Thiophenium-ylides: Synthesis and reactivity

Article abstract of DOI:10.2478/s11696-012-0222-7

The reaction of propanedioic acid, 2-diazo-1,3-bis(1,1-dimethylethyl) ester (di-tert-butyl diazomalonate) with a series of cyclopenta[b]thiophenes in the presence of catalytic rhodium acetate was studied. The resulting SC ylides underwent a rearrangement to form a heterocycle with different topology; thialene, in very low yields. Experimental and spectral data for all compounds are provided.

Full text of DOI:10.2478/s11696-012-0222-7

Chemical Papers 67 (1) 59–65 (2013)
DOI: 10.2478/s11696-012-0222-7
ORIGINAL PAPER
Thiophenium-ylides: Synthesis and reactivity
Aleš Machara, Jiří Svoboda*
Department of Organic Chemistry, Institute of Chemical Technology, Technická 5, 16628 Prague 6, Czech Republic
Received 27 March 2012; Revised 16 May 2012; Accepted 19 May 2012
Dedicated to Professor Štefan Toma on the occasion of his 75th birthday
The reaction of propanedioic acid, 2-diazo-1,3-bis(1,1-dimethylethyl) ester (di-tert-butyl diazoma-
lonate) with a series of cyclopenta[b]thiophenes in the presence of catalytic rhodium acetate was
studied. The resulting S—C ylides underwent a rearrangement to form a heterocycle with different
topology; thialene, in very low yields. Experimental and spectral data for all compounds are pro-
vided.
c
ꢀ 2012 Institute of Chemistry, Slovak Academy of Sciences
Keywords: cyclopenta[b]thiophene, thiophenium-ylide, rhodium catalysis, thialene
Introduction
Chemistry of sulfur is a specific branch of or-
ganic chemistry, where thiopyran derivatives rep-
resent an important sub-class of compounds ex-
tensively exploited by nature and mankind. Dif-
Fig. 1. Canonical structures of thialene.
ferent types of thiopyran compounds have been
synthesized in the past years. In contrast, a lim-
ited number of examples of a particular type of
thiopyrans/thiopyranium derivatives, those incorpo-
rated in pseudoazulenes, were reported. Thialene (cy-
clopenta[b]thiopyran) (Mayer et al., 1961; Mayer &
Franke, 1965; Klein & Horák, 1986), an intensively
blue–violet heteroarene, although it is isoelectronic
with extensively used benzo[b]thiophene (benzothio-
phene) congeners, represents rather an underappre-
ciated structural motive. Pseudoazulenes (Klein &
Horák, 1986), iso-π-electronic heteroanalogues of bi-
cyclo[5.3.0]decapentaene (azulene) exhibiting unique
spectroscopic properties, have not yet been thoroughly
investigated. Due to their low stability but obvious
heteroaromaticity (Elguero et al., 1978), they were for-
merly called “uncommon” arenes. A simple drawing of
their resonance structures explains this phenomenon
(Mayer et al., 1961) (Fig. 1).
Recently, the structure and reactivity of thiophe-
nium- and selenophenium-ylides were investigated
with the goal to prepare new fused thialene derivatives
employing an uncommon thiophene to thiopyran ring
expansion (Machara et al., 2004, 2009) in the crucial
step (Fig. 2).
This transformation, related to the Stevens rear-
rangement, has been already investigated and mech-
anistic aspects were rationalized in a series of pa-
pers (Bowles et al., 1985, 1988a, 1988b; Smith, 1990;
MacKenzie & Thomson, 1982). In the continuation
of our effort, a preliminary study associated with
cyclopentathiophenium-ylides and their thermally in-
duced rearrangement evaluation was done in order to
find an alternative synthetic way providing the parent
thialene derivatives (Fig. 3).
*Corresponding author, e-mail: Jiri.Svoboda@vscht.cz

60
A. Machara, J. Svoboda/Chemical Papers 67 (1) 59–65 (2013)
Fig. 2. Outline of the reactivity of thiophenes and thiophenium-ylides.
Fig. 3. Desired outcome of the present study.
Experimental
153.2–153.8◦C (methanol), was obtained (Ito et al.,
1995; m.p. 145–148◦C).
