Tandem Chemoselective 1,2-/1,4-Migration of the Thio Group in Keto Thioesters: An Efficient Approach to Substituted Butenolides

Article abstract of DOI:10.1002/adsc.201600640

We report herein an efficient and mechanistically unique tandem chemoselective 1,2-/1,4-migration of the thio group in keto thioesters that provides substituted butenolides in moderate to excellent yields. Thus, α-keto thioesters in the presence of stabilized phosphonate carbanions undergo tandem 1,2-sulfur migration; whereas 1,4-migration of the thio group has been achieved with the same thioesters after the treatment with Wittig reagents followed by BF₃?OEt₂-catalyzed tandem reaction. The crossover experiments and the isolation of intermediates reveal a stepwise mechanism for both of these transformations. (Figure presented.).

Full text of DOI:10.1002/adsc.201600640

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DOI: 10.1002/adsc.201600640
Tandem Chemoselective 1,2-/1,4-Migration of the Thio Group in
Keto Thioesters: An Efficient Approach to Substituted
Butenolides
Kanchan Mal,a Sandip Naskar,a Shovan Kumar Sen,a Ramalingam Natarajan,a
and Indrajit Dasa,*
a
Organic and Medicinal Chemistry Division, CSIR-Indian Institute of Chemical Biology, 4 Raja S. C. Mullick Road,
Jadavpur, Kolkata – 700032, India
Fax : (+91)- 33-2473-5197; e-mail: id@csiriicb.in
Received: June 20, 2016; Revised: July 15, 2016; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201600640.
Abstract: We report herein an efficient and mecha- ers after the treatment with Wittig reagents followed
nistically unique tandem chemoselective 1,2-/1,4-mi- by BF3·OEt2-catalyzed tandem reaction. The cross-
gration of the thio group in keto thioesters that pro- over experiments and the isolation of intermediates
vides substituted butenolides in moderate to excel- reveal a stepwise mechanism for both of these trans-
lent yields. Thus, a-keto thioesters in the presence of formations.
stabilized phosphonate carbanions undergo tandem
1,2-sulfur migration; whereas 1,4-migration of the Keywords: heterocycles; isomerization; keto thioest-
thio group has been achieved with the same thioest- ers; rearrangement; sulfanyl group migration
Introduction
of the thio group in the past few years.[1] Among the
numerous methods developed, the most common
Sulfanyl group migration is an important chemical route reported so far proceeds mainly through a key
transformation and has been extensively studied in thiiranium intermediate, which undergoes either rear-
the synthesis of modified carbohydrates, heterocycles rangement and elimination or substitution reactions
as well as acyclic compounds.[1,2] Several elegant ap- [Scheme 1; Eq. (1)]. Unlike 1,2-migration of the thio
proaches have been developed for the 1,2-migration group, there has been limited success in 1,4-sulfanyl
Scheme 1. Common strategies for the 1,2-/1,4-migration of the thio group.
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group migration.[1a,2] The most common route report- Results and Discussion
ed so far proceeds through the thiolanium intermedi-
ate [Scheme 1; Eq. (2)]. To the best of our knowledge, To optimize the reaction conditions for the tandem
there are no reports of tandem chemoselective 1,2-/ chemoselective 1,2-migration of the thio group, we
1,4-migration of the thio group from keto thioesters.
began our investigation with a-keto thioester 1a as
Substituted butenolides with one or more quaterna- the model substrate and commercially available phos-
ry centres are privileged structural motifs occurring in phonates/Wittig salts as the source of olefin (see the
a plethora of biologically active natural products and Supporting Information for optimization studies). To
pharmaceutically important molecules.[3] However, our delight, the conversion could be achieved smooth-
chemical synthesis of such molecules is very challeng- ly and efficiently when one equivalent of dimethyl 2-
ing and has remained a dynamic area of research for oxopropylphosphonate (A) was used in the presence
the past few decades.[4,5] Several elegant approaches of NaH (1.5 equiv.) and THF at 08C. We isolated 2a
have been developed for their synthesis,[4] which are in 81% yield, although minor amount of 3a resulting
mostly limited to the direct functionalization of pre- from the tandem 1,4-sulfur migration was also ob-
existing substituted butenolide scaffolds.[5] Therefore, served. However, decrease or increase in base/phos-
general approaches for the construction of these es- phonate loading led to a reduction in product yield. A
sential scaffolds, under metal-free/ligand-free condi- brief screening of the phosphonate/Wittig salt indicat-
tions, are still highly desirable.
ed that the electronic nature/steric bulk/nucleophilici-
Herein we describe a novel tandem chemoselective ty of the reagents have an obvious effect on the reac-
1,2-/1,4-migration of the thio group in keto thioesters tion and phosphonate A proved to be the best with
(Scheme 2). This unprecedented cascade allows the respect to both the yields and the reaction time. Dif-
development of an efficient and practical method for ferent bases such as NaOEt, NaO-t-Bu, and DBU
the synthesis of substituted butenolide skeletons bear- failed to deliver the desired product 2a in good yields.
ing multiple reactive sites for further functionaliza-
Subsequently, we investigated the substrate scope
tion. We found that a-keto thioesters in the presence and generality of this transformation with a-keto thio-
of Horner–Wadsworth–Emmons reaction conditions esters[6] having aromatic thiols under the optimized
undergo tandem 1,2-sulfur migration whereas tandem conditions (Table 1). We observed that all these reac-
1,4-migration of the thio group has been observed in tions proceeded smoothly via tandem 1,2-migration of
the presence of BF3·OEt2 with g-keto thioesters. More the thio group and produced the substituted buteno-
importantly, we have shown for the first time that lides in moderate to good yields (2a–j, Table 1). How-
1,2-/1,4-migration of the thio group proceeds without ever, the presence of a phenyl group in the phospho-
any conventional thiiranium/thiolanium ion inter- nate delivered the corresponding butenolides (2k–m,
mediates, respectively.
Table 1) only in moderate yields, ostensibly owing to
the electronic nature/steric bulk of the phosphonate.
The structure of 2c was established by a single crystal
X-ray diffraction analysis.[7] Surprisingly, replacement
Scheme 2. Proposed tandem chemoselective1,2-/1,4-migration of the thio group for accessing substituted butenolides.
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Table 1. Substrate scope for accessing butenolides via the tandem 1,2-migration of the thio group.[a,b]
[a]
Reaction conditions: NaH (1.5 equiv./mmol), phosphonate (1.0 equiv./mmol), and THF (2.0 mL) were stirred at 08C for
1 h; the phosphonate-stabilized carbanion was added dropwise via syringe to a stirred solution of 1 (0.05 g, 1.0 equiv.) in
THF (1.5 mL) at 08C, employing the time as mentioned; yields are of isolated products.
Minor amount of the tandem 1,4-sulfur migration product 3 was observed.
Isolated exclusively as the 1,4-sulfur migration product.
Along with 3p, inseparable mixtures of the 1,2-sulfur migration product 2p and the corresponding olefin were isolated in
[b]
[c]
[d]
minor amounts.
of an aromatic thiol with an aliphatic thiol in a-keto responding a-keto thioesters having aliphatic thiol/a-
thioesters led to the formation of butenolides result- alkyl group, although the exact reason is not very
ing from the tandem 1,4-migration of the thio group clear at the moment. The formation of a-styrenyl-sub-
(3n–p, Table 1), instead of the expected 1,2-sulfur mi- stituted butenolide 5a in low yields might be attribut-
gration (see also Table 4, vide infra). Similarly, re- ed, after the initial formation of the highly conjugated
placement of the a-phenyl group with either an isobu- g-keto thioester via Horner–Wadsworth–Emmons ole-
tyl group (3q, Table 1) or a styrenyl substrate (5a, fination reaction, to the possibility of a competing Mi-
Table 3, vide infra) revealed the same situation. This chael-type addition which might play an important
might be attributed to the higher reactivity of the cor- role.
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To expand the domain for the 1,4-sulfur migration ers 4 were synthesized from a-keto thioesters or a-
and to achieve higher yields with a-styrenyl sub- keto oxoesters 1 via the standard Wittig olefination
strates, conjugated g-keto thioesters or g-keto oxoest- reaction (Table 2).[8,9] All the reactions proceeded in
Table 2. Synthesis of g-keto thioesters or g-keto oxoesters 4 from substituted a-keto thioesters or a-keto oxoesters 1 via
Wittig olefination.[a]
[a]
Reaction conditions: 1 (0.1 g, 1.0 equiv.), corresponding Wittig reagent (2.0 equiv./mmol), dry THF (4.0 mL), argon atmos-
phere, ambient temperature or at 08C, employing the time as mentioned; yields are of isolated products.
Used directly in the next step after passage through a short column.
See the Supporting Information for their syntheses.
[b]
[c]
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full conversion and only the corresponding trans- mation for optimization studies). To our delight, the
isomer was isolated, except in a few cases where both conversion could be achieved smoothly and in excel-
cis- and trans-isomers were formed (4ao and 4at, lent yield when one equivalent of BF3·OEt2 was used
Table 2). The structure of 4ae was established by as a catalyst in the presence of 3ꢁ MS and DCM as
a single-crystal X-ray diffraction analysis.[7]
a solvent. However, decrease or increase in catalyst
After successfully synthesizing conjugated g-keto loading led to a reduction in product yield. Among
thioesters, we began our optimization studies with 4aa the solvents tested, DCM proved to be the best with
as the model substrate for the chemoselective 1,4-mi- respect to both the yields and the reaction time. The
gration of the thio group (see the Supporting Infor- reaction did not proceed well when conducted with
Table 3. Substrate scope of g-ketomethyl, g-aldehyde, and g-ketophenyl derivatives for accessing butenolides via the tandem
1,4-sulfur migration.[a,b]
[a]
Reaction conditions: 4 (0.05 g, 1.0 equiv.), BF3·OEt2 (1.0 equiv.), 3ꢁ MS (0.05 g), DCM (2.0 mL), 08C, argon atmosphere,
employing the time as mentioned; yields are of isolated products.
Reaction conditions same as in Table 1.
Batch size: 2.03 mmol of 4aa, DCM (20 mL), and BF3·OEt2 (50 mol%).
The reaction was carried out at 08C for 30 min followed by stirring at room temperature.
[b]
[c]
[d]
[e]
The reaction was carried out at À108C.
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a Brønsted acid such as trifluoromethanesulfonic acid tandem 1,4-sulfur migration, providing the desired bu-
(CF3SO3H) or with different Lewis acids such as tenolides in moderate to good yields (3a, 3o, 6a–d,
Sc(OTf)3, In(OTf)3, TiCl4, SnCl4, or TMSOTf.
Table 4). However, no expected product was ever ob-
Under the optimized conditions, we investigated served when unconjugated g-carbonyl thioesters 4bg–
the substrate scope and generality for this transforma- h or g-keto oxoesters 4bf were tested under the same
tion with a-substituted conjugated g-ketomethyl thio- reaction conditions. This is not unexpected for 4bf as
À
esters (Table 3). We observed that various a-substitut- the C O bond in oxoesters is stronger and hence less
ed styrenyl substrates and vinyl substituted polynuc- reactive compared to the C S bond in thioesters. In
À
lear aromatic hydrocarbons or heteroaryl substituents, addition, the poor nucleophilicity of the oxygen atom
and substituted aromatic substrates underwent impedes the oxygen migration.
smooth conversion via tandem 1,4-sulfanyl group mi-
In order to gain mechanistic insights, we conducted
gration and produced the substituted butenolides in control and crossover experiments, as described in
good to excellent yields (5a–m, 5o, Table 3). To show Scheme 3. When the reaction of 1a and phosphonate
the efficacy of the developed cascade, we conducted (B) was conducted under standard conditions, along
the reaction with 2.0 mmol of 4aa, and isolated 5a with 2a (64%) and 3a (10%), olefin 4az was also iso-
without any significant diminution in the yield lated in 5% yield [Eq. (a), Scheme 3]. In a parallel ex-
(Table 3). However, the presence of an alkynyl group periment, 4az was treated with NaH under standard
on the a-position of g-ketomethyl thioester 4an did conditions and 2a was isolated in 80% yield [Eq. (b),
not result in any expected product, may be due to the Scheme 3)]; thus suggesting that the tandem 1,2-sulfur
high reactivity of the alkynyl group.
migration might proceed through the corresponding
Subsequently, various g-aldehyde/g-ketophenyl olefin intermediate. To determine whether tandem
thioesters were tested and found to be compatible 1,2-sulfur migration is a stepwise process, when an
under the standard reaction conditions (5p–x, equimolar mixture of keto thioesters 1d and 1r was
Table 3). The moderate yields obtained (5p–x, treated under the standard conditions, the crossover
Table 3) were due either to the lack of stability of the products 2a and 2s were isolated in addition to the ex-
in situ generated secondary carbocation for g-alde- pected products 2d and 2r [Eq. (c), Scheme 3]; thus
hyde substituents or to the inherent reactivity of g-ke- suggesting that the 1,2-migration of the thio group
tophenyl derivatives. However, in case of g-ketophen- proceeds in an intermolecular manner, and also indi-
yl derivatives (5v–x, Table 3) the involvement of cates a stepwise mechanism for this reaction. The
steric factors during 1,4-migration of the thio group crossover experiments either with 4bd and 4aa [Eq.
cannot be ruled out. On the other hand, the presence (d), Scheme 3] or with 4az and benzyl mercaptan [Eq.
of an ester group on the g-position in 4ay resulted in (e), Scheme 3] under standard conditions also con-
no conversion, ostensibly due to the lack of poor nu- firmed that 1,4-migration of the thio group proceeds
cleophilic character of the ester carbonyl group. The in a stepwise mechanism. Furthermore, to confirm
structures of 5e and 5t was established by a single whether 1,4-sulfur migration product 3a was generat-
crystal X-ray diffraction analysis.[7]
ed via 1,2-sulfur migration product 2a followed by re-
Turning our attention to a broad range of thiols arrangement,[10] 2a was treated with BF3·OEt2 under
containing g-keto thioesters (Table 4), we observed optimized reaction conditions [Eq. (f), Scheme 3].
that all these reactions proceeded smoothly via However, we have not isolated any 3a even upon stir-
Table 4. Substrate scope of S-Ar/S-Alk derivatives for 1,4-sulfur migration.[a]
[a]
Unless otherwise noted, reactions were carried out under the reaction conditions in Table 3, yields are of isolated prod-
ucts.
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Scheme 3. Crossover and control experiments. Eqs. (a), (b), and (c) for 1,2-migration of the thio group. Eqs. (d), (e), and (f)
for 1,4-migration of the thio group.
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Scheme 4. A plausible reaction mechanism.
ring the reaction mixtures for several hours, thus sug- G.[2a] Subsequent tandem lactonization and nucleo-
gesting 3a was formed directly from g-keto thioester philic attack by the thiolate would furnish substituted
4az via (E,Z) isomerization, intramolecular lactoniza- butenolides (5, 6), resulting in 1,4-migration of the
tion, and 1,4-sulfur migration without the intermedia- thio group (Scheme 4). Research is currently in prog-
cy of any 2a.
ress to further confirm the proposed mechanistic
Based on the above results and the crossover ex- pathway.
periments, we propose a plausible mechanism for
To demonstrate the potential utility of the synthe-
these two tandem reactions as outlined in Scheme 4. sized butenolides, we have carried out the synthesis of
For the phosphonate/base-mediated tandem reaction, g-aminobutenolides under mild reaction conditions
we presume that initial Horner–Wadsworth–Emmons (Scheme 5). Thus, direct displacement of the thio-
reaction of 1 with the stabilized phosphonate carban- methyl group with neat amines (cyclohexylamine, cy-
ions could lead to the olefin A, which undergoes clopropylamine, and benzylamine) in the presence of
rapid trans to cis (B) isomerization under basic condi-
tions. Subsequent tandem lactonization (C) followed
by thiolate capture would furnish butenolides (2a–m)
via intermediate D, resulting in 1,2-sulfur migration.
