Synthesis of 5-Aryl-3(2 H)-furanones Using Intramolecular Cyclization of Sulfonium Salts

Article abstract of DOI:10.1021/acs.joc.8b02153

Base-induced intramolecular cyclization of novel (4-aryl-2,4-dioxobutyl)methylphenylsulfonium salts prepared from the commercially available 1-arylethanone by a cost-effective process is described in this paper. The reaction was completed within 10 min to produce a family of 2-unsubstituted 5-aryl-3(2H)-furanones in excellent yield. This procedure is simple, and can be carried out under mild conditions and an ambient atmosphere.

Full text of DOI:10.1021/acs.joc.8b02153

Subscriber access provided by University of Sunderland
Article
Synthesis of 5-Aryl-3(2H)-furanones Using
Intramolecular Cyclization of Sulfonium Salts
Sho Inagaki, Kai Saito, Soichiro Suto, Hiromi Aihara, Aoi Sugawara, Satoru Tamura, and Tomikazu Kawano
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b02153 • Publication Date (Web): 31 Oct 2018
Downloaded from http://pubs.acs.org on November 1, 2018
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 41
The Journal of Organic Chemistry
1
2
3
Synthesis of 5-Aryl-3(2H)-furanones Using Intramolecular Cyclization of Sulfonium Salts
4
5
6
7
8
9
Sho Inagaki*, Kai Saito, Soichiro Suto, Hiromi Aihara, Aoi Sugawara, Satoru Tamura and Tomikazu
Kawano*
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Department of Medicinal and Organic Chemistry, School of Pharmacy, Iwate Medical University, Yahaba,
Iwate 028-3694, Japan
Corresponding author’s e-mail address: shoinaga@iwate-med.ac.jp (Sho Inagaki)
Corresponding author’s e-mail address: tkawano@iwate-med.ac.jp (Tomikazu Kawano)
Table of contents
Abstract
Base-induced intramolecular cyclization of novel (4-aryl-2,4-dioxobutyl)methylphenylsulfonium salts
prepared from the commercially available 1-arylethanone by a cost-effective process is described in this
paper. The reaction was completed within 10 min to produce a family of 2-unsubstituted 5-aryl-3(2H)-
furanones in excellent yield. This procedure is simple, and can be carried out under mild conditions and
an ambient atmosphere.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 2 of 41
1
2
3
4
Introduction
5
6
7
8
9
The 3(2H)-furanone core is a significant subunit present in several natural products and
pharmaceuticals.1 Many techniques have been developed for the synthesis of functionalized 3(2H)-
furanones.2 Among 3(2H)-furanone derivatives, 5-aryl-3(2H)-furanone is an important partial structure
present in biologically active compounds such as polmacoxib,3 hyperolactone C,4 and bullatenone.5 In
addition, 5-aryl-3(2H)-furanones can be used as scaffolds for the synthesis of fluorescent organic dyes.6
Most of the synthetic methods available for 5-aryl-3(2H)-furanones are used to produce 2,2-disubstituted
5-aryl-3(2H)-furanones, and there are very few methods for synthesizing 5-aryl-3(2H)-furanones that are
unsubstituted at the 2-position of the 3(2H)-furanone ring. A few synthetic methods of 5-phenyl-3(2H)-
furanone are reported, for example, the procedure including hydrogenation of isoxazole followed by
intramolecular cyclization (Scheme 1a).6,7a-d Additionally, to our knowledge, the synthesis of 5-
(substituted phenyl)-3(2H)-furanones has been only reported by Bouchet and co-workers (Scheme 1b).7e
Furthermore, these methods have been suffered from some problem to be solved, such as limited substrate
scope and unsatisfactory yield of the desired products. Thus, the development of a novel method for the
preparation of 5-aryl-3(2H)-furanones is an ongoing challenge.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
We have previously reported methods for the synthesis of 5-alkoxy-3(2H)-furanones via the
intramolecular cyclization of sulfonium salts 1 having an ester group at the 3-position (Scheme 1c).8a In
addition, the reaction between an enolate generated by the treatment of sulfonium salt 1 with a base and
various electrophiles furnished various functionalized 3(2H)-furanone derivatives.8a–c Based on these
studies, we expected that using novel sulfonium salts 2 having an aroyl group instead of an ester group at
the 3-position, intramolecular cyclization with the elimination of sulfonio group would efficiently proceed
to give 5-aryl-3(2H)-furanones 3 (Scheme 1d). In this paper, we report an efficient method for the
synthesis of 5-aryl-3(2H)-furanones via the intramolecular cyclization of sulfonium salts. This reaction
is simple to operate and highly productive, and proceeds to completion within 10 min under an ambient
ACS Paragon Plus Environment

Page 3 of 41
The Journal of Organic Chemistry
1
2
3
4
5
6
7
atmosphere.
Scheme 1. Approaches to 5-Aryl-3(2H)-furanones
8
9
(a) Suliman's work6
O
1. H2, Pd-C, MeOH, rt, 6 h
O N
HO
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2. 1 M HCl aq., rt, 4 h
3. neutralization
Ph
O
Ph
62%
(b) Bouchet's work7e
N
S
O
NH2
O
O
Br
O
acetone, rt
or
EtOH, reflux
R
R
10–55%
(c) Our previous work8a
O
Ph
S
O
O
BF4
Ph
t-BuOK
OR
THF
O
OR
1
rt, 1 h
86–99%
(d) This work
O
Me
S
O
O
BF4
Ph
K2CO3
Ar
EtOAc/H2O (4:1)
rt, 10 min
O
Ar
2
3
97%–quant.
Results & Discussion
In starting our study, methods for accessing these substrates have not been reported to date, although a
straightforward preparation of 4-aryl-2,4-dioxobutylsulfonium salt (2) was required. A reaction between
4-bromo-1-phenyl-1,3-butadione 4 and diphenylsulfide (Ph2S) was attempted in the presence of silver (I)
tetrafluoroborate (AgBF4) under our previously reported conditions,8a but a complex mixture was obtained
and it was difficult to isolate the desired sulfonium salt (Scheme 2a). Therefore, we planned a synthetic
route to sulfonium salts involving the S-methylation of asymmetric sulfide 6 as the key step. 1-Aryl-1,3-
butadione 5 was obtained in high yield by Claisen-type condensation between 1-arylethanone and ethyl
acetate (EtOAc) in the presence of 4.0 equiv of sodium hydride (NaH) (Scheme 2b).9 Subsequently,
starting sulfides 6 were prepared in good yields by mono-bromination at the 4-position of the
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 4 of 41
1
2
3
4
5
6
corresponding 1-aryl-1,3-butadiones 5, followed by nucleophilic substitution using sodium
benzenethiolate (PhSNa) (Scheme 2c).10 However, it was difficult to obtain the target sulfides 6 in some
7
8
9
case.
1-Arylethanones, such as 4-nitrophenyl, 4-t-butoxycarbonylaminophenyl and 4-
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
trifluoromethanesulfonyloxyphenyl resulted in complex mixture through the Claisen-type reaction
(Scheme 2b). Furthermore, 1-aryl-1,3-butadiones, such as 4-methanesulfonylphenyl and nitrogen-
containing aromatic rings such as 2-pyrrolyl, 4-pyridinyl and 3-indolyl resulted in complex mixture
through bromination/sulfanylation (Scheme 3c).
Scheme 2. Reaction of 4 and Ph2S and Preparation of Starting Sulfides 6
AgBF4 (1.0 equiv)
Ph2S (5.0 equiv)
O
O
(a)
(b)
complex mixture
Br
Ph
CH2Cl2
rt, 48 h
4
O
O
O
NaH (4.0 equiv)
Ar
1-arylethanone
Ar
EtOAc
rt, 12 h
5
O
O
1. Br2 (1.0 equiv), Et2O, rt, 24 h
(c)
5
S
Ph
Ar
2. PhSNa (1.0 equiv), THF
rt, 30 min, then 60° C, 0.5 h
6
Next, we examined the S-methylation reaction using 1-phenyl-4-(phenylsulfanyl)-1,3-butadione 6a as
the substrate among the resulting sulfides (Table 1). Reaction of sulfide with methyl iodide (MeI) in
acetone at room temperature or under reflux did not produce the desired product 7, and the starting
materials were recovered (entries 1 and 2). We then attempted to use more reactive conditions by the
addition of 1.0 equiv of AgBF4, but the reaction gave a complex mixture (entries 3 and 4). Fortunately,
when more powerful methylating reagents, methyl trifluoromethanesulfonate (MeOTf) and
trimethyloxonium tetrafluoroborate (Me3OBF4), were used, the reaction proceeded successfully.
Among the tested reagents, Me3OBF4 afforded the highest yield of 85% (entry 6).
Table 1. Preparation of Sulfonium Salts 2aa,b
ACS Paragon Plus Environment

Page 5 of 41
The Journal of Organic Chemistry
1
2
3
4
5
6
X
Me
S
O
O
O
O
reagent (1.0 equiv)
PhS
Ph
Ph
Ph
solvent
rt, 12 h
6a
2a
: (X = BF4)
: (X = I)
7
8
7
8
: (X = OTf)
9
entr
additi solve produ yield/
reagent
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
aceto
aceto
aceto
CH2Cl
CH2Cl
CH2Cl
1
2d
3
MeI
7
7
n.r.c
n.r.c
MeI
e
MeI
AgBF4
AgBF4
2a
2a
8
–
e
4
MeI
–
5
MeOTf
Me3OBF4
75
85
6
2a
aReaction conditions: sulfide 6a (3.0 mmol) and reagent (1.0 equiv), additive (1.0 equiv) in solvent (12 mL). MeI = methyl
iodide, MeOTf = methyl trifluoromethanesulfonate, Me3OBF4 = trimethyloxonium tetrafluoroborate. bThe crude product was
purified by recrystallization; the isolated yield is based on 6a. cNo reaction. dThe reaction was performed under reflux
conditions. eComplex mixture.
With the optimized conditions in hand, we attempted to synthesize sulfonium salts bearing a variety of
aromatic rings (Table 2). First, we focused on the conversion of sulfides bearing a number of functional
groups on phenyl moiety into sulfonium salts. Electron-donating groups (6b–6g) as well as electron-
withdrawing groups (6h–6j) on the phenyl ring were tolerant to the reaction conditions, affording the
desired sulfonium salts (2b–2j) in high yields. In addition, the reaction proceeded smoothly without
being influenced by the substituent pattern (6k–6m) and halogen group (6m–6p). Sulfonium salts
having 2-naphthyl (2q), 2,3-dihydro-1,4-benzodioxin-6-yl (2r), and heteroaromatic rings such as 2-furyl
(2s) and 2-thienyl (2t) were also obtained in 89%, 84%, 81%, and 84% yield, respectively. It is
noteworthy that all the resulting sulfonium salts were in the solid state and hence could be purified by
recrystallization from acetonitrile/diethyl ether (2a–2q) or methanol/diethyl ether (2r–2t). Moreover,
the 1H NMR spectrum in acetonitrile-d3 indicated that the sulfonium salts were present almost entirely in
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 41
1
2
3
4
5
6
enol tautomers.
Table 2. Synthesis of Sulfonium Salts 2a,b
7
8
9
BF4
O
O
Me
S
O
O
Me3OBF4 (1.0 equiv)
Ar
CH2Cl2, rt, 12 h
S
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Ph
Ph
Ar
6
2
Me
, 87%
n-Bu
, 88%
Ph
, 90%
2a
2b
2c
2d
, 85%
CF3
2h
, 89%
OMe
, 84%
OPh
OBn
, 85%
2e
2f
2g
, 84%
, 88%
Cl
Cl
CO2Et
, 86%
CN
2i
2j
2k
2o
2s
2l
, 86%
, 85%
Cl
, 83%
F
Br
I
2m
2n
2p
, 85%
, 83%
O
, 84%
S
O
O
, 84%
2q
2r
2t
, 84%
, 89%
, 81%
aReaction conditions: sulfide 6 (3.0 mmol), Me3OBF4 (1.0 equiv) in CH2Cl2 (12 mL). bThe crude product was purified by
recrystallization; the isolated yield is based on 6.
After establishing a novel procedure for the preparation of sulfonium salts, we focused on intramolecular
cyclization using sulfonium salt 2a as the model substrate (Table 3). Although the reaction was
completed within 1 h using 1.0 equiv of potassium t-butoxide (t-BuOK) under our previously reported
conditions,8a the cyclized product 3a was obtained in only 33% yield, and longer reaction time was found
to be less effective (entries 1 and 2). The use of other bases such as 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU), DMAP, trimethylamine (Et3N), N,N-diisopropylethylamine (DIPEA), and potassium bicarbonate
(K2CO3) also gave the desired products in low yields (entries 3–7). Next, solvent effects on the
ACS Paragon Plus Environment

