Studies on the reactions of thiocarbonyl S-methanides with hetaryl thioketones

Article abstract of DOI:10.1002/hlca.201500057

Dihetaryl thioketones react with thiocarbonyl ylides to give 1,3-dithiolanes in high yields. No competitive side reactions of the thiocarbonyl ylides were observed, evidencing the 'superdipolarophilic' character of this less-known group of thioketones. De

Full text of DOI:10.1002/hlca.201500057

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Studies on the Reactions of Thiocarbonyl S-Methanides with Hetaryl
Thioketones
by Grzegorz Mloston´*a), Paulina Pipiaka)1), Anthony Lindenb), and Heinz Heimgartner*b)
a
´
´
) University of Łódz, Department of Organic and Applied Chemistry, Tamka 12, PL-91-403 Łódz
(phone: þ 48-42-6355761; fax: þ 48-42-6655162; e-mail: gmloston@uni.lodz.pl)
b) University of Zürich, Department of Chemistry, Winterthurerstrasse 190, CH-8057 Zürich
(phone: þ 41-44-6354282; fax: þ 41-44-6356812; e-mail: heinz.heimgartner@chem.uzh.ch)
Dihetaryl thioketones react with thiocarbonyl ylides to give 1,3-dithiolanes in high yields. No
competitive side reactions of the thiocarbonyl ylides were observed, evidencing the ꢀsuperdipolarophilicꢁ
character of this less-known group of thioketones. Depending on the type of substituents present in
both the thiocarbonyl ylide and the thioketone, formal [3 þ 2] cycloadditions occur with complete
regioselectivity or with formation of a mixture of both regioisomers. Regioselective formation of the
sterically more crowded 1,3-dithiolanes is explained via a mechanism involving stabilized 1,5-biradicals.
In systems with less-efficient radical stabilization, e.g., in the case of adamantanethione S-methanide,
substantial violation of the regioselectivity was observed as a result of steric hindrance.
Introduction. – Thiocarbonyl ylides belong to the class of the so-called S-centered
1,3-dipoles, and they are widely used for the preparation of S-heterocycles with diverse
sizes of the formed ring [1]. The reactive thiocarbonyl S-methanides, generated via
thermal N2 elimination from 2,5-dihydro-1,3,4-thiadiazoles, easily react with various
dipolarophiles, and special attention is paid to their reactions with ꢀsuperdipolarophilicꢁ
thioketones [2]. These reactions, leading to 1,3-dithiolane derivatives (Schçnberg
reaction [3]), are of interest not only for the preparation of these products, but also for
studies on organic reaction mechanisms. Important features of these reactions are the
regioselectivity and the nature of the postulated intermediates. Whereas S-methanides
of cycloaliphatic thioketones, e.g., adamantane-2-thione S-methanide (1a), react with
adamantane-2-thione (2a) to give the sterically less-hindered 2,2,4,4-tetrasubstituted
1,3-dithiolane of type 3a, the reaction of 1a with 9H-fluorene-9-thione (2b) gave a ca.
1:3 mixture of the regioisomeric 1,3-dithiolanes 3b and 4b in favor of the sterically
more crowded isomer [4] (Scheme 1). On the other hand, S-methanides derived from
aromatic thioketones, e.g., thiobenzophenone S-methanide (1b), react with thioben-
zophenone (2c) to give the 4,4,5,5-tetrasubstituted 1,3-dithiolane of type 4c as the sole
product [3a].
Recently, we described the synthesis and selected reactions of aryl/hetaryl and
dihetaryl thioketones [5]. Unexpectedly, the experiments with CH2N2 revealed that the
presence of a hetaryl substituent such as thiophen-2-yl, selenophen-2-yl, or furan-2-yl
results in a spontaneous evolution of N2 even at À 608. In contrast to thiobenzophe-
1
´
)
Part of the planned Ph.D. thesis of P. P., University of Łódz.
ꢂ 2015 Verlag Helvetica Chimica Acta AG, Zürich

Helvetica Chimica Acta – Vol. 98 (2015)
463
Scheme 1
none, the precursors of the corresponding S-methanides of type 1, i.e., 2,5-dihydro-2,2-
diaryl-1,3,4-thiadiazoles 5 (cf. Scheme 2), could not be prepared in solution. Instead, a
reactive intermediate trapped the starting thioketone 2 and yielded the sterically more
crowded 1,3-dithiolane in a regioselective manner. However, in the case of phenyl
selenophen-2-yl thioketone (2e), the formation of a second product, a novel macro-
cyclic dimer of the thiocarbonyl S-methanide was observed [6]. Based on these results,
we proposed that the intermediate ꢀthiocarbonyl ylideꢁ displays a biradical character.
Thus, the formation of the twelve-membered cyclodimer can be considered as
experimental evidence for the formation of a delocalized biradical. An earlier
computational study suggested the participation of a 1,5-biradical in the formation of
1,3-dithiolane derivatives via formal [3 þ 2] cycloaddition of thioketones with
thiocarbonyl S-methanides [7].
The aim of the present study was the investigation of the formation of 1,3-
dithiolanes via formal [3 þ 2] cycloaddition of thiocarbonyl S-methanides and aryl/
hetaryl and dihetaryl thioketones. Of special interest is the regioselectivity of the ring
formation.
Results and Discussion. – The thermal decomposition of 2,2-disubstituted 2,5-
dihydro-1,3,4-thiadiazoles 5 is considered as a straightforward method for the in situ
generation of reactive thiocarbonyl S-methanides of type 1 [1a][8]. The stability of
these precursors strongly depends on the type of substitutents, and the presence of
bulky cycloaliphatic groups allows them to be prepared as crystalline, shelf-stable
compounds. On the other hand, 2,2-diaryl-substituted 2,5-dihydro-1,3,4-thiadiazoles 5
(Scheme 2) can be prepared only at low temperature and have to be used as
thiocarbonyl S-methanide precursors at À 408 without being isolated.

