A new approach to the synthesis of 2-vinylthiophenes and selenophenes; competition between free radical and anionic cycloaromatization of bridged di- and tetrapropargylic sulfides and selenides

Article abstract of DOI:10.1016/S0040-4020(03)00327-2

A series of unknown di- and tetrapropargylic sulfides and selenides have been prepared. In the presence of t-BuOK in dry THF these compounds underwent isomerization to the corresponding diallenes, followed by a tandem anionic cyclization and aromatization

Full text of DOI:10.1016/S0040-4020(03)00327-2

Tetrahedron 59 (2003) 2641–2649
A new approach to the synthesis of 2-vinylthiophenes
and selenophenes; competition between free radical
and anionic cycloaromatization of bridged di-
and tetrapropargylic sulfides and selenides
*
Yossi Zafrani, Marina Cherkinsky, Hugo E. Gottlieb and Samuel Braverman
Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel
Received 27 November 2002; revised 10 February 2003; accepted 28 February 2003
Abstract—A series of unknown di- and tetrapropargylic sulfides and selenides have been prepared. In the presence of t-BuOK in dry THF
these compounds underwent isomerization to the corresponding diallenes, followed by a tandem anionic cyclization and aromatization
to 2-vinylthiophene or selenophene derivatives. Some mechanistic studies indicated competition between free radical and anionic
cycloaromatization. The latter is influenced by the nature of the bridging heteroatom, substitution of the allenyl group and base
concentration. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
substitution, see Scheme 1).20 Surprisingly, we have also
found that the rate of cyclization step was independent of
the nature of the bridging functionality.
Rearrangements involving the cyclization of p and
heteroatom bridged diallenes have received considerable
attention over the last three decades.1–3 An important
mechanistic question related to these reactions has been
whether the process is concerted or free radical in nature.
The latter was suggested to apply for the cyclization of
diallenic sulfones and sulfides.4–11 In the past decade,
considerable attention has been focused on cyclization
reactions of diallenes or diacetylenes involving free radical
species.12–15 The trigger for renewed interest in this type of
reaction was the elegant mode of action of the naturally
occurring enediynes,16 – 18 whose biological activity
involves a diradical cycloaromatization.19 Prompted by
these studies, our interest in such rearrangements was also
revived, especially in studying the effect of tandem
cyclization and aromatization of some novel dipropargylic
systems such as 1a–c, which besides their potential
biological activity, would also be of considerable synthetic
and mechanistic interest. During the course of our studies,
we found that in the presence of amine bases at room
temperature, p-conjugated bis-propargylic selenides, sul-
fides, sulfoxides and sulfones undergo facile and high
yielding isomerization to the corresponding diallenes,
followed by tandem cyclization and aromatization via a
probable diradical intermediate (for the case of g-phenyl
As a natural extension of this tandem reaction of various
p-conjugated bis-propargylic compounds, we decided to
test the possibility of a double tandem process of
tetrapropargylic systems, in order to prepare some more
complex polycyclic aromatic compounds. This investi-
gation resulted in some surprising and unprecedented
findings.
2. Results and discussion
The synthesis of the required tetrapropargylic compounds
10a–d is presented in Scheme 2. Thus, palladium-catalyzed
coupling of propargyl alcohol with p-dibromobenzene
afforded diol 8.21 Mesylation of 8 with methanesulfonyl
chloride and triethylamine afforded dimesylate 9 in 72%
yield. The latter was treated with potassium hydroxide and
the appropriate propargyl thioacetate,22 to yield the
corresponding sulfides 10a and 10c in 85 and 62% yields,
respectively. Finally, oxidation of bis-sulfides 10a,c using
oxone, led to the formation of bis-sulfones 10b and 10d in
53 and 63% yields, respectively.
We first examined the double cycloaromatization of bis-
sulfone 10b, in order to test its conversion to the appropriate
anthracene or phenanthrene derivatives. However, this
compound was so reactive that even in the presence of
weak bases such as 2,6-lutidine at low temperatures it
Keywords: sulfur and selenium heterocycles; allenes; acetylenes; anionic
cyclizations; radical cyclization.
*
Corresponding author. Tel.: þ972-3-5318322; fax: þ972-3-5351250;
e-mail: bravers@mail.biu.ac.il
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00327-2

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Y. Zafrani et al. / Tetrahedron 59 (2003) 2641–2649
Scheme 1. Tandem isomerization, cyclization and aromatization of bridged propargylic compounds 1a–c.
underwent decomposition. Therefore, we decided to test the
reactivity of the corresponding bis-sulfide 10a. The reaction
of this compound under similar conditions used for bis-g-
phenylpropargyl sulfide (1a, DBU in acetonitrile), resulted
in the formation of diketones 14a and 15a (1:1 ratio) but in
only 8% yield each (Scheme 3). As already suggested in our
previous report,20b for the formation of thienyl ketone 7,
formation of 14a and 15a may indicate similar behavior of
the tetraradical intermediate which prefers to react with
oxygen to yield the observed products via a hydroperoxide
or cyclic peroxide precursor.
yield), a stable product. Similar behavior was observed for
bis-sulfone 10d, when treated with triethylamine in DMSO,
which led to the formation of terphenyl compound 13d in
54% yield. Recent studies from our group have shown that
unsymmetrical dipropargylic sulfoxides underwent cycliza-
tion in both possible directions, presumably as a function of
the relative reactivity of the appropriate diradical inter-
mediates.22 In general, when the latter involved a benzyl
radical, the observed preference was recombination by
intramolecular addition to an alkene rather than to a benzene
ring; the preference is enhanced in a more polar solvent.
In sharp contrast to these results, treatment of bis-sulfide
10a with t-BuOK in dry THF resulted in formation of the
two conjugated cyclic aromatic products 16a and 17a in
14% and 28% yield, respectively. In spite of the extensive
studies on the behavior of bridged dipropargylic systems
under basic conditions,11,23,24 there seems to be no
precedent to this essentially spontaneous reaction at room
temperature. Moreover, when the related tetrapropargylic
sulfide 10c was subjected to the action of t-BuOK in THF at
room temperature, again, a fast reaction was observed as
before, but no products analogous to 16a and 17a were
observed. Interestingly, no intramolecular addition of the
radical to the benzene ring takes place, but instead the
tetraradical 11c undergoes recombination to form 12c (36%
In view of the above mentioned results, we decided to study
the scope of the new tandem reaction and its mechanism.
