Ring enlargement and sulfur-transfer processes in SiO2-catalyzed reactions of thiocarbonyl compounds with optically active oxiranes

Article abstract of DOI:10.1002/hlca.200590261

The reactions of 1,3-dioxolane-2-thione (3) with (S)-2-methyloxirane ((S)-1) and with (R)-2-phenyloxirane ((R)-2) in the presence of SiO₂ in anhydrous dichloroalkanes led to the optically active spirocyclic 1,3-oxathiolanes 8 with Me at C(7) and 9 with Ph at C(8), respectively (Schemes 2 and 3). The analogous reaction of 1,3-dimethylimidazolidine-2-thione (4a) with (R)-2 yielded stereoselectively (S)-2-phenylthiirane ((S)-10) in 83% yield and 97% ee together with 1,3-dimethylimidazolidin-2-one (11a). In the cases of 3-phenyloxazolidine-2-thione (4b) and 3-phenylthiazolidine-2-thione (4c), the reaction with (RS)-2 yielded the racemic thiirane (RS)-10, and the corresponding carbonyl compounds 11b and 11c (Scheme 4 and Table 1). The analogous reaction of 4a with 1,2-epoxycyclohexane (=7-oxabicyclo[4.1.0]heptane; 7) afforded thiirane 12 and the corresponding carbonyl compound 11a (Scheme 5). On the other hand, the BF₃-catalyzed reaction of imidazolidine-2-thione (5) with (RS)-2 yielded the imidazolidine-2-thione derivative 13 almost quantitatively (Scheme 6). In a refluxing xylene solution, 1,3-diacetylimidazolidine-2-thione (6) and (RS)-2 reacted to give two imidazolidine-2-thione derivatives, 13 and 14 (Scheme 7). The structures of 13 and 14 were established by X-ray crystallography (Fig.).

Full text of DOI:10.1002/hlca.200590261

Helvetica Chimica Acta – Vol. 88 (2005)
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Ring Enlargement and Sulfur-Transfer Processes in SiO2-Catalyzed Reactions
of Thiocarbonyl Compounds with Optically Active Oxiranes
by Sergej Malaschichin1), Changchun Fu, Anthony Linden, and Heinz Heimgartner*
Organisch-chemisches Institut der Universität Zürich, Winterthurerstr. 190, CH-8057 Zürich
The reactions of 1,3-dioxolane-2-thione (3) with (S)-2-methyloxirane ((S)-1) and with (R)-2-phenyloxirane
((R)-2) in the presence of SiO2 in anhydrous dichloroalkanes led to the optically active spirocyclic 1,3-oxathio-
lanes 8 with Me at C(7) and 9 with Ph at C(8), respectively (Schemes 2 and 3). The analogous reaction of 1,3-
dimethylimidazolidine-2-thione (4a) with (R)-2 yielded stereoselectively (S)-2-phenylthiirane ((S)-10) in 83%
yield and 97% ee together with 1,3-dimethylimidazolidin-2-one (11a). In the cases of 3-phenyloxazolidine-2-thi-
one (4b) and 3-phenylthiazolidine-2-thione (4c), the reaction with (RS)-2 yielded the racemic thiirane (RS)-10,
and the corresponding carbonyl compounds 11b and 11c (Scheme 4 and Table 1). The analogous reaction of 4a
with 1,2-epoxycyclohexane (=7-oxabicyclo[4.1.0]heptane; 7) afforded thiirane 12 and the corresponding car-
bonyl compound 11a (Scheme 5). On the other hand, the BF3-catalyzed reaction of imidazolidine-2-thione
(5) with (RS)-2 yielded the imidazolidine-2-thione derivative 13 almost quantitatively (Scheme 6). In a refluxing
xylene solution, 1,3-diacetylimidazolidine-2-thione (6) and (RS)-2 reacted to give two imidazolidine-2-thione
derivatives, 13 and 14 (Scheme 7). The structures of 13 and 14 were established by X-ray crystallography (Fig.).