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Scheme 2
According to the typical procedure for the generation of diaryl-substituted
thiocarbonyl S-methanides of type 1b, solutions of thiobenzophenone (2c) or 9H-
fluorene-9-thione (2b) in THF were treated with CH2N2 at À 608. Equimolar amounts
of hetarylphenyl, or dihetaryl thioketones, 2d and 2e, or 2f and 2g, respectively, were
added to the colorless solutions, and the mixtures were warmed to À 408. After N2
1
evolution had finished, the crude products were analyzed by H-NMR spectroscopy
with a weighed amount of 1,1,2,2-tetrachloroethane as a standard. In all reactions, only
one product was obtained in good yields and identified as the sterically crowded 4,4,5,5-
tetrasubstituted 1,3-dithiolane 4 (Scheme 2). The proposed structures of the products
were elucidated from the characteristic absorption of the CH2(2) group in the
13C-NMR spectra at 30.5 – 32.5 ppm [3].
In the second series, adamantane-2-thione S-methanide (1a) was generated from its
precursor 5a at 458 in THF in the presence of equimolar amounts of thioketones 2. In all
cases, the formation of mixtures of regioisomeric 1,3-dithiolanes was indicated by
1H-NMR spectroscopy (weighed standard). In analogy to earlier reported products
obtained from 1a and aromatic thioketones 2c and 2b (Scheme 1), the major products
were identified as the sterically more crowded 4,4,5,5-tetrasubstituted 1,3-dithiolanes of
type 4 (Scheme 3). The isomer ratios 3/4 established by NMR spectroscopy were
between ca. 1:3 and 1:4, and in the case of the mixtures of 3e/4k and 3h/4n, the major
products 4k and 4n, respectively, were isolated as pure crystalline compounds and fully
characterized.
Reactions with the 2,2,4,4-tetramethyl-3-thioxocyclobutanone S-methanide with
hetaryl phenyl thioketones 2d and 2e, as well as with the dihetaryl thioketone 2h, led

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465
Scheme 3
also to mixtures of regioisomeric 1,3-dithiolanes 3 and 4, with the sterically more
crowded product of type 4 as the major component (Scheme 4). In comparison with the
series of 1,3-dithiolanes obtained in the case of 1a (Scheme 3), the ratio of isomers
increased in favor of the sterically more crowded isomers of type 4. However, the
analogous reactions with di(thiophen-2-yl) thioketone (2f) and di(selenophen-2-yl)
thioketone (2g) led to the sterically more crowded 1,3-dithiolanes 4r and 4s,
respectively, as the sole products.
Finally, the structure of compound 4r, deduced from the NMR data, was
unambiguously confirmed by X-ray crystallography (Fig.). Although the molecule is
achiral, the compound has crystallized in a chiral space group, and the absolute
structure has been determined by the diffraction experiment. There are two symmetry-
independent molecules in the asymmetric unit. Both molecules show disorder of the
thiophene rings due to 1808 rotation of each ring around its parent CÀC bond. The five-
membered dithiolane ring in each molecule has a half-chair conformation twisted on
the CÀC bond.
Scheme 4

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Figure. ORTEP Plot [9] of the molecular structure of one of the two symmetry-independent molecules of
4r (with 50% probability ellipsoids; arbitrary numbering of the atoms; only the major conformations of
the disordered thiophene rings are shown)
It is worth mentioning that the thiocarbonyl ylides 1a – 1d reacted with hetaryl
thioketones 2 without competitive formation of 1,4-dithianes or thiiranes (see [1a][8]).
These results confirm that hetaryl thioketones belong to the group of ꢀsuperdipolar-
ophilesꢁ in reactions with thiocarbonyl S-methanides [2]. According to Huisgenꢁs
reactivity scale, the most reactive thioketone is 9H-fluorene-9-thione (2b), followed by
thiobenzophenone (2c). For comparison purposes, the competition experiments of
thiobenzophenone S-methanide (1b) with equimolar amounts of 2b and di(thiophen-2-
yl) thioketone (2f), as well as with 2c and 2f, were performed in THF at ca. À 408. The
1
obtained products were analyzed by H-NMR spectroscopy. In the first case, the only
product formed was the sterically crowded 5,5-diphenylspiro[1,3-dithiolane-4,9’-
[9H]fluorene [3b]. In the second experiment, however, the ratio of 4c/4f was
determined to be ca. 4 :3. These results indicate that the symmetrical hetaryl
thioketone 2f is less reactive than 9H-fluorene-9-thione (2b), but almost as reactive
as thiobenzophenone (2c).
Conclusions. – The present study revealed that hetaryl thioketones extend the
group of ꢀsuperdipolarophilesꢁ in reactions with thiocarbonyl S-methanides 1. The
observed regioselectivity of the 1,3-dithiolane formation evidences that the formal [3 þ
2] cycloaddition occurs, most likely, via biradical intermediates. The latter mechanism
leads to complete regioselectivity only when the heteroatom-containing substituents
stabilize the biradical structure, e.g., via delocalization in tetraaryl-substituted systems
(cf. [6]). In such systems, the intermediate 1,5-biradical 6a is the precursor of the

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sterically crowded 4,4,5,5-tetrasubstituted 1,3-dithiolane, such as 4d – 4h [7] (cf.
Scheme 2). The same regioisomers were only obtained as sole products in the reaction
of 2,2,4,4-tetramethyl-3-thioxocyclobutanone S-methanide (1c) with dihetaryl thioke-
tones 2f and 2g, which possess S- or Se-atoms in both heterocycles. In these cases, the
stabilization of the 1,5-biradical intermediate 6b results from delocalization within the
hetaryl rings and, likely, from an additional stabilizing effect across the cyclobutanone
ring [10]. The presence of Se- or S-atoms in the five-membered heteroaromatic rings is
essential for the exclusive formation of an intermediate of type 6b (see also [6]). Both
heteroatoms are known to stabilize radicals in the a-position.