Page 7 of 41
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
intramolecular cyclization were examined. N,N-dimethylformamide (DMF), which is a polar aprotic
solvent, afforded 3a in 90% yield (entry 11). Further investigation revealed that polar protic solvents
dramatically accelerated the reaction. When methanol was used, the reaction was completed within 10
min, but the yield of 3a decreased slightly in comparison with that obtained by using DMF (entry 12).
Furthermore, the reaction proceeded more efficiently in the presence of water than in the presence of
methanol and gave 3a in 90% yield, similar to the case of DMF (entry 13). Considering these results,
we carefully examined solvent systems containing water. After optimization, we found that the reaction
in EtOAc/H2O = 4:1 (v/v), which is a heterogeneous solvent system, furnished 3a in an excellent yield of
99% (entry 16). Incidentally, the use of sodium hydroxide (NaOH) or potassium hydroxide (KOH)
instead of K2CO3, or the reaction in homogeneous solvent systems such as THF/H2O = 4:1 (v/v) resulted
in somewhat lower yields (entries 17–19).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 3. Optimization of Intramolecular Cyclizationa,b
O
BF4
Me
S
O
O
base (1.0 equiv)
Ph
solvent, time
Ph
O
Ph
2a
3a
entr
yield/
base
solvent
time
y
(%)
1
t-BuOK
t-BuOK
DBU
THF
1 h
12 h
1 h
33
2
3
THF
32
25
39
40
38
40
16
4
THF
4
DMAP
Et3N
THF
1 h
5
THF
1 h
6
DIPEA
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
THF
1 h
7
THF
1 h
8
CH2Cl2
CHCl3
MeCN
DMF
MeOH
1 h
9
1 h
10
11
12
1 h
20
90
82
1 h
10 min
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 41
1
2
3
4
5
6
7
8
9
13
14
15
16
17
18
19
K2CO3
K2CO3
K2CO3
K2CO3
NaOH
KOH
H2O
10 min
90
90
92
99
92
94
95
EtOAc/ H2O (1:4) 10 min
EtOAc/ H2O (1:1) 10 min
EtOAc/H2O (4:1)
EtOAc/H2O (4:1)
EtOAc/H2O (4:1)
THF/H2O (4:1)
10 min
10 min
10 min
10 min
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
K2CO3
aReaction conditions: sulfonium salt 2a (0.2 mmol) and base (1.0 equiv) in solvent (2 mL).
DBU = 1.8-
diazabicyclo[5.4.0]undec-7-ene, DMAP = 4-(dimethylamino)pyridine, DIPEA = N,N-diisopropylethylamine, THF =
tetrahydrofuran, MeCN = acetonitrile, DMF = N,N-dimethylformamide. bThe residue was purified by silica gel column
chromatography; the isolated yield is based on 2a.
Next, we investigated the scope of the intramolecular cyclization (Table 4). Sulfonium salts bearing
electron-donating groups and electron-withdrawing groups on the phenyl ring successfully underwent
intramolecular cyclization to give the corresponding 5-aryl-3(2H)-furanones (3b–3j) in excellent yields.
Moreover, the reaction was successful for various types of halogen-substituted phenyl rings (Table 4, 3k–
3p). Furthermore, 3(2H)-furanone derivatives having 2-napthyl (3q), 2,3-dihydro-1,4-benzodioxin-6-yl
(3r), 2-furyl (3s), and 2-thienyl (3t) were obtained in excellent yields. Notably, all the reactions were
completed within 10 min under an ambient atmosphere, resulting in an almost quantitative yield of the
products.
ACS Paragon Plus Environment

Page 9 of 41
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
Table 4. Intramolecular Cyclization of Sulfonium Salts 2a,b
O
Me
S
O
O
BF4
Ph
K2CO3 (1.0 equiv)
Ar
EtOAc/H2O = 4:1
rt, 10 min
O
Ar
2
3
9
O
O
O
O
O
O
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
O
O
O
O
Me
n-Bu
Ph
OMe
3a
3b
3c
3d
3e
, 97%
, 99%
, 97%
, 99%
, 98%
O
O
O
O
O
O
O
O
O
O
O
O
CO2Et
CF3
OPh
OBn
Cl
CN
3f
3g
3h
3i
3j
, 99%
, quant.
Cl
, 99%
, 98%
, 99%
O
O
O
O
O
O
O
O
Cl
F
Br
3k
3l
3m
3n
3o
, 99%
, 98%
, 98%
, 97%
, quant.
O
O
O
O
O
O
O
O
O
O
S
O
O
O
I
3p
3q
3r
3s
3t
, 99%
, 99%
, 97%
, 97%
, quant.
aReaction conditions: sulfonium salt 2 (0.2 mmol) and 0.5 M K2CO3 aq. (0.4 mL, 1.0 equiv) in EtOAc (1.6 mL). bThe residue
was purified by silica gel column chromatography; the isolated yield is based on 2.
Further investigations were conducted to elucidate the reaction mechanism; the results are shown in
Table 3. Thus, we believe that the reactivity of intramolecular cyclization depends on the nature of the
solvent rather than the nature of the base. In order to investigate the effects of solvents on the reaction,
1H NMR spectra of sulfonium salt 2a in CD3CN and CD3CN containing 20% water were measured (Figure
1). The 1H NMR spectrum of 2a recorded in CD3CN showed the characteristic four peaks for the enol
tautomer at  6.47 (C3-H), 4.86 (J = 15.8 Hz, C3-H), 4.76 (J = 15.8 Hz, C3-H), and 3.27 (-CH3) ppm in a
1:1:1:3 ratio, indicating that most of 2a existed as the enol tautomer in the polar aprotic solvent CD3CN
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 10 of 41
1
2
3
4
5
6
7
8
9
(Figure 1a). On the other hand, in the spectrum of 2a recorded in CD3CN containing 20% water, three
new signals derived from the keto tautomer were observed at  5.07, 4.38, and 3.20 ppm in addition to the
signals of the enol tautomer (Figure 1b). These results indicated that the keto tautomer was more
stabilized in CD3CN containing water, which is a protic polar solvent having a high dielectric constant,
than in CD3CN.10 In addition, the spectrum in the aqueous solvent revealed that the keto and enol
tautomers of 2a existed in 1:3 ratio nearly. In order to obtain further mechanistic information, in the
presence of a half equivalent of K2CO3, 1H NMR of 2a in CD3CN was measured. The spectrum after 10
min treatment showed small peaks of keto tautomer in addition to the peaks of enol tautomer, but cyclized
product was not observed (Figure S1). On the other hand, in the spectrum after 1 h, the ratio of keto
tautomer increased and cyclized product 3a was detected slightly (Figure S2). However, in the spectrum
after longer time, the ratio among enol tautomer, keto tautomer and 3a was observed not to be almost
changed (Figure S3–S5). In contrast, in the presence of a half equivalent of K2CO3 in CD3CN containing
20% water, the spectrum after 10 min revealed that the added base was consumed for intramolecular
cyclization and the ratio of enol tautomer, keto tautomer, and 3a was 4:1:9 (Figure S6). From the above
results, it is suggested that the generation of keto tautomer of 2 is essential for the intramolecular
cyclization and the water dramatically promotes both the generation of keto tautomer of 2 and the
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
intramolecular cyclization.
Besides, the role of the base in cyclization is presumed to be also important,
but in generation of keto tautomer is supposed to be rather weak.
ACS Paragon Plus Environment

Page 11 of 41
The Journal of Organic Chemistry
1
2
3
(a) 500 MHz (CD3CN)
4
5
6
7
8
BF4
Ph
CH3
S
O
OH
Ph
1
3
9
2a-enol
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
-CH3 (enol)
C3-H (enol)
C1-H (enol)
(b) 500 MHz (CD3CN containing 20% water)
BF4
Ph
CH3
S
O
OH
Ph
1
3
2a-enol
-CH3 (enol)
keto:enol = 1:3
O O
BF4
Ph
CH3
S
Ph
3'
1'
2a-keto
C3'-H (keto)
C1-H (enol)
-CH3 (keto)
C3-H (enol)
C1'-H (keto)
Figure 1. 1H NMR spectra of sulfonium salt 2a (a) in CD3CN and (b) in CD3CN containing 20% water.
Based on the above results, a plausible mechanism is described in Scheme 3.8a Initially, generation of
the keto tautomer of 2 was promoted by the presence of water. The resulting 2-keto was treated with a
base to give enolate anion A. Finally, intramolecular nucleophilic attack of the oxygen anion onto the
C1 carbon atom of A led to the formation of 5-aryl-3(2H)-furanone 3 and methylphenylsulfide.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 12 of 41
1
2
3
4
Scheme 3. Proposed Mechanism
5
6
7
8
O
Me
S
O
O
PhSMe
BF4
Ph
BF4
Ph
Me
S
O
OH
Ar
Me
S
O
O
base
Ph
Ar
O
EtOAc/H2O
Ar
9
Ar
2-enol
3
2-keto
A
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
To substantiate the potential utility of our method, we performed the reaction on gram scale. The
treatment of sulfide 6a (8.11 g, 30 mmol) with 1.0 equiv of Me3OBF4 furnished 9.25 g of 2a in 83% yield
(Scheme 4a). Subsequently, intramolecular cyclization of 2a on a 20 mmol scale proceeded smoothly to
give the cyclized product 5-phenyl-3(2H)-furanone 3a in 98% yield (Scheme 4b). Further, 3a could be
converted into various useful compounds. For instance, 2,2-dimethylation of 3a using 2.5 equiv of MeI
and 2.5 equiv of NaH in MeCN led to the formation of 2,2,-dimethyl-5-phenyl-3(2H)-furanone 9,
bullatenone, in 63% yield (Scheme 4c).
Scheme 4. Gram-Scale Synthesis and Conversion of 3a into Bullatenone 9
BF4
Ph
O
O
Me
S
O
O
Me3OBF4 (1.0 equiv)
S
(a)
(b)
(c)
Ph
Ph
Ph
CH2Cl2
rt, 12 h
6a
8.11 g
2a
9.25 g, 83%
O
BF4
Me
O
O
K2CO3 (1.0 equiv)
S
Ph
Ph
EtOAc/H2O (4:1)
rt, 10 min
O
Ph
2a
3.72 g
3a
1.57 g, 98%
O
O
NaH (2.5 equiv)
MeI (2.5 equiv)
MeCN
O
O
Ph
Ph
0 °C, 1 h, then rt, 1 h
3a
9
63%
Conclusion
In summary, we have developed an efficient protocol for the synthesis of 5-aryl-3(2H)-furanones via the
intramolecular cyclization of 4-aryl-2,4-dioxobutylsulfonium salts. In this reaction, the sulfonio group
ACS Paragon Plus Environment

