Lewis acid catalyzed reactions of thioketones with 1,2-epoxycyclohexane and 1,2-epoxycyclopentane

Article abstract of DOI:10.1002/(SICI)1522-2675(19991215)82:12<2316::AID-HLCA2316>3.0.CO;2-3

Non-enolizable thioketones and 1,2-epoxycyeloalkanes undergo a Lewis acid catalyzed addition reaction to give 1,3-oxathiolanes. Appropriate reaction conditions are CH₂Cl₂ as the solvent BF₃. Et₂O as the Lewis acid, and a temperature between -78°and r.t. Under the reaction conditions, the 1,3-oxathiolanes are only moderately stable. They decompose to yield the corresponding epithiocycloalkane and ketone. In general, 1,3-dithiolanes are isolated as minor products or, after prolonged reaction, as the main product. These secondary products are formed via the Lewis acid catalyzed reaction of the intermediate epithiocycloalkane and a second molecule of the thioketone. In the reaction of thiobenzophenone and 1,2-epoxycyclohexane, trans-8,8- diphenyl-7,9-dioxabicyclo[4.3.0]nonane is formed in small amounts as an additional side product (Scheme 12). In all cases, the newly formed heterocycle and the carbocycle are trans-fused. This result is consistent with a nucleophilic ring-opening of the complexed oxirane by the thioketone via inversion of the configuration and subsequent formation of the O(1)-C(2) bond of the 1,3-oxathiolane (Scheme 13). The surprising formation of the fused 1,4-oxathiepan derivative 23 (Scheme 9) is in accordance with an ionic reaction mechanism (cf. Scheme 15).

Full text of DOI:10.1002/(SICI)1522-2675(19991215)82:12<2316::AID-HLCA2316>3.0.CO;2-3

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Helvetica Chimica Acta ± Vol. 82 (1999)
Lewis Acid Catalyzed Reactions of Thioketones with
1,2-Epoxycyclohexane and 1,2-Epoxycyclopentane
1
by Milen Blagoev ), Anthony Linden, and Heinz Heimgartner*
Organisch-chemisches Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich
Non-enolizable thioketones and 1,2-epoxycycloalkanes undergo a Lewis acid catalyzed addition reaction to
give 1,3-oxathiolanes. Appropriate reaction conditions are CH2Cl2 as the solvent, BF3 ´ Et2O as the Lewis acid,
and a temperature between 788 and r.t. Under the reaction conditions, the 1,3-oxathiolanes are only
moderately stable. They decompose to yield the corresponding epithiocycloalkane and ketone. In general, 1,3-
dithiolanes are isolated as minor products or, after prolonged reaction, as the main product. These secondary
products are formed via the Lewis acid catalyzed reaction of the intermediate epithiocycloalkane and a second
molecule of the thioketone. In the reaction of thiobenzophenone and 1,2-epoxycyclohexane, trans-8,8-diphenyl-
7,9-dioxabicyclo[4.3.0]nonane is formed in small amounts as an additional side product (Scheme 12). In all
cases, the newly formed heterocycle and the carbocycle are trans-fused. This result is consistent with a
nucleophilic ring-opening of the complexed oxirane by the thioketone via inversion of the configuration and
subsequent formation of the O(1) C(2) bond of the 1,3-oxathiolane (Scheme 13). The surprising formation of
the fused 1,4-oxathiepan derivative 23 (Scheme 9) is in accordance with an ionic reaction mechanism (cf.
Scheme 15).
1. Introduction. ± Various preparative methods for the synthesis of 1,3-oxathiolanes
are known [2]. Among them are reactions between thiocarbonyl compounds and
oxiranes. Depending on the reaction conditions, the oxirane serves as the precursor
of a C
O C fragment (Path a) or of a C C O fragment (Path b, Scheme 1).
Whereas, in the first case, the reaction with CˆS groups is believed to proceed via
1,3-dipolar cycloaddition of an intermediate carbonyl ylide (cf. [3][4])2), the
reaction mechanism of the cycloaddition in the second case is a non-concerted one
(cf. [1]).
Scheme 1
In reactions of type b with CˆS groups, the ring opening of the oxirane via cleavage
of a C O bond requires an activation of the oxirane with an electrophile. For example,
treatment of oxiranes 1 with isothiocyanates leads to 1,3-oxathiolan-2-imines 2 [6 ± 10]
1
)
)
Part II of the planned Ph.D. thesis of M.B., University of Zürich. For Part I, see [1].
Analogously, 1,3-oxathiolanes have been prepared by 1,3-dipolar cycloaddition of thiocarbonyl ylides with
carbonyl compounds [5].
2

Helvetica Chimica Acta ± Vol. 82 (1999)
2317
Scheme 2
(cf. [11]) (Scheme 2). It is most likely that zwitterions of type A are intermediates in
these reactions3)4).
Reactions of oxiranes with CS2 have been described in several reports (cf. [13][14]
and refs. cited therein). In general, product mixtures consisting of 1,3-oxathiolane-2-
thiones 3, 1,3-oxathiolan-2-ones, 1,3-dithiolane-2-thiones, and thiiranes were obtained
in low yields. Taniguchi et al. showed that the reaction in the presence of Et3N is
markedly accelerated when it is performed under high pressure [13]. A reaction
mechanism via intermediate B is proposed (Scheme 2); the latter is formed by the
nucleophilic ring opening of the oxirane with the adduct of Et3N and CS2. Analogous
reactions have been reported for epoxy-5a-cholestane derivatives, which produce
steroidal 1,3-oxathiolane-2-thiones [15]. In these cases, the reaction at room temper-
ature and normal pressure was catalyzed either by Et3N or LiBr5).
On the other hand, formation of 1,3-oxathiolanes from oxiranes and non-cumulated
CˆS compounds is scarcely known [9b][21][22]6). In these cases, the oxirane ring-
opening by nucleophilic attack of the S-atom is accelerated by Lewis acids, e.g., BF3 ´
Et2O [22]. Recently, we have reported the BF3-catalyzed reaction of 1,3-thi-
azole-5(4H)-thiones 4 with oxiranes [1][24]. In the case of 1,2-epoxycyclohexane
(5a), spirocyclic 1,3-oxathiolanes of type 6a were formed as the main products
(Scheme 3).
3
)
)
)
In some cases, the formation of mixtures of 1,3-oxathiolan-2-imines and 1,3-oxazolidine-2-thiones has been
observed (e.g., [6]). This result is easily explained by the presence of A as an intermediate.
The reaction of oxirane and HSCN gave 2-hydroxyethyl thiocyanate, which yielded 1,3-oxathiolan-2-imine
on treatment with HCl [12].
Reactions of a-hydroxyoxiranes and CS2 in the presence of NaH or KH yielded cyclic a-hydroxyxanthates
(1,3-oxathiolane-2-thiones) [16 ± 18]. This stereospecific transformation involves the initial formation of a
xanthate anion, followed by an intramolecular nucleophilic opening of the oxirane. Analogously, a-
hydroxyoxiranes were reacted with thiocarbonyl diimidazole to give a thioimidazolide, which, upon
treatment with aniline, followed by hydrolysis of the intermediate iminocarbonate, yielded 3-(a-
hydroxyalkyl)-1,3-oxathiolan-2-ones (cyclic thiocarbonates) in a stereospecific manner [19][20].
With the aim of converting 1,3-dithiolane-2-thiones to the corresponding 1,3-dithiolan-2-ones, reactions
with oxiranes in the presence of HBF4 ´ Et2O have been performed [23]. The intermediate spirocyclic 1,3-
oxathiolanes were detected but not isolated.
4
5
6
)