In the presented cases, electronic effects are decisive; however, in the reactions with
adamantanethione S-methanide (1a), no radical stabilization is possible at the
adamantane-substituted terminus of the intermediate. Accordingly, the influence of
steric factors is of increasing importance, and the formation of the sterically less
crowded 1,3-dithiolanes as minor products is also observed in all cases.
In summary, the results presented herein, additionally supported by computational
studies [7], evidence that, in the case of S-centered thiocarbonyl ylides, some of the
formal [3 þ 2] cycloadditions occur stepwise via biradical intermediates. This con-
clusion supports the concept of the radical character of ꢀ1,3-dipolar cycloaddition
reactionsꢁ formulated by Firestone [11], at least for some systems with the required
structural features.
The authors thank the National Science Center (PL-Cracow) for financial support within the project
Maestro (Grant Maestro-3; Dec-2012/06/A/ST5/00219).
Experimental Part
1. General. M.p.: MEL-TEMP. II (Aldrich); uncorrected. Column chromatography (CC): silica gel
1
(70 – 230 mesh; Merck). IR Spectra: NEXUS FT-IR instrument; in KBr; n˜ in cmÀ1. H- and 13C-NMR
spectra: Bruker Avance III instrument; at 600 and 150 MHz, resp., with the solvent signal as reference; in
CDCl3; d in ppm; J in Hz; ad, adamanthane. ESI-MS: Varian 500 MS LC ion trap spectrometer; in m/z
(rel. %). Elemental analyses were performed in the Laboratory of the Faculty of Chemistry, University
´
of Łódz; in%.
2. Starting Materials. 1,1,3,3-Tetramethyl-8-thia-5,6-diazaspiro[3.4]oct-5-en-2-one (5d) [12] and
spiro[1,3,4-thiadiazole-2(5H),2’-tricyclo[3.3.1.13,7]decane] (5a) [13] were prepared by known methods.
9H-Fluorene-9-thione (2b), thiobenzophenone (2c), the nonsymmetrical heteroaromatic thioketones
phenyl(thiophen-2-yl)methanethione (2d), phenyl(selenophen-2-yl)methanethione (2e), and (furan-2-
yl)(thiophen-2-yl)methanethione (2h), as well as the symmetrical heteroaromatic thioketones di(thio-
phen-2-yl)methanethione (2f) and di(selenophen-2-yl)methanethione (2g) were obtained from the

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corresponding ketones according to the known thionation procedure with Lawssonꢁs reagent [5]. Other
reagents used were commercially available.
3. Reactions of Hetaryl Phenyl Thioketones 2d – 2e or Dihetaryl Thioketones 2f – 2g with 2,5-Dihydro-
2,2-diphenyl-1,3,4-thiadiazole (5c). General Procedure. Thiobenzophenone (2c; 1 mmol) dissolved in
2 ml of THF was cooled to À 708 and treated with small portions of ethereal CH2N2 soln. until the dark-
blue color disappeared. A soln. of the corresponding thioketone 2d – 2g (1 mmol) in 2 ml of THF was
added at À 708, and the mixture was kept in a cold bath (À458 to À 408, acetone/dry ice) for 2.5 h. Then,
the mixture was allowed to warm slowly to r.t. During the reaction, a colorless precipitate was formed.
The mixture was kept at r.t. for ca. 30 min. Then, the solvent was evaporated, and the crude product was
purified by crystallization or by treatment with small portions of hexane.
3.1. 4,4,5-Triphenyl-5-(thiophen-2-yl)-1,3-dithiolane (4d). Reaction with 2d; purification by crystal-
lization from CH2Cl2/hexane. Yield: 320 mg (77%). Colorless crystals. M.p. 175.2 – 176.58 (CH2Cl2/
1
hexane). IR: 3050w, 1597w, 1488m, 1440m, 1233m, 1033w, 747m, 722m, 708s. H-NMR: 3.01, 3.89 (AB,
JAB ¼ 9.6, CH2); 6.76 – 6.77 (m, 1 arom. H); 6.85 (d, J ¼ 3.6, 1 arom. H); 7.10 – 7.20 (m, 10 arom. H); 7.39 –
7.43 (m, 4 arom. H); 7.50 (d, J ¼ 8.4, 2 arom. H). 13C-NMR: 30.5 (CH2(2)); 74.5, 78.3 (C(4,5)); 125.1,
125.6, 126.3, 126.4, 126.6, 126.7, 126.8, 127.0, 130.0, 130.6, 131.4, 131.8 (18 arom. CH); 142.3, 143.0 (br., 4
arom. C). HR-ESI-MS: 416.072719 (Mþ, C25H20S3þ ; calc. 416.073100).
3.2. 4,4,5-Triphenyl-5-(selenophen-2-yl)-1,3-dithiolane (4e). Reaction with 2e; purification by
crystallization from CH2Cl2/hexane. Yield: 320 mg (70%). Colorless crystals. M.p. 177.4 – 178.88
(CH2Cl2/hexane). IR: 3049w, 1597w, 1489m, 1439m, 1232m, 1186w, 1083w, 1034w, 746m, 716s, 696s.
1H-NMR: 3.81, 3.90 (AB, JAB ¼ 9.6, CH2); 7.00 – 7.01 (m, 2 arom. H); 7.07 – 7.19 (m, 9 arom. H); 7.37 (d,
J ¼ 7.2, 2 arom. H); 7.46 – 7.50 (m, 4 arom. H); 7.89 (dd, J ¼ 4.8, 1.8, 1 arom. H). 13C-NMR: 30.6 (CH2(2));
76.4, 78.2 (C(4,5)); 126.2, 126.6, 126.7, 126.7, 126.9, 127.1, 127.9, 130.6, 131.6, 131.8, 131.9 (18 arom. CH);
142.7, 142.8 (br., 4 arom. C). Anal. calc. for C25H20S2Se (463.53): C 64.78, H 4.35, S 13.83; found: C 64.55,
H 4.38, S 13.75.
3.3. 4,4-Diphenyl-5,5-di(thiophen-2-yl)-1,3-dithiolane (4f). Reaction with 2f; purification by
repeated treatment with small portions of hexane. Yield: 320 mg (76%). Colorless crystals. M.p.