Page 13 of 41
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
effectively worked as a leaving group, which gave the corresponding 5-aryl-3(2H)-furanone in excellent
yields. The examination on reaction mechanism showed that water as a protic solvent dramatically
promoted the conversion of enol tautomer of sulfonium salt into keto tautomer followed by intramolecular
cyclization. Furthermore, our procedure did not require anhydrous conditions and was completed within
10 min. Moreover, 20 novel sulfonium salts could be easily prepared with good yields from the readily
accessible 1-arylethanones and ethyl acetate through the series reactions, Claisen-type reaction,
bromination, sulfanylation, and S-methylation. Our method is practically applicable for the synthesis of
various related heterocyclic compounds.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Experimental Section
The reagents and solvents were used as received from commercial suppliers without further purification,
unless otherwise indicated. Silica gel (40–50 mesh) was used for flash column chromatography.
Components separated by thin-layer chromatography (TLC) were detected under UV light at 254 nm or
by staining with ethanoic p-anisaldehyde. IR spectra were recorded on an FT-IR spectrometer. 1H and
13C NMR spectra recorded in CDCl3 were referenced to TMS (0.00 ppm) and the solvent peak (77.0 ppm).
13
1H and C NMR spectra recorded in CD3CN were referenced to the solvent peaks (1.94 ppm and 1.32
ppm, respectively). High-resolution mass spectra (HRMS) were obtained using ESI-TOF, ESI-Orbitrap
and APCI Orbitrap mass spectrometers.
General Procedure for Synthesis of 1-Aryl-1,3-butadione (5).9a To a suspension of NaH (1.60 g of
dispersion in oil, 40 mmol) in EtOAc (20 mL) was added a solution of 1-arylethanone (10 mmol) in EtOAc
(20 mL) slowly at 0 °C, and then, the mixture was stirred at room temperature for 12 h. The mixture was
carefully treated with 10% aqueous NH4Cl (30 mL) and adjusted to pH 5 with hydrochloric acid. The
aqueous phase was separated and extracted with EtOAc. The combined organic extracts were dried over
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 14 of 41
1
2
3
4
anhydrous Na2SO4 and concentrated under reduced pressure.
Purification by flash column
5
6
7
8
9
chromatography on silica gel (n-hexane/EtOAc = 7:1) gave the desired 1-aryl-1,3-butadione 5 (keto–enol
mixture).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1-Phenyl-1,3-butadione (5a).11 1.48 g, 91% yield; pale yellow solid; mp 47.5–48.2 °C; Rf = 0.60 (n-
1
hexane/EtOAc = 2:1); IR (KBr): 1600, 1570, 1484, 766, 699 cm−1; H NMR (500 MHz, CDCl3) (enol
form):  7.90–7.87 (m, 2 H), 7.55–7.51 (m, 1 H), 7.47–7.44 (m, 2 H), 6.19 (s, 1 H), 2.21 (s, 3 H); 13C{1H}
NMR (126 MHz, CDCl3) (enol form):  193.8, 183.3, 134.8, 132.3, 128.6 (2C), 127.0 (2C), 96.7, 25.8;
HRMS (ESI-TOF): m/z [M − H]− calcd for C10H9O2, 161.0608; found, 161.0614.
1-(4-Methylphenyl)-1,3-butadione (5b).11
1.61 g, 91% yield; pale yellow oil; Rf = 0.66 (n-
hexane/EtOAc = 2:1); IR (neat): 1611, 1504, 777 cm−1; 1H NMR (500 MHz, CDCl3) (enol form):  7.77
(d, J = 8.3 Hz, 2 H), 7.24 (d, J = 8.3 Hz, 2 H), 6.15 (s, 1 H), 2.40 (s, 3 H), 2.18 (s, 3 H); 13C{1H} NMR
(126 MHz, CDCl3) (enol form):  193.0, 183.7, 143.0, 132.1, 129.3 (2C), 127.0 (2C), 96.2, 25.6, 21.5;
HRMS (ESI-TOF): m/z [M − H]− calcd for C11H11O2, 175.0765; found, 175.0763.
1-(4-n-Butylphenyl)-1,3-butadione (5c). 2.03 g, 93% yield; yellow solid; mp 30.8–31.2 °C; Rf = 0.66
(n-hexane/EtOAc = 2:1); IR (KBr): 1609, 1502, 848, 780 cm−1; 1H NMR (500 MHz, CDCl3) (enol form):
 7.80–7.79 (m, 2 H), 7.26–7.24 (m, 2 H), 6.15 (s, 1 H), 2.66 (t, J = 7.7 Hz, 2 H), 2.19 (s, 3 H), 1.64–1.58
(m, 2 H), 1.40–1.32 (m, 2 H), 0.93 (t, J = 7.3 Hz, 3 H); 13C{1H} NMR (126 MHz, CDCl3) (enol form): 
193.1, 183.7, 148.0, 132.4, 128.7 (2C), 127.1 (2C), 96.3, 35.6, 33.3, 25.7, 22.3, 13.9; HRMS (ESI-TOF):
m/z [M − H]− calcd for C14H17O2, 217.1234; found, 217.1228.
1-(4-Biphenyl)-1,3-butadione (5d).12 2.27 g, 95% yield; pale yellow solid; mp 159.8–160.1 °C; Rf =
1
0.64 (n-hexane/EtOAc = 2:1); IR (KBr): 1604, 1576, 1483, 849, 766, 695 cm−1; H NMR (500 MHz,
CDCl3) (enol form):  7.95 (d, J = 8.6 Hz, 2 H), 7.68 (d, J = 8.6 Hz, 2 H), 7.64–7.62 (m, 2 H), 7.48–7.45
(m, 2 H), 7.41–7.38 (m, 1 H), 6.22 (s, 1 H), 2.22 (s, 3 H); 13C{1H} NMR (126 MHz, CDCl3) (enol form):
 193.7, 182.9, 145.0, 139.9, 133.6, 128.9 (2C), 128.1, 127.5 (2C), 127.24 (2C), 127.18 (2C), 96.7 (2C),
ACS Paragon Plus Environment

Page 15 of 41
The Journal of Organic Chemistry
1
2
3
25.9; HRMS (ESI-TOF): m/z [M − H]− calcd for C16H13O2, 237.0921; found, 237.0920.
4
5
6
7
8
1-(4-Methoxyphenyl)-1,3-butadione (5e).11 1.80 g, 94% yield; white solid; mp 54.5–55.2 °C; Rf = 0.52
(n-hexane/EtOAc = 2:1); IR (KBr): 1606, 1503, 1259, 1180, 1025, 841, 780 cm−1; 1H NMR (500 MHz,
CDCl3) (enol form):  7.86 (d, J = 8.9 Hz, 2 H), 6.94 (d, J = 8.9 Hz, 2 H), 6.12 (s, 1 H), 3.87 (s, 3 H), 2.17
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
13
(s, 3 H); C{1H} NMR (126 MHz, CDCl3) (enol form):  191.6, 184.1, 163.1, 129.1 (2C), 127.5 (2C),
113.9, 95.8, 55.4, 25.3; HRMS (ESI-TOF): m/z [M − H]− calcd for C11H11O3, 191.0714; found, 191.0714.
1-(4-Phenoxyphenyl)-1,3-butadione (5f). 2.34 g, 92% yield; white solid; mp 84.4–84.6 °C; Rf = 0.62
(n-hexane/EtOAc = 2:1); IR (KBr): 1604, 1587, 1486, 1258, 853, 777, 697 cm−1; H NMR (500 MHz,
1
CDCl3) (enol form):  7.86 (d, J = 8.9 Hz, 2 H), 7.41–7.37 (m, 2 H), 7.21–7.18 (m, 1 H), 7.08–7.06 (m, 2
H), 7.01 (d, J = 8.9 Hz, 2 H), 6.12 (s, 1 H), 2.18 (s, 3 H); 13C{1H} NMR (126 MHz, CDCl3) (enol form):
 192.3, 183.5, 161.4, 155.7, 130.0 (2C), 129.4, 129.1 (2C), 124.5, 120.0 (2C), 117.6 (2C), 96.1, 25.5;
HRMS (ESI-TOF): m/z [M + H]+ calcd for C16H15O3, 255.1016; found, 255.1013.
1-(4-Benzyloxyphenyl)-1,3-butadione (5g).11 2.50 g, 93% yield; white solid; mp 115.1–115.5 °C; Rf =
0.56 (n-hexane/EtOAc = 2:1); IR (KBr): 1604, 1503, 1256, 1174, 1008, 836, 783, 747, 698 cm−1; 1H NMR
(500 MHz, CDCl3) (enol form):  7.86 (d, J = 9.0 Hz, 2 H), 7.44–7.38 (m, 4 H), 7.36–7.33 (m, 1 H), 7.01
(d, J = 9.0 Hz, 2 H), 6.11 (s, 1 H), 5.12 (s, 2 H), 2.16 (s, 3 H); 13C{1H} NMR (126 MHz, CDCl3) (enol
form):  191.7, 184.0, 162.2, 136.2, 129.1 (2C), 128.7 (2C), 128.2, 127.7, 127.5 (2C), 114.7 (2C), 95.8,
70.1, 25.3; HRMS (ESI-TOF): m/z [M + H]+ calcd for C17H17O3, 269.1172; found, 269.1174.
1-(4-Trifluoromethylphenyl)-1,3-butadione (5h).13 2.10 g, 91% yield; pale yellow solid; mp 45.0–45.4
°C; Rf = 0.58 (n-hexane/EtOAc = 2:1); IR (KBr): 1613, 1572, 1328, 1130, 860, 787 cm−1; 1H NMR (500
MHz, CDCl3) (enol form):  7.98 (d, J = 8.3 Hz, 2 H), 7.71 (d, J = 8.3 Hz, 2 H), 6.20 (s, 1 H), 2.24 (s, 3
H); 13C{1H} NMR (126 MHz, CDCl3) (enol form):  195.2, 180.9, 138.09–138.06 (m), 133.6 (q, J = 32.7
Hz), 127.3 (2C), 125.6 (q, J = 3.8 Hz, 2C), 123.7 (q, J = 272.5 Hz), 97.4, 26.2; HRMS (ESI-Orbitrap):
m/z [M − H]− calcd for C11H8F3O2, 229.0482; found, 229.0482.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 16 of 41
1
2
3
4
5
6
7
8
9
Ethyl 4-(1,3-Dioxobutyl)benzoate (5i). 2.23 g, 95% yield; pale yellow solid; mp 81.3–81.8 °C; Rf =
0.54 (n-hexane/EtOAc = 2:1); IR (KBr): 1714, 1604, 1281, 771 cm−1; 1H NMR (500 MHz, CDCl3) (enol
form):  8.11 (d, J = 8.7 Hz, 2 H), 7.92 (d, J = 8.7 Hz, 2 H), 6.21 (s, 1 H), 4.41 (q, J = 7.2 Hz, 2 H), 2.24
(s, 3 H), 1.42 (t, J = 7.2 Hz, 3 H); 13C{1H} NMR (126 MHz, CDCl3) (enol form):  195.3, 181.1, 165.8,
138.5, 133.5, 129.7 (2C), 126.8 (2C), 97.5, 61.4, 26.3, 14.3; HRMS (ESI-TOF): m/z [M − H]− calcd for
C13H13O4, 233.0819; found, 233.0817.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1-(4-Cyanophenyl)-1,3-butadione (5j).12 1.76 g, 94% yield; white solid; mp 93.5–94.1 °C; Rf = 0.46
(n-hexane/EtOAc = 2:1); IR (KBr): 2226, 1588, 848, 782 cm−1; 1H NMR (500 MHz, CDCl3) (enol form):
13
 7.96 (d, J = 8.7 Hz, 2 H), 7.74 (d, J = 8.7 Hz, 2 H), 6.20 (s, 1 H), 2.21 (s, 3 H); C{1H} NMR (126
MHz, CDCl3) (enol form):  195.8, 179.8, 138.7, 132.4 (2C), 127.4 (2C), 118.1, 115.4, 97.6, 26.3; HRMS
(ESI-TOF): m/z [M − H]− calcd for C11H8NO2, 186.0561; found, 186.0554.
1-(2-Chlorophenyl)-1,3-butadione (5k).12 1.93 g, 98% yield; yellow oil; Rf = 0.60 (n-hexane/EtOAc =
2:1); IR (neat): 1605, 1557, 1540, 767 cm−1; 1H NMR (500 MHz, CDCl3) (enol form):  7.57 (dd, J = 7.6,
13
1.8 Hz, 1 H), 7.43 (dd, J = 7.9, 1.2 Hz, 1 H), 7.38–7.31 (m, 2 H), 6.04 (s, 1 H), 2.18 (s, 3 H); C{1H}
NMR (126 MHz, CDCl3) (enol form):  192.7, 184.6, 135.5, 131.6, 131.5, 130.6, 129.9, 126.8, 101.8,
35
25.4; HRMS (ESI-TOF): m/z [M − H]− calcd for C10H8 ClO2, 195.0218; found, 195.0218.
1-(3-Chlorophenyl)-1,3-butadione (5l). 1.96 g, quant.; pale yellow solid; mp 42.2–43.1 °C; Rf = 0.62
(n-hexane/EtOAc = 2:1); IR (KBr): 1610, 1565, 784, 678 cm−1; 1H NMR (500 MHz, CDCl3) (enol form):
 7.86–7.85 (m, 1 H), 7.76–7.74 (m, 1 H), 7.49 (ddd, J = 7.9, 2.1, 1.1 Hz, 1 H), 7.41–7.38 (m, 1 H), 6.15
13
(s, 1 H), 2.22 (s, 3 H); C{1H} NMR (126 MHz, CDCl3):  194.1, 181.8, 136.7, 134.8, 132.1, 129.9,
35
127.1, 125.0, 96.9, 25.9; HRMS (ESI-TOF): m/z [M − H]− calcd for C10H8 ClO2, 195.0218; found,
195.0217.
1-(4-Chlorophenyl)-1,3-butadione (5m).11 1.96 g, quant.; pale yellow solid; mp 71.2–71.9 °C; Rf = 0.64
(n-hexane/EtOAc = 2:1); IR (KBr): 1612, 1594, 1484, 840, 779 cm−1; 1H NMR (500 MHz, CDCl3) (enol
ACS Paragon Plus Environment