General
Methyl 3-(thien-2-yl)propanoate (III)
All solvents were used as obtained unless other-
wise stated. THF and diethyl ether were distilled from
sodium benzophenone ketyl; DMF, Et3N, and pyri-
dine from CaH2. All other reagents were obtained from
commercial sources (Sigma–Aldrich, USA; Lach-Ner,
A sealed tube charged with acid II (4.0 g, 0.026
mol), 10% Pd/C (0.4 g) and dry methanol (100 mL)
was hydrogenated (pressure of hydrogen = 600 kPa)
and stirred at 70◦C for 12 h. The catalyst was filtered
off, washed with methanol and the combined filtrate
was removed under reduced pressure to leave the ester
III as yellowish oil in the yield of 4.35 g (98 %) (Yuen,
2004).
1
Czech Republic). H NMR (300 MHz) and 13C NMR
(75 MHz) spectra were recorded on a Varian Merkury
Plus(Varian, Germany) as solutions in CDCl3 at 25◦C.
Chemical shifts are given in the δ scale. Melting points
(uncorrected) were determined using a Leica Galen
III melting point apparatus (Wagner & Munz, Ger-
many). Infrared spectra were recorded on a Nicolet
6700 instrument (Thermo Scientific, USA) in CHCl3
solutions and are reported as wave numbers (cm−1).
Merck 60 Kieselgel (Merck, Germany) was used for
column chromatography. Thin layer chromatography
(TLC) was performed on Kieselgel 60 F254-coated alu-
minum sheets (Merck, Germany).
3-(Thien-2-yl)propanoic acid (IV)
A mixture of ester III (3.57 g, 0.02 mol) and
sodium hydroxide (4.0 g, 0.10 mol) in water/THF
solution (55 mL, ϕr = 10 : 1) was heated to reflux
for 3 h. The mixture was then cooled to laboratory
temperature and poured into aqueous solution of HCl
(10 %, 100 mL). The product was extracted with ether
(3 × 30 mL); the combined organic layers were washed
with water (10 mL) and brine (2 × 10 mL), dried over
MgSO4, and concentrated under reduced pressure to
yield 3.1 g (99 %) of acid IV, m.p. 46◦C (Stuckwisch
& Bailey, 1963; m.p. 45–46.5◦C).
3-(Thien-2-yl)acrylic acid (II)
A mixture of thiophene-2-carbaldehyde (I ) (10.17
g, 0.09 mol), malonic acid (20.57 g, 0.2 mol), dry pyri-
dine (80 mL), and piperidine (2 mL) was stirred at
100◦C for 4.5 h. Then, the reaction mixture was al-
lowed to cool down and it was poured into 6 M HCl
(200 mL). The solid was filtered, washed thoroughly
with distilled water (2 × 50 mL) and dried under re-
duced pressure. The yield of 12.43 g (89 %) of II, m.p.
5,6-Dihydrocyclopenta[b]thiophen-4-one (V)
To vigorously stirred polyphosphoric acid (570 g),
a solution of acid IV (11.4 g, 0.073 mol) in chloroben-
zene (290 mL) was added dropwise (during 3 min) at

A. Machara, J. Svoboda/Chemical Papers 67 (1) 59–65 (2013)
61
130◦C in argon atmosphere. After 20 min, the mix-
4-Ethoxy-5,6-dihydro-4H-cyclopenta[b]
thiophene (VIIc)
ture was poured on ice; the organic layer was sepa-
rated, and the aqueous solution was extracted with
1,2-dichloroethane (5 × 50 mL). The combined or-
ganic solution was washed with saturated aqueous so-
lution of NaHCO3 (50 mL) and water (50 mL), and
dried with anhydrous MgSO4. The solvent was evapo-
rated and the residue chromatographed (hexane/ethyl
acetate, ϕr = 2 : 1) to yield 3.64 g (36 %) of V, m.p.
123–124◦C (Poirier & Lozach, 1966; m.p. 118◦C).
To a solution of VIIa (500 mg, 3.6 mmol) in dry
THF (10 mL), a 60 % sodium hydride solution in oil
(150 mg, 3.6 mmol) was added and after stirring for
5 min also ethyl bromide (0.27 mL, 3.6 mmol) was
added. The mixture was stirred at laboratory tem-
perature for 1 h, diluted with water (20 mL), and
extracted with ethyl acetate EtOAc (2 × 10 mL).