1. Introduction. – The regio- and stereoselective formation of 1,3-oxathiolanes in
the Lewis acid-catalyzed reaction of thiocarbonyl compounds with oxiranes has been
investigated thoroughly in recent years. So far, the reactions of oxiranes with 1,3-thia-
zole-5(4H)-thiones, cyclic trithiocarbonates, nonenolizable thioketones, enolizable
thiocamphor, enolized dibenzyl thioketone, a rhodanine derivative, and thiolactones
have been reported [1–13]. The results for this novel synthetic approach to 1,3-oxathio-
lanes show that the reactions proceed with high regio- and stereoselectivity via an SN2-
type mechanism (Scheme 1). In the case of 2-alkyl-substituted oxiranes (e.g., (S)-1), the
nucleophilic thiocarbonyl S-atom attacks preferentially at C(3) to give the 5-substituted
1,3-oxathiolanes with retention of the configuration at C(2) of the oxirane. On the other
hand, 2-phenyl- and 2-vinyloxirane (e.g., (R)-2) are attacked mainly at C(2) under
inversion of the configuration to yield 4-phenyl- and 4-vinyl-substituted products.
Scheme 1
1
)
Stay at the University of Zürich, 06.–09.2003 and 06.–09.2004; Saint-Petersburg State University, Universi-
tetskij pr. 26, 198504 Saint Petersburg, Russia; present address: Organisch-chemisches Institut der Univer-
sität Zürich, Winterthurerstr. 190, CH-8057 Zürich.
© 2005 Verlag Helvetica Chimica Acta AG, Zürich

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In addition to 1,3-oxathiolanes, the corresponding carbonyl compounds and 1,3-
dithiolanes were sometimes isolated from the reactions of thicarbonyl compounds
with oxiranes. The formation of the carbonyl compounds can be explained by the
decomposition of 1,3-oxathiolanes in the presence of Lewis acids. However, the forma-
tion of 1,3-dithiolanes implies that the decomposition of 1,3-oxathiolanes should give
thiiranes as the second product, which react again with thiocarbonyl compounds to pro-
duce the observed by-products. This proposal was supported by a control experiment,
in which 4,4-dimethyl-2-phenyl-1,3-thiazole-5(4H)-thione and 1,2-epithiocyclohexane
(=7-thiabicyclo[4.1.0]heptane), in the presence of BF3, afforded the corresponding spi-
rocyclic 1,3-dithiolane in 85% yield with respect to the consumed thiazolethione deriv-
ative [3]. Analogous reactions have been reported where racemic oxiranes react with
thiourea [14], with dimethylthioformamide [15], and with 3-methylbenzothiazole-2-thi-
one [16], respectively, to give racemic thiiranes. If the conversion of oxiranes to thiir-
anes occurs stereoselectively, as shown in the reaction of stilbene oxides with 3-meth-
ylbenzothiazole-2-thione [16] (see also [17]), this methodology should be an attractive
access to optically active thiiranes, because thiocarbonyl compounds, as well as opti-
cally active oxiranes, are conveniently accessible (for other approaches, see [17–20]
and refs. cit. therein).
With the aim of further extending the scope of the formation of 1,3-oxathiolanes,
reactions of 1,3-dioxolane-2-thione (3; cf. Scheme 2), 1,3-dimethylimidazolidine-2-thi-
one (4a), 3-phenyloxazolidine-2-thione (4b), 3-phenylthiazolidine-2-thione (4c; cf.
Table 1), imidazolidine-2-thione (5; cf. Scheme 6), and 1,3-diacetylimidazolidine-2-thi-
one (6; cf. Scheme 7) with oxiranes were carried out. In the present paper, the results of
the reactions with (S)-2-methyloxirane ((S)-1), (R)- and (RS)-2-phenyloxirane ((R)-
and (RS)-2, resp.), and 1,2-epoxycyclohexane (=7-oxabicyclo[4.1.0]heptane, 7; cf.
Scheme 5) are described.
2. Results. – 2.1. Reaction of 1,3-Dioxolane-2-thione (3) with (S)-2-Methyloxirane
((S)-1). The reaction of (S)-1 with 3 in a molar ratio of 1:2 was carried out in anhydrous
1,2-dichloroethane at 2–58 under an N2 atmosphere in the presence of SiO2. After stir-
ring for 2 d, filtration and the usual workup by column chromatography (CC) gave the
spirocyclic 1,3-oxathiolane 8 as the only product in 27% yield (Scheme 2).
Scheme 2
The analogous reaction of 3 with (R)-2-phenyloxirane ((R)-2; molar ratio 1:1.5) in
anhydrous CH2Cl2 at 0–58 for 2 d under an N2 atmosphere in the presence of SiO2 gave
the spirocyclic 1,3-oxathiolane 9 in 34% yield (Scheme 3). The enantiomeric excess (ee)
of the product (>90%) was determined by analytical HPLC (S,S-Whelk-O-1; hexane/
i-PrOH/CH2Cl2 500 :1:2).
