NBS-Mediated Oxygen Transfer Reaction of Carbonyl in Ester: Efficient Synthesis of Benzil–o-carboxylate Derivative From o-Alkynylbenzoate

Article abstract of DOI:10.1002/adsc.201700168

A neighbouring ester group-participated diketonization of o-alkynylbenzoate is described here for the synthesis of benzil-o-carboxylate. Application of the resulting benzil-o-carboxylate in the synthesis of quinoxalines is also reached from o-alkynylbenzoate in an one-pot fashion. This diketonization proceeds smoothly with a high regioselectivity under mild conditions. Importantly, neighbouring group plays an important role in diketonization. A plausible mechanism suggests that a bromo-incoporated isocoumarin cation is described as an intermediate, and the whole process is constituted by NBS-mediated electrophilic 6-endo annulation and oxygen transfer reaction through NBS-mediated oxidative ring-opening. Water serves as a nucleophile of ring-opening. (Figure presented.).

Full text of DOI:10.1002/adsc.201700168

Title: NBS-Mediated Oxygen Transfer Reaction of Carbonyl in Ester:
Efficient Synthesis of Benzil-o-carboxylate Derivative From o-
Alkynylbenzoate
Authors: Sitian Yuan, Yan-Hua Wang, Jinbiao Liu, and Guanyinsheng
Qiu
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201700168
Link to VoR: http://dx.doi.org/10.1002/adsc.201700168

Advanced Synthesis & Catalysis
10.1002/adsc.201700168
UPDATE
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
NBS-Mediated Oxygen Transfer Reaction of Carbonyl in Ester:
Efficient Synthesis of Benzil-o-carboxylate Derivative From o-
Alkynylbenzoate
a,b
b
b
a
Si-Tian Yuan, Yan-Hua Wang, Jin-Biao Liu, * and Guanyinsheng Qiu*
a
College of Biological, Chemical Science and Engineering, Jiaxing University, 118 Jiahang Road, Jiaxing, China
Email: 11110220028@fudan.edu.cn (G.Qiu); Phone: +86-573-83642057; Fax: +86-573-83642057
School of Metallurgical and Chemical Engineering, Jiangxi University of Science and Technology, 86 Hongqi Road,
Ganzhou 341000, China; Email: liujbgood@hotmail.com
b
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
Abstract. A neighbouring ester group-participated other groups (Scheme 1a).[6] Among these
diketonization of o-alkynylbenzoate is described achievements, Br
2
, I , and ICl etc. were
2
here for the synthesis of benzil-o-carboxylate. recognized as efficient electrophiles to trigger 6-
Application of the resulting benzil-o-carboxylate in endo halocyclization to form 4-haloisocoumarins,
the synthesis of quinoxalines is also reached from o- a versatile handle for further structural elaboration.
alkynylbenzoate in an one-pot fashion. This
diketonization proceeds smoothly with a high
However, the above established reactions were
basically carried out in organic solvent. Therefore,
we would like to develop a 6-endo cyclization of
o-alkynylbenzoate in water or co-solvent of water
and organic solvent.
Our initial trials intended to use water as solvent
to realize 6-endo bromocyclization of methyl o-
regioselectivity under mild conditions. Importantly,
neighbouring group plays an important role in
diketonization. A plausible mechanism suggests that a
bromo-incoporated isocoumarin cation is described as
an intermediate, and the whole process is constituted
by NBS-mediated electrophilic 6-endo annulation and
oxygen transfer reaction through NBS-mediated
oxidative ring-opening. Water serves as a nucleophile
of ring-opening.
phenylalkynylbenzoate
1
in the presence of NBS
N-bromosuccinimide) at room temperature
Scheme 1b). To our surprise, this projected
(
(
transformation just provided a trace amount of the
desired 4-bromoisocoumarin 4, with a recovery of
most parts of starting material
compound benzil-o-carboxylate
be observed in a promising isolated yield (17%
yield). We reasoned that the synthesis of benzil-o-
1. A distinctive
Keywords:NBS;Electrophilic Bromocyclization; o-
alkynylbenzoate; Oxidative Ring-opening; Metal-free
3 was pleased to
carboxylate
3 was probably ascribed to a catalyst
and metal-free diketonization of triple bond in o-
phenylalkynylbenzoate
According to the findings from Liu and co-
o-Alkynylbenzoate was a kind of powerful dual-
1
.
[
1-7]
functional building blocks.
Traditionally, this
type of substrates was always employed to
construct isocoumarin derivatives through a 6-
endo cyclization due to its easy accessibility of
the starting materials.To date, three well-
recognized strategies, which were accordingly
concluded as electrophile-mediated 6-endo
[8]
workers,
a gold catalyst/Selectfluor system
enabled the diketonization of o-alkynylbenzoate
for the synthesis of benzil-o-carboxylate.
Mechanism
investigation
suggested
that
neighboring ester group served as a directing
group to assist difluorohydration of triple bond in
o-alkynylbenzoate. The difluorohydrative product
was in situ hydrolyzed into benzil-o-carboxylate.
However, 2-alkynylheteroaryl carboxylate and 2-
alkylethynylbenzoate did not give the desired
products. As we know, the success of Liu's work
resorted to the use of the gold catalyst. However,
our above observation was metal-free, probably
indicating a distinctive mechanism to explain the
[
1,5,6]
cyclization,
Bronsted
acid/Lewis
acid-
[
2-3]
promoted 6-endo cyclization
and transitional-
metal-catalyzed 6-endo cyclization,[ enabled the
4]
synthesis of various isocoumarins under mild
conditions
with
high
efficiency
and
regioselectivity. As one of electrophilic
cyclization, 6-endo halocyclization was initially
investigated by Oliver and Gandour, and was
further developed in perpetuity by Larock and
[
5]
1
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Advanced Synthesis & Catalysis
10.1002/adsc.201700168
synthesis of benzil-o-carboxylate, a versatile reaction of ester carbonyl. As presented in Table
[
9]
synthon .
