Aerobic oxidative esterification and thioesterification of aldehydes using dibromoisocyanuric acid under mild conditions: No metal catalysts required

Article abstract of DOI:10.1039/c8nj01085d

A practical direct method for the direct preparation of esters and thioesters from aldehydes is described. Esters and thioesters were synthesized by oxidative esterification and thioesterification via in situ generated acyl bromide intermediates, which were used to react with various alcohols and thiols. The esterification and thioesterification were readily performed in the presence of dibromoisocyanuric acid in dichloromethane, without any metal catalysts and under mild conditions. By using this reaction protocol, various esters and thioesters were prepared in high yields. This effective method offers a promising approach for the facile esterification and thioesterification of aldehydes.

Full text of DOI:10.1039/c8nj01085d

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Aerobic Oxidative Esterification and Thioesterification of
Aldehyde using Dibromoisocyanuric Acid under Mild Condition:
No Metal Catalysts Required
YoungꢀDo Kwon,ab Minh Thanh Labc and HeeꢀKwon Kim*bc
a School of Energy, Materials & Chemical Engineering, Korea University of Technology and
Education, Cheonan 31253, Republic of Korea
b
Department of Nuclear Medicine, Molecular Imaging & Therapeutic Medicine Research
Center, Chonbuk National University Medical School and Hospital, Jeonju 54907, Republic
of Korea
c
Research Institute of Clinical Medicine of Chonbuk National UniversityꢀBiomedical
Research Institute of Chonbuk National University Hospital, Jeonju 54907, Republic of
Korea
* Corresponding author.
Tel: +82 63 250 2768; Fax: +82 63 255 1172.
E-mail address: hkkim717@jbnu.ac.kr (HꢀK Kim).
1

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Abstract
A practical direct method for the direct preparation of esters and thioesters from aldehydes is
described. Esters and thioesters were synthesized by oxidative esterification and
thioesterification via in situ generated acyl bromide intermediates, which were used to react
with various alcohols and thiols. The esterification and thioesterification were readily
performed in the presence of dibromoisocyanuric acid in dichloromethane, without any metal
catalysts and under mild conditions. By using this reaction protocol, various esters and
thioesters were prepared in high yields. This effective method offers a promising approach for
the facile esterification and thioesterification of aldehydes.
2

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Introduction
Esters are one of the most fundamental structural units in organic chemistry. These
compounds are frequently found in numerous natural products and bioactive materials, such
as enzyme inhibitors,1 antitumor agents,2 antiꢀmycobacteria agents,3 and antagonists of
natural receptors.4 Thioesters are also biologically important compounds, which are
commonly utilized as intermediates for the preparation of various bioactive compounds.5
Due to the significance of esters and thioesters, development of an efficient method for
their synthesis is highly valuable. One of the traditional approaches for synthesizing of esters
and thioesters involves the nucleophilic substitution of carboxylic acid derivatives with
alcohols and thiols.6 Additionally, aldehydes have been utilized to generate esters and thiols
by oxidative esterification and thioesterifcation.7–16 The classical oxidative esterification and
thioesterification of aldehydes requires two reaction steps: a hemiacetal unit generation,
followed by the oxidation. Various reagents, such as iodine and its derivatives,7 oxone,8
hydrogen peroxide,9 and tertꢀbutyl hydroperoxideꢀtris(pentafluorophenyl)borane10 have been
developed and utilized in numerous oxidative esterifications and thioesterifications using
hemiacetal intermediates. Although these methods are widely used, the drawbacks of using
such reagents include instability of the hemiacetal intermediate and steric hindrance from the
key structure, such as the aldehyde or alcohol. Thus, only more reactive aldehydes can be
used to prepare esters or thioesters, or nonꢀbulky esters can be produced in good yield via
reactions using these reagents. Metalꢀcatalyzed methods have also been developed for
oxidative esterification and thioesterification of aldehydes. A variety of transition metals,
such as cobalt,11 copper,12 iron,13 gold,14 and palladium15 have been utilized to generate esters
and thioesters. Even though these methods were efficient, they need harsh and airꢀprotected
reaction conditions. Thus, metalꢀcatalyzed esterification and thioesterification are only
3

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suitable for a limited range of substrates. Besides, such expensive reagents are
disadvantageous for reactions on an industrial scale. Alternatively, treatment of alcohols and
thiols with Nꢀheterocyclic carbene (NHC) catalysts has been developed for oxidative
esterification and thioesterification of aldehydes, without generation of the hemiacetal
intermediates.16 However, in largeꢀscale NHCꢀcatalyzed esterification and thioesterification,
only primary alcohols and thiols can be coupled with aldehydes to give esters and thioesters.
Thus, the development of a practical synthetic method for esters and thioesters remains a
challenge. In this context, acyl halides are a potential intermediate to synthesize esters and
thioesters because they lend themselves as useful tools in various organic syntheses.17
Especially, the utilization of a bromo source can offer an effective approach because the
successful formation of the acyl bromides from aldehydes could result in the facile
preparation of the target esters and thioesters. Dibromoisocyanuric acid (DBI) is attractive for
the preparation of esters and thioesters, as it is a wellꢀestablished and effective brominating
agent and oxidant.18 Furthermore, DBI is interesting because it can brominate organic
compounds under mild condition in high yield, and it can be treated safely without the need
for an inert atmosphere. Moreover, a synthetic method using DBI for the direct esterification
and thioesterification of aldehydes has not yet been described in the literature. Herein, we
report a DBIꢀmediated direct synthetic protocol to produce a variety of esters and thioesters
from aldehydes (Scheme 1).
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Scheme 1 Oxidative esterification and thioesterification of aldehydes.
Results and discussion
The main difficulty in the synthesis of esters and thioesters from aldehydes is the low
reactivity of the aldehyde group to give the corresponding acyl halide. Only a few methods
have been developed for conversion of aldehydes to acyl bromide, to date.19 We envisioned
that under more efficient reaction conditions, a direct synthesis of esters and thioesters
utilizing acyl bromide intermediates starting from aldehydes would be realizable. We
hypothesized that a reaction of DBI as a bromo donor with aldehyde could be employed for
the in situ generation of acyl bromides, which are active intermediates to give esters and
thioesters. To test our hypothesis, benzaldehyde was selected as the model substrate, and the
possibility of DBI as an agent for the conversion of aldehydes into esters was examined.
The initial reaction involved the treatment of aldehyde along with DBI in dichloromethane
at room temperature. The reactions of benzaldehyde (1a) with a series of equivalents of DBI
(0.2, 0.5, 1.0, 1.5, and 2.0 equiv.) were performed to produce the desired benzoyl bromide
(2a), and the reaction was evaluated by TLC. During the reaction, the reaction mixture
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changed from white to orange, indicating production of benzoyl bromide. Also, the benzoyl
bromide was readily prepared in quantitative yield from the reaction with 0.5 equiv. or more
DBI after the reaction proceeded for 5 h. Several solvents were also tested to identify the
optimal reaction condition. Reactions in toluene, tetrahydrofuran (THF), and 1,4ꢀdioxane
resulted in low yields of benzoyl bromide, while dichloromethane and acetonitrile showed the
more effective synthesis of the desired product (100% and 92%, respectively; Table 1). Thus,
the reaction conditions, including 0.5 equiv. DBI and dichloromethane were chosen for the
subsequent studies.