The combined organic solution was washed with wa-
ter (10 mL) and dried with anhydrous MgSO4. After
column chromatography (hexane/ethyl acetate, ϕr =
6 : 1), 390 mg (65 %) of ether VIIc were isolated as
yellowish oil.
5,6-Dihydro-4H-cyclopenta[b]thiophene (VI)
A mixture of ketone V (0.84 g, 6.1 mmol), hy-
drazine hydrate (1.5 mL, 30 mmol), and diethylene
glycol was stirred at 120◦C for 2 h. Then, powdered
potassium hydroxide (2.5 g, 45 mmol) was added and
the mixture was heated at 200◦C for 4 h. After cool-
ing to laboratory temperature, the mixture was di-
luted with water (50 mL) and the product was ex-
tracted with hexane (3 × 20 mL). The combined or-
ganic solution was washed with water (10 mL) and
dried with anhydrous MgSO4. After evaporation, the
product was purified by column chromatography (hex-
ane) to yield 0.22 g (29 %) of oily VI.
(5,6-Dihydro-4H-cyclopenta[b]thiophen-4-yl)
acetate (VIId)
Acetic anhydride (710 mg, 7 mmol) was added
to a solution of VIIa (890 mg, 6.3 mmol), DMAP
(80 mg, 0.6 mmol), triethylamine (5 mL), and dry
dichloromethane (2 mL). The mixture was stirred at
room temperature for 1 h, diluted with water (30 mL),
and extracted with ethyl acetate (2 × 20 mL). The
organic solution was washed with water (10 mL) and
dried with anhydrous MgSO4. The solvent was evap-
orated and the product was purified by column chro-
matography (hexane/ethyl acetate, ϕr = 6 : 1). The
amount of 460 mg (40 %) of oily ester VIId was ob-
tained.
5,6-Dihydro-4H-cyclopenta[b]thiophen-4-ol
(VIIa)
A mixture of ketone V (500 mg, 3.6 mmol), LiAlH4
(70 mg, 1.8 mmol), and dry THF (50 mL) was stirred
at room temperature for 1 h in argon atmosphere. The
reaction was quenched by a subsequent addition of
ethyl acetate (10 mL) and water (10 mL). The mix-
ture was extracted with ethyl acetate (3 × 30 mL);
the combined organic solution was washed with water
(20 mL) and dried with anhydrous MgSO4. The sol-
vent was removed and the crude product was purified
by column chromatography (hexane/ethyl acetate, ϕr
= 2 : 1). The amount of 430 mg (85 %) of VIIa was
isolated.
Reaction of VI with diazomalonate di-tert-
butyl diazomalonate VIII
A mixture of VI (220 mg, 1.8 mmol), diazoma-
lonate VIII (640 mg, 2.7 mmol), rhodium acetate
(5 mg), and 1,2-dichloroethane (5 mL) was stirred
at 80◦C for 15 min. After removing the solvent,
the residue was separated by column chromatogra-
phy (gradient elution with hexane/ethyl acetate, ϕr
= 4 : 1, to chloroform/methanol, ϕr = 9 : 1). The
amount of 20 mg (9 %) of the starting compound
VI was isolated followed by 20 mg (3 %) of ylide di-
tert-butyl (5,6-dihydro-1λ4-4H-cyclopenta[b]thiophen-
1-ylidene)malonate(IXa) and 60 mg (10 %) of di-
tert-butyl 6,7-dihydro-5H-cyclopenta[b]thiopyran-2,2-
dicarboxylate (Xa).
4-(tert-Butyldimethylsilyloxy)-5,6-dihydro-4H-
cyclopenta[b]thiophene (VIIb)
A solution of tert-butyldimethylsilyl chloride (500
mg, 3.3 mmol) in DMF (10 mL) was added dropwise
to a solution of VIIa (420 mg, 3.0 mmol) in pyridine
(5 mL) and DMF (10 mL) during 40 min in argon
atmosphere. The mixture was stirred at room tem-
perature for 1 h, diluted with water (100 mL) and ex-
tracted with ethyl acetate (3 × 20 mL). The organic
solution was washed with water (10 mL) and dried
with anhydrous MgSO4. After removing the solvent,
the residue was purified by column chromatography
(hexane/toluene, ϕr = 2 : 1). to yield 500 mg (66 %)
of VIIb as yellowish oil.