1, NBS was the best choice among I
2
, Br , NIS
2
Additionally, I
2
or ICl-mediated diketonization of and NCS (entries 1-7, Table 1). Pleasingly,
triple bond in o-alkynylbenzaldehyde was already treating the model reaction of 1a with 2.1 NBS in
witnessed by Srinivasan and co-workers for the a co-solvent (DCE:H
2
O, v/v = 1:1) at room
In the temperature provided benzil-o-carboxylate 3a in
neighboring aldehyde group- moderate yield (46% yield) as well as 4-
participated 6-endo cyclization and water- bromoisocoumarin in 11% yield (entry 7, Table
attacked oxidative ring opening were involved. 1), with recovery of the starting material 1a
[
10]
synthesis of tricarbonyl compounds.
reaction,
a
4
.
Here oxygen in aldehyde carbonyl of o- Consequently, increase of reaction temperature
alkynylbenzaldehyde already transferred into was then explored with a wish to improve
triple bond to produce one of keto carbonyl. reaction efficiency. As expected, the desired
However, I
compatible
2
or ICl/water reaction system was not benzil-o-carboxylate 3a was afforded in 71%
for diketonization of o- yield as well as the formation of 4-
in 12% yield when the
alkynylbenzoate for the synthesis of benzil-o- bromoisocoumarin
4
o
carboxylate. model reaction was performed at 50 C (entry 8,
Inspired by what mention above, it seemed that it Table 1). Further increase of reaction temperature
was highly desirable to optimize the reaction was favorable for improving reaction efficiency
presented in Scheme 1b. It was believed that the and chem-selectivity. When the model reaction
o
procedure in Scheme 1b represented a metal-free was conducted at 80 C, the desired benzil-o-
diketonization of o-alkynylbenzoate, which carboxylat 3a was produced in 90% yield and the
served as a supplement of the previous side product 4-bromoisocoumarin
4
was reduced
[
8,10,11]
works.
In the process,
a
plausible into 5% yield (entry 9, Table 1). Subsequently,
mechanism involving oxygen transfer of carbonyl solvent effect was also examined accordingly.
in ester was proposed[ .As illustrated in Scheme From screening results, it seemed that water was
11]
1
b, the above diketonization went through a NBS- essential for this oxygen transfer reaction. A
mediated 6-endo cyclization with the formation of blank reaction using DCE as a solvent uniquely
bromo-incorporated isocoumarin cation offered 4-bromoisocoumarin in 65% yield
followed by water-based nucleophilic addition (entry 13, Table 1). Other co-solvents including
and oxidative ring-opening. The resulting MeCN:H O, DMF:H O, and THF:H O gave
dibromohydrative intermediate was in situ inferior yields and chem-selectivity (entries 10-12,
hydrolyzed into benzil-o-carboxylate. It was Table 1). Changing ratio between DCE and H
noteworthy that oxygen of ester carbonyl in from 5:1 to 1:5 indicated that DCE:H O (1:1, v/v)
A
,
4
2
2
2
B
2
O
2
starting material transferred into triple bond to was the best choice (entries 14-15, Table 1).
form one of keto carbonyl group.
Table 1.Initial studies for the reaction of neibouring group-
participated dibromohydration of 2-alkynylbenzoate.
+
En
try
1
[X ]
(2.1 equiv)
NBS
Temp
(℃)
rt
Yield
(3a, %)
17
Yield
(4, %)
trace
22
Solvent
a,
a
H
2
2
O
O
2
I
2
H
rt
0
MeCN:H
2
O
O
3
4
5
I
2
rt
rt
rt
0
0
47
trace
11
(1:1, v/v)
Br
2
2
H O
DCE : H
2
NBS
NIS
46
(1:1, v/v)
DCE : H
2
O
6
7
8
9
rt
41
37
71
90
79
14
9
(1:1, v/v)
DCE : H
2
O
NCS
NBS
NBS
NBS
rt
(1:1, v/v)
DCE : H
2
O
50
80
80
12
5
(1:1, v/v)
Scheme 1.Proposed route for the synthesis of benzil-o-
carboxylate
DCE : H
2
O
(1:1, v/v)
Initial trials were focused on finding efficient
electrophile to promote the above oxygen transfer
2
MeCN : H O
1
0
14
(1:1, v/v)
2
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Advanced Synthesis & Catalysis
10.1002/adsc.201700168
DMF : H
2
O
phenylethynyl-linked benzil-o-carboxylate 3o in
68% yield. This result was supportive for the fact
that neighboring ester group was required in this
diketonization for the synthesis of benzil-o-
carboxylate. The dibromo function survived under
1
1
NBS
80
trace
35
(1:1, v/v)
2
THF : H O
1
1
1
1
2
3
4
5
NBS
NBS
NBS
NBS
80
80
80
80
85
trace
52
10
65
30
25
(
1:1, v/v)
DCE
DCE : H
standard
conditions
when
methyl
methyl
2-
2-
2
O
ethynylbenzoate
and
(5:1, v/v)
(
trimethylsilyl)ethynylbenzoate were employed as
DCE : H
2
O
the starting materials, releasing methyl 2-(2,2-
dibromoacetyl)benzoate 3s in moderate yields. It
was noteworthy that oxygen of carbonyl ester in
starting materials was transferred into the internal
carbon of triple bond to form a new keto carbonyl.
64
(1:5, v/v)
a)
b)
Isolated yield based on 2-alkynylbenzoate 1a. Standard
conditions: 2-alknylbenzoate 1a (0.2 mmol), NBS (2.1
equiv), solvent (2 mL). DCE = 1, 2-dichloroethane; NIS =
N-iodosuccinimide; NCS = N-chlorosuccinimide.
This was probably attributed to a 5-exo-dig
cyclization[
6a,12]
and water-attacked oxidative
With the optimized conditions (entry 9, Table 1)
in hand, we then explored the generality of our
method. The results were illustrated in Scheme 2.
