Hetero-Diels–Alder reactions of hetaryl thiochalcones with acetylenic dienophiles

Article abstract of DOI:10.1080/17415993.2016.1230857

Hetaryl-substituted thiochalcones react with acetylenic mono- and diesters in the THF solution in the presence of LiClO₄ at 65°C to give, after 24 h, 4H-thiopyran carboxylates and dicarboxylates, respectively, in moderate to good yields. The same reactions were performed also in the THF solution without a catalyst under microwave irradiation. In that case, the reaction time was reduced to three minutes and, in most cases, an improvement in the yield of the [4+2]-cycloadduct was observed. The reactions with methyl propiolate occurred regioselectively and the 3-carboxylates were formed exclusively.

Full text of DOI:10.1080/17415993.2016.1230857

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
Hetero-Diels–Alder reactions of hetaryl
thiochalcones with acetylenic dienophiles
Grzegorz Mlostoń, Paulina Grzelak & Heinz Heimgartner
To cite this article: Grzegorz Mlostoń, Paulina Grzelak & Heinz Heimgartner (2016): Hetero-
Diels–Alder reactions of hetaryl thiochalcones with acetylenic dienophiles, Journal of Sulfur
Chemistry, DOI: 10.1080/17415993.2016.1230857
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Date: 19 September 2016, At: 06:10

JOURNAL OF SULFUR CHEMISTRY, 2016
http://dx.doi.org/10.1080/17415993.2016.1230857
Hetero-Diels–Alder reactions of hetaryl thiochalcones with
acetylenic dienophiles
Grzegorz Mlostońa, Paulina Grzelaka and Heinz Heimgartnerb
aDepartment of Organic and Applied Chemistry, University of Łódź, Łódź, Poland; bDepartment of Chemistry,
University of Zurich, Zurich, Switzerland
ABSTRACT
ARTICLE HISTORY
Received 24 June 2016
Accepted 28 August 2016
Hetaryl-substituted thiochalcones react with acetylenic mono- and
diesters in the THF solution in the presence of LiClO4 at 65°C to give,
after 24 h, 4H-thiopyran carboxylates and dicarboxylates, respec-
tively, in moderate to good yields. The same reactions were per-
formed also in the THF solution without a catalyst under microwave
irradiation. In that case, the reaction time was reduced to three
minutes and, in most cases, an improvement in the yield of the
[4+2]-cycloadduct was observed. The reactions with methyl propi-
olate occurred regioselectively and the 3-carboxylates were formed
exclusively.
KEYWORDS
Chalcones; thiochalcones;
acetylenic dienophiles;
hetero-Diels–Alder reactions;
4H-thiopyrans; microwave
irradiation
1. Introduction
Hetero-Diels–Alder reactions of heterodienes are widely applied for the synthesis of six-
membered heterocycles, including important intermediates in natural product synthesis
[1,2]. In that case, the asymmetric version is of special importance [3]. The most fre-
quently reported hetero-Diels–Alder reactions belong to the so-called aza- or oxa-types
=
=
with the C N or C O units in the diene or dienophile. In contrast, examples for thia-type
hetero-Diels–Alder reactions are less well known. Whereas reactions of dienes with diaryl
thioketones leading to dihydrothiopyrans were studied to some extent [4], the [4+2]-
cycloadditions with thiochalcones are rarely described [5]. In most cases, the studied
thia-hetero-Diels–Alder reactions comprised reactions of other types of thia-heterodienes,
such as enaminothiones [5] or α,β-unsaturated thioamides [5,6]. In a series of recent
CONTACT Grzegorz Mlostoń
gmloston@uni.lodz.pl
Department of Organic and Applied Chemistry, University
of Łódź, Tamka 12, PL-91-403 Łódź, Poland
© 2016 Informa UK Limited, trading as Taylor & Francis Group

2
G. MLOSTOŃ ET AL.
Scheme 1. Hetero-Diels–Alder reactions with hetaryl thioketone 1.
Scheme 2. [4+2]-Cycloaddition of diphenylchalcone with acrylonitrile.
publications, 5-arylidene-4-thioxo-2-thiazolidinones were used as more complex 1-thia-
1,3-dienes in reactions with diverse ethylenic dipolarophiles [7–10]. Furthermore, a few
thia-hetero-Diels–Alder reactions of diverse 1-thia-1,3-dienes (but not thiochalcones!)
with propiolates [6,7], benzynes [11], and an intramolecular reaction with a propargyl
ether [12] are known.