Therefore, a number of substituted bridged dipropargylic
sulfides and selenides was prepared, and their reaction with
t-BuOK in THF investigated. The first such compound to
be examined was the mono-g-phenyl dipropargyl sulfide
18a. This unsymmetrical dipropargylic sulfide reacted
essentially instantaneously under these conditions and
afforded a mixture of cis- and trans-2-styrylthiophenes
19a and 20a (1:1 ratio) in 70% yield (Scheme 4). The latter
products have been synthesized before25 and therefore,
could be easily identified by their spectral data. Substitution
of the acetylenic hydrogen in 18a by a t-butyl group (18b)
provided unambiguous structural proof of the thiophene
Scheme 2. Synthesis of tetrapropargylic systems. (a) PdCl2(PPh3)2, PPh3, CuI, Et3N, propargyl alcohol, 808C, 4 h; (b) CH3SO2Cl, Et3N, ether, 08C, 1 h;
(c) KOH, propargyl thioacetate, THF–MeOH, 258C, 20 min; (d) oxone, H2O–MeOH, 0–258C, 1 week.

Y. Zafrani et al. / Tetrahedron 59 (2003) 2641–2649
2643
Scheme 3. Tandem reactions of tetrapropargylic systems 10a–d.
products, and demonstrated the high regioselectivity of the
reaction, namely bonding of the a-carbon of the phenyl
substituted propargyl group to the g-carbon of the
unsubstituted or alkyl substituted propargyl group, but not
vice versa (see also below for mechanism). Thus, reaction of
sulfide 18b with t-BuOK in dry THF at room temperature
resulted in conversion to a mixture of the expected isomeric
products 19b and 20b (2:3 ratio).
To further test the generality of this unusual reaction, we
subjected bis-g-phenyl-propargyl sulfide 1a to the same
reaction conditions. Compound 1a was one of the first to be
studied20 using DBU as base in DMSO. On treatment with
t-BuOK in dry THF, a mixture of products was obtained
including the usual products of diradical cycloaromatization
5 and 7, as well as products of the new cyclization, 21 and
22 (Scheme 5). The distribution of the products obtained in
Scheme 4. Reaction of dipropargylic compounds 18a–c with t-BuOK in THF.

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Y. Zafrani et al. / Tetrahedron 59 (2003) 2641–2649
Scheme 5. Reaction of bis-g-phenyl propargyl sulfide 1a with t-BuOK in THF.
Table 1. Reaction of bridged dipropargylic systems with t-BuOK in THF
Entry
Substrate
t-BuOK (equiv.)
Product distribution (%)a
Anionic cyclization
Radical cyclization
1
2
3
4
5
6
7
8
18a
18b
18c
1a
1a
1a
2
2
2
2.5
1
0.7
2
E-19a (50)þZ-20a (50)
E-19b (41)þZ-20b (59)
E-19c (36)þZ-20c (64)
E-21 (27)þZ-22 (35)
E-21 (8)þZ-22 (9)
–
–
–
–
{5þ7} (38)
{5þ7} (83)
{5þ7} (100)
24 (100)
–
23a
23b
–
2
E-25 (10)þ26 (75.7)bþ27 (14.3)b
a
The ratio of isomers was determined by 1H NMR spectra and normalized to 100%.
The cis-isomer is not stable under reaction conditions and underwent further rearrangements to 26 and 27.
b
the last reaction exhibited high sensitivity to the base
concentration as shown in Table 1. In sharp contrast to this
behavior, the corresponding selenide 18c yielded only the
products expected from the ‘new’ cyclization, 19c and 20c
(36:64 ratio), regardless of the base concentration.
seem to be derived from the cis-isomer of 25. Presumably,
this conjugated p-system is not stable under the reaction
conditions and undergoes further cyclizations to the
corresponding products 26 and 27.
Inspection of the data presented in Table 1 indicates a
general preference for the formation of the cis-isomer of
2-styrylthiophene products (entries 2–5, 8). Another
significant observation is the effect of base concentration
on the distribution of products obtained from bis-g-
phenylpropargyl sulfide (1a). For example, while using
0.7 equiv. of base (entry 6), only diradical cyclization is
observed, raising the concentration of the base to 2.5 equiv.
(entry 4), results in the formation of the 2-styrylthiophenes
as the major products. Finally, dipropargylic systems
bridged by selenium, such as 18c (entry 3) and 23b (entry
Similarly to the reaction of 1a, sulfide 23a reacts readily
with t-BuOK in THF. In this case, the only product
obtained, was thiophene derivative 24, which is the product
of the free radical cycloaromatization (Scheme 6).20 Here
again, different behavior for the reaction of the related
selenide 23b was observed. Thus, in the reaction of 23b with
t-BuOK in THF, three products were obtained (25–27).
While product 25 having a trans-configuration of double
bonds is the one expected from the new anionic mechanism
presented in Scheme 7, the other two products 26 and 27
Scheme 6. Reaction of bis-propargylic compounds 23a,b with t-BuOK in THF.

Y. Zafrani et al. / Tetrahedron 59 (2003) 2641–2649
2645
Scheme 7. Suggested mechanism for the formation of 2-vinylthiophenes and selenophenes from the reaction of di- and tetrapropargyl sulfides and selenides
with t-BuOK in THF.
8), or those substituted by alkyl substituents (entry 2)
exclusively undergo the new type of cyclization. We believe
that the results described above, including the complete
regiospecifity can be explained by the tentative mechanism
presented in Scheme 7.
One may raise the question whether the involvement of the
a-allenic carbanion is strictly necessary for the formation of
the appropriate 5-membered heterocyclic ring, or whether
the a-propargylic carbanion of the monoallenic sulfide can
alternatively undergo a similar intramolecular nucleophilic
addition to the g-allenic carbon of the allenyl group.
Therefore, a further mechanistic test to support the above
mechanism has been advanced. We prepared benzyl
propargyl sulfide 28 and subjected it to the action of
t-BuOK in THF at room temperature. No cyclization
product 29 was observed. Instead, sulfide 28 only
isomerized to the acetylenic isomer 30 in 97% yield
(Scheme 8). Interestingly, it was recently reported by
Schwan and co-workers,27 that compound 30 undergoes
cyclization to 29. However, this happened only in low yield
under significantly more forcing conditions (heating with
t-BuOK/acetonitrile solution for 24 h).