From the results, an array of benzil-o-
ring-opening. In light of the above results, it was
believed that diketonization of o-alknylbenzoate
developed here represented a supplementary for
Liu's work since we expanded the diketonization
of the substrates failed in Liu's work.
carboxylates
3 were achieved accordingly. For
example, the reactions using substrates 1b-1d
Scheme2.Generation of benzil-o-carboxylate 3 through
with methyl, bromo, and ester group attached on
1
neighboring
alkynylbenzoate 1
ester
participated
reaction
of
o-
R site provided the corresponding products 3b-
[
a]
3
d in good to excellent yields. Particularly,
Interestingly, o-alkynylnicotinate 1e was an
efficient reaction partner, leading to the desired
product 3e in 85% yield. Furthermore, o-
alkynylcyclohex-1-ene-1-carboxylate 1f was
compatible for the reaction, with the formation of
the product 3f in 79% yield. Interestingly, by the
previous pathway the substrates (such as 3e and
3f) did not produced the corresponding benzil-o-
[
8]
carboxylate.
Subsequently, we explored the influence of the R
2
substituent. From the results, it seemed that the
reactions using the substrates with aryl or
2
heteroaryl on R were more favorable than these
of the substrates with alkyl. For instance, under
standard conditions the reactions of methyl 2-
(
naphthalen-1-ylethynyl)benzoate and methyl 2-
thiophen-2-ylethynyl)benzoate gave rise to
(
benzil-o-carboxylate 3m and 3n in 86% and 89%
yields, respectively, while the reaction of methyl
2
7
-(cyclopropylethynyl)benzoate produced 3p in
8% yield. The alkyl-connected benzil-o-
carboxylates (such as 3p and 3q) were not
[
8]
achieved
by
the
previous
procedure .
Additionally, electronic effect of aryl substituent
2
on R made slight impact on the reactions'
outcomes. 4-chlorophenyl, 4-fluorophenyl, 4-
methylphenyl, and 4-pentylphenyl-connected
substrates provided the corresponding benzil-o-
carboxylates 3g-3j in similar yields. Effect of
2
steric hinderance on R substituent was also
2
detected. Interestingly, the steric hinderance of R
substituent did not make significant impact on the
reactions' yields. For example, the reactions of the
substrates with 4-methoxylphenyl and 2-
methoxylphenyl offered the corresponding
products 3k and 3l in similar yields. Interestingly,
methyl 2-(phenylbuta-1,3-diyn-1-yl)benzoate was
effective under standard conditions, producing
[a]Based on
2-alkynylbenzoate
2
(0.2 mmol), NBS (2.1 equiv), DCE:H O
1
;[b] Standard
Conditions:
1
o
(
v/v = 1:1, 2 mL), 80 C, 14-16 hrs.
Various benzoates were also tested. Benzyl
benzoate and allylic benzoate were efficient
3
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Advanced Synthesis & Catalysis
10.1002/adsc.201700168
reaction partners, leading to the corresponding
8
could be achieved in an one-pot fashion from o-
benzil-o-carboxylates 3t and 3u in good yields. alkynylbenzoate
1
, avoiding isolation of benzil-o-
intermediate. To our delight, this
phenylethynylbenzoate 1v did not product benzil- one-pot procedure worked well by adding 1.2
o-carboxylate, but a 4-bromoisocoumarin in equiv 1,2-diamine after completion of
9% yield (Scheme 3), probably due to relatively diketonization of o-alkynylbenzoate . The
less instability of phenyl-connected 4- condensation of in situ generated benzil-o-
bromoisocoumarin cation intermediate. carboxylate with 1,2-diamine proceeded
However, we found that the reaction of phenyl 2- carboxylate
3
4
7
7
1
7
smoothly without any catalyst at room
temperature. As shown in Scheme 4, a number of
Scheme 3. Effect on different neighboring groups [a]
o-alkynylbenzoate
compatible for the condensation, delivering an
array of quinoxalines in moderate to good yields.
1 and 1,2-diamine 7 could be
8
To understand the reaction, several control
experiments were carried out (Scheme 5). Firstly,
we would like to identify the role of neighboring
ester group. The reactions using the substrate
without neighboring ester group and the substrate
with meta ester group were then ran.
Disappointingly, either the reaction of
9 or the
reaction of 10 did not give the corresponding
diketone compounds, and the both reactions
became complex under standard conditions
(
Scheme 5a). Secondly, we wanted to identify the
role of water. Therefore, the reaction of 2-(4-
methoxylphenyl)ethynylbenzoate 1k in
(v/v, 1:1) was carried out. The
[
a]
Based on 2-alkynylbenzoate 1.
By altering neighboring group to aldehyde and
ketone group, the neighboring carbonyl group-
participated diketonization of triple bonds took
place with the formation of tricarbonyl compound
1
8
DCE:H O
2
1
8
reaction provided benzil-o-carboxylate 3k-O in
8
6% yield. Electrospray ionization mass
18
[
9]
spectroscopic analysis of the product 3k-O
5
and 6 in moderate to good yields (Scheme 3).
showed a strong signal at [M+H] = 303,
However, the reaction of 2-alkynylbenzoic acid
did not the desired benzil-o-carboxylic acid (data
not shown in Scheme 3).
1
8
suggesting two equivalent
H
2
O
being
incorporated into 3k. To clarify exact site of
1
8
oxygen-18, the condensation of 3k-O with
benzene-1,2-diamine was conducted. The reaction
offered the desired quinoxaline 8g in 72% yield.
Electrospray ionization mass spectroscopic
analysis showed the product 8g contained one
oxygen-18, whose [M+H] was equal to 373
Scheme 4. The reaction of benzil-o-carboxylate with
1
,2-diamine[
a]
(
Scheme 5b). The above information implied that
two equivalent water were installed into
diketonization of o-alkynylbenzoate. One of them
was incorporated into ester group of benzil-o-
carboxylate, and the other was installed into triple
bond to form one of carbonyl group in benzil-o-
carboxylate.
