Synthesis of hetaryl-substituted 1,2,4-trithiolanes via a three-component reaction with dihetaryl thioketones, benzyl azide, and 2,2,4,4-tetramethyl-3-thioxocyclobutanone

Article abstract of DOI:10.1080/17415993.2015.1082182

The three-component reactions with a hetaryl thioketone, 2,2,4,4-tetramethyl-3-thioxocyclobutanone, and excess benzyl azide performed at 60°C in the presence of LiClO₄ lead to the formation of two types of 1,2,4-trithiolanes. As the major produ

Full text of DOI:10.1080/17415993.2015.1082182

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
Synthesis of hetaryl-substituted 1,2,4-trithiolanes
via a three-component reaction with dihetaryl
thioketones, benzyl azide, and 2,2,4,4-
tetramethyl-3-thioxocyclobutanone
Grzegorz Mlostoń, Małgorzata Celeda, Anthony Linden & Heinz Heimgartner
To cite this article: Grzegorz Mlostoń, Małgorzata Celeda, Anthony Linden & Heinz
Heimgartner (2015): Synthesis of hetaryl-substituted 1,2,4-trithiolanes via a three-
component reaction with dihetaryl thioketones, benzyl azide, and 2,2,4,4-tetramethyl-3-
thioxocyclobutanone, Journal of Sulfur Chemistry, DOI: 10.1080/17415993.2015.1082182
To link to this article: http://dx.doi.org/10.1080/17415993.2015.1082182
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Date: 16 September 2015, At: 22:20

Journal of Sulfur Chemistry, 2015
http://dx.doi.org/10.1080/17415993.2015.1082182
Synthesis of hetaryl-substituted 1,2,4-trithiolanes via a
three-component reaction with dihetaryl thioketones, benzyl
azide, and 2,2,4,4-tetramethyl-3-thioxocyclobutanone
Grzegorz Mloston´a∗, Małgorzata Celedaa, Anthony Lindenb and Heinz Heimgartnerb
aDepartment of Organic and Applied Chemistry, University of Łódz´, Tamka 12, PL-91-403 Łódz´, Poland;
bDepartment of Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
(Received 7 July 2015; accepted 6 August 2015)
The three-component reactions with a hetaryl thioketone, 2,2,4,4-tetramethyl-3-thioxocyclobutanone,
and excess benzyl azide performed at 60°C in the presence of LiClO4 lead to the formation of two
types of 1,2,4-trithiolanes. As the major products, the non-symmetrical dihetaryl-substituted spiro-1,2,4-
trithiolanes are formed. In addition, the symmetrical dispiro-1,2,4-trithiolane is identified. These products
are formed in competitive [3 + 2] cycloadditions of the in-situ-generated thiocarbonyl S-sulfide with the
thioketones used in the reaction.
S
S
S
Ar1
Ar2
Ar2
Ar1
O
S
S
-
S
O
S
+
O
S
S
O
S
O
thiocarbonyl S-sulfide
Keywords: thioketones; organic azides; [3 + 2] cycloadditions; thiocarbonyl S-sulfides; sulfur
heterocycles
1. Introduction
Among five-membered poly-sulfur heterocycles, 1,2,4-trithiolanes constitute an important class
of compounds. Some of them, for example, the parent 1,2,4-trithiolane and its 3,5-dialkyl-
substituted derivatives are widely spread in nature. The parent compound was isolated as the
major component from Shiitaki mushrooms (Lentinus edodes) [1] and later on also from bitter
beans (Parkia speciosa).[2] Cis- and trans-3,5-dimethyl-1,2,4-trithiolane are known as impor-
tant components in the mixture of sulfur-heterocycles, which determine the flavor of boiled
beef meat.[3,4] The corresponding diethyl derivatives were identified in the composition of
*Corresponding author. Email: gmloston@uni.lodz.pl
© 2015 Taylor & Francis