The reaction is initiated by a double base catalyzed
propargyl–allene isomerization to yield the appropriate
diallenyl sulfide or selenide. The latter can choose between
two alternative routes. Path a leads to cycloaromatization
via a diradical intermediate as previously described.20 The
other route (path b) involves deprotonation of the carbon
atom a to the heteroatom. Next, the generated a-carbanion
undergoes an intramolecular nucleophilic addition at the
g-allenic carbon of the other allenyl group with the
formation of a 5-membered heterocyclic ring, which then
by a series of base catalyzed prototropic shifts leads to the
observed thiophene derivatives. The difference in behavior
between the sulfide and the selenide may be a result of the
lower aromatic resonance stabilization of selenophene vs
thiophene,26 that allows for the extension of the life span of
the corresponding diallenic selenide and thus increases its
chances for deprotonation. The competition of the anionic
mechanism is thus influenced by the nature of the bridging
moiety, substitution of the allenyl groups and the base
concentration.
Furthermore, we have found that treatment of allyl
propargyl sulfide 31 with t-BuOK in THF resulted in
formation of the cyclic sulfide 32, apparently, by nucleo-
philic addition of the appropriate allyl anion to the central
carbon of the allenyl group (Scheme 9). Again, no
cyclization product 33 was observed.
Finally, it is worthwhile to note that the novel anionic
Scheme 8. Reaction of benzyl propargyl sulfide 28 with t-BuOK.
Scheme 9. Reaction of allyl propargyl sulfide 31 with t-BuOK.

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Y. Zafrani et al. / Tetrahedron 59 (2003) 2641–2649
cyclization reported above has also been applied by us for
the cyclization/aromatization of cyclic dipropargylic sul-
fides and selenides; the latter proceeds under similar
reaction conditions and with good yields.28
reaction mixture was diluted with ether (100 mL), washed
with water (3£100 mL) and dried over anhydrous MgSO4.
The solvent was removed under reduced pressure to give
1
0.82 g (85%) of bis-sulfide 10a as yellow oil. H NMR
(300 MHz, CDCl3): d 7.28 (s, 4H), 3.58 (s, 4H), 3.39 (d,
J¼2 Hz, 4H), 2.21 (t, J¼2 Hz, 2H); 13C NMR (75.5 MHz,
CDCl3): d 131.5 (CH), 122.7 (C), 86.2 (C), 82.9 (C), 79.1
(C), 71.5 (CH), 19.9 (CH2), 19.0 (CH2); IR (neat): 3010,
2212, 1478, 1184, 744 cm21; MS (CI): m/z 295 (MHþ,
31.7%), 223 (100%); HRMS calcd for C18H15S2 295.0612;
found 295.0625.
In conclusion, we have discovered a new anionic cyclo-
aromatization reaction of di- and tetrapropargyl sulfides and
selenides, which is not only of considerable mechanistic
interest but also of synthetic utility. It is also interesting to
note that in spite of the detailed studies by Garratt,11 Iwai23
and Ollis24 on bridged dipropargylic systems under
practically identical condition, this type of anionic cyclo-
aromatization had remained undiscovered.
3.1.3. 1,4-Bis{3-[(4-methylpent-4-en-2-ynyl)thio]prop-1-
ynyl}benzene (10c). The title compound was prepared from
9 and g-isopropenylpropargyl thioacetate22 by the pro-
cedure described above, and obtained in 62% yield as
3. Experimental
3.1. General
1
yellowish viscous oil. H NMR (300 MHz, CDCl3): d 7.36
(s, 4H), 5.29–5.30 (m, 2H), 5.23 (quintet. J¼1.5 Hz, 2H),
3.66 (s, 4H), 3.60 (s, 4H), 1.89 (dd, J¼1.5, 1 Hz, 6H); 13C
NMR (75.5 MHz, CDCl3): d 131.6 (CH), 126.4 (C), 122.7
(C), 122.1 (CH2), 86.5 (C), 84.7 (C), 83.4 (C), 82.8 (C), 23.5
Melting points were obtained on a Thomas Hoover melting
point apparatus and are uncorrected. IR spectra were
(CH3), 20.2 (CH2), 20.1 (CH2); IR (neat): 2187, 1654 cm21
;
1
recorded on a Nicolet 60 SXB FTIR. H NMR and 13C
MS (CI): m/z 375 (MHþ, 42.5%), 263 (49.3%), 143 (100%);
HRMS calcd for C24H23S2 375.1241; found 375.1210.
NMR were recorded on Bruker AC-200, DPX-300 or DMX-
600 spectrometers in either CDCl3 or other deuterated
solvents, using TMS as internal standard. Chemical shifts
are reported in d units, and coupling constants in Hz.
High-resolution mass spectra were obtained on a VG-Fison
Autospec instrument. Other mass spectra were obtained on a
Finningan GC/Ms 4021, with either electronic (EI) or
chemical ionization (CI). Column chromatography was
performed with Merck silica gel 60 (230–400 mesh), and
TLC was run on precoated Merck silica gel plates 60 F254
(2.00 mm). Tetrahydrofuran was distilled from Na, diethyl
ether was dried over Na wire. Other commercially available
chemicals were used without further purification.
3.1.4. [3-(Prop-2-ynylthio)prop-1-ynyl]benzene (18a).
The title compound was prepared from g-phenylpropargyl
bromide and propargyl thioacetate by the procedure
described above, and obtained in 66% yield as colorless
oil, after separation by column chromatography (silica gel,
ethyl acetate–hexane 5:95). 1H NMR (300 MHz, CDCl3): d
7.41–7.44 (m, 2H), 7.29–7.32 (m, 3H), 3.66 (s, 2H), 3.47
(d, J¼2.4 Hz, 2H), 2.28 (t, J¼2.4 Hz, 1H); 13C NMR
(75.5 MHz, CDCl3): d 131.7 (CH), 128.2 (CH), 122.8 (C),
84.3 (C), 83.4 (C), 79.2 (C), 71.3 (CH), 19.9 (CH2), 18.9
(CH2); IR (neat): 2924, 2130, 1491, 1240, 1074, 745 cm21
;
MS (CI): m/z 185 ([M2H]þ, 69.7%), 153 (13.2%), 115
(100%); HRMS calcd for C12H9S 185.0420; found
185.0421.
