Friedel-Crafts Coupling of Electron-Deficient Benzoylacetones Tuned by Remote Electronic Effects

Article abstract of DOI:10.1021/acs.joc.5b01371

Acid-catalyzed electrophilic aromatic substitution for C-C bond formation, commonly referred to as the Friedel-Crafts reaction in recognition of its discoverers, has been one of the most useful reactions in organic chemistry for over a century. However, t

Full text of DOI:10.1021/acs.joc.5b01371

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The Journal of Organic Chemistry
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Friedel−Crafts Coupling of Electron-Deficient Benzoylacetons Tuned by
Remote Electronic Effects
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Hongmei Luo, Ling Pan,* Xianxiu Xu and Qun Liu*
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Department of Chemistry, Northeast Normal University, Changchun 130024, China
ABSTRACT: Acid-catalyzed electrophilic aromatic substitution for C–C bond-formation, commonly
referred to as the Friedel−Crafts reaction in recognition of its discoverers, is one of the most useful
reactions in organic chemistry for over a century. However, the Friedel−Crafts reaction can not occur
on a benzene ring having a strongly electron-withdrawing group, such as an acyl group, which
deactivates the aromatic ring toward electrophilic substitutions and remains a major challenge. Herein,
the synthesis of naphthoquinones and 1,3-indandiones, bearing two acyl groups at ortho-positions to
each other on a benzene ring, are demonstrated by means of copper-catalyzed intramolecular aerobic
oxidative acylation of benzoylacetone derivative precursors. This unusual Friedel−Crafts reaction
reveals a new activation mode for the in-situ polarity-reverse of an electron-deficient aromatic ring to a
reactive, electron-rich one tuned by remote electronic effects.
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INTRODUCTION
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The Friedel−Crafts reaction, an acid-catalyzed electrophilic aromatic substitution reaction first reported
by Friedel and Crafts on the AlCl3-catalyzed alkylation or acylation of benzene with an alkyl halide and
a carboxylic acid chloride, respectively, is the most common reaction of aromatic compounds and one
of the most useful synthetic methods in organic chemistry for over a century.1 Cyclization of aromatic
compounds by intramolecular attack on an aromatic ring is the intramolecular version of the
Friedel−Crafts reactions,2 such as the Haworth reaction based on a three-step synthesis of 1-tetralone
derivatives through Friedel−Crafts acylation, Clemmensen reduction, and intramolecular
Friedel−Crafts acylation starting from an arene and succinic anhydride (Scheme 1a).3 Recently,
Ohwada and co-workers described that arylacetoacetates can be transformed into dihydronaphthalenes
(as a mixture of acid and ester) through self-condensation in the superacid, trifluoromethanesulfonic
acid (TFSA, 10 equiv, Scheme 1b).4 For this intramolecular aromatic substitution, the tricationic,
superelectrophilic species was proposed to interpret the enhanced electrophilicity of the preferred keto
cyclization based on the principle of superacid-promoted Friedel−Crafts reactions for the activation of
electrophiles.4,5 In 2011, Siegel and co-workers showed an intramolecular Friedel−Crafts aryl–aryl
coupling of fluoroarenes,6 which is activated by silyl cation through the exchange of C−F bond for the
more stronger Si−F bond to generate active aryl carbocations from fluoroarenes.6,7 These results4–6
largely expanded the utility of Friedel−Crafts reaction and are in accord with the electrophilic aromatic
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substitution reaction for C–C bond-formation as well.1–8
Friedel−Crafts alkylation and acylation reactions are very useful methods for C–C bond formations.
However, the Friedel−Crafts reaction can’t occur on the benzene ring having the strongly
electron-withdrawing acyl group, which deactivates the aromatic ring toward electrophilic substitutions.
This is a strict limitation of the Friedel−Crafts reaction.1–8 Recently, we disclosed a concept,
“polarity-reversible conjugate addition”, showing that the polarity of a classical Michael acceptor can
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Scheme 1. Intramolecular Friedel−Crafts Coupling
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be reversed through remote electronic effects.9 Mechanism studies10 and related experimental results
support this concept.10,11 In our recent research on the CuI-catalyzed oxidative C–C bond cleavage
reaction of methyl ketones using molecular oxygen as the oxidant,12,13 it was found that the reaction of
4-phenylbutan-2-one gave the sequential C–C bond cleavage product, benzaldehyde, in high yield via
2-oxo-4-phenylbutanal as an intermediate.12 An attempted extension of the C–C bond cleavage
methodology in connection with our research on the ketene dithioacetal chemistry,13–17 we found that,
catalyzed by Cu(OAc)2 in the presence of molecular oxygen as the oxidant, the aldehyde,
2-(1,3-dithiolan-2-ylidene)-3-oxo-3-phenylpropanal 3 (Scheme 1c), is inert to further transformation.
This result is similar to our previous results.12 Interestingly, under identical reaction conditions, the
1,2-diacylbenzene derivatives, 3-(1,3-dithiolan-2-ylidene)naphthalene-1,2,4(3H)-triones
2
and
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2-(1,3-dithiolan-2-ylidene)-1H-indene-1,3(2H)-diones 5, were obtained from the reactions of
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2-(1,3-dithiolan-2-ylidene)-1-phenylbutane-1,3-diones
1
and
2-(1,3-dithiolan-2-ylidene)-
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1-phenylpentane-1,3-diones 4, respectively (Scheme 1c). These transformations represent the unusual
modes of the Friedel−Crafts reaction involving the C–C bond formation on a benzene ring having a
strongly electron-withdrawing acyl group. In this paper, we disclose the realization of the
intramolecular Friedel−Crafts reaction of benzoylacetone derivatives for the concise synthesis of
naphthoquinones and 1,3-indandiones in a single operation starting from readily available substrates
and reveal an umpolung strategy for the polarity-reverse from an electron-deficient aromatic ring into a
reactive, electron-rich one tuned by remote electronic effects, for the first time.