2
G. Mloston´ et al.
Scheme 1. Sulfur transfer reaction leading to 1,2,4-trithiolane 6.
common onion (Allium cepa) essential oil.[5] Both the parent compound [1] and 3,5-dialkyl
1,2,4-trithiolanes [6] have been prepared by heterocyclization reactions starting with chloroalka-
nes using Na2S as the sulfur source. An alternative approach, based on the reaction of ammonia
(or a primary amine), H2S and elemental sulfur, as well as an aliphatic oxo-compound, was
developed by Asinger.[7] In recent decades, an elegant method for the preparation of tetrasub-
stituted 1,2,4-trithiolanes via [3 + 2] cycloadditions of thioketone S-sulfides (thiosulfines) [8]
with thioketones was elaborated by Huisgen.[9,10] In that case, the elusive thiosulfines are gen-
=
erated in situ and immediately trapped by the C S group of the ‘superdipolarophilic’ thioketone.
The Huisgen method for the generation of thiosulfine comprises the transfer of the S-atom of a
=
thiirane onto the C S group.
Some time ago, we reported on a new method for the in situ generation of thiosulfines in
the reaction of thioketones with organic azides. Thus, heating of adamantanethione (1a) with
benzyl azide (2) led to dispiro-1,2,4-trithiolane 6 as the [3 + 2] cycloadduct of adamantanethione
S-sulfide (5) with 1a (Scheme 1).[11]
In this reaction, the intermediate thiaziridine 4a is believed to act as the sulfur donor
involved in the generation of the reactive 1,3-dipole 5. On the other hand, similar reactions of
thiobenzophenone (1b) with organic azides produce benzophenone imines and not the expected
tetraphenyl-1,2,4-trithiolanes.[12] These results demonstrate the thermolability of the tetraaryl-
1,2,4-trithiolanes, which therefore cannot be isolated. Finally, a three-component mixture of an
aromatic thioketone, 1a and an organic azide furnished non-symmetrical 1,2,4-trithiolanes via
the [3 + 2] cycloaddition reaction, and the obtained product is stable enough to be isolated.[11]
Aromatic thioketones are more reactive than cycloaliphatic analogs toward organic azides and
therefore 3,3-diarylthiaziridines are the sulfur-donating intermediates. Along with 1a, the steri-
cally crowded 2,2,4,4-tetramethyl-3-thioxocyclobutanone (1c) is a good model for the synthesis
of non-symmetrical 1,2,4-trithiolanes using three-component reactions.[13]
Thiocarbonyl S-sulfides were also postulated as reactive intermediates in a multi-step reaction
between aromatic thioketone S-oxides and 1c in which some non-symmetrical 1,2,4-trithiolanes
were found as the final products.[14]
In a recent publication we described a convenient access to differently substituted aryl/hetaryl
thioketones.[15] The presence of heteroatoms in the hetaryl ring influences the reactivity of
these thioketones significantly, for example, in [3 + 2] cycloadditions with diazomethane [16]
and with thiocarbonyl ylides.[17] In both cases, the cycloaddition reactions seem to occur via
diradical intermediates.

Journal of Sulfur Chemistry
3
The present study was aimed at testing the reactivity of selected hetaryl thioketones in three-
component reactions leading to hetaryl-substituted non-symmetrical 1,2,4-trithiolanes.
2. Results and discussion
In the test experiment, the reactivity of di(selenophen-2-yl) thioketone (1d) toward benzyl azide
(2) was compared with that of thiobenzophenone (1b). The evolution of N2 from the reaction
mixture heated to 80°C was complete after 4 h, which indicates that 1d is less reactive than 1b
(80°C, ca. 2.5 h) in the [3 + 2] cycloaddition with 2. When the same reaction was performed
in the presence of a catalytic amount of LiClO4, the reaction temperature could be reduced to
60°C, and the conversion was complete after 3 h. The crude reaction mixture was separated
chromatographically (prep. TLC) and the only product was identified as di(selenophen-2-yl)
ketone (8d) [15] formed via hydrolysis of the corresponding N-benzylimine 7 (Scheme 2). It is
worth of mentioning that the observed least polar fraction with Rf value ca. 0.9 was attributed
to elemental sulfur S8. This result fits well with that reported for thiobenzophenone (1b) [12,18]
and indicates that the intermediate dihetarylthiaziridine 4b can be expected to act as a sulfur
donor.
The three-component reaction with the aromatic 1d and cycloaliphatic thioketone 1c in excess
benzyl azide (2) in the presence of LiClO4 was performed at 60°C. In that case, the chromato-
graphic separation of the crude mixture led to a crystalline product (less polar fraction), which in
the 1H-NMR spectrum showed two characteristic signals of methyl groups and three multiplets
attributed to the selenophen-2-yl substituents. In the IR spectrum, the intense absorption at 1787
cm–1 confirms the presence of the cylobutanone unit. Finally, the structure of the spirocyclic
1,2,4-trithiolane 9a (Scheme 3) was established by X-ray crystallography (Figure 1).
The more polar fraction isolated after chromatography was identified as a mixture of the
known symmetrical dispiro-1,2,4-trithiolane 10 [13] and di(selenophen-2-yl)ketone (8d).[15]
The analogous experiments with di(thiophen-2-yl) thioketone (1e) and N-methylpyrrol-2-yl
phenyl thioketone (1f), respectively, yielded also the desired spiro-1,2,4-trithiolanes 9b and 9c
side by side with 10 and the corresponding hetaryl ketones 8e, f (Scheme 3).
In an extension of this study, the reaction of diferrocenyl thioketone and benzyl azide (2) was
tested at 60°C. Only after 6 h did the evolution of N2 cease, but the attempted separation of
Scheme 2. Two-fold extrusion reaction leading to imine 7 and its subsequent hydrolysis.