3.1.1. 3-(4-{3-[(Methylsulfonyl)oxy]prop-1-ynyl}-phenyl)-
prop-2ynyl methanesulfonate (9). Diol 821 (0.56 g,
3.0 mmol) and triethylamine (0.7 g, 6.9 mmol) were
dissolved in dry diethyl ether (50 mL). After the mixture
was cooled to 08C, a solution of methanesulfonyl chloride
(0.77 g, 6.8 mmol) in dry diethyl ether (10 mL) was added,
and the reaction mixture was stirred for 3 h before it was
warmed to room temperature and stirred for further 2 h. The
reaction mixture was then diluted with chloroform, and
washed with water (3£100 mL), 3% HCl (100 mL), 3%
NaHCO3 (100 mL) and water (3£100 mL). After drying
over anhydrous MgSO4, filtration and evaporation of the
solvent, the desired dimesylate 9 was obtained as a yellow
solid (0.74 g, 72% yield), which was recrystallized from
ether as white crystals. Mp 128–1298C. 1H NMR
(300 MHz, CDCl3): d 7.43 (s, 4H), 5.09 (s, 4H), 3.15 (s,
6H); 13C NMR (75.5 MHz, CDCl3): d 131.9 (CH), 122.2
(C), 88.3 (C), 83.0 (C), 57.9 (CH2), 38.9 (CH3); IR (KBr):
3023, 2222, 1500, 1361, 1174, 938 cm21; MS (EI): m/z 342
(Mþ, 8%), 247 (100%), 151 (23%); HRMS calcd for
C14H14O6S2 342.0232; found 342.0245.
3.1.5. {3-[4,4-Dimethylpent-2-ynyl)thio]prop-1-ynyl}-
benzene (18b). The title compound was prepared from
g-phenylpropargyl bromide and g-t-butylpropargyl thio-
acetate22 by the procedure mentioned above, and obtained
in 75% yield as a yellowish oil, after separation by column
chromatography (silica gel, ethyl acetate–hexane 5:95). 1H
NMR (300 MHz, CDCl3): d 7.43–7.46 (m, 2H), 7.30–7.32
(m, 3H), 3.65 (s, 2H), 3.48 (s, 2H), 1.25 (s, 9H); 13C NMR
(75.5 MHz, CDCl3): d 131.7 (CH), 128.2 (CH), 128.1 (CH),
123.0 (C), 92.5 (C), 84.8 (C), 83.0 (C), 73.2 (C), 31.0
(CH3)3), 27.5 (C), 19.8 (CH2), 19.7 (CH2); IR (neat): 2195,
1490, 1361, 1266, 756, 690 cm21; MS (CI): m/z 243 (MHþ,
12.3%), 209 (21.5%), 115 (100%); HRMS calcd for
C16H19S 243.1207; found 243.1206.
3.1.6. [(1E)-3-(Prop-2-ynylthio)prop-1-enyl]benzene
(31). The title compound was prepared from cinnamyl
methanesulfonate and propargyl thioacetate, by the pro-
cedure described above, and obtained in 35% yield as
colorless oil, after separation by column chromatography
(silica gel, ethyl acetate–hexane 5:95). 1H NMR (300 MHz,
CDCl3): 7.23–7.40 (m, 5H), 6.50 (br d, J¼15.6 Hz, 1H),
6.15 (dt, J¼15.6, 7.5 Hz, 1H), 3.46 (dd, J¼7.5, 1.2 Hz, 2H),
3.1.2. 1,4-Bis[3-(but-2-ynylthio)prop-1-ynyl]benzene
(10a). A solution of KOH (0.52 g, 13 mmol) in methanol
(20 mL) was slowly added to a magnetically stirred solution
of propargyl thioacetate (0.75 g, 6.6 mmol)22 and disulfo-
nate 9 (1.12 g, 3.3 mmol) in THF (20 mL). After 40 min the

Y. Zafrani et al. / Tetrahedron 59 (2003) 2641–2649
2647
3.19 (d, J¼2.7 Hz, 2H), 2.27 (t, J¼2.7 Hz, 1H); 13C NMR
(75.5 MHz, CDCl3): d 136.5 (C), 132.9 (CH), 128.5 (CH),
127.6 (CH), 126.3 (CH), 124.4 (CH), 78.0 (C), 71.1 (CH),
33.4 (CH2), 17.8 (CH2); MS (CI): m/z 189 (MHþ, 30.4%),
155 (6.2%), 117 (100%); HRMS calcd for C12H13S
189.0738; found 189.0721.
MHz, CDCl3): d; 7.93 (s, 2H), 7.91 (s, 2H), 7.87 (d, J¼3 Hz,
1H), 7.72 (d, J¼1.5 Hz, 1H), 7.38 (dt, J¼3, 0.5 Hz, 1H),
7.28 (q, J¼1 Hz, 1H), 4.75 (s, 2H), 2.54 (d, J¼1 Hz, 3H);
13C NMR (75.5 MHz, CDCl3): d 191.8 (C), 189.1 (C), 143.6
(C), 142.1 (C), 141.5 (C), 141.3 (C), 140.8 (C), 138.9 (C),
138.8 (CH), 133.2 (CH), 129.5 (CH), 129.2 (CH), 126.1
(CH), 125.6 (CH), 59.9 (CH2), 15.2 (CH3); IR (neat): 1657,
1645 cm21; MS (CI): m/z 342 (Mþ, 78.6%), 325 (64.6%),
245 (10.6%) 203 (100%); HRMS calcd for C18H14O3S2
342.0384; found 342.0390.
3.1.7. 1,4-Bis-[3-(but-2-ynylsulfonyl)prop-1-ynyl]ben-
zene (10b). To a magnetically stirred solution of bis-sulfide
10a (1.0 g, 3.4 mmol) in methanol (20 mL) at 08C was
added a solution of 49.5% KHSO5 (2.5 equiv.) in water
(20 mL). The reaction mixture was stirred for six days at
room temperature before it was diluted with water and
extracted with chloroform. The organic layer was washed
with water (3£100 mL), satd. NaCl and then dried over
anhydrous MgSO4. Evaporation of the solvent gave a
mixture of products, which was separated by column
chromatography (silica gel, ethyl acetate–hexane 1:1).