192.7 – 193.48. IR: 3095w, 3068w, 1595w, 1488m, 1440m, 1238m, 1086w, 849w, 747s, 734m, 707s. 1H-NMR:
3.94 (s, CH2); 6.80 (dd, J ¼ 5.4, 3.6, 2 arom. H); 7.03 (dd, J ¼ 3.6, 1.2, 2 arom. H); 7.10 – 7.18 (m, 8 arom.
H); 7.40 – 7.41 (m, 4 arom. H). 13C-NMR: 31.4 (CH2(2)); 71.4, 79.1 (C(4,5)); 125.6, 125.7, 126.5, 126.9,
129.1, 131.4 (16 arom. CH); 142.2, 147.9 (4 arom. C). ESI-MS (MeOH): 461 (55, [M þ K]þ), 445 (45,
[M þ Na]þ), 423 (100, [M þ H]þ). Anal. calc. for C23H18S4 (422.64): C 65.36, H 4.29, S 30.35; found: C
64.81, H 4.39, S 30.32.
3.4. 4,4-Diphenyl-5,5-di(selenophen-2-yl)-1,3-dithiolane (4g). Reaction with 2g; purification by
repeated treatment with small portions of hexane. Yield: 310 mg (58%). Colorless crystals. M.p. 184.8 –
185.38. IR: 3096w, 3050w, 1624w, 1487w, 1439m, 1227m, 1033w, 729m, 697s. 1H-NMR: 3.99 (s, CH2); 7.08 –
7.09 (m, 2 arom. H); 7.13 – 7.19 (m, 6 arom. H); 7.30 (dd, J ¼ 4.2, 1.2, 2 arom. H); 7.45 – 7.46 (m, 4 arom.
H); 7.89 (dd, J ¼ 5.4, 1.2, 2 arom. H). 13C-NMR: 31.6 (CH2(2)); 75.2, 78.9 (C(4,5)); 126.5, 127.0, 128.3,
130.9, 131.5, 132.1 (16 arom. CH); 142.4, 145.0 (br., 4 arom. C). Anal. calc. for C23H18S2Se2 (516.44): C
53.49, H 3.51, S 12.42; found: C 53.58, H 3.65, S 12.63.
4. Reaction of Spiro[9H-fluorene-9,2’(5’H)-[1,3,4]thiadiazole] (5b) with di(thiophen-2-yl)methane-
thione (2f). A soln. of 2b (1 mmol) in 2 ml of THF was cooled to À 708 and treated with small portions of
a soln. of CH2N2 in Et2O, until the green soln. became yellow. Then, a soln. of 2f (1 mmol) in 2 ml of THF
was added at À 708, and the mixture was kept in a cold bath (À458 to À 408, acetone/dry ice) for 1 h.
Then, the mixture was allowed to warm slowly to r.t., whereby a colorless precipitate was formed. The
mixture was kept at r.t. for ca. 30 min, then the solvent was evaporated, and the residue was crystallized
from CH2Cl2/hexane.
5,5-Di(thiophen-2-yl)spiro[1,3-dithiolane-4,9’-[9H]fluorene] (4h). Yield: 295 mg (70%). Colorless
crystals. M.p. 216.4 – 218.08 (CH2Cl2/hexane). IR: 3066w, 2924w, 1624w, 1446m, 1427w, 1227m, 1239m,
1048w, 1034w, 851w, 789s, 745s, 736s, 719s, 706s. 1H-NMR: 4.50 (s, CH2); 6.61 (dd, J ¼ 3.6, 1.2, 2 arom. H);
6.74 (dd, J ¼ 5.4, 3.6, 2 arom. H); 7.07 – 7.13 (m, 6 arom. H); 7.32 – 7.35 (m, 2 arom. H); 7.69 (d, 2J ¼ 7.2, 2
arom. H). 13C-NMR: 32.5 (CH2(2)); 70.3, 75.5 (C(4,5)); 119.8, 125.3, 125.7, 125.9, 127.5, 127.8, 128.6 (14
arom. CH); 140.2, 144.1, 147.9 (6 arom. C). ESI-MS (MeOH): 443 (100, [M þ Na]þ).

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5. Reactions of Hetaryl Phenyl Thioketones 2d – 2e or Dihetaryl Thioketones 2f – 2h with 5a. General
Procedure. Compound 5a (1.1 mmol) and the corresponding thioketone 2 (1.05 mmol) were dissolved in
freshly distilled THF (2.5 ml). The mixture was heated in an oil bath (45 – 508), until the intense color of
the thioketone vanished; the gas burette combined with the flask indicated the evolution of
stoichiometric amounts of N2. After removal of the solvent under vacuum, the residue was subjected
1
to H-NMR analysis in CDCl3 soln. with a weighed amount of 1,1,2,2-tetrachloroethane as a standard.
Crude products were purified by CC (CH2Cl2/petroleum ether (PE) 4 :6). In all cases, formation of
mixtures of regioisomeric 1,3-dithiolanes 3 and 4 was observed.
5.1. Reaction with 2d: 5-Phenyl-5-(thiophen-2-yl)spiro[1,3-dithiolane-4,2’-tricyclo[3.3.1.13,7]decane]
(4i; major) and 4-Phenyl-4-(thiophen-2-yl)spiro[1,3-dithiolane-2,2’-tricyclo[3.3.1.13,7]decane] (3d; mi-
nor) (crude product ratio 75 :25). Reaction time: 8 h. Isolated as a mixture of isomers. Yield: 332 mg
(82%). Yellow crystals. M.p. 139.8 – 141.08. IR: 2905s, 2855s, 1443m, 1233w, 1220w, 1099w, 743w, 708w.