In light of the above results, a plausible mechanism
was proposed in Scheme 2. As illustrated in Scheme 2,
this reaction went through
a
NBS-promoted
electrophilic annulation and water-attacked oxygen
transfer reaction. In the process, bromo-incorporated
isocoumarin cation A, generated from NBS-mediated
[
a]
; [b] Condensation was
Based on 2-alkynylbenzoate
1
6
-endo-dig annulation, was postulated as a key
o
conducted at 50 C
intermediate. Two possibility probably happened to
the intermediate A. First of them was removal of an
alcohol to afford isocoumarin 4. Otherwise, water
served as a nucleophile to attack ester cation in
intermediate A to form an intermediate B. The
Additionally, application of the resulting benzil-o-
carboxylate in organic synthesis was then
explored. Considering importance of quinoxaline
core in organic, medicine and material
chemistry ,we explored condensation of benzil-
o-carboxylate with 1,2-diamine . To reduce
reaction cost, we envisioned that the quinoxalines
3
intermediate
B
was readily converted into
[
13]
dibromohydrative product C through NBS-mediated
[14]
oxidative ring-opening.
oxygen in ester group was transferred into triple bond
It was noteworthy that
7
4
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Advanced Synthesis & Catalysis
10.1002/adsc.201700168
to form a carbonyl. The resulting dibromohydrative
product C was hydrolyzed into the final benzil-o-
carboxylate 3. Therefore, two keto carbonyl in final
product were derived from different sources. One of
them was from ester by oxygen transfer reaction, and
another came from water by hydrolysis.
Experimental Section
General procedure for the synthesis of compound 3.
-alkynylbenzoate1(0.2 mmol), NBS (2.1 equiv) were
added to a test tube, and then co-solvent DCE:H O (v/v
1:1, 2 mL) was added. The mixture was stirred at 80 C
2
2
=
for 14-16 h. After completion of reaction as indicated by
TLC, the mixture was filtrated and the resulting filtrate was
dried by Na SO . Then filtration again, evaporation of the
2 4
solvent and purification by flash column chromatograph
provided the desired product 3. The final products 5 and 6
were also synthesized according to the above procedure.
General procedure for the synthesis of compound 8.
2
-alkynylbenzoate1(0.2 mmol), NBS (2.1 equiv) were
added to a test tube, and then co-solvent DCE:H O (v/v
1:1, 2 mL) was added. The mixture was stirred at 80 C
2
=
for 14-16 h. After completion of reaction as indicated by
TLC, aryl-1,2-diamine 7 (0.2 mmol) was added. The
mixture was stirred at room temperature for 6-8 h. After
completion of reaction as indicated by TLC,the mixture
2 4
was filtrated and the resulting filtrate was dried by Na SO .
Then filtration again, evaporation of the solvent and
purification by flash column chromatograph provided the
desired product 8.
Methyl 2-(2-oxo-2-phenylacetyl)benzoate (3a)[8a]( yellow
powder, 48.3 mg, 90%)
1
H NMR (400 MHz, CDCl
3
) δ 8.27 – 8.11 (m, 1H), 8.10 –
7
3
1
1
.96 (m, 1H), 7.79 – 7.59 (m, 4H), 7.59 – 7.45 (m, 3H),
.66 (s, 3H); C NMR (100 MHz, CDCl ) δ 193.64, 188.98,
3
66.86, 138.73, 133.92, 133.10, 132.95, 131.64, 130.80,
30.09, 129.71, 129.49, 128.46, 52.75.
13
Methyl 5-methyl-2-(2-oxo-2-phenylacetyl)benzoate (3b)
Light yellow liquid, 48.0 mg, 85%)
(
1
H NMR (400 MHz, CDCl
3
) δ 8.22 – 8.13 (m, 2H), 7.80 (s,
1
2
H), 7.70 – 7.59 (m, 2H), 7.57 – 7.44 (m, 3H), 3.63 (s, 3H),
.47 (s, 3H); C NMR (100 MHz, CDCl ) δ 193.51, 189.34,
3
13
1
1
67.03, 142.67, 135.32, 133.84, 133.48, 133.04, 130.69,
30.38, 130.32, 129.87, 128.42, 52.58, 21.44; HRMS (ESI)
+
+
15 4
calcd for C17H O : 283.0965 (M +H), found: 283.0973
Scheme 5.Control experiments and possible mechanism.
Methyl 5-bromo-2-(2-oxo-2-phenylacetyl)benzoate (3c)
Light yellow liquid, 63.9 mg, 92%)
(
In conclusion, we have developed a neighbouring
ester group-participated metal-free diketonization of
o-alkynylbenzoate for the synthesis of benzil-o-
carboxylate. Application of the resulting benzil-o-
carboxylate in the synthesis of quinoxalines was also
accomplished in an one-pot fashion. This
diketonization proceeded smoothly with a high
regioselectivity under mild conditions. Importantly,
neighbouring group played an important role in
diketonization. Mechanism studies suggested that a
bromo-incoporated isocoumarin cation was described
as an intermediate and the whole process was
constituted by NBS-mediated electrophilic 6-endo
annulation and oxygen transfer reaction through NBS-
mediated oxidative ring-opening. Water served as a
nucleophile of ring-opening.