The bis-sulfone product (0.63 g, 53%) was recrystallized
from chloroform as yellowish crystals. Mp 194–1958C. 1H
NMR (300 MHz, DMSO-d6): d 7.58 (s, 4H), 4.72 (s, 4H),
4.53 (d, J¼2.4 Hz, 4H), 3.64 (t, J¼2.4 Hz, 2H); 13C NMR
(75.5 MHz, DMSO-d6): d 132.9 (CH), 122.9 (C), 86.7 (C),
80.9 (C), 79.7 (CH), 73.0 (C), 45.5 (CH2), 44.8 (CH2); IR
(neat): 1320, 1121 cm21; MS (EI): m/z 358 (Mþ, 42.6%),
294 (6.2%), 152 (100%); HRMS calcd for C18H14O4S2
358.0334; found 358.0362.
3.1.11. 6-Methyl-4-[4-(6-methyl-1,3-dihydro-2-benzo-
thien 2,2-dioxide-4-yl)phenyl]-1,3-dihydro-2-benzothio-
phene 2,2-dioxide (13d). To a solution of bis-sulfone 10d
(1.49 g, 3.4 mmol) in DMSO (30 mL) was added Et3N
(1.9 mL, 13.6 mmol). After stirring at room temperature for
12 h, the reaction mixture was diluted with dichloromethane
(100 mL), washed with water (3£100 mL) and dried over
anhydrous MgSO4. Evaporation of the solvent gave a crude
product in 54% yield. The yellowish solid was purified
by chromatography (silica gel, ethyl acetate) and then
recrystallized from chloroform–hexane as white crystals.
Mp 150–1808C (decomp.). 1H NMR (300 MHz, CDCl3): d
7.39 (s, 4H), 7.22 (s, 2H), 7.16 (s, 2H), 4.42 (s, 4H), 4.35 (s,
4H), 2.44 (s, 6H); 13C NMR (75.5 MHz, CDCl3): d 139.4
(C), 139.2 (C), 131.9 (C), 130.4 (CH), 128.7 (CH), 126.5
(C), 125.9 (CH), 57.1 (CH2), 56.4 (CH2), 21.4 (CH3); IR
(KBr): 2977, 1697, 1490, 1384, 1064, 759 cm21; MS (CI):
m/z 439 (MHþ, 100%), 375 (39.6%); HRMS calcd for
C24H23O4S2 439.1038; found 439.1020.
3.1.8. 1,4-Bis-{3-[(4-methylpent-4-en-2-ynylsulfonyl)-
prop-1-ynyl]}benzene (10d). The title compound was
prepared from bis-sulfide 10c and oxone reagent, according
to the above procedure and recrystallized from hexane–
chloroform as white crystals in 63% yield. Mp 115–1218C
3.2. General procedure for the reaction of sulfur and
selenium bridged di- and tetrapropargylic systems with
t-BuOK
1
(decomp.). H NMR (300 MHz, CDCl3): d 7.45 (s, 4H),
5.41–5.42 (m, 2H), 5.36 (quintet, J¼1.5 Hz, 2H), 4.29 (s,
4H), 4.20 (s, 4H), 1.92 (dd, J¼1.5, 1 Hz, 6H); 13C NMR
(75.5 MHz, CDCl3): d 132.0 (CH), 125.4 (C), 124.4 (CH2),
122.3 (C), 89.4 (C), 87.2 (C), 78.2 (C), 74.7 (C), 44.7 (CH2),
44.4 (CH2), 22.9 (CH3); IR (neat): 1611, 1508, 1321,
1128 cm21; MS (CI): m/z 439 (MHþ, 27%), 375 (15.5%),
295 (66%), 231 (100%); HRMS calcd for C24H23O4S2
439.1038; found 439.1012.
To a stirred solution of t-BuOK (1.0 equiv.) in dry THF
(5 mL) was added in one portion a solution of the desired di-
or tetrapropargylic compound (0.5 mmol) in 10 mL of dry
THF. After the mixture was stirred for 1 min at room
temperature, it was diluted with water–dichloromethane
(40 mL, each) and the organic layer was washed with 3%
HCl (2£50 mL), water (3£50 mL) and satd. NaCl
(1£50 mL). The organic layer was dried over anhydrous
MgSO4 and solvent removed under reduced pressure. The
data for all cyclization products are listed below.
3.1.9. (4-Methylthien-3-yl){4-[(4-methylthien-3-yl)carbo-
nyl]phenyl}methanone (14a). To a solution of bis-sulfide
10a (1.0 g, 3.4 mmol) in acetonitrile (30 mL) was added
DBU (2 mL, 13.6 mmol). After stirring at room temperature
for 12 h, the reaction mixture was diluted with dichloro-
methane (100 mL), washed with water (3£100 mL) and
dried over anhydrous MgSO4. Evaporation of the solvent
gave a mixture of two products 14a and 15a, which was
separated by column chromatography (silica gel, ethyl
acetate–hexane 1:1) as a colorless oil in 8% yield each. 1H
NMR (300 MHz, CDCl3): d 7.91 (s, 4H), 7.71 (d, J¼1.5 Hz,
2H), 7.28 (quintet, J¼1.5 Hz, 2H), 2.53 (d, J¼1 Hz, 6H);
13C NMR (75.5 MHz, CDCl3): d 189.3 (C-q), 141.5 (C-q),
141.2 (C-q), 140.9 (C-q), 133.1 (CH), 129.1 (CH), 126.1 (CH),
15.2 (CH3); IR (neat): 1643, 1455, 846, 723 cm21; MS (CI):
m/z 326 (Mþ, 100%), 310 (13%), 229 (14%), 125 (51.5%);
HRMS calcd for C18H14O2S2 326.0435; found 326.0430.
3.2.1. 6-Methyl-4-[4-(6-methyl-4,5-dihydro-2-benzo-
thien-4-yl)phenyl]-4,5-dihydro-2-benzothiophene (12c).