The structures of 8 and 9 were assigned on the basis of their elemental analyses, MS,
IR, 1H- and 13C-NMR (HSQC, HSQC-TOCSY, and HMBC in the case of 9) data. The

Helvetica Chimica Acta – Vol. 88 (2005)
3255
Scheme 3
formation of 8 proceeded by nucleophilic attack of the thiocarbonyl S-atom at C(3),
and, for this reason, the configuration at C(2) of the oxirane (S)-1 is retained. There-
fore, the configuration at C(7) in 8 has to be (S). In the case of 9, the nucleophilic S-
atom attacked C(2) of (R)-2 with inversion of the configuration, leading to the (S)-con-
figuration at C(8) in 9. These results are in accordance with those reported previously
[7–11].
2.2. Reaction of Heterocyclic Thiones 4a–4c with 2. The reaction of 4a with (R)-2
(molar ratio 1:1.7) in anhydrous CH2Cl2 at 58 for 2 h under an N2 atmosphere in the
presence of SiO2 afforded (S)-2-phenylthiirane ((S)-10) stereoselectively in 83%
yield, together with the corresponding carbonyl compound 11a (Scheme 4 and Table
1). The ee value of 10 (97%) was determined by analytical HPLC (S,S-Whelk-O-1; hex-
ane), and the configuration was assumed to be (S) by comparison of the observed opti-
cal rotation of the product (+) with that reported for (R)-10 ([a]2D5 =À15.7 (c=2.48,
heptane, 35.8% ee)) [17], see also [21])2). A repetition of the experiment with (R)-2
(91.9% ee (HPLC); [a]2D5 =À21.8 (c=1.35, CHCl3)) led to (S)-10 with 93.5% ee
(HPLC) and [a]2D5 =+29.2 (c=1.17, heptane).
Scheme 4
2
)
There is an inconsistency in the literature (see comment in [22]). For example, the partially stereoselective
formation of (À)-(R)-10 from (À)-(S)-styrene oxide, which had been prepared from (+)-(S)-mandelic acid,
has been reported [17]. On the other hand, according to [20], the transformation of (+)-(R)-styrene oxide
with NH4SCN and RuCl3 led to (À)-(S)-10 in 78% optical purity. Soai and Mukaiyama described an enan-
tioselective synthesis of (À)-(R)-10 [19].

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Table 1. SiO2-Catalyzed Reactions of 4a–4c with 2 in CH2Cl2
Substrates
Reaction time
Products and yields
4a–4c
2
10
11a–11c
(R)-2
2 h
(S)-10 83% (97% ee)
–
(RS)-2
(RS)-2
10 h
10 h
(RS)-10 66%
(RS)-10 58%
79%
92%
The analogous reactions of 3-phenyloxazolidine-2-thione (4b) and 3-phenylthiazo-
lidine-2-thione (4c) with (RS)-2 (molar ratio 1:2 in both cases) under the same condi-
tions for 10 h afforded racemic thiirane (RS)-10 in 66 and 58% yield, and the corre-
sponding carbonyl compounds 11b and 11c in 79 and 92% yield, respectively
(Scheme 4 and Table 1).
A reaction mechanism for the stereoselective S transfer reaction is proposed in
Scheme 4. In accordance with the previously described formation of 4-phenyl-1,3-
oxthiolanes (cf. [7–11]), the ring opening of 2 by nucleophilic attack by the S-atom
at C(2) occurs via inversion of the configuration, leading to intermediate A. Ring clo-
sure gives the 1,3-oxathiolane B, which, in the case of X=RN, rearranges to yield C.
The latter then decomposes to give the isolated products 10 and 11.
2.3. Reaction of 1,3-Dimethylimidazolidine-2-thione (4a) with 1,2-Epoxycyclohex-
ane (7). The SiO2-catalyzed reaction of 4a with 7 (molar ratio of 1:3.75) in anhydrous
CH2Cl2 at 58 under an N2 atmosphere for 40 h gave thiabicyclo compound 12 in 98%
1
yield based on the H-NMR analysis of the reaction mixture and a weighed amount
of 1,1,2,2-tetrachloroethane as a standard (Scheme 5).