1H-NMR: 1.19 – 3.04 (m, 28 H); 3.50, 3.56 (AB, JAB ¼ 9.0, CH2 of 4i); 3.83, 3.94 (AB, JAB ¼ 12.6, CH2 of
3d); 6.78 – 7.94 (m, 16 arom. H). 13C-NMR: 26.3, 26.4, 26.6, 26.8, 36.4, 36.8, 42.0, 42.1 (8 CH(ad)); 27.2
(CH2(2) of 4i); 33.2, 33.6, 36.5, 36.5, 36.6, 36.9, 37.6, 38.2, 38.9, 40.5 (10 CH2(ad)); 50.2 (CH2(5) of 3d);
70.5, 75.4, 77.6, 78.5 (2 C(4), 2 C(5)); 124.8, 125.0, 126.0, 126.1, 126.6, 127.2, 127.4, 127.9, 128.1, 128.8, 130.8
(16 arom. CH); 140.8, 148.5 (2 arom. C of 4i); 144.0, 151.2 (2 arom. C of 3d). Anal. calc. for C22H24S3
(384.63): C 68.70, H 6.29, S 25.01; found: C 68.37, H 6.00, S 25.01.
5.2. Reaction with 2e: 5-Phenyl-5-(selenophen-2-yl)spiro[1,3-dithiolane-4,2’-tricyclo[3.3.1.13,7]de-
cane] (4k; major) and 4-Phenyl-4-(selenophen-2-yl)spiro[1,3-dithiolane-2,2’-tricyclo[3.3.1.13,7]decane]
(3e; minor) (crude product ratio 77:23). Reaction time: 7 h. After chromatography, 4k and 3e were
isolated as a mixture of regioisomers. Yield: 358 mg (80%). After repeated crystallization from hexane,
4k was isolated in pure form. Colorless crystals. M.p. 152.1 – 153.08 (hexane). IR: 2903s, 2858m, 1441m,
1231m, 1221m, 709s, 695m, 684s. 1H-NMR: 1.04 – 3.05 (m, 14 H); 3.54, 3.60 (AB, JAB ¼ 8.4, CH2); 7.17 –
2
2
7.96 (m, 4 arom. H); 7.59 (d, J ¼ 3.6, 1 arom. H); 7.83 (d, J ¼ 6.6, 1 arom. H); 7.96 (br. s, 2 arom. H).
13C-NMR: 26.7, 26.9, 36.4, 37.1 (4 CH(ad)); 27.5 (CH2(2)); 33.2, 33.3, 38.0, 39.0, 40.8 (5 CH2(ad)); 77.5, 77.6
(C(4,5)); 127.5, 128.0, 129.1, 130.5, 130.9 131.0 (8 arom. CH); 140.8, 157.2 (2 arom. C). Anal. calc. for
C22H24S2Se (431.52): C 61.24, H 5.61, S 14.86; found: C 61.17, H 5.39, S 15.16.
Spectroscopic Data of 3e (from the spectra of a mixture of 3e with the major product 4k). 1H-NMR:
1.04 – 3.05 (m, 14 H); 3.78 – 3.96 (m, CH2); 7.17 – 7.96 (m, 8 arom. H). 13C-NMR: 26.3, 26.4, 41.9, 42.0
(4 CH(ad)); 36.3, 36.6, 36.6, 37.0, 37.6 (5 CH2(ad)); 50.6 (CH2(5)); 72.5, 78.5 (C(2,4)); 127.1, 127.4, 127.8,
127.9, 129.0, 130.7 (8 arom. CH); 144.2, 159.3 (2 arom. C).
5.3. Reaction with 2f: 5,5-Di(thiophen-2-yl)spiro[1,3-dithiolane-4,2’-tricyclo[3.3.1.13,7]decane] (4l;
major) and 4,4-Di(thiophen-2-yl)spiro[1,3-dithiolane-2,2’-tricyclo[3.3.1.13,7]decane] (3f; minor) (crude
product ratio 82 :18). Reaction time: 9 h. Isolated as a mixture of isomers. Yield: 309 mg (76%). Yellow
crystals. M.p. 127.0 – 128.78. IR: 2899s, 2851s, 1628w, 1442m, 1425m, 1225m, 1097m, 707s, 697s. 1H-NMR:
1.48 – 2.82 (m, 28 H); 3.78 (s, CH2 of 4l); 3.93 (s, CH2 of 3f); 7.00 – 7.41 (m, 12 arom. H). 13C-NMR: 26.2,
26.3, 26.9, 35.6, 42.0 (8 CH(ad)); 26.8 (CH2(2) of 4l); 32.9, 36.4, 36.7, 37.5, 38.8, 39.1 (10 CH2(ad)); 52.4
(CH2(5) of 3f); 67.3, 72.0, 76.5, 79.0 (2 C(4), 2 C(5)); 125.1, 125.1, 125.9, 126.6, 127.7, 127.0 (12 arom. CH);
147.9 (2 arom. C of 4l); 150.0 (2 arom. C of 3f). ESI-MS (MeOH): 391 (100, [M þ H]þ).
5.4. Reaction with 2g: 5,5-Di(selenophen-2-yl)spiro[1,3-dithiolane-4,2’-tricyclo[3.3.1.13,7]decane]
(4m; major) and 4,4-Di(selenophen-2-yl)spiro[1,3-dithiolane-2,2’-tricyclo[3.3.1.13,7]decane] (3g; minor)
(crude product ratio 74 :26.) Reaction time: 8 h. Isolated as a mixture of isomers. Yield: 325 mg (64%).
M.p. 151.8 – 153.08. IR: 2926s, 2899s, 2845s, 1625w, 1439m, 1234m, 1220m, 1097m, 717m, 695s, 703s.
1H-NMR: 1.39 – 2.76 (m, 28 H); 3.72 (s, CH2 of 4m); 3.82 (s, CH2 of 3g); 7.07 – 7.81 (m, 12 arom. H).
13C-NMR: 26.3, 26.4, 27.0, 27.1, 35.7, 41.9 (8 CH(ad)); 27.3 (CH2(2) of 4m); 33.1, 38.9, 39.1, 36.5, 36.7, 37.5
(10 CH2(ad)); 53.4 (CH2(5) of 3g); 71.5, 79.3, 76.4, 76.4 (2 C(4), 2 C(5)); 127.7, 129.3, 131.0, 129.2, 130.1,
131.6 (12 arom. CH); 156.7 (2 arom. C of 3g), 158.0 (2 arom. C of 4m). Anal. calc. for C20H22S2Se2
(484.45): C 49.59, H 4.58, S 13.24; found: C 49.81, H 4.45, S 13.66.