1
H NMR (400 MHz, CDCl
3
) δ 8.27 – 8.12 (m, 3H), 7.97 –
7
3
.75 (m, 1H), 7.71 – 7.61 (m, 1H), 7.59 – 7.50 (m, 3H),
.68 (s, 3H); C NMR (100 MHz, CDCl ) δ 192.57, 188.68,
3
13
1
1
65.63, 137.35, 136.04, 134.05, 132.73, 132.68, 131.55,
31.13, 130.76, 128.47, 126.17, 53.01; HRMS (ESI) calcd
+
+
4
for C16H12BrO : 346.9913 (M +H), found: 346.9914
Dimethyl
2-(2-oxo-2-phenylacetyl)terephthalate
(3d)
(
Light yellow liquid, 50.9 mg, 78%)
1
H NMR (400 MHz, CDCl
3
) δ 8.33 (d, J = 1.5 Hz, 1H),
8
.28 (dd, J = 8.1, 1.7 Hz, 1H), 8.22 – 8.19 (m, 2H), 8.08 (d,
J = 8.1 Hz, 1H), 7.75 – 7.62 (m, 1H), 7.60 – 7.52 (m, 2H),
3
1
1
5
.97 (s, 3H), 3.70 (s, 3H); 13C NMR (100 MHz, CDCl
92.49, 188.61, 166.16, 165.28, 139.02, 134.26, 134.08,
3
) δ
32.96, 132.73, 132.40, 131.04, 130.80, 129.82, 128.49,
+
3.03, 52.71; HRMS (ESI) calcd for C18
H
15
O
6
: 327.0863
+
(
M +H), found: 327.0863
5
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Advanced Synthesis & Catalysis
10.1002/adsc.201700168
Ethyl 2-(2-oxo-2-phenylacetyl)nicotinate (3e) (Light Methyl 2-(2-(4-methoxyphenyl)-2-oxoacetyl)benzoate (3k)
yellow liquid, 48.2 mg, 85%) (Light yellow liquid, 48.9 mg, 82%)
1
1
H NMR (400 MHz, CDCl
3
) δ 8.79-8.78 (m, 1H), 8.13 (dd,
3
H NMR (400 MHz, CDCl ) δ 8.35 – 8.16 (m, 2H), 7.99 (d,
J = 7.8, 1.4 Hz, 1H), 7.76 (d, J = 8.1 Hz, 2H), 7.47 – 7.33 J = 7.8 Hz, 1H), 7.77 – 7.66 (m, 2H), 7.67 – 7.51 (m, 1H),
1
3
(
m, 2H), 7.25 (m, 2H), 4.23 (q, J = 7.1 Hz, 2H), 1.26 (t, J = 7.08 – 6.96 (m, 2H), 3.91 (s, 3H), 3.66 (s, 3H); C NMR
13
7
1
1
C
.1 Hz, 3H); C NMR (100 MHz, CDCl
3
) δ 185.28, 165.19, (100 MHz, CDCl
3
) δ 194.05, 187.69, 166.82, 164.23,
55.88, 150.90, 139.55, 132.51, 132.02, 130.59, 127.88, 138.85, 133.19, 132.87, 131.45, 130.02, 129.60, 125.93,
24.71, 124.23, 62.25, 13.96; HRMS (ESI) calcd for 113.82, 55.52, 52.62. HRMS (ESI) calcd for C17
+
H
15
O
5
:
+
+
+
16
H
14NO
4
: 284.0917 (M +H), found: 284.0921
299.0914 (M +H), found: 299.0916
Ethyl 2-(2-oxo-2-phenylacetyl)cyclohex-1-enecarboxylate Methyl 2-(2-(2-methoxyphenyl)-2-oxoacetyl)benzoate (3l)
3f) (Light yellow liquid, 45.2 mg, 79%) (Light yellow liquid, 47.7 mg, 80%)
(
1
1
H NMR (400 MHz, CDCl
3
) δ 8.17-8.15 (m, 2H), 7.63 –
3
H NMR (400 MHz, CDCl ) δ 7.97-7.96 (m, 1H), 7.82 –
7
2
3
1
2
C
.58 (m, 1H), 7.53 – 7.45 (m, 2H), 4.03 (q, J = 7.2 Hz, 2H), 7.72 (m, 2H), 7.71 – 7.49 (m, 3H), 7.20 – 7.07 (m, 1H),
.50 – 2.36 (m, 4H), 1.80– 1.70 (m, 4H), 1.14 (t, J = 7.1 Hz, 6.97 (d, J = 8.4 Hz, 1H), 3.80 (s, 3H), 3.73 (s, 3H); 13
C
13
H); C NMR (100 MHz, CDCl
3
) δ 195.60, 188.79, 167.34, NMR (100 MHz, CDCl
3
) δ 191.83, 191.25, 168.29, 160.05,
49.44, 133.66, 132.97, 131.21, 130.81, 128.27, 61.40, 135.68, 134.02, 132.39, 132.35, 131.44, 131.26, 130.76,
8.74, 24.58, 21.40, 21.26, 14.00; HRMS (ESI) calcd for 129.09, 123.53, 121.00, 112.17, 55.81, 52.59; HRMS (ESI)
+
+
+
+
17
H
19
O
4
: 287.1278 (M +H), found: 287.1280
15 5
calcd for C17H O : 299.0914 (M +H), found: 299.0916
Methyl 2-(2-(4-chlorophenyl)-2-oxoacetyl)benzoate (3g) Methyl 2-(2-(naphthalen-1-yl)-2-oxoacetyl)benzoate (3m)
Light yellow liquid, 55.7 mg, 92%) (yellow liquid, 54.8 mg, 86%)
(
1
1
H NMR (400 MHz, CDCl
3
) δ 8.15 (d, J = 8.6 Hz, 2H),
3
H NMR (400 MHz, CDCl ) δ 8.79 (d, J = 8.4 Hz, 1H),
8
8
1
.02 (d, J = 7.7 Hz, 1H), 7.78 – 7.58 (m, 3H), 7.51 (d, J = 8.47 (d, J = 7.3 Hz, 1H), 8.12 (d, J = 8.2 Hz, 1H), 8.03 (d, J