Page 17 of 41
The Journal of Organic Chemistry
1
2
3
4
5
6
7
form):  7.82 (d, J = 8.7 Hz, 2 H), 7.42 (d, J = 8.7 Hz, 2 H), 6.14 (s, 1 H), 2.21 (s, 3 H); 13C{1H} NMR
(126 MHz, CDCl3) (enol form):  193.7, 182.3, 138.5, 133.3, 128.9 (2C), 128.3 (2C), 96.6, 25.8; HRMS
8
9
35
(ESI-TOF): m/z [M − H]− calcd for C10H8 ClO2, 195.0218; found, 195.0218.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1-(4-Fluorophenyl)-1,3-butadione (5n).11 1.78 g, 99% yield; pale yellow solid; mp 37.0–37.8 °C; Rf =
0.62 (n-hexane/EtOAc = 2:1); IR (KBr): 1604, 1505, 849, 785 cm−1; 1H NMR (500 MHz, CDCl3) (enol
form):  7.91–7.89 (m, 2 H), 7.15–7.11 (m, 2 H), 6.13 (s, 1 H), 2.20 (s, 3 H); 13C{1H} NMR (126 MHz,
CDCl3) (enol form):  192.9, 182.9, 165.3 (d, J = 253.4 Hz), 131.2 (d, J = 3.0 Hz), 129.4 (d, J = 9.0 Hz)
(2C), 115.7 (d, J = 21.9 Hz) (2C), 96.3, 25.5; HRMS (ESI-TOF): m/z [M − H]− calcd for C10H8FO2,
179.0514; found, 179.0510.
1-(4-Bromophenyl)-1,3-butadione (5o).14 2.30 g, 95% yield; pale yellow solid; mp 84.4–84.9 °C; Rf =
0.64 (n-hexane/EtOAc = 2:1); IR (KBr): 1613, 1587, 1479, 842, 782 cm−1; 1H NMR (500 MHz, CDCl3)
(enol form):  7.75 (d, J = 8.7 Hz, 2 H), 7.59 (d, J = 8.7 Hz, 2 H), 6.15 (s, 1 H), 2.21 (s, 3 H); 13C{1H}
NMR (126 MHz, CDCl3) (enol form):  193.9, 182.3, 133.8, 131.9 (2C), 128.5 (2C), 127.1, 96.6, 25.8;
79
HRMS (ESI-TOF): m/z [M − H]− calcd for C10H8 BrO2, 238.9713; found, 238.9711.
1-(4-Iodophenyl)-1,3-butadione (5p).15 2.77 g, 96% yield; pale yellow solid; mp 119.5–120.0 °C
(sealed tube); Rf = 0.64 (n-hexane/EtOAc = 2:1); IR (KBr): 1612, 1584, 1480, 837, 784 cm−1; 1H NMR
(500 MHz, CDCl3) (enol form):  7.81–7.79 (m, 2 H), 7.60–7.58 (m, 2 H), 6.14 (s, 1 H), 2.20 (s, 3 H);
13C{1H} NMR (126 MHz, CDCl3) (enol form):  194.0, 182.3, 137.9 (2C), 134.3, 128.4 (2C), 99.6, 96.6,
25.9; HRMS (ESI-TOF): m/z [M − H]− calcd for C10H8IO2, 286.9575; found, 286.9573.
1-(2-Naphthyl)-1,3-butadione (5q).11 2.04 g, 96% yield; pale yellow solid; mp 78.0–78.5 °C; Rf = 0.60
(n-hexane/EtOAc = 2:1); IR (KBr): 1604, 1588, 1564, 870, 830, 788 cm−1; 1H NMR (500 MHz, CDCl3)
(enol form):  8.44 (s, 1 H), 7.96–7.86 (m, 4 H), 7.59–7.53 (m, 2 H), 6.33 (s, 1 H), 2.25 (s, 3 H); 13C{1H}
NMR (126 MHz, CDCl3) (enol form):  193.8, 183.1, 135.2, 132.7, 132.1, 129.3, 128.4, 128.2, 128.0,
127.7, 126.7, 123.1, 97.0, 25.9; HRMS (ESI-TOF): m/z [M − H]− calcd for C14H11O2, 211.0765; found,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 18 of 41
1
2
3
4
211.0766.
5
6
7
8
1-(2,3-Dihydro-1,4-benzodioxin-6-yl)-1,3-butadione (5r).11 2.08 g, 94% yield; pale yellow solid; mp
89.6–89.8 °C; Rf = 0.56 (n-hexane/EtOAc = 2:1); IR (KBr): 1611, 1544, 1493, 1284, 862, 770 cm−1; 1H
NMR (500 MHz, CDCl3) (enol form):  7.44 (d, J = 2.1 Hz, 1 H), 7.41 (dd, J = 8.4, 2.1 Hz, 1 H), 6.90 (d,
J = 8.4 Hz, 1 H), 6.08 (s, 1 H), 4.33–4.31 (m, 2 H), 4.29–4.27 (m, 2 H), 2.16 (s, 3 H); 13C{1H} NMR (126
MHz, CDCl3) (enol form):  191.7, 183.8, 147.4, 143.4, 128.5, 120.9, 117.3, 116.5, 95.9, 64.6, 64.1, 25.3;
HRMS (ESI-TOF): m/z [M − H]− calcd for C12H11O4, 219.0663; found, 219.0661.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1-(2-Furyl)-1,3-butadione (5s).16 1.41 g, 93% yield; orange oil; Rf = 0.56 (n-hexane/EtOAc = 2:1); IR
(neat): 1614, 1469, 760 cm−1; 1H NMR (500 MHz, CDCl3) (enol form):  7.57 (dd, J = 1.6, 0.8 Hz, 1 H),
7.15 (dd, J = 3.5, 0.8 Hz, 1 H), 6.55 (dd, J = 3.5, 1.6 Hz, 1 H), 6.55 (s, 1 H), 2.15 (s, 3 H); 13C{1H} NMR
(126 MHz, CDCl3) (enol form):  189.5, 176.2, 150.5, 145.9, 115.5, 112.4, 96.1, 25.4; HRMS (ESI-TOF):
m/z [M − H]− calcd for C8H7O3, 151.0401; found, 151.0404.
1-(2-Thienyl)-1,3-butadione (5t).11 1.58 g, 94% yield; pale orange solid; mp 35.5–36.0 °C; Rf = 0.54
(n-hexane/EtOAc = 2:1); IR (KBr): 1613, 1519, 1410, 778, 722 cm−1; 1H NMR (500 MHz, CDCl3) (enol
form):  7.69 (dd, J = 3.8, 1.1 Hz, 1 H), 7.60 (dd, J = 4.9, 1.1 Hz, 1 H), 7.13 (dd, J = 4.9, 3.8 Hz, 1 H),
6.03 (s, 1 H), 2.14 (s, 3 H); 13C{1H} NMR (126 MHz, CDCl3) (enol form):  187.2, 181.8, 141.7, 132.3,
130.1, 128.2, 96.4, 23.8; HRMS (ESI-TOF): m/z [M − H]− calcd for C8H7O2S, 167.0172; found, 167.0169.
General Procedure for Synthesis of Sulfide (6).9b Bromine (0.26 mL, 5.1 mmol) was added dropwise
to a solution of 1-aryl-1,3-butadione 5 (5.0 mmol) in dry diethyl ether (8 mL) at 0 °C under an argon
atmosphere. The mixture was stirred at 0 °C for 2 h and at room temperature for further 24 h. The
mixture was treated with ice water and extracted with diethyl ether. The combined organic extracts were
washed with a saturated aqueous solution of NaHCO3 and brine, dried over anhydrous Na2SO4, and
concentrated under reduced pressure to give crude 1-aryl-4-bromo-1,3-butadione. Benzenethiol (0.51
mL, 5.0 mmol) was added slowly to a suspension of NaH (0.20 g of a dispersion in oil, 5.0 mmol) in dry
ACS Paragon Plus Environment