5.5. Reaction with 2h: 5-(Furan-2-yl)-5-(thiophen-2-yl)spiro[1,3-dithiolane-4,2’-tricyclo[3.3.1.13,7]de-
cane] (4n; major) and 4-(Furan-2-yl)-4-(thiophen-2-yl)spiro[1,3-dithiolane-2,2’-tricyclo[3.3.1.13,7]de-
cane] (3h; minor) (crude product ratio 77:23). Reaction time: 5 h. After CC, 4n and 3h were isolated
as a mixture of regioisomers. Yield: 340 mg (86%). After repeated crystallization from hexane, 4n was

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Helvetica Chimica Acta – Vol. 98 (2015)
isolated in pure form. Yellow crystals. M.p. 120.2 – 121.28. IR: 2899s, 2853s, 1636w, 1449m, 1235m, 1149m,
1097m, 1021m, 751m, 727s, 693s. 1H-NMR: 1.02 – 2.74 (m, 14 H); 3.73, 3.84 (AB, JAB ¼ 9.0, CH2); 6.33 (dd,
J ¼ 3.0, 1.8, 1 arom. H); 6.75 (dd, J ¼ 3.6, 1.2, 1 arom. H); 6.99 (dd, J ¼ 5.4, 3.6, 1 arom. H); 7.20 (dd, J ¼
4.8, 1.2, 1 arom. H); 7.43 – 7.44 (m, 2 arom. H). 13C-NMR: 26.4 (CH2(2)); 26.9, 27.2, 35.0, 35.7 (4 CH(ad));
32.6, 33.1, 38.3, 39.2, 40.0 (5 CH2(ad)); 69.8, 77.1 (C(4,5)); 111.0, 112.3, 124.8, 126.6, 127.5, 141.4 (6 arom.
CH); 146.5, 152.1 (2 arom. C). Anal. calc. for C20H22OS3 (374.59): C 64.13, H 5.92, S 25.68; found: C
64.05, H 6.00, S 25.65.
Spectroscopic Data of 3h (from the spectra of a mixture of 3h with the major product 4n). 1H-NMR:
1.02 – 2.74 (m, 14 H); 3.75 – 4.03 (m, CH2); 6.32 – 7.38 (m, 6 arom. H). 13C-NMR: 26.2, 26.4, 42.0, 42.1
(4 CH(ad)); 36.3, 36.5, 36.7, 36.9, 37.6 (5 CH2(ad)); 48.8 (CH2(5)); 65.5, 78.8 (C(2,4)); 109.0, 110.3, 125.1,
125.7, 126.6, 142.1 (6 arom. CH); 147.6, 155.8 (2 arom. C).
6. Reactions of Hetaryl Phenyl Thioketones 2d – 2e or Dihetaryl Thioketones 2f – 2h with 5d. General
Procedure. A soln. of 5d (1.1 mmol) and a thioketones 2d – 2h (1.05 mmol) in freshly dist. THF (2.5 ml)
was heated in an oil bath (45 – 508), until the color of the thioketone disappeared; a gas burette indicated
the liberation of a stoichiometric amount of N2. After removal of the solvent under vacuum, the residue
1
was subjected to H-NMR analysis in CDCl3 with a weighed amount of 1,1,2,2-tetrachloroethane as a
standard.
6.1. Reaction with 2d: 1,1,3,3-Tetramethyl-8-phenyl-8-(thiophen-2-yl)-5,7-dithiaspiro[3.4]octan-2-one
(4o; major) and 1,1,3,3-Tetramethyl-6-phenyl-6-(thiophen-2-yl)-5,8-dithiaspiro[3.4]octan-2-one (3i; mi-
nor) (crude product ratio 86 :14). Reaction time: 3.5 h. The crude mixture was purified by CC (CH2Cl2/
hexane 4 :6). Product isolated as a mixture of regioisomers. Yield: 372 mg (94%). Colorless crystals. M.p.
109.0 – 112.08. IR: 1778s (C¼O), 1636w, 1597w, 1443m, 1230m, 1164m, 1022m, 744m, 707s. 1H-NMR: 1.26,
1.33, 1.36, 1.38, 1.47, 1.58, 1.65, 1.72 (8s, 8 Me); 3.62 – 3.66 (m, CH2 of 4o); 3.83, 3.92 (AB, JAB ¼ 12.0, CH2
of 3i); 6.86 – 7.82 (m, 16 arom. H). 13C-NMR: 22.3, 22.5, 24.6, 24.8, 24.8, 25.5, 25.68, 25.70 (8 Me); 26.8
(CH2(6) of 4o); 51.7 (CH2(7) of 3i); 66.5 (br.), 66.6, 67.0, 68.8 (br.) (2 C(1), 2 C(3)); 71.0, 74.5, 75.8, 76.1
(C(4), C(8) of 4o, C(4), C(7) of 3i); 125.2, 126.1, 126.3, 126.6, 127.4, 127.6, 127.7, 127.9, 128.1, 128.4, 129.1,
130.2 (16 arom. CH); 132.2, 134.1 (2 arom. C of 3i); 143.4, 150.3 (2 arom. C of 4o); 219.9 (C¼O of 4o);
220.1 (C¼O of 3i). Anal. calc. for C20H22OS3 (374.59): C 64.13, H 5.92, S 25.68; found: C 64.02, H 5.93, S
25.95.