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RESULTS AND DISCUSSION
The starting materials, 2-(1,3-dithiolan-2-ylidene)-1-arylbutane-1,3-diones 1 were readily prepared by
the reaction of aroylacetones with CS2 and Br(CH2)2Br (or Cl(CH2)2Cl) under basic conditions or by
Friedel−Crafts-type acylation of the corresponding acyl/aroyl ketene dithioacetals.14,15 In the present
research, initially, the reactions of 1 bearing a terminal acetyl group were examined with
2-(1,3-dithiolan-2-ylidene)-1-phenylbutane-1,3-dione 1a as a model employing the catalyst system
applied to the oxidative C–C bond cleavage reaction of methyl ketones.12,13 Catalyzed by CuI in the
o
solvent, dimethyl sulfoxide (DMSO), under oxygen atmosphere (balloon)12,13 at 115 C for 40 h, the
reaction
of
1a
gave
the
naphthoquinone
product,
3-(1,3-dithiolan-2-ylidene)naphthalene-1,2,4(3H)-trione 2a, in 32% yield (Table 1, entry 1). This result
suggests that the formation of naphthoquinone 2a involves the acetyl sp3C–H bond oxidation of 1a,
similar to the oxidation of 4-phenylbutan-2-one12 followed by intramolecular cyclization to form a
six-membered ring through an unusual Csp2–Csp2 bonding between the ortho-C–H of the
electron-deficient aryl ring and the terminal aldehydic C–H bond (vide infra). Encouraged by this result,
the reaction conditions were then optimized as shown in Table 1. Increasing CuI loading resulted in a
higher yield of 2a (Table 1, entry 2). Similar results were obtained by using CuCl and CuBr as the
catalysts, respectively (Table 1, entries 3 and 4). In comparison, Cu(OAc)2 as the catalyst led to the best
result for the formation of 2a (Table 1, entry 7, along with 7% yield of
2-(1,3-dithiolan-2-ylidene)-3-oxo-3-phenylpropanal 3 formed via oxidative C–C bond cleavage12,13).
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Table 1. Catalyst screening and optimization of reaction conditionsa
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O
S
O
S
O
S
O2, catalyst
S
S
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9
S
solvent
temperarure
O
H
O
O
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O
1a
2a
3
Entry
1
Catalyst (mol%)
CuI (30)
Solvent
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
T (oC)
115
115
115
115
115
115
115
115
115
115
115
115
80
Time (h)
40
Yield (%)b
32
2
CuI (60)
20
57
3
CuCl (60)
64
68
4
CuBr (60)
60
63
5
CuCl2 (60)
48
75
6
Cu(OTf)2 (60)
Cu(OAc)2 (60)
Cu(OAc)2 (30)
PdCl2 (60)
72
42
7
24
90
8
48
87
9
24
N.R.c
N.R.c
78
10
11
12
13
14
15
16
17
Pd(OAc)2 (60)
Cu(OAc)2 (60)
Cu(OAc)2 (60)
Cu(OAc)2 (60)
Cu(OAc)2 (60)
Cu(OAc)2 (60)
Cu(OAc)2 (60)
CuBr2 (60)
24
24
TCP
72
46
N.R.c
DMSO
DMSO
DMSO
DMSO
DMSO
24
100
115
115
115
70
82
30
56d
NRc,e
24
24
5
aReaction conditions: 2-(1,3-dithiolan-2-ylidene)-1-phenylbutane-1,3-dione 1a (0.5 mmol scale), O2
(balloon), solvent (8 mL). bIsolated yields. cNo reaction was observed. dThe reaction was performed in the
open air. eThe reaction was performed under nitrogen atmosphere.
These results indicated either the higher catalytic activity of Cu(II) than Cu(I) (Table 1, entry 3 versus
entry 5) and the significant influence of the counteranion of catalysts on the transformation from 1a to
2a (Table 1, entry 7 versus entries 5 and 6). Under identical conditions, PdCl2 and Pd(OAc)2 as
catalysts were ineffective (Table 1, entries 9 and 10). Among the solvents tested, DMSO gave the
highest yield of 2a (Table 1, entry 7) in comparison with dimethylformamide (DMF, Table 1, entry 11)
or 1,2,3-trichloropropane (1,2,3-TCP, Table 1, entry 12). It was found that no reaction occurred at all
(1a was recovered quantitatively) when the reaction of 1a was performed under the optimal conditions
as in Table 1, entry 7 but under a nitrogen atmosphere (Table 1, entry 16). It was also found that,
catalyzed by CuBr2, the reaction of 1a could be completed in about 4 h, however gave only 24% yield
of 2a isolated from the reaction mixture (Table 1, entry 17).
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Table 2. Synthesis of Naphthoquinonesa,b
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a Reaction conditions: 2-(1,3-dithiolan-2-ylidene)-1-aryllbutane-1,3-dione 1 (0.5 mmol scale), solvent (8
mL), O2 (balloon) at 115 oC. b Isolated yields.
The transformation of 1a to 2a is an unusual oxidative intramolecular acylation reaction because the
benzene ring of 1a having an acyl group. This transformation is previously unknown in Friedel−Crafts
reactions.1–8 Thus, with the optimal conditions (Table 1, entry 7) in hand, the scope of the
transformation from -acetyl ketene dithioacetals 1 to naphthoquinones 2 was examined. As shown in
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Table 2, a wide range of naphthoquinone derivatives 2 were prepared, which all participated in a
straightforward manner for the unusual intramolecular acylation reaction, thereby furnishing the
desired naphthoquinones 2 with high efficiency. For the aryl ketone substrates 1 with either
electron-donating (1b−1g, 1j, 1k and 1l) or electron-withdrawing substitutes (1h, 1i and 1m) on the
aryl ring of 1 gave the corresponding acylation products 2 in good to excellent yields. In addition, the
desired naphthoquinones 2n and 2o were also obtained in good yields from aryl ketones 1n and 1o
having a heteraryl and a 2-naphthalenyl unit, respectively (Table 2).
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Clearly, naphthoquinones 2b−2g, 2j, 2k and 2l/2l’ can be prepared in high to excellent yields from
those -acetyl ketene dithioacetals 1 bearing electron-donating substituents on the aryl ring. In
comparison, naphthoquinones 2h, 2i, 2m/2m’ can also be synthesized from the corresponding -acetyl
ketene dithioacetals 1 although bearing an additional electron-withdrawing substituent on the aryl ring
(Table 2). These results indicate that the above ortho-acylation reactions are a powerful tool to expand
the conventional Friedel−Crafts reactions.1–8
The unusual intramolecular oxidative ortho-acylation of aryl ketones 1 mentioned above (Table 2)
provides a new and an efficient access to naphthoquinone derivatives.18 For further understanding the
unusual coupling reaction, selected experiments were performed using the readily available
2-(1,3-dithiolan-2-ylidene)-1-arylpentane-1,3-diones 4 as the substrates.14,15 It was found that no
reaction occurred when 2-(1,3-dithiolan-2-ylidene)-1-arylpentane-1,3-dione 4a was treated under the
identical reaction conditions as described for the synthesis of naphthoquinones 2 (Table 2). Whereas,
o
when the reactions of 4 were carried at a higher temperature (145 C) than the reaction of 1,
2-(1,3-dithiolan-2-ylidene)-1H-indene-1,3(2H)-dione derivatives 5 were produced in good to high
yields via a formal deethylation/intramolecular ortho-acylation sequence to form the five-membered
ring (Table 3).19 Similar to the synthesis of naphthoquinones 2, the substrate,
2-(1,3-dithiolan-2-ylidene)-1-arylpentane-1,3-diones 4g and 4h, bearing an additional
electron-withdrawing substituent on the aryl ring gave relatively lower yields of the 1,3-indandione
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products 5g and 5h than 1,3-indandiones 5a−d having an electron-donating substituent on the aryl ring.