1
3
.6 Hz, 2H), 3.71 (s, 3H). C NMR (100 MHz, CDCl
3
) δ = 7.6 Hz, 1H), 7.93 (d, J = 7.8 Hz, 1H), 7.85 – 7.39 (m,
13
93.48, 187.71, 166.89, 140.35, 138.81, 133.18, 132.16, 6H), 3.72 (s, 3H); C NMR (100 MHz, CDCl ) δ 193.74,
3
1
31.61, 131.42, 129.97, 129.66, 129.32, 128.79, 52.80; 190.99, 167.10, 138.72, 134.53, 134.35, 133.92, 132.89,
+
+
HRMS (ESI) calcd for C16
H
12ClO
4
: 303.0419 (M +H), 131.57, 131.46, 130.22, 130.09, 129.54, 128.73, 128.62,
found: 303.0420
128.41, 126.39, 125.37, 124.42, 52.78; HRMS (ESI) calcd
for C20H O : 319.0965 (M +H), found: 319.0966
15 4
+
+
Methyl 2-(2-(4-fluorophenyl)-2-oxoacetyl)benzoate (3h)
Light yellow liquid, 49.2 mg, 86%)
(
Methyl 2-(2-oxo-2-(thiophen-2-yl)acetyl)benzoate (3n)
3
) δ 8.36 – 8.17 (m, 2H), 8.02 (d, (Light yellow liquid, 48.8 mg, 89%)
1
H NMR (400 MHz, CDCl
J = 7.7 Hz, 1H), 7.77 – 7.53 (m, 3H), 7.26 – 7.14 (m, 2H),
3
1
1
H NMR (400 MHz, CDCl
) δ 193.66, 187.41, J = 7.8 Hz, 1H), 7.82-7.80 (m, 1H), 7.73 – 7.58 (m, 3H),
66.90, 166.19 (d, J = 254.9 Hz), 138.90, 133.59 (d, J = 9.5 7.31 – 7.19 (m, 1H), 3.70 (s, 3H); 13C NMR (100 MHz,
3
) δ 8.27-8.26 (m, 1H), 8.02 (d,
13
.70 (s, 3H); C NMR (100 MHz, CDCl
3
3
Hz), 133.18, 131.60, 129.98, 129.67, 129.42 (d, J = 3.0 Hz), CDCl ) δ 193.30, 180.35, 166.60, 138.48, 138.12, 136.76,
1
29.34, 115.70 (d, J = 21.8 Hz), 52.80; HRMS (ESI) calcd 136.33, 133.00, 131.36, 129.66, 129.55, 129.38, 128.47,
+
+
+
for C16
H
12FO
4
: 287.0714 (M +H), found: 287.0709
52.63; HRMS (ESI) calcd for C14
H
11
O
4
S : 275.0373
+
(
M +H), found: 275.0374
Methyl 2-(2-oxo-2-(p-tolyl)acetyl)benzoate (3i) (Light
yellow liquid, 50.2 mg, 89%)
H NMR (400 MHz, CDCl ) δ 8.11 (d, J = 8.2 Hz, 2H), (yellow liquid, 39.7 mg, 68%)
3
Methyl
2-(2-oxo-4-phenylbut-3-ynoyl)benzoate
(3o)
1
1
8
.00 (d, J = 7.6 Hz, 1H), 7.69 (d, J = 4.1 Hz, 2H), 7.66 –
H NMR (400 MHz, CDCl
3
) δ 8.05 (d, J = 7.8 Hz, 1H),
7
3
.60 (m, 1H), 7.34 (d, J = 8.0 Hz, 2H), 3.65 (s, 3H), 2.46 (s, 7.77 – 7.59 (m, 4H), 7.58 – 7.47 (m, 2H), 7.46 – 7.38 (m,
H); C NMR (100 MHz, CDCl ) δ 193.80, 188.72, 166.83, 2H), 3.90 (s, 3H); C NMR (100 MHz, CDCl ) δ 190.34,
3 3
13
13
1
1
45.01, 138.74, 132.99, 131.57, 130.89, 130.44, 130.09, 174.85, 166.55, 137.68, 133.79, 133.29, 131.46, 129.62,
29.67, 129.57, 129.23, 52.69, 21.92; HRMS (ESI) calcd 129.13, 128.67, 119.54, 98.21, 86.30, 52.96; HRMS (ESI)
+
+
+
+
for C17
H
15
O
4
: 283.0965 (M +H), found: 283.0969
calcd for C18
H
13
O
4
: 293.0808 (M +H), found: 293.0810
Methyl 2-(2-oxo-2-(4-pentylphenyl)acetyl)benzoate (3j) Methyl
2-(2-cyclopropyl-2-oxoacetyl)benzoate
[
8a]
(
Light yellow liquid, 61.6 mg, 91%)
(3p) ( yellow liquid, 36.2 mg, 78%)
1
1
H NMR (400 MHz, CDCl
3
) δ 8.12 (d, J = 8.3 Hz, 2H),
3
H NMR (400 MHz, CDCl ) δ 7.98 (d, J = 7.7 Hz, 1H),
8
1
.00 (d, J = 7.6 Hz, 1H), 7.69-7.68 (m, 2H), 7.66 – 7.55 (m, 7.69 – 7.63 (m, 1H), 7.61 – 7.55 (m, 1H), 7.54 – 7.49 (m,
13
H), 7.35 (d, J = 8.3 Hz, 2H), 3.65 (s, 3H), 2.70 (t, J = 7.8 1H), 3.86 (s, 3H), 2.93 (s, 1H), 1.20 – 1.14 (m, 4H); C
) δ 198.49, 193.34, 166.80, 138.41,
) δ 193.83, 133.05, 131.05, 129.60, 129.35, 128.89, 52.72, 16.06,
Hz, 2H), 1.76 – 1.58 (m, 2H), 1.41 – 1.30 (m, 4H), 0.91 (t, NMR (100 MHz, CDCl
J = 6.9 Hz, 3H); C NMR (100 MHz, CDCl
3
1
3
3
1
1
3
C
88.76, 166.85, 149.91, 138.75, 132.97, 131.55, 130.91, 13.19.