Reaction of VIIb with diazomalonate VIII
A mixture of VIIb (270 mg, 1.06 mmol), diazoma-
lonate VIII (390 mg, 1.6 mmol), and rhodium acetate
(5 mg) in 1,2-dichloroethane (5 mL) was stirred at
80◦C for 15 min. The solvent was removed and the
residue separated by column chromatography (gradi-
ent elution with hexane/ethyl acetate, ϕr = 4 : 1, to
chloroform/methanol, ϕr = 9 : 1). Up to 200 mg (74 %)

62
A. Machara, J. Svoboda/Chemical Papers 67 (1) 59–65 (2013)
of VIIb were recovered along with 1.5 mg (3 %) of
ylide di-tert-butyl (4-tert-butyldimethylsilyloxy-1λ4-
5,6-dihydro-4H-cyclopenta[b]thiophen-1-ylidene)malo-
nate (IXb) and 55 mg (11 %) of di-tert-butyl 5-(tert-
butyldimethylsilyloxy)-6,7-dihydro-5H-cyclopenta[b]
thiopyran-2,2-dicarboxylate (Xb).
Di-tert-butyl 4-ethoxy-5,6-dihydro-slbf 1λ4-
4H-cyclopenta[b]thiophen-1-ylidene)malonate
(Xc)
A mixture of VIIc (230 mg, 1.37 mmol), dia-
zomalonate VIII (500 mg, 2 mmol), rhodium acetate
(5 mg), and 1,2-dichloroethane (5 mL) was stirred at
80◦C for 15 min. The solvent was evaporated and the
residue chromatographed (gradient elution with hex-
ane/ethyl acetate, ϕr = 4 : 1, to chloroform/methanol,
ϕr = 9 : 1). The amount of 50 mg (22 %) of the start-
ing ether VIIc and 40 mg (8 %) of product Xc were
obtained.
Di-tert-butyl 5-acetoxy-6,7-dihydro-5H-
cyclopenta[b]thiopyran-2,2-dicarboxylate (Xd)
A mixture of acetate VIId (450 mg, 2.44 mmol),
diazomalonate VIII (890 mg, 3.7 mmol), rhodium
acetate (5 mg), and 1,2-dichloroethane (5 mL) was
stirred at 80◦C for 15 min. The solvent was evapo-
rated and the residue chromatographed (gradient elu-
tion with hexane/ethyl acetate, ϕr = 4 : 1, to chlo-
roform/methanol, ϕr = 9 : 1) to yield 40 mg (4 %)
of ester Xd along with 220 mg (49 %) of the starting
compound VIId.
Fig. 4. Synthesis of ketone V.
Results and discussion
To obtain acid IV, the Knoevenagel reaction of
thiophene-2-carbaldehyde (I) and malonic acid was
employed in the first step to obtain unsaturated acid
II (Fig. 4). In the next step, an attempt to obtain
acid IV by standard hydrogenation of II in methanol
at slightly elevated temperature. However, during the
hydrogenation, the palladium catalyst acted obviously
also as a Lewis acid and the saturated ester III was
isolated in a one pot-procedure in high yield. Subse-
quent saponification of ester III yielded acid IV in the
overall yield of 86 % in four formal steps. Although 5-
exo-trig cyclization is allowed, in this particular case,
despite numerous attempts, intramolecular acylation
of acid IV proceeded only with difficulty and provided
low yields. Initial experiments performed using the in
situ prepared acid chloride in the presence of various
Lewis acids (SnCl4, TiCl4, AlCl3) failed in accordance
with literature (Poirier & Lozach, 1966). Moreover, cy-
clization through the mixed mesyl anhydride (Bonini
et al., 2004) and methyl ester III, respectively, in the
presence of Lewis acids was also unsuccessful. Finally,
the reaction of acid IV in neat polyphosphoric acid
Fig. 5. Synthesis of derivatives VI and VIIa–VIId.