4
G. Mloston´ et al.
10 [13]
Scheme 3. Formation of symmetrical and non-symmetrical 1,2,4-trithiolanes 9 and 10 via stepwise sulfur transfer
reaction.
Figure 1. ORTEP plot [19] of the molecular structure of conformation A of 9a (with 50% probability ellipsoids;
arbitrary numbering of atoms).
the complex mixture was unsuccessful. Similarly, the three-component reaction with 1c led to a
complex mixture of non-identified products.
3. Conclusions
The presented study demonstrated that hetaryl thioketones are less reactive than thioben-
zophenone in [3 + 2] cycloadditions with benzyl azide, and a catalytic amount of LiClO4
is necessary to reduce the reaction temperature to 60°C. In the presence of the sterically
crowded 2,2,4,4-tetramethyl-3-thioxocyclobutanone (1c), mixtures of spiro-1,2,4-trithiolanes 9
containing hetaryl substituents and dispiro-1,2,4-trithiolane 10 are formed. Both products can be
separated chromatographically.
The formation of 1,2,4-trithiolanes of type 9 can occur via the [3 + 2] cycloadditions of
either the thiocarbonyl S-sulfide of the hetaryl thioketone or the cycloaliphatic analog. On

Journal of Sulfur Chemistry
5
the other hand, the formation of the dispiro-1,2,4-trithiolane 10 proves the appearance of
the intermediate 2,2,4,4-tetramethyl-3-thioxocyclobutanone S-sulfide. Aromatic thioketones are
known as ‘superdipolarophiles’ and therefore, the first step of the reaction sequence is the [3 + 2]
cycloaddition of benzyl azide (2) with the thioketone 1. Additional evidence for this sequence is
the absence of the products observed previously in the two-component reaction of 1c with 2.[20]
For that reason, we propose that 1c acts as a sulfur trapping agent and generates the correspond-
ing thiosulfine as a key intermediate. The latter reacts in competitive [3 + 2] cycloaddition with
the hetaryl thioketone as well as with 1c.
Hetaryl-substituted 1,2,4-trithiolanes are attractive substrates for coordination chemistry and
their reactions with thiophilic Pt° complexes are of special interest.[21,22]
4. Experimental Design
4.1. General
Melting points were determined in a capillary using a Melt-Temp. II (Aldrich) apparatus and
are uncorrected. The IR spectra were recorded on an NEXUS FT-IR spectrophotometer in KBr;
absorptions in cm–1. The 1H and 13C NMR spectra were measured on a Bruker Avance III instru-
ment (600 and 150 MHz, resp.) using solvent signals as reference. Chemical shifts (δ) are given
in ppm and coupling constants J in Hz. All crude mixtures were separated by preparative TLC.
4.2. Starting materials
Dihetaryl thioketones 1d and 1e were obtained in a typical manner from the corresponding
ketones and Lawesson’s reagent in boiling toluene or benzene,[15] whereas 1f was prepared
by the treatment of N-methylpyrrol with thiophosgene in the presence of triethylamine.[23]
2,2,4,4-Tetramethyl-3-thioxo-cyclobutanone (1c) was prepared according to [24] by thionation
of 2,2,4,4-tetramethylcyclobutane-1,3-dione with phosphorus pentasulfide in pyridine. Ben-
zyl azide (2) was prepared from benzyl bromide and sodium azide according to a literature
procedure.[25]
4.3. Two-component reaction of di(selenophen-2-yl) thioketone (1d) and benzyl azide (2)
A solution of 152 mg (0.5 mmol) thioketone 1d dissolved in excess benzyl azide (2, 0.5 mL) was
stirred magnetically and heated in an oil bath at 80°C. After 4 h evolution of nitrogen ceased and
excess benzyl azide was removed in vacuo (Kugel-Rohr apparatus, 0.2 Torr, 60°C). The residual
brownish oil was purified on preparative TLC plates (SiO2, hexane/dichloromethane 1:1). The
least polar fraction with Rf ca. 0.9 formed elemental sulfur, which hast not been isolated. The only
fraction isolated from the plate (Rf ca. 0.5; 108 mg (75%)) was a colorless oil, which solidified at
room temperature. Based on comparison of the 1H NMR and IR spectra with an original sample
it was identified as di(selenophen-2-yl) ketone (8d).[15]
4.4. Three-component reaction with dihetaryl thioketones 1, benzyl azide (2) and
2,2,4,4-tetramethyl-3-thioxocyclobutanone (1c) – general procedure
A mixture of the corresponding thioketone 1d–1f (1 mmol), 2,2,4,4-tetramethyl-3-thioxocyclo-
butanone (1c, 0.5 mmol), benzyl azide (2, 1 mL) and a catalytic amount of LiClO4 was heated
in an oil bath at 60°C. After 3 h excess of azide 2 was removed under reduced pressure. The