On the other hand, the formation of the 1,4-sulfur mi-
gration product 2n–q could be explained by the thio-
late capture to the intermediate E. For the BF3·OEt2-
catalyzed pathway, the reaction is believed to proceed
through the initial trans (4) to cis (H) isomerization
via intermediates F and G, probably as a result of the
stabilization of the allylic carbocationic intermediate Scheme 5. Synthetic applications to g-aminobutenolides.
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THF (4.0 mL) were added successively to a round-bottom
flask under an argon atmosphere, and the resulting mixture
was stirred either at ambient temperature or at 08C employ-
ing the time as mentioned. After completion of the reaction
(TLC), saturated ammonium chloride solution was added,
and the product was extracted with EtOAc. The combined
organic layers were dried over anhydrous Na2SO4 and fil-
tered, and the filtrate was concentrated under reduced pres-
sure to get a residue. The crude residue was passed through
a short pad of silica gel column [230–400; eluent: ethyl ace-
tate/n-hexane] to obtain 4.
20 mol% InCl3 at 508C produced the amine deriva-
tives in moderate yields (7a–c, 40–48%, Scheme 5).
Conclusions
In conclusion, we have demonstrated an unprecedent-
ed tandem chemoselective 1,2-/1,4-migration of the
thio group in keto thioesters that provides substituted
butenolides in moderate to excellent yields. a-Keto
thioesters in the presence of Horner–Wadsworth–
Emmons reaction conditions undergo tandem 1,2-
sulfur migration whereas tandem 1,4-migration of the
thio group has been observed in the presence of
BF3·OEt2 with g-keto thioesters. The potential of
these derivatives has been extended by synthesizing
g-aminobutenolides under mild reaction conditions.
Research is currently in progress to develop the asym-
metric version of this tandem reaction and to reiterate
the superior reactivity of the keto thioesters towards
the synthesis of biologically active heterocycles.
General Procedure for the Synthesis of 5 and 6
To a well-stirred solution of 4 (0.05 g, 1 equiv.) in dry DCM
(2.0 mL) and 3ꢁ MS (0.05 g), BF3·OEt2 (1 equiv/mmol) was
added dropwise at 08C. The resulting reaction mixture was
stirred at the same temperature or at ambient temperature
employing time as mentioned. After completion of the reac-
tion (TLC), the reaction mixture was extracted with DCM
(10 mL), and washed with saturated NH4Cl solution. The
combined organic layers were dried over anhydrous Na2SO4
and filtered, and the filtrate was concentrated under re-
duced pressure to get a residue. The crude residue was puri-
fied by silica gel column chromatography [230–400; eluent:
ethyl acetate/n-hexane] to obtain 5 and 6.
Experimental Section
General Procedure for the Synthesis of 7a–c
General Information
To a stirred solution of 5a (0.05 g, 0.203 mmol, 1 equiv.) in
neat amine [cyclohexylamine, cyclopropylamine, and benzyl-
amine; 1.5 mL], InCl3 (20 mol%) was added, and the result-
ing mixture was heated at 508C for 1 h. After completion of
the reaction (TLC), saturated ammonium chloride solution
was added, and the product was extracted with ethyl acetate.
The combined organic layers were dried over anhydrous
Na2SO4 and filtered, and the filtrate was concentrated under
reduced pressure to get a residue. The crude residue was pu-
rified through silica gel column chromatography [230–400;
eluent: ethyl acetate/n-hexane] to obtain 7a–c.
Melting points were determined in open-end capillary tubes
and are uncorrected. TLC was performed on silica gel plates
(Merck silica gel 60, f254), and the spots were visualized with
UV light (254 and 365 nm) or by charring the plate dipped
1
in 5% H2SO4-MeOH or vanillin charring solution. H and
13C NMR spectra were recorded in CDCl3 solvent using
TMS as the internal standard. HR-MS (m/z) were measured
using EI (magnetic sector, positive ion) and ESI (Q-TOF,
positive ion) techniques. Infrared (IR) spectra were record-
ed on a Fourier transform infrared spectrometer, only in-
tense peaks are reported.
5-Methyl-3-phenyl-3-(phenylthio)furan-2(3H)-one
(2a):
Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (2%); isolated
yield: 0.047 g (81%); white solid; mp 69–718C. 1H NMR
(300 MHz, CDCl3): d=7.69 (d, J=6.6 Hz, 2H), 7.30–7.48
(m, 8H), 5.55 (d, J=1.2 Hz, 1H), 1.81 (d, J=0.6 Hz, 3H);
13C NMR (75 MHz, CDCl3): d=175.4, 151.9, 137.0 (2 CH),
135.0, 130.0, 130.0, 128.7 (2 CH), 128.6 (2 CH), 128.5, 127.3
(2 CH), 106.0, 62.1, 13.6; IR (KBr): nmax =3061, 1794, 1680,
General Procedure for the Synthesis of 2
To a well-stirred solution of NaH (1.5 equiv./mmol) in dry
THF (2.0 mL) at 08C, the corresponding phosphonate
(1.0 equiv./mmol) was added. The resulting reaction mixture
was stirred at the same temperature for 1 h. The in situ gen-
erated phosphonate-stabilized carbanions were added drop-
wise via syringe to a stirred solution of 1 (0.05 g, 1.0 equiv.)
in THF (1.5 mL) at 08C, employing the time as mentioned.
After completion of the reaction (TLC), saturated ammoni-
um chloride solution was added, and the product was ex-
tracted with EtOAc. The combined organic layers were
dried over anhydrous Na2SO4 and filtered, and the filtrate
was concentrated under reduced pressure to get a residue.
The crude residue was passed through a short pad of silica
gel column [230–400; eluent: ethyl acetate/n-hexane] to
obtain 2.
1492, 1441, 1383, 1291, 1234, 1144, 1081, 950, 750, 694 cmÀ1
;
HR-MS (ESI): m/z=305.0612, calcd. for C17H14O2SNa [M+
Na]+: 305.0613.
3-[(4-Chlorophenyl)thio]-5-methyl-3-phenylfuran-2(3H)-
one (2b): Prepared according to the general procedure dis-
cussed above: Rf =0.3; eluent, EtOAc/n-hexane (1.5%); iso-
lated yield: 0.045 g (79%); white solid; mp 79–818C.
1H NMR (600 MHz, CDCl3): d=7.62–7.64 (m, 2H), 7.32–
7.39 (m, 5H), 7.26–7.29 (m, 2H), 5.55 (d, J=1.2 Hz, 1H),
1.86 (d, J=1.2 Hz, 3H); 13C NMR (150 MHz, CDCl3): d=
175.0, 152.4, 138.3 (2 CH), 136.7, 134.7, 128.9 (2 CH), 128.8
(2 CH), 128.6, 128.4, 127.4 (2 CH), 105.8, 62.0, 13.8; IR
(KBr): nmax =2921, 1795, 1680, 1572, 1475, 1446, 1386, 1290,
1144, 1084, 1013, 949, 824, 747, 695, 505 cmÀ1; HR-MS
General Procedure for the Synthesis of 4
a-Keto thioesters/a-keto oxoesters 1 (0.1 g, 1.0 equiv.), the
corresponding Wittig reagent (2.0 equiv./mmol), and dry
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(ESI): m/z=339.0228, calcd. for C17H13ClO2SNa [M+Na]+:
339.0223.
(KBr): nmax =2971, 1776, 1671, 1563, 1466, 1357, 1261, 1156,
1091, 1063, 1012, 941, 807, 698 cmÀ1; HR-MS (ESI): m/z=
396.9877, calcd. for C18H15BrO2SNa [M+Na]+: 396.9874.
5-Ethyl-3-phenyl-3-(p-tolylthio)furan-2(3H)-one (2h): Pre-
pared according to the general procedure discussed above:
Rf =0.3; eluent, EtOAc/n-hexane (1.5%); isolated yield:
3-[(4-Bromophenyl)thio]-5-methyl-3-phenylfuran-2(3H)-
one (2c): Prepared according to the general procedure dis-
cussed above: Rf =0.3; eluent, EtOAc/n-hexane (1%); iso-
lated yield: 0.039 g (69%); white solid; mp 83–858C.
1H NMR (300 MHz, CDCl3): d=7.62 (dd, J=1.8, 8.4 Hz,
2H), 7.37–7.44 (m, 4H), 7.28–7.35 (m, 3H), 5.55 (d, J=
1.5 Hz, 1H), 1.86 (d, J=1.5 Hz, 3H); 13C NMR (75 MHz,
CDCl3): d=175.0, 152.4, 138.4 (2 CH), 134.7, 131.9 (2 CH),
129.0, 128.7 (2 CH), 128.6, 127.3 (2 CH), 125.1, 105.8, 61.9,
13.8; IR (KBr): nmax =1783, 1679, 1443, 1380, 1290, 1172,
1143, 1080, 1008, 951, 809, 749, 691, 598 cmÀ1; HR-MS
(ESI): m/z=382.9718, calcd. for C17H13BrO2SNa [M+Na]+:
382.9718.
1
0.038 g (63%); colorless gum. H NMR (300 MHz, CDCl3):
d=7.68 (d, J=7.2 Hz, 2H), 7.30–7.40 (m, 5H), 7.11 (d, J=
7.8 Hz, 2H), 5.51 (s, 1H), 2.34 (s, 3H), 1.99–2.18 (m, 2H),
0.93 (t, J=7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3): d=
175.7, 157.0, 140.4, 137.1 (2 CH), 135.2, 129.5 (2 CH), 128.7
(2 CH), 128.5, 127.4 (2 CH), 126.6, 104.5, 61.9, 21.3, 21.2
(CH2), 9.6; IR (KBr): nmax =2978, 1795, 1674, 1596, 1492,
1452, 1307, 1145, 1084, 945, 807, 750, 696, 505 cmÀ1; HR-MS
(ESI): m/z=333.0925, calcd. for C19H18O2SNa [M+Na]+:
333.0926.
5-Methyl-3-phenyl-3-(p-tolylthio)furan-2(3H)-one
(2d):
Prepared according to the general procedure discussed
above: Rf =0.35; eluent, EtOAc/n-hexane (1.5%); isolated
yield: 0.032 g (56%); white solid; mp 74–768C. 1H NMR
(300 MHz, CDCl3): d=7.64–7.67 (m, 2H), 7.31–7.39 (m,
5H), 7.11 (d, J=7.8 Hz, 2H), 5.53 (s, 1H), 2.35 (s, 3H), 1.80
(s, 3H); 13C NMR (75 MHz, CDCl3): d=175.4, 151.9, 140.4,
137.0 (2 CH), 135.1, 129.4 (2 CH), 128.6 (2 CH), 128.5, 127.4
(2 CH), 126.5, 106.1, 62.1, 21.3, 13.7; IR (KBr): nmax =2922,
1794, 1681, 1595, 1492, 1444, 1383, 1292, 1234, 1144, 1083,
950, 810, 749, 696, 599, 505 cmÀ1; HR-MS (ESI): m/z=
319.0761, calcd. for C18H16O2SNa [M+Na]+: 319.0769.
5-Pentyl-3-phenyl-3-(phenylthio)furan-2(3H)-one
(2i):
Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (1%); isolated
yield: 0.048 g (69%); colorless gum. 1H NMR (300 MHz,
CDCl3): d=7.67–7.70 (m, 2H), 7.46–7.48 (m, 2H), 7.37–7.41
(m, 2H), 7.28–7.37 (m, 4H), 5.51 (t, J=1.2 Hz, 1H), 2.04–
2.09 (m, 2H), 1.14–1.32 (m, 6H), 0.86 (t, J=6.9 Hz, 3H);
13C NMR (75 MHz, CDCl3): d=175.7, 156.0, 137.1 (2 CH),
135.2, 130.1, 130.0, 128.7 (2 CH), 128.7 (2 CH), 128.5, 127.3
(2 CH), 105.1, 61.9, 31.0 (CH2), 27.8 (CH2), 25.0 (CH2), 22.2
(CH2), 13.8; IR (KBr): nmax =2949, 2861, 1789, 1675, 1440,
1313, 1168, 1140, 1081, 950, 752, 694 cmÀ1; HR-MS (ESI):
m/z=361.1230, calcd. for C21H22O2SNa [M+Na]+: 361.1239.
5-Ethyl-3-phenyl-3-(phenylthio)furan-2(3H)-one (2e): Pre-
pared according to the general procedure discussed above:
Rf =0.3; eluent, EtOAc/n-hexane (1.5%); isolated yield:
5-Pentyl-3-phenyl-3-(p-tolylthio)furan-2(3H)-one
(2j):
1
0.032 g (52%); colorless gum. H NMR (300 MHz, CDCl3):
Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (0.75%); isolated
yield=0.058 g (85%); colorless gum. 1H NMR (300 MHz,
CDCl3): d=7.68 (dd, J=1.8, 8.4 Hz, 2H), 7.32–7.41 (m,
5H), 7.11 (d, J=8.1 Hz, 2H), 5.51 (t, J=0.9 Hz, 1H), 2.34
(s, 3H), 2.05–2.10 (m, 2H), 1.14–1.34 (m, 6H), 0.87 (t, J=
6.6 Hz, 3H); 13C NMR (75 MHz, CDCl3): d=175.8, 155.9,
140.4, 137.0 (2 CH), 135.3, 129.5 (2 CH), 128.7 (2 CH),
128.5, 127.4 (2 CH), 126.6, 105.2, 62.0, 31.1 (CH2), 27.9
d=7.69 (d, J=6.9 Hz, 2H), 7.46–7.49 (m, 2H), 7.29–7.42 (m,
6H), 5.52 (s, 1H), 1.97–2.19 (m, 2H), 0.91 (t, J=7.5 Hz,
3H); 13C NMR (75 MHz, CDCl3): d=175.7, 157.1, 137.1 (2
CH), 135.1, 130.1 (CH, C0), 128.7 (4 CH), 128.6, 127.4 (2
CH), 104.5, 61.9, 21.2 (CH2), 9.6; IR (KBr): nmax =2978,
1794, 1674, 1492, 1443, 1309, 1145, 1083, 945, 750, 694,
495 cmÀ1
;
HR-MS (ESI): m/z=319.0764, calcd. for
C18H16O2SNa [M+Na]+: 319.0769.
3-[(4-Chlorophenyl)thio]-5-ethyl-3-phenylfuran-2(3H)-one
(2f): Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (1%); isolated
yield: 0.035 g (59%); colorless gum. 1H NMR (600 MHz,
CDCl3): d=7.64–7.66 (m, 2H), 7.32–7.40 (m, 5H), 7.27–7.29
(m, 2H), 5.53 (t, J=1.8 Hz, 1H), 2.09–2.22 (m, 2H), 0.98 (t,
J=7.2 Hz, 3H); 13C NMR (150 MHz, CDCl3): d=175.3,
157.5, 138.3 (2 CH), 136.7, 134.8, 128.9 (2 CH), 128.8 (2
CH), 128.7, 128.5, 127.3 (2 CH), 104.2, 61.8, 21.3 (CH2), 9.7;
IR (KBr): nmax =2968, 1789, 1671, 1570, 1473, 1389, 1358,
1152, 1083, 992, 946, 827, 748, 694, 507 cmÀ1; HR-MS (ESI):
m/z=353.0378, calcd. for C18H15ClO2SNa [M+Na]+:
353.0379.