(PPA) at 100◦C led to the required ketone V, albeit in
a very low yield (< 10 %). Encouraged by this result,
further optimizations of the reaction (concentration
of PPA, solvent, reaction temperature, time) were at-
tempted yielding compound V in an acceptable 36 %
yield, i.e. higher than that previously reported (Sam
& Thompson, 1963).
Furthermore, starting with ketone V, a short series
of derivatives exihibing different steric and electronic
effects in the planned transformations (Fig. 5) was
prepared. The Wolff–Kishner reduction (Mohamadi et

A. Machara, J. Svoboda/Chemical Papers 67 (1) 59–65 (2013)
Table 1. Characterization data of prepared compounds
63
wi(calc.)/%
wi(found)/%
Yield
M.p.
Compound
Formula
Mr
C
H
%
29
85
66
65
40
3
◦C
VI
VIIa
VIIb
VIIc
VIId
IXa
Xa
C7H8S
C7H8OS
124.21
140.20
254.47
169.30
182.20
338.50
338.50
468.70
384.50
396.50
67.69
67.44
59.97
60.12
61.36
61.15
63.86
63.92
59.32
59.45
63.88
63.67
63.88
63.96
61.50
61.30
62.47
62.58
60.58
60.65
6.49
6.52
5.75
4.71
8.71
8.86
7.74
7.80
5.53
5.59
7.74
7.89
7.74
7.66
8.60
8.41
8.39
8.48
7.12
7.20
–
90–91
C13H22OSSi
C9H13OS
–
–
–
–
–
–
–
–
C9H10O2S
C18H26O4S
C18H26O4S
C24H40O5SSi
C20H32O5S
C20H28O6S
10
11
8
Xb
Xc
Xd
4
Fig. 6. Reaction of V, VI, and VIIb–VIId with diazomalonate VIII.
al., 1992) afforded the parent heterocycle VI in a low
yield, and the reduction of ketone by LiAlH4 yielded
alcohol VIIa which was further transformed to the cor-
responding silyl derivative VIIb, ethyl ether VIIc, and
acetate VIId by standard methods.
Compound V did not react with the in situ formed
carbenoid which can be explained by the presence of
the electron-withdrawing carbonyl group in position
3. A similar phenomenon was observed for a series
of various benzothiophenes (Vuorinen et al., 1991).
Therefore, the conclusion was drawn that it is easier
to obtain the desired intermediate using the parent cy-
clopentathiophene VI. Indeed, the corresponding ylide
IXb was isolated from a complex mixture along with
the thiopyran derivative Xb as a result of a spon-
taneous rearrangement of the formed ylide (Fig. 6).
Analogously, for the silyl derivative VIIb, both ylide
IXc and the rearranged product Xc were isolated in
low yields (3 % and 11 %, respectively). In order to
rule out the influence of the steric effect on the course
of the reaction, further investigations were carried out
with VIIc and VIId. Reaction of VIIc with diazoma-
lonate VIII provided ylide IXd as the sole product.
However, the ylide showed a remarkable stability and
Based on the previous results (Machara et al.,
2009), a smooth addition of rhodium carbenoid gener-
ated from VIII to the aromatic sulfur resulting in the
formation ylide which can undergo a successive rear-
rangement to the required thialene derivative, even at
room temperature, was expected. However, the ylide
formation turned out to be the critical step of the
planned reaction sequence. The reaction was carried
out by heating VIII with the corresponding interme-
diates V, VI, VIIb–VIId in 1,2-dichloroethane for 15
min under argon atmosphere. The formed products
were carefully separated by column chromatography,
their physico–chemical data are summarized in Ta-
ble 1, spectral data in Table 2 and yields in Table 3.