30.61, 130.08, 129.66, 129.59, 128.59, 52.68, 36.20,
1.49, 30.74, 22.53, 14.04; HRMS (ESI) calcd for Methyl 2-(2-oxohexanoyl)benzoate (3q) (Light yellow
+
+
21
H
23
O
4
: 339.1591 (M +H), found: 339.1590
liquid, 35.3 mg, 71%)
6
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Advanced Synthesis & Catalysis
10.1002/adsc.201700168
1H NMR (400 MHz, CDCl
) δ 7.98 (d, J = 7.7 Hz, 1H), Methyl 2-(2-phenylquinoxalin-3-yl)benzoate (8a) (yellow
3
7
.70 – 7.63 (m, 1H), 7.61 – 7.54 (m, 1H), 7.49 (d, J = 7.5 brown solid, 48.3 mg, 71%)
1
Hz, 1H), 3.86 (s, 3H), 3.01 (t, J = 7.4 Hz, 2H), 1.70 – 1.61
H NMR (400 MHz, CDCl
m, 2H), 1.47 – 1.37 (m, 2H), 0.96 (t, J = 7.3 Hz, 3H); C 7.84 (m, 1H), 7.82 – 7.74 (m, 2H), 7.66 – 7.54 (m, 2H),
NMR (100 MHz, CDCl ) δ 199.18, 194.08, 167.07, 138.74, 7.50 – 7.44 (m, 1H), 7.43 – 7.38 (m, 2H), 7.34 – 7.20 (m,
3
) δ 8.27 – 8.11 (m, 2H), 7.86-
13
(
3
1
3
1
2
2
3
33.12, 131.01, 129.39, 129.29, 128.91, 52.77, 36.09, 3H), 3.50 (s, 3H); C NMR (100 MHz, CDCl ) δ 166.87,
4.99, 22.25, 13.87; HRMS (ESI) calcd for C14
49.1121 (M +H), found: 249.1126
+
H
17
O
4
:
154.43, 153.76, 141.32, 140.82, 140.74, 138.25, 132.38,
131.20, 130.33, 130.16, 129.94, 129.79, 129.71, 129.33,
+
1
29.08, 128.79, 128.77, 127.99, 52.10; HRMS (ESI) calcd
+
+
Methyl 2-(2,2-dibromoacetyl)benzoate (3s)
17 2 2
for C22H N O : 341.1285 (M +H), found: 341.1280
1
H NMR (400 MHz, CDCl
.70 – 7.62 (m, 1H), 7.61 – 7.52 (m, 2H), 6.36 (s, 1H), 3.94 Methyl 2-(3-butylquinoxalin-2-yl)benzoate (8b) (yellow
s, 3H). 13C NMR (100 MHz, CDCl
) δ 191.81, 166.15, brown solid, 39.7 mg, 62%)
3
) δ 8.05 (d, J = 7.8 Hz, 1H),
7
(
1
4
(
3
1
37.82, 133.08, 130.70, 130.39, 130.25, 127.39, 53.21,
3
H NMR (400 MHz, CDCl ) δ 8.17 (d, J = 7.9 Hz, 1H),
+
4.24. HRMS (ESI) calcd for C10
H
9
Br
2
O
3
: 334.8913 8.09 (d, J = 8.2 Hz, 1H), 8.04 (d, J = 8.2 Hz, 1H), 7.78 –
7.65 (m, 3H), 7.62 – 7.54 (m, 1H), 7.44 (d, J = 7.6 Hz, 1H),
+
M +H), found: 334.8915
3
.60 (s, 3H), 2.95 – 2.57 (m, 2H), 1.72 – 1.60 (m, 2H), 1.27
13
Benzyl 2-(2-oxo-2-phenylacetyl)benzoate (3t) (yellow – 1.18 (m, 2H), 0.79 (t, J = 7.3 Hz, 3H); C NMR (100
liquid, 61.3 mg, 89%)
H NMR (400 MHz, CDCl
MHz, CDCl
3
) δ 166.54, 156.54, 155.99, 141.33, 140.73,
1
3
) δ 8.25 – 8.16 (m, 2H), 8.07 – 140.20, 132.72, 130.78, 130.19, 129.40, 129.14, 128.96,
8
7
.00 (m, 1H), 7.72 – 7.59 (m, 4H), 7.58 – 7.49 (m, 2H), 128.91, 128.89, 128.64, 52.16, 35.47, 30.45, 22.53, 13.77;
.38 – 7.27 (m, 5H), 5.15 (s, 2H); 1 C NMR (100 MHz, HRMS (ESI) calcd for C20
) δ 193.69, 189.03, 166.46, 139.03, 135.06, 133.80, found: 321.1595
33.09, 133.07, 131.52, 130.82, 130.05, 129.66, 129.62,
28.55, 128.41, 128.36, 128.25, 67.55; HRMS (ESI) calcd Methyl 2-(3-(phenylethynyl)quinoxalin-2-yl)benzoate (8c)
3
+
+
21 2 2
H N O : 321.1598 (M +H),
CDCl
1
1
3
+
+
for C22
H
17
O
4
: 345.1121 (M +H), found: 345.1128
(yellow brown solid, 40.8 mg, 56%)
1
H NMR (400 MHz, CDCl
Allyl 2-(2-oxo-2-phenylacetyl)benzoate (3u) (yellow liquid, 7.70 (m, 3H), 7.69 – 7.60 (m, 2H), 7.40 – 7.27 (m, 5H),
7.1 mg, 80%) ) δ 167.04,
3.63 (s, 3H); 13C NMR (100 MHz, CDCl
) δ 8.28 – 8.15 (m, 2H), 8.07 – 157.02, 140.89, 140.28, 139.38, 139.26, 132.59, 132.14,
3
) δ 8.26 – 8.08 (m, 3H), 7.85 –
4
3
1
H NMR (400 MHz, CDCl
3
8
5
2
1
1
.00 (m, 1H), 7.77 – 7.60 (m, 4H), 7.59 – 7.47 (m, 2H), 131.01, 130.46, 130.36, 130.22, 130.09, 129.54, 129.38,
.94 – 5.78 (m, 1H), 5.30 – 5.16 (m, 2H), 4.64 – 4.57 (m, 129.21, 128.94, 128.35, 121.32, 95.03, 87.15, 52.23;
H); C NMR (100 MHz, CDCl ) δ 193.67, 189.01, 166.24, HRMS (ESI) calcd for C24H N O : 365.1285 (M +H),
3 17 2 2
13
+
+
38.97, 133.84, 133.10, 133.06, 131.55, 131.29, 130.83, found: 365.1290
30.07, 129.67, 129.58, 128.38, 118.96, 66.44; HRMS
+
+
(
ESI) calcd for C18
H
15
O
4
: 295.0965 (M +H), found: Methyl 2-(6,7-dimethyl-2-phenylquinoxalin-3-yl)benzoate
2
95.0973
(8d) (yellow brown solid, 54.5 mg, 74%)
H NMR (400 MHz, CDCl ) δ 7.95 (s, 1H), 7.89 (s, 1H),
3
1
4
-bromo-3-phenyl-1H-isochromen-1-one (4)[6d] (White 7.84 (d, J = 7.8 Hz, 1H), 7.60 – 7.50 (m, 2H), 7.47 – 7.36
powder, 47.6 mg, 79%)
(m, 3H), 7.31 – 7.20 (m, 3H), 3.48 (s, 3H), 2.51 (s, 3H),
1
13
3 3
H NMR (400 MHz, CDCl ) δ 8.35 (d, J = 7.9 Hz, 1H), 2.50 (s, 3H); C NMR (100 MHz, CDCl ) δ 167.01,
7
(
.98 (d, J = 8.1 Hz, 1H), 7.89 – 7.83 (m, 1H), 7.83 – 7.77 153.30, 152.72, 140.93, 140.43, 140.43, 140.26, 139.77,
m, 2H), 7.64 – 7.57 (m, 1H), 7.53 – 7.44 (m, 3H); 13
138.53, 132.17, 131.23, 130.51, 130.12, 129.69, 128.53,
) δ 161.14, 151.81, 136.60, 135.46, 128.52, 128.35, 128.14, 127.94, 52.04, 20.45; HRMS (ESI)
C
NMR (100 MHz, CDCl
1
1
3
+
+
32.76, 130.18, 129.79, 129.66, 129.16, 128.10, 126.65, calcd for C24
20.57, 101.37.