Interestingly, 1,3-indandiones 5e and 5f were produced in relatively lower yields although the
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corresponding substrates bearing an electron-donating methoxy and ethyoxy group, respectively.
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Table 3. Synthesis of 1,3-Indandionesa,b
a Reaction conditions: 2-(1,3-dithiolan-2-ylidene)-1-arylpentane-1,3-diones 4 (0.5 mmol scale), solvent (8
mL), O2 (balloon) at 145 oC. bIsolated yields.
The above reactions exhibit high levels of chemoselectivity and broad functional-group tolerance.
The intramolecular cyclization of 2-(1,3-dithiolan-2-ylidene)-1-phenylbutane-1,3-diones 1 forms a
six-membered
ring
(Table
2).
Whereas,
the
cyclization
of
2-(1,3-dithiolan-2-ylidene)-1-phenylpentane-1,3-diones 4 under similar reaction conditions forms a
five-membered ring (Table 3). To understand the reaction mechanisms, a series of experiments was
designed and conducted.
Firstly, the cyclization reaction of 2-(1,3-dithiolan-2-ylidene)-1-phenylhexane-1,3-dione 6a was
performed to examine the influence of alkyl chain length of the aroyl ketone substrates on the synthesis
of indene-1,3(2H)-dione derivatives 5. As the result, 5a was obtained in moderate yield by treatment of
6a under identical conditions as for the synthesis of 5 (Scheme 2a). This result indicates that the
cyclization reactions of 4 and 6 share the same mechanism. The relatively lower yield of 5a from 6a is
likely due to the less reactivity of 6a than 4a because the former has a longer alkyl chain.
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Scheme 2. Mechanism Studies
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Secondly, the reaction of 2-(1,3-dithiolan-2-ylidene)-3-oxo-3-phenylpropanal 3 was examined in
details under the conditions for the formation of either naphthoquinones 2 (Table 2) and
1,3-indandiones 5 (Table 3), respectively. In both cases, compound 3 was inert and was recovered in
nearly quantitative yield (Scheme 2b). These results imply that 3 is very stable under the reaction
conditions applied. In addition, these results exclude the mechanism accounting for
cross-dehydrogenative coupling (CDC) reactions to form the C–C bond20 leading to 1,3-dione 5a.
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Thirdly, it was found that compound 3 could be prepared in excellent isolated yield by aerobic
oxidation of 2-(1,3-dithiolan-2-ylidene)-1-phenylpropan-1-one 7 (Scheme 2c) under identical
conditions as described in Table 3. This result give further evidence for the stability of 3 under the
reaction conditions as indicated above.
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Forthly, to provide further insights into the reaction mechanisms, the tandem oxidative C–C bond
cleavage/intramolecular
Friedel−Crafts
alkylation/aerobic
oxidation
reaction
of
2-(1,3-dithiolan-2-ylidene)-N-methyl-3-oxo-N-phenylbutanamides 8 were investigated. As the results,
3-(1,3-dithiolan-2-ylidene)-1-methylquinoline-2,4(1H,3H)-diones 9a and 9b were obtained in moderate
yields (Scheme 2d). Although the Friedel−Crafts-type CDC process for the formation of 9 via aldehyde
intermediate 10 can’t be excluded,20 a mechanism involving Friedel−Crafts cyclization1–5 to form
alcohol intermediate 11 followed by aerobic oxidation12,13 to form 9 is preferred due to N-acyl anilines
8 have the electron-rich aromatic ring.
Based on the above experimental results, a mechanism for the formation of naphthoquinones 2 is
proposed with the reaction of 1a as an example (Scheme 3a). Similar as the previous work,
Cu-catalyzed aerobic oxidation of 1a gives aldehyde intermediate I via the enol form of 1a’.12,13,21
Aldehyde intermediate I should be inert for the intramolecular Friedel−Crafts alkylation because I has
a strongly electron-withdrawing acyl substituent on the benzene ring1–5 (also see Scheme 2b and
Scheme 2c for the stability of 3 under the identical conditions). On the other hand, the CDC reaction20
of I through Csp2–Csp2 bond-formation between the ortho-C–H bond of the aryl ring and the aldehydic
C–H bond to afford naphthoquinones 2 seems impossible because the related compound 3 is very stable
under the identical reaction conditions (Scheme 2b and Scheme 2c).
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Scheme 3. Suggested Mechanism for Formation of Products 2 and 5
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Thereby, the Cu(II) enolate complex intermediate III will be generated by coordination of the
hydrate intermediate II with Cu(OAc)2.15,22 Complex III, as the key intermediate, the aryl ring has been
tuned to the electron-rich one at this stage by the remote electron-donating enol p- conjugation
structure of the side chain.23 As the result of the umpolung of the innate reactivity of aryl ketone 1a at
the ortho-position of the aryl ring, the intramolecular Friedel−Crafts reaction of intermediate III
enables the formation of naphthoquinone 2a through an intramolecular Friedel−Crafts reaction as the
crucial step, followed by deprotonation, regeneration of the catalyst, Cu(OAc)2, and
Cu(OAc)2-catalyzed aerobic oxidation sequence (Scheme 3a).12,13,21 It should be mentioned that,
similar to the polarity-reversible conjugate addition,9–11 the zwitterionic resonance contribution of III’
attributing to an S…O interaction of the -oxo ketene dithioacetal moiety (Scheme 3a)15,24,25 may play
an important role for the remote electronic effects to make the polarity reverse of the electron-deficient
aromatic ring to the electron-rich one. As described above, the formation of 1,3-indandiones 5 should
follow a similar umpolung procedure, whereas leading to a five- instead of six-membered carbocycle
via intramolecular Friedel−Crafts reaction (Scheme 3b).