Table 1 Screening of reaction conditions for the in situ preparation of benzoyl bromidea
O
O
DBI
H
Br
Solvent
rt, 5 h
1a
2a
Entry DBI (equiv.)
Solvent
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
toluene
THF
Temp.
Yieldb (%)
1
2
3
4
5
6
7
8
9
0.2
0.5
1.0
1.5
2.0
0.5
0.5
0.5
0.5
rt
rt
rt
rt
rt
rt
rt
rt
rt
44
100
100
100
100
4
8
1,4ꢀdioxane
CH3CN
35
92
a
b
Reaction conditions: benzaldehyde (1a) (2.0 mmol) and 4.0 mL of solvent. Isolated yield
after purification (fraction distillation).
Next, we investigated the second reaction condition of esterification. Once the aldehyde
disappeared, the in situ prepared benzoyl bromide was treated with benzyl alcohol at room
temperature. The desired ester was readily prepared after 20 min of reaction. In order to
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derive the optimal reaction conditions for ester formation, reactions with benzyl alcohol (3a
)
were screened in the presence of a series of commercially available bases. Our initial
screening results indicated that the formation of esters from benzoyl bromide varied
significantly, according to the bases, as shown in Table 2. The activities of K2CO3, NaHCO3,
4ꢀdimethylaminopyridine (DMAP), 1,4ꢀdiazabicyclo[2.2.2]octane (DABCO), and 1,8ꢀ
diazabicyclo(5.4.0)undecꢀ7ꢀene (DBU) were considered moderate and low, respectively,
while triethylamine, diisopropylethylamine (DIPEA), and pyridine displayed better activity.
However, the yield for the synthesis of ester was still insufficient to provide the
corresponding product in high yield (Table 2, entries 3, 4, and 8). It was reported that DMAP
catalyzed several reactions including esterification and acetylation of alcohols and amines,
and the effect of auxiliary base on catalytic activity of DAMP was also studied.20 Thus, the
combination effect of base and DAMP was investigated. In the present study, although
DMAP alone had poor activity, it revealed a profound influence on the yield of the desired
product, when combined with either DIPEA or pyridine. Specifically, the addition of 0.1
equiv. DMAP as the catalyst significantly enhanced the conversion yield for the ester (85%
for pyridine with DMAP and 93% for DIPEA with DMAP). In addition, reaction was
performed under N2 atmosphere to compare the yield with that of the reaction under air. The
result indicated that there was no difference between reaction with N2 and without N2 (Table
2, entry 11). Thus, the second reaction conditions (conversion of acyl bromide into ester),
including 1.5 equiv. DIPEA and 0.1 equiv. DMAP, and dichloromethane were selected for the
next studies.
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Table 2 Screening of reaction conditions for the preparation of estersa
OH
O
O
O
3a
DBI
H
Base
O
Br
CH2Cl2
rt, 5 h
CH2Cl2
rt, 20 min
1a
4a
2a
Alcohol
(equiv.)
Yieldb
(%)
Entry
Base
K2CO3
Temp.
1
2
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
41
35
60
71
27
14
8
NaHCO3
Et3N
3
4
DIPEA
DMAP
DABCO
DBU
5
6
7
8
Pyridine
63
85
93
93d
9
Pyridine/DMAPc
DIPEA/DMAPc
DIPEA/DMAPc
10
11
a Reaction conditions: benzaldehyde (1a) (2.0 mmol), DBI (1.0 mmol), base (3.0 mmol), and
b
c
CH2Cl2 (4.0 mL). Isolated yield after purification by flash column chromatography. 0.1
equiv. DMAP. d Reaction was conducted under N2 atmosphere.
With the optimized reaction conditions established, the scope of this direct procedure for
esters was explored (Table 3). The reactions were carried out with various alcohols, and the
desired esters were obtained in high yields (76–93%). Alkyl alcohols, including nꢀbutyl
alcohol were used to assess the breadth of our method. Besides the reaction protocol proving
useful for the synthesis of the corresponding esters, the introduction of cyclohexanol (a
general secondary alcohol) and diphenylmethanol (a relatively bulkier secondary alcohol) to
the reaction generated the corresponding esters in high yields (4c and 4d). In addition,
phenol, an aromatic compound, was treated with the benzoyl bromide and proved effective to
produce the corresponding ester in satisfactory yield, without production of side products.
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The results provided a demonstration of the importance of DBI as an agent for the conversion
of aldehydes to esters.
Table 3 The scope of oxidative esterification of aromatic aldehydesa,b
R2 OH 3
O
O
O
R2
DBI
DIPEA, DMAP
O
R1
H
R1
R1
Br
CH2Cl2
rt, 3-5 h
CH2Cl2
rt, 20 min
1
2
4
...............................................................................................................................................
O
O
O
O
O
O
4b 92%
4a 93%
4c 84%
O
O
O
O
O
O
4d 83%
4f 76%
4e 84%
O
O
O
O
O
O
NO2
4g 80%
4h 83%
4i 81%
O
O
O
O
O
O
Cl
NO2
Cl
Cl
4l 93%
4j 90%
4k 92%
O
O
O
O
O
O
O2N
Cl
Cl
4n 88%
4m 84%
4o 81%
O
O
O
O
O
O
O2N
O2N
O2N
4q 87%
4r 91%
4p 84%
a
Reaction conditions: aldehyde (2.0 mmol), DBI (1.0 mmol), alcohol (3.0 mmol), DIPEA
b
(3.0 mmol), DMAP (0.2 mmol), and CH2Cl2 (4.0 mL). Isolated yield after purification by
flash column chromatography.
In the present study, the scope of utilization of DBI was extended to different aromatic
aldehydes. The syntheses of esters were not significantly affected by the electron properties
of substituents on the aromatic ring. The reaction of aromatic aldehydes bearing electronꢀ
donating group (pꢀtolualdehyde) and electronꢀwithdrawing groups (4ꢀchlorobenzaldehyde
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and 4ꢀnitrobenzaldehyde) with various alcohols also produced the desired ester compounds in
similar and high yield. Additionally, allylic and propargylic alcohols were investigated and
confirmed efficient for the direct preparation of esters from aldehydes. It was noteworthy that
aromatic aldehydes bearing an electronꢀdonating group generated acyl bromide within 3 h,
suggesting that it was faster than benzaldehyde and aromatic aldehydes bearing an electronꢀ
withdrawing group.