(CH2), 25.1 (CH2), 22.3 (CH2), 21.3, 13.8; IR (KBr): nmax
=
2928, 2862, 1794, 1673, 1596, 1492, 1451, 1145, 1083, 949,
696 cmÀ1
;
HR-MS (ESI): m/z=375.1392, calcd. for
C22H24O2SNa [M+Na]+: 375.1395.
3,5-Diphenyl-3-(phenylthio)furan-2(3H)-one (2k): Pre-
pared according to the general procedure discussed above:
Rf =0.3; eluent, EtOAc/n-hexane (1%); isolated yield:
0.025 g (35%); white solid; mp 169–1718C. 1H NMR
(300 MHz, CDCl3): d=7.74 (dd, J=1.8, 8.4 Hz, 2H), 7.35–
7.48 (m, 10H), 7.18–7.29 (m, 3H), 6.16 (s, 1H); 13C NMR
(75 MHz, CDCl3): d=174.7, 152.2, 137.0 (2 CH), 135.0,
130.1 (2 CH), 129.7, 128.8 (2 CH), 128.7 (2 CH), 128.7, 128.6
(2 CH), 127.5 (2 CH), 125.1 (2 CH), 104.2, 62.7; IR (KBr):
nmax =1760, 1492, 1444, 1272, 1158, 1099, 1013, 959, 743,
3-[(4-Bromophenyl)thio]-5-ethyl-3-phenylfuran-2(3H)-one
(2g): Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (1%); isolated
691 cmÀ1
;
HR-MS (ESI): m/z=367.0780, calcd. for
C22H16O2SNa [M+Na]+: 367.0769.
1
yield: 0.035 g (60%); white solid; mp 119–1218C. H NMR
3,5-Diphenyl-3-(p-tolylthio)furan-2(3H)-one (2l): Pre-
pared according to the general procedure discussed above:
Rf =0.3; eluent, EtOAc/n-hexane (1%); isolated yield:
0.029 g (40%); white solid; mp 189–1918C. 1H NMR
(600 MHz, CDCl3): d=7.74 (d, J=7.8 Hz, 2H), 7.46–7.47
(m, 2H), 7.33–7.41 (m, 8H), 7.01 (d, J=7.8 Hz, 2H), 6.15 (s,
1H), 2.25 (s, 3H); 13C NMR (150 MHz, CDCl3): d=174.7,
(600 MHz, CDCl3): d=7.64–7.66 (m, 2H), 7.42–7.45 (m,
2H), 7.37–7.39 (m, 2H), 7.32–7.35 (m, 1H), 7.29–7.31 (m,
2H), 5.52 (t, J=1.2 Hz, 1H), 2.09–2.22 (m, 2H), 0.98 (t, J=
7.2 Hz, 3H); 13C NMR (150 MHz, CDCl3): d=175.3, 157.5,
138.5 (2 CH), 134.8, 131.9 (2 CH), 129.1, 128.8 (2 CH),
128.7, 127.3 (2 CH), 125.1, 104.2, 61.7, 21.3 (CH2), 9.7; IR
Adv. Synth. Catal. 0000, 000, 0 – 0
10
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152.1, 140.5, 137.0 (2 CH), 135.1, 130.0, 129.5 (2 CH), 128.8
(2 CH), 128.6, 128.6 (2 CH), 127.6, 127.5 (2 CH), 126.2,
125.1 (2 CH), 104.4, 62.7, 21.2; IR (KBr): nmax =1790, 1758,
13C NMR (75 MHz, CDCl3): d=172.0, 150.6, 136.6 (2 CH),
133.1, 129.7, 129.0 (2 CH), 128.9, 92.2, 33.6 (CH2), 26.8, 24.9,
22.1, 22.1; IR (KBr): nmax =2959, 2927, 1767, 1468, 1441,
1374, 1255, 1087, 1038, 958, 882, 751, 696 cmÀ1; HR-MS
(ESI): m/z=285.0926, calcd. for C15H18O2SNa [M+Na]+:
285.0926.
1490, 1447, 1269, 1153, 1090, 1016, 946, 809, 761, 692 cmÀ1
;
HR-MS (ESI): m/z=381.0927, calcd. for C23H18O2SNa [M+
Na]+: 381.0926.
3-[(4-Bromophenyl)thio]-3,5-diphenylfuran-2(3H)-one
(2m): Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (0.5%); isolated
S-Methyl (E)-4-oxo-2-[(E)-styryl]pent-2-enethioate (4aa):
Prepared according to the general procedure discussed
above: Rf =0.4; eluent, EtOAc/n-hexane (7%); isolated
yield: 0.1 g (84%); yellow gum. 1H NMR (300 MHz,
CDCl3): d=8.01 (d, J=16.5 Hz, 1H), 7.52 (d, J=6.6 Hz,
2H), 7.31–7.38 (m, 3H), 7.08 (d, J=16.5 Hz, 1H), 6.41 (s,
1H), 2.47 (s, 3H), 2.35 (s, 3H); 13C NMR (75 MHz, CDCl3):
d=198.4, 194.8, 149.1, 140.7, 136.0, 129.5, 128.7 (2 CH),
127.8 (2 CH), 124.0, 120.3, 32.4, 12.4; IR (KBr): nmax =3027,
2928, 1672, 1609, 1565, 1494, 1447, 1422, 1356, 1192, 977,
750, 696, 614 cmÀ1; HR-MS (ESI): m/z=269.0599, calcd. for
C14H14O2SNa [M+Na]+: 269.0613.
1
yield: 0.026 g (40%); white solid; mp 139–1418C. H NMR
(600 MHz, CDCl3): d=7.70–7.71 (m, 2H), 7.48–7.50 (m,
2H), 7.38–7.42 (m, 5H), 7.33–7.37 (m, 3H), 7.28–7.29 (m,
2H), 6.16 (s, 1H); 13C NMR (150 MHz, CDCl3): d=174.3,
152.5, 138.4 (2 CH), 134.6, 132.0 (2 CH), 130.4, 128.9 (2
CH), 128.8, 128.7 (2 CH), 127.4 (2 CH), 125.1 (2 CH), 103.8,
62.5; IR (KBr): nmax =1776, 1446, 1265, 1159, 1090, 1012,
942, 814, 754, 690 cmÀ1; HR-MS (ESI): m/z=444.9875,
calcd. for C22H15BrO2SNa [M+Na]+: 444.9874.
5-(Benzylthio)-5-ethyl-3-phenylfuran-2(5H)-one (3n): Pre-
pared according to the general procedure discussed above:
Rf =0.3; eluent, EtOAc/n-hexane (2.5%); isolated yield:
0.05 g (83%); colorless gum. 1H NMR (300 MHz, CDCl3):
d=7.75 (dd, J=3.0, 6.9 Hz, 2H), 7.39–7.41 (m, 3H), 7.22–
7.28 (m, 6H), 3.70 (d, J=13.2 Hz, 1H), 3.62 (d, J=13.2 Hz,
1H), 2.06–2.22 (m, 2H), 1.02 (t, J=6.9 Hz, 3H); 13C NMR
(75 MHz, CDCl3): d=170.1, 148.8, 136.8, 131.3, 129.7, 128.8
(2 CH), 128.7 (2 CH), 128.6 (2 CH), 127.2, 127.2 (2 CH),
93.9, 33.1 (CH2), 31.6 (CH2), 8.5; IR (KBr): nmax =2929,
1761, 1452, 1191, 1104, 959, 904, 789, 697 cmÀ1; HR-MS
(ESI): m/z=333.0926, calcd. for C19H18O2SNa [M+Na]+:
333.0926.
S-Methyl
(E)-2-[(E)-4-methoxystyryl]-4-oxopent-2-ene-
thioate (4ab): Prepared according to the general procedure
discussed above: Rf =0.35; eluent, EtOAc/n-hexane (10%);
isolated yield: 0.077 g, (66%). H NMR (300 MHz, CDCl3):
1
d=7.94 (d, J=16.5 Hz, 1H), 7.47 (d, J=8.7 Hz, 2H), 7.03
(d, J=16.5 Hz, 1H), 6.88 (d, J=8.7 Hz, 2H), 6.34 (s, 1H),
3.83 (s, 3H), 2.46 (s, 3H), 2.33 (s, 3H); 13C NMR (75 MHz,
CDCl3): d=198.3, 195.0, 160.8, 149.6, 140.5, 129.3 (2 CH),
128.9, 122.7, 118.3, 114.2 (2 CH), 55.3, 32.3, 12.3; IR (KBr):
nmax =2929, 1671, 1601, 1557, 1511, 1421, 1251, 1174, 1030,
977, 825 cmÀ1
; HR-MS (EI): m/z=276.0823, calcd. for
C15H18O3S [M]+: 276.0820.
S-Methyl
(E)-2-[(E)-3,4-dimethoxystyryl]-4-oxopent-2-
5-(Benzylthio)-5-methyl-3-phenylfuran-2(5H)-one
(3o):
enethioate (4ac): Prepared according to the general proce-
dure discussed above: Rf =0.4; eluent, EtOAc/n-hexane
(20%); isolated yield: 0.07 g (61%); yellow gum. H NMR
Prepared according to the general procedure discussed
above under phosphonate/NaH-mediated reaction: Rf =0.3;
eluent, EtOAc/n-hexane (4%); isolated yield: 0.035 g
(60%); colorless gum. 1H NMR (300 MHz, CDCl3): d=
7.72–7.76 (m, 2H), 7.39–7.41 (m, 3H), 7.31 (s, 1H), 7.22 (m,
5H), 3.71 (d, J=13.2 Hz, 1H), 3.63 (d, J=13.5 Hz, 1H),
1.84 (s, 3H); 13C NMR (75 MHz, CDCl3): d=169.9, 149.9,
136.7, 130.6, 129.7, 128.8 (3 CH), 128.6 (3 CH), 127.2, 127.2
(3 CH), 90.3, 33.7 (CH2), 25.4; IR (KBr): nmax =3064, 1762,
1493, 1448, 1212, 1090, 959, 879, 790, 698 cmÀ1; HR-MS
(EI): m/z=296.0876, calcd. for C18H16O2S [M]+: 296.0871.
5-Ethyl-5-(ethylthio)-3-phenylfuran-2(5H)-one (3p): Pre-
pared according to the general procedure discussed above:
Rf =0.3; eluent, EtOAc/n-hexane (3%); isolated yield:
1
(600 MHz, CDCl3): d=7.95 (dd, J=0.6, 16.2 Hz, 1H), 7.09
(dd, J=1.8, 8.4 Hz, 1H), 7.05 (d, J=2.4 Hz, 1H), 7.03 (d,
J=16.8 Hz, 1H), 6.84 (d, J=8.4 Hz, 1H), 6.35 (s, 1H), 3.92
(s, 3H), 3.90 (s, 3H), 2.46 (s, 3H), 2.34 (s, 3H); 13C NMR
(150 MHz, CDCl3): d=198.4, 195.0, 150.5, 149.6, 149.1,
140.8, 129.2, 122.7, 122.0, 118.5, 111.0, 109.5, 55.9, 55.9, 32.4,
12.4; IR (KBr): nmax =2929, 1671, 1588, 1514, 1461, 1266,
1141, 1026, 978, 808, 758 cmÀ1
329.0851, calcd. for C16H18O4SNa [M+Na]+: 329.0824.
S-Methyl (E)-2-[(E)-4-methylstyryl]-4-oxopent-2-ene-
; HR-MS (ESI): m/z=
thioate (4ad): Prepared according to the general procedure
discussed above: Rf =0.3; eluent, EtOAc/n-hexane (5%);
isolated yield: 0.084 g (71%); yellow gum. 1H NMR
(600 MHz, CDCl3): d=7.99 (d, J=16.2 Hz, 1H), 7.42 (d, J=
8.4 Hz, 2H), 7.16 (d, J=7.8 Hz, 2H), 7.06 (d, J=16.8 Hz,
1H), 6.37 (s, 1H), 2.46 (s, 3H), 2.36 (s, 3H), 2.34 (s, 3H);
13C NMR (150 MHz, CDCl3): d=198.3, 194.9, 149.4, 140.8,
139.8, 133.3, 129.5 (2 CH), 127.8 (2 CH), 123.4, 119.4, 32.4,
21.4, 12.4; IR (KBr): nmax =2925, 1671, 1606, 1562, 1191, 977,
1
0.015 g (23%); colorless gum. H NMR (300 MHz, CDCl3):
d=7.87–7.90 (m, 2H), 7.41–7.44 (m, 4H), 2.44 (q, J=7.5,
14.7 Hz, 2H), 2.04–2.28 (m, 2H), 1.21 (t, J=7.2 Hz, 3H),
1.03 (t, J=7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3): d=
170.2, 148.7, 131.3 (2 C0), 129.7, 128.7 (2 CH), 127.1 (2 CH),
93.9, 31.5 (CH2), 22.5 (CH2), 14.6, 8.5; IR (KBr): nmax =2974,
1760, 1492, 1451, 1192, 1106, 960, 905, 791, 748, 694 cmÀ1
;
HR-MS (ESI): m/z=271.0760, calcd. for C14H16O2SNa [M+
810 cmÀ1
;
HR-MS (ESI): m/z=283.0779, calcd. for
Na]+: 271.0769.
C15H16O2SNa [M+Na]+: 283.0769.
3-Isobutyl-5-methyl-5-(phenylthio)furan-2(5H)-one (3q):
Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (4%); isolated
yield: 0.02 g (34%); colorless gum. 1H NMR (300 MHz,
CDCl3): d=7.44–7.49 (m, 2H), 7.29–7.35 (m, 3H), 6.81 (s,
1H), 1.90 (d, J=6.9 Hz, 2H), 1.78 (s, 3H), 0.88–0.99 (m,
1H), 0.70 (d, J=6.6 Hz, 3H), 0.67 (d, J=6.9 Hz, 3H);
S-Methyl (E)-2-[(E)-2,6-dichlorostyryl]-4-oxopent-2-ene-
thioate (4ae): Prepared according to the general procedure
discussed above: Rf =0.35; eluent, EtOAc/n-hexane (7%);
isolated yield: 0.073 g (64%); yellow crystalline soild; mp
115–1178C. 1H NMR (600 MHz, CDCl3): d=7.90 (d, J=
16.8 Hz, 1H), 7.33 (d, J=8.4 Hz, 2H), 7.16 (d, J=16.8 Hz,
1H), 7.13 (d, J=8.4 Hz, 1H), 6.54 (s, 1H), 2.47 (s, 3H), 2.35
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(s, 3H); 13C NMR (150 MHz, CDCl3): d=198.2, 194.2, 147.3,
134.8, 134.1, 133.4, 129.2, 128.7 (2 CH), 128.3, 126.6, 32.2,
12.4; IR (KBr): nmax =1665, 1615, 1563, 1426, 1353, 1181,
978, 946 cmÀ1; HR-MS (ESI): m/z=336.9841, calcd. for
C14H12Cl2O2SNa [M+Na]+: 336.9833.