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Helvetica Chimica Acta ± Vol. 82 (1999)
Scheme 3
Analogously, cyclic thiocarbonates (e.g., 1,3-dioxolane-2-thiones, 1,3-dithiolane-2-
thiones) and oxiranes undergo a Lewis acid catalyzed addition reaction to give
spirocyclic 1,3-oxathiolanes with an orthocarbonate structure [25].
To establish the scope and limitations, as well as the reaction mechanism, of this
Lewis acid catalyzed 1,3-oxathiolane synthesis, we investigated reactions with other
CˆS compounds. In the present paper, the results of the reactions of 1,2-epoxycyclo-
hexane oxide (5a) and 1,2-epoxy-cyclopentane oxide (5b) with various non-enolizable
thioketones are described.
2. Results. ± 2.1. Reactions of 1,1,3,3-Tetramethylindane-2-thione (7). The reaction
of 7 with 5a was carried out in dry CH2Cl2 under an N2 atmosphere at room
temperature (Scheme 4). The addition of BF3 ´ Et2O to the solution of 7 resulted in a
slight reddening of the pink-orange color. After the addition of 3 equiv. of 5a, the
mixture was stirred overnight. As 7 was still not completely consumed (TLC), another
2.5 equiv. of 5a were added, and the mixture was stirred until no 7 could be detected.
After two days, the almost colorless solution was evaporated, and the products were
separated by prep. TLC to give 8, 9, and 10 in 9, 20, and 51% yield, respectively
(Scheme 4, Table 1). The structures of the spirocyclic 1,3-oxathiolane 8 and the 1,3-
dithiolane 9 were established by X-ray crystal-structure determinations (Fig. 1). In
both cases, the cyclohexane ring and the heterocycle are trans-fused.
As in previously described examples, the initially formed product is the 1:1 adduct 8
(cf. [1][23 ± 25]). This has clearly been shown by performing the reaction under
different conditions (Table 1). After 15 h at room temperature, when still 32%
of 7 was recoverable, 8, 9, and 10 were obtained in 50, 16, and 41% yield, respectively,
whereas after 1.5 h at 08, the 1,3-oxathiolane 8 was nearly the sole product (69%
isolated).
Scheme 4

Helvetica Chimica Acta ± Vol. 82 (1999)
2319
Fig. 1. ORTEP Plots [26] of the molecular structures of a) 8 and b) 9 (major conformations only; disorder not
shown; only one of the three independent molecules of 9 shown; arbitrary numbering of the atoms; 50%
probability ellipsoids)
Table 1. BF3-Catalyzed Reaction of 5a with 7
Ratio
Temp.
Reaction time
[h]
Yields of products [%]a)
5a/7
[8]
8
9
10
5 : 1
5 : 1
5 : 1
r.t.
r.t.
08
50
15
1.5
9
50
69
20
16
2
51
21b)
±c)
c
a) Calculated with respect to consumed 7. b) Recovered 7: 32%. ) Recovered 7: 23%.
With the aim of corroborating the proposal that 9 and 10 are formed from 8 in a
consecutive reaction (Scheme 5), several control experiments were carried out. a) To
check the stability of 8 under the reaction conditions, a solution of 8 and 1.1 equiv. of
BF3 ´ Et2O in CH2Cl2 was stirred at room temperature. After four days, no 8 could be
detected, and 1,1,3,3-tetramethylindan-2-one (10) was isolated in 80% yield (cf. [23]).
b) The BF3-catalyzed reaction of 7 with 1,2-epithiocyclohexane (11), which is proposed
to be the second product of the decomposition of 8, gave, after 14 h at room
temperature, dithiolane 9 as the only product (85% yield). c) On the other hand, all
attempts to obtain 8 by treatment of a mixture of ketone 10 and epithio compound 11
with BF3 ´ Et2O were in vain; only starting material 10 was recovered.

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Helvetica Chimica Acta ± Vol. 82 (1999)
Scheme 5
In an analogous manner, the reaction of 7 with an excess of 1,2-epoxycyclopentane
(5b) was performed at room temperature overnight. Only 7 and the corresponding
ketone 10 could be detected by TLC. After addition of another 2 equiv. of 5b and
stirring the mixture for an additional 14 h, 25% of 7 and 68% of 10 were isolated.
Repeating the reaction at 08 overnight yielded 10 (77%)7) and the 1:1 adduct 12
(7%)7) (Scheme 6). When the reaction was carried out at 308 for 15 min, 64% of the
starting material 7 was recovered, while 10 and 12 were isolated in 17 and 38% yield8),
respectively9). The trans-fusion of cyclopentane and 1,3-oxathiolane was not proven
but is assumed in analogy to other adducts (vide infra).
Scheme 6
2.2. Reactions of 2,2,4,4-Tetramethyl-3-thioxocyclobutanone (13). Because of the
known high reactivity of 13, the reaction with 5a was performed at low temperature. To
a solution of 13 in CH2Cl2 at 788, 3 equiv. of 5a were added, and the mixture was
stirred for 2 h. Then, at 408, another 3 equiv. of 5a were added. Workup after 20 h
yielded a unique product, which was identified as the 1 : 1 adduct 14 (Scheme 7).
Repeating the reaction at room temperature led to a mixture of 14 and 1,3-dithiolane
15, isolated in 23% and 14% yield, respectively10).
7
)
)
)
)
Yields calculated with respect to the amount of 7 consumed; 26% of 7 recovered.
Calculated on the basis of the amount of 7 consumed.
8
9
Reducing the temperature to 788 was not appropriate, because the reaction was too slow.
Two additional products, which crystallized accidentally from fractions of the chromatographic separation,
were obtained in very small amounts (< 1%). Their structures have been established by MS and X-ray
crystallography as the cyclotetramer 17 of 1,2-epithiocyclohexane 11 and the cyclohexamer 18 of 1,2-
epoxycyclohexene (5a). The crystal structures will be published elsewhere.
10