To explore the range of reaction of aldehydes, aliphatic aldehydes were treated with DBI to
generate esters. Aldehydes containing aliphatic chains were readily converted into the desired
esters in high yields (77–91%) by the same protocol, using several aliphatic and aromatic
alcohols (Table 4). Besides, the treatment of cyclohexanecarboxaldehyde under the optimized
condition also successfully resulted in the generation of desired esters 4s, 4t, and 4u in 91%,
84%, and 77% yield, respectively. In particular, when a variety of alcohols containing
electronꢀdonating and electronꢀwithdrawing groups were employed in the reaction of
aliphatic aldehydes, the reaction was successfully accomplished 4w, 4x, 4z, and 4aa in good
yield. It was also observed that the conversion of aliphatic aldehydes to acyl bromides was
achieved in 2 h, which was a shorter time than those of aromatic aldehydes. Moreover, no
side products were found during the reactions of the aliphatic aldehydes. Besides, reaction of
long aliphatic chain aldehyde and sterically hindered aldehyde were investigated. Reaction of
1ꢀoctanal with benzyl alcohol and reaction of pivalaldehyde with heptanol yielded the
corresponding esters (4ab and 4ac). In addition, the tolerance of heterocycles was explored.
Reaction of thiopheneꢀ2ꢀcarbaldehyde with nꢀbutanol and reaction of isovaleraldehyde with
thiophenꢀ2ꢀylmethanol successfully produced the corresponding esters (4ad and 4ae).
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Table 4 Scope of oxidative esterification of aliphatic aldehydesa,b
R3 OH
3
O
O
O
R1
R1
R2
R1
R2
R3
DBI
DIPEA , DMAP
O
Br
H
R2
CH2Cl2
rt, 2 h
CH2Cl2
rt, 20 min
2
4
1
...............................................................................................................................................
O
O
O
O
O
O
O
Cl
4t 84%
4s 91%
4u 77%
Br
O
O
O
O
O
O
4w 85%
4x 90%
4v 88%
O
Cl
O
O
O
O
O
O
4z 83%
4y 90%
4aa 80%
O
O
O
O
S
O
O
4ab 91%
4ad 90%
4ac 92%
O
O
S
4ae 85%
a
Reaction conditions: aldehyde (2.0 mmol), DBI (1.0 mmol), alcohol (3.0 mmol), DIPEA
b
(3.0 mmol), DMAP (0.2 mmol), and CH2Cl2 (4.0 mL). Isolated yield after purification by
flash column chromatography.
Next, we explored the scope of this methodology for the synthesis of thioesters (Table 5).
Various aldehydes were employed in the reaction with thiols. The aromatic and aliphatic
aldehydes were treated with aromatic and aliphatic thiols under the same reaction condition.
The desired thioesters were prepared in high yields (83–95%). In addition, the aldehydes
were reacted with electronꢀrich and electronꢀdeficient aromatic thiols to give the desired
thioesters in high yield.
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Table 5 Scope of oxidative thioesterification of aldehydesa,b
O
R3 SH 5
O
O
R1
R1
R2
R1
R2
R3
DBI
DIPEA, DMAP
S
Br
H
R2
CH2Cl2
rt, 2-5 h
CH2Cl2
rt, 20 min
6
2
1
...............................................................................................................................................
O
O
O
S
S
S
H3C
6b 83%
6a 91%
6c 86%
O
S
O
S
O
S
Cl
Cl
6f 94%
6e 86%
6d 89%
O
S
Cl
CH3
O
O
S
S
6i 95%
6h 84%
6g 91%
a
Reaction conditions: aldehyde (2.0 mmol), DBI (1.0 mmol), thiol (3.0 mmol), DIPEA (3.0
b
mmol), DMAP (0.2 mmol), and CH2Cl2 (4.0 mL). Isolated yield after purification by flash
column chromatography.
Next, a scaleꢀup oxidative esterification was carried out (Scheme 2). The reaction
was proven to be scalable and practical because the gramꢀscale reaction was also
efficiently performed. The reaction of benzaldehyde (1a) (20.0 mmol, 2.12 g) and
benzyl alcohol (3a) (30.0 mmol, 1.5 equiv.) gave the corresponding product (4a) in
83% yield under optimized reaction conditions.
OH
O
O
O
3a
DBI
H
DIPEA, DMAP
O
Br
CH2Cl2
rt, 5 h
CH2Cl2
rt, 20 min
1a
4a
3.51 g, 83%
2a
20.0 mmol, 2.12 g
Scheme 2 The gramꢀscale reaction of benzaldehyde (1a) with benzyl alcohol (3a).
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A plausible reaction pathway based on the previous report21 and our result can be proposed,
as shown in Scheme 3. The initial addition of DBI to aldehyde probably produced acyl
bromide using a radical pathway. Then, the desired ester or
1
2
4
6
was prepared via the
treatment of acyl bromide
2
with alcohol 3 or thiol 5.
O
O
DBI
R1
R1
H
Br
(1)
radical pathway
2
1
R2 OH
3
or
R2 SH
O
O
O
5
R2
R2
(2)
R1
R1
R1
or
O
S
Br
DIPEA, DMAP
2
4
6
Scheme 3 Proposed reaction pathway for thioesterification and esterification from aldehydes.
Conclusions
In summary, a novel facile direct method for the synthesis of esters and thioesters from
aldehydes has been developed. In the present study, DBI was used as a bromo donor for the
in situ preparation of acyl bromide from aromatic and aliphatic aldehydes. The use of DBI
was demonstrated from the reactions of aldehydes with various alcohols and thiols, including
benzylic, aliphatic, and propargylic alcohols. Moreover, the reaction protocol used mild
aerobic reaction conditions. Our results suggest that a novel method to prepare esters and
thioesters is practical and applicable for the synthesis of a variety of esters and thioesters
from aldehydes.
Experimental
General information
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All chemicals were purchased from SigmaꢀAldrich and used without further purification.
Reaction progress was monitored by thinꢀlayer chromatography (TLC) analysis. TLC
analysis was performed using an aluminum plate with silica gel 60 F254, and TLC spots were
visualized by UV light (254nm) exposure. Flash chromatography was performed using 230–
400 mesh silica gel and analytical grade solvent. Melting points were recorded using a Stuart
1
13
SMP10 Melting Point Apparatus. H and C NMR spectra were recorded on a 600 MHz &
150 MHz respectively JEOL JNMꢀECA600 spectrometer or a 400 MHz & 100 MHz
respectively Bruker Avance 400 spectrometer. The chemical shifts were reported in δ units
(ppm) relative to the residual protonated solvent resonance, and the coupling constants (J)
quoted in Hz.
General experimental procedure for the preparation of ester and thioester compounds
(4a–4aa and 6a–6i)
To a solution of benzaldehyde (1a) (0.212 g, 2.00 mmol) in CH2Cl2 (4 mL) was added
dibromoisocyanuric acid (0.287 g, 1.00 mmol). The mixture was allowed to stir at room
temperature for 5 h. Benzyl alcohol (0.324 g, 3.00 mmol), DIPEA (0.388 g, 3.00 mmol), and
DMAP (0.244 g, 0.200 mmol) were added to the reaction mixture. After being stirred for 20
min at room temperature, the solid (cyanuric acid) was filtered, and the filtrate was extracted
with CH2Cl2 (2 x 30 mL). The organic layer was dried over sodium sulfate and concentrated
under reduced pressure. The resulting residue was then purified by flash column
chromatography on silica gel with hexaneꢀEtOAc as eluent to afford the desired product 4a
(0.396 g, 93%).