(s, 1H), 2.48 (s, 3H), 2.37 (s, 3H); 13C NMR (150 MHz,
CDCl3): d=198.3, 194.3, 148.6, 147.6, 137.9, 137.5, 132.7,
129.7, 126.0, 123.6, 123.1, 122.6, 32.4, 12.4; IR (KBr): nmax
=
;
2926, 1671, 1568, 1530, 1425, 1351, 1194, 976, 736, 697 cmÀ1
HR-MS (ESI): m/z=314.0486, calcd. for C14H13NO4SNa
S-Methyl
(E)-2-[(E)-4-chlorostyryl]-4-oxopent-2-ene-
[M+Na]+: 314.0463.
thioate (4af): Prepared according to the general procedure
discussed above: Rf =0.3; eluent, EtOAc/n-hexane (7%);
isolated yield: 0.094 g (81%); yellow solid; mp 119–1218C.
1H NMR (300 MHz, CDCl3): d=7.98 (d, J=16.5 Hz, 1H),
7.45 (d, J=8.4 Hz, 2H), 7.32 (d, J=8.4 Hz, 2H), 7.03 (d, J=
16.2 Hz, 1H), 6.44 (s, 1H), 2.47 (s, 3H), 2.35 (s, 3H);
13C NMR (75 MHz, CDCl3): d=198.3, 194.6, 148.6, 139.1,
135.1, 134.5, 128.9 (2 CH), 128.8 (2 CH), 124.4, 120.8, 32.4,
12.3; IR (KBr): nmax =2928, 1672, 1609, 1564, 1490, 1410,
1356, 1266, 1192, 1092, 977, 818, 749, 691, 613 cmÀ1; HR-MS
(ESI): m/z=303.0212, calcd. for C14H13ClO2SNa [M+Na]+:
303.0223.
S-Methyl (E)-2-[(E)-2-(naphthalen-2-yl)vinyl]-4-oxopent-
2-enethioate (4ak): Prepared according to the general proce-
dure discussed above: Rf =0.35; eluent, EtOAc/n-hexane
1
(6%); isolated yield: 0.103 g (89%); yellow gum. H NMR
(300 MHz, CDCl3): d=8.18 (d, J=16.5 Hz, 1H), 7.90 (s,
1H), 7.82–7.85 (m, 3H), 7.75 (d, J=8.7 Hz, 1H), 7.48–7.52
(m, 2H), 7.27 (d, J=16.5 Hz, 1H), 6.45 (s, 1H), 2.51 (s, 3H),
2.39 (s, 3H); 13C NMR (75 MHz, CDCl3): d=198.4, 194.8,
149.1, 140.8, 133.8, 133.6, 133.3, 129.1, 128.4, 128.4, 127.7,
126.8, 126.5, 123.8, 123.6, 120.6, 32.4, 12.4; IR (KBr): nmax
=
2926, 1672, 1601, 1561, 1356, 1187, 976, 814, 747 cmÀ1; HR-
MS (ESI): m/z=319.0773, calcd. for C18H16O2SNa [M+
Na]+: 319.0769.
S-Methyl
(E)-2-[(E)-4-fluorostyryl]-4-oxopent-2-ene-
thioate (4ag): Prepared according to the general procedure
discussed above: Rf =0.3; eluent, EtOAc/n-hexane (5%);
isolated yield: 0.094 g (80%); yellow solid; mp 109–1118C.
1H NMR (300 MHz, CDCl3): d=7.94 (d, J=16.8 Hz, 1H),
7.50 (dd, J=6.0, 8.7 Hz, 2H), 7.07 (s, 1H), 7.03 (d, J=
8.4 Hz, 2H), 6.41 (s, 1H), 2.46 (s, 3H), 2.34 (s, 3H);
13C NMR (75 MHz, CDCl3): d=198.3, 194.7, 163.4 (d, J=
249.0 Hz, 1 C), 148.8, 139.3, 132.3 (d, J=3.7 Hz, 1 C), 129.5,
129.4, 124.0, 120.0 (d, J=2.2 Hz, 1 C), 116.0, 115.7, 32.4,
12.3; IR (KBr): nmax =2928, 1672, 1597, 1563, 1508, 1418,
1357, 1231, 1191, 977, 827, 743 cmÀ1; HR-MS (ESI): m/z=
287.0510, calcd. for C14H13FO2SNa [M+Na]+: 287.0518.
S-Methyl (E)-2-[(E)-2-(naphthalen-1-yl)vinyl]-4-oxopent-
2-enethioate (4al): Prepared according to the general proce-
dure discussed above: Rf =0.3; eluent, EtOAc/n-hexane
1
(7%); isolated yield: 0.096 g (83%); yellow gum. H NMR
(600 MHz, CDCl3): d=8.09 (d, J=8.4 Hz, 1H), 8.03 (d, J=
16.2 Hz, 1H), 7.95 (d, J=16.2 Hz, 1H), 7.83–7.86 (m, 3H),
7.53–7.56 (m, 1H), 7.48–7.52 (m, 2H), 6.51 (s, 1H), 2.52 (s,
3H), 2.37 (s, 3H); 13C NMR (150 MHz, CDCl3): d=198.4,
194.9, 148.8, 137.6, 133.6, 133.5, 131.4, 129.7, 128.7, 126.5,
126.0, 125.6, 124.8, 124.7, 123.4, 122.8, 32.4, 12.5; IR (KBr):
nmax =1667, 1561, 1354, 1195, 975, 797, 776, cmÀ1; HR-MS
(ESI): m/z=319.0776, calcd. for C18H16O2SNa [M+Na]+:
319.0769.
S-Methyl
(E)-2-[(E)-2-bromostyryl]-4-oxopent-2-ene-
thioate (4ah): Prepared according to the general procedure
discussed above: Rf =0.35; eluent, EtOAc/n-hexane (6%);
isolated yield: 0.067 g (58%); yellow gum. 1H NMR
(300 MHz, CDCl3): d=7.91 (d, J=16.5 Hz, 1H), 7.72 (d, J=
7.8 Hz, 1H), 7.58 (d, J=8.1 Hz, 1H), 7.50 (d, J=16.5 Hz,
1H), 7.33 (t, J=7.5 Hz, 1H), 7.15–7.21 (m, 1H), 6.51 (s,
1H), 2.50 (s, 3H), 2.37 (s, 3H); 13C NMR (75 MHz, CDCl3):
d=198.6, 194.6, 148.5, 139.2, 136.1, 133.3, 130.5, 127.8, 127.7,
125.3, 125.3, 123.0, 32.6, 12.6; IR (KBr): nmax =1670, 1565,
1434, 1356, 1193, 1023, 976, 752 cmÀ1; HR-MS (ESI): m/z=
346.9710, calcd. for C14H13BrO2SNa [M+Na]+: 346.9718.
S-Methyl (E)-4-oxo-2-[(E)-2-(thiophen-2-yl)vinyl]pent-2-
enethioate (4am): Prepared according to the general proce-
dure discussed above: Rf =0.35; eluent, EtOAc/n-hexane
1
(6%); isolated yield: 0.097 g (82%); yellow gum. H NMR
(600 MHz, CDCl3): d=7.84 (d, J=16.2 Hz, 1H), 7.33 (d, J=
4.8 Hz, 1H), 7.23 (d, J=16.2 Hz, 1H), 7.17 (d, J=3.0 Hz,
1H), 7.02 (dd, J=3.6, 4.8 Hz, 1H), 6.38 (s, 1H), 2.46 (s,
3H), 2.33 (s, 3H); 13C NMR (150 MHz, CDCl3): d=198.2,
194.7, 148.7, 141.9, 133.5, 129.5, 128.0, 127.8, 123.5, 119.6,
32.4, 12.4; IR (KBr): nmax =2927, 1715, 1662, 1423, 1357,
1180, 966, 756, 706 cmÀ1; HR-MS (ESI): m/z=275.0166,
calcd. for C12H12O2S2Na [M+Na]+: 275.0177.
S-Methyl
(E)-2-[(E)-3-cyanostyryl]-4-oxopent-2-ene-
thioate (4ai): Prepared according to the general procedure
discussed above: Rf =0.3; eluent, EtOAc/n-hexane (15%);
isolated yield: 0.1 g (85%); yellow gum. H NMR (600 MHz,
S-Methyl
(E)-4-oxo-2-(phenylethynyl)pent-2-enethioate
(4an): Prepared according to the general procedure dis-
cussed above: Rf =0.3; eluent, EtOAc/n-hexane (4%); iso-
lated yield: 0.05 g (42%); brown gum. H NMR (600 MHz,
1
1
CDCl3): d=7.99 (dd, J=0.6, 16.2 Hz, 1H), 7.73–7.75 (m,
2H), 7.58 (d, J=7.8 Hz, 1H), 7.46 (t, J=7.2 Hz, 1H), 7.05
(d, J=16.2 Hz, 1H), 6.52 (s, 1H), 2.47 (s, 3H), 2.36 (s, 3H);
13C NMR (150 MHz, CDCl3): d=198.3, 194.3, 147.7, 137.5,
137.4, 132.3, 131.3, 131.1, 129.6, 125.8, 122.6, 118.4, 113.1,
32.4, 12.4; IR (KBr): nmax =2929, 1792, 1718, 1673, 1556,
1514, 1266, 1141, 1025 cmÀ1; HR-MS (ESI): m/z=294.0552,
calcd. for C15H13NO2SNa [M+Na]+: 294.0565.
CDCl3): d=7.61–7.62 (m, 2H), 7.39–7.44 (m, 3H), 7.12 (s,
1H), 2.56 (s, 3H), 2.44 (s, 3H); 13C NMR (150 MHz,
CDCl3): d=197.6, 190.3, 134.6, 131.9 (2 CH), 130.1, 128.6 (2
CH), 121.5, 103.7, 84.4, 30.9, 12.9; IR (KBr): nmax =2928,
2199, 1666, 1573, 1361, 1248, 1180, 1110, 1010, 760, 690 cmÀ1
;
HR-MS (ESI): m/z=267.0463, calcd. for C14H12O2SNa [M+
Na]+: 267.0456.
S-Methyl (E)-2-[(E)-3-nitrostyryl]-4-oxopent-2-enethioate
(4aj): Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (15%); isolated
S-Methyl 2-(4-nitrophenyl)-4-oxopent-2-enethioate (4ao):
Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (15%); isolated
yield: 0.083 g (71%); yellow solid; mp 119–1218C; trans:-
cis= ~1:1; NMR of mixture, major peaks: 1H NMR
(300 MHz, CDCl3): d=8.26 (d, J=8.4 Hz, 2H), 7.45 (d, J=
8.7 Hz, 2H), 7.13 (s, 1H), 2.39 (s, 3H), 2.15 (s, 3H);
1
yield: 0.059 g (51%); yellow soild; mp 117–1198C. H NMR
(600 MHz, CDCl3): d=8.30 (m, 1H), 8.16 (dd, J=1.8,
8.4 Hz, 1H), 8.04 (d, J=16.2 Hz, 1H), 7.85 (d, J=7.8 Hz,
1H), 7.54 (t, J=8.4 Hz, 1H), 7.13 (d, J=16.2 Hz, 1H), 6.54
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12
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13C NMR (75 MHz, CDCl3): d=198.2, 192.3, 148.3, 144.7,
140.3, 132.3, 130.8 (2 CH), 123.4 (2 CH), 31.5, 12.9; IR
(KBr): nmax =2926, 1656, 1595, 1519, 1421, 1345, 1174, 1071,
1020, 857, 803, 731, 703 cmÀ1; HR-MS (ESI): m/z=288.0288,
calcd. for C12H11NO4SNa [M+Na]+: 288.0307.
142.1, 134.0, 133.3, 132.9, 129.4, 128.8, 128.5, 127.8, 127.3,
127.2, 126.8, 123.2, 118.1, 12.3; IR (KBr): nmax =2926, 1716,
1665, 1507, 1176, 968, 816, 753 cmÀ1; HR-MS (ESI): m/z=
305.0633, calcd. for C17H14O2SNa [M+Na]+: 305.0613.
S-Methyl (E)-4-oxo-2-[(E)-2-(thiophen-3-yl)vinyl]but-2-
enethioate (4au): Prepared according to the general proce-
dure discussed above: Rf =0.3; eluent, EtOAc/n-hexane
S-Methyl (E)-4-oxo-2-[(E)-styryl]but-2-enethioate (4ap):
Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (4%); isolated
yield: 0.04 g (36%); yellow gum. 1H NMR (300 MHz,
CDCl3): d=10.20 (d, J=7.2 Hz, 1H), 7.47–7.56 (m, 3H),
7.40–7.42 (m, 3H), 7.06 (d, J=15.9 Hz, 1H), 6.48 (d, J=
6.6 Hz, 1H), 2.50 (s, 3H); 13C NMR (75 MHz, CDCl3): d=
194.0, 190.8, 152.2, 142.1, 135.4, 130.0, 129.0 (2 CH), 127.7 (2
CH), 127.6, 117.9, 12.3; IR (KBr): nmax =2927, 1721, 1666,
1
(10%); isolated yield: 0.031 g (27%); yellow gum. H NMR
(300 MHz, CDCl3): d=10.18 (d, J=6.9 Hz, 1H), 7.46 (s,
1H), 7.33–7.38 (m, 3H), 7.08 (d, J=15.9 Hz, 1H), 6.43 (d,
J=6.9 Hz, 1H), 2.49 (s, 3H); 13C NMR (75 MHz, CDCl3):
d=194.1, 190.6, 152.3, 138.6, 135.6, 127.3, 127.0, 126.8, 124.7,
117.6, 12.3; IR (KBr): nmax =2925, 1717, 1668, 1604, 1082,
967, 779 cmÀ1; HR-MS (ESI): m/z=261.0043, calcd. for
C11H10O2S2Na [M+Na]+: 261.0020.
1159, 1080, 971, 754, 699 cmÀ1
255.0454, calcd. for C13H12O2SNa [M+Na]+: 255.0456.
S-Methyl (E)-2-[(E)-4-methylstyryl]-4-oxobut-2-ene-
; HR-MS (ESI): m/z=
Ethyl
(2E,4E)-3-[(methylthio)carbonyl]-5-phenylpenta-
2,4-dienoate (4ay): Prepared according to the general proce-
dure discussed above: Rf =0.3; eluent, EtOAc/n-hexane
(2%); isolated yield: 0.07 g (52%); yellow gum. 1H NMR
(300 MHz, CDCl3): d=8.09 (d, J=16.5 Hz, 1H), 7.53 (d, J=
6.6 Hz, 2H), 7.31–7.38 (m, 3H), 7.06 (d, J=16.2 Hz, 1H),
6.14 (s, 1H), 4.26 (q, J=7.2, 14.1 Hz, 2H), 2.47 (s, 3H), 1.34
(t, J=6.9 Hz, 3H); 13C NMR (75 MHz, CDCl3): d=194.5,
165.4, 151.5, 139.3, 136.1, 129.3, 128.7 (2 CH), 127.6 (2 CH),
119.9, 118.8, 60.7 (CH2), 14.2, 12.3; IR (KBr): nmax =2982,
thioate (4aq): Prepared according to the general procedure
discussed above: Rf =0.3; eluent, EtOAc/n-hexane (6%);
isolated yield: 0.05 g (44%); yellow gum. 1H NMR
(300 MHz, CDCl3): d=10.18 (d, J=6.9 Hz, 1H), 7.37–7.44
(m, 3H), 7.21 (d, J=7.8 Hz, 2H), 7.03 (d, J=15.9 Hz, 1H),
6.44 (d, J=6.9 Hz, 1H), 2.48 (s, 3H), 2.39 (s, 3H); 13C NMR
(75 MHz, CDCl3): d=194.1, 190.8, 152.5, 142.1, 140.4, 132.7,
129.7 (2 CH), 127.6 (2 CH), 127.0, 116.8, 21.4, 12.3; IR
(KBr): nmax =2925, 1719, 1669, 1606, 1179, 1082, 972,
810 cmÀ1; HR-MS (EI): m/z=246.0722, calcd. for C14H14O2S
[M]+: 246.0715.