2.4. Reaction of Imidazolidine-2-thione (5) with (RS)-2. To a suspension of 1 equiv.
of 5 in anhydrous CH2Cl2 and Et2O (9 :1) under an N2 atmosphere, 2.2 equiv. of BF3 ·
Et2O were added at À668. After stirring the mixture for 15 min at À668, 4 equiv. of
Scheme 5

Helvetica Chimica Acta – Vol. 88 (2005)
3257
(RS)-2 were added dropwise during 20 min. The reaction was quenched by addition of
H2O, and, after workup, a 95% yield of 1,3-bis[(E)-2-phenylethen-1-yl]imidazolidine-2-
thione (13) was obtained as a yellow powder (Scheme 6).
Scheme 6
The analogous BF3-catalyzed reaction of 1,3-diacetylimidazolidine-2-thione (6)
with (RS)-2 in anhydrous CH2Cl2 at À788 did not take place. Therefore, the reaction
was carried out by heating a solution of 6 (1 equiv.) and (RS)-2 (5 equiv.) in xylene
under an N2 atmosphere to reflux for 38 h. After workup, column chromatography of
the residue gave two imidazolidine-2-thione derivatives 14 and 13 in 45 and 7%
yield, respectively (Scheme 7).
Scheme 7
The structures of 13 and 14 were assigned as usual (HSQC, HMBC, 1D-NOESY
NMR spectra in the case of 13). The 1D-NOESY spectrum of 13, which has a molecular
symmetry of C2v, on irradiation of 2 HÀC(1’) at 8.25 ppm, gave one NOE signal for four
aromatic ortho-H-atoms at 7.41–7.39 ppm, indicating the (E)-configuration of the two
olefinic bonds. On the other hand, irradiation of 2 HÀC(2’) at 5.93 ppm led to another
NOE signal at 4.02 ppm for four H-atoms of the ethylene group, indicating the s-trans-
conformation of the two NÀC(1’) bonds. Finally, the structures of 13 and 14 were estab-
lished by X-ray crystallography (Fig.).
The five-membered ring of 13 is planar, and the whole molecule is essentially pla-
nar, with only small deviations of the Ph-ring planes from that of the five-membered
ring. The maximum deviation from the mean plane of the molecule is 0.266(2) Å for
N(3). As a result of the planarity, the molecular symmetry is close to C2v.
The molecule of 14 is also almost planar with an r.m.s. deviation of all non-H-atoms
from perfect Cs symmetry of 0.086 Å. The five-membered ring is very slightly puckered
into a half-chair conformation twisted on C(4)ÀC(5).
3. Discussion and Conclusion. – The results presented show that 1,3-dioxolane-2-
thione (3) reacts with optically active oxiranes (S)-1 and (R)-2 in the presence of
SiO2 to afford spirocyclic 1,3-oxathiolanes 8 and 9, respectively, with high regio- and
stereoselectivity. In contrast, the SiO2-catalyzed reactions of the thiocarbonyl com-
pounds 4a–4c with phenyloxirane (2) do not give 1,3-oxathiolanes, but thiirane (S)-

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Helvetica Chimica Acta – Vol. 88 (2005)
Figure. ORTEP Plots [23] of the molecular structures of a) 13 and b) 14 (arbitrary numbering of the atoms;
displacement ellipsoids with 50% probability)
10 and the corresponding carbonyl compounds 11a–11c. In the case of 4a and (R)-2, the
optically active thiirane (S)-10 was formed in good yield and in high optical purity
(Scheme 4 and Table 1). The starting material 4a can easily be regenerated by thiona-
tion of the byproduct 11a with Lawesson’s reagent [24]. The analogous reaction of
4a with oxirane 7 leads to thiirane 12 in 98% yield. This novel approach to thiiranes,
including optically active ones, is very convenient and is worthy of further investigation
in order to generalize this methodology3). It has to be pointed out that only thiocar-
bonyl compounds with an attached N-atom, i.e., thiourea derivatives and analogues,
undergo this S-transfer reaction efficiently, whereas thioketones, thiocarbonates, etc.
yield mainly the ring-enlarged 1,3-oxathiolanes (cf. Scheme 4).