Kinetic studies of the [4+2]-cycloadditions of cyclic and acyclic dienes with diaryl
thioketones led to the introduction of the name ‘superdienophiles’ for the latter [4].
An interesting class of S-heterodienes consists of hetaryl thioketones of type 1, which
react with activated ethylene and acetylene derivatives yielding fused thiopyran derivatives
of types 2 and 3, respectively [13,14] (Scheme 1).
Thiochalcones 4, which are α,β-unsaturated thioketones, form a class of attractive thia-
dienes. They have rarely been explored in hetero-Diels–Alder reactions [5], mainly with
ethylenic dienophiles. For example, the reaction of 2,4-diphenyl-1-thiabuta-1,3-diene (4a)
with acrylonitrile led to dihydrothiopyran 5 in a regioselective manner [15] (Scheme 2).
Reactive thiochalcone 4a was generated in situ by thermolysis of its dimer 6.
Remarkably, thiochalcone 4a reacted also with the electron-rich n-butyl vinyl ether to
give the [4+2]-cycloadduct in a Diels–Alder reaction with inverse electron demand [16].
Furthermore, the reaction of dimethyl acetylene dicarboxylate (DMAD, 8a) with in situ-
generated thiochalcones yielded 4H-thiopyrans [17]. In the case of enaminethiones, the
reactions with methyl propiolate (MP, 8b) occurred regioselectively leading to 4-amino-
4H-thiopyran-3-carboxylates as primary products, which upon heating isomerized to
2-amino-2H-thiopyran-3-carboxylates [18,19].
Due to our continuing interest in the chemistry of hetaryl thioketones, a series of
new thiochalcones with hetaryl groups was prepared and subsequently applied in hetero-
Diels–Alder reactions with DMAD and MP.

JOURNAL OF SULFUR CHEMISTRY
3
2. Results and discussion
Hetaryl thiochalcones 4b–g (Table 1) were prepared from the corresponding chalcones
by treatment with Lawesson’s reagent in refluxing THF solution and isolated after chro-
matographic work-up. The 1H NMR spectra of analytically pure samples showed that they
exist in CDCl3 solution in equilibrium with dimeric forms similar to the observations with
diarylchalcones [20] (Scheme 3).
Nevertheless, the cycloaddition reactions performed with acetylenic dienophiles 8
occur smoothly in the THF solution in the presence of catalytic amounts of LiClO4. After
24 h of heating at 65°C in a glass tube with a screw cap, the reactions were complete and
1
the H NMR analysis evidenced the presence of a single product in all cases. The spec-
troscopic data confirmed the structure of 4H-thiopyran derivatives 9 (Scheme 4, Table 1).
Thus, in the case of the products formed from DMAD (8a) and 4b and 4d, respectively, two
isomeric compounds were identified. In the first one, 9b, the 1H NMR spectrum showed
two characteristic doublets at 6.24 and 5.27 ppm with J = 6.6 Hz attributed to HC(5) and
HC(4) of the thiopyran ring. The analogous set of signals in the spectrum of 9d appeared
at 6.22 and 4.85 ppm (J = 6.6 Hz). In the 13C NMR spectra, a significant difference in the
Table 1. Synthesis of 4H-thiopyrans 9 via hetero-Diels–Alder reactions.
Acetylene
Thiochalconea
Yield [%]b
Thiopyran
8
R
4
Ar1
Ar2
9
Method A
Method B
a
a
a
a
a
a
a
b
b
b
b
b
b
b
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
H
H
H
H
H
a
b
c
d
e
f
g
a
b
c
d
e
f
Ph
Thi
Fur
Ph
Ph
Ph
Thi
Ph
Thi
Fur
Ph
Ph
Ph
Thi
Ph
Ph
Ph
Thi
Fur
Sel
Thi
Ph
Ph
Ph
Thi
Fur
Sel
Thi
a [17]
b
c
d
e
f
g
h
i
j
k
l
m
n
80
85
77
36
6
16
67
85
92
94
48
6
93
86
95
48
c
56
d
93
92
98
71
c
H
H
15
97
60
d
g
aPh = Phenyl; Thi = Thiophen-2-yl; Fur = Furan-2-yl; Sel = Selenophen-2-yl.
bYield of isolated product. Method A: THF, LiClO4, 65°C; Method B: THF, MW, r.t.
cOnly decomposition products were obtained.
dExperiment has not been performed.