Helvetica Chimica Acta ± Vol. 82 (1999)
2321
Scheme 7
The analogous reaction of 13 with 5b was carried out at room temperature. After
stirring the mixture overnight, 13 was completely consumed (TLC), and 1,3-dithiolane
16 was isolated as the only product in 26% yield. When the reaction was performed at
788 for 14 h, 25% of 13 were recovered, and 16 was obtained in 25% yield. The
expected 1,3-oxathiolane, which must have been formed as the initial product, could
not be detected.
Crystals of 16 suitable for an X-ray crystal-structure determination were grown
from CH2Cl2/i-PrOH. The molecular structure is shown in Fig. 2; the cyclopentane and
1,3-dithiolane rings are trans-fused.
Fig. 2. ORTEP Plot [26] of the molecular structure of 16 (arbitrary numbering of the atoms; 50% probability
ellipsoids)
2.3. Reactions with 2,2,4,4-Tetramethylcyclobutane-1,3-dithione (19). To a solution
of dithione 19 in CH2Cl2, 2.2 equiv. of BF3 ´ Et2O and 5 equiv. of 5a were added, and the
mixture was stirred at room temperature. Another 2 equiv. of 5a were added after 2.5 h
and again after 14 h. After 26.5 h, the mixture was almost colorless, and no 17 could be
detected by TLC. The usual workup of the complex mixture, and separation by prep.
TLC and HPLC gave the mono-adducts 20, 21, and 14 in 4, 2, and 31% yield,
respectively, as well as the bis-adducts trans-22 and cis-22 in 21 and 16% yield,
respectively (Scheme 8). Crystallization of the minor fraction of the bis-adducts from
i-PrOH/CH2Cl2 gave single crystals suitable for an X-ray analysis. The molecular
structure of cis-22a is shown in Fig. 3. The molecule is almost s-symmetric with two

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Helvetica Chimica Acta ± Vol. 82 (1999)
Scheme 8
Fig. 3. ORTEP Plot [26] of the molecular structure of one of the two symmetry-independent molecules of cis-22a
(arbitrary numbering of the atoms; 50% probability ellipsoids)
trans-fused 7-oxa-9-thiabicyclo[4.3.0]nonane ring systems and both cyclohexane rings
in the chair conformation.
The 1H- and 13C-NMR spectra of cis-22, which was isolated after chromatography,
showed 6 s and 6 q, respectively, for Me groups. In addition, two s for C(1) and C(6) of
the fused-ring systems, as well as for Me2C, appear in the 13C-NMR spectrum. These
data are in agreement with the presence of a mixture of cis-22a and cis-22b that differ in
the relative configurations of the fused rings, i.e., the four Me groups of the s-
symmetric cis-22a are all different, whereas cis-22b, with C2 symmetry, contains only
two types of Me groups. Similarly, the NMR data of the other fraction of the bis-adducts
are consistent with the presence of a mixture of trans-22a and trans-22b.
Repeating the reaction of 19 with only 2 equiv. of 5a and workup after 30 min gave
mixtures of the mono-adducts 20 and 21 in 10% yield, and of bis-adducts 22 in 15%
yield. In addition, 27% of 19 were recovered.

Helvetica Chimica Acta ± Vol. 82 (1999)
2323
The reaction of 19 with 5b led to a quite different result. Apparently, many side
reactions produced many products in low yields. The only products which were isolated
and characterized were 16 and the fused 1,4-oxathiepane derivative 23 (9 and 17%
yield, resp.; Scheme 9). The structure of the unexpected ring-enlargement product 23
has been established by X-ray crystal-structure analysis; the molecular structure is
shown in Fig. 4.
Scheme 9
Fig. 4. ORTEP Plot [26] of the molecular structure of 23 (arbitrary numbering of the atoms; 50% probability
ellipsoids)
2.4. Reactions with 9H-Xanthene-9-thione (24). After the addition of BF3 ´ Et2O to a
solution of 24 in CH2Cl2, the color changed to red-brown. Then, 5 equiv. of 5a were
added, and the mixture was stirred overnight. The usual workup gave, in addition to 9%
recovered 24, the 1,3-dithiolane 26 and xanthone (27) in 6 and 90% yield11),
respectively (Scheme 10).
With the aim of obtaining the expected initial product 25, the reaction was
performed at 788. After 10 min, 50% of 24 was recovered. The main product (44%)
was again xanthone (27), but the 1,3-oxathiolane 25 was also isolated (5%).
The spirocyclic products 25 and 26 were crystallized from i-PrOH/CH2Cl2 and
CHCl3/CH2Cl2, respectively, and their structures were established by X-ray crystallog-
raphy (Fig. 5).
All attempts to obtain addition products of 24 and 5b, i.e., a spirocyclic 1,3-
oxathiolane or 1,3-dithiolane corresponding to 25 and 26, respectively, failed. The only
product which could be detected was 27, even when the reaction was performed at 788
for only 1 to 3 min12).
11
)
)
Yields with respect to the amount of 24 consumed.
After 1 min at 788, 66% of 24 was recovered, and 29% of 27 was isolated as the only product.
12

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Helvetica Chimica Acta ± Vol. 82 (1999)
Scheme 10
Fig. 5. ORTEP Plots [26] of the molecular structures of a) 25 and b) 26 (major conformation of 26 only shown;
disorder not shown; arbitrary numbering of the atoms; 50% probability ellipsoids)
2.5. Reactions with 9H-Fluorene-9-thione (28). As expected, 28 proved to be a very
reactive thioketone. Performing the reaction with 5a at room temperature (15 min) or
at 788 (30 min) gave similar results: ca. 3% of the 1,3-oxathiolane 29, 7 ± 10% of the
1,3-dithiolane 30, and 78 ± 80% of 9H-fluoren-9-one (31) were isolated (Scheme 11). In
addition, ca. 5% of 1,2-dithiane 32, the known dimer of 28 [27], which is formed via a
Diels-Alder reaction, was obtained.
Repeating the reaction at 788 with workup after only 2 min yielded 29 (11%), 31
(70%), and 32 (15%), but none of the 1,3-dithiolane 30 was detected.
The analogous reaction of 28 with 5b was also performed under different
conditions, but no adduct could be isolated. The only indication for the expected
addition reaction was the formation of 9H-fluoren-9-one (31), the product of the