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Thus, Cu-catalyzed aerobic oxidation of ethyl ketone 5a gives hydroxyl -diketone intermediate A
followed by formation of the Cu(II) enolate complex intermediate B in equilibrium with C as the key
intermediate. Whereby, the intramolecular Friedel−Crafts cyclization will lead to a five-membered ring
by reaction at the -carbon of the -unsaturated aldehyde moiety of the side chain. Subsequent
proton elimination (transfer) of intermediate D results in intermediate E. Finally, 1,3-indandione 5a is
formed through the sequential release of Cu(OAc)2 and oxalaldehyde. In comparison, intermediate C
should be less reactive than intermediate IV as described in Scheme 3b due to the existence of the
terminal
electron-withdrawing
formyl
group.
The
transformation
from
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2-(1,3-dithiolan-2-ylidene)-1-phenylhexane-1,3-dione 6a to 1,3-indandione 5a (Scheme 2a) gives
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further evidence for the proposed mechanism.
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CONCLUSION
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In summary, the rapid and concise synthesis of naphthoquinones 2 and 1,3-indandiones 5 in a single
operation starting from readily available benzoylacetone derivative precursors has been described for
the first time. It has been revealed that although the aromatic rings of
2-(1,3-dithiolan-2-ylidene)-1-arylbutane-1,3-diones
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and
2-(1,3-dithiolan-2-ylidene)-1-arylpentane-1,3-diones 4 bear strongly electron-withdrawing groups and
are not reactive for the traditional Friedel−Crafts reactions, the intramolecular Friedel−Crafts reaction
of these substrates can be achieved by the umpolung of the normal reactivity of the aryl ring during the
reaction. This new concept, namely electron-deficient aromatic ring umpolung, for the in-situ
polarity-reverse of an electron-deficient aromatic ring to a reactive, electron-rich one tuned by
electronic effects, provides new insights into the Friedel−Crafts reactions. The reactions exhibit high
levels of chemoselectivity and broad functional-group tolerance. Efforts toward expanding the
umpolung methodology are currently underway in our laboratory and will be reported in due course.
EXPERIMENTAL SECTION
General Information. All reagents were purchased from commercial sources and used without
further purification, unless otherwise indicated. All reactions were monitored by TLC, which was
performed on precoated aluminum sheets of silica gel. The products were purified by column
chromatography on flash silica gel. Melting points were uncorrected. NMR spectra were obtained by
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500 MHz and 400 MHz for H NMR; 125 MHz for C NMR, with TMS as the internal standard. All
chemical shifts are given in ppm. The solvent peaks were not integrated in all the NMR spectra.
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High-resolution mass spectra (HRMS) were obtained using a micro TOF focus spectrometer (ESI).
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General experimental procedures for the synthesis of naphthoquinones (with 2a as an example).
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To the solution of 2-(1,3-dithiolan-2-ylidene)-1-phenylbutane-1,3-dione 1a (132 mg, 0.5 mmol) in
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DMSO (8.0 mL) was added anhydrous Cu(OAc)2 (99.0 %, 55 mg, 0.3 mmol) at room temperature, then
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the reaction was heated up to 115 C and stirred under O2 atmosphere. After 1a was consumed as
indicated by TLC, the resulting mixture was cooled to room temperature, poured into water (30 mL)
and extracted with dichloromethane (15 mL × 3). The combined organic phase was washed with water
(15 mL ×3), dried over anhydrous Na2SO4 and concentrated in vacuo. The crude product was purified
by column chromatography on silica gel (dichloromethane: ethyl acetate: petroleum ether = 0.25/1/5,
V/V/V) to give 3-(1,3-dithiolan-2-ylidene)naphthalene-1,2,4(3H)-trione 2a (124 mg, 90%, 0.45 mmol).
3-(1,3-dithiolan-2-ylidene)naphthalene-1,2,4(3H)-trione (2a). Obtained as a yellow solid; isolated
yield: 124 mg (90%); m.p. 218–219 oC. Eluent dichloromethane/ethyl acetate/petroleum ether (0.25/1/5,
V/V/V). 1H NMR (DMSO, 500 MHz, ppm):3.57 (s, 4H), 7.82 (t, J = 7.5 Hz, 1H), 7.90 (t, J = 7.5 Hz,
1H), 8.04 (d, J = 7.5 Hz, 1H), 8.16 (d, J = 7.5 Hz, 1H) 13C NMR (DMSO, 125 MHz, ppm):38.0,
38.2, 122.8, 127.6, 127.8, 132.5, 134.1, 134.6, 135.5, 175.1, 179.3, 180.0, 192.5. HRMS (ESI-TOF)
m/z Calcd. for C13H9O3S2 [M + H]+: 276.9988, found: 276.9990.
3-(1,3-dithiolan-2-ylidene)-7-methylnaphthalene-1,2,4(3H)-trione (2b). Obtained as a yellow solid;
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isolated yield: 132 mg (91%); m.p. 253–254 C. Eluent dichloromethane/ethyl acetate/n-hexane
(0.25/1/5, V/V/V). 1H NMR (CDCl3, 500 MHz, ppm):2.51 (s, 3H), 3.52 (s, 4H), 7.64 (d, J = 7.5 Hz,
1H), 8.01 (s, 1H), 8.20 (d, J = 7.5 Hz, 1H). 13C NMR (CDCl3, 125 MHz, ppm): 21.7, 37.7, 37.9,
122.5, 128.2, 131.7, 132.1, 136.4, 144.8, 175.1, 179.8, 179.9, 193.1. HRMS (ESI-TOF) m/z Calcd. for
C14H10NaO3S2 [M+Na]+: 312.9964, found 312.9970.
3-(1,3-dithiolan-2-ylidene)-7-ethylnaphthalene-1,2,4(3H)-trione (2c). Obtained as a yellow solid;
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isolated yield: 132 mg (87%); m.p. 214–215 C. Eluent dichloromethane/ethyl acetate/n-hexane
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(0.25/1/5, V/V/V). H NMR (CDCl3, 500 MHz, ppm): 1.31 (t, J = 7.5 Hz, 3H), 2.80 (q, J = 7.5 Hz,
2H), 3.52 (s, 4H), 7.66 (d, J = 7.5 Hz, 1H), 8.03 (s, 1H), 8.21 (d, J = 7.5 Hz, 1H). 13C NMR (CDCl3,
125 MHz, ppm): 14.9, 28.9, 37.7, 37.9, 122.5, 127.0, 128.2, 131.7, 132.3, 135.3, 150.9, 175.1,
179.8(2C), 193.1. HRMS (ESI-TOF) m/z Calcd. for C15H13O3S2 [M + H]+: 305.0301, found 305.0292.