Page 19 of 41
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
THF (5.0 mL) at 0 °C under an argon atmosphere, and the mixture was stirred at room temperature for 30
min. To a suspension of sodium benzenethiolate in THF was added a solution of the crude 1-aryl-4-
bromo-1,3-butadione in THF (5 mL) via a cannula. The mixture was stirred at room temperature for 30
min and then at 60 °C for 1 h. The mixture was concentrated under reduced pressure, and purification
by flash column chromatography on silica gel (n-hexane/EtOAc = 7:1) gave sulfide 6 (keto-enol mixture).
1-Phenyl-4-(phenylsulfanyl)-1,3-butadione (6a).17 1.19 g, 88% yield; pale orange solid; mp 49.8–50.2
°C; Rf = 0.50 (n-hexane/EtOAc = 3:1); IR (KBr): 1599, 1573, 1480, 758, 740, 687 cm−1; 1H NMR (500
MHz, CDCl3) (enol form):  7.83–7.81 (m, 2 H), 7.54–7.50 (m, 1 H), 7.45–7.40 (m, 4 H), 7.31–7.28 (m,
2 H), 7.24–7.21 (m, 1 H), 6.38 (s, 1 H), 3.74 (s, 2 H); 13C{1H} NMR (126 MHz, CDCl3) (enol form): 
193.1, 182.1, 134.9, 134.2, 132.5, 130.0 (2C), 129.1 (2C), 128.6 (2C), 127.0 (3C), 95.6, 41.3; HRMS
(ESI-TOF): m/z [M − H]− calcd for C16H13O2S, 269.0642; found, 269.0646.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1-(4-Methylphenyl)-4-(phenylsulfanyl)-1,3-butadione (6b). 1.23 g, 87% yield; yellow oil; Rf = 0.52 (n-
hexane/EtOAc = 3:1); IR (neat): 1609, 1571, 1507, 794, 740, 690 cm−1; 1H NMR (500 MHz, CDCl3) (enol
form):  7.73–7.72 (m, 2 H), 7.42–7.40 (m, 2 H), 7.32–7.28 (m, 2 H), 7.24–7.22 (m, 3 H), 6.34 (s, 1 H),
3.73 (s, 2 H), 2.40 (s, 3 H); 13C{1H} NMR (126 MHz, CDCl3) (enol form):  192.4, 182.6, 143.4, 135.0,
131.5, 130.0 (2C), 129.4 (2C), 129.1 (2C), 127.1 (2C), 127.0, 95.2, 41.2, 21.6; HRMS (ESI-TOF): m/z [M
− H]− calcd for C17H15O2S, 283.0798; found, 283.0798.
1-(4-n-Butylphenyl)-4-(phenylsulfanyl)-1,3-butadione (6c). 1.48 g, 91% yield; red oil; Rf = 0.58 (n-
hexane/EtOAc = 3:1); IR (neat): 1608, 1566, 1506, 794, 739, 690 cm−1; 1H NMR (500 MHz, CDCl3) (enol
form):  7.74 (d, J = 8.2 Hz, 2 H), 7.41–7.40 (m, 2 H), 7.31–7.28 (m, 2 H), 7.25–7.22 (m, 3 H), 6.35 (s, 1
H), 3.73 (s, 2 H), 2.65 (t, J = 7.7 Hz, 2 H), 1.63–1.57 (m, 2 H), 1.39–1.31 (m, 2 H), 0.93 (t, J = 7.4 Hz, 3
H); 13C{1H} NMR (126 MHz, CDCl3) (enol form):  192.4, 182.5, 148.3, 134.9, 131.6, 130.0 (2C), 129.1
(2C), 128.7 (2C), 127.1 (2C), 126.9, 95.2, 41.1, 35.6, 33.2, 22.3, 13.9; HRMS (ESI-TOF): m/z [M − H]−
calcd for C20H21O2S, 325.1268; found, 325.1266.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 20 of 41
1
2
3
4
1-(4-Biphenyl)-4-(phenylsulfanyl)-1,3-butadione (6d).
1.56 g, 90% yield; white solid; mp 87.0–
5
6
7
8
1
87.5 °C; Rf = 0.52 (n-hexane/EtOAc = 3:1); IR (KBr): 1606, 1579, 1556, 847, 768, 749, 689 cm−1; H
NMR (500 MHz, CDCl3) (enol form):  7.90 (d, J = 8.6 Hz, 2 H), 7.67 (d, J = 8.6 Hz, 2 H), 7.63–7.61 (m,
2 H), 7.48–7.45 (m, 2 H), 7.43–7.38 (m, 3 H), 7.33–7.29 (m, 2 H), 7.25–7.22 (m, 1 H), 6.41 (s, 1 H), 3.76
(s, 2 H); 13C{1H} NMR (126 MHz, CDCl3) (enol form):  193.1, 181.7, 145.3, 139.8, 134.9, 132.9, 130.1
(2C), 129.1 (2C), 129.0 (2C), 128.2, 127.6 (2C), 127.3 (2C), 127.2 (2C), 127.0, 95.5, 41.3; HRMS (ESI-
TOF): m/z [M − H]− calcd for C22H17O2S, 345.0955; found, 345.0952.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1-(4-Methoxyphenyl)-4-(phenylsulfanyl)-1,3-butadione (6e). 1.26 g, 84% yield; pale orange solid; mp
71.9–72.0 °C; Rf = 0.54 (n-hexane/EtOAc = 3:1); IR (KBr): 1603, 1567, 1508, 1263, 1178, 841, 796, 740,
691 cm−1; 1H NMR (500 MHz, CDCl3) (enol form):  7.79 (d, J = 9.0 Hz, 2 H), 7.41–7.39 (m, 2 H), 7.30–
7.25 (m, 2 H), 7.23–7.19 (m, 1 H), 6.90 (d, J = 9.0 Hz, 2 H), 6.29 (s, 1 H), 3.84 (s, 3 H), 3.71 (s, 2 H);
13C{1H} NMR (126 MHz, CDCl3) (enol form):  190.9, 182.9, 163.2, 135.0, 129.9 (2C), 129.1 (2C), 129.0
(2C), 126.9, 126.7, 113.9 (2C), 94.7, 55.4, 40.8; HRMS (ESI-TOF): m/z [M − H]− calcd for C17H15O3S,
299.0747; found, 299.0744.
1-(4-Phenoxyphenyl)-4-(phenylsulfanyl)-1,3-butadione (6f). 1.58 g, 87% yield; pale orange solid; mp
60.0–60.4 °C; Rf = 0.50 (n-hexane/EtOAc = 3:1); IR (KBr): 1604, 1584, 1487, 1245, 844, 780, 746, 694
cm−1; 1H NMR (500 MHz, CDCl3) (enol form):  7.80 (d, J = 8.9 Hz, 2 H), 7.41–7.38 (m, 4 H), 7.31–7.28
(m, 2 H), 7.24–7.18 (m, 2 H), 7.08–7.05 (m, 2 H), 6.99 (d, J = 8.9 Hz, 2 H), 6.30 (s, 1 H), 3.73 (s, 2 H);
13C{1H} NMR (126 MHz, CDCl3) (enol form):  191.7, 182.3, 161.7, 155.5, 134.9, 130.03 (2C), 129.99
(2C), 129.2 (2C), 129.1 (2C), 128.6, 127.0, 124.6, 120.1 (2C), 117.6 (2C), 95.0, 41.0; HRMS (ESI-TOF):
m/z [M − H]− calcd for C22H17O3S, 361.0904; found, 361.0902.
1-(4-Benzyloxyphenyl)-4-(phenylsulfanyl)-1,3-butadione (6g). 1.60 g, 85% yield; white solid; mp
61.2–61.5 °C; Rf = 0.46 (n-hexane/EtOAc = 3:1); IR (KBr): 1604, 1509, 1263, 1174, 842, 789, 753, 744,
697 cm−1; 1H NMR (500 MHz, CDCl3) (enol form):  7.80 (d, J = 9.0 Hz, 2 H), 7.43–7.38 (m, 6 H), 7.36–
ACS Paragon Plus Environment