Helvetica Chimica Acta ± Vol. 82 (1999)
2325
Scheme 11
decomposition of the initially formed 1,3-oxathiolane (cf. Sect. 2.1). For example,
workup of the reaction mixture after 1 min at 788 yielded 31, 32, and bis-
fluorenylidene (33 [28], Scheme 11) (37, 16, and 2%, resp.).
2.6. Reactions with Thiobenzophenone (34a) and 4,4'-Dimethoxythiobenzophenone
(34b). To a mixture of 34a and BF3 ´ Et2O in CH2Cl2 at 308, 7 equiv. of 5a were added
all at once, leading to a color change from deep blue to red-orange. The reaction was
complete after 10 min; the sole product was benzophenone (38a), isolated in 85%
yield. The analogous reaction at 508 gave the 1,3-dithiolane 36a and the 1,3-dioxolane
37a13) (4 and 5% yield), in addition to 67% of 38a (Scheme 12).
After crystallization from i-PrOH/CH2Cl2, the structure of 37a has been
established by X-ray crystallography (Fig. 6).
The reaction of the more stable 34b with 5a was performed at 788. After a reaction
time of 30 s, the 1,3-oxathiolane 35b and 4,4'-dimethoxybenzophenone (38b) were
isolated in 20 and 78% yield, respectively.
3. Discussion. ± The intention of the present study was to establish the reaction of
thioketones with oxiranes as a method for the preparation of 1,3-oxathiolanes. For
convenience, we have chosen compounds with non-tautomerizable thiocarbonyl
13
)
In a control experiment, a mixture of benzophenone (38a) and 5a was treated with BF3 ´ Et2O at 08. After
120 min, 37a was isolated in low yield (6%).

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Helvetica Chimica Acta ± Vol. 82 (1999)
Scheme 12
Fig. 6. ORTEP Plot [26] of the molecular structure of 37a (major conformation only shown; disorder not
shown; arbitrary numbering of the atoms; 50% probability ellipsoids)
groups. Because of the pronounced tendency of enolizable thioketones to exist
predominantly in the enethiol form [29], they show a different reactivity, e.g., they
undergo other reactions with oxiranes (cf. [30][31]).
Based on the described results, we propose that the reaction of thioketones and
oxiranes 5 proceeds by activation of the oxirane via complexation with the Lewis
acid14) and nucleophilic ring opening to give a zwitterion of type C (Scheme 13). The
latter then cyclizes to give the 1,3-oxathiolane. In all investigated cases, the cis-fused
oxiranes 5a and 5b were transformed into trans-fused 1,3-oxathiolanes, i.e., the
nucleophilic ring opening occurs with inversion of the configuration at one stereogenic
center. This is in accordance with the proposed mechanism, which is analogous to that
of the formation of 1,3-dioxolanes from ketones and oxiranes. The mechanism of this
latter reaction has been studied thoroughly [32][33].
14
)
The presence of a Lewis acid is necessary as in its absence no reaction occurs.

Helvetica Chimica Acta ± Vol. 82 (1999)
2327
Scheme 13
In addition to 1,3-oxathiolanes, the corresponding 1,3-dithiolanes, as well as the
carbonyl analogue of the starting thioketone, are formed under the reaction conditions.
Under more drastic conditions, these compounds are obtained as the main or sole
products. Their formation can be rationalized by assuming a decomposition of the
primarily formed 1,3-oxathiolane to give a thiirane D, and a second molecule of the
thioketone undergoes an acid-catalyzed reaction to give the 1,3-dithiolane
(Scheme 14). This mechanistic proposal is supported by results of several control
experiments (cf. Sect. 2.1).
Scheme 14
On the other hand, 1,2-epithiocyclohexane (11) and 1,1,3,3-tetramethylindan-2-one
(10) in the presence of BF3 ´ Et2O do not react to give a 1,3-oxathiolane, but the
analogous reaction of 1,2-epoxycyclohexane (5a) and benzophenone (38a) at 08 gave
the corresponding 1,3-oxathiolane 37a in low yield.
Apparently, the 1,3-oxathiolanes formed from 1,2-epoxycyclopentane (5b) are less
stable than the homologues from 5a. In general, the amount of secondary products was
larger, and, in some cases, the initially formed products could not be detected. For
instance, the reaction of the dithione 17 with 5b yielded only the 1,3-dithiolane 16 and
the unexpected product 23. Formally, the formation of the latter can be explained via
the intermediate zwitterion C' (Scheme 15). Nucleophilic attack of the alkoxide O-
atom at the CˆO group of the cyclobutanone leads to the bridged acetal E which, via
ring opening, yields the final product 23. On the other hand, no 23 was formed in the
reaction of 5b with 13, and, therefore, the alternative intermediate G, instead of C'
seems to be more likely. A conceivable mechanism for formation of the zwitterion G is
the addition of a second molecule of 5b to the 1:1 adduct F. A transacetalization of G
can lead to the bridged acetal E', followed by the opening of the four-membered ring to
give I. The latter then decomposes to yield 1,2-epithiocyclopentane and 23. Although
1,2-epithiocyclopentane could not be isolated nor detected, its intermediate formation
is strongly indicated by the presence of the 1,3-dithiolane 16 (Scheme 9, cf. also
Scheme 5).