6.2. Reaction with 2e: 1,1,3,3-Tetramethyl-8-phenyl-8-(selenophen-2-yl)-5,7-dithiaspiro[3.4]octan-2-
one (4p; major) and 1,1,3,3-Tetramethyl-6-phenyl-6-(selenophen-2-yl)-5,8-dithiaspiro[3.4]octan-2-one
(3k; minor) (crude product ratio 92 :8). Reaction time: 6.5 h. The crude product was crystallized from
CH2Cl2/MeOH. Yield: 420 mg (95%). Colorless crystals. M.p. 140.0 – 142.08. IR: 1170s (C¼O), 1443m,
1227m, 1164w, 1020w, 706s, 695s. 1H-NMR: 1.23, 1.25, 1.28, 1.31, 1.47, 1.61, 1.62, 1.71 (8s, 8 Me); 3.70 – 3.74
(m, CH2 of 4p); 3.78 – 3.92 (m, CH2 of 3k); 7.13 – 7.97 (m, 16 arom. H). 13C-NMR: 22.1, 22.5, 24.5, 24.8,
25.2, 25.5, 25.7, 25.8 (8 Me); 27.0 (CH2(6) of 4p); 52.1 (CH2(7) of 3k); 60.2, 65.4, 66.2, 69.7 (2 C(1),
2 C(3)); 67.1, 73.0, 76.1, 76.7 (C(4), C(8) of 4p, C(4), C(7) of 3k); 127.4, 127.5, 127.8, 128.0, 128.3, 128.4
(br.), 128.9, 129.1, 130.8 (br.), 130.9, 131.3, 131.7 (16 arom. CH); 140.8, 160.8, 143.5, 158.1 (4 arom. C);
219.7, 219.9 (2 C¼O). Anal. calc. for C20H22OS2Se (421.49): C 56.99, H 5.26, S 15.21; found: C 56.55, H
5.12, S 15.17.
6.3. Reaction with 2h: 1,1,3,3-Tetramethyl-8-(furan-2-yl)-8-(thiophen-2-yl)-5,7-dithiaspiro[3.4]octan-
2-one (4q; major) and 1,1,3,3-Tetramethyl-6-(furan-2-yl)-6-(thiophen-2-yl)-5,8-dithiaspiro[3.4]octan-2-
one (3l; minor) (crude product ratio 94 :6). Reaction time: 4 h. The crude product was purified by CC
(CH2Cl2/hexane 4 :6). Yield: 370 mg (96%). Yellow crystals. M.p. 130.0 – 132.48. IR: 1784s (C¼O),
1464m, 1381s, 1227s, 1130m, 1074m, 1027s, 1016s, 808s, 742s, 695s, 593m. 1H-NMR: 0.81, 1.24, 1.29, 1.34,
1.38, 1.45, 1.57, 1.59 (8s, 8 Me); 3.61 – 3.92 (m, CH2 of 3l); 3.86 – 3.90 (m, CH2 of 4q); 6.35 – 7.44 (m, 12
arom. H). 13C-NMR: 19.3, 22.1, 22.4, 23.3, 24.6, 24.7 28.3, 28.9 (8 Me); 29.1 (CH2(6) of 4q); 50.6 (CH2(7)
of 3l); 65.6, 66.6, 67.0, 67.3 (2 C(1), 2 C(3)); 65.0, 67.2, 76.8, 77.3 (C(4,8) of 4q, C(4,7) of 3l); 109.1, 110.4,
111.6, 112.0, 125.3, 125.7, 126.0, 126.2, 126.4, 126.8, 140.8, 142.4 (12 arom. CH); 146.8, 148.1, 155.0, 152.2 (4
arom. C); 219.4, 219.7 (2 C¼O). Anal. calc. for C18H20O2S3 (364.55): C 59.31, H 5.53, S 26.39; found: C
58.93, H 5.19, S 26.04.
6.4. Reaction with 2f: 1,1,3,3-Tetramethyl-8,8-di(thiophen-2-yl)-5,7-dithiaspiro[3.4]octan-2-one (4r).
The reaction was complete after 2 h. The solvent was evaporated, and the crude product was purified by

Helvetica Chimica Acta – Vol. 98 (2015)
471
CC (CH2Cl2/hexane 4 :6). Yield: 320 mg (81%). Colorless crystals. M.p. 140.6 – 141.58. IR: 1774s (C¼O),
1
1630w, 1385w, 1234m, 710s. H-NMR: 1.45, 1.64 (2s, 4 Me); 3.80 (s, CH2,); 6.94 – 6.95 (m, 2 arom. H);
7.24 – 7.25 (m, 2 arom. H); 7.29 – 7.30 (m, 2 arom. H). 13C-NMR: 24.1, 26.5 (4 Me); 28.3 (CH2(6)); 67.0
(C(1,3)); 70.1, 76.6 (C(4,8)); 125.7, 126.3, 127.8 (6 arom. CH); 148.2 (2 arom. C); 219.5 (C¼O). Anal. calc.
for C18H20OS4 (380.62): C 56.80, H 5.30, S 33.70; found: C 57.02, H 5.52, S 33.68.
Suitable crystals for the X-ray crystal-structure determination were grown from MeOH in the
refrigerator.
6.5. Reaction with 2g: 1,1,3,3-Tetramethyl-8,8-di(selenophen-2-yl)-5,7-dithiaspiro[3.4]octan-2-one
(4s). The reaction was complete after 4 h. The crude product was crystallized from MeOH. Yield: 323 mg
(85%). Pale yellow crystals. M.p. 157.0 – 158.08 (MeOH). IR: 1770s (C¼O), 1442m, 1383m, 1232s, 1012m,
808m, 696s. 1H-NMR: 1.45, 1.63 (2s, 4 Me); 3.86 (s, CH2); 7.17 – 7.18 (m, 2 arom. H); 7.37 – 7.38 (m, 2 arom.
H); 7.95 – 7.96 (m, 2 arom. H). 13C-NMR: 24.4, 26.8 (4 Me); 28.9 (CH2(6)); 66.9 (C(1,3)); 74.2, 76.5
(C(4,8)); 129.0, 129.2, 132.4 (6 arom. CH); 156.6 (2 arom. C); 219.4 (C¼O). Anal. calc. for C18H20OS2Se2
(474.41): C 45.57, H 4.25, S 13.52; found: C 45.84, H 4.32, S 13.55.