Page 21 of 41
The Journal of Organic Chemistry
1
2
3
7.33 (m, 1 H), 7.32–7.27 (m, 2 H), 7.23–7.20 (m, 1 H), 7.00 (d, J = 9.0 Hz, 2 H), 6.30 (s, 1 H), 5.12 (s, 2
4
5
6
7
13
H), 3.72 (s, 2 H); C{1H} NMR (126 MHz, CDCl3) (enol form):  191.1, 182.8, 162.4, 136.1, 135.0,
8
9
129.9 (2C), 129.2 (2C), 129.1 (2C), 128.7 (2C), 128.2, 127.5 (2C), 127.0, 126.9, 114.8 (2C), 94.7, 70.1,
40.9; HRMS (ESI-TOF): m/z [M − H]− calcd for C23H19O3S, 375.1060; found, 375.1060.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
4-(phenylsulfanyl)-1-(4-trifluoromethylphenyl)-1,3-butadione (6h). 1.41 g, 83% yield; pale yellow
solid; mp 48.5–49.1 °C; Rf = 0.54 (n-hexane/EtOAc = 3:1); IR (KBr): 1624, 1605, 1330, 1122, 856, 799,
748, 692 cm−1; 1H NMR (500 MHz, CDCl3) (enol form):  7.91 (d, J = 8.3 Hz, 2 H), 7.69 (d, J = 8.3 Hz,
2 H), 7.42–7.40 (m, 2 H), 7.32–7.29 (m, 2 H), 7.26–7.23 (m, 1 H), 6.38 (s, 1 H), 3.75 (s, 2 H); 13C{1H}
NMR (126 MHz, CDCl3) (enol form):  194.5, 179.5, 137.4 (q, J = 1.2 Hz), 134.5, 133.7 (q, J = 32.7 Hz),
130.2 (2C), 129.2 (2C), 127.3 (2C), 127.2, 125.6 (q, J = 3.6 Hz, 2C), 123.6 (q, J = 272.5 Hz), 96.3, 41.5;
HRMS (ESI-Orbitrap): m/z [M − H]− calcd for C17H12F3O2S, 337.0516; found, 337.0516.
Ethyl 4-[1,3-Dioxo-4-(phenylsulfanyl)butyl]benzoate (6i). 1.37 g, 80% yield; yellow solid; mp 88.5–
88.9 °C; Rf = 0.42 (n-hexane/EtOAc = 3:1); IR (KBr): 1712, 1604, 1569, 1281, 1105, 763, 728, 687 cm−1;
1H NMR (500 MHz, CDCl3) (enol form):  8.09 (d, J = 8.7 Hz, 2 H), 7.86 (d, J = 8.7 Hz, 2 H), 7.42–7.40
(m, 2 H), 7.32–7.29 (m, 2 H), 7.26–7.22 (m, 1 H), 6.39 (s, 1 H), 4.40 (q, J = 7.1 Hz, 2 H), 3.75 (s, 2 H),
13
1.41 (t, J = 7.1 Hz, 3 H); C{1H} NMR (126 MHz, CDCl3) (enol form):  194.5, 179.8, 165.7, 137.8,
134.6, 133.6, 130.1 (2C), 129.7 (2C), 129.2 (2C), 127.1, 126.8 (2C), 96.4, 61.4, 41.6, 14.3; HRMS (ESI-
TOF): m/z [M − H]− calcd for C19H17O4S, 341.0853; found, 341.0853.
1-(4-Cyanophenyl)-4-(phenylsulfanyl)-1,3-butadione (6j). 1.24 g, 83% yield; pale orange solid; mp
76.3–76.6 °C; Rf = 0.36 (n-hexane/EtOAc = 3:1); IR (KBr): 2230, 1614, 1583, 1559, 852, 795, 743, 691
1
cm−1; H NMR (500 MHz, CDCl3) (enol form):  7.89 (d, J = 8.7 Hz, 2 H), 7.72 (d, J = 8.7 Hz, 2 H),
7.41–7.39 (m, 2 H), 7.33–7.29 (m, 2 H), 7.26–7.23 (m, 1 H), 6.39 (s, 1 H), 3.75 (s, 2 H); 13C{1H} NMR
(126 MHz, CDCl3) (enol form):  195.2, 178.2, 138.0, 134.4, 132.4 (2C), 130.1 (2C), 129.2 (2C), 127.3
(2C), 127.2, 118.0, 115.5, 96.6, 41.6; HRMS (ESI-TOF): m/z [M − H]− calcd for C17H12NO2S, 294.0594;
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 22 of 41
1
2
3
4
found, 294.0594.
5
6
7
8
9
1-(2-Chlorophenyl)-4-(phenylsulfanyl)-1,3-butadione (6k). 1.24 g, 81% yield; yellow oil; Rf = 0.48 (n-
hexane/EtOAc = 3:1); IR (neat): 1603, 1583, 1479, 766, 740, 690 cm−1; 1H NMR (500 MHz, CDCl3) (enol
form):  7.54 (dd, J = 7.7, 1.8 Hz, 1 H), 7.42–7.40 (m, 3 H), 7.38–7.34 (m, 1 H), 7.32–7.28 (m, 3 H),
7.25–7.21 (m, 1 H), 6.27 (s, 1 H), 3.72 (s, 2 H); 13C{1H} NMR (126 MHz, CDCl3) (enol form):  192.0,
183.0, 134.7, 134.5, 131.9, 131.8, 130.7, 130.2, 130.1, 129.1, 127.1, 126.9, 101.1, 41.0; HRMS (ESI-
TOF): m/z [M − H]− calcd for C16H1235ClO2S, 303.0252; found, 303.0253.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1-(3-Chlorophenyl)-4-(phenylsulfanyl)-1,3-butadione (6l). 1.35 g, 88% yield; yellow oil; Rf = 0.52 (n-
1
hexane/EtOAc = 3:1); IR (neat): 1604, 1566, 787, 746, 689 cm−1; H NMR (500 MHz, CDCl3) (enol
form):  7.77–7.76 (m, 1 H), 7.69–7.66 (m, 1 H), 7.49–7.46 (m, 1 H), 7.42–7.39 (m, 2 H), 7.38–7.35 (m,
13
1 H), 7.32–7.29 (m, 2 H), 7.26–7.22 (m, 1 H), 6.30 (s, 1 H), 3.73 (s, 2 H); C{1H} NMR (126 MHz,
CDCl3) (enol form):  193.5, 180.3, 136.0, 134.9, 134.6, 132.3, 130.2, 129.9, 129.2, 127.2, 127.1, 125.0,
95.9, 41.3; HRMS (ESI-TOF): m/z [M − H]− calcd for C16H1235ClO2S, 303.0252; found, 303.0251.
1-(4-Chlorophenyl)-4-(phenylsulfanyl)-1,3-butadione (6m). 1.27 g, 83% yield; pale orange solid; mp
49.9–50.1 °C; Rf = 0.56 (n-hexane/EtOAc = 3:1); IR (KBr): 1634, 1588, 1479, 845, 794, 739, 691 cm−1;
1H NMR (500 MHz, CDCl3) (enol form):  7.75 (d, J = 8.7 Hz, 2 H), 7.42–7.40 (m, 4 H), 7.32–7.29 (m,
2 H), 7.25–7.23 (m, 1 H), 6.32 (s, 1 H), 3.74 (s, 2 H); 13C{1H} NMR (126 MHz, CDCl3) (enol form): 
193.1, 180.9, 138.8, 134.7, 132.6, 130.1 (2C), 129.1 (2C), 129.0 (2C), 128.3 (2C), 127.1, 95.5, 41.2;
HRMS (ESI-TOF): m/z [M − H]− calcd for C16H1235ClO2S, 303.0252; found, 303.0255.
1-(4-Fluorophenyl)-4-(phenylsulfanyl)-1,3-butadione (6n). 1.20 g, 83% yield; pale yellow solid; mp
55.6–56.1 °C; Rf = 0.54 (n-hexane/EtOAc = 3:1); IR (KBr): 1637, 1598, 1508, 1232, 848, 795, 736, 689
cm−1; 1H NMR (500 MHz, CDCl3) (enol form):  7.85–7.82 (m, 2 H), 7.41–7.40 (m, 2 H), 7.31–7.28 (m,
2 H), 7.24–7.22 (m, 1 H), 7.13–7.09 (m, 2 H), 6.31 (m, 1 H), 3.73 (m, 2 H); 13C{1H} NMR (126 MHz,
CDCl3) (enol form):  192.3, 181.6, 165.4 (d, J = 254.1 Hz), 134.8, 130.5 (d, J = 3.0 Hz), 130.0 (2C),
ACS Paragon Plus Environment

Page 23 of 41
The Journal of Organic Chemistry
1
2
3
4
5
6
7
129.5 (d, J = 9.1 Hz) (2C), 129.1 (2C), 127.1, 115.8 (d, J = 22.0 Hz) (2C), 95.3, 41.0; HRMS (ESI-TOF):
m/z [M − H]− calcd for C16H12FO2S, 287.0548; found, 287.0548.
8
9
1-(4-Bromophenyl)-4-(phenylsulfanyl)-1,3-butadione (6o). 1.61 g, 92% yield; pale orange solid; mp
58.0–58.2 °C; Rf = 0.56 (n-hexane/EtOAc = 3:1); IR (KBr): 1604, 1585, 1479, 841, 787, 740, 690 cm−1;
1H NMR (500 MHz, CDCl3) (enol form):  7.67 (d, J = 8.7 Hz, 2 H), 7.56 (d, J = 8.7 Hz, 2 H), 7.41–7.39
(m, 2 H), 7.31–7.28 (m, 2 H), 7.25–7.21 (m, 1 H), 6.32 (s, 1 H), 3.73 (s, 2 H); 13C{1H} NMR (126 MHz,
CDCl3) (enol form):  193.3, 180.9, 134.7, 133.1, 131.9 (2C), 130.1 (2C), 129.1 (2C), 128.5 (2C), 127.3,
127.1, 95.5, 41.3; HRMS (ESI-TOF): m/z [M − H]− calcd for C16H1279BrO2S, 346.9747; found, 346.9748.
1-(4-Iodophenyl)-4-(phenylsulfanyl)-1,3-butadione (6p). 1.61 g, 81% yield; pale yellow solid; mp
70.1–70.6 °C; Rf = 0.56 (n-hexane/EtOAc = 3:1); IR (KBr): 1586, 1553, 1481, 840, 793, 740, 689 cm−1;
1H NMR (500 MHz, CDCl3) (enol form):  7.79–7.77 (m, 2 H), 7.52–7.51 (m, 2 H), 7.41–7.38 (m, 2 H),
7.31–7.28 (m, 2 H), 7.23 (tt, J = 7.3, 1.2 Hz, 1 H), 6.32 (s, 1 H), 3.73 (s, 2 H); 13C{1H} NMR (126 MHz,
CDCl3) (enol form):  193.4, 181.0, 137.9 (2C), 134.7, 133.6, 130.1 (2C), 129.1 (2C), 128.4 (2C), 127.1,
99.9, 95.5, 41.3; HRMS (ESI-TOF): m/z [M − H]− calcd for C16H12IO2S, 394.9608; found, 394.9608.
1-(2-Naphthyl)-4-(phenylsulfanyl)-1,3-butadione (6q). 1.36 g, 85% yield; white solid; mp 95.2–
95.7 °C; Rf = 0.50 (n-hexane/EtOAc = 3:1); IR (KBr): 1627, 1577, 1560, 1477, 867, 795, 755, 737, 689
cm−1; 1H NMR (500 MHz, CDCl3) (enol form):  8.37 (s, 1 H), 7.92 (d, J = 8.0 Hz, 1 H), 7.87–7.81 (m, 3
H), 7.59–7.52 (m, 2 H), 7.45–7.43 (m, 2 H), 7.32–7.29 (m, 2 H), 7.25–7.22 (m, 1 H), 6.49 (s, 1 H), 3.77
(s, 2 H); 13C{1H} NMR (126 MHz, CDCl3) (enol form):  193.0, 182.0, 135.3, 134.9, 132.6, 131.4, 130.1
(2C), 129.3, 129.1 (2C), 128.4, 128.3, 128.2, 127.7, 127.1, 126.8, 123.0, 95.9, 41.4; HRMS (ESI-TOF):
m/z [M − H]− calcd for C20H15O2S, 319.0798; found, 319.0796.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1-(2,3-Dihydro-1,4-benzodioxin-6-yl)-4-(phenylsulfanyl)-1,3-butadione (6r). 1.50 g, 91% yield; pale
yellow solid; mp 70.6–71.0 °C; Rf = 0.28 (n-hexane/EtOAc = 3:1); IR (KBr): 1605, 1575, 1507, 1284,
1066, 887, 771, 734, 686 cm−1; 1H NMR (500 MHz, CDCl3) (enol form):  7.41–7.38 (m, 3 H), 7.35 (dd,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 24 of 41
1
2
3
4
J = 8.5, 2.1 Hz, 1 H), 7.31–7.28 (m, 2 H), 7.22 (tt, J = 7.3, 1.5 Hz, 1 H), 6.89 (d, J = 8.5 Hz, 1 H), 6.26 (s,
5
6
7
13
1 H), 4.32–4.30 (m, 2 H), 4.28–4.27 (m, 2 H), 3.72 (s, 2 H); C{1H} NMR (126 MHz, CDCl3) (enol
8
9
form):  191.1, 182.6, 147.7, 143.5, 135.0, 130.0 (2C), 129.1 (2C), 127.7, 126.9, 121.0, 117.4, 116.5, 94.9,
64.7, 64.1, 40.9; HRMS (ESI-TOF): m/z [M − H]− calcd for C18H15O4S, 327.0697; found, 327.0698.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1-(2-Furyl)-4-(phenylsulfanyl)-1,3-butadione (6s).
1.05 g, 81% yield; yellow oil; Rf = 0.40 (n-
hexane/EtOAc = 3:1); IR (neat): 1611, 1585, 1546, 759, 741, 690 cm−1; 1H NMR (500 MHz, CDCl3) (enol
form):  7.56 (dd, J = 1.7, 0.7 Hz, 1 H), 7.41–7.39 (m, 2 H), 7.31–7.27 (m, 2 H), 7.24–7.20 (m, 1 H), 7.13
(dd, J = 3.5, 0.7 Hz, 1 H), 6.54 (dd, J = 3.5, 1.7 Hz, 1 H), 6.26 (s, 1 H), 3.70 (s, 2 H); 13C{1H} NMR (126
MHz, CDCl3) (enol form):  189.2, 174.6, 149.8, 146.3, 134.8, 130.1 (2C), 129.1 (2C), 127.0, 116.0, 112.6,
95.2, 40.4; HRMS (ESI-TOF): m/z [M − H]− calcd for C14H11O3S, 259.0434; found, 259.0433.
4-(Phenylsulfanyl)-1-(2-thienyl)-1,3-butadione (6t). 1.16 g, 84% yield; pale yellow solid; mp 37.6–
37.8 °C; Rf = 0.42 (n-hexane/EtOAc = 3:1); IR (KBr): 1602, 1579, 1481, 734, 724, 687 cm−1; 1H NMR
(500 MHz, CDCl3) (enol form):  7.62 (dd, J = 3.8, 1.1 Hz, 1 H), 7.59 (dd, J = 4.9, 1.1 Hz, 1 H), 7.42–
7.41 (m, 2 H), 7.31–7.28 (m, 2 H), 7.25–7.21 (m, 1 H), 7.11–7.10 (m, 1 H), 6.16 (s, 1 H), 3.69 (s, 2 H);
13C{1H} NMR (126 MHz, CDCl3) (enol form):  186.6, 180.6, 140.7, 134.8, 132.7, 130.5, 130.3 (2C),
129.1 (2C), 128.3, 127.1, 95.8, 39.9; HRMS (ESI-TOF): m/z [M − H]− calcd for C14H11O2S2, 275.0206;
found, 275.0204.
General Procedure for Synthesis of Sulfonium salts (2). To a suspension of trimethyloxonium
tetrafluoroborate (0.45 g, 3.0 mmol) in dry CH2Cl2 (10 mL) was added sulfide 6 (3.0 mmol) in dry CH2Cl2
(2 mL) via a cannula under an argon atmosphere. After stirring at room temperature for 12 h, the reaction
mixture was concentrated under reduced pressure. t-Butyl methyl ether was added to the precipitated
crude product, the mixture was stirred vigorously, and the t-butyl methyl ether phase was decanted. The
solid was washed with t-butyl methyl ether several times, and the residue was collected and recrystallized
to give sulfonium salt 2 (keto–enol mixture).
ACS Paragon Plus Environment