6
G. Mloston´ et al.
obtained mixtures were purified by preparative TLC (SiO2), using as the eluent a mixture of
petroleum ether and ethyl acetate (97:3) for 9a and 9b and a mixture of dichloromethane and
petroleum ether (1:1) for 9c. Products 9, isolated as the less polar fraction, were additionally
crystallized from diethyl ether. The more polar fraction was a mixture of the known dispiro
compounds 10 [13] and the corresponding hetaryl ketones 8d–8f.[11]
1,1,3,3-Tetramethyl-7,7-di(selenophen-2-yl)-5,6,8-trithiaspiro[3.4]octan-2-one (9a)
1
Colorless crystals; yield: 217 mg (44%); m.p. 106–108°C (diethyl ether). H NMR: 1.48,
1.51 (2s, 12H, 4CH3); 7.20 (dd, JH,H = 5.6 Hz, JH,H = 3.8 Hz, 2CHarom); 7.34 (dd, JH,H = 3.8
Hz, JH,H = 0.6 Hz, 2CHarom); 8.00 (dd, JH,H = 5.6 Hz, JH,H = 0.6 Hz, 2CHarom). 13C NMR:
21.3, 26.4 (4CH3); 67.7 (2Cq(CH3)2); 84.0, 89.7 (2CqS); 129.6, 130.8, 133.7 (6CHarom); 154.5
=
(2Carom); 218.0 (C O). IR (KBr): 3087m, 2962m, 1787vs (νC=O), 1636m, 1458m, 1378m,
1236m, 1227m, 1171w, 1026m, 922m, 820m, 709s, 688vs. Anal. calcd for C17H18OS3Se2
(492.44): C 41.46, H 3.68, S 19.53; found: C 41.60, H 3.76, S 20.04.
1,1,3,3-Tetramethyl-7,7-bis(2-thienyl)-5,6,8-trithiaspiro[3.4]octan-2-one (9b)
1
Colorless crystals; yield: 200 mg (50%); m.p. 113–115°C (diethyl ether). H NMR: 1.47,
1.52 (2s, 12H, 4CH3); 6.96 (dd, JH,H = 5.2 Hz, JH,H = 3.7 Hz, 2CHarom); 7.15 (dd, JH,H = 3.7
Hz, JH,H = 1.1 Hz, 2CHarom); 8.00 (dd, JH,H = 5.6 Hz, JH,H = 0.6 Hz, 2CHarom). 13C NMR:
21.3, 26.3 (4CH3); 67.6 (2Cq(CH3)2); 79.7, 89.5 (2CqS); 126.7, 126.9, 128.6 (6CHarom); 147.5
=
(2Carom); 218.1 (C O). IR (KBr): 3088m, 2963s, 1789vs (νC=O), 1640m, 1459s, 1426s, 1378m,
1363m, 1237s, 1228s, 1170m, 1042m, 1027m, 922m, 857m, 817m, 775m, 753m, 716s, 700vs.
Anal. calcd for C17H18OS5 (398.65): C 51.22, H 4.55, S 40.22; found: C 51.15, H 4.53, S 40.62.
1,1,3,3-Tetramethyl-7-(1-methylpyrrol-2-yl)-7-phenyl-5,6,8-trithiaspiro[3.4]octan-2-one (9c)
1
Colorless crystals; yield: 116 mg (30%); m.p. 120–122°C (diethyl ether). H NMR: 1.43,
1.48, 1.49, 1.55 (4s, 12H, 4CH3); 3.25 (s, 3H, CH3N); 6.07 (dd, JH,H = 3.6 Hz, JH,H = 2.8
Hz, 2CHarom); 6.62 (dd, JH,H = 3.6 Hz, JH,H = 2.2 Hz, 2CHarom); 6.67 (br. t, JH,H = 2.2 Hz,
2CHarom); 7.28–7.33 (m, 3CHarom); 7.49–7.51 (m, 2CHarom). 13C NMR: 21.2, 21.5, 26.0, 26.2
(4CH3); 35.8 (CH3N); 66.8, 67.7 (2Cq(CH3)2); 81.4, 89.1 (2CqS); 105.8, 113.9, 125.5, 127.7,
=
128.2, 128.4 (6 signals for 8CHarom); 131.1, 140.5 (2Carom); 218.5 (C O). IR (KBr): 2962s,
2923m, 1783vs (νC=O), 1593m, 1487m, 1449s, 1438s, 1377m, 1360m, 1299s, 1233m, 1167m,
1093m, 1025m, 882m, 828m, 776m, 737m, 718vs, 702s. Anal. calcd for C20H23NOS3 (389.60):
C 61.66, H 5.95, N 3.60, S 24.69; found: C 61.57, H 6.13, N 3.42, S 24.86.
4.5. X-ray crystal-structure determination of 9a
All measurements were made on an Agilent Technologies SuperNova area-detector diffrac-
tometer [26] using graphite-monochromated MoKa radiation (λ 0.71073 Å) from a micro-focus
X-ray source and an Oxford Instruments Cryojet XL cooler. Data reduction was performed
with CrysAlisPro.[26] The intensities were corrected for Lorentz and polarization effects, and
an empirical absorption correction using spherical harmonics [25] was applied. Equivalent
reflections were merged. Data collection and refinement parameters are given below,[27] and
a view of the molecule is shown in Figure 1. The structure was solved by direct methods using
SHELXS-2013,[28] which revealed the positions of all non-H-atoms. The carbonyl group is dis-
ordered over two conformations. Two sets of positions were defined for the C- and O-atoms
of the carbonyl group and the site occupation factor of the major conformation refined to
0.768(11). Similarity restraints were applied to the chemically equivalent bond lengths and
angles involving all disordered atoms, while corresponding atoms in the two conformations of