Scheme 3. Equilibrium of thiochalcones with dimers.

4
G. MLOSTOŃ ET AL.
Scheme 4. Hetero-Diels–Alder reactions of thiochalcones 4 with acetylene carboxylates.
chemical shift of HC(4) was observed. Whereas in 9d the signal appeared at 44.5 ppm, it
was shifted upfield to 38.6 ppm in 9b.
The structure of the products obtained regioselectively in the experiments with methyl
1
propiolate (8b) was unambiguously established on the basis of the H NMR spectra.
In all compounds 9h–n, the signals of HC(4) appeared as a doublet in the range of
4.81–5.26 ppm. In addition, the singlet for HC(2) was located in a narrow range at
7.67–7.90 ppm. The same regioselectivity was observed in the reaction of the parent
thiochalcone 4a with 8b, and the structure of 9 h was elucidated spectroscopically. The
comparison of the chemical shifts observed in the 13C NMR spectra of 9 h and 9i evi-
dences that the shielding effect of the thiophen-2-yl substituent is stronger than that in the
case of the phenyl ring.
The microwave technique has been widely applied to accelerate organic reactions. In the
present study, the reactions of DMAD (8a) and PM (8b) with hetaryl thiochalcones 4 were
carried out in THF solutions under microwave irradiations (Method B). As a matter of
fact, the reaction times were drastically reduced (ca. 3 min) and the yields of the products
were higher (Table 1). Only in the case of thiochalcone 4e with the furan-2-yl group at C(1),
decomposition was observed, similar to the reaction performed under standard conditions.
3. Conclusions
Hetaryl thiochalcones bearing the hetaryl group either at C(2) or C(4) of the 1-thiabuta-
1,3-diene structure react smoothly with acetylene carboxylates yielding the expected
4H-thiopyran derivatives. In the case of methyl propiolate (MP), the [4+2]-cycloaddition
occurs regioselectively yielding 4H-thiopyran-3-carboxylates. Whereas thermal reactions
performed at 65°C in the presence of LiClO4 as a catalyst required ca. 24 h for completion,
the non-catalyzed microwave-supported reactions were finished after ca. 3 min.
4. Experimental design
4.1. General
Melting points were determined in a capillary using an MEL-TEMP II apparatus (Aldrich)
and were uncorrected. IR spectra were recorded with an FT-IR NEXUS spectrophotome-
ter as KBr pellets; absorptions (ν) in cm–1. 1H and 13C NMR spectra were measured on a
Bruker Avance III (1H at 600 and 13C at 150 MHz) instrument in CDCl3; chemical shifts
(δ) are given in ppm, coupling constants (J) in Hz. The multiplicity of the 13C signals was

JOURNAL OF SULFUR CHEMISTRY
5
deduced from DEPT, supported by 1H-13C HMQC spectra. 1H NMR data are presented
as follows: chemical shift, multiplicity (br = broad, s = singlet, d = doublet, t = triplet,
q = quartet, m = multiplet), coupling constant, and integration. The mass spectra were
recorded on a Finnigan MAT-95 (ESI), Bruker maxis (HR-ESI), or SYNAPT G2-S HMDS
(HR MALDI-TOF) instrument. Elemental analyses were performed in the Microanalyt-
ical Laboratory of the Chemistry Faculty in Łódź. Microwave experiments were carried
out with CEM-focused Microwave-type Discover SPD. Applied reagents such as dimethyl
acetylenedicarboxylate (DMAD, 8a), methyl propiolate (MP, 8b), inorganic reagents, and
solvents are commercially available (Aldrich) and were used as received.