64
A. Machara, J. Svoboda/Chemical Papers 67 (1) 59–65 (2013)
Table 2. Spectral data of prepared compounds
Compound
Spectral data
VI
IR, ν˜/cm−1: 2924, 2852, 1462, 1377, 804
1H NMR (CDCl3), δ: 7.19 (d, 1H, J2,3 = 4.9 Hz, H-2), 6.84 (d, 1H, H-3), 2.94 (t, 2H, J = 6.9 Hz), 2.74 (t, 2H, J =
6.9 Hz), 2.52 (m, 2H, J = 6.9 Hz)
13C NMR (CDCl3), δ: 146.6, 142.3, 127.5 (CH), 122.2 (CH), 29.7 (CH2), 28.7 (CH2), 28.0 (CH2)
VIIa
VIIb
VIIc
IR, ν˜/cm−1: 3595, 3441, 2970, 2941, 2865, 1456, 1395, 1308, 1044, 944
1H NMR (CDCl3), δ: 7.20 (d, 1H, J2,3 = 4.9 Hz, H-2), 6.95 (d, 1H, H-3), 5.17 (bs, 1H, H-4), 3.08 (m, 1H), 2.88 (m,
1H), 2.81 (m, 1H), 2.34 (m, 1H), 1.81 (bs, 1H, OH)
13C NMR (CDCl3), δ: 148.3, 145.3, 128.7 (CH), 121.3 (CH), 71.6 (CH), 40.3 (CH2), 26.5 (CH2)
1H NMR (CDCl3), δ: 7.20 (dd, 1H, J2,3 = 5.0 Hz, J2,6 = 0.6 Hz, H-2), 6.89 (d, 1H, H-3), 5.25 (t, 1H, J = 5.1 Hz,
H-4), 3.08 (m, 1H), 2.82 (m, 2H), 2.33 (m, 1H), 0.97 (s, 9H, C(CH3)3), 0.17 (s, 6H, 2 × CH3)
13C NMR (CDCl3), δ: 148.1, 144.3, 128.6 (CH), 121.5 (CH), 72.7 (CH), 40.9 (CH2), 26.7 (CH2), 25.9, 18.3 (3 × CH3),
–4.51 (2 × CH3)
IR, ν˜/cm−1: 2971, 2935, 2862, 1440, 1331, 1090, 703
1H NMR (CDCl3), δ: 7.19 (d, 1H, J2,3 = 5.0 Hz, H-2), 6.95 (d, 1H, H-3), 4.86 (dd, 1H, J = 7.0 Hz, J = 3.5 Hz,
H-4), 3.58 (q, 2H, J = 7.0 Hz, CH2), 3.10 (m, 1H), 2.78 (m, 2H), 2.47 (m, 1H), 1.22 (t, 3J = 7.0 Hz, CH3)
13C NMR (CDCl3), δ: 146.4, 146.1, 128.3 (CH), 122.0 (CH), 78.6 (CH), 63.5 (CH2), 37.3 (CH2), 26.8 (CH2), 15.5
(CH3)
IR, ν˜/cm−1: 2944, 1740 (C O), 1371, 1247, 1018, 943
—
VIId
IXa
—
1H NMR (CDCl3), δ: 7.18 (d, 1H, J2,3 = 5.0 Hz, H-2), 6.93 (d, 1H, H-3), 5.97 (m, 1H, H-4), 3.18 (m, 1H), 2.84 (m,
2H), 2.46 (m, 1H), 2.03 (s, 3H, CH3)
13C NMR (CDCl3), δ: 170.7, 147.3, 144.5, 128.7 (CH), 122.3 (CH), 74.1 (CH), 36.8 (CH2), 26.6 (CH2), 21.0 (CH3)
IR, ν˜/cm−1: 2967, 2839, 1662, 1607, 1462, 1312, 1271, 1176, 1029, 847
1H NMR (CDCl3), δ: 6.76 (d, 1H, J = 6.1 Hz), 6.15 (d, 1H, J = 6.1 Hz), 3.15 (m, 2H), 2.63 (m, 2H), 2.47 (m, 2H),
1.44 (s, 18H, 2 × C(CH3)3)
13
—
C NMR (CDCl3), δ: 165.6 (C O), 154.2, 136.6, 130.4 (CH), 125.0 (CH), 78.7, 51.2, 30.0 (CH2), 29.7 (CH2), 28.2
—
(CH2), 27.8 (6 × CH3)
IR, ν˜/cm−1: 2982, 2932, 1725 (C O), 1707 (C O), 1631, 1495, 1369, 1326, 1158, 1054, 909, 840
—
—
—
—
IXb
1H NMR (CDCl3), δ: 7.07 (d, 1H, J2,3 = 4.8 Hz), 6.75 (d, 1H, J2,3 = 4.8 Hz), 4.76 (m, 1H, J = 7.0 Hz), 2.54 (m,