Benzyl benzoate (4a). Purified by flash column chromatography (EtOAc:hexane = 1:50) in
1
93% yield (396 mg, 1.87 mmol) as a colorless oil. H NMR (600 MHz, CDCl3) δ 8.09–8.08
(m, 2H), 7.58–7.55 (m, 1H), 7.46–7.34 (m, 7H), 5.37 (s, 2H). 13C NMR (150 MHz, CDCl3) δ
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166.6, 136.2, 133.2, 130.2, 129.8 (2C), 128.7 (2C), 128.5 (2C), 128.4, 128.3 (2C), 66.8.
HRMS (ESI) m/z [M + H]+ calcd for C14H13O2
=
213.0916, found 213.0918.
Butyl benzoate (4b). Purified by flash column chromatography (EtOAc:hexane = 1:50) in
1
92% yield (330 mg, 1.84 mmol) as a colorless oil. H NMR (600 MHz, CDCl3) δ 8.08–8.05
(m, 2H), 7.59–7.55 (m, 1H), 7.48–7.43 (m, 2H), 4.35 (t, J = 3.6 Hz, 2H), 1.80–1.74 (m, 2H),
1.54–1.48 (m, 2H), 1.01 (t, J = 7.4 Hz, 3H).13C NMR (150 MHz, CDCl3) δ 166.7, 132.8,
130.5, 129.5 (2C), 128.3 (2C), 64.8, 30.8, 19.3, 13.8. HRMS (ESI) m/z [M + H]+ calcd for
C11H15O2
= 179.1072, found 179.1076 .
Cyclohexyl benzoate (4c). Purified by flash column chromatography (EtOAc:hexane =
1
1:90) in 84% yield (302 mg, 1.69 mmol) as a colorless oil. H NMR (600 MHz, CDCl3) δ
8.06–8.04 (m, 2H), 7.58–7.53 (m, 1H), 7.45–7.42 (m, 2H), 5.03 (tt, J = 9.0, 3.6 Hz, 1H),
1.96–1.93 (m, 2H), 1.82–1.77 (m, 2H), 1.62–1.55 (m, 3H), 1.49–1.42 (m, 2H), 1.38–1.32 (m,
1H). 13C NMR (150 MHz, CDCl3) δ 166.1, 132.8, 131.1, 129.7 (2C), 128.4 (2C), 73.2, 31.8
(2C), 25.6, 23.8 (2C). HRMS (ESI) m/z [M + H]+ calcd for C13H17O2
= 205.1229, found
205.1227.
Benzhydryl benzoate (4d). Purified by flash column chromatography (EtOAc:hexane =
1:90) in 83% yield (480 mg, 1.66 mmol) as a white solid, mp 83–85 oC. 1H NMR (600 MHz,
CDCl3) δ 8.18 (d, J = 7.6 Hz, 2H), 7.61 (t, J = 7.2 Hz, 1H), 7.49 (dd, J = 8.0, 3.6 Hz, 6H),
7.41 (t, J = 6.4 Hz, 4H), 7.34 (t, J = 7.2 Hz, 2H), 7.17 (s, 1H). 13C NMR (150 MHz, CDCl3) δ
165.7, 140.4 (2C), 133.3 (2C), 130.3, 129.9 (3C), 128.7 (3C), 128.6 (2C), 128.1 (2C), 127.3
(3C), 77.5. HRMS (ESI) m/z [M + H]+ calcd for C20H17O2
= 289.1229, found 289.1230.
Phenyl benzoate (4e). Purified by flash column chromatography (EtOAc:hexane = 1:30) in
84% yield (336 mg, 1.69 mmol) as a white solid, mp 70–72 oC. 1H NMR (600 MHz, CDCl3)
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δ
8.24 (dd, J = 6.8, 1.6 Hz, 2H), 7.67 (dd, J = 7.2, 3.6 Hz, 1H), 7.51 (t, J = 7.6 Hz, 2H), 7.47 (dd,
7.25 (m, 3H). 13C NMR (150 MHz, CDCl3) δ 165.2, 151.0, 133.6,
130.2 (2C), 129.6 (2C), 129.5, 128.6 (2C), 125.9, 121.8 (2C). HRMS (ESI) m/z [M + H]+
J = 8.0, 4.0 Hz, 2H), 7.33
–
calcd for C13H11O2
= 199.0759, found 199.0755.
Benzyl 4-methylbenzoate (4f). Purified by flash column chromatography (EtOAc:hexane =
1:70) in 76% yield (346 mg, 1.52 mmol) as a white solid, mp 39–41 oC. 1H NMR (600 MHz,
CDCl3) δ 7.98 (d, J = 8.4 Hz, 2H), 7.46–7.45 (m, 2H), 7.41–7.35 (m, 3H), 7.24 (d, J = 7.8 Hz,
2H), 5.36 (s, 2H), 2.41 (s, 3H). 13C NMR (150 MHz, CDCl3) δ 166.6, 143.9, 136.3, 129.9
(2C), 129.2 (2C), 128.7 (2C), 128.3, 128.2 (2C), 127.5, 66.6, 21.8. HRMS (ESI) m/z [M +
H]+ calcd for C15H15O2
= 227.1072, found 227.1073.
4-Nitrobenzyl 4-methylbenzoate (4g). Purified by flash column chromatography
o
(EtOAc:hexane = 1:20) in 80% yield (436 mg, 1.60 mmol) as a white solid, mp 102–104 C.
1H NMR (600 MHz, CDCl3) δ 8.25 (d, J = 8.4 Hz, 2H), 7.98 (d, J = 8.4 Hz, 2H), 7.60 (d, J =
8.4 Hz, 2H), 7.27 (d, J = 8.4 Hz, 2H), 5.44 (s, 2H), 2.43 (s, 3H). 13C NMR (150 MHz, CDCl3)
δ 166.3, 147.8, 144.4, 143.7, 129.9 (2C), 129.4 (2C), 128.4 (2C), 126.8, 124.0 (2C), 65.1,
21.9. HRMS (ESI) m/z [M + H]+ calcd for C15H14NO4
= 272.0923, found 272.0925.
4-Methylbenzyl 4-methylbenzoate (4h). Purified by flash column chromatography
1
(EtOAc:hexane = 1:70) in 83% yield (402 mg, 1.67 mmol) as a colorless oil. H NMR (600
MHz, CDCl3) δ 7.96 (d, J = 8.4 Hz, 2H), 7.34 (d, J = 7.2 Hz, 2H), 7.23 (d, J = 8.4 Hz, 2H),
7.20 (d, J = 8.4 Hz, 2H), 5.31 (s, 2H), 2.40 (s, 3H), 2.37 (s, 3H). 13C NMR (150 MHz, CDCl3)
δ 166.7, 143.8, 138.2, 133.3, 129.9 (2C), 129.4 (2C), 129.2 (2C), 128.5 (2C), 127.6, 66.6,
21.8, 21.4. HRMS (ESI) m/z [M + H]+ calcd for C16H17O2
= 241.1229, found 241.1226.