4.2. Starting materials
Chalcones were obtained from aryl methyl ketones and aromatic aldehydes in the presence
of NaOH according to the known general procedure [21]. 1,3-Diphenylpropen-3-one: Pale
yellow crystals; yield: 91%; m.p. 55.5–56.0°C (C2H5OH) ([22]: m.p. 56.0°C). 1-Phenyl-3-
(thiophen-2-yl)prop-2-en-1-one: Yellow crystals; yield: 84%; m.p. 58.0–59.0°C (C2H5OH)
([23]: m.p. 58.0–59.0°C). 3-Phenyl-1-(thiophen-2-yl)prop-2-en-1-one: Pale yellow crystals;
yield: 78%; m.p. 82.5–83.0°C (C2H5OH) ([24], m.p. 82°C). 3-(Furan-2-yl)-1-phenylprop-2-
en-1-one: Pale yellow crystals; yield: 85%; m.p. 42.0–42.5°C (C2H5OH) ([25], m.p. 40.0°C).
1-(Furan-2-yl)-3-phenylprop-2-en-1-one: Pale yellow crystals; yield: 71%; m.p. 86.0–87.0°C
(C2H5OH) ([26]: m.p. 87.0–88.0°C). 3-Phenyl-1-(selenophen-2-yl)prop-2-en-1-one: Pale
yellow crystals; yield: 82%; m.p. 81.5–82.0°C (C2H5OH) ([27]: m.p. 81.0–82.5°C). 1,3-
Di(thiophen-2-yl)prop-2-en-1-one: Yellow crystals; yield: 70%; m.p.95.5–96.0°C (C2H5OH)
([25]: m.p.94–95°C).
4.3. Synthesis of hetaryl thiochalcones (4a–g)
A solution of 5 mmol of the corresponding chalcone and 5.1 mmol of Lawesson’s reagent
in 10 mL of dry THF were placed in a two-necked flask. The mixture was heated under
argon at reflux for 3 h. Then, the solvent was evaporated in vacuo and the residue was
purified chromatographically, using as the eluent a mixture of petroleum ether and chlo-
roform (1:1). The 1H NMR spectra showed the presence of variable mixtures of monomers
and dimers of thiocalcones 4.
4.3.1. 1,3-Diphenylpropen-3-thione (4a)
Purple solid; yield: 672 mg (65%); m.p. 129.0–130.0°C (lit. [15]: m.p. 134.0–135.0°C). Anal.
calcd for C15H12S (224.33): C 80.30, H 5.40, S 14.29; found: C 80.14, H 5.64, S 14.37.
4.3.2. 1-Phenyl-3-(thiophen-2-yl)prop-2-en-1-thione (4b)
Purple solid; yield: 862.5 mg (75%); m.p. 60.5–61.0°C. Anal. calcd for C13H10S2 (230.35):
C 67.78, H 4.38, S 27.83; found: C 67.69 , H 4.54, S 27.84.
4.3.3. 3-(Furan-2-yl)-1-phenylprop-2-en-1-thione (4c)
Purple solid; yield: 770.4 mg (72%); m.p. 59.0–59.5°C. Anal. calcd for C13H10OS (214.29):
C 72.86, H 4.71, S 14.96; found: C 72.76 , H 4.71, S 14.81.

6
G. MLOSTOŃ ET AL.
4.3.4. 3-Phenyl-1-(thiophen-2-yl)prop-2-en-1-thione (4d)
Green solid; yield: 931.5 mg (81%); m.p. 76.0–76.5°C. Anal. calcd for C13H10S2 (230.35):
C 67.78, H 4.38, S 27.83; found: C 67.59, H 4.56, S 27.73.
4.3.5. 1-(Furan-2-yl)-3-phenylprop-2-en-1-thione (4e)
Green solid; yield: 802.5 mg (75%); m.p. 110.0–110.5°C. Anal. calcd for C13H10OS
(214.29): C 72.86, H 4.71, S 14.96; found: C 72.86, H 4.97, S 14.70.
4.3.6. 3-Phenyl-1-(selenophen-2-yl)prop-2-en-1-thione (4f)
Green solid; yield: 844.5 mg (61%); m.p. 115.0–115.5°C. Anal. calcd for C13H10SeS
(277.25): C 56.31, H 3.64, S 11.56; found: C 56.16 , H 3.89, S 11.58.
4.3.7. 1,3-Di(thiophen-2-yl)prop-2-en-1-thione (4g)
Green solid; yield: 840 mg (70%); m.p. 80.0–80.5°C. Anal. calcd for C11H8S3 (236.37): C
55.89, H 3.42, S 40.69; found: C 55.73, H 3.67, S 40.53.