1H), 2.41 (m, 1H), 2.09 (m, 1H), 1.94 (m, 1H), 1.38 (s, 9H, C(CH3)3), 1.37 (s, 9H, C(CH3)3), 0.80 (s, 9H, C(CH3)3),
0.12 (s, 3H, CH3), 0.10 (s, 3H, CH3)
13
—
—
—
C NMR (CDCl3), δ: 165.2 (C O), 162.0 (C O), 154.3, 139.2, 128.6 (CH), 121.6 (CH), 84.0, 82.9, 73.5 (CH),
—
58.1, 44.4 (CH2), 39.5 (CH2), 28.8 (3 × CH3), 27.8 (3 × CH3), 25.1 (3 × CH3), 18.1, –5.0 (CH3)
IR, ν˜/cm−1: 2978, 2934, 1732 (C O), 1457, 1370, 1258, 1167, 848
—
—
Xa
Xb
1H NMR (CDCl3), δ: 6.13 (d, 1H, J3,4 = 10.2 Hz, H-4), 5.60 (d, 1H, H-3), 2.49 (t, 2H, J = 7.2 Hz, CH2), 2.42 (t,
2H, J = 7.2 Hz, CH2), 1.90 (kv, 2H, J = 7.2, CH2), 1.46 (s, 18H, 2 × C(CH3)3)
13
—
C NMR (CDCl3), δ: 166.7 (C O), 128.9, 128.5, 125.8 (CH), 114.4 (CH), 82.8, 44.3, 35.2 (CH2), 33.4 (CH2), 27.8
—
(6 × CH3), 22.1 (CH2)
IR, ν˜/cm−1: 2982, 2931, 1730 (C O), 1472, 1371, 1159, 1144, 1046, 909
—
—
1H NMR (CDCl3), δ: 6.20 (d, 1H, J3,4 = 10.3 Hz, H-4), 5.66 (d, 1H, H-3), 4.83 (m, 1H, J = 5.2 Hz), 2.59 (m, 1H),
2.39 (m, 1H), 2.32 (m, 1H), 1.73 (m, 1H), 1.45 (s, 9H, C(CH3)3), 1.44 (s, 9H, C(CH3)3), 0.87 (s, 9H, C(CH3)3),
0.07 (s, 3H, CH3), 0.05 (s, 3H, CH3)
13
—
—
—
C NMR (CDCl3), δ: 166.8 (C O), 166.4 (C O), 132.3, 130.8, 124.3 (CH), 114.7 (CH), 83.1, 82.9, 76.9 (CH),
—
60.8, 33.6 (CH2), 32.5 (CH2), 27.6 (9 × CH3), 25.8 (3 × CH3), 18.1, –4.2 (CH3), –4.7 (CH3)
IR, ν˜/cm−1: 2979, 2935, 1744 (C O), 1630, 1459, 1370, 1255, 1151
—
—
Xc
Xd
1H NMR (CDCl3), δ: 7.02 (d, 1H, J2,3 = 5.5 Hz), 6.81 (d, 1H, J2,3 = 5.5 Hz), 4.75 (m, 1H, H-4), 3.54 (m, 2H, J =
7.0 Hz, J = 4.4 Hz, CH2), 2.78 (m, 2H), 2.69 (m, 1H), 2.38 (m, 1H), 1.39 (s, 18H, 2 × C(CH3)3), 1.20 (t, 3H, J =
7.0 Hz, CH3)
13
—
C NMR (CDCl3), δ: 164.8 (2 × C O), 150.9, 146.4, 128.4 (CH), 122.0 (CH), 79.3, 78.7 (CH), 64.6, 63.6, 37.3
—
(CH2), 35.9 (CH2), 27.6 (6 × CH3), 15.5 (CH3)
IR, ν˜/cm−1: 2978, 1725, 1370, 1255, 1160, 1058
1H NMR (CDCl3), δ: 6.30 (d, 1H, J2,3 = 10.2 Hz, H-2), 5.68 (dd, 1H, J3,4 = 1.2 Hz, H-3), 4.75 (bs, 1H, H-5), 2.64
(m, 1H,), 2.40 (m, 1H), 2.16, (s, 3H, CH3), 1.78 (m, 1H), 1.45 (s, 18H, 2 × C(CH3)3
13
—
—
—
C NMR (CDCl3), δ: 170.6 (C O), 166.8 (2 × C O), 128.5, 128.0, 125.7 (CH), 114.3 (CH), 83.0, 82.6, 75.5 (CH),
—
44.3, 35.0 (CH2), 33.5 (CH2), 27.8 (3 × CH3), 27.7 (3 × CH3), 21.0 (CH3)
it did not rearrange to the required thialene derivative
even at a long-term heating in toluene. On the con-
trary, the only product isolated from the reaction of
thiophene VIId was thiopyran Xd in a very low yield
of 4 %.