3-(1,3-dithiolan-2-ylidene)-7-isopropylnaphthalene-1,2,4(3H)-trione (2d). Obtained as a yellow solid;
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isolated yield: 141.5 mg (89%); m.p. 202–203 C. Eluent dichloromethane/ethyl acetate/n-hexane
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(0.25/1/5, V/V/V). H NMR (CDCl3, 500 MHz, ppm):  1.32 (d, J = 7.0 Hz, 6H), 3.04–3.09 (m, 1H),
3.53 (s, 4H), 7.70 (dd, J1 = 8.0 Hz, J2 = 1.5 Hz, 1H), 8.06 (d, J =1.5 Hz, 1H), 8.22 (d, J = 8.0 Hz, 1H).
13C NMR (CDCl3, 125 MHz, ppm): 23.4, 34.3, 37.7, 37.9, 122.5, 125.7, 128.3, 131.8, 132.4, 134.0,
155.4, 175.2, 179.8(2C), 193.1. HRMS (ESI-TOF) m/z Calcd. for C16H15O3S2 [M + H]+: 319.0457,
found 319.0449.
7-(tert-butyl)-3-(1,3-dithiolan-2-ylidene)naphthalene-1,2,4(3H)-trione (2e). Obtained as a yellow
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solid; isolated yield: 141 mg (85%); m.p. 212–213 C. Eluent dichloromethane/ethyl acetate/n-hexane
(0.25/1/5, V/V/V). 1H NMR (CDCl3, 500 MHz, ppm):  1.40 (s, 9H), 3.54 (s, 4H), 7.88 (dd, J1 = 8.0 Hz,
J2 = 2.0 Hz, 1H), 8.19 (d, J = 2.0 Hz, 1H), 8.23 (d, J = 8.0 Hz, 1H). 13C NMR (CDCl3, 125 MHz, ppm):
30.7, 35.3, 37.6, 37.8, 122.3, 124.4, 127.9, 131.3, 131.9, 132.8, 157.6, 175.1, 179.6, 179.8, 193.1.
HRMS (ESI-TOF) m/z Calcd. for C17H17O3S2 [M + H]+: 333.0614, found 333.0604.
3-(1,3-dithiolan-2-ylidene)-7-methoxynaphthalene-1,2,4(3H)-trione (2f). Obtained as a yellow solid;
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isolated yield: 127 mg (83%); m.p. 189–190 C. Eluent dichloromethane/ethyl acetate/n-hexane
(0.25/1/5, V/V/V). 1H NMR (DMSO, 500 MHz, ppm): 3.55 (s, 4H), 3.93 (s, 3H), 7.45 (m, 2H), 8.11
(d, J = 8.5 Hz, 1H). 13C NMR (DMSO, 125 MHz, ppm): 56.5, 110.5, 122.3, 122.5, 128.0,
130.3, 134.4, 163.7, 175.2, 179.2, 179.5, 191.6. HRMS (ESI-TOF) m/z Calcd. for C14H11O4S2 [M +
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H]+ :307.0093, found 307.0098.
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3-(1,3-dithiolan-2-ylidene)-7-(trifluoromethoxy)naphthalene-1,2,4(3H)-trione (2g). Obtained as a
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yellow solid; isolated yield: 156.6 mg (87%); m.p. 207–208 C. Eluent dichloromethane/ethyl
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acetate/n-hexane (0.25/1/5, V/V/V). 1H NMR (CDCl3, 500 MHz, ppm): 3.54 (s, 4H), 7.64 (d, J = 8.5
Hz, 1H), 8.00 (s, 1H), 8.38 (d, J = 8.5 Hz, 1H). 13C NMR (CDCl3, 125 MHz, ppm):  37.9, 38.0, 118.6,
120.2 (q, J = 258.9 Hz, CF3), 122.2, 127.0, 130.7, 132.4, 133.5, 153.0, 174.2, 178.5(2C), 194.8. HRMS
(ESI-TOF) m/z Calcd. for C14H8F3O4S2 [M + H]+: 360.9811, found 360.9801.
7-chloro-3-(1,3-dithiolan-2-ylidene)naphthalene-1,2,4(3H)-trione (2h). Obtained as a yellow solid;
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isolated yield: 97.6 mg (63%); m.p. 220–221 C. Eluent dichloromethane/ethyl acetate/n-hexane
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(0.25/1/5, V/V/V). H NMR (DMSO, 500 MHz, ppm): 3.58 (s, 4H), 7.93–7.96 (m, 2H), 8.16 (d, J =
8.5 Hz, 1H). 13C NMR (DMSO, 125 MHz, ppm): 38.1, 38.2, 122.6, 126.7, 130.0, 133.2, 134.1, 135.1,
139.0, 174.7, 178.1, 179.2, 192.7. HRMS (ESI-TOF) m/z Calcd. for C13H8ClO3S2 [M + H]+ :310.9598,
found 310.9595.
7-bromo-3-(1,3-dithiolan-2-ylidene)naphthalene-1,2,4(3H)-trione (2i). Obtained as a yellow solid;
isolated yield:101 mg (57%); m.p. 243–244 oC. Eluent dichloromethane/ethyl acetate/n-hexane
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(0.25/1/5, V/V/V). H NMR (DMSO, 500 MHz, ppm): 3.58 (s, 4H), 8.08–8.10 (m, 3H). 13C NMR
(DMSO, 125 MHz, ppm): 38.1, 38.2, 122.7, 127.9, 129.6, 130.0, 133.5, 134.1, 138.0, 174.7, 178.1,
179.4, 192.7. HRMS (ESI-TOF) m/z Calcd. for C13H8BrO3S2 [M + H]+: 354.9093, found 354.9102.
3-(1,3-dithiolan-2-ylidene)-5-methylnaphthalene-1,2,4(3H)-trione (2j). Obtained as a yellow solid;
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isolated yield: 98.6 mg (68%); m.p. 224–225 C. Eluent dichloromethane/ethyl acetate/n-hexane
(0.25/1/5, V/V/V). 1H NMR (CDCl3, 500 MHz, ppm): 2.87 (s, 3H), 3.50 (m, 4H), 7.58–7.63 (m, 2H),
8.14 (d, J = 7.5 Hz, 1H). 13C NMR (CDCl3, 125 MHz, ppm): 23.7, 37.6, 37.7, 123.6, 126.9, 131.9,
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132.5, 133.1, 139.7, 142.3, 174.9, 180.7, 182.5, 192.6. HRMS (ESI-TOF) m/z Calcd. for C14H11O3S2
[M + H]+: 291.0144, found 291.0145.