4.4. Reaction of thiochalcones 4 with acetylenic dienophiles 8 – General procedures
Method A: A solution of 1 mmol of the corresponding thiochalcone 4, 1.1 mmol of the
corresponding acetylenic dienophile 8 and 10 mol% of LiClO4 in 1 mL of dry THF were
placed in a thick-wall glass tube, which then was closed with a screw cap. The mixture was
heated at 65°C for 24 h. The solvent was evaporated in vacuo. The residue was purified
chromatographically, using as the eluent a mixture of petroleum ether and ethyl acetate
(1:1).
Method B: A solution of 1 mmol of the corresponding thiochalcone and 1.1 mmol of
the corresponding acetylenic dienophile 8 in 1 mL of dry THF were placed in a reaction
tube. The reaction tube was sealed and transferred to the microwave reactor Discover SPD
(150 W, 3 min). After cooling the reaction mixture to room temperature, the solvent was
evaporated in vacuo. The residue was purified chromatographically, using as the eluent a
mixture of petroleum ether and ethyl acetate (1:1).
4.4.1. Dimethyl 4,6-diphenyl-4H-thiopyran-2,3-dicarboxylate (9a) [17]
1
Yellow oil; yield (method B): 340.4 mg (93%). H NMR (600 MHz, CDCl3): 3.58, 3.77
(2s, 6H, 2OCH3), 4.82 (d, J = 6.6 Hz, 1H), 6.06 (d, J = 6.6 Hz, 1H), 7.16–7.18 (m, 1H),
7.23–7.26 (m, 5H), 7.29–7.31 (m, 2H), 7.38–7.39 (m, 2H).
4.4.2. Dimethyl 6-phenyl-4-(thiophen-2-yl)-4H-thiopyran-2,3-dicarboxylate (9b)
Orange oil; yield (method B): 319.9 mg (86%). 1H NMR (600 MHz, CDCl3): 3.77, 3.87 (2s,
6H, 2OCH3), 5.27 (d, J = 6.6 Hz, 1H), 6.24 (d, J = 6.6 Hz, 1H), 6.94–6.95 (m, 1H), 7.01
(d, J = 3.6 Hz, 1H), 7.20 (d, J = 4.8 Hz, 1H), 7.36–7.38 (m, 3H), 7.51–7.52 (m, 2H). 13
C
NMR (150 MHz, CDCl3): 38.6 (C(4)), 52.6, 53.2 (2OCH3), 126.1, 132.6, 135.5, 136.5, 144.1
2
2
=
(5C(sp )), 119.9, 125.1, 126.9, 127.0, 128.8, 129.2 (9CH(sp )), 165.2, 165.4 (2C O). IR
(film): 3025w, 2952w, 1736, 1715vs (2vC O), 1597w, 1492w, 1442w, 1337w, 1261s, 1021w,
=
761w, 694m. Anal. calcd for C19H16O4S2 (372.47): C 61.26, H 4.34, S 17.21; found: C 61.12,
H 4.5, S 17.14.

JOURNAL OF SULFUR CHEMISTRY
7
4.4.3. Dimethyl 4-(furan-2-yl)-6-phenyl-4H-thiopyran-2,3-dicarboxylate (9c)
1
Orange oil; yield (method B): 338.2 mg (95%). H NMR (600 MHz, CDCl3): 3.77, 3.88
(2s, 6H, 2OCH3), 5.12 (d, J = 6.6 Hz, 1H), 6.17–6.19 (m, 2H), 6.29–6.30 (m, 1H), 7.35–7.37
(m, 4H), 7.49–7.51 (m, 2H). 13C NMR (150 MHz, CDCl3): 37.9 (C(4)), 52.7, 53.3 (2OCH3),
124.6, 133.7, 136.4, 136.6, 152.6 (5C(sp2)), 106.7, 110.5, 117.5, 126.9, 128.8, 129.2, 142.5
2
=
(9CH(sp )), 165.2, 165.6 (2C O). IR (film): 3056w, 2949w, 1733, 1714vs (2vC O), 1594w,
=
1492w, 1442w, 1255s, 1011m, 764m, 698w. Anal. calcd for C19H16O5S (356.41): C 64.02,
H 4.53, S 8.99; found: C 63.87, H 4.65, S 8.85.