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Helvetica Chimica Acta ± Vol. 82 (1999)
Scheme 15
We thank the analytical units of our institute for spectra and analyses, Mr. J. Tödtli for his assistance with
the determination of the crystal structures, Dr. J. Romanski and Dr. M. Kägi for samples of the thioketones, and
the Swiss National Science Foundation and F. Hoffmann-La Roche AG, Basel, for financial support.
Experimental Part
1. General. See [34].
2. Reaction of 1,2-Epoxycycloalkanes with Thioketones. General Procedure. To a soln. of a thioketone (ca.
1 mmol) in dry CH2Cl2 (10 ± 15 ml) under N2, BF3 ´ Et2O (1.1 equiv.) was added at r.t. In general, this leads to a
more or less pronounced change in the color of the soln. Then, the mixture was stirred for ca. 30 min. Several
equiv. of 1,2-epoxycyclohexane (5a) or 1,2-epoxycyclopentane (5b) were added dropwise at different temp.
(from 788 up to r.t.), depending on the reactivity of the starting materials. The reaction time varied from
0.5 min to more than 2 d, taking into account the reactivity of the starting materials as well as the stability of the
products. When the reaction was terminated (TLC), the mixture was extracted with sat. aq. NaCl-soln. The
combined org. layers were dried (MgSO4) and evaporated i.v. The products were separated by chromatography
(SiO2; CC or prep. TLC (PLC)).
2.1. With 1,1,3,3-Tetramethylindane-2-thione (7). a) Reaction of 5a (272 mg, 2.8 mmol) with 7 (112 mg,
0.55 mmol), 50 h, r.t.; CC and PLC (hexane/AcOEt 20 :1) yielded 15 mg (9.0%) of 1,1,3,3-tetramethylspiro-
[indane-2,8'-(7'-oxa-9'-thiabicyclo[4.3.0]nonane)] (8), 35 mg (20.0%) of 1,1,3,3-tetramethylspiro[indane-2,8'-
(7',9'-dithiabicyclo[4.3.0]nonane)] (9), and 53 mg (51.4%) of 1,1,3,3-tetramethylindan-2-one (10).
Data of 8: Colorless crystals. M.p. 170 ± 1718. IR (KBr): 2940s, 2860m, 1480m, 1450m, 1375m, 1360w, 1290w,
1070s, 1028m, 990m, 952m, 913w, 900w, 770s. 1H-NMR: 7.77 ± 7.13 (m, 4 arom. H); 3.51 ± 3.43 (m, H C(6')); 2.85
(ddd, 3J ˆ 11.4, 9.8, 3.5, H C(1')); 2.22 ± 2.17, 2.10 ± 2.01 (2m, 2 CH2); 1.84 ± 1.68 (m, 2 CH2); 1.40, 1.39, 1.28,
1.27 (4s, 4 Me). 13C-NMR: 148.9, 148.2 (2s, 2 arom. C); 126.9, 126.8, 122.5, 122.3 (4d, 4 arom. C); 110.9 (s, spiro-
C); 87.7 (d, C(6')); 52.8 (d, C(1')); 51.9, 51.4 (2s, 2 Me2C); 32.4 (q, Me); 30.2 (t, CH2); 29.9 (q, Me); 29.1, 25.4 (2t,
‡
‡
2 CH2); 23.9 (q, Me); 23.9 (t, CH2); 22.0 (q, Me). CI-MS: 320 (100, [M ‡ NH4] ), 303 (19, [M ‡ 1] ), 206 (13),
115 (10). Anal. calc. for C19H26OS (302.48): C 75.45, H 8.66; found: C 75.25, H 8.66.
Crystals of 8 suitable for X-ray crystal-structure determination were grown from CH2Cl2/i-PrOH.