The observed low yields of the formed ylides are
probably caused by their low thermal stability com-
pared to that of the known substituted thiophenium
ylides (Bowles et al., 1988a, 1988b). It can be ar-
gued that stability of ylides is sensitive to electronic

A. Machara, J. Svoboda/Chemical Papers 67 (1) 59–65 (2013)
Table 3. Yields and recovery of starting material for the reaction with diazomalonate
Products
65
Starting material
Recovery/%
Compound
Yield/%
Compound
Yield/%
VI
9
74
22
49
IXa
IXb
IXc
IXd
3
3
8
0
Xa
Xb
Xc
Xd
10
11
0
VIIb
VIIc
VIId
4
effects (Porter, 1989) but herein reported findings
are not consistent enough for such a general state-
ment. Perhaps the synergic effect of low transforma-
tion to the corresponding ylides (Table 3) and their
inherent instability which also can lead to undesirable
dealkylation to the starting VIIb–VIId can account
for the acquired results. In addition, variable amounts
of unidentifiable polymeric by-products of the studied
reaction were obtained.
ethylenediamine. Tetrahedron Letters, 36, 6087–6090. DOI:
10.1016/0040-4039(95)01210-9.
Klein, R. F. X., & Horák, V. (1986). New synthesis and spectro-
scopic studies of thialene (cyclopenta[b]thiapyran). Journal
of Organic Chemistry, 51, 4644–4651. DOI: 10.1021/jo00374
a027.
Mayer, R., Franke, J., Horák, V., Hanker, I.,
& Zahrad-
ník, V. (1961). Synthese und Eigenschaften des Thialens
(Cyclopenta-Thiapyran). Tetrahedron Letters, 2, 289–294.
DOI: 10.1016/s0040-4039(01)84064-8.
Mayer, R., & Franke, J. (1965). Schwefel–Helerocyclen. XLII.
Eine weitere Synthese von Thialen (Cyclopenta[b]thiopyran)
und die erste Darstellung des Benzothialens Indeno[2,1-b]
thiopyran. Journal fu¨r Praktische Chemie, 30, 262–272. DOI:
10.1002/prac.19650300505.
Conclusions
The apparent low stability and the lack of the
ability to rearrange to thermodynamically more sta-
ble thiopyrans is distinct from the reactivity of fused
thiophenium-ylides reported recently. Hence, all stud-
ied reactions provided only unsatisfactory yields of the
expected thiopyrans, showing that the initial task has
to be reconsidered.
Machara, A., Kurfu¨rst, M., Kozmík, V., Petříčková, H., Dvořá-
ková, H., & Svoboda, J. (2004). A nonconcerted cycloaddi-
tion of fused 2-vinylthiophenes with dimethyl acetylenedicar-
boxylate. Tetrahedron Letters, 45, 2189–2192. DOI: 10.1016/
j.tetlet.2004.01.030.
Machara, A., Kozmík, V., Pojarová, M., Dvořáková, H., & Svo-
boda, J. (2009). Preparation and rearrangement study of
novel thiophenium- and selenophenium-ylides. Collection of
Czechoslovak Chemical Communications, 74, 785–798. DOI:
10.1135/cccc2009001.
Acknowledgements. This work was partially funded by the
Czech Science Foundation (project. No P204/11/0723).
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of thiochroman-4-ones and thiochromen-4-ones. Journal of
the Chemical Society, Perkin Transactions 1, 1982, 395–402.
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