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3-(1,3-dithiolan-2-ylidene)-6,8-dimethylnaphthalene-1,2,4(3H)-trione (2k). Obtained as a yellow
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solid; isolated yield: 123 mg (81%); m.p. 175–176 C. Eluent dichloromethane/ethyl acetate/n-hexane
(0.25/1/5, V/V/V). 1H NMR (CDCl3, 500 MHz, ppm):  2.47 (s, 3H), 2.74 (s, 3H), 3.51 (s, 4H), 7.34 (s,
1H), 8.01 (s, 1H). 13C NMR (CDCl3, 125 MHz, ppm): 21.9, 22.7, 37.7, 37.9, 121.7, 127.1, 127.7,
135.9, 137.9, 143.1, 145.7, 175.9, 180.4, 181.1, 192.3. HRMS (ESI-TOF) m/z Calcd. for C15H13O3S2
[M + H]+: 305.0301, found 305.0294.
3-(1,3-dithiolan-2-ylidene)-6-methylnaphthalene-1,2,4(3H)-trione
(2l);
3-(1,3-dithiolan-2-ylidene)-5-methylnaphthalene-1,2,4(3H)-trione (2l’). Obtained as a yellow solid;
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isolated yield: 104.4 mg (72%); m.p. 125–127 C; 2l/2l’ = 1.0:1.4. Eluent dichloromethane/ethyl
acetate/n-hexane (0.25/1/5, V/V/V). 2l, 1H NMR (CDCl3, 500 MHz, ppm): 2.53 (s, 3H), 3.53 (m, 4H),
7.53–7.54 (m, 1H), 8.10– 8.11 (m, 2H); 2l’, 1H NMR (CDCl3, 500 MHz, ppm):  2.78 (s, 3H), 3.53
(m, 4H), 7.53–7.54 (m, 1H), 7.68 (t, J = 7.5 Hz, 1H), 8.24 (d, J = 7.5 Hz, 1H). 13C NMR (CDCl3, 125
MHz, ppm): 22.2, 22.8, 37.7, 37.9, 121.6, 122.6, 126.5, 128.3(2C), 129.6, 129.8, 134.3(2C), 134.5,
135.9, 137.2, 142.8, 147.0, 175.2, 175.6, 179.2, 180.1, 180.2, 181.7, 192.7, 193.3. HRMS (ESI-TOF)
m/z Calcd. for C14H11O3S2 [M + H]+: 291.0144, found 291.0152.
6-chloro-3-(1,3-dithiolan-2-ylidene)naphthalene-1,2,4(3H)-trione
(2m);
8-chloro-3-(1,3-dithiolan-2-ylidene)naphthalene-1,2,4(3H)-trione (2m’). Obtained as a yellow solid;
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isolated yield: 94.5 mg (61%); m.p. 125–127 C; 2m/2m’ = 1.0:1.2. Eluent dichloromethane/ethyl
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acetate/n-hexane (0.25/1/5, V/V/V). 2m, H NMR (CDCl3, 400 MHz, ppm): 3.54 (s, 4H), 7.68–7.75
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(m, 1H), 8.15 (d, J = 8.4 Hz, 1H), 8.27 (d, J = 2.0 Hz, 1H); 2m’, H NMR (CDCl3, 400 MHz, ppm):
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3.54 (s, 4H), 7.68–7.75 (m, 2H), 8.30 (dd, J1 = 7.6 Hz, J2 = 1.6 Hz, 1H). 13C NMR (CDCl3, 125 MHz,
ppm): 37.9, 38.0, 121.2, 122.3, 127.2, 128.1, 128.5, 129.6, 130.0, 133.6, 133.8, 134.8, 135.6, 136.7,
137.0, 142.6, 174.5, 174.9, 178.5, 178.6(2C), 179.0, 194.0, 194.7. HRMS (ESI-TOF) m/z Calcd. for
C13H8ClO3S2 [M + H]+: 310.9598, found 310.9581.
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6-(1,3-dithiolan-2-ylidene)benzo[b]thiophene-4,5,7(6H)-trione (2n). Obtained as a yellow solid;
isolated yield: 81.8 mg (58%); m.p. 210–211 oC. Eluent dichloromethane/ethyl acetate/petroleum ether
(0.25/1/5, V/V/V). 1H NMR (DMSO, 500 MHz, ppm): 3.56 (s, 4H), 7.59 (d, J = 5.0 Hz, 1H), 8.08 (d,
J = 5.0 Hz, 1H). 13C NMR (DMSO, 125 MHz, ppm): 38.0, 38.2, 121.4, 126.8, 135.2, 140.2, 149.2,
173.7, 175.7, 176.2, 190.7. HRMS (ESI-TOF) m/z Calcd. for C11H7O3S3 [M + H]+: 282.9552, found
282.9560.
2-(1,3-dithiolan-2-ylidene)phenanthrene-1,3,4(2H)-trione (2o). Obtained as a yellow solid; isolated
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yield: 73 mg (45%); m.p. 205–206 C. Eluent dichloromethane/ethyl acetate/n-hexane (0.25/1/5,
V/V/V). 1H NMR (DMSO, 500 MHz, ppm): 3.61 (s, 4H), 7.76 (t, J = 8.0 Hz, 1H), 7.83 (t, J = 8.0 Hz,
1H), 8.12 (d, J = 8.0 Hz, 1H), 8.30 (d, J = 8.5 Hz, 1H), 8.44 (d, J = 8.5 Hz, 1H), 9.38 (d, J = 8.5 Hz,
1H). 13C NMR (DMSO, 125 MHz, ppm): 38.1, 38.3, 121.0, 123.3, 127.7, 128.3, 129.3, 129.6, 130.0,
130.7, 135.7, 135.9, 136.6, 175.5, 180.2, 182.2, 191.6. HRMS (ESI-TOF) m/z Calcd. for C17H11O3S2
[M + H]+ : 327.0144, found 327.0132.
General experimental procedures for the synthesis of 1,3-Indandiones (with 5a as an example).
To the solution of 2-(1,3-dithiolan-2-ylidene)-1-phenylpentane-1,3-dione 4a (139 mg, 0.5 mmol) in
DMSO (8.0 mL) was added anhydrous Cu(OAc)2 (99.0%, 55 mg, 0.3 mmol) at room temperature, then
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the reaction was heated up to 145 C and stirred for 12.0 h under O2 atmosphere. After 4a was
consumed as indicated by TLC, the resulting mixture was poured into water (30 mL) and extracted
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with dichloromethane (15 mL × 3). The combined organic phase was washed with water (15 mL ×3),
dried over anhydrous Na2SO4 and concentrated in vacuo. The crude product was purified by column
chromatography on silica gel (dichloromethane: ethyl acetate: petroleum ether = 0.1/1/6, V/V/V) to
give 2-(1,3-dithiolan-2-ylidene)-1H-indene-1,3(2H)-dione 5a (107.9 mg, 87%) .