Helvetica Chimica Acta ± Vol. 82 (1999)
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Data of 9: Colorless crystals. M.p. 108 ± 1098. IR (KBr): 2990w, 2925s, 2855m, 1480m, 1445s, 1375m, 1310w,
1270w, 1187w, 1027w, 908m, 766m. 1H-NMR: 7.20 ± 7.11 (m, 4 arom. H); 3.07 ± 3.03 (m, H C(1'), H C(6'));
2.11 ± 2.03 (m, 2 CH2); 1.86 ± 1.83 (m, 2 CH2); 1.60, 1.44 (2s, 4 Me). 13C-NMR: 149.2 (s, 2 arom. C); 126.9, 122.3
(2d, 4 arom. C); 87.6 (s, spiro-C); 59.1 (d, C(1'), C(6')); 51.7 (s, 2 Me2C); 30.1 (q, 2 Me); 30.0 (t, 2 CH2); 29.3 (q,
‡
2 Me); 25.3 (t, 2 CH2). CI-MS: 319 (100, [M ‡ 1] ), 205 (10).
Crystals of 9 suitable for X-ray crystal-structure determination were grown from CH2Cl2/i-PrOH.
An analogous experiment with 5a (245 mg, 2.5 mmol) and 7 (102 mg, 0.5 mmol), 15 h, r.t. gave 52 mg
(34.4%) of 8, 17 mg (10.7%) of 9, and 21 mg (22.3%) of 10; 33 mg (32.4%) of 7 were recovered.
The reaction of 5a (406 mg, 4.2 mmol) and 7 (169 mg, 0.83 mmol) at 08, 1.5 h, yielded 124 mg (49.4%) of 8
and 3 mg (11.1%) of 9; 46 mg (27.2%) of 7 were recovered.
b) Reaction of 5b (554 mg, 6.5 mmol) with 7 (168 mg, 0.82 mmol), 15 h, 08, CC and PLC (hexane/AcOEt
20 :1) yielded 13 mg (5.5%) of 1,1,3,3-tetramethylspiro[indane-2,3'-(2'-oxa-4'-thiabicyclo[3.3.0]octane)] (12)
and 88 mg (57.5%) of 10; 43 mg (25.6%) of 7 were recovered.
Data of 12: Colorless oil. IR (CHCl3): 2965m, 2876w, 1479m, 1458m, 1378w, 1312w, 1262s, 1102s, 1023s,
907w. 1H-NMR: 7.24 ± 7.13 (m, 4 arom. H); 4.09 (ddd, 3J ˆ 11.3, 10.2, 6.5, H C(1')); 3.30 (ddd, 3J ˆ 12.1, 10.2, 6.4,
H
C(5')); 2.26 ± 2.12, 1.97 ± 1.75, 1.60 ± 1.40 (3m, 3 CH2); 1.50, 1.44, 1.39, 1.34 (4s, 4 Me). 13C-NMR: 148.8, 148.1
(2s, 2 arom. C); 127.1, 127.0 (2d, 2 arom. C); 123.9 (s, spiro-C); 122.6, 122.3 (2d, 2 arom. C); 95.1 (d, C(1')); 55.5
(d, C(5')); 52.4, 51.8 (2s, 2 Me2C); 32.1, 29.5 (2q, 2 Me); 26.4 (t, CH2); 24.2 (q, Me); 24.1, 23.2 (2t, CH2); 22.1 (q,
‡
Me). CI-MS: 289 (100, [M ‡ 1] ), 233 (7), 206 (11), 188 (18), 171 (7), 160 (6), 145 (6).
An analogous experiment with 5b (344 mg, 4.1 mmol) and 7 (108 mg, 0.53 mmol), 0.25 h, 308 gave 21 mg
(13.7%) of 12 and 6 mg (6.0%) of 10; 69 mg (63.9%) of 7 were recovered.
2.2. With 2,2,4,4-Tetramethyl-3-thioxocyclobutanone (13). a) Reaction of 5a (316 mg, 3.2 mmol) with 13
(84 mg, 0.54 mmol), 20 h, 788 to r.t.; CC (hexane/AcOEt 50 : 1) yielded 67 mg (48.8%) of 2,2,4,4-tetramethyl-
spiro[cyclobutane-1,8'-(7'-oxa-9'-thiabicyclo[4.3.0]nonane)]-3-one (14). Colorless oil. IR (CHCl3): 2962m,
2944m, 2865w, 1769s, 1463w, 1454w, 1381w, 1262s, 1220m, 1084s, 1024m. 1H-NMR: 3.18 (ddd, 3J ˆ 10.7, 9.6, 3.7,
3
H
C(6')); 2.74 (ddd, J ˆ 11.4, 9.6, 3.5, H C(1')); 2.21 ± 2.09, 1.90 ± 1.74 (2m, 2 CH2); 1.50 ± 1.20 (m, 2 CH2);
1.26, 1.23, 1.16, 1.11 (4s, 4 Me). 13C-NMR: 221.5 (s, CˆO); 98.4 (s, spiro-C); 88.1 (d, C(6')); 66.0, 65.1 (2s,
2 Me2C); 52.8 (d, C(1')); 30.4, 29.2, 25.4 (3t, 3 CH2); 24.4 (q, Me); 23.9 (t, CH2); 23.7, 18.4, 17.0 (3q, 3 Me). CI-
‡
MS: 255 (100, [M ‡ 1] ), 184 (72).
An analogous experiment with 5a (315 mg, 3.2 mmol) and 13 (148 mg, 0.95 mmol), 14 h, r.t.; CC and PLC
(hexane/AcOEt 50 :1) gave 56 mg (23.2%) of 14 and 37 mg (14.4%) of 2,2,4,4-tetramethylspiro[cyclobutane-
1,8'-(7',9'-dithiabicyclo[4.3.0]nonan)]-3-one (15)10). Colorless crystals. M.p. 62 ± 63.58. IR (KBr): 2965m, 2928s,
2857m, 1778vs, 1452w, 1441m, 1375w, 1362m, 1263w, 1248w, 1169w, 1130w, 1027m, 930m, 834w. 1H-NMR: 2.94 ±
2.88 (m, H C(1'), H C(6')); 2.20 ± 2.10, 1.90 ± 1.80 (2m, 2 CH2); 1.60 ± 1.25 (m, 2 CH2); 1.36, 1.27 (2s, 4 Me).
13C-NMR: 220.8 (s, CˆO); 73.1 (s, spiro-C); 66.2 (s, 2 Me2C); 59.3 (d, C(1'), C(6')); 29.9, 25.3 (2t, 4 CH2); 23.8,
‡
23.6 (2q, 4 Me). CI-MS: 271 (100, [M ‡ 1] ), 200 (29).
The reaction of 5a (739 mg, 7.5 mmol) and 13 (184 mg, 1.07 mmol) at r.t., 25 h, yielded 84 mg (30.8%) of 14.
b) Reaction of 5b (410 mg, 4.9 mmol) with 13 (171 mg, 1.1 mmol), 14 h, r.t., and CC (hexane/AcOEt 50 :1)
yielded 74 mg (26%) of 2,2,4,4-tetramethylspiro[cyclobutane-1,3'-(2',4'-dithiabicyclo[3.3.0]octan)]-3-one (16).
Colorless crystals. M.p. 70 ± 728. IR (KBr): 2963m, 2827w, 1775vs, 1745w, 1453m, 1380w, 1365w, 1027w, 933w.
1H-NMR: 3.23 ± 3.11 (m, H C(1'), H C(5')); 2.29 ± 2.17, 2.04 ± 1.93, 1.65 ± 1.47 (3m, 3 CH2); 1.36, 1.27 (2s,
4 Me). 13C-NMR: 220.6 (s, CˆO); 87.7 (s, spiro-C); 67.0 (s, 2 Me2C); 64.9 (d, C(1'), C(5')); 28.5, 26.6 (2t, 3 CH2);
‡
23.5, 23.3 (2q, 4 Me). CI-MS: 257 (100, [M ‡ 1] ), 186 (21). Anal. calc. for C13H20OS2 (256.43): C 60.89, H 7.86;
found: C 60.69, H 7.68.
Crystals of 16 suitable for X-ray crystal-structure determination were grown from CH2Cl2/i-PrOH.
An analogous experiment with 5b (442 mg, 5.3 mmol) and 13 (172 mg, 1.1 mmol), 14 h, 788, gave 53 mg
(18.8%) of 16; 47 mg (27.3%) of 13 were recovered.
2.3. With 2,2,4,4-Tetramethylcyclobutane-1,3-dithione (19). a) Reaction of 5a (739 mg, 7.5 mmol) with 19
(184 mg, 1.07 mmol), 25 h, r.t.; CC (hexane/AcOEt 20 :1) and PLC (hexane/AcOEt 50 :1) yielded 11 mg
(3.8%) of 2,2,4,4-tetramethylspiro[cyclobutane-1,8'-(7'-oxa-9'-thiabicyclo[4.3.0]nonane)]-3-thione (20)15), 6 mg
(2.0%) of 2,2,4,4-tetramethylspiro[cyclobutane-1,8'-(7',9'-dithiabicyclo[4.3.0]nonane)]-3-thione (21)15), 29 mg
15
)
The mixture 20/21 obtained after CC and PLC was separated by HPLC (Bischoff Nucleosil 100 (7 mm),
hexane/AcOEt 100 :1).