Page 25 of 41
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
(2,4-Dioxo-4-phenylbutyl)methylphenylsulfonium Tetrafuoroborate (2a). 0.98 g, 85% yield; yellow
solid (MeCN/Et2O); mp 129.4–130.2 °C; Rf = 0.54 (CH2Cl2/MeOH = 9:1); IR (KBr): 1626, 1589, 1576,
1073, 1045, 1034, 748, 681 cm−1; 1H NMR (500 MHz, CD3CN) (enol form):  7.99–7.97 (m, 2 H), 7.90–
7.88 (m, 2 H), 7.82–7.78 (m, 1 H), 7.73–7.70 (m, 2 H), 7.65–7.62 (m, 1 H), 7.54–7.51 (m, 2 H), 6.47 (s,
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
13
1 H), 4.85 (d, J = 15.8 Hz, 1 H), 4.76 (d, J = 15.8 Hz, 1 H), 3.27 (s, 3 H); C{1H} NMR (126 MHz,
CD3CN) (enol form):  188.0, 181.7, 135.9, 134.7, 133.4, 132.0 (2C), 131.7 (2C), 130.1 (2C), 128.2 (2C),
124.1, 97.6, 54.2, 27.2; HRMS (ESI-TOF): m/z [M − BF4]+ calcd for C17H17O2S, 285.0944; found,
285.0942.
(4-Methylphenyl-2,4-dioxobutyl)methylphenylsulfonium Tetrafluoroborate (2b). 1.01 g, 87% yield;
pale yellow solid (MeCN/Et2O); mp 143.0–143.7 °C; Rf = 0.54 (CH2Cl2/MeOH = 9:1); IR (KBr): 1621,
1581, 1570, 1509, 1073, 1047, 1034, 835, 792, 749, 681 cm−1; 1H NMR (500 MHz, CD3CN) (enol form):
 7.98–7.96 (m, 2 H), 7.81–7.78 (m, 3 H), 7.73–7.69 (m, 2 H), 7.33 (d, J = 8.0 Hz, 2 H), 6.43 (s, 1 H),
4.83 (d, J = 15.7 Hz, 1 H), 4.83 (d, J = 15.7 Hz, 1 H), 3.27 (s, 3 H), 2.40 (s, 1 H); C{1H} NMR (126
13
MHz, CD3CN) (enol form):  187.2, 182.2, 146.1, 135.9, 132.0 (2C), 131.7 (2C), 130.8 (2C), 130.7, 128.3
(2C), 124.1, 97.2, 54.0, 27.2, 21.7; HRMS (ESI-TOF): m/z [M − BF4]+ calcd for C18H19O2S, 299.1100;
found, 299.1098.
(4-n-Butylphenyl-2,4-dioxobutyl)methylphenylsulfonium Tetrafluoroborate (2c). 1.13 g, 88% yield;
white solid (MeCN/Et2O); mp 120.5–120.9 °C; Rf = 0.56 (CH2Cl2/MeOH = 9:1); IR (KBr): 1620, 1581,
1509, 1074, 1049, 1037, 845, 787, 747, 680 cm−1; 1H NMR (500 MHz, CD3CN) (enol form):  7.98–7.96
(m, 2 H), 7.81–7.78 (m, 3 H), 7.73–7.70 (m, 2 H), 7.35 (d, J = 8.4 Hz, 2 H), 6.42 (s, 1 H), 4.82 (d, J = 15.7
Hz, 1 H), 4.72 (d, J = 15.7 Hz, 1 H), 3.27 (s, 3 H), 2.68 (t, J = 7.7 Hz, 2 H), 1.63–1.57 (m, 2 H), 1.38–1.30
(m, 2 H), 0.92 (t, J = 7.4 Hz, 3 H); 13C{1H} NMR (126 MHz, CD3CN) (enol form):  187.2, 182.2, 150.9,
135.9, 132.0 (2C), 131.7 (2C), 130.9, 130.2 (2C), 128.3 (2C), 124.1, 97.2, 54.1, 36.2, 34.0, 27.2, 23.0,
14.1; HRMS (ESI-TOF): m/z [M − BF4]+ calcd for C21H25O2S, 341.1570; found, 341.1570.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 26 of 41
1
2
3
4
5
6
7
8
9
(4-Biphenyl-2,4-dioxobutyl)methylphenylsulfonium Tetrafluoroborate (2d). 1.21 g, 90% yield; light
yellow solid (MeCN/Et2O); mp 134.1–134.8 °C; Rf = 0.58 (CH2Cl2/MeOH = 9:1); IR (KBr): 1608, 1580,
1574, 1555, 1078, 1053, 845, 761, 746, 686 cm−1; 1H NMR (500 MHz, CD3CN) (enol form):  7.98–7.96
(m, 4 H), 7.83–7.79 (m, 3 H), 7.74–7.71 (m, 4 H), 7.52–7.49 (m, 2 H), 7.46–7.42 (m, 1 H), 6.50 (s, 1 H),
4.84 (d, J = 15.8 Hz, 1 H), 4.75 (d, J = 15.8 Hz, 1 H), 3.27 (s, 3 H); 13C{1H} NMR (126 MHz, CD3CN)
(enol form):  187.8, 181.3, 146.9, 140.2, 135.9, 132.0 (3C), 131.7 (2C), 130.1 (2C), 129.6, 128.8 (2C),
128.5 (2C), 128.1 (2C), 124.1, 97.5, 54.2, 27.2; HRMS (ESI-TOF): m/z [M − BF4]+ calcd for C23H21O2S,
361.1257; found, 361.1257.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(4-Methoxyphenyl-2,4-dioxobutyl)methylphenylsulfonium Tetrafluoroborate (2e). 1.01 g, 84% yield;
amber solid (MeCN/Et2O); mp 123.8–124.2 °C; Rf = 0.52 (CH2Cl2/MeOH = 9:1); IR (neat): 1628, 1602,
1568, 1509, 1244, 1175, 1073, 1045, 1032, 843, 793, 748, 681 cm−1; 1H NMR (500 MHz, CD3CN) (enol
form):  7.97–7.95 (m, 2 H), 7.87 (d, J = 9.0 Hz, 2 H), 7.82–7.78 (m, 1 H), 7.72–7.69 (m, 2 H), 7.03 (d, J
= 9.0 Hz, 2 H), 6.37 (s, 1 H), 4.79 (d, J = 15.5 Hz, 1 H), 4.69 (d, J = 15.5 Hz, 1 H), 3.86 (s, 3 H), 3.26 (s,
13
3 H); C{1H} NMR (126 MHz, CD3CN) (enol form):  185.7, 182.5, 165.4, 135.9, 132.0 (2C), 131.6
(2C), 130.6 (2C), 125.6, 124.1, 115.5 (2C), 96.7, 56.5, 53.8, 27.1 HRMS (ESI-TOF): m/z [M − BF4]+
calcd for C18H19O3S, 315.1049; found, 315.1043.
(2,4-Dioxo-4-Phenyloxyphenylbutyl)methylphenylsulfonium Tetrafluoroborate (2f). 1.17 g, 84% yield;
pale yellow solid (MeCN/Et2O); mp 138.0–138.4 °C (dec.); Rf = 0.52 (CH2Cl2/MeOH = 9:1); IR (KBr):
1627, 1604, 1585, 1504, 1238, 1072, 1044, 1033, 848, 794, 751, 692 cm−1; 1H NMR (500 MHz, CD3CN)
(enol form):  7.97–7.95 (m, 2 H), 7.89–7.87 (m, 2 H), 7.81–7.78 (m, 1 H), 7.73–7.70 (m, 2 H), 7.47–7.43
(m, 2 H), 7.28–7.25 (m, 1 H), 7.12–7.10 (m, 2 H), 7.05–7.02 (m, 2 H), 6.39 (s, 1 H), 4.80 (d, J = 15.6 Hz,
1 H), 4.71 (d, J = 15.6 Hz, 1 H), 3.27 (s, 3 H); 13C{1H} NMR (126 MHz, CD3CN) (enol form):  186.6,
181.7, 163.6, 156.2, 135.9, 132.0 (2C), 131.7 (2C), 131.3 (2C), 130.7 (2C), 127.6, 126.0, 124.1, 121.3
(2C), 118.6 (2C), 97.1, 53.9, 27.2 HRMS (ESI-TOF): m/z [M − BF4]+ calcd for C23H21O3S, 377.1206;
ACS Paragon Plus Environment

