detrembleur, ChemCatChem 10 (2018) 2584e2592.
20 4
4.9, 23.6, 21.0 ppm; HRMS (ESI): C16H O
[
[
36] R. M eꢀ reau, B. Grignard, A. Boyaval, C. Detrembleur, C. Jerome, T. Tassaing,
ChemCatChem 10 (2018) 956e960.
37] J. Hu, J. Ma, Q. Zhu, Q. Qian, H. Han, Q. Mei, B. Han, Green Chem. 18 (2016)
calculated 299.1254, found 299.1291.
3
82e385.
Acknowledgments
[
[
38] M.E. Jung, J. Gervay, J. Am. Chem. Soc. 113 (1991) 224e232.
39] K.L. Arthur, Q.L. Wang, D.M. Bregel, N.A. Smythe, B.A. O'Neil, K.I. Goldberg,
K.G. Moloy, Organometallics 24 (2005) 4624e4628.
This work was supported by the National Natural Science