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Helvetica Chimica Acta ± Vol. 82 (1999)
(10.7%) of 14, 85 mg (21.6%) of trans-1',1',3',3'-tetramethyldispiro[7-oxa-9-thiabicyclo[4.3.0]nonane-8,1'-cyclo-
butan-3',8''-(7''-oxa-9''-thiabicyclo[4.3.0]nonane)] (trans-22a/trans-22b), and 66 mg (16.7%) of cis-1',1',3',3'-
tetramethyldispiro[7-oxa-9-thiabicyclo[4.3.0]nonane-8,1'-cyclobutan-3',8''-(7''-oxa-9''-thiabicyclo[4.3.0]nonane)]
(cis-22a/cis-22b).
Data of 20: Red oil. IR (CHCl3): 2970m, 2944s, 2863m, 1464s, 1450m, 1374w, 1360m, 1303m, 1261w, 1092w,
1070s, 1001m, 946w, 898w, 843w. 1H-NMR: 3.30 ± 3.21 (m, H C(6')); 2.84 ± 2.75 (m, H C(1')); 2.25 ± 2.10, 1.94 ±
1.75 (2m, 2 CH2); 1.54 ± 1.25 (m, 2 CH2); 1.36, 1.31, 1.27, 1.22 (4s, 4 Me). 13C-NMR: 235.8 (s, CˆS); 102.2 (s,
spiro-C); 88.0 (d, C(6')); 69.7, 68.7 (2s, 2 Me2C); 52.8 (d, C(1')); 30.2, 29.2 (2t, 2 CH2); 28.2, 27.7 (2q, 2 Me); 25.4,
‡
23.9 (2t, 2 CH2); 22.4, 21.0 (2q, 2 Me). CI-MS: 271 (100, [M ‡ 1] ).
Data of 21: Red oil. IR (CHCl3): 2930s, 2860m, 1734w, 1464m, 1448m, 1375w, 1360w, 1302m, 1262m, 1223w,
1142m, 1094m, 1010w, 918w, 809w. 1H-NMR: 2.98 ± 2.93 (m, H C(1'), H C(6')); 2.30 ± 2.06, 1.93 ± 1.80 (2m,
2 CH2); 1.60 ± 1.25 (m, 2 CH2); 1.45, 1.36 (2s, 4 Me). 13C-NMR: 69.5 (s, 2 Me2C); 59.4 (d, C(1'), C(6')); 30.0 (t,
2 CH2); 27.6, 27.3 (2q, 4 Me); 25.3 (t, 2 CH2); the signals for CˆS and spiro-C could not be detected. CI-MS: 287
‡
(100, [M ‡ 1] ).
Data of trans-22a/trans-22b: Colorless crystals. M.p. 153 ± 1558. IR (KBr): 2936s, 2858w, 1466m, 1448m,
1376w, 1350w, 1260w, 1204w, 1093m, 1070s, 1030m, 1004m, 968w, 916w, 895w, 834w. 1H-NMR: 3.14 ± 3.04 (m,
H
C(6), H C(6'')); 2.65 ± 2.55 (m, H C(1), H C(1'')); 2.19 ± 2.05 (m, 2 CH2); 1.87 ± 1.70 (m, 2 CH2); 1.46 ±
1.30 (m, 4 CH2); 1.19, 1.17, 1.16, 1.13 (4s, 4 Me). 13C-NMR: 101.6 (s, 2 spiro-C); 87.4, 87.3 (2d, C(6), C(6'')); 55.4,
54.4 (2s, 2 Me2C); 52.4, 52.3 (2d, C(1), C(1'')); 30.3, 29.2, 25.5 (3t, 6 CH2); 24.2, 24.1 (2q, 2 Me); 24.0 (t, 2 CH2);
‡
23.0, 22.8 (2q, 2 Me). CI-MS: 369 (40, [M ‡ 1] ), 255 (100), 184 (32).
Data of cis-22a/cis-22b: Colorless crystals. M.p. 127 ± 1298. IR (KBr): 2934s, 2856m, 1467m, 1450m, 1374m,
1350m, 1260w, 1205m, 1094m, 1071s, 1052m, 984m, 959m, 899w, 865w, 833w. 1H-NMR: 3.22 ± 3.10 (m, H C(6),
H-C(6'')); 2.64 ± 2.54 (m, H C(1), H C(1'')); 2.25 ± 2.17 (m, CH2); 2.13 ± 2.03 (m, CH2); 1.88 ± 1.71 (m, CH2);
1.49 ± 1.13 (m, CH2); 1.32, 1.28, 1.23, 1.05, 0.97, 0.91 (6s, 4 Me). 13C-NMR: 102.8 (s, 2 spiro-C); 88.0, 87.8 (2d,
C(6), C(6'')); 56.2, 54.4 (2s, 2 Me2C); 52.0, 51.9 (2d, C(1), C(1'')); 30.5, 30.4 (2t, CH2); 29.9 (q, Me); 29.2, 29.1 (2t,
‡
CH2); 28.6, 27.2 (2q, Me); 25.5, 24.0 (2t, CH2); 18.4, 17.1, 15.6 (3q, Me). CI-MS: 369 (52, [M ‡ 1] ), 255 (100),
184 (20).
Crystals of cis-22a suitable for X-ray crystal-structure determination were grown from CH2Cl2/i-PrOH.
An analogous experiment of 5a (160 mg, 1.6 mmol) with 19 (141 mg, 0.82 mmol), 0.5 h, r.t.; CC (hexane/
AcOEt 20 :1) and PLC (hexane/AcOEt 50 :1) gave 19 mg (6.3%) of trans-22a/trans-22b and 13 mg (4.3%) of
16
cis-22a/cis-22b ); 38 mg (27.0%) of 19 were recovered.
b) Reaction of 5b (800 mg, 9.5 mmol) with 19 (234 mg, 1.36 mmol), 3 h, r.t.; CC (hexane/AcOEt 20 :1) and
PLC (hexane/AcOEt 50 :1) yielded 29 mg (8.3%) of 16 and 55 mg (16.9%) of 4,4-dimethyl-5-(1-methylethy-
lidene)-6-thia-2-oxabicyclo[5.3.0]decan-3-one (23). Colorless crystals. M.p. 91 ± 938. IR (KBr): 2980m, 2937m,
2870m, 1725vs, 1468w, 1450w, 1392m, 1365m, 1291w, 1238s, 1220m, 1191w, 1121vs, 1103s, 1090s, 1060m, 750w.
1H-NMR: 4.57 ± 4.48 (m, H C(1)); 3.02 (ddd, 3J ˆ 12.2, 10.2, 6.9, H C(7)); 2.11 ± 1.97, 1.83 ± 1.71, 1.57 ± 1.42
(3m, 3 CH2); 2.04, 1.94, 1.65, 1.60 (4s, 4 Me). 13C-NMR: 175.1 (s, CˆO); 142.4, 124.8 (2s, Me2CˆC); 79.9 (d,
C(1)); 55.5 (s, Me2C); 50.5 (d, C(7)); 28.8 (t, 1 CH2); 27.1 (q, 1 Me); 26.8 (t, 1 CH2); 25.8, 25.7, 22.4 (3q, 3 Me);
‡
‡
19.4 (t, 1 CH2). CI-MS: 258 (39, [M ‡ NH4] ), 241 (100, [M ‡ 1] ). Anal. calc. for C13H20O2S (239.57): C 65.18,
H 8.41; found: C 65.08, H 8.27.
Crystals of 23 suitable for X-ray crystal-structure determination were grown from CH2Cl2/hexane.
2.4. With 9H-Xanthene-9-thione (24). a) Reaction of 5a (490 mg, 5 mmol) with 24 (210 mg, 0.99 mmol)
14 h, r.t.; CC (hexane/AcOEt 20 :1) and PLC (hexane/CH2Cl2 4 :1) yielded 19 mg (9.0%) of 24, 160 mg (83.4%)
of 9H-xanthen-9-one (27), and 17 mg (5.3%) of spiro[7,9-dithiabicyclo[4.3.0]nonane-8,9'-[9H]xanthene] (26).
Colorless crystals. M.p. 191 ± 1938. IR (KBr): 2933s, 2851m, 1658m, 1621w, 1608m, 1480m, 1461m, 1442s, 1330m,
1268w, 1186w, 1018m, 987w, 874w, 841w, 758m. 1H-NMR: 8.10 ± 8.05 (m, 2 arom. H); 7.30 ± 7.22 (m, 2 arom. H);
7.20 ± 7.13 (m, 2 arom. H); 7.07 ± 7.03 (m, 2 arom. H); 3.78 ± 3.66 (m, H C(1), H C(6)); 2.30 ± 1.25 (m, 4 CH2).
13C-NMR: 150.0 (s, 2 arom. C); 130.1, 128.7 (2d, 4 arom. C); 127.1 (s, 2 arom. C); 123.4, 116.2 (2d, 4 arom. C);
‡
62.5 (d, C(1), C(6)); 60.4 (s, spiro-C); 29.5, 15.2 (2t, 4 CH2). CI-MS: 327 (96, [M ‡ 1] ), 261 (100), 213 (29).
Crystals of 26 suitable for X-ray crystal-structure determination were grown from CH2Cl2/CHCl3.
An analogous experiment with 5a (495 mg, 5 mmol) and 24 (212 mg, 1 mmol), 10 min, 788, and CC
(hexane/CH2Cl2 3 : 1) yielded 107 mg (50.5%) of 24, 85 mg (43.8%) of 27, and 16 mg (5.2%) of spiro[7-oxa-9-
thiabicyclo[4.3.0]nonane-8,9'-[9H]xanthene] (25). Colorless crystals. M.p. 164 ± 1668. IR (CHCl3): 2943m,
16
)
The mixture 20/21 was not further purified.