21 2 2
H N O : 369.1598 (M +H), found:369.1601
Methyl 2-(6,7-dichloro-3-phenylquinoxalin-2-yl)benzoate
1
-(2-acetylphenyl)-2-phenylethane-1,2-dione (5)10 (Light (8e) (Brick red solid, 57.1 mg, 70%)
1
yellow liquid, 32.8 mg, 65%)
3
H NMR (400 MHz, CDCl ) δ 8.30 (s, 1H), 8.25 (s, 1H),
1
3
H NMR (400 MHz, CDCl ) δ 8.29 – 8.17 (m, 2H), 7.94 – 7.87-7.85 (m, 1H), 7.63-7.56 (m, 1H), 7.56-7.47 (m, 2H),
7
2
1
1
.89 (m, 1H), 7.76 – 7.61 (m, 4H), 7.58 – 7.51 (m, 2H), 7.38-7.31 (m, 2H), 7.26-7.24 (m, 3H), 3.50 (s, 3H); 13
C
13
.57 (s, 3H); C NMR (101 MHz, CDCl
3
) δ 199.97, 194.03, NMR (100 MHz, CDCl
3
) δ 166.65, 155.69, 154.86, 140.23,
89.27, 138.55, 137.04, 133.89, 133.48, 133.22, 131.43, 140.10, 139.56, 137.58, 134.32, 134.12, 132.51, 131.00,
30.84, 130.33, 129.30, 128.41, 26.60. 130.23, 130.20, 129.95, 129.74, 129.69, 129.23, 128.05,
+
5
2 2 2
2.18; HRMS (ESI) calcd for C22H15Cl N O : 409.0505
-(2-oxo-2-phenylacetyl)benzaldehyde (6)[10] (Light yellow (M +H), found: 409.0510
+
2
liquid, 35.3 mg, 74%)
H NMR (400 MHz, CDCl
Methyl 2-(3-phenylbenzo[g]quinoxalin-2-yl)benzoate (8f)
3
) δ 10.05 (s, 1H), 8.19 (d, J = (Brick red solid, 53.8 mg, )
1
1
8
–
.4 Hz, 2H), 7.96 – 7.89 (m, 1H), 7.80 – 7.69 (m, 3H), 7.69
H NMR (400 MHz, CDCl
7.63 (m, 1H), 7.61 – 7.45 (m, 2H). C NMR (100 MHz, 1H),8.11-8.10 (m, 2H), 7.86 (d, J = 7.7 Hz, 1H), 7.67-7.66
) δ 194.43, 192.47, 189.46, 137.05, 135.81, 134.40, (m, 2H), 7.56-7.47 (m, 2H), 7.47-7.45 (m, 3H), 7.28-7.25
3
) δ 8.77 (s, 1H), 8.72 (s,
1
3
CDCl
34.23, 132.94, 132.42, 132.41, 130.82, 130.65, 128.58.
3
1
(m, 3H), 3.49 (s, 3H); 13C NMR (100 MHz, CDCl
3
) δ
7
This article is protected by copyright. All rights reserved.

Advanced Synthesis & Catalysis
10.1002/adsc.201700168
1
1
1
66.78, 155.43, 154.48, 140.93, 138.32, 137.61, 134.02,
33.87, 132.52, 131.11, 130.32, 129.73, 128.98, 128.92,
28.51, 127.97, 127.69, 127.48, 126.72, 126.69, 52.12;
Aggarwal, A. P. Singh, J. Org. Chem. 2010, 75, 7691;
f) A. K. Verma, T. Aggarwal, V. Rustagi, R. C. Larock,
Chem. Commun. 2010, 46, 4064; g) J. Barluenga,L.
Llavona, M. Yus, J.M. Concellon, Tetrahedron Lett.
1991, 47, 7875.
+
+
HRMS (ESI) calcd for C26
found:391.1441
19 2 2
H N O : 391.1441 (M +H),
[
7]a) G. Dai, J. Chang, J. Luo, S. Dong, N. Aratani, B.
Zheng, K.-W. Huang, H. Yamada, C. Chi, Angew.
Chem., Int. Ed. 2016, 55, 2693; b) M. Alami, F.
Liron, M. Gervais, J.-F. Peyrat, J.-D. Brion, Angew.
Chem., Int. Ed. 2002, 41, 1578; c) H. Kusama, H.
Funami, N. Iwasawa, Synthesis2007, 2014; d) H.
Kusama, H. Funami, J. Takaya, N. Iwasawa, Org.
Lett.2004, 6, 605; e) K, C. Majumdar, I. Ansary, R.
Narayan De, B. Roy, Synthsis, 2011, 2951; f) H.
Yanai, N. Ishii, T. Matsumoto, Chem. Commun.
Acknowledgements
Financial support from the Natural Science Foundation of China
(
No: 21502069 and 21502075), the Natural Science Foundation
of Zhejiang Province (No: LQ15B020006) and the Ph.D.
Scientific Research Starting Foundation of Jiaxing University (No:
7
0515015) is gratefully acknowledged.
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UPDATE
NBS-Mediated Oxygen
Transfer Reaction of
Carbonyl in Ester: Efficient
Synthesis of Benzil-o-
carboxylate Derivative From
o-Alkynylbenzoate
Adv. Synth. Catal.Year, Volume, Page – Page
Si-Tian Yuan, Yan-hua Wang, Jin-Biao Liu,* and
Guanyinsheng Qiu*
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