Imidazolidine-2-thione (5) and its 1,3-diacetyl derivative 6, which is deactivated by
two electron-withdrawing Ac groups, undergo very different reactions with (RS)-2, i.e.,
the ring opening of the oxirane occurs via nucleophilic attack of the N-atom and sub-
sequent extrusion of H2O and AcOH, respectively, to give the N-styryl-substituted
products, 13 and 14, exclusively (Scheme 7). Neither 1,3-oxathiolanes nor thiirane 10
were observed. For the formation of 13, two mechanisms are proposed in Scheme 8.
a) The ring opening of the complexed oxirane via attack of the N-atom of 5 could
lead to D, which undergoes elimination of H2O to give 15. An analogous reaction
with the other NH group could afford 13. There are two weak points in this mechanism:
firstly, the N-atom has to be the more reactive nucleophile, and secondly, the ring open-
ing of (RS)-2 takes place by cleavage of the OÀC(3) bond in a reaction, which is cata-
3
)
For previously described transformations of oxiranes into thiiranes, see [15–20] and refs. cit. therein.

Helvetica Chimica Acta – Vol. 88 (2005)
3259
Scheme 8
lyzed by the strong Lewis acid BF3. This interpretation is contrary to the common
observation for the ring opening of 2-phenyloxirane in the presence of Lewis acids.
b) As a second mechanism, the enethiol form of 5, i.e., 5a, could react with phenylace-
taldehyde (16)4) in an ene-like reaction, leading to intermediate E. Dehydration of the
latter yields again 15. The second mechanism seems to be more reasonable, although
there is no proof.
It is even more difficult to formulate a convincing mechanism for the transforma-
tion of 6 and (RS)-2 to 13 and 14. The simplest explanation would be a hydrolytic deace-
tylation followed by one of the sequences shown in Scheme 8.
We thank the analytical services of our institute for NMR and mass spectra and elemental analyses, Mr. B.
Bürgi for his assistance with the determination of the crystal structures, and the Swiss National Science Founda-
tion and F. Hoffmann-La Roche AG, Basel, for financial support.
Experimental Part
1. General. See [25]. Optical rotations: a Perkin-Elmer-241 polarimeter (c=1, in THF). IR Spectra: film or
KBr, cmÀ1. NMR Spectra: at 300 or 600 (1H), and 75.5 or 150.9 MHz (13C) in CDCl3. Enantiomeric excesses (ee)
were determined by anal. HPLC on a (S,S)-Whelk-O-1 column.
2. General Procedure for the Reactions of Thiocarbonyl Compounds 3 and 4a–4c with Oxiranes (S)-1, (R)-2,
and 7. To the soln. of 3 or 4a–4c (ca. 1 mmol) and an oxirane (ca. 2 mmol) in anh. CH2Cl2 (10–15 ml) under an
N2 atmosphere, 4.5 g of silica gel were added at 08. After stirring the suspension for 10 h–2 d at 08, the mixture
was filtered, and the residue was washed with Et2O (4×). Then, the combined filtrate was evaporated in vacuo.
The products were separated by column chromatography (CC; SiO2; hexane/Et2O).
3. Reactions of 1,3-Dioxolane-2-thione (3). 3.1. With (S)-2-Methyloxirane ((S)-1). Reaction of 3 (104 mg,
1 mmol) with (S)-1 (116 mg, 2 mmol) in 15 ml of 1,2-dichloroethane and 4.5 g of SiO2 at 2–58, 2 d, and CC
(SiO2, hexane/Et2O 1:1) yielded 44 mg (27%) of (S)-7-methyl-1,4,6-trioxa-9-thiaspiro[4.4]nonane (8). Colorless
oil. [a]2D3 =+12.2. 1H-NMR (300 MHz, CDCl3): 4.44 (m, HÀC(7)); 4.21 (m, 2 HÀC(2), 2 HÀC(3)); 3.17 (dd,
4
)
From some reactions of thiocarbonyl compounds with phenyloxirane, 2,4-diphenylbut-2-enal, i.e., the prod-
uct of the aldol condensation of phenylacetaldehyde (16), was isolated as a yellow oil. This indicates that the
precursor 16 has been formed in situ by the BF3-catalyzed ring opening (OÀC(2) cleavage) of (RS)-2 and a
subsequent rearrangement via a 1,2-H shift.