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2-(1,3-dithiolan-2-ylidene)-1H-indene-1,3(2H)-dione (5a). Obtained as a yellow solid; isolated yield:
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107.9 mg (87%); m.p. 193–194 C. Eluent dichloromethane/ethyl acetate/petroleum ether (0.1/1/6,
V/V/V). 1H NMR (CDCl3, 400 MHz, ppm):3.56 (s, 4H), 7.67–7.69 (m, 2H), 7.85–7.87 (m, 2H). 13C
NMR (CDCl3, 125 MHz, ppm): 37.6, 119.1, 122.6, 134.1, 140.2, 174.6, 188.0. HRMS (ESI-TOF)
m/z Calcd. for C12H9O2S2 [M+H]+ : 249.0038, found 249.0030.
2-(1,3-dithiolan-2-ylidene)-5-methyl-1H-indene-1,3(2H)-dione (5b). Obtained as a yellow solid;
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isolated yield: 116.6 mg (89%); m.p. 177–178 C. Eluent dichloromethane/ethyl acetate/petroleum
ether (0.1/1/6, V/V/V). 1H NMR (CDCl3, 500 MHz, ppm): 2.50 (s, 3H), 3.55 (s, 4H), 7.48 (d, J = 7.5
Hz, 1H), 7.65 (s, 1H), 7.75 (d, J = 7.5 Hz, 1H). 13C NMR (CDCl3, 125 MHz, ppm): 22.1, 37.5, 119.5,
122.6, 123.0, 134.9, 138.0, 140.7, 145.4, 173.6, 187.9, 188.1. HRMS (ESI-TOF) m/z Calcd. for
C13H11O2S2 [M + H]+ : 263.0195, found 263.0184.
2-(1,3-dithiolan-2-ylidene)-5-isopropyl-1H-indene-1,3(2H)-dione (5c). Obtained as a yellow solid;
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isolated yield: 123.2 mg (85%); m.p. 147–148 C. Eluent dichloromethane/ethyl acetate/petroleum
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ether (0.1/1/6, V/V/V). H NMR (CDCl3, 500 MHz, ppm): 1.31 (d, J = 7.0 Hz, 6H), 3.03–3.08 (m,
1H), 3.55 (s, 4H), 7.54 (d, J = 7.5 Hz, 1H), 7.73 (s, 1H), 7.78 (d, J = 7.5 Hz, 1H). 13C NMR (CDCl3,
125 MHz, ppm): 23.6, 34.7, 37.4, 37.5, 119.6, 120.3, 122.7, 132.7, 138.3, 140.7, 156.3, 173.5, 187.9,
188.2. HRMS (ESI-TOF) m/z Calcd. for C15H15O2S2 [M + H]+ : 291.0508, found 291.0511.
2-(1,3-dithiolan-2-ylidene)-5-(trifluoromethoxy)-1H-indene-1,3(2H)-dione (5d). Obtained as a
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yellow solid; isolated yield: 134.5 mg (81%); m.p. 163–164 C. Eluent dichloromethane/ethyl
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acetate/n-hexane (0.1/1/6, V/V/V). H NMR (CDCl3, 500 MHz, ppm):3.58 (s, 4H), 7.47 (d, J = 7.5
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Hz, 1H), 7.66 (s, 1H), 7.90 (d, J = 7.5 Hz, 1H). 13C NMR (CDCl3, 125 MHz, ppm): 37.7(2C), 114.4,
118.8, 120.2 (q, J = 258.2 Hz, CF3), 124.6, 126.0, 138.0, 142.4, 153.4, 176.5, 186.2, 186.4. HRMS
(ESI-TOF) m/z Calcd. for C13H8F3O3S2 [M+H]+: 332.9861, found 332.9856.
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2-(1,3-dithiolan-2-ylidene)-5-methoxy-1H-indene-1,3(2H)-dione (5e). Obtained as a yellow solid;
isolated yield: 70.9 mg (51%);m.p. 195–196 oC. Eluent dichloromethane/ethyl acetate/ petroleum ether
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(0.1/1/6, V/V/V). H NMR (CDCl3, 500 MHz, ppm):3.54 (s, 4H), 3.93 (s, 3H), 7.16 (d, J = 8.0 Hz,
1H), 7.30 (s, 1H), 7.78 (d, J = 8.0 Hz, 1H). 13C NMR (CDCl3, 125 MHz, ppm): 37.4, 37.5, 56.0,
105.9, 119.7, 121.1, 124.4, 133.3, 143.0, 164.8, 172.6, 187.2, 187.7. HRMS (ESI-TOF) m/z Calcd. for
C13H11O3S2 [M+H]+: 279.0144, found 279.0154.
2-(1,3-dithiolan-2-ylidene)-5-ethoxy-1H-indene-1,3(2H)-dione (5f). Obtained as a yellow solid;
isolated yield: 77.4 mg (53%); m.p. 185–186 oC. Eluent dichloromethane/ethyl acetate/ petroleum ether
(0.1/1/6, V/V/V). 1H NMR (CDCl3, 500 MHz, ppm):1.46 (t, J = 7.0 Hz, 3H), 3.53 (s, 4H), 4.16 (q, J
= 7.0 Hz, 2H), 7.14 (dd, J1= 8.0 Hz, J2= 1.5 Hz, 1H), 7.28 (d, J= 1.5 Hz, 1H), 7.78 (d, J = 8.0 Hz, 1H).
13C NMR (CDCl3, 125 MHz, ppm): 14.637.4, 37.5, 64.4, 106.3, 119.7, 121.5, 124.5, 133.2, 143.1,
164.2, 172.4, 187.2, 187.8. HRMS (ESI-TOF) m/z Calcd. for C14H13O3S2 [M+H]+: 293.0301, found
293.0309.
5-chloro-2-(1,3-dithiolan-2-ylidene)-1H-indene-1,3(2H)-dione (5g). Obtained as a yellow solid;
isolated yield: 73.3 mg (52%); m.p. 198–199 oC. Eluent dichloromethane/ethyl acetate/ petroleum ether
(0.1/1/6, V/V/V). 1H NMR (CDCl3, 400 MHz, ppm):3.58 (s, 4H), 7.63 (d, J = 8.0 Hz, 1H), 7.78–7.80
(m, 2H). 13C NMR (CDCl3, 125 MHz, ppm): 37.7(2C), 118.7, 122.9, 124.0, 134.1, 138.2, 140.6,
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141.6, 176.1, 186.5, 186.8. HRMS (ESI-TOF) m/z Calcd. for C12H8ClO2S2 [M+H]+: 282.9649, found
282.9638.