4.4.4. Dimethyl 4-phenyl-6-(thiophen-2-yl)-4H-thiopyran-2,3-dicarboxylate (9d)
Orange oil; yield (method B): 178.6 mg (48%). 1H NMR (600 MHz, CDCl3): 3.66, 3.86 (2s,
6H, 2OCH3), 4.85 (d, J = 6.6 Hz, 1H), 6.22 (d, J = 6 Hz, 1H), 6.99 (dd, J = 4.8, 3.6 Hz,
1H), 7.18–7.19 (m, 1H), 7.23–7.27 (m, 2H), 7.30–7.36 (m, 4H). 13C NMR (150 MHz,
CDCl3): 44.5 (C(4)); 52.6, 55.3 (2OCH3), 125.0, 129.1, 133.0, 139.8, 141.3 (5C(sp2)), 119.7,
2
=
125.2, 125,8, 127.7, 127.8, 128.1, 128.8 (9CH(sp )), 166.2, 164.9 (2C O). IR (film): 3028w,
2952w, 1730, 1721vs (2vC O), 1597w, 1451w, 1429m, 1258s, 1023m, 761w, 698m. Anal.
calcd for C19H16O4S2 (372.47): C 61.26, H 4.34, S 17.21; found: C 61.43, H 4.58, S 17.19.
=
4.4.5. Dimethyl 6-(furan-2-yl)-4-phenyl-4H-thiopyran-2,3-dicarboxylate (9e)
Yield (method A): 6%. The compound was identified only on the basis of the 1H NMR
spectra and could not be isolated in pure form. The yield was calculated based on the 1H
NMR spectra of the crude mixture using a weighed amount of 1,1,2,2-tetrachloroethane as
a standard. 1H NMR (600 MHz, CDCl3): 3.86, 3.66 (2s, 6H, 2OCH3), 4.85 (d, J = 6.6 Hz,
1H), 6.40–6.41 (m, 2H), 6.46 (d, J = 3.0 Hz, 1H), 7.28–7.33 (m, 3H), 7.35–7.37 (m, 3H).
4.4.6. Dimethyl 4-phenyl-6-(selenophen-2-yl)-4H-thiopyran-2,3-dicarboxylate (9f)
1
Orange oil; yield (method B): 234.5 mg (56%). H NMR (600 MHz, CDCl3): 3.67, 3.86
(2s, 6H, 2OCH3), 4.84 (d, J = 6.6 Hz, 1H), 6.18 (d, J = 6.6 Hz, 1H), 7.22–7.27 (m, 2H),
7.31–7.34 (m, 2H), 7.36–7.37 (m, 3H), 7.92 (d, J = 5.4 Hz, 1H). 13C NMR (150 MHz,
CDCl3): 44.7 (C(4)), 52.6, 55.3 (2OCH3), 127.0, 128.8, 133.2, 141.2, 144.6 (5C(sp2)), 120.3,
2
=
127.4, 127.8, 128.2, 129.1, 130.2, 131.1 (9CH(sp )), 164.9, 166.2 (2C O). IR (film): 3025w,
2952w, 1736, 1726vs (2vC O), 1600w, 1454w, 1435m, 1261s, 1021w, 786w, 697m. Anal.
calcd for C19H16SeO4S (419.37): C 54.41, H 3.85, S 7.64; found: C 54.67, H 3.86, S 7.43.
=
4.4.7. Dimethyl 4,6-bis(thiophen-2-yl)-4H-thiopyran-2,3-dicarboxylate (9g)
Yield (method A): 253.2 mg (67%). The compound was identified only on the basis of
1
the H NMR spectra and could not be isolated in pure form. The yield was calculated
based on the 1H NMR spectra of the crude mixture using a weighed amount of 1,1,2,2-
tetrachloroethane as a standard. 1H NMR (600 MHz, CDCl3): 3.77, 3.86 (2s, 6H, 2OCH3),
5.20 (d, J = 20.4 Hz, 1H), 6.30 (d, J = 20.4 Hz, 1H), 6.91–7.04 (m, 3H), 7.17–7.30 (m, 3H).