The title compound was obtained from 10c by the use of
the general procedure in 36% yield as a yellowish viscous
oil, after purification by column chromatography (silica gel,
1
ethyl acetate–hexane 1:1). H NMR (600 MHz, CDCl3): d
7.25 (s, 4H), 6.86 (d, J¼3 Hz, 2H), 6.53 (ddd, J¼2.5, 1.5,
1 Hz, 2H), 6.36 (bs, 2H), 4.06 (ddd, J¼11.5, 6.5, 1.5 Hz,
2H), 2.52 (bdd, J¼16, 11.5 Hz, 2H), 2.43 (ddt, J¼16, 6.5,
0.5 Hz, 2H), 1.89 (s, 6H); 13C NMR (50.3 MHz, CDCl3): d
142.5 (C), 139.98 (C), 137.9 (C), 136.7 (C), 128.2 (CH),
120.0 (CH), 118.6 (CH), 116.7 (CH), 42.7 (CH), 38.7 (CH2)
23.4 (CH3); MS (CI): m/z; 374 (MHþ, 100%), 225 (34%),
149 (90.8%); HRMS calcd for C24H23S2 375.1241; found
375.1232.
3.1.10. [4-(Hydroxymethyl)thien-3-yl]{4-[(4-methylthiene-
3-yl)carbonyl]phenyl}methanone (15a). 1H NMR (300
Compounds 16a and 17a were obtained from 10a by the

2648
Y. Zafrani et al. / Tetrahedron 59 (2003) 2641–2649
general procedure as inseparable mixture and purified by
column chromatography (silica gel, hexane); colorless oil,
total yield 42%.
isomers—129.3 (CH), 129.2 (CH), 129.1 (CH), 128.7 (CH),
128.6 (CH), 128.39 (CH), 128.37 (CH), 128.36 (CH), 127.6
(CH), 127.5 (CH), 127.2 (CH), 127.1 (CH)], 123.3 (CH),
121.2 (CH); MS (CI): m/z 263 (MHþ, 100%); HRMS calcd
for C18H15S 263.0816; found 263.0810.
3.2.2. 2-((E)-2-{4-[(Z)-2-Thien-2-ylvinyl]phenyl}vinyl)-
1
thiophene (16a). H NMR (600 MHz, CDCl3): d 7.54–
1
7.56 (m, 2H), 7.45 (dm, J¼16.2 Hz, 1H), 7.37 (m, 2H), 7.36
(m, 1H), 7.27 (td, J¼5.0, 1.5 Hz, 1H), 7.19 (dm, J¼3.5 Hz,
1H), 7.06–7.08 (m, 1H), 7.05 (dd, J¼5.0, 3.5 Hz, 1H), 7.00
(d, J¼16.2 Hz, 1H), 6.94 (ddd, J¼5.5, 3.5, 1.5 Hz, 1H), 6.76
(d, J¼12.0 Hz, 1H), 6.57 (d, J¼12.0 Hz, 1H); 13C NMR
(151 MHz, CDCl3): d 143.6 (C), 140.3 (C), 137.4 (C), 137.2
(C), 130.0 (CH), 129.4 (CH), 129.36 (CH), 129.2 (CH),
128.5 (CH), 128.4 (CH), 127.4 (CH), 127.2 (CH), 126.6
(CH), 125.5 (CH), 124.1 (CH), 122.9 (CH); IR (neat) (in
mixture with 17a): 1660, 1625, 1426, 1271, 1201, 957, 814,
690 cm21; MS (CI): m/z 295 (MHþ, 72%), 294 (100%);
HRMS calcd for C18H15S2 295.0615; found 295.0616.
3.2.7. 3-Phenyl-2-[(Z)-2-phenylvinyl]thiophene (22). H
NMR (600 MHz, CDCl3): d 7.46–7.48 (m, 2H), 7.41–7.43
(m, 2H), 7.23–7.40 (m, 6H), 7.12 (d, J¼5 Hz, 1H), 7.05 (d,
J¼5 Hz, 1H), 6.63 (d, J¼12 Hz, 1H), 6.61 (d, J¼12 Hz,
1H); 13C NMR (151 MHz, CDCl3): d 141.7 (C), 137.0
(C), 136.3 (C), 134.2 (C), 130.4 (CH), [o, m and p of both
isomers—129.3 (CH), 129.2 (CH), 129.1 (CH), 128.7 (CH),
128.6 (CH), 128.39 (CH), 128.37 (CH), 128.36 (CH), 127.6
(CH), 127.5 (CH), 127.2 (CH), 127.1 (CH)], 128.2 (CH),
124.7 (CH), 123.0 (CH).
Compounds 19c and 20c were obtained from 18c by the
general procedure as inseparable mixture and purified by
column chromatography (silica gel, hexane); colorless oil,
total yield 24%.
3.2.3. 2-((Z)-2-{4-[(Z)-2-Thien-2-ylvinyl]phenyl}vinyl)-
1
thiophene (17a). H NMR (600 MHz, CDCl3): d 7.36 (s,
4H), 7.27 (td, J¼5.0, 1.5 Hz, 2H), 7.04–7.09 (m, 2H), 6.94
(ddd, J¼5.5, 3.5, 1.5 Hz, 2H), 6.78 (d, J¼12.0 Hz, 2H), 6.60
(d, J¼12.0 Hz, 2H); 13C NMR (151 MHz, CDCl3): d 140.3
(C), 137.5 (C), 129.7 (CH), 129.5 (CH), 129.1 (CH), 127.2
(CH), 126.6 (CH), 124.3 (CH).
3.2.8. 3-Phenyl-2-[(E)-2-phenylvinyl]selenophene (19c).
1H NMR (600 MHz, CDCl3): d 7.83 (d, J¼5.5 Hz, 1H;
2JSe–H¼23.4 Hz), 7.43–7.46 (m, 2H), 7.41–7.42 (m, 2H),
7.39 (m, 2H), 7.36 (d, J¼5.5 Hz, 1H), 7.32–7.34 (m, 1H),
7.29–7.31 (m, 2H), 7.26 (d, J¼15.5 Hz, 1H), 7.22 (m, 1H),
6.88 (d, J¼15.5 Hz, 1H); 13C NMR (151 MHz, CDCl3): d
142.8 (C), 143.4 (C), 137.3 (C), 137.2 (C), 133.5 (CH),
130.5 (CH), 129.3 (CH), 128.7 (CH), 128.5 (CH), 127.6
(CH), 127.1 (CH), 127.2 (CH), 123.4 (CH); IR (neat) (in
mixture with 20c): 1645, 1597, 1487, 1446, 1252, 1066,
Compounds 19b and 20b were obtained from 18b by the
general procedure as inseparable mixture and purified by
column chromatography (silica gel, hexane); colorless oil,
total yield 21%.