1711, 1673, 1613, 1587, 1201, 1166, 1034, 980, 755, 694 cmÀ1
;
HR-MS (ESI): m/z=299.0726, calcd. for C15H16O3SNa [M+
Na]+: 299.0718.
S-Methyl (E)-2-[(E)-4-chlorostyryl]-4-oxobut-2-enethioate
(4ar): Prepared according to the general procedure dis-
cussed above: Rf =0.3; eluent, EtOAc/n-hexane (7%); iso-
lated yield: 0.062 g (56%); yellow solid; mp 109–1118C.
1H NMR (300 MHz, CDCl3): d=10.18 (d, J=6.6 Hz, 1H),
7.46–7.49 (m, 2H), 7.37–7.41 (m, 3H), 7.02 (d, J=15.9 Hz,
1H), 6.49 (d, J=6.6 Hz, 1H), 2.49 (s, 3H); 13C NMR
(75 MHz, CDCl3): d=193.9, 190.6, 151.7, 140.5, 135.8, 133.8,
129.2 (2 CH), 128.8 (2 CH), 127.6, 118.4, 12.3; IR (KBr):
nmax =1669, 1609, 1565, 1080, 972, 946 cmÀ1; HR-MS (EI):
m/z=266.0159, calcd. for C13H11ClO2S [M]+: 266.0168.
S-Methyl (E)-2-[(E)-4-cyanostyryl]-4-oxobut-2-enethioate
(4as): Prepared according to the general procedure dis-
cussed above: Rf =0.3; eluent, EtOAc/n-hexane (15%); iso-
lated yield: 0.04 g (36%); yellowish white solid; mp 95–
S-Phenyl (E)-4-oxo-2-phenylpent-2-enethioate (4az): Pre-
pared according to the general procedure discussed above:
Rf =0.4; eluent, EtOAc/n-hexane (4%); isolated yield:
0.05 g (43%); yellow solid; mp 111–1138C. 1H NMR
(300 MHz, CDCl3): d=7.38–7.50 (m, 10H), 7.03 (s, 1H),
1.96 (s, 3H); 13C NMR (75 MHz, CDCl3): d=200.1, 191.6,
146.1, 134.4 (2 CH), 133.1, 132.9, 129.8 (2 CH), 129.7 (2
CH), 129.3 (2 CH), 128.4 (2 CH), 127.4, 30.6; IR (KBr):
nmax =2925, 1678, 1478, 1440, 1356, 1175, 1066, 1020, 748,
697 cmÀ1
;
HR-MS (ESI): m/z=305.0616, calcd. for
C17H14O2SNa [M+Na]+: 305.0613.
S-(Naphthalen-2-yl) (E)-4-oxo-2-phenylpent-2-enethioate
(4ba): Prepared according to the general procedure dis-
cussed above: Rf =0.3; eluent, EtOAc/n-hexane (5%); iso-
lated yield: 0.04 g (35%); yellow solid; mp 84–868C.
1H NMR (600 MHz, CDCl3): d=7.93 (s, 1H), 7.88 (d, J=
9.0 Hz, 1H), 7.86 (d, J=7.8 Hz, 1H), 7.82 (d, J=7.8 Hz,
1H), 7.46–7.56 (m, 5H), 7.43 (dd, J=1.2, 8.4 Hz, 1H), 7.41
(dd, J=1.2, 7.8 Hz, 2H), 7.04 (s, 1H), 1.95 (s, 3H);
13C NMR (150 MHz, CDCl3): d=200.2, 191.9, 146.1, 134.5,
133.5, 133.4, 133.1, 133.0, 130.6, 129.9 (2 CH), 129.7, 128.9,
128.5 (2 CH), 128.0, 127.8, 127.3, 126.6, 124.8, 30.7; IR
(KBr): nmax =1672, 1493, 1349, 1067, 1014, 813, 748,
702 cmÀ1; HR-MS (EI): m/z=332.0874, calcd. for C21H16O2S
[M]+: 332.0871.
S-Benzyl (E)-4-oxo-2-phenylpent-2-enethioate (4bb): Pre-
pared according to the general procedure discussed above:
Rf =0.3; eluent, EtOAc/n-hexane (3%); isolated yield:
0.081 g (70%); yellow solid; mp 124–1268C. 1H NMR
(300 MHz, CDCl3): d=7.38–7.46 (m, 4H), 7.27–7.30 (m,
6H), 6.99 (s, 1H), 4.19 (s, 2H), 1.91 (s, 3H); 13C NMR
(75 MHz, CDCl3): d=200.3, 192.7, 146.1, 136.6, 133.1, 132.8,
129.8 (2 CH), 129.6, 129.0 (2 CH), 128.7 (2 CH), 128.4 (2
CH), 127.5, 34.6 (CH2), 30.7; IR (KBr): nmax =3060, 3029,
1
978C. H NMR (300 MHz, CDCl3): d=10.17 (d, J=6.0 Hz,
1H), 7.67–7.70 (m, 2H), 7.53–7.62 (m, 3H), 7.07 (d, J=
15.9 Hz, 1H), 6.56 (d, J=6.3 Hz, 1H), 2.49 (s, 3H);
13C NMR (75 MHz, CDCl3): d=193.2, 192.7, 143.6, 143.2,
140.4, 136.9, 136.2, 132.6, 131.5, 127.6, 122.1, 118.6, 112.3,
12.3; IR (KBr): nmax =2925, 2224, 1674, 1602, 1130, 970 cmÀ1
;
HR-MS (ESI): m/z=280.0407, calcd. for C14H11NO2SNa
[M+Na]+: 280.0408.
S-Methyl 2-[(E)-2-(naphthalen-2-yl)vinyl]-4-oxobut-2-ene-
thioate and S-methyl (Z)-2-[(E)-2-(naphthalen-2-yl)vinyl]-4-
oxobut-2-enethioate (4at): Prepared according to the gener-
al procedure discussed above: Rf =0.3; eluent, EtOAc/n-
hexane (6%); isolated yield: 0.034 g (31%); yellow solid;
mp 114–1168C; trans:cis=7:1. NMR of mixtures (major
1
peaks): H NMR (600 MHz, CDCl3): d=10.23 (d, J=7.2 Hz,
1H), 7.90 (s, 1H), 7.83–7.86 (m, 3H), 7.70 (dd, J=1.8,
9.0 Hz, 1H), 7.57 (d, J=15.6 Hz, 1H), 7.51–7.52 (m, 2H),
7.22 (d, J=15.6 Hz, 1H), 6.48 (d, J=6.6 Hz, 1H), 2.50 (s,
3H); 13C NMR (150 MHz, CDCl3): d=194.1, 190.7, 152.3,
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2925, 2853, 1660, 1614, 1494, 1449, 1417, 1358, 1198, 1176,
1072, 1022, 766, 703 cmÀ1; HR-MS (EI): m/z=296.0869,
calcd. for C18H16O2S [M]+: 296.0871.
(CH2); IR (KBr): nmax =2921, 1687, 1591, 1447, 995, 938,
749, 693 cmÀ1; HR-MS (ESI): m/z=369.0934, calcd. for
C22H18O2SNa [M+Na]+: 369.0926.
S-Benzyl (E)-4-oxo-2,4-diphenylbut-2-enethioate (4bc):
Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (3%); isolated
yield: 0.056 g (40%); yellow gum. 1H NMR (600 MHz,
CDCl3): d=7.83–7.85 (m, 2H), 7.60 (s, 1H), 7.50–7.53 (m,
1H), 7.37–7.40 (m, 2H), 7.27–7.32 (m, 6H), 7.24–7.26 (m,
4H), 4.23 (s, 2H); 13C NMR (150 MHz, CDCl3): d=192.8,
192.6, 146.5, 136.7, 136.5, 133.7, 133.0, 131.4, 129.9 (2 CH),
129.1, 129.0 (2 CH), 128.9 (2 CH), 128.7 (2 CH), 128.6 (2
CH), 128.0 (2 CH), 127.5, 34.6 (CH2); IR (KBr): nmax =1663,
1599, 1493, 1449, 1236, 1178, 1073, 1023, 920, 867, 764,
S-Phenyl 4-oxo-2-phenylpentanethioate (4bh): Prepared
according to the general procedure discussed above: Rf =
0.35; eluent, EtOAc/n-hexane (8%); isolated yield: 0.027 g
(54%); colorless gum. 1H NMR (300 MHz, CDCl3): d=
7.28–7.38 (m, 10H), 4.45 (dd, J=4.5, 9.3 Hz, 1H), 3.45 (dd,
J=9.6, 18.0 Hz, 1H), 2.76 (dd, J=4.5, 18.0 Hz, 1H), 2.15 (s,
3H); 13C NMR (75 MHz, CDCl3): d=205.5, 198.0, 137.3,
134.4 (2 CH), 129.2, 129.0 (2 CH), 128.9 (2 CH), 128.2 (2
CH), 127.8, 127.5, 54.2, 46.9 (CH2), 29.9; IR (KBr): nmax
=
2922, 1702, 1441, 1398, 1361, 1232, 1162, 1075, 1029, 746,
696 cmÀ1; HR-MS (EI): m/z=284.0877, calcd. for C17H16O2S
[M]+: 284.0871.
696 cmÀ1
;
HR-MS (ESI): m/z=381.0928, calcd. for
C23H18O2SNa [M+Na]+: 381.0926.
(E)-5-Methyl-5-(methylthio)-3-styrylfuran-2(5H)-one (5a):
Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (5%); isolated
yield: 0.048 g (96%); white solid; mp 71–738C. 1H NMR
(600 MHz, CDCl3): d=7.72 (d, J=16.2 Hz, 1H), 7.50 (d, J=
7.8 Hz, 2H), 7.35–7.38 (m, 2H), 7.30–7.32 (m, 1H), 7.09 (s,
1H), 6.81 (d, J=16.2 Hz, 1H), 1.96 (s, 3H), 1.81 (s, 3H);
13C NMR (150 MHz, CDCl3): d=170.0, 148.8, 136.1, 136.0,
129.1, 128.9, 128.8 (2 CH), 127.0 (2 CH), 115.8, 90.2, 25.1,
11.5; IR (KBr): nmax =1754, 1054, 985, 960, 889, 747,
S-(Methyl-d3) (E)-2-[(E)-3,4-dimethoxystyryl]-4-oxopent-
2-enethioate (4bd): Prepared according to the general pro-
cedure discussed above: Rf =0.3; eluent, EtOAc/n-hexane
1
(22%); isolated yield: 0.065 g (57%); yellow gum. H NMR
(600 MHz, CDCl3): d=7.95 (dd, J=0.6, 16.2 Hz, 1H), 7.08
(dd, J=1.8, 8.4 Hz, 1H), 7.05 (d, J=1.8 Hz, 1H), 7.03 (d,
J=16.2 Hz, 1H), 6.84 (d, J=8.4 Hz, 1H), 6.35 (s, 1H), 3.92
(s, 3H), 3.90 (s, 3H), 2.33 (s, 3H); 13C NMR (150 MHz,
CDCl3): d=198.4, 195.0, 150.5, 149.6, 149.1, 140.8, 129.2,
122.7, 122.0, 118.4, 111.0, 109.5, 55.9, 55.9, 32.4; IR (KBr):
nmax =2927, 1669, 1555, 1513, 1461, 1267, 1140, 1025,
693 cmÀ1
;
HR-MS (ESI): m/z=269.0605, calcd. for
C14H14O2SNa [M+Na]+: 269.0613.
975 cmÀ1
;
HR-MS (ESI): m/z=332.1021, calcd. for
(E)-3-(4-Methoxystyryl)-5-methyl-5-(methylthio)furan-
2(5H)-one (5b): Prepared according to the general proce-
dure discussed above: Rf =0.4; eluent, EtOAc/n-hexane
(10%); isolated yield: 0.041 g (82%); colorless gum.
1H NMR (600 MHz, CDCl3): d=7.66 (d, J=16.2 Hz, 1H),
7.44 (d, J=8.4 Hz, 2H), 7.02 (s, 1H), 6.89 (d, J=8.4 Hz,
2H), 6.67 (d, J=16.2 Hz, 1H), 3.83 (s, 3H), 1.95 (s, 3H),
1.80 (s, 3H); 13C NMR (150 MHz, CDCl3): d=170.2, 160.3,
147.6, 135.5, 129.3, 128.9, 128.4 (2 CH), 114.2 (2 CH), 113.6,
90.2, 55.3, 25.1, 11.5; IR (KBr): nmax =2926, 1756, 1601, 1509,
C16H15D3O4SNa [M+Na]+: 332.1012.
S-(Methyl-d3) (E)-4-oxo-2-[(E)-styryl]pent-2-enethioate
(4be): Prepared according to the general procedure dis-
cussed above: Rf =0.4; eluent, EtOAc/n-hexane (8%); iso-
1
lated yield: 0.088 g (74%); yellow gum. H NMR (600 MHz,
CDCl3): d=8.00 (dd, J=0.6, 16.2 Hz, 1H), 7.51–7.53 (m,
2H), 7.31–7.36 (m, 3H), 7.08 (d, J=16.8 Hz, 1H), 6.41 (s,
1H), 2.34 (s, 3H); 13C NMR (150 MHz, CDCl3): d=198.3,
194.8, 149.0, 140.7, 136.0, 129.5, 128.7 (2 CH), 127.8 (2 CH),
124.1, 120.3, 32.4; IR (KBr): nmax =3028, 2931, 2133, 1661,
1445, 1255, 1176, 1108, 1053, 972, 889, 849, 817, 770 cmÀ1
;
1566, 1494, 1449, 1357, 1190, 1110, 1032, 977, 756, 699 cmÀ1
;
HR-MS (ESI): m/z=299.0717, calcd. for C15H16O3SNa [M+
HR-MS (ESI): m/z=272.0772, calcd. for C14H11D3O2SNa
Na]+: 299.0718.
[M+Na]+: 272.0801.
(E)-3-(3,4-Dimethoxystyryl)-5-methyl-5-(methylthio)fur-
an-2(5H)-one (5c): Prepared according to the general proce-
dure discussed above: Rf =0.3; eluent, EtOAc/n-hexane
Methyl (E)-4-oxo-2-[(E)-styryl]pent-2-enoate (4bf): Pre-
pared according to the general procedure discussed above:
Rf =0.3; eluent, EtOAc/n-hexane (8%); isolated yield:
0.038 g (31%); yellow solid; mp 127–1298C. 1H NMR
(300 MHz, CDCl3): d=8.04 (d, J=16.5 Hz, 1H), 7.53 (d, J=
6.3 Hz, 2H), 7.31–7.38 (m, 4H), 6.62 (s, 1H), 3.90 (s, 3H),
2.35 (s, 3H); 13C NMR (75 MHz, CDCl3): d=199.0, 167.6,
141.4, 140.6, 136.5, 129.4, 128.9 (2 CH), 127.8 (2 CH), 127.7,
121.1, 52.8, 32.5; IR (KBr): nmax =1726, 1608, 1573, 1437,
1250, 751, 696 cmÀ1; HR-MS (ESI): m/z=253.0849, calcd.
for C14H14O3Na [M+Na]+: 253.0841.