4.4.8. Methyl 4,6-diphenyl-4H-thiopyran-3-carboxylate (9h)
Yellow solid; yield (method B): 286.4 mg (93%); m.p. 76.2–76.7°C (chromatographic purifi-
cation). 1H NMR (600 MHz, CDCl3): 3.61 (s, 3H, OCH3), 4.81 (d, J = 6 Hz, 1H), 6.10 (d,
J = 6.6 Hz, 1H), 7.12–7.16 (m, 1H), 7.21–7.27 (m, 5H), 7.33–7.37 (m, 4H), 7.67 (s, 1H). 13
C
NMR (150 MHz, CDCl3): 41.5 (C(4)), 52.0 (OCH3), 123.9, 129.2, 137.7, 144.2 (4C(sp2)),

8
G. MLOSTOŃ ET AL.
2
=
122.3, 126.5, 127.2, 128.1, 128.77, 128.81, 128.84, 132.8 (12CH(sp )), 165.2 (C O). IR
(KBr): 3025w, 2955w, 1708vs (vC O), 1594w, 1429m, 1249s, 1046w, 755m, 694m. Anal.
calcd for C19H16O2S (308.41): C 73.99, H 5.24, S 10.39; found: C 74.06 , H 5.47, S 10.49.
=
4.4.9. Methyl 6-phenyl-4-(thiophen-2-yl)-4H-thiopyran-3-carboxylate (9i)
Orange oil; yield (method B): 288.9 mg (92%). 1H NMR (600 MHz, CDCl3): 3.78 (s, 3H,
OCH3), 5.28 (d, J = 6.6 Hz, 1H), 6.27 (d, J = 6.6 Hz, 1H), 6.95 (dd, J = 5.4, 3.6 Hz 1H),
7.02 (d, J = 3.6 Hz, 1H), 7.18 (d, J = 5.4 Hz, 1H), 7.36–7.39 (m, 3H), 7.51–7.52 (m, 2H),
7.74 (s, 1H). 13C NMR (150 MHz, CDCl3): 35.9 (C(4)), 52.0 (OCH3), 123.6, 131.1, 137.3,
2
2
=
146.8 (4C(sp )), 120.9, 124.6, 126.7, 126.9, 128.8, 128.9, 132.9 (10CH(sp )), 164.9 (C O).
IR (film): 3060w, 2949w, 1708vs (vC O), 1581m, 1432m, 1236s, 1036m, 761w, 694m. Anal.
calcd for C17H14O2S2 (314.43): C 64.93, H 4.50, S 20.39; found: C 64.83, H 4.73, S 20.47.
=
4.4.10. Methyl 4-(furan-2-yl)-6-phenyl-4H-thiopyran-3-carboxylate (9j)
Orange solid; yield (method B): 292.0 mg (98%); m.p. 75.5–76.0°C (chromatographic
purification).1H NMR (600 MHz, CDCl3): 3.78 (s, 3H, OCH3), 5.12 (d, J = 6.6 Hz, 1H),
6.12 (br s, 1H), 6.20 (d, J = 6.6 Hz, 1H), 6.29 (br s, 1H), 7.34–7.37 (m, 4H), 7.49 (d,
J = 7.2 Hz, 2H), 7.79 (s, 1H). 13C NMR (150 MHz, CDCl3): 35.0 (C(4)), 52.2 (OCH3),
121.3, 131.9, 137.4, 154.9 (4C(sp2)), 106.0, 110.5, 118.6, 126.6, 128.8, 129.0, 134.2, 142.0
2
=
(10CH(sp )), 165.0 (C O). IR (KBr): 3044w, 2942w, 1704vs (vC O), 1591w, 1432w, 1242s,
=
1033w, 742m. Anal. calcd for C17H14O3S (298.37): C 68.43, H 4.74, S 10.74; found: C 68.67,
H 4.98, S 10.91.
4.4.11. Methyl 4-phenyl-6-(thiophen-2-yl)-4H-thiopyran-3-carboxylate (9k)
Orange oil; yield (method B): 222.9 mg (71%). 1H NMR (600 MHz, CDCl3): 3.70 (s, 3H,
OCH3), 4.86 (d, J = 6.6 Hz, 1H), 6.27 (d, J = 6.6 Hz, 1H), 6.99 (dd, J = 5.4, 3.6 Hz, 1H),
7.15–7.16 (m, 1H), 7.22–7.24 (m, 2H), 7.31 (t, J = 7.2 Hz, 2H), 7.41 (d, J = 7.2 Hz, 2H),
7.72 (s, 1H). 13C NMR (150 MHz, CDCl3): 41.2 (C(4)), 52.1 (OCH3), 123.2, 124.4, 140.7,
143.7 (4 C(sp2)), 121.4, 124.7, 125.3, 127.3, 127.6, 128.2, 128.9, 132.1 (10CH(sp2)), 165.1
=
(C O). IR (KBr): 3025w, 2949w, 1711vs (vC O), 1587m, 1423m, 1230s, 1036m, 761vs.