Prop-2-ynyl 4-methylbenzoate (4i). Purified by flash column chromatography
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(EtOAc:hexane = 1:70) in 81% yield (284 mg, 1.62 mmol) as a white solid, mp 44–45 oC. 1H
NMR (600 MHz, CDCl3) δ 7.96 (d, J = 7.8 Hz, 2H), 7.25 (d, J = 8.4 Hz, 2H), 4.91 (d, J = 2.4
Hz, 2H), 2.51 (t, J = 2.4 Hz, 1H), 2.41 (s, 3H). 13C NMR (150 MHz, CDCl3) δ 166.0, 144.3,
130.0 (2C), 129.3 (2C), 126.8, 78.0, 75.0, 52.4, 21.8. HRMS (ESI) m/z [M + H]+ calcd for
C11H11O2
= 175.0759, found 175.0761.
Benzyl 4-chlorobenzoate (4j). Purified by flash column chromatography (EtOAc:hexane =
1
1:80) in 90% yield (424 mg, 1.80 mmol) as a colorless oil. H NMR (600 MHz, CDCl3) δ
8.01 (d, J = 8.4 Hz, 2H), 7.45–7.35 (m, 7H), 5.36 (s, 2H). 13C NMR (150 MHz, CDCl3) δ
165.7, 139.6, 135.9, 131.2 (2C), 128.9 (2C), 128.8 (2C), 128.7, 128.5, 128.4 (2C), 67.1.
HRMS (ESI) m/z [M + H]+ calcd for C14H12ClO2
= 247.0526, found 247.0528.
4-Nitrobenzyl 4-chlorobenzoate (4k). Purified by flash column chromatography
o
(EtOAc:hexane = 1:20) in 92% yield (592 mg, 1.84 mmol) as a white solid, mp 134–135 C.
1H NMR (600 MHz, CDCl3) δ 8.25 (d, J = 9.0 Hz, 2H), 8.02 (d, J = 8.4 Hz, 2H), 7.60 (d, J =
9.0 Hz, 2H), 7.44 (d, J = 9.0 Hz, 2H), 5.45 (s, 2H). 13C NMR (150 MHz, CDCl3) δ 165.4,
147.9, 143.1, 140.1, 131.2 (2C), 129.1 (2C), 128.6 (2C), 128.0, 124.0 (2C), 65.5. HRMS (ESI)
m/z [M + H]+ calcd for C14H11ClNO4
= 292.0377, found 292.0378.
4-Methylbenzyl 4-chlorobenzoate (4l). Purified by flash column chromatography
(EtOAc:hexane = 1:90) in 93% yield (486 mg, 1.86 mmol) as a white solid, mp 50–51 oC. 1H
NMR (600 MHz, CDCl3) δ 8.00 (d, J = 8.4 Hz, 2H), 7.40 (d, J = 9.0 Hz, 2H), 7.34 (d, J = 8.4
Hz, 2H), 7.21 (d, J = 8.4 Hz, 2H), 5.32 (s, 2H), 2.37 (s, 3H). 13C NMR (150 MHz, CDCl3) δ
165.8, 139.6, 138.4, 132.9, 131.2 (2C), 129.4 (2C), 128.83 (2C), 128.80, 128.6 (2C), 67.1,
21.4. HRMS (ESI) m/z [M + H]+ calcd for C15H14ClO2
= 261.0682, found 261.0685.
Cyclohexyl 4-chlorobenzoate (4m). Purified by flash column chromatography
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(EtOAc:hexane = 1:90) in 84% yield (402 mg, 1.68 mmol) as a white solid, mp 38–40 oC. 1H
NMR (600 MHz, CDCl3) δ 7.98 (d, J = 9.0 Hz, 2H), 7.40 (d, J = 7.8 Hz, 2H), 5.01 (tt, J = 9.0,
3.6 Hz, 1H), 1.95–1.92 (m, 2H), 1.81–1.77 (m, 2H), 1.61–1.55 (m, 3H), 1.48–1.41 (m, 2H),
1.37–1.33 (m, 1H). 13C NMR (150 MHz, CDCl3) δ 162.3, 139.2, 131.1 (2C), 129.6, 128.7
(2C), 73.6, 31.7 (2C), 25.6, 23.8 (2C). HRMS (ESI) m/z [M + H]+ calcd for C13H16ClO2
=
239.0839, found 239.0838.
Butyl 4-chlorobenzoate (4n). Purified by flash column chromatography (EtOAc:hexane =
1
1:80) in 88% yield (376 mg, 1.76 mmol) as a colorless oil. H NMR (600 MHz, CDCl3) δ
7.97 (d, J = 9.0 Hz, 2H), 7.40 (d, J = 8.4 Hz, 2H), 4.31 (t, J = 6.6 Hz, 2H), 1.76–1.71 (m, 2H),
1.49–1.43 (m, 2H), 0.97 (t, J = 7.2 Hz, 3H). 13C NMR (150 MHz, CDCl3) δ 165.9, 139.3,
131.1 (2C), 129.1, 128.8 (2C), 65.2, 30.8, 19.4, 13.9. HRMS (ESI) m/z [M + H]+ calcd for
C11H14ClO2
= 213.0682, found 213.0684.
Benzyl 4-nitrobenzoate (4o). Purified by flash column chromatography (EtOAc:hexane =
1:30) in 81% yield (420 mg, 1.62 mmol) as a white solid, mp 87–88 oC. 1H NMR (600 MHz,
CDCl3) δ 8.28 (d, J = 9.0 Hz, 2H), 8.24 (d, J = 9.0 Hz, 2H), 7.47–7.38 (m, 5H), 5.41 (s, 2H).
13C NMR (150 MHz, CDCl3) δ 164.7, 150.7, 135.6, 135.4, 131.0 (2C), 128.9 (2C), 128.8,
128.6 (2C), 123.7 (2C), 67.8. HRMS (ESI) m/z [M + H]+ calcd for C14H12NO4
= 258.0766,
found 258.0767.
Cyclopropylmethyl 4-nitrobenzoate (4p). Purified by flash column chromatography
(EtOAc:hexane = 1:30) in 84% yield (374 mg, 1.68 mmol) as a white solid, mp 56–57 oC. 1H
NMR (600 MHz, CDCl3) δ 8.29 (d, J = 8.4 Hz, 2H), 8.23 (d, J = 7.8 Hz, 2H), 4.20 (d, J = 6.6
Hz 2H), 1.31–1.24 (m, 1H), 0.67–0.63 (m, 2H), 0.40–0.37 (m, 2H). 13C NMR (150 MHz,
CDCl3) δ 165.0, 150.6, 136.0, 130.9 (2C), 123.6 (2C), 70.9, 9.94, 3.57 (2C). HRMS (ESI)
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m/z [M + H]+ calcd for C11H12NO4
= 222.0766, found 222.0767.