Journal of Sulfur Chemistry
7
the disordered carbonyl group were restrained to have similar atomic displacement parameters.
The non-H-atoms were refined anisotropically. All of the H-atoms were placed in geometrically
calculated positions and refined by using a riding model where each H-atom was assigned a fixed
isotropic displacement parameter with a value equal to 1.2Ueq of its parent C-atom (1.5Ueq for
the methyl groups). The refinement of the structure was carried out on F2 by using full-matrix
2
2 2
least-squares procedures, which minimized the function ꢀw(Fo -Fc ) . A correction for sec-
ondary extinction was not applied. Neutral atom scattering factors for non-H-atoms were taken
from ref. [29] and the scattering factors for H-atoms were taken from ref. [30] Anomalous disper-
sion effects were included in Fc;[31] the values for f ’ and f ” were those of ref. [32] The values
of the mass attenuation coefficients are those of ref. [33] All calculations were performed using
the SHELXL-2014 [34] program.
Crystal data for 9a: C17H18OS3Se2, M = 492.31, crystallized from diethyl ether, colorless,
¯
prism, crystal dimensions 0.07 × 0.10 × 0.20 mm, triclinic, space group P1, Z = 2, reflections
for cell determination 12,824, 2θ range for cell determination 5–61°, a = 6.67580(7) Å, b =
8.24707(11) Å, c = 18.08016(17) Å, α = 93.4135(9)°, β = 94.0158(8)°, γ = 106.2097(10)°,
V = 950.243(19) Å3, T = 160(1) K, DX = 1.720 g cm–3, μ(MoKα) = 4.219 mm–1, scan type
ω, 2θ(max) = 60.7°, transmission factors (min; max) = 0.714; 1.000, total reflections mea-
sured 23,628, symmetry independent reflections 5239, reflections with I > 2σ(I) 4584,
reflections used in refinement 5239, parameters refined 231, restraints 19; R(F) [I > 2σ(I)
reflections] = 0.0246, wR(F2) [all data] = 0.0575 (w = [σ2(Fo ) + (0.0232P)2 + 0.5336P]–1,
2
2
2
where P = (Fo + 2Fc )/3), goodness of fit 1.055, final ꢁmax/σ 0.001, ꢁρ (max; min) = 0.47;
–0.46 e Å–3.
Acknowledgements
The authors thank Dr K. Urbaniak (University of Łódz´) for her help in preparation of the manuscript.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the National Science Center (Cracow, Poland) within the project Maestro [Grant Number:
Dec-2012/06/A/ST5/00219].
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