1
(20%); isolated yield: 0.04 g (80%); colorless gum. H NMR
(300 MHz, CDCl3): d=7.65 (d, J=16.2 Hz, 1H), 7.04–7.08
(m, 3H), 6.86 (d, J=8.1 Hz, 1H), 6.68 (d, J=16.2 Hz, 1H),
3.93 (s, 3H), 3.91 (s, 3H), 1.96 (s, 3H), 1.81 (s, 3H);
13C NMR (75 MHz, CDCl3): d=170.2, 149.9, 149.1, 147.7,
135.7, 129.2, 129.2, 120.7, 113.7, 111.1, 109.0, 90.3, 55.9, 55.8,
25.1, 11.5; IR (KBr): nmax =2929, 1762, 1638, 1596, 1514,
1461, 1265, 1141, 1052, 1026, 966 cmÀ1; HR-MS (ESI): m/z=
329.0820, calcd. for C16H18O4SNa [M+Na]+: 329.0824.
(E)-5-Methyl-3-(4-methylstyryl)-5-(methylthio)furan-
S-Phenyl 4-oxo-2,4-diphenylbutanethioate (4bg): Prepared
according to the general procedure discussed above: Rf =
0.3; eluent, EtOAc/n-hexane (4%); isolated yield: 0.043 g
2(5H)-one (5d): Prepared according to the general proce-
dure discussed above: Rf =0.3; eluent, EtOAc/n-hexane
1
1
(86%); colorless gum. H NMR (600 MHz, CDCl3): d=7.96
(5%); isolated yield: 0.035 g (70%); yellow gum. H NMR
(d, J=7.2 Hz, 2H), 7.55 (t, J=7.2 Hz, 1H), 7.44 (t, J=
7.8 Hz, 2H), 7.32–7.39 (m, 10H), 4.66 (dd, J=4.2, 9.0 Hz,
1H), 4.03 (dd, J=9.6, 18.0 Hz, 1H), 3.32 (dd, J=4.8,
18.0 Hz, 1H); 13C NMR (150 MHz, CDCl3): d=198.1, 197.1,
137.7, 136.3, 134.5 (2 CH), 133.3, 129.3, 129.1 (4 CH), 128.6
(2 CH), 128.3 (2 CH), 128.1 (2 CH), 127.9, 127.8, 54.5, 42.8
(600 MHz, CDCl3): d=7.68 (d, J=16.2 Hz, 1H), 7.39 (d, J=
8.4 Hz, 2H), 7.17 (d, J=7.8 Hz, 2H), 7.06 (s, 1H), 6.76 (d,
J=16.2 Hz, 1H), 2.36 (s, 3H), 1.95 (s, 3H), 1.80 (s, 3H);
13C NMR (150 MHz, CDCl3): d=170.1, 148.2, 139.0, 135.9,
133.4, 129.5 (2 CH), 129.3, 126.9 (2 CH), 114.8, 90.2, 25.1,
21.3, 11.5; IR (KBr): nmax =2925, 1763, 1099, 1052, 967 cmÀ1
;
Adv. Synth. Catal. 0000, 000, 0 – 0
14
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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HR-MS (ESI): m/z=283.0779, calcd. for C15H16O2SNa [M+
Na]+: 283.0769.
684 cmÀ1
;
HR-MS (ESI): m/z=294.0560, calcd. for
C15H13NO2SNa [M+Na]+: 294.0565.
(E)-5-Methyl-5-(methylthio)-3-(3-nitrostyryl)furan-2(5H)-
one (5j): Prepared according to the general procedure dis-
cussed above: Rf =0.3; eluent, EtOAc/n-hexane (15%); iso-
lated yield: 0.039 g (78%); yellowish white solid; mp 124–
(E)-3-(2,6-Dichlorostyryl)-5-methyl-5-(methylthio)furan-
2(5H)-one (5e): Prepared according to the general proce-
dure discussed above: Rf =0.3; eluent, EtOAc/n-hexane
(4%); isolated yield: 0.044 g (88%); yellow crystalline solid;
1
1
1268C. H NMR (600 MHz, CDCl3): d=8.36–8.37 (m, 1H),
mp 79–818C. H NMR (300 MHz, CDCl3): d=7.81 (d, J=
8.15 (dd, J=1.2, 7.8 Hz, 1H), 7.83 (d, J=16.8 Hz, 1H), 7.77
(d, J=7.8 Hz, 1H), 7.55 (t, J=7.8 Hz, 1H), 7.19 (s, 1H),
6.94 (d, J=16.2 Hz, 1H), 1.97 (s, 3H), 1.83 (s, 3H);
13C NMR (150 MHz, CDCl3): d=169.6, 151.0, 148.7, 138.0,
133.4, 133.1, 129.8, 128.2, 123.2, 121.0, 118.8, 90.3, 24.9, 11.5;
IR (KBr): nmax =1763, 1523, 1437, 1351, 1090, 1049, 968, 888,
733, 699 cmÀ1; HR-MS (ESI): m/z=314.0444, calcd. for
C14H13NO4SNa [M+Na]+: 314.0463.
(E)-5-Methyl-5-(methylthio)-3-[2-(naphthalen-2-yl)vinyl]-
furan-2(5H)-one (5k): Prepared according to the general
procedure discussed above: Rf =0.3; eluent, EtOAc/n-
hexane (6%); isolated yield: 0.038 g (76%); colorless gum.
1H NMR (600 MHz, CDCl3): d=7.87–7.90 (m, 2H), 7.80–
7.84 (m, 3H), 7.67 (dd, J=1.2, 9.0 Hz, 1H), 7.46–7.50 (m,
2H), 7.12 (s, 1H), 6.92 (d, J=16.2 Hz, 1H), 1.97 (s, 3H),
1.82 (s, 3H); 13C NMR (150 MHz, CDCl3): d=170.1, 148.8,
136.0, 133.6, 133.5, 133.5, 129.1, 128.5, 128.3, 128.1, 127.7,
16.8 Hz, 1H), 7.35 (d, J=8.1 Hz, 2H), 7.12–7.17 (m, 2H),
6.90 (d, J=16.5 Hz, 1H), 1.99 (s, 3H), 1.83 (s, 3H);
13C NMR (75 MHz, CDCl3): d=169.5, 150.7, 134.5 (2 C0),
133.4, 130.1, 128.9, 128.6 (2 CH), 128.5, 124.2, 90.0, 24.9,
11.5; IR (KBr): nmax =2926, 1764, 1431, 1095, 1052, 966, 890,
844, 777 cmÀ1; HR-MS (ESI): m/z=336.9860, calcd. for
C14H12Cl2O2SNa [M+Na]+: 336.9833.
(E)-3-(4-Chlorostyryl)-5-methyl-5-(methylthio)furan-
2(5H)-one (5f): Prepared according to the general proce-
dure discussed above: Rf =0.3; eluent, EtOAc/n-hexane
1
(5%); isolated yield: 0.04 g (80%); colorless gum. H NMR
(600 MHz, CDCl3): d=7.69 (d, J=16.2 Hz, 1H), 7.42 (d, J=
8.4 Hz, 2H), 7.33 (d, J=8.4 Hz, 2H), 7.10 (s, 1H), 6.77 (d,
J=16.2 Hz, 1H), 1.95 (s, 3H), 1.81 (s, 3H); 13C NMR
(150 MHz, CDCl3): d=169.9, 149.3, 134.7, 134.6, 129.0 (2
CH), 128.8, 128.1 (2 CH), 116.3, 90.2, 25.0, 11.5; IR (KBr):
nmax =2926, 1762, 1489, 1091, 1051, 996, 890, 854, 769 cmÀ1
;
126.6, 126.5, 123.0, 116.0, 90.2, 25.1, 11.5; IR (KBr): nmax
=
HR-MS (ESI): m/z=303.0246, calcd. for C14H13ClO2SNa
2925, 1761, 1096, 1052, 964, 891, 861, 816, 775 cmÀ1; HR-MS
(ESI): m/z=319.0767, calcd. for C18H16O2SNa [M+Na]+:
319.0769.
[M+Na]+: 303.0223.
(E)-3-(4-Fluorostyryl)-5-methyl-5-(methylthio)furan-
2(5H)-one (5g): Prepared according to the general proce-
dure discussed above: Rf =0.3; eluent, EtOAc/n-hexane
(E)-5-Methyl-5-(methylthio)-3-[2-(naphthalen-1-yl)vinyl]-
furan-2(5H)-one (5l): Prepared according to the general pro-
cedure discussed above: Rf =0.3; eluent, EtOAc/n-hexane
1
(5%); isolated yield: 0.037 g (74%); colorless gum. H NMR
(600 MHz, CDCl3): d=7.70 (d, J=16.8 Hz, 1H), 7.45–7.48
(m, 2H), 7.08 (s, 1H), 7.05 (t, J=9.0 Hz, 2H), 6.72 (d, J=
16.8 Hz, 1H), 1.95 (s, 3H), 1.80 (s, 3H); 13C NMR
(150 MHz, CDCl3): d=170.0, 163.0 (d, J=247.5 Hz, 1 C),
148.9, 134.8, 132.4 (d, J=3.0 Hz, 1 C), 128.9, 128.7, 128.6,
115.9, 115.8, 115.5 (d, J=1.5 Hz, 1 C), 90.2, 25.0, 11.5; IR
(KBr): nmax =2926, 1763, 1598, 1508, 1436, 1236, 1098, 1052,
967, 855, 767 cmÀ1; HR-MS (ESI): m/z=287.0516, calcd. for
C14H13FO2SNa [M+Na]+: 287.0518.
1
(7%); isolated yield: 0.041 g (82%); yellow gum. H NMR
(600 MHz, CDCl3): d=8.61 (d, J=16.2 Hz, 1H), 8.23 (d, J=
8.4 Hz, 1H), 7.84–7.87 (m, 2H), 7.72 (d, J=7.2 Hz, 1H),
7.55–7.58 (m, 1H), 7.51–7.53 (m, 1H), 7.49 (t, J=7.2 Hz,
1H), 7.14 (s, 1H), 6.88 (d, J=16.2 Hz, 1H), 2.00 (s, 3H),
1.85 (s, 3H); 13C NMR (150 MHz, CDCl3): d=170.0, 149.3,
133.8, 133.7, 133.2, 131.3, 129.3, 129.2, 128.6, 126.5, 126.1,
125.5, 123.7, 123.6, 118.5, 90.2, 25.1, 11.6; IR (KBr): nmax
=
1762, 1091, 1056, 963, 779 cmÀ1; HR-MS (ESI): m/z=
319.0748, calcd. for C18H16O2SNa [M+Na]+: 319.0769.
(E)-5-Methyl-5-(methylthio)-3-[2-(thiophen-2-yl)vinyl]fur-
an-2(5H)-one (5m): Prepared according to the general pro-
cedure discussed above: Rf =0.35; eluent, EtOAc/n-hexane
(E)-3-(2-Bromostyryl)-5-methyl-5-(methylthio)furan-
2(5H)-one (5h): Prepared according to the general proce-
dure discussed above: Rf =0.3; eluent, EtOAc/n-hexane
1
(5%); isolated yield: 0.038 g (76%); colorless gum. H NMR
1
(600 MHz, CDCl3): d=8.01 (d, J=16.2 Hz, 1H), 7.58–7.60
(m, 2H), 7.31 (t, J=7.2 Hz, 1H), 7.19 (s, 1H), 7.15–7.18 (m,
1H), 6.74 (d, J=16.2 Hz, 1H), 1.97 (s, 3H), 1.82 (s, 3H);
13C NMR (150 MHz, CDCl3): d=169.9, 149.4, 136.1, 134.7,
133.3, 130.0, 129.1, 127.6, 126.8, 124.6, 118.2, 90.2, 25.0, 11.5;
IR (KBr): nmax =2984, 1763, 1434, 1096, 1053, 965, 890, 751,
(5%); isolated yield: 0.045 g (90%); yellow gum. H NMR
(600 MHz, CDCl3): d=7.89 (d, J=16.2 Hz, 1H), 7.26–7.27
(m, 1H), 7.14 (d, J=3.6 Hz, 1H), 7.01–7.03 (m, 2H), 6.60
(d, J=15.6 Hz, 1H), 1.94 (s, 3H), 1.79 (s, 3H); 13C NMR
(150 MHz, CDCl3): d=169.9, 148.5, 141.7, 129.1, 128.7,
128.5, 127.9, 126.2, 115.2, 90.3, 25.1, 11.5; IR (KBr): nmax
=
574 cmÀ1
;
HR-MS (ESI): m/z=346.9709, calcd. for
2984, 1761, 1632, 1428, 1251, 1183, 1093, 1052, 960, 890,
C14H13BrO2SNa [M+Na]+: 346.9718.
705 cmÀ1
;
HR-MS (ESI): m/z=275.0164, calcd. for
C12H12O2S2Na [M+Na]+: 275.0177.
(E)-3-{2-[5-Methyl-5-(methylthio)-2-oxo-2,5-dihydrofuran-
3-yl]vinyl}benzonitrile (5i): Prepared according to the gener-
al procedure discussed above: Rf =0.3; eluent, EtOAc/n-
hexane (15%); isolated yield: 0.04 g (80%); colorless gum.
1H NMR (300 MHz, CDCl3): d=7.69–7.78 (m, 3H), 7.59 (d,
J=7.5 Hz, 1H), 7.48 (t, J=8.1 Hz, 1H), 7.17 (s, 1H), 6.86
(d, J=16.2 Hz, 1H), 1.97 (s, 3H), 1.82 (s, 3H); 13C NMR
(75 MHz, CDCl3): d=169.6, 150.8, 137.5, 133.5, 131.8, 131.2,
130.0, 129.6, 128.3, 118.4, 118.4, 113.1, 90.2, 24.9, 11.5; IR
(KBr): nmax =2985, 2230, 1762, 1247, 1094, 1053, 890, 770,
5-Methyl-5-(methylthio)-3-(4-nitrophenyl)furan-2(5H)-
one (5o): Prepared according to the general procedure dis-
cussed above: Rf =0.35; eluent, EtOAc/n-hexane (15%); iso-
lated yield: 0.041 g (82%); white solid; mp 111–1138C.
1H NMR (600 MHz, CDCl3): d=8.29 (d, J=9.0 Hz, 2H),
8.09 (d, J=8.4 Hz, 2H), 7.62 (s, 1H), 1.99 (s, 3H), 1.89 (s,
3H); 13C NMR (150 MHz, CDCl3): d=169.0, 152.5, 148.3,
134.6, 129.1, 128.1 (2 CH), 124.0 (2 CH), 89.7, 24.7, 11.5; IR
(KBr): nmax =1760, 1596, 1519, 1348, 1213, 1093, 958,
Adv. Synth. Catal. 0000, 000, 0 – 0
15
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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855 cmÀ1
;
HR-MS (ESI): m/z=288.0309, calcd. for
MS (ESI): m/z=305.0583, calcd. for C17H14O2SNa [M+
Na]+: 305.0613.
C12H11NO4SNa [M+Na]+: 288.0307.