Isobutyl 4-nitrobenzoate (4q). Purified by flash column chromatography (EtOAc:hexane =
1:30) in 87% yield (390 mg, 1.74 mmol) as a white solid, mp 70–71 oC. 1H NMR (600 MHz,
CDCl3) δ 8.29 (d, J = 8.4 Hz, 2H), 8.21 (d, J = 9.0 Hz, 2H), 4.16 (d, 2H), 2.14–2.08 (m, 1H),
1.04 (d, J = 6.0 Hz, 6H). 13C NMR (150 MHz, CDCl3) δ 164.8, 150.6, 136.0, 130.8 (2C),
123.7 (2C), 72.0, 28.0, 19.3 (2C). HRMS (ESI) m/z [M + H]+ calcd for C11H14NO4
=
224.0923, found 224.0921.
Allyl 4-nitrobenzoate (4r). Purified by flash column chromatography (EtOAc:hexane =
1
1:30) in 91% yield (408 mg, 1.82 mmol) as a colorless oil. H NMR (600 MHz, CDCl3) δ
8.29 (d, J = 9.0 Hz, 2H), 8.23 (d, J = 8.4 Hz, 2H), 6.08–6.01 (m, 1H), 5.45–5.42 (m, 1H),
5.35–5.33 (m, 1H), 4.88–4.86 (m, 2H). 13C NMR (150 MHz, CDCl3) δ 164.5, 150.7, 135.7,
131.6, 130.9 (2C), 123.7 (2C), 119.3, 66.6. HRMS (ESI) m/z [M + H]+ calcd for C10H10NO4
=
208.0610, found 208.0613.
Benzyl cyclohexanecarboxylate (4s). Purified by flash column chromatography
1
(EtOAc:hexane = 1:50) in 91% yield (400 mg, 1.83 mmol) as a colorless oil. H NMR (600
MHz, CDCl3) δ 7.38–7.30 (m, 5H), 5.11 (s, 2H), 2.36 (tt, J =11.4, 3.6 Hz, 1H), 1.95–1.92 (m,
2H), 1.78–1.74 (m, 2H), 1.65–1.64 (m, 1H), 1.50–1.44 (m, 2H), 1.31–1.21 (m, 3H). 13C NMR
(150 MHz, CDCl3) δ 176.1, 136.4, 128.6 (2C), 128.2, 128.1 (2C), 66.0, 43.3, 29.1 (2C), 25.9,
25.6 (2C). HRMS (ESI) m/z [M + H]+ calcd for C14H19O2
= 219.1385, found 219.1384.
4-Chlorobenzyl cyclohexanecarboxylate (4t). Purified by flash column chromatography
1
(EtOAc:hexane = 1:50) in 84% yield (426 mg, 1.68 mmol) as a colorless oil. H NMR (600
MHz, CDCl3) δ 7.32 (d, J = 8.4 Hz, 2H), 7.27 (d, J = 8.4 Hz, 2H), 5.06 (s, 2H), 2.34 (tt, J =
11.4, 3.6 Hz, 1H), 1.93–1.90 (m, 2H), 1.76–1.73 (m, 2H), 1.65–1.62 (m, 1H), 1.48–1.42 (m,
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2H), 1.31–1.20 (m, 3H). 13C NMR (150 MHz, CDCl3) δ 175.9, 135.0, 134.1, 129.5 (2C),
128.8 (2C), 65.2, 43.3, 29.1 (2C), 25.8, 25.5 (2C). HRMS (ESI) m/z [M + H]+ calcd for
C14H18ClO2
= 253.0995, found 253.0997.
4-Methoxyphenyl cyclohexanecarboxylate (4u). Purified by flash column chromatography
(EtOAc:hexane = 1:40) in 77% yield (364 mg, 1.55 mmol) as a white solid, mp 66–68 oC. 1H
NMR (600 MHz, CDCl3) δ 6.97 (d, J = 9.0 Hz, 2H), 6.88 (d, J = 9.0 Hz, 2H), 3.79 (s, 3H),
2.53 (tt, J = 11.4, 3.6 Hz, 1H), 2.06–2.04 (m, 2H), 1.83–1.80 (m, 2H), 1.70–1.68 (m, 1H),
1.61–1.55 (m, 2H), 1.39–1.25 (m, 3H). 13C NMR (150 MHz, CDCl3) δ 175.1, 157.2, 144.5,
122.4 (2C), 114.5 (2C), 55.7, 43.3, 29.1 (2C), 25.9, 25.5 (2C). HRMS (ESI) m/z [M + H]+
calcd for C14H19O3
= 235.1334, found 235.1337.
Benzyl butyrate (4v). Purified by flash column chromatography (EtOAc:hexane = 1:80) in
1
88% yield (316 mg, 1.76 mmol) as a colorless oil. H NMR (600 MHz, CDCl3) δ 7.39–7.32
(m, 5H), 5.13 (s, 2H), 2.35 (t, J = 7.5 Hz, 2H), 1.69 (qt, J = 7.4 Hz, 2H), 0.96 (t, J = 7.5 Hz,
3H). 13C NMR (150 MHz, CDCl3) δ 173.6, 136.2, 128.6 (2C), 128.3 (3C), 66.1, 36.3, 18.6,
13.8. HRMS (ESI) m/z [M + H]+ calcd for C11H15O2
= 179.1072, found 179.1073.
2-Bromophenyl butyrate (4w). Purified by flash column chromatography (EtOAc:hexane
1
= 1:70) in 85% yield (414 mg, 1.70 mmol) as a colorless oil. H NMR (600 MHz, CDCl3) δ
7.61–7.60 (m, 1H), 7.34–7.31 (m, 1H), 7.13–7.10 (m, 2H), 2.61 (t, J = 7.8 Hz, 2H), 1.83 (qt,
J = 7.4 Hz, 2H), 1.07 (t, J = 7.8 Hz, 3H). 13C NMR (150 MHz, CDCl3) δ 171.3, 148.4, 133.5,
128.6, 127.4, 124.0, 116.4, 36.1, 18.5, 13.9. HRMS (ESI) m/z [M + H]+ calcd for C10H12BrO2
=
243.0021, found 243.0023.
p-Tolyl butyrate (4x). Purified by flash column chromatography (EtOAc:hexane = 1:80) in
90% yield (324 mg, 1.85 mmol) as a colorless oil. 1H NMR (600 MHz, CDCl3) δ 7.17 (d, J =
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8.4 Hz, 2H), 6.96 (d, J = 8.4 Hz, 2H), 2.53 (t, J = 7.2 Hz, 2H), 2.35 (s, 3H), 1.79 (qt, J = 7.4
Hz, 2H), 1.05 (t, J = 7.5 Hz, 3H). 13C NMR (150 MHz, CDCl3) δ 172.5, 148.6, 135.4, 130.0
(2C), 121.4 (2C), 36.4, 21.0, 18.6, 13.8. HRMS (ESI) m/z [M + H]+ calcd for C11H15O2
=
179.1072, found 179.1071.