Page 27 of 41
The Journal of Organic Chemistry
1
2
3
found, 377.1206.
4
5
6
7
8
9
(4-Benzyloxyphenyl-2,4-dioxobutyl)methylphenylsulfonium Tetrafluoroborate (2g). 1.22 g, 85% yield;
orange solid (MeCN/Et2O); mp 137.0–137.5 °C; Rf = 0.52 (CH2Cl2/MeOH = 9:1); IR (KBr): 1603, 1547,
1509, 1245, 1177, 1053, 1038, 845, 789, 754, 682 cm−1; 1H NMR (500 MHz, CDCl3) (enol form):  7.97–
7.95 (m, 2 H), 7.87 (d, J = 9.0 Hz, 2 H), 7.81–7.78 (m, 1 H), 7.72–7.69 (m, 2 H), 7.46–7.45 (m, 2 H),
7.42–7.39 (m, 2 H), 7.36–7.34 (m, 1 H), 7.10 (d, J = 9.0 Hz, 2 H), 6.37 (s, 1 H), 5.18 (s, 2 H), 4.78 (d, J
= 15.5 Hz, 1 H), 4.68 (d, J = 15.5 Hz, 1 H), 3.26 (s, 3 H); 13C{1H} NMR (126 MHz, CD3CN) (enol form):
 185.8, 182.4, 164.4, 137.5, 135.9, 132.0 (2C), 131.6 (2C), 130.6 (2C), 129.6 (2C), 129.2, 128.8 (2C),
125.9, 124.1, 116.3 (2C), 96.8, 71.1, 53.8, 27.1; HRMS (ESI-TOF): m/z [M − BF4]+ calcd for C24H23O3S,
391.1362; found, 391.1362.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(4-Trifluoromethylphenyl-2,4-dioxobutyl)methylphenylsulfonium Tetrafluoroborate (2h). 1.09 g, 83%
yield; pale yellow solid (MeCN/Et2O); mp 132.0–132.8 °C (dec.); Rf = 0.52 (CH2Cl2/MeOH = 9:1); IR
(KBr): 1628, 1575, 1326, 1128, 1065, 1047, 1036, 859, 778, 770, 681 cm−1; 1H NMR (500 MHz, CD3CN)
(enol form):  8.04–8.02 (m, 2 H), 7.99–7.97 (m, 2 H), 7.84–7.79 (m, 3 H), 7.74–7.71 (m, 2 H), 6.52 (s, 1
H), 4.88 (d, J = 16.1 Hz, 1 H), 4.79 (d, J = 16.1 Hz, 1 H), 3.28 (s, 3 H); 13C{1H} NMR (126 MHz, CD3CN)
(enol form):  189.5, 178.9, 137.1, 135.9, 134.6 (q, J = 32.5 Hz), 132.0 (2C), 131.7 (2C), 130.1, 128.8
(2C), 127.0 (q, J = 3.8 Hz, 2C), 124.8 (q, J = 271.8 Hz), 98.5, 54.5, 27.2; HRMS (ESI-Orbitrap): m/z [M
− BF4]+ calcd for C18H16F3O2S, 353.0818; found, 353.0814.
(4-Ethoxycarbonylphenyl-2,4-dioxobutyl)methylphenylsulfonium Tetrafluoroborate (2i). 1.15 g, 86%
yield; white solid (MeCN/Et2O); mp 133.5–133.9 °C; Rf = 0.52 (CH2Cl2/MeOH = 9:1); IR (KBr): 1736,
1633, 1584, 1567, 1275, 1107, 1070, 1047, 1037, 774, 748, 682 cm−1; 1H NMR (500 MHz, CD3CN) (enol
form):  8.11–8.09 (m, 2 H), 7.98–7.95 (m, 4 H), 7.83–7.79 (m, 1 H), 7.74–7.71 (m, 2 H), 6.50 (s, 1 H),
4.87 (d, J = 16.1 Hz, 1 H), 4.78 (d, J = 16.1 Hz, 1 H), 4.36 (q, J =7.1 Hz, 2 H), 3.27 (s, 3 H), 1.37 (t, J =
7.1 Hz, 3 H); 13C{1H} NMR (126 MHz, CD3CN) (enol form):  189.4, 179.4, 166.3, 137.2, 135.9, 135.6,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 28 of 41
1
2
3
4
5
6
132.0 (2C), 131.7 (2C), 130.7 (2C), 128.2 (2C), 124.1, 98.3, 62.4, 54.5, 27.2, 14.5; HRMS (ESI-TOF):
m/z [M − BF4]+ calcd for C20H21O4S, 357.1155; found, 357.1156.
7
8
9
(4-Cyanophenyl-2,4-dioxobutyl)methylphenylsulfonium Tetrafluoroborate (2j). 1.05 g, 88% yield;
cream yellow solid (MeCN/Et2O); mp 141.3–142.1 °C (dec.); Rf = 0.52 (CH2Cl2/MeOH = 9:1); IR (KBr):
2234, 1639, 1577, 1560, 1066, 1050, 1035, 860, 783, 750, 682 cm−1; 1H NMR (500 MHz, CD3CN) (enol
form):  8.00–7.97 (m, 4 H), 7.87–7.85 (m, 2 H), 7.82–7.79 (m, 1 H), 7.74–7.70 (m, 2 H), 6.51 (s, 1 H),
4.89 (d, J = 16.1 Hz, 1 H), 4.80 (d, J = 16.1 Hz, 1 H), 3.27 (s, 3 H); 13C{1H} NMR (126 MHz, CD3CN)
(enol form):  189.8, 178.2, 137.4, 135.9, 133.9 (2C), 132.0 (2C), 131.7 (2C), 128.6 (2C), 124.0, 118.9,
117.0, 98.7, 54.6, 27.2; HRMS (ESI-TOF): m/z [M − BF4]+ calcd for C18H16NO2S, 310.0896; found,
310.0896.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(2-Chlorophenyl-2,4-dioxobutyl)methylphenylsulfonium Tetrafluoroborate (2k). 1.04 g, 85% yield;
shell pink solid (MeCN/Et2O); mp 107.9–108.5 °C; Rf = 0.56 (CH2Cl2/MeOH = 9:1); IR (KBr): 1620,
1597, 1579, 1043, 766, 747, 681 cm−1; 1H NMR (500 MHz, CD3CN) (enol form):  7.98–7.96 (m, 2 H),
7.83–7.80 (m, 1 H), 7.74–7.71 (m, 2 H), 7.59–7.57 (m, 1 H), 7.54–7.52 (m, 2 H), 7.46–7.42 (m, 1 H), 6.21
(s, 1 H), 4.73 (d, J = 15.9 Hz, 1 H), 4.73 (d, J = 15.9 Hz, 1 H), 3.27 (s, 3 H); 13C{1H} NMR (126 MHz,
CD3CN) (enol form):  187.5, 182.0, 136.0, 134.0, 133.9, 132.6, 132.0 (2C), 131.9, 131.7 (2C), 131.4,
128.6, 123.9, 102.9, 54.1, 27.2; HRMS (ESI-TOF): m/z [M − BF4]+ calcd for C17H1635ClO2S, 319.0554;
found, 319.0548.
(3-Chlorophenyl-2,4-dioxobutyl)methylphenylsulfonium Tetrafluoroborate (2l). 1.05 g, 86% yield;
pink solid (MeCN/Et2O); mp 133.5–133.9 °C; Rf = 0.56 (CH2Cl2/MeOH = 9:1); IR (KBr): 1624, 1579,
1564, 1072, 1045, 1036, 789, 747, 681 cm−1; 1H NMR (500 MHz, CD3CN) (enol form):  7.98–7.96 (m,
2 H), 7.87–7.86 (m, 1 H), 7.82–7.79 (m, 2 H), 7.74–7.70 (m, 2 H), 7.64–7.62 (m, 1 H), 7.52–7.49 (m, 1
H), 6.46 (s, 1 H), 4.85 (d, J = 15.9 Hz, 1 H), 4.75 (d, J = 15.9 Hz, 1 H), 3.27 (s, 3 H); 13C{1H} NMR (126
MHz, CD3CN) (enol form):  188.4, 179.7, 135.9, 135.6, 135.5, 134.2, 132.0 (2C), 131.8, 131.7 (2C),
ACS Paragon Plus Environment

Page 29 of 41
The Journal of Organic Chemistry
1
2
3
4
5
6
7
127.9, 126.6, 124.0, 98.1, 54.2, 27.2; HRMS (ESI-TOF): m/z [M − BF4]+ calcd for C17H1635ClO2S,
319.0554; found, 319.0546.
8
9
(4-Chlorophenyl-2,4-dioxobutyl)methylphenylsulfonium Tetrafluoroborate (2m). 1.01 g, 83% yield;
pale pink solid (MeCN/Et2O); mp 151.9–152.4 °C; Rf = 0.56 (CH2Cl2/MeOH = 9:1); IR (KBr): 1626, 1593,
1561, 1071, 1046, 1035, 841, 789, 749, 681 cm−1; 1H NMR (500 MHz, CD3CN) (enol form):  7–7.95
(m, 2 H), 7.86 (d, J = 8.8 Hz, 2 H), 7.82–7.79 (m, 1 H), 7.74–7.70 (m, 2 H), 7.54 (d, J = 8.8 Hz, 2 H), 6.43
(s, 1 H), 4.83 (d, J = 15.9 Hz, 1 H), 4.73 (d, J = 15.9 Hz, 1 H), 3.26 (s, 3 H); 13C{1H} NMR (126 MHz,
CD3CN) (enol form):  188.2, 180.3, 140.2, 135.9, 132.2, 132.0 (2C), 131.7 (2C), 130.3 (2C), 129.8 (2C),
124.0, 97.7, 54.2, 27.2; HRMS (ESI-TOF): m/z [M − BF4]+ calcd for C17H1635ClO2S, 319.0554; found,
319.0546.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(4-Fluorophenyl-2,4-dioxobutyl)methylphenylsulfonium Tetrafluoroborate (2n). 1.00 g, 85% yield;
pale orange solid (MeCN/Et2O); mp 142.5–143.0 °C; Rf = 0.56 (CH2Cl2/MeOH = 9:1); IR (KBr): 1627,
1600, 1577, 1507, 1230, 1072, 1045, 1035, 850, 795, 748, 681 cm−1; 1H NMR (500 MHz, CD3CN) (enol
form):  7.98–7.93 (m, 4 H), 7.82–7.78 (m, 1 H), 7.73–7.70 (m, 2 H), 7.27–7.24 (m, 1 H), 6.43 (s, 1 H),
4.83 (d, J = 15.8 Hz, 1 H), 4.73 (d, J = 15.8 Hz, 1 H), 3.27 (s, 3 H); 13C{1H} NMR (126 MHz, CD3CN)
(enol form):  187.3, 181.0, 166.9 (d, J = 253.2 Hz), 135.9, 132.0 (2C), 131.7 (2C), 131.1 (d, J = 9.7 Hz)
(2C), 130.0 (d, J = 3.0 Hz), 124.0, 117.2 (d, J = 22.6 Hz) (2C), 97.5, 54.0, 27.2; HRMS (ESI-TOF): m/z
[M − BF4]+ calcd for C17H16FO2S, 303.0850; found, 303.0847.
(4-Bromophenyl-2,4-dioxobutyl)methylphenylsulfonium Tetrafluoroborate (2o). 1.12 g, 83% yield;
pale pink solid (MeCN/Et2O); mp 141.3–142.2 °C; Rf = 0.60 (CH2Cl2/MeOH = 9:1); IR (KBr): 1625, 1590,
1560, 1067, 1046, 1036, 838, 787, 749, 681 cm−1; 1H NMR (500 MHz, CD3CN) (enol form):  7.97–7.95
(m, 2 H), 7.82–7.76 (m, 3 H), 7.73–7.67 (m, 4 H), 6.44 (s, 1 H), 4.84 (d, J = 15.9 Hz, 1 H), 4.74 (d, J =
15.9 Hz, 1 H), 3.26 (s, 3 H); 13C{1H} NMR (126 MHz, CD3CN) (enol form):  188.3, 180.3, 135.9, 133.3
(2C), 132.6, 132.0 (2C), 131.7 (2C), 129.9 (2C), 128.9, 124.0, 97.7, 54.2, 27.2; HRMS (ESI-TOF): m/z
ACS Paragon Plus Environment