(E)-5-(Methylthio)-3-[2-(thiophen-3-yl)vinyl]furan-2(5H)-
one (5u): Prepared according to the general procedure dis-
cussed above: Rf =0.3; eluent, EtOAc/n-hexane (12%); iso-
(E)-5-(Methylthio)-3-styrylfuran-2(5H)-one (5p): Pre-
pared according to the general procedure discussed above:
Rf =0.3; eluent, EtOAc/n-hexane (10%); isolated yield=
1
1
lated yield: 0.02 g (40%); yellow gum. H NMR (600 MHz,
0.025 g, 50%; yellow gum. H NMR (300 MHz, CDCl3): d=
CDCl3): d=7.75 (d, J=16.2 Hz, 1H), 7.38 (d, J=1.8 Hz,
1H), 7.32–7.33 (m, 1H), 7.30 (dd, J=1.2, 4.8 Hz, 1H), 7.09
(d, J=2.4 Hz, 1H), 6.66 (d, J=16.2 Hz, 1H), 6.03 (d, J=
1.8 Hz, 1H), 2.15 (s, 3H); 13C NMR (150 MHz, CDCl3): d=
170.5, 142.9, 139.1, 131.0, 130.3, 126.6, 125.3, 124.5, 115.8,
83.9, 12.0; IR (KBr): nmax =2924, 1761, 1639, 1424, 1080,
1047, 970, 938, 769 cmÀ1; HR-MS (ESI): m/z=261.0024,
calcd. for C11H10O2S2Na [M+Na]+: 261.0020.
7.75 (d, J=16.2 Hz, 1H), 7.51 (d, J=6.9 Hz, 2H), 7.31–7.40
(m, 3H), 7.15 (d, J=2.1 Hz, 1H), 6.83 (d, J=16.2 Hz, 1H),
6.05 (d, J=1.8 Hz, 1H), 2.17 (s, 3H); 13C NMR (75 MHz,
CDCl3): d=170.6, 143.5, 136.2, 136.0, 130.9, 129.0, 128.8 (2
CH), 127.1 (2 CH), 115.9, 83.9, 12.0; IR (KBr): nmax =2925,
1762, 1641, 1429, 1078, 1047, 972, 939, 751, 696 cmÀ1; HR-
MS (ESI): m/z=255.0461, calcd. for C13H12O2SNa [M+
Na]+: 255.0456.
(E)-5-(Methylthio)-5-phenyl-3-styrylfuran-2(5H)-one (5v):
Prepared according to the general procedure discussed
above: Rf =0.4; eluent, EtOAc/n-hexane (8%); isolated
yield: 0.028 g (56%); yellow gum. 1H NMR (600 MHz,
CDCl3): d=7.74 (d, J=16.2 Hz, 1H), 7.57–7.59 (m, 2H),
7.49 (d, J=7.2 Hz, 2H), 7.40–7.42 (m, 3H), 7.35–7.37 (m,
3H), 7.31 (t, J=7.2 Hz, 1H), 6.82 (d, J=16.8 Hz, 1H), 2.03
(s, 3H); 13C NMR (150 MHz, CDCl3): d=169.8, 147.3, 136.9,
136.4, 136.1, 129.0, 128.9, 128.8 (2 CH), 128.8 (2 CH), 128.5,
127.0 (2 CH), 125.6 (2 CH), 115.8, 93.6, 12.7; IR (KBr):
nmax =2924, 1767, 1147, 1056, 975, 746, 694 cmÀ1; HR-MS
(EI): m/z=308.0879, calcd. for C19H16O2S [M]+: 308.0871.
(E)-3-(4-Methylstyryl)-5-(methylthio)-5-phenylfuran-
(E)-3-(4-Methylstyryl)-5-(methylthio)furan-2(5H)-one
(5q): Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (5%); isolated
yield: 0.02 g (40%); yellow gum. 1H NMR (600 MHz,
CDCl3): d=7.70 (d, J=16.2 Hz, 1H), 7.40 (d, J=7.8 Hz,
2H), 7.17 (d, J=8.4 Hz, 2H), 7.10 (d, J=2.4 Hz, 1H), 6.78
(d, J=16.2 Hz, 1H), 6.03 (d, J=1.8 Hz, 1H), 2.36 (s, 3H),
2.16 (s, 3H); 13C NMR (150 MHz, CDCl3): d=170.6, 142.8,
139.1, 136.2, 133.3, 131.1, 129.5 (2 CH), 127.0 (2 CH), 114.9,
83.9, 21.3, 12.0; IR (KBr): nmax =2924, 1763, 1670, 1607,
1568, 1077, 1047, 974, 935, 846, 777 cmÀ1; HR-MS (ESI):
m/z=269.0598, calcd. for C14H14O2SNa [M+Na]+: 269.0613.
(E)-3-(4-Chlorostyryl)-5-(methylthio)furan-2(5H)-one
(5r): Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (10%); isolated
yield: 0.023 g (46%); yellowish white solid; mp 114–1168C.
1H NMR (600 MHz, CDCl3): d=7.71 (d, J=16.8 Hz, 1H),
7.42 (d, J=8.4 Hz, 2H), 7.33–7.34 (m, 2H), 7.15 (d, J=
1.8 Hz, 1H), 6.79 (d, J=16.8 Hz, 1H), 6.04 (d, J=1.8 Hz,
1H), 2.16 (s, 3H); 13C NMR (150 MHz, CDCl3): d=170.4,
144.0, 134.9, 134.7, 134.6, 130.7, 129.0 (2 CH), 128.2 (2 CH),
116.5, 83.9, 12.1; IR (KBr): nmax =1755, 1081, 1048, 975, 935,
857, 817 cmÀ1; HR-MS (ESI): m/z=289.0062, calcd. for
C13H11ClO2SNa [M+Na]+: 289.0066.
2(5H)-one (5w): Prepared according to the general proce-
dure discussed above: Rf =0.4; eluent, EtOAc/n-hexane
1
(4%); isolated yield: 0.022 g (44%); yellow gum. H NMR
(600 MHz, CDCl3): d=7.71 (d, J=16.8 Hz, 1H), 7.57–7.59
(m, 2H), 7.39–7.42 (m, 3H), 7.38 (s, 1H), 7.34–7.37 (m, 2H),
7.17 (d, J=7.8 Hz, 2H), 6.77 (d, J=16.2 Hz, 1H), 2.36 (s,
3H), 2.02 (s, 3H); 13C NMR (150 MHz, CDCl3): d=169.9,
146.7, 139.1, 137.0, 136.3, 133.3, 129.5 (2 CH), 128.9, 128.8 (2
CH), 128.7, 127.0 (2 CH), 125.6 (2 CH), 114.8, 93.6, 21.3,
12.7; IR (KBr): nmax =2923, 1767, 1146, 1056, 976, 749,
695 cmÀ1
;
HR-MS (ESI): m/z=345.0914, calcd. for
C20H18O2SNa [M+Na]+: 345.0926.
(E)-4-{2-[5-(Methylthio)-2-oxo-2,5-dihydrofuran-3-yl]vi-
nyl}benzonitrile (5s): Prepared according to the general pro-
cedure discussed above: Rf =0.3; eluent, EtOAc/n-hexane
(E)-3-(2,4-Dichlorostyryl)-5-(methylthio)-5-phenylfuran-
2(5H)-one (5x): Prepared according to the general proce-
dure discussed above: Rf =0.3; eluent, EtOAc/n-hexane
1
1
(25%); isolated yield: 0.025 g (50%); yellow gum. H NMR
(2%); isolated yield: 0.03 g (60%); colorless gum. H NMR
(600 MHz, CDCl3): d=7.79 (d, J=16.2 Hz, 1H), 7.66 (d, J=
8.4 Hz, 2H), 7.58 (d, J=8.4 Hz, 2H), 7.25 (d, J=1.8 Hz,
1H), 6.92 (d, J=16.2 Hz, 1H), 6.07 (d, J=1.2 Hz, 1H), 2.18
(s, 3H); 13C NMR (150 MHz, CDCl3): d=170.1, 145.8, 140.5,
134.2, 132.6 (2 CH), 130.2, 127.4 (2 CH), 119.3, 118.6, 112.0,
84.0, 12.2; IR (KBr): nmax =2923, 2225, 1762, 1082, 1048, 975,
(600 MHz, CDCl3): d=8.00 (d, J=16.2 Hz, 1H), 7.58–7.59
(m, 1H), 7.56–7.57 (m, 1H), 7.53 (d, J=9.0 Hz, 1H), 7.48 (s,
1H), 7.40–7.43 (m, 3H), 7.35–7.38 (m, 1H), 7.25 (dd, J=1.8,
8.4 Hz, 1H), 6.78 (d, J=16.2 Hz, 1H), 2.03 (s, 3H);
13C NMR (150 MHz, CDCl3): d=169.5, 148.4, 136.7, 134.9,
134.6, 132.9, 131.3, 129.8, 129.1, 128.9 (2 CH), 128.2, 127.4,
127.3, 125.6 (2 CH), 118.6, 93.7, 12.7; IR (KBr): nmax =2924,
1768, 1582, 1469, 1102, 1055, 976, 749 cmÀ1; HR-MS (ESI):
m/z=398.9972, calcd. for C19H14Cl2O2SNa [M+Na]+:
398.9990.
939 cmÀ1
;
HR-MS (EI): m/z=257.0507, calcd. for
C14H11NO2S [M]+: 257.0510.
(E)-5-(Methylthio)-3-[2-(naphthalen-2-yl)vinyl]furan-
2(5H)-one (5t): Prepared according to the general procedure
discussed above: Rf =0.3; eluent, EtOAc/n-hexane (10%);
isolated yield: 0.028 g (56%); yellowish white solid; mp 120–
5-Methyl-3-phenyl-5-(phenylthio)furan-2(5H)-one
(3a):
Prepared according to the general procedure discussed
above under BF3·OEt2-catalyzed conditions: Rf =0.35;
eluent, EtOAc/n-hexane (3%); isolated yield: 0.03 g (60%);
1
1228C. H NMR (600 MHz, CDCl3): d=7.90–7.92 (m, 2H),
7.81–7.85 (m, 3H), 7.68 (dd, J=1.2, 8.4 Hz, 1H), 7.48–7.50
(m, 2H), 7.18 (d, J=1.8 Hz, 1H), 6.95 (d, J=16.8 Hz, 1H),
6.06 (d, J=1.8 Hz, 1H), 2.18 (s, 3H); 13C NMR (150 MHz,
CDCl3): d=170.6, 143.4, 136.3, 133.6, 133.5, 133.5, 131.0,
128.5, 128.3, 128.3, 127.7, 126.6, 126.5, 123.1, 116.1, 84.0,
12.0; IR (KBr): nmax =1754, 1088, 1046, 971, 938 cmÀ1; HR-
1
white solid; mp 99–1018C. H NMR (600 MHz, CDCl3): d=
7.48–7.51 (m, 4H), 7.30–7.33 (m, 3H), 7.26–7.29 (m, 4H),
1.89 (s, 3H); 13C NMR (150 MHz, CDCl3): d=169.7, 149.3,
137.1 (2 CH), 131.2, 129.9, 129.4, 128.9 (2 CH), 128.7, 128.5
(2 CH), 128.5, 127.1 (2 CH), 91.6, 24.5; IR (KBr): nmax
=
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16
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1753, 1442, 1301, 1216, 1115, 1085, 958, 789, 750, 691 cmÀ1
;
2(3H)-one (2r) plus 3-(4-methoxyphenyl)-5-methyl-3-(p-tol-
ylthio)furan-2(3H)-one (2s)]: NMR of mixtures of 2d plus
2a; major peaks: H NMR (600 MHz, CDCl3): d=7.64–7.69
HR-MS (ESI): m/z=305.0606, calcd. for C17H14O2SNa [M+
Na]+: 305.0613.
1
5-(Benzylthio)-5-methyl-3-phenylfuran-2(5H)-one
(3o):
(m, 2H), 7.45 (dd, J=8.2, 1.2 Hz, 1H), 7.35–7.41 (m, 2H),
7.29–7.35 (m, 3H), 7.11 (d, J=7.8 Hz, 1H), 5.51–5.55 (m,
1H), 2.35 (s, 2H), 1.81 (d, J=1.4 Hz, 2H), 1.79 (d, J=
1.4 Hz, 1H); 13C NMR (150 MHz, CDCl3): d=175.4, 152.0,
151.9, 140.4, 137.1, 137.0, 135.1, 135.0, 130.0, 129.4, 128.7,
128.7, 128.5, 128.5, 127.4, 126.5, 106.1, 106.0, 62.1, 21.3, 13.7,
Prepared according to the general procedure discussed
above under BF3·OEt2-catalyzed conditions: Rf =0.3; eluent,
EtOAc/n-hexane (4%); isolated yield: 0.04 g (80%); color-
less gum. Analytical data were exactly matched with the
previously discussed data.
1
5-Methyl-5-(naphthalen-2-ylthio)-3-phenylfuran-2(5H)-
one (6a): Prepared according to the general procedure dis-
cussed above: Rf =0.3; eluent, EtOAc/n-hexane (3%); iso-
13.7. NMR of mixtures 2r plus 2s; major peaks: H NMR
(600 MHz, CDCl3): d=7.56–7.61 (m, 2H), 7.43–7.47 (m,
1H), 7.29–7.34 (m, 2H), 7.11 (d, J=7.8 Hz, 1H), 6.87–6.91
(m, 2H), 5.48–5.53 (m, 1H), 3.81 (s, 3H), 2.35 (s, 2H), 1.80
(d, J=1.3 Hz, 2H), 1.78 (d, J=1.4 Hz, 1H); 13C NMR
(150 MHz, CDCl3): d=175.6, 159.6, 151.8, 151.7, 140.3,
137.0, 137.0, 130.2, 129.9, 129.4, 128.7, 128.6, 127.0, 126.7,
114.0, 114.0, 106.2, 106.1, 61.8, 55.3, 21.3, 13.7, 13.6.
1
lated yield: 0.025 g (50%); yellow gum. H NMR (600 MHz,
CDCl3): d=8.05 (s, 1H), 7.78–7.80 (m, 1H), 7.75–7.77 (m,
1H), 7.73 (d, J=8.4 Hz, 1H), 7.54 (dd, J=1.8, 8.4 Hz, 1H),
7.47–7.49 (m, 2H), 7.41 (dd, J=1.2, 7.8 Hz, 2H), 7.36 (s,
1H), 7.23–7.27 (m, 3H), 1.90 (s, 3H); 13C NMR (150 MHz,
CDCl3): d=169.7, 149.2, 137.1, 133.4, 133.2, 132.8, 131.4,
129.3, 128.6, 128.6, 128.4 (2 CH), 128.0, 127.6, 127.3, 127.0 (2
CH), 126.6, 125.9, 91.9, 24.7; IR (KBr): nmax =2924, 1764,
1495, 1215, 1088, 959, 871, 788, 748, 693 cmÀ1; HR-MS (EI):
m/z=332.0877, calcd. for C21H16O2S [M]+: 332.0871.
5-(Benzylthio)-3,5-diphenylfuran-2(5H)-one (6b): Pre-
pared according to the general procedure discussed above:
Rf =0.3; eluent, EtOAc/n-hexane (3%); isolated yield=
0.02 g (40%); colorless gum. 1H NMR (600 MHz, CDCl3):
d=7.77–7.79 (m, 2H), 7.63–7.64 (m, 3H), 7.35–7.43 (m,
6H), 7.21–7.25 (m, 5H), 3.80 (d, J=12.6 Hz, 1H), 3.68 (d,
J=12.6 Hz, 1H); 13C NMR (150 MHz, CDCl3): d=169.7,
148.3, 136.9, 136.3, 130.3, 129.8, 129.1, 129.0 (2 CH), 128.9 (2
CH), 128.7 (2 CH), 128.6 (2 CH), 128.5, 127.3 (3 CH), 125.7
(2 CH), 93.6, 34.9 (CH2); IR (KBr): nmax =2925, 1764, 1492,
1450, 1157, 1086, 959, 899, 747, 696 cmÀ1; HR-MS (ESI):
m/z=381.0935, calcd. for C23H18O2SNa [M+Na]+: 381.0926.