Benzyl 3-methylbutanoate (4y). Purified by flash column chromatography (EtOAc:hexane
1
= 1:80) in 90% yield (348 mg, 1.80 mmol) as a colorless oil. H NMR (600 MHz, CDCl3) δ
7.38–7.31 (m, 5H), 5.12 (s, 2H), 2.25 (d, J = 7.8 Hz, 2H), 2.15–2.11 (m, 1H), 0.96 (d, J = 6.6
Hz, 6H). 13C NMR (150 MHz, CDCl3) δ 173.1, 136.3, 128.7 (2C), 128.35, 128.26 (2C), 66.1,
43.5, 25.9, 22.6 (2C). HRMS (ESI) m/z [M + H]+ calcd for C12H17O2
= 193.1229, found
193.1230.
4-Chlorophenyl 3-methylbutanoate (4z). Purified by flash column chromatography
1
(EtOAc:hexane = 1:70) in 83% yield (354 mg, 1.66 mmol) as a colorless oil. H NMR (600
MHz, CDCl3) δ 7.34 (d, J = 8.4 Hz, 2H), 7.02 (d, J = 9.0 Hz, 2H), 2.43 (d, J = 6.6 Hz, 2H),
2.24–2.22 (m, 1H), 1.05 (d, J = 7.2 Hz, 6H). 13C NMR (150 MHz, CDCl3) δ 171.5, 149.3,
131.2, 129.6 (2C), 123.1 (2C), 43.4, 26.0, 22.5 (2C). HRMS (ESI) m/z [M + H]+ calcd for
C11H14ClO2
= 213.0682, found 213.0681.
4-Methoxybenzyl 3-methylbutanoate (4aa). Purified by flash column chromatography
1
(EtOAc:hexane = 1:70) in 80% yield (358 mg, 1.60 mmol) as a colorless oil. H NMR (600
MHz, CDCl3) δ 7.29 (d, J = 9.0 Hz, 2H), 6.89 (d, J = 9.0 Hz, 2H), 5.05 (s, 2H), 3.81 (s, 3H),
2.21 (d, J = 6.6 Hz, 2H), 2.14–2.07 (m, 1H), 0.94 (d, J = 6.0 Hz, 6H). 13C NMR (150 MHz,
CDCl3) δ 173.2, 159.7, 130.2 (2C), 128.4, 114.0 (2C), 65.9, 55.4, 43.6, 25.9, 22.5 (2C).
HRMS (ESI) m/z [M + H]+ calcd for C13H19O3
= 223.1334, found 223.1335.
Benzyl octanoate (4ab). Purified by flash column chromatography (EtOAc:hexane = 1:70)
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in 91% yield (428 mg, 1.82 mmol) as a colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.42ꢀ7.30
(m, 5H), 5.14 (s, 2H), 2.38 (t, J = 7.6 Hz, 2H), 1.72ꢀ1.62 (m, 2H), 1.40ꢀ1.20 (m, 8H), 0.90 (t,
J = 6.8 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 173.7, 136.2, 128.5 (2C), 128.2 (3C), 66.0,
34.3, 31.6, 29.1, 28.9, 25.0, 22.6, 14.1. HRMS (ESI) m/z [M + H]+ cacld for C15H23O2 =
235.1698, found 235.1699.
Heptyl pivalate (4ac). Purified by flash column chromatography (EtOAc:hexane = 1:70) in
92% yield (370 mg, 1.84 mmol) as a colorless oil. 1H NMR (400 MHz, CDCl3) δ 4.06 (t, J =
6.4 Hz, 2H), 1.64 (quint, J = 6.8 Hz, 2H), 1.40ꢀ1.25 (m, 8H), 1.21 (s, 9H), 0.90 (t, J = 6.8 Hz,
3H). 13C NMR (100 MHz, CDCl3) δ 178.6, 64.5, 38.7, 31.7, 28.9, 28.6, 27.2 (3C), 25.9, 22.6,
14.0. HRMS (ESI) m/z [M + H]+ cacld for C12H25O2 = 201.1855, found 201.1857.
Thiophen-2-ylmethyl 3-methylbutanoate (4ad). Purified by flash column chromatography
1
(EtOAc:hexane = 1:70) in 90% yield (359 mg, 1.80 mmol) as a colorless oil. H NMR (400
MHz, CDCl3) δ 7.33 (dd, J = 4.2, 1.2 Hz, 1H), 7.11 (dd, J = 2.8, 0.4 Hz, 1H), 7.00 (dd, J =
4.2, 3.2 Hz, 1H), 5.29 (s, 2H), 2.24 (d, J = 6.8 Hz, 2H), 2.13 (nontet, J = 6.4 Hz, 1H), 0.96 (d,
J = 6.8 Hz, 6H). 13C NMR (100 MHz, CDCl3) δ 172.8, 138.2, 128.0, 126.8, 126.7, 60.2, 43.3,
25.7, 22.4 (2C). HRMS (ESI) m/z [M + H]+ cacld for C10H15O2S = 199.0793, found 199.0798.
Butyl thiophene-2-carboxylate (4ae). Purified by flash column chromatography
1
(EtOAc:hexane = 1:70) in 85% yield (315 mg, 1.70 mmol) as a light yellow oil. H NMR
(400 MHz, CDCl3) δ 7.82 (dd, J = 3.6, 1.2 Hz, 1H), 7.56 (dd, J = 4.8, 1.2 Hz, 1H), 7.11 (dd, J
= 4.8, 3.6 Hz, 1H), 4.32 (t, J = 6.4 Hz, 2H), 1.76 (quint, J = 6.4 Hz, 2H), 1.49 (sextet, J = 7.2
Hz, 2H), 0.99 (t, J = 7.6 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 162.3, 134.1, 133.2, 132.1,
127.7, 65.0, 30.8, 19.2, 13.7. HRMS (ESI) m/z [M + H]+ cacld for C9H13O2S = 185.0636,
found 185.0638.
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S-Cyclohexyl benzothioate (6a). Purified by flash column chromatography
1
(dichloromethane:hexane = 1:2) in 91% yield (403 mg, 1.82 mmol) as a colorless oil. H
NMR (400 MHz, CDCl3) δ 7.97 (dd, J = 8.4, 1.2 Hz, 2H), 7.57 (tt, J = 7.6, 1.2 Hz, 1H), 7.45
(t, J = 8.0 Hz, 2H), 3.79–3.73 (m, 1H), 2.07–2.03 (m, 2H), 1.79 (m, 2H), 1.65 (m, 1H), 1.57
(m, 4H), 1.30 (m, 1H). 13C NMR (100 MHz, CDCl3) δ 191.8, 137.5, 133.1, 128.5 (2C), 127.1
(2C), 42.5, 33.2 (2C), 26.0 (2C), 25.6. HRMS (ESI) m/z [M + H]+ calcd for C13H17OS
=
221.1000, found 221.1005.