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Helvetica Chimica Acta – Vol. 88 (2005)
J=10.2, 4.6, 1 HÀC(8)); 3.00 (t-like, Jꢀ10.0, 1 HÀC(8)); 1.44 (d, J=6.1, Me). 13C-NMR (75.5 MHz, CDCl3):
135.8 (s, C(5)); 77.9 (d, C(7)); 65.7, 64.8 (2t, C(2), C(3)); 40.1 (t, C(8)); 19.0 (q, Me). CI-MS (NH3): 165 (5),
164 (7), 163 (100, [M+H]+), 106 (25). Anal. calc. for C6H10O3S (162.21): C 44.43, H 6.21; found C 44.08, H 5.79.
3.2. With (R)-2-Phenyloxirane ((R)-2). Reaction of 3 (104 mg, 1 mmol) with (R)-2 (240 mg, 2 mmol) in 15
ml of anh. CH2Cl2 and 4.5 g of SiO2 at 0–58, 2 d, and CC (SiO2, hexane/Et2O 3 :1) yielded 76 mg (34%) of (S)-8-
phenyl-1,4,6-trioxa-9-thiaspiro[4.4]nonane (9). Colorless oil. [a]2D3 =À10.3. IR (film): 3061w, 3029w, 2975m,
2898s, 1602w, 1493s, 1453s, 1359w, 1346w, 1302w, 1276m, 1247m, 1210s, 1147vs, 1119vs, 1079s, 1063s, 1030vs,
1
1004vs, 950vs, 861w, 797w, 762s, 700vs. H-NMR (600 MHz, CDCl3): 7.48–7.46 (m, 2 arom. H); 7.35–7.32 (m,
2 arom. H); 7.29–7.26 (m, 1 arom. H); 4.86 (dd, J=6.9, 5.9, HÀC(8)); 4.41 (dd, J=9.2, 5.7, 1 HÀC(7));
4.20–4.09 (m, 2 HÀC(2), 2 HÀC(3)); 4.08 (dd, J=9.2, 7.0, 1 HÀC(7)). 13C-NMR (150.9 MHz, CDCl3): 138.4
(s, 1 arom. C); 137.1 (s, C(5)); 128.8 (d, 2 arom. CH); 128.0 (d, 1 arom. CH); 127.9 (d, 2 arom. CH); 75.5 (t,
C(7)); 65.6, 65.4 (2t, C(2), C(3)); 54.2 (d, C(8)). CI-MS (NH3): 227 (6), 226 (13), 225 (100, [M+H]+), 106
(12). Anal. calc. for C11H12O3S (224.28): C 58.91, H 5.39; found C 59.31, H 5.72.
4. Reaction of 1,3-Dimethylimidazolidine-2-thione (4a) with (R)-2. Reaction of 4a (97 mg, 0.74 mmol) with
(R)-2 (150 mg, 1.25 mmol) in 10 ml of anh. CH2Cl2 and 3.6 g of SiO2 at 08, 2 h, and CC (SiO2, hexane) yielded 84
mg (83%) of (S)-2-phenylthiirane ((S)-10) in 97% ee (HPLC) as a colorless oil and 1,3-dimethylimidazolidin-2-
one (11a; Table 1).
An analogous experiment was carried out with (À)-(R)-2 (91.9% ee (HPLC)). The isolated (+)-(S)-10
showed [a]2D3 +29.2 (c=1.17, in heptane; 93.5% ee (HPLC)).
5. Reaction of 3-Phenyloxazolidine-2-thione (4b) with (RS)-2. Reaction of 4b (94 mg, 0.5 mmol) with (RS)-2
(120 mg, 1 mmol) in 10 ml of anh. CH2Cl2 and 3.0 g of SiO2 at 08, 10 h, and CC (SiO2, hexane/AcOEt) yielded 45
mg (66%) of (RS)-10 and 64 mg (79%) of 3-phenyloxazolidin-2-one (11b; Table 1).
6. Reaction of 3-Phenylthiazolidine-2-thione (4c) with (RS)-2. Reaction of 4c (49 mg, 0.25 mmol) with (RS)-
2 (60 mg, 0.5 mmol) in 10 ml of anh. CH2Cl2 and 1.5 g of SiO2 at 08, 10 h, yielded 19.6 mg (58%) of (RS)-10 and
1
41 mg (92%) of 3-phenylthiazolidin-2-one (11c) based on the H-NMR analysis of the reaction mixture and a
weighed amount of 1,1,2,2-tetrachloroethane as a standard (Table 1).