(E)-3-(3,4-Dimethoxystyryl)-5-methyl-5-[(methyl-d3)thio]-
{(E)-5-Methyl-5-(methylthio)-3-styrylfuran-2(5H)-one
(5a) plus (E)-5-methyl-5-[(methyl-d3)thio]-3-styrylfuran-
2(5H)-one (6d)} and {(E)-3-(3,4-dimethoxystyryl)-5-methyl-
5-(methylthio)furan-2(5H)-one (5c) plus (E)-3-(3,4-dime-
thoxystyryl)-5-methyl-5-[(methyl-d3)thio]furan-2(5H)-one
(6c)}: NMR of mixtures 5a/6d; major peaks: 1H NMR
(600 MHz, CDCl3): d=7.72 (d, J=16.8 Hz, 1H), 7.50 (d, J=
7.2 Hz, 2H), 7.37 (t, J=7.2 Hz, 2H), 7.30–7.32 (m, 1H), 7.09
(s, 1H), 6.81 (d, J=16.2 Hz, 1H), 1.96 (s, 2H), 1.81 (s, 3H);
13C NMR (150 MHz, CDCl3): d=170.0, 148.8, 148.8, 136.1,
136.0, 129.1, 128.9, 128.8 (2 CH), 127.0 (2 CH), 115.8, 90.2,
90.1, 25.1, 25.1, 11.5. NMR of mixtures 5c/6c; major peaks:
1H NMR (600 MHz, CDCl3): d=7.66 (d, J=16.2 Hz, 1H),
7.08 (dd, J=1.8, 8.4 Hz, 1H), 7.06 (s, 1H), 7.04 (d, J=
1.8 Hz, 1H), 6.87 (d, J=8.4 Hz, 1H), 6.69 (d, J=16.2 Hz,
1H), 3.93 (s, 3H), 3.92 (s, 3H), 1.97 (s, 2H), 1.82 (s, 3H);
13C NMR (150 MHz, CDCl3): d=170.3, 149.9, 149.2, 147.7,
135.8, 129.2, 120.7, 113.8, 111.1, 109.0, 90.3, 90.3, 55.9, 55.9,
25.2, 25.1, 11.5. NMR data of 5a/6d/5c/6c were exactly
matched with our previous data discussed in the Experimen-
tal Section.
ACHTUNGTRENNUNGfuran-2(5H)-one (6c): Prepared according to the general
procedure discussed above: Rf =0.3; eluent, EtOAc/n-
hexane (20%); isolated yield: 0.038 g (76%); colorless gum.
1H NMR (600 MHz, CDCl3): d=7.65 (d, J=16.2 Hz, 1H),
7.06 (dd, J=1.8, 8.4 Hz, 1H), 7.03–7.04 (m, 2H), 6.86 (d, J=
8.4 Hz, 1H), 6.68 (d, J=16.8 Hz, 1H), 3.92 (s, 3H), 3.90 (s,
3H), 1.80 (s, 3H); 13C NMR (150 MHz, CDCl3): d=170.3,
149.9, 149.1, 147.7, 135.8, 129.2, 129.2, 120.7, 113.8, 111.1,
109.0, 90.2, 55.9, 55.9, 25.1; IR (KBr): nmax =2925, 1761,
1595, 1513, 1461, 1265, 1140, 1050, 1026 cmÀ1; HR-MS
(ESI): m/z=332.1036, calcd. for C16H15D3O4SNa [M+Na]+:
332.1012.
[5-(Benzylthio)-5-methyl-3-phenylfuran-2(5H)-one
(3o)
and 5-methyl-3-phenyl-5-(phenylthio)furan-2(5H)-one (3a)]:
1
NMR of mixtures 3o/3a; major peaks: H NMR (600 MHz,
CDCl3): d=7.73–7.75 (m, 2H), 7.40–7.41 (m, 3H), 7.31 (s,
1H), 7.20–7.24 (m, 5H), 3.71 (d, J=13.2 Hz, 1H), 3.64 (d,
J=13.2 Hz, 1H), 1.89 (s, CH3, minor compound peak), 1.84
(s, 3H, CH3, major compound peak); 13C NMR (150 MHz,
CDCl3): d=169.9, 149.9, 136.7, 129.7, 128.8, 128.7, 128.6,
127.3, 127.2, 90.3, 33.7, 25.4. NMR data of 3o and 3a were
exactly matched with our previous data discussed in the Ex-
perimental Section.
(E)-5-(Cyclohexylamino)-5-methyl-3-styrylfuran-2(5H)-
one (7a): Prepared according to the general procedure dis-
cussed above: Rf =0.3; eluent, EtOAc/n-hexane (15%); iso-
lated yield: 0.027 g (45%); colorless gum. 1H NMR
(300 MHz, CDCl3): d=7.76 (d, J=15.9 Hz, 1H), 7.47 (d, J=
7.2 Hz, 2H), 7.29–7.36 (m, 3H), 6.78 (d, J=16.5 Hz, 1H),
6.67 (s, 1H), 3.33–3.44 (m, 1H), 2.23–2.42 (m, 2H), 1.84–
1.85 (m, 2H), 1.66–1.69 (m, 4H), 1.58 (s, 3H), 1.25–1.28 (m,
2H); 13C NMR (150 MHz, CDCl3): d=167.6, 140.9, 136.8,
134.9, 133.9, 128.7 (2 CH), 128.3, 126.8 (2 CH), 118.0, 88.4,
52.0, 30.6 (CH2), 30.2 (CH2), 26.4 (2 CH2), 25.3 (CH2), 23.0;
IR (KBr): nmax =2930, 2855, 1758, 1674, 1446, 1426, 1373,
(E)-5-Methyl-5-[(methyl-d3)thio]-3-styrylfuran-2(5H)-one
(6d): Prepared according to the general procedure discussed
above: Rf =0.4; eluent, EtOAc/n-hexane (8%); isolated
yield: 0.04 g (80%); yellow gum. 1H NMR (600 MHz,
CDCl3): d=7.72 (d, J=16.2 Hz, 1H), 7.50 (d, J=7.8 Hz,
2H), 7.37 (t, J=7.2 Hz, 2H), 7.30–7.32 (m, 1H), 7.09 (s,
1H), 6.81 (d, J=16.2 Hz, 1H), 1.81 (s, 3H); 13C NMR
(150 MHz, CDCl3): d=170.0, 148.8, 136.1, 136.0, 129.1,
128.9, 128.8 (2 CH), 127.0 (2 CH), 115.8, 90.1, 25.1; IR
(KBr): nmax =2926, 1755, 1443, 1277, 1051, 964, 889, 742,
691 cmÀ1
;
HR-MS (ESI): m/z=272.0815, calcd. for
C14H11D3O2SNa [M+Na]+: 272.0801.
[5-Methyl-3-phenyl-3-(p-tolylthio)furan-2(3H)-one
plus 5-methyl-3-phenyl-3-(phenylthio)furan-2(3H)-one (2a)]
and [3-(4-methoxyphenyl)-5-methyl-3-(phenylthio)furan-
(2d)
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1126, 967, 752, 695 cmÀ1; HR-MS (ESI): m/z=320.1599,
calcd. for C19H23NO2Na [M+Na]+: 320.1627.
[2] For 1,4-sulfur migration, see review in ref.[1] and for ref-
erences, see: a) L. Peng, X. Zhang, M. Ma, J. Wang,
Angew. Chem. 2007, 119, 1937; Angew. Chem. Int. Ed.
2007, 46, 1905; Angew. Chem. 2007, 119, 1937; b) Z.
Fang, J. Liu, Q. Liu, X. Bi, Angew. Chem. 2014, 126,
7337; Angew. Chem. Int. Ed. 2014, 53, 7209; Angew.
Chem. 2014, 126, 7337.
[3] For selected reviews of natural products containing bu-
tenolides, see: a) Y. S. Rao, Chem. Rev. 1976, 76, 625;
b) F. Q. Alali, X-X. Liu, J. L. McLaughlin, J. Nat. Prod.
1999, 62, 504; c) P. A. Roethlem, D. Trauner, Nat. Prod.
Rep. 2008, 25, 298; d) A. Bermejo, B. Figadere, M.-C.
Zafra-Polo, I. Barrachina, E. Estornellc, D. Cortes, Nat.
Prod. Rep. 2005, 22, 269.
[4] For selected reviews on the synthesis of butenolides,
see: a) G. Casiraghi, F. Zanardi, G. Appendino, G.
Rassu, Chem. Rev. 2000, 100, 1929; b) S. E. Denmark,
J. R. Heemstra Jr, G. L. Beutner, Angew. Chem. 2005,
117, 4760; Angew. Chem. Int. Ed. 2005, 44, 4682;
Angew. Chem. 2005, 117, 4760; c) T. Montagnon, M.
Tofi, G. Vassilikogiannakis, Acc. Chem. Res. 2008, 41,
1001; d) R. R. A. Kitson, A. Millemaggi, R. J. K.
Taylor, Angew. Chem. 2009, 121, 9590; Angew. Chem.
Int. Ed. 2009, 48, 9426; Angew. Chem. 2009, 121, 9590;
e) S. V. Pansare, E. K. Paul, Chem. Eur. J. 2011, 17,
8770; f) S. Ma, Acc. Chem. Res. 2003, 36, 701; g) E. Ne-
gishi, M. Kotora, Tetrahedron 1997, 53, 6707.
[5] For selected references on the synthesis of butenolides
having one or more quaternary centres, see: a) Y. Liu,
F. Song, S. Guo, J. Am. Chem. Soc. 2006, 128, 11332;
b) Q. Zhang, M. Cheng, X. Hu, B.-G. Li, J.-X. Ji, J.
Am. Chem. Soc. 2010, 132, 7256; c) H. Miura, K. Take-
uchi, T. Shishido, Angew. Chem. 2016, 128, 286; Angew.
Chem. 2016, 128, 286; Angew. Chem. Int. Ed. 2016, 55,
278; d) W. Zhang, D. Tan, R. Lee, G. Tong, W. Chen, B.
Qi, K.-W. Huang, C.-H. Tan, Z. Jiang, Angew. Chem.
2012, 124, 10216; Angew. Chem. Int. Ed. 2012, 51,
10069; e) K. Endo, S. Yakeishi, R. Takayama, T. Shiba-
ta, Chem. Eur. J. 2014, 20, 8893; f) H.-L. Cui, J.-R.
Huang, J. Lei, Z.-F. Wang, S. Chen, L. Wu, Y.-C. Chen,
Org. Lett. 2010, 12, 720; g) H. Xiao, H.-y. Duan, J. Ye,
R.-s. Yao, J. Ma, Z.-z. Yuan, G. Zhao, Org. Lett. 2014,
16, 5462; h) C. Zheng, W. Yao, Y. Zhang, C. Ma, Org.
Lett. 2014, 16, 5028; i) A. Quintard, A. Lefranc, A.
Alexakis, Org. Lett. 2011, 13, 1540; j) W. Mao, C. Zhu,
Org. Lett. 2015, 17, 5710; k) S. Li, B. Miao, W. Yuan, S.
Ma, Org. Lett. 2013, 15, 977; l) A. M. Hyde, S. L. Buch-
wald, Org. Lett. 2009, 11, 2663.
(E)-5-(Cyclopropylamino)-5-methyl-3-styrylfuran-2(5H)-
one (7b): Prepared according to the general procedure dis-
cussed above: Rf =0.3; eluent, EtOAc/n-hexane (25%); iso-
lated yield: 0.025 g (48%); white solid; mp 129–1318C.
1H NMR (300 MHz, CDCl3): d=7.69 (d, J=16.2 Hz, 1H),
7.46 (d, J=7.5 Hz, 2H), 7.27–7.36 (m, 3H), 6.76 (d, J=
16.2 Hz, 1H), 6.70 (s, 1H), 2.41–2.48 (m, 1H), 2.25 (br. s.,
1H), 1.67 (s, 3H), 1.23–1.29 (m, 1H), 0.90–0.97 (m, 1H),
0.72–0.80 (m, 2H); 13C NMR (150 MHz, CDCl3): d=169.8,
141.7, 136.7, 135.0, 133.3, 128.7 (2 CH), 128.4, 126.8 (2 CH),
117.7, 88.9, 22.9, 21.2, 5.7 (CH2), 3.0 (CH2); IR (KBr): nmax
=
2990, 1684, 1636, 1411, 1128, 975, 746, 694 cmÀ1; HR-MS
(ESI): m/z=278.1173, calcd. for C16H17NO2Na [M+Na]+:
278.1157.
(E)-5-(Benzylamino)-5-methyl-3-styrylfuran-2(5H)-one
(7c): Prepared according to the general procedure discussed
above: Rf =0.3; eluent, EtOAc/n-hexane (20%); isolated
yield: 0.025 g (40%); colorless gum. 1H NMR (300 MHz,
CDCl3): d=7.74 (d, J=16.5 Hz, 1H), 7.50 (d, J=6.9 Hz,
2H), 7.28–7.40 (m, 8H), 6.82 (d, J=16.5 Hz, 1H), 6.75 (s,
1H), 4.75 (d, J=15.3 Hz, 1H), 4.51 (d, J=15.3 Hz, 1H),
2.65 (br. s., 1H), 1.40 (s, 3H); 13C NMR (150 MHz, CDCl3):
d=168.8, 142.1, 138.3, 136.7, 135.1, 133.0, 128.7 (2 CH),
128.5 (3 CH), 127.9 (2 CH), 127.2, 126.9 (2 CH), 117.8, 88.2,
41.8 (CH2), 23.5; IR (KBr): nmax =2926, 1670, 1493, 1415,
1127, 750, 698 cmÀ1; HR-MS (ESI): m/z=328.1311, calcd.
for C20H19NO2Na [M+Na]+: 328.1314.
Acknowledgements
I.D. thanks CSIR – New Delhi (Network Project ORIGIN-
CSC0108), and Dr. Basudeb Achari for valuable discussions.
K. M. thanks CSIR – India, S.N. and S.K.S. thank UGC –
India for their fellowships. R.N. thanks SERB (SR/S2/RJN-
62/2012) for funding. We thank the reviewers for their valua-
ble comments and suggestions, which helped significantly to
improve the quality of the manuscript.
References
[1] For 1,2-sulfur migration, see reviews: a) D. J. Fox, D.
House, S. Warren, Angew. Chem. 2002, 114, 2572;
Angew. Chem. Int. Ed. 2002, 41, 2462; b) A. W.
Sromek, V. Gevorgyan, Top. Curr. Chem. 2007, 274, 77;
c) I. P. Smoliakova, Curr. Org. Chem. 2000, 4, 589; for
selected references, see: d) J. T. Kim, A. V. Kel’in, V.
Gevorgyan, Angew. Chem. 2003, 115, 102; Angew.
Chem. Int. Ed. 2003, 42, 98; Angew. Chem. 2003, 115,
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porting Information.
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20 Tandem Chemoselective 1,2-/1,4-Migration of the Thio
Group in Keto Thioesters: An Efficient Approach to
Substituted Butenolides
Adv. Synth. Catal. 2016, 358, 1 – 20
Kanchan Mal, Sandip Naskar, Shovan Kumar Sen,
Ramalingam Natarajan, Indrajit Das*
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These are not the final page numbers!