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5-bromo-2-(1,3-dithiolan-2-ylidene)-1H-indene-1,3(2H)-dione (5h). Obtained as a yellow solid;
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isolated yield: 91 mg (56%); m.p. 168–169 C. Eluent dichloromethane/ethyl acetate/ petroleum ether
(0.1/1/6, V/V/V). 1H NMR (CDCl3, 500 MHz, ppm):3.57 (s, 4H), 7.72 (d, J = 8.0 Hz, 1H), 7.80 (d, J
= 8.0 Hz, 1H), 7.97 (s, 1H). 13C NMR (CDCl3, 125 MHz, ppm): 37.7(2C), 118.6, 124.1, 125.9, 129.1,
137.0, 138.7, 141.6, 176.2, 186.4, 186.9. HRMS (ESI-TOF) m/z Calcd. for C12H8BrO2S2 [M+H]+:
326.9144, found 326.9166.
Synthesis of 2-(1,3-dithiolan-2-ylidene)-3-oxo-3-phenylpropanal 3. To the solution of
2-(1,3-dithiolan-2-ylidene)-1-phenylpropan-1-one 7 (118 mg, 0.5 mmol) in DMSO (8.0 mL) was added
anhydrous Cu(OAc)2 (99.0 %, 55 mg, 0.3 mmol) at room temperature, then the reaction was heated up
to 145 oC and stirred for 24.0 h under O2 atmosphere. After 7 was consumed as indicated by TLC, the
resulting mixture was poured into water (30 mL) and extracted with dichloromethane (15 mL × 3). The
combined organic phase was washed with water (15 mL ×3), dried over anhydrous Na2SO4 and
concentrated in vacuo. The crude product was purified by column chromatography on silica gel
(ethyl acetate: petroleum ether =1/6, V/V) to give 2-(1,3-dithiolan-2-ylidene)-3-oxo-3-phenylpropanal
3 (116 mg, 93%) as a yellow solid. Reaction time 24.0 h.
2-(1,3-dithiolan-2-ylidene)-3-oxo-3-phenylpropanal (3). Obtained as a yellow solid; isolated yield:
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116 mg (93%); m.p. 93–94 C. Eluent ethyl acetate/ petroleum ether (1/6, V/V). H NMR (CDCl3,
500 MHz, ppm):3.42 (m, 2H), 3.50 (m, 2H), 7.47 (t, J = 7.0 Hz, 2H), 7.54 (t, J = 7.0 Hz, 1H), 7.62 (d,
J = 7.0 Hz, 2H), 9.71 (s, 1H). 13C NMR (CDCl3, 125 MHz, ppm): 37.0, 37.6, 124.2, 128.5, 129.0,
131.8, 138.3, 186.5, 187.0, 192.1. HRMS (ESI-TOF) m/z Calcd. for C12H11O2S2 [M+H]+: 251.0195,
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found 251.0201.
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Synthesis of 3-(1,3-dithiolan-2-ylidene)-1-methylquinoline-2,4(1H,3H)-dione. To the solution of
2-(1,3-dithiolan-2-ylidene)-N-methyl-3-oxo-N-phenylbutanamide 8a (146.5 mg, 0.5 mmol) in DMSO
(8.0 mL) was added anhydrous Cu(OAc)2 (99.0%, 9.2 mg, 0.05 mmol) at room temperature, then the
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reaction was heated up to 145 C and stirred for 24.0 h under O2 atmosphere. After 8a was consumed
as indicated by TLC, the resulting mixture was poured into water (30 mL) and extracted with
dichloromethane (15 mL × 3). The combined organic phase was washed with water (15 mL ×3), dried
over anhydrous Na2SO4 and concentrated in vacuo. The crude product was purified by column
chromatography on silica gel (dichloromethane/ethyl acetate/ petroleum ether = 0.1/2/5, V/V/V) to give
3-(1,3-dithiolan-2-ylidene)-1-methylquinoline-2,4(1H,3H)-dione 9a (48.5 mg, 35 %) as a yellow solid.
Reaction time 24.0 h.
3-(1,3-dithiolan-2-ylidene)-1-methylquinoline-2,4(1H,3H)-dione (9a). Obtained as a yellow solid;
isolated yield: 48.5 mg (35%); m.p. 179–180 oC. Eluent dichloromethane/ethyl acetate/ petroleum ether
(0.1/2/5, V/V/V). 1H NMR (CDCl3, 500 MHz, ppm): 3.42–3.44 (m, 2H), 3.47–3.50 (m, 2H), 3.63 (s,
3H), 7.21–7.25 (m, 2H), 7.62 (t, J = 8.0 Hz, 1H), 8.30 (d, J = 8.0 Hz, 1H). 13C NMR (CDCl3, 125
MHz, ppm): 29.3, 37.2, 38.1, 114.2, 116.3, 121.0, 122.3, 128.1, 134.4, 141.1, 162.0, 177.4, 190.3.
HRMS (ESI-TOF) m/z Calcd. for C13H12NO2S2 [M + H]+: 278.0304, found 278.0306.
3-(1,3-dithiolan-2-ylidene)-1,6-dimethylquinoline-2,4(1H,3H)-dione (9b). Obtained as a yellow solid;
isolated yield: 59.7 mg (41%); m.p. 189–190 oC. Eluent dichloromethane/ethyl acetate/ petroleum ether
(0.1/2/5, V/V/V). 1H NMR (CDCl3, 500 MHz, ppm): 2.40 (s, 3H), 3.40–3.43 (m, 2H), 3.46–3.48 (m,
2H), 3.60 (s, 3H), 7.13 (d, J = 8.0 Hz, 1H), 7.42 (d, J = 8.0 Hz, 1H), 8.09 (s, 1H). 13C NMR (CDCl3,
125 MHz, ppm): 20.5, 29.3, 37.2, 38.1, 114.2, 116.4, 120.8, 128.0, 131.9, 135.3, 139.0, 161.9, 177.5,
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190.0. HRMS (ESI-TOF) m/z Calcd. for C14H14NO2S2 [M + H]+: 292.0460, found 292.0463.
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ACKNOWLEDGMENTS
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Financial support of this research by the National Natural Sciences Foundation of China (21172030, 21202015 and
21272034) is greatly acknowledged.
ASSOCIATED CONTENT
Supporting Information. Crystallographic data and spectral data for all the new compounds. This
material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
* E-mail: liuqun@nenu.edu.cn and panl948@nenu.edu.cn
Notes
The authors declare no competing financial interest.
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