7. Reaction of 4a with 1,2-Epoxycyclohexane (=7-Oxabicyclo[4.1.0]heptane; 7). Reaction of 4a (104 mg, 0.8
mmol) with 7 (297 mg, 3 mmol) in 15 ml of anh. CH2Cl2 and 4.0 g of SiO2 at 08, 40 h, yielded 89 mg (98%) of 7-
thiabicyclo[4.1.0]heptane (12) based on the 1H-NMR analysis of the reaction mixture and a weighed amount of
1,1,2,2-tetrachloroethane as a standard.
8. Reaction of Imidazolidine-2-thione (5) with (RS)-2. To the suspension of 5 (102 mg, 1 mmol) in anh.
CH2Cl2 (18 ml) and Et2O (2 ml) under an N2 atmosphere, 2.2 equiv. of BF3 ·Et2O were added at À668, which
led to an almost homogenous soln. After stirring the mixture for 15 min at À668, 480 mg (4 mmol) of (RS)-2
were added dropwise over 20 min. After stirring for an additional 10 min, the reaction was quenched by addition
of H2O, and the mixture was washed with sat. aq. NaCl soln. (3×). The combined org. layers were dried (MgSO4)
and evaporated in vacuo. The residue was washed with hexane (4×), filtered, and dried under high vacuum: 290
mg (95%) of 1,3-bis[(E)-2-phenylethen-1-yl]imidazolidine-2-thione (13). Yellow powder. M.p. 2488 (dec.). IR
(KBr): 3054m, 3023m, 2953w, 2890w, 1641s, 1597m, 1574w, 1475s, 1450s, 1428s, 1386s, 1291s, 1261s, 1207m,
1182m, 1124w, 1084m, 1074m, 1031w, 978w, 952s, 939s, 904w, 869m, 841w, 830w, 821m, 760m, 748s, 691s. 1H-
NMR (600 MHz, CDCl3): 8.25 (d, J=14.7, 2 HÀC(1’)); 7.41–7.39 (m, 4 arom. H); 7.32–7.30 (m, 4 arom. H);
7.21–7.18 (m, 2 arom. H); 5.93 (d, J=14.7, 2 HÀC(2’)); 4.02 (s, 2 HÀC(4), 2 HÀC(5)). 13C-NMR (150.9
MHz, CDCl3): 176.3 (s, C(2)); 136.4 (s, 2 arom. C); 129.0 (d, 4 arom. C); 126.97, 126.95 (2d, 2 arom. C, 2
C(1’)); 126.0 (d, 4 arom. C); 112.0 (d, 2 C(2’)); 44.4 (t, C(4), C(5)). CI-MS (NH3): 309 (11), 308 (23), 307
(100, [M+H]+), 277 (7).
Crystals of 13 suitable for the X-ray crystal-structure determination were grown from CH2Cl2/hexane.
9. Reaction of 1,3-Diacetylimidazolidine-2-thione (6) with (RS)-2. The soln. of 6 (186 mg, 1 mmol) and (RS)-
2 (600 mg, 5 mmol) in xylene was heated to reflux for 38 h. After evaporation of the solvent in vacuo, 10 ml of
Et2O/hexane (2 :8) were added to the solid residue. The mixture was stirred vigorously for 5 min and then fil-
tered. The filter cake was washed with hexane (3×). CC (SiO2, hexane/ AcOEt 5 :1) of the filter cake yielded 111
mg (45%) of 1-acetyl-3-[(E)-2-phenylethen-1-yl]imidazolidine-2-thione (14) and 20 mg (7%) of 13.
Data of 14. Colorless crystals. M.p. 169.3–169.78. IR (KBr): 3063w, 3046w, 3031w, 3002w, 2980w, 2949w,
2911w, 1682s, 1635s, 1597m, 1575w, 1487s, 1470s, 1448m, 1420s, 1388s, 1371s, 1324m, 1268s (br.), 1201s, 1100m,
1088m, 1071m, 1039m, 1021m, 963m, 942s, 902w, 861w, 836w, 825m, 752s, 718w, 690s. 1H-NMR (300 MHz,
CDCl3): 8.20 (d, J=14.8, HÀC(1’)); 7.42–7.20 (m, 5 arom. H); 6.05 (d, J=14.8, HÀC(2’)); 4.16–4.10 (m, 2
HÀC(5)); 3.88–3.83 (m, 2 HÀC(4)); 2.88 (s, Me). 13C-NMR (75.5 MHz, CDCl3): 175.9 (s, C=S); 171.7 (s,
C=O); 135.5 (s, 1 arom. C); 128.7 (d, 2 arom. C); 127.2, 126.2 (2d, 1 arom. C, C(1’)); 125.9 (d, 2 arom. C);

Helvetica Chimica Acta – Vol. 88 (2005)
3261
114.8 (d, C(2’)); 43.7, 43.4 (2t, C(4), C(5)); 26.8 (q, Me). CI-MS (NH3): 249 (6), 248 (16), 247 (100, [M+H]+), 217
(9), 173 (23). Anal. calc. for C13H14N2OS (246.33): C 63.39, H 5.73, N 11.37, S 13.02; found C 63.25, H 5.72,
N 11.41, S 12.81.