3.2.4. 3-t-Butyl-2-[(E)-2-phenylvinyl]thiophene (19b). 1H
NMR (600 MHz, CDCl3): d 7.58 (d, J¼15.5 Hz, 1H), 7.43–
7.45 (m, 2H), 7.32–7.37 (m, 2H), 7.22–7.26 (m, 1H), 7.04
(d, J¼5.0 Hz, 1H), 6.99 (d, J¼5.0 Hz, 1H), 6.84 (d, J¼
15.5 Hz, 1H), 1.44 (s, 9H); 13C NMR (151 MHz, CDCl3): d
148.2 (C), 137.4 (C), 136.0 (C), 128.7 (CH), 128.3 (CH),
127.8 (CH), 127.4 (CH), 126.3 (CH), 125.7 (CH), 122.5
(CH), 34.3 (C), 32.0 ((CH3)3); IR (neat) (in mixture with
948, 700 cm21; MS (CI): m/z 306, 307, 308, 310, 312 (Mþ,
80
14
1:1:3:7:1, 100%), 229 (46%); HRMS calcd for C18H Se
310.0250; found 310.0251.
3.2.9. 3-Phenyl-2-[(Z)-2-phenylvinyl]selenophene (20c).
1H NMR (600 MHz, CDCl3): d 7.78 (d, J¼5.5 Hz, 1H;
2JSe–H¼22.5 Hz), 7.43–7.45 (m, 2H), 7.41–7.42 (m, 2H),
7.39–7.40 (m, 2H), 7.36–7.37 (m, 2H), 7.33–7.35 (m, 1H),
7.29–7.32 (m, 1H), 7.29 (d, J¼5.5 Hz, 1H), 6.67 (d, J¼
12 Hz, 1H), 6.61 (d, J¼12 Hz, 1H); 13C NMR (151 MHz,
CDCl3): d 144.5 (C), 139.4 (C), 136.8 (C), 131.6 (CH),
129.9 (CH), 129.4 (CH), 129.3 (CH), 129.2 (CH), 128.7
(CH), 128.3 (CH), 127.8 (CH), 127.1 (CH), 125.5 (CH).
20b): 2927, 1681, 1491, 1462, 1448, 1363, 1263, 694 cm21
;
MS (CI): m/z 243 (MHþ, 100%); HRMS calcd for C16H19S
243.1207; found 243.1209.
3.2.5. 3-t-Butyl-2-[(Z)-2-phenylvinyl]thiophene (20b). 1H
NMR (600 MHz, CDCl3): d 7.16–7.21 (m, 5H), 7.07 (d,
J¼5 Hz, 1H), 7.00 (d, J¼5 Hz, 1H), 6.81 (d, J¼12 Hz, 1H),
6.58 (d, J¼12 Hz, 1H), 1.39 (s, 9H); 13C NMR (151 MHz,
CDCl3): d 147.7 (C), 136.4 (C), 132.7 (C), 131.8 (CH),
129.4 (CH), 128.6 (CH), 128.1 (CH), 127.3 (CH), 123.4
(CH), 124.0 (CH), 34.3 (C), 31.1 (CH3).
Compounds 25, 26 and 27 were obtained from 23b by the
general procedure and purified by column chromatography
(silica gel, hexane).
3.2.10. 3-Isopropenyl-2-[(1E)-3-methylbuta-1,3-dienyl]-
selenophene (25). Colorless oil; yield 3%; 1H NMR
(600 MHz, CDCl3): d 7.70 (d, J¼5.7 Hz, 1H), 7.18 (d, J¼
5.7 Hz, 1H), 6.86 (d, J¼15.7 Hz, 1H), 6.59 (d, J¼15.7 Hz,
1H), 5.24 (dq, J¼2.2, 1.5 Hz, 1H), 5.06 (dq, J¼1.3, 0.8 Hz,
1H), 5.02 (quintet, J¼1.0 Hz, 1H), 4.96 (dq, J¼2.2, 1.0 Hz,
1H), 2.06 (dd, J¼1.5, 1.0 Hz, 3H), 1.93 (dd, J¼1.5, 0.8 Hz,
3H); 13C NMR (151 MHz, CDCl3): d 144.1 (C), 143.3 (C),
142.1 (C), 140.8 (C), 132.8 (CH), 131.5 (CH), 126.7 (CH),
123.9 (CH), 116.8 (CH2), 116.6 (CH2), 24.0 (CH3), 18.7 (CH3).
Compounds 21 and 22 were obtained from 1a by the general
procedure as inseparable mixture and purified by column
chromatography (silica gel, hexane); colorless oil, total
yield 22%.
1
3.2.6. 3-Phenyl-2-[(E)-2-phenylvinyl]thiophene (21). H
NMR (600 MHz, CDCl3): d 7.43–7.45 (m, 2H), 7.33–7.42
(m, 7H), 7.29–7.33 (m, 1H), 7.27 (d, J¼16 Hz, 1H), 7.21 (d,
J¼5 Hz, 1H), 7.09 (d, J¼5 Hz, 1H), 6.99 (d, J¼16 Hz, 1H);
13C NMR (151 MHz, CDCl3): d 140.6 (C), 137.4 (C), 137.1
(C), 136.3 (C), 129.9 (CH), 129.1 (CH), [o, m and p of both
3.2.11. 5a,7a-Dimethyl-5a,6,7,7a-tetrahydrocyclobuta-
[3,4]benzo[1,2b]selenophene (26). Colorless oil; yield

Y. Zafrani et al. / Tetrahedron 59 (2003) 2641–2649
2649
23%; 1H NMR (600 MHz, CDCl3): d 7.73 (dd, J¼5.6,
0.6 Hz, 1H; 2JSe–H¼47.0 Hz), 7.17 (dd, J¼5.6, 0.8 Hz, 1H;
3JSe–H¼9.2 Hz), 6.35 (dd, J¼9.7, 0.8 Hz, 1H), 5.44 (dd, J¼
9.7, 0.6 Hz, 1H), 2.32 (ddd, J¼11.0, 9.0, 6.3 Hz, 1H), 2.19
(ddd, J¼10.8, 9.0, 6.2 Hz, 1H), 2.02 (ddd, J¼11.0, 9.0,
6.3 Hz, 1H), 1.90 (ddd, J¼10.8, 9.0, 6.2 Hz, 1H), 1.36 (s,
3H), 1.15 (s, 3H); 13C NMR (151 MHz, CDCl3): d 143.2
(C), 137.1 (C), 132.9 (CH), 129.1 (CH), 127.0 (CH), 119.7
(CH), 42.7 (C), 41.4 (C), 36.5 (CH2), 35.0 (CH2), 22.6
(CH3), 22.5 (CH3); MS (CI): m/z 234, 235, 236, 238, 240
3. Huntsman, W. D. In The Chemistry of Ketenes, Allenes and
Related Compounds; Part 1, Patai, S., Ed.; Wiley: London,
1980; pp 521–667.