Anal. calcd for C17H14O2S2 (314.43): C 64.93, H 4.50, S 20.39; found: C 64.95, H 4.77, S
20.14.
=
4.4.12. Methyl 6-(furan-2-yl)-4-phenyl-4H-thiopyran-3-carboxylate (9l)
1
Yield: 6% (method A). The compound was identified only on the basis of the H NMR
spectra and could not be isolated in pure form. The yield was calculated based on the 1H
NMR spectra of the crude mixture using a weighed amount of 1,1,2,2-tetrachloroethane
as a standard. 1H NMR (600 MHz, CDCl3): 3.69 (s, 3H, OCH3), 4.84 (d, J = 6.6 Hz, 1H),
6.39–6.41 (m, 2H), 6.44 (d, J = 6 Hz, 1H), 7.28–7.31 (m, 3H), 7.36–7.39 (m, 3H), 7.71
(s, 1H). MS (ESI): m/z (%) = 321 (100, [M + Na]+).
4.4.13. Methyl 4-phenyl-6-(selenophen-2-yl)-4H-thiopyran-3-carboxylate (9m)
Orange oil; yield (method B): 216.4 mg (60%). 1H NMR (600 MHz, CDCl3): 3.70 (s, 3H,
OCH3), 4.85 (d, J = 6.6 Hz, 1H), 6.22 (d, J = 6.6 Hz, 1H), 7.22–7.25 (m, 2H), 7.30–7.33
(m, 3H), 7.40–7.42 (m, 2H), 7.70 (s, 1H), 7.90 (dd, J = 6.0, 1.2 Hz, 1H). 13C NMR
(150 MHz, CDCl3): 41.4 (C(4)), 52.0 (OCH3), 124.5, 125.2, 143.6, 146.5 (4C(sp2)), 122.0,

JOURNAL OF SULFUR CHEMISTRY
9
2
=
126.9, 127.3, 128.2, 128.9, 130.1, 130.5, 132.2 (10CH(sp )), 165.1 (C O). IR (film): 3060w,
2949w, 1710vs (vC O), 1587w, 1432m, 1226s, 1040m, 742m. Anal. calcd for C17H14O2SeS
(361.33): C 56.50, H 3.91, S 8.87; found: C 56.41, H 4.25 , S 8.57.
=
4.4.14. Methyl 4,6-bis(thiophen-2-yl)-4H-thiopyran (9n)
1
Orange oil; yield (method A): 310.4 mg (97%). H NMR (600 MHz, CDCl3): 3.78 (s,
3H, OCH3), 5.22 (d, J = 6.6 Hz, 1H), 6.34 (d, J = 6.6 Hz, 1H), 6.92–6.93 (m, 1H), 6.98
(d, J = 3.6 Hz, 1H), 7.01–7.02 (m, 1H), 7.16 (dd, J = 5.4, 1.2 Hz, 1H), 7.20 (dd, J = 53.6,
0.6 Hz, 1H), 7.25–7.26 (m, 1H), 7.68 (s, 1H). 13C NMR (150 MHz, CDCl3): 35.7 (C(4)),
52.2 (OCH3), 124.3, 125.0, 140.3, 146.2 (4C(sp2)), 120.0, 124.76, 124.84, 125.1, 125.7, 127.0,
2
=
127.7, 132.4 (8CH(sp )), 164.8 (C O). IR (film): 3041w, 2952w, 1706vs (vC O), 1581m,
=
1432m, 1242s, 1226s, 1024m, 755w, 701vs. Anal. calcd for C15H12O2S3 (320.45): C 56.22,
H 3.78, S 30.01; found: C 56.37, H 3.91, S 29.88.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the National Science Center (Cracow, Poland) within the project
Maestro [grant number: Dec-2012/06/A/ST5/00219].
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