7. Competition Experiments. a) Compound 2f vs. Compound 2b with 5c. A soln. of 2c (1 mmol) in
2 ml of THF was cooled to À 708 and treated with small portions of a soln. of CH2N2 in Et2O, until the
dark-blue color disappeared. Then, equimolar amounts of 2f (1 mmol) and 2b (1 mmol) dissolved in 3 ml
of THF were added at À 708, and the mixture was kept at À 458 to À 408 (acetone/dry ice bath) for 2 h.
Then, the soln. was allowed to warm slowly to r.t. and kept at r.t. for ca. 30 min, and then the solvent was
evaporated. The residue was subjected to 1H-NMR analysis in CDCl3 with a weighed amount of 1,1,2,2-
tetrachloroethane as a standard. The only observed product was the known 5,5-diphenylspiro[1,3-
dithiolane-4,9’-[9H]fluorene] [3b]. Yield: 99% (1H-NMR).
b) Compound 2f vs. Compound 2c with 5c. In analogy to the procedure described above, a soln. of 2c
(0.57 mmol) in 2 ml of THF at À 708 was treated with an ethereal CH2N2 soln., followed by a soln. of 2f
(0.57 mmol) and 2c (0.57 mmol) in 3 ml of THF. The mixture was stirred at À 458 to À 408 for 2 h and
then allowed to warm slowly to r.t. After 30 min at r.t., the solvent was evaporated, and the residue was
subjected to 1H-NMR analysis (CDCl3; 1,1,2,2-tetrachloroethane as a standard). The crude product was
identified as a mixture of the known 4,4,5,5-tetraphenyl-1,3-dithiolane (4c) [3b] (40%) and 4f (29%;
1H-NMR).
8. X-Ray Crystal Structure Determination of 4r (Table and Fig.)2). All measurements were carried
out on an Agilent Technologies SuperNova area-detector diffractometer [14] using MoKa radiation (l
0.71073 Š) from a micro-focus X-ray source and an Oxford Instruments Cryojet XL cooler. Data
reduction was performed with CrysAlisPro [14]. The intensities were corrected for Lorentz and
polarization effects, and an empirical absorption correction using spherical harmonics [14] was applied.
Equivalent reflections, other than Friedel pairs, were merged. The data collection and refinement
parameters are compiled in the Table. A view of the molecule is shown in the Figure. The structure was
solved by direct methods using SHELXS-2013 [15], which revealed the positions of all non-H-atoms.
There are two symmetry-independent molecules in the asymmetric unit. The atomic coordinates of the
two molecules were tested carefully for a relationship from a higher-symmetry space group using the
program PLATON [16], but none could be found. Both molecules show disorder of both thiophene rings
due to 1808 rotation of each ring around its parent CÀC bond, which swaps the positions of the S- and C-
atoms in the 2,5-positions of the ring. Two positions were defined for these S- and C-atoms in each
disordered ring, and the site occupation factors of the major orientations of these rings refined to 0.680(4)
and 0.845(3) in molecule A and 0.954(3) and 0.794(3) in molecule B. Similarity restraints were applied to
the chemically equivalent bond lengths involving all disordered S- and C-atoms. In addition, the bond
lengths involving disordered C-atoms were restrained to 1.40(1) Š. Neighboring disordered atoms
between each orientation of the disordered thiophene rings were restrained to have similar atomic
displacement parameters. One thiophene ring was additionally restrained to be planar. The non-H-atoms
were refined anisotropically. All of the H-atoms were placed in geometrically calculated positions and
2
)
CCDC-1052007 contains the supplementary crystallographic data for this article. These data can be
obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.

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Helvetica Chimica Acta – Vol. 98 (2015)
Table. Crystallographic Data for Compound 4r
Crystallized from
MeOH
C18H20OS4
380.60
m(MoKa) [mmÀ1
Scan type
2q(max) [8]
Transmission factors (min; max)
Total reflections measured
Symmetry-independent reflections 9322
]
0.535
w
Empirical formula
Formula weight [g molÀ1
Crystal color, habit
]
60.9
0.932; 1.000
23111
colorless, prism
Crystal dimensions [mm] 0.23 Â 0.24 Â 0.37
Temp. [K]
Crystal system
Space group
Z
160(1)
monoclinic
P21
Reflections with I > 2s(I)
Reflections used in refinement
Parameters refined; restraints
Final R(F) [I > 2s(I)
reflections]
8753
9322
499; 319
0.0301
4
Reflections for cell
determination
2q Range for cell
determination [8]
Unit cell parameters:
a [Š]
14706
5 – 60
wR(F2) (all data)
0.0708
Weights
w ¼ [s2(F2o ) þ (0.0314P)2
þ 0.4989]À1 where
P ¼ (F2o þ 2F2c )/3
1.039
0.001
0.55; À0.43
8.69316(11)
12.82765(15)
15.94089(19)
90.7785(11)
1777.45(4)
1.422
b [Š]
c [Š]
b [8]
Goodness-of-fit
Final Dmax/s
D1 (max; min) [e Š
V [Š3]
]
À3
Dx [g cmÀ3
]
refined by using a riding model where each H-atom was assigned a fixed isotropic displacement
parameter with a value equal to 1.2 Ueq of its parent C-atom (1.5 Ueqfor the Me groups). The refinement
of the structure was carried out on F2 by using full-matrix least-squares procedures, which minimized the
function Sw(F2o À Fc2 )2. A correction for secondary extinction was not applied. Refinement of the
absolute structure parameter [17] yielded a value of 0.01(1), which confidently confirms that the refined
model represents the true absolute structure. Neutral atom-scattering factors for non-H-atoms
were taken from [18a], and the scattering factors for H-atoms were taken from [19]. Anomalous
dispersion effects were included in Fc [20]; the values for f ’ and f ’’ were those of [18b]. The values of the
mass attenuation coefficients are those of [18c]. The SHELXL-2014 program [21] was used for all
calculations.
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Received March 5, 2015