S-Phenyl benzothioate (6b). Purified by flash column chromatography
(dichloromethane:hexane = 1:2) in 83% yield (357 mg, 1.66 mmol) as a white solid, mp 56–
58 oC. 1H NMR (400 MHz, CDCl3) δ 8.01 (dd, J = 6.8, 1.2 Hz, 2H), 7.64 (tt, J = 7.2, 1.6 Hz,
1H), 7.52 (m, 7H). 13C NMR (100 MHz, CDCl3) δ 190.1, 136.7, 135.1 (2C), 133.7, 129.5,
129.3 (2C), 128.8 (2C), 127.5 (2C), 127.4. HRMS (ESI) m/z [M + H]+ calcd for C13H11OS
=
215.0531, found 215.0534.
S-Benzyl 4-methylbenzothioate (6c). Purified by flash column chromatography
1
(dichloromethane:hexane = 1:2) in 86% yield (420 mg, 1.73 mmol) as a colorless oil. H
NMR (400 MHz, CDCl3) δ 7.90 (d, J = 8.0 Hz, 2H), 7.41 (d, J = 8.4 Hz, 2H), 7.34 (t, J = 7.2
Hz, 2H), 7.28 (m, 3H), 4.34 (s, 2H), 2.43 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 190.9,
144.3, 137.6, 134.3, 129.3 (2C), 129.0 (2C), 128.6 (2C), 127.4 (2C), 127.3, 33.3, 21.7.
HRMS (ESI) m/z [M + H]+ calcd for C15H15OS
= 243.0844, found 243.0842.
S-Benzyl 4-chlorobenzothioate (6d). Purified by flash column chromatography
(dichloromethane:hexane = 1:2) in 89% yield (470 mg, 1.79 mmol) as a white solid, mp 50–
52 oC. 1H NMR (400 MHz, CDCl3) δ 7.93 (d, J = 8.4 Hz, 2H), 7.44 (d, J = 8.8 Hz, 2H), 7.40
13
(d, J = 7.2 Hz, 2H), 7.35 (t, J = 6.8 Hz, 2H), 7.28 (t, J =8.4 Hz, 1H), 4.35 (s, 2H). C NMR
(100 MHz, CDCl3) δ 190.1, 139.8, 137.2, 135.1, 128.98 (2C), 128.95 (2C), 128.7 (2C), 128.6
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(2C), 127.4, 33.5. HRMS (ESI) m/z [M + H]+ calcd for C14H12ClOS
= 263.0297, found
263.0299.
S-Butyl 4-chlorobenzothioate (6e). Purified by flash column chromatography
1
(dichloromethane:hexane = 1:2) in 86% yield (394 mg, 1.72 mmol) as a colorless oil. H
NMR (400 MHz, CDCl3) δ 7.92 (d, J = 8.8 Hz, 2H), 7.43 (d, J = 8.8 Hz, 2H), 3.10 (t, J = 7.2
Hz, 2H), 1.68 (quint, J = 7.6 Hz, 2H), 1.49 (sextet, J = 7.6 Hz, 2H), 0.97 (t, J = 7.2 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ 190.9, 139.6, 135.6, 128.8 (2C), 128.5 (2C), 31.6, 28.9, 22.1,
13.6. HRMS (ESI) m/z [M + H]+ calcd for C11H14ClOS
= 229.0454, found 229.0455.
S-Phenyl butanethioate (6f). Purified by flash column chromatography
1
(dichloromethane:hexane = 1:2) in 94% yield (341 mg, 1.88 mmol) as a colorless oil. H
NMR (400 MHz, CDCl3) 7.46–7.42 (m, 5H), 2.67 (t, J = 7.2 Hz, 2H), 1.79 (sextet, J =7.2 Hz,
2H), 1.03 (t, J = 7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 197.4, 134.5 (2C), 129.3, 129.2
(2C), 128.0, 45.6, 19.1, 13.5. HRMS (ESI) m/z [M + H]+ calcd for C10H13OS
= 181.0687,
found 181.0688.
S-4-Chlorophenyl butanethioate (6g). Purified by flash column chromatography
1
(dichloromethane:hexane = 1:2) in 91% yield (392 mg, 1.82 mmol) as a colorless oil. H
NMR (400 MHz, CDCl3) 7.40 (d, J = 8.4 Hz, 2H), 7.35 (d, J = 8.4 Hz, 2H), 2.67 (t, J = 7.2
Hz, 2H), 1.79 (sextet, J =7.6 Hz, 2H), 1.03 (t, J = 7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3)
δ 196.8, 135.7 (3C), 129.4 (2C), 126.4, 45.6, 19.1, 13.5. HRMS (ESI) m/z [M + H]+ calcd for
C10H12ClOS
= 215.0297, found 215.0299.
S-Benzyl 3-methylbutanethioate (6h). Purified by flash column chromatography
1
(dichloromethane:hexane = 1:2) in 84% yield (352 mg, 1.68 mmol) as a colorless oil. H
NMR (400 MHz, CDCl3) δ 7.32–7.28 (m, 5H), 4.15 (s, 2H), 2.47 (d, J = 7.2 Hz, 2H), 2.21
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(nontet, J = 6.8 Hz, 1H), 0.98 (d, J = 6.8 Hz, 6H). 13C NMR (100 MHz, CDCl3) δ 198.3,
137.8, 128.8 (2C), 128.6 (2C), 127.2, 52.6, 33.2, 26.5, 22.3 (2C). HRMS (ESI) m/z [M + H]+
calcd for C12H17OS
= 209.1000, found 209.1002.
S-p-Tolyl 3-methylbutanethioate (6i). Purified by flash column chromatography
1
(dichloromethane:hexane = 1:2) in 95% yield (398 mg, 1.90 mmol) as a colorless oil. H
NMR (400 MHz, CDCl3) δ 7.31 (d, J = 8.0 Hz, 2H), 7.24 (d, J = 8.0 Hz, 2H), 2.55 (d, J = 6.8
Hz, 2H), 2.40 (s, 3H), 2.25 (nontet, J = 6.8 Hz, 1H), 1.03 (d, J = 6.4 Hz, 6H). 13C NMR (100
MHz, CDCl3) δ 197.4, 139.5, 134.4 (2C), 130.0 (2C), 124.5, 52.3, 26.5, 22.3 (2C), 21.3.
HRMS (ESI) m/z [M + H]+ calcd for C12H17OS
= 209.1000, found 209.1003.
Electronic supplementary material
Electronic Supplementary Material (ESI) available: 1H and 13C NMR spectra of all
compounds. See DOI:
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This research was supported by Basic Science Research Program through the National
Research Foundation of Korea (NRF) funded by the Ministry of Education
(2014R1A1A2057943).
Notes and references
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<Table of Contents>
Esters and thioesters were successfully prepared through oxidative esterification and
thioesterification of corresponding aldehydes in the presence of dibromoisocyanuric acid.