Crystals of 14 suitable for the X-ray crystal-structure determination were grown from CH2Cl2/hexane.
10. X-Ray Crystal-Structure Determination of 13 and 14 (Table 2 and Fig.)5). All measurements were per-
formed on a Nonius KappaCCD area-detector diffractometer [26] using graphite-monochromated MoKa radi-
ation (l 0.71073 Å) and an Oxford Cryosystems Cryostream 700 cooler. The data collection and refinement
parameters are given in Table 2, and views of the molecules are shown in the Figure. Data reduction was per-
formed with HKL Denzo and Scalepack [27]. The intensities were corrected for Lorentz and polarization
effects, and an absorption correction based on the multi-scan method [28] was applied. The structures were
solved by direct methods using SIR92 [29], which revealed the positions of all non-H-atoms. The non-H-
atoms were refined anisotropically. All of the H-atoms were placed in geometrically calculated positions and
Table 2. Crystallographic Data of Compounds 13 and 14
13
14
Crystallized from
CH2Cl2/hexane
C19H18N2S
306.42
colorless, prism
0.12×0.17×0.30
160(1)
CH2Cl2/hexane
C13H14N2OS
246.33
colorless, prism
0.15×0.22×0.25
160(1)
Empirical formula
Formula weight [g molÀ1
Crystal color, habit
Crystal dimensions [mm]
Temp. [K]
]
Crystal system
Space group
monoclinic
P21/c
monoclinic
P21/n
Z
4
4
Reflections for cell determination
2q Range for cell determination [8]
29762
4–60
19981
4–60
Unit cell parameters
a [Å]
b [Å]
c [Å]
b [8]
15.7032(3)
8.3479(2)
12.3836(3)
104.668(1)
1570.45(6)
1.296
0.204
f and w
60
9.6656(1)
11.5899(2)
10.8533(2)
92.0332(7)
1215.06(4)
1.346
0.251
f and w
60
V [Å3]
DX [gcmÀ3
]
m(MoKa) [mmÀ1
Scan type
2q [8]
]
Transmission factors (min; max)
Total reflections measured
Symmetry independent reflections
Reflections with I>2s(I)
Reflections used in refinement
Parameters refined
0.779; 0.980
43637
4568
2973
4568
0.897; 0.965
32396
3548
2850
3546
200
155
Final R(F) [I>2s (I) reflections]
0.0512
0.1385
0.0709; 0.1534
1.026
0.0378
0.1060
0.0544; 0.3109
1.044
wR(F2) (all data)
Weighting parameters [a; b]a)
Goodness-of-fit
Secondary extinction coefficient
Final Dmax/s
0.007(2)
0.001
0.30; À0.32
–
0.001
0.37; À0.47
D1 (max; min) [e ÅÀ3
]
a) w=[s2(F2o)+(aP)2 +bP]À1, where P=(Fo2 +2F2c )/3.
5
)
CCDC-286002–286003 contain the supplementary crystallographic data for this paper. These data can be
obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.

3262
Helvetica Chimica Acta – Vol. 88 (2005)
refined 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 Ueq for the Me group in 14). The refinement of each structure was
carried out on F2 using full-matrix least-squares procedures, which minimized the function Sw(Fo2 – Fc2)2. A cor-
rection for secondary extinction was applied in the case of 13. In 14, two reflections, whose intensities were con-
sidered to be extreme outliners, were omitted from the final refinement. Neutral atom scattering factors for non-
H-atoms were taken from [30a], and the scattering factors for H-atoms were taken from [31]. Anomalous dis-
persion effects were included in Fc [32]; the values for f’ and f’’ were those of [30b]. The values of the mass
attenuation coefficients are those of [30c]. All calculations were performed using the SHELXL97 [33] program.
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Received October 12,2005