4. Braverman, S.; Segev, D. J. Am. Chem. Soc. 1974, 96,
1245–1247.
5. Braverman, S.; Duar, Y.; Segev, D. Tetrahedron Lett. 1976,
3181–3184.
6. Braverman, S.; Reisman, D. J. Am. Chem. Soc. 1977, 99,
605–607.
7. Braverman, S.; Reisman, D. Tetrahedron Lett. 1977,
1753–1756.
(Mþ, 1:1:3:7:1, 63%), 210 (100%), 197 (36%); HRMS calcd
80
14
for C12H Se 238.0261; found 238.0280.
8. Braverman, S.; Cohen, D.; Reisman, D.; Basch, H. J. Am.
Chem. Soc. 1980, 102, 6556–6558.
3.2.12. 7-Methyl-4-methylene-4,5,6,9-tetrahydrocyclo-
octa[b]selenophene (27). Colorless oil; yield 4%; 1H
NMR (600 MHz, CDCl3): d 7.50 (d, J¼5.7 Hz, 1H), 7.16
(d, J¼5.7 Hz, 1H), 5.57 (tq, J¼7.0, 1.5 Hz, 1H), 5.09 (d,
J¼1.8 Hz, 1H), 4.98 (dt, J¼1.8, 1.0 Hz, 1H), 3.56 (d, J¼
7.0 Hz, 2H), 2.58–2.59 (m, 2H), 2.36–2.40 (m, 2H), 1.63–
1.70 (m, 3H); 13C NMR (151 MHz, CDCl3): d 133.5 (CH),
124.9 (CH), 121.6 (CH), 114.7 (CH2), 34.8 (CH2), 33.0
(CH2), 29.7 (CH2), 25.0 (CH3); MS (CI): m/z 234, 235, 236,
9. Braverman, S.; Duar, Y. J. Am. Chem. Soc. 1983, 105,
1061–1063.
10. Braverman, S.; Duar, Y. J. Am. Chem. Soc. 1990, 112,
5830–5837.
11. (a) Garratt, P. J.; Neoh, S. B. J. Am. Chem. Soc. 1975, 97,
3255–3257. (b) Garratt, P. J.; Neoh, S. B. J. Org. Chem. 1979,
44, 2667–2674.
12. Nicolaou, K. C.; Smith, A. L. In Modern Acetylene Chemistry;
Stang, P. S., Diedrich, F., Eds.; VCH: Weinheim, 1995;
pp 203–283.
238, 240 (Mþ, 1:1:3:7:1, 35%), 223 (100%); HRMS calcd
80
14
for C12H Se 238.0261; found 238.0290. Due to the small
13. Grissom, J. W.; Ganawardene, G. U.; Klingberg, D.; Huang,
D. Tetrahedron Report No. 399. Tetrahedron 1996, 52,
6453–6518.
amount of this product, quaternary carbons are not
observed.
14. Maier, M. E. Synlett 1995, 13–26.
3.2.13. 3-Methyl-4-phenyl-4H-thiopyran (32). The title
compound was obtained from 31 by the use of the general
procedure in 70% yield as yellowish oil, after purification by
column chromatography (silica gel, ethyl acetate–hexane
5:200). 1H NMR (600 MHz, CDCl3): d 7.30–7.34 (m, 5H),
6.16 (ddd, J¼10.0, 2.5, 1.2 Hz, 1H), 5.91 (dq, J¼2.5,
1.2 Hz, 1H), 5.74 (dd, J¼10.0, 5.1 Hz, 1H), 4.00 (d, J¼
5.1 Hz, 1H), 1.65 (dd, J¼1.2, 0.5 Hz, 3H); 13C NMR
(151 MHz, CDCl3): d 128.8 (CH), 128.1 (CH), 126.9 (CH),
122.9 (CH), 115.8 (CH), 110.7 (CH), 45.9 (CH), 23.7
(CH3); MS (CI): m/z 189 (MHþ, 100%), 157 (19.3%), 111
(93.7%); HRMS calcd for C12H13S 189.0738; found
189.0734.
15. Wang, K. K. Chem. Rev. 1996, 96, 207–222.
16. Pogozelski, W. K.; Tullius, T. D. Chem. Rev. 1998, 98,
1089–1107.
17. Maier, M. E.; Bosse, F.; Niestroj, A. J. Eur. J. Org. Chem.
1999, 1, 1–13.
18. Thorson, J. S.; Shen, B.; Whitwam, R. E.; Liu, W.; Li, Y.;
Ahlert, J. Bioorg. Chem. 1999, 27, 172–188.
19. Nicolaou, K. C.; Dai, W. M. Angew. Chem., Int. Ed. Engl.
1991, 30, 1387–1416, and references cited therein.
20. (a) Braverman, S.; Zafrani, Y.; Gottlieb, H. E. Tetrahedron
Lett. 2000, 41, 2675–2678. (b) Braverman, S.; Zafrani, Y.;
Gottlieb, H. E. Tetrahedron 2001, 57, 9177–9185.
21. Hopf, H.; Jones, P. G.; Bubenitschek, P.; Werner, C. Angew.
Chem., Int. Ed. Engl. 1995, 34, 2367–2368.
22. Braverman, S.; Zafrani, Y.; Gottlieb, H. E. J. Org. Chem.
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Acknowledgements
23. Iwai, I.; Ide, J. Chem. Pharm. Bull. Jpn 1964, 12, 1094–1100.
24. (a) Bartlett, A. J.; Laird, T.; Ollis, W. D. J. Chem. Soc. Perkin
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W. D. Chem. Commun. 1974, 496–497.
The financial support of this study by the Israel Science
Foundation is gratefully acknowledged.
25. Ishino, Y.; Mihara, M.; Nishihama, S.; Nishiguchi, I. Bull.
Chem. Soc. Jpn 1998, 71, 2669–2672.
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