Helvetica Chimica Acta ± Vol. 82 (1999)
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2862m, 1601m, 1575w, 1475m, 1454s, 1313m, 1293w, 1261m, 1249w, 1216m, 1100m, 1067m, 1014w, 918w, 882w.
1H-NMR: 7.95 ± 7.90 (m, 1 arom. H); 7.80 ± 7.73 (m, 1 arom. H); 7.38 ± 7.30 (m, 2 arom. H); 7.24 ± 7.15 (m, 4
arom. H); 4.10 (ddd, 3J ˆ 11.0, 9.7, 3.8, H C(6)); 3.24 (ddd, 3J ˆ 11.7, 9.7, 3.6, H C(1)); 2.40 ± 2.15, 2.05 ± 1.85
(2m, 2 CH2); 1.75 ± 1.40 (m, 2 CH2). 13C-NMR: 150.9, 150.3 (2s, 2 arom. C); 129.2, 129.1, 127.7 (3d, 3 arom. C);
127.1 (s, 1 arom. C); 126.7 (d, 1 arom. C); 126.0 (s, 1 arom. C); 116.6, 116.4 (2d, 4 arom. C); 89.2 (d, C(6)); 86.2
‡
(s, spiro-C); 55.2 (d, C(1)); 30.8, 28.7, 25.5, 24.0 (4t, 4 CH2). CI-MS: 311 (100, [M ‡ 1] ), 197 (24).
Crystals of 25 suitable for X-ray crystal-structure determination were grown from CH2Cl2/i-PrOH.
b) Reaction of 5b (420 mg, 5 mmol) with 24 (212 mg, 1 mmol), 3 min, 788, and CC (hexane/CH2Cl2 3 : 1)
yielded 98 mg (50.0%) of 27 as the only product; 93 mg (43.9%) of 24 were recovered.
2.5. With 9H-Fluorene-9-thione (28). a) Reaction of 5a (690 mg, 7 mmol) with 28 (200 mg, 1.02 mmol),
0.5 h, 788, CC (hexane/AcOEt 20 : 1) and PLC (hexane/CH2Cl2 2 : 1) yielded 8 mg (2.7%) of spiro[9H-
fluorene-9,8'-(7'-oxa-9'-thiabicyclo[4.3.0]nonane)] (29) and 33 mg (10.8%) of spiro[7,9-dithiabicyclo[4.3.0]no-
nane-8,9'-[9H]fluorene] (30), 141 mg (76.8%) of 9H-fluorene-9-one (31), and 19 mg (9.5%) of 10b'H-
spiro[fluorene-9,3'-fluoreno[9,1-cd][1,2]dithiane] (32) [27].
Data of 29: Colorless crystals. M.p. 110 ± 1118. IR (KBr): 2934m, 2860m, 1446m, 1347w, 1292w, 1260w,
1203m, 1088m, 1066m, 1008m, 963w, 937w, 887w, 862w, 768m, 747m, 730m, 683w. 1H-NMR: 7.71 ± 7.67 (m, 1
3
arom. H); 7.60 ± 7.54 (m, 3 arom. H); 7.39 ± 7.28 (m, 4 arom. H); 4.05 (ddd, J ˆ 10.7, 9.5, 3.7, H C(6')); 3.42
(ddd, 3J ˆ 11.7, 9.5, 3.5, H C(1')); 2.39 ± 2.24, 2.04 ± 1.90 (2m, 2 CH2); 1.74 ± 1.40 (m, 2 CH2). 13C-NMR: 148.3,
148.1, 139.3, 138.5 (4s, 4 arom. C); 129.5, 129.4, 128.5, 128.1, 125.6, 124.5, 119.8, 119.7 (8d, 8 arom. C); 94.5 (s,
.
‡
spiro-C); 88.5 (d, C(6')); 55.1 (d, C(1')); 31.0, 29.5, 25.6, 24.4 (4t, 4 CH2). EI-MS: 294 (17, M ), 180 (100), 149
(17), 81 (20), 57 (23).
Data of 30: Colorless crystals. M.p. 173 ± 1758. IR (KBr): 2931m, 2857w, 1474w, 1440m, 1330w, 1262m,
1213w, 1186w, 1091w, 1007w, 915w, 821w, 787w, 737s. 1H-NMR: 7.77 ± 7.72 (m, 2 arom. H); 7.63 ± 7.58 (m, 2 arom.
H); 7.38 ± 7.30 (m, 4 arom. H); 3.76 ± 3.70 (m, H C(1), H C(6)); 2.31 ± 2.25, 2.04 ± 1.95 (2m, 2 CH2); 1.72 ± 1.41
(m, 2 CH2). 13C-NMR: 151.2, 138.4 (2s, 4 arom. C); 128.4, 128.2, 125.4, 119.7 (4d, 8 arom. C); 65.2 (s, spiro-C);
‡
61.7 (d, C(1), C(6)); 30.1, 25.3 (2t, 4 CH2). CI-MS: 311 (100, [M ‡ 1] ), 197 (8).
An analogous experiment with 5a (680 mg, 6.9 mmol) and 28 (196 mg, 1.0 mmol) at r.t. (0.25 h) gave 10 mg
(3.4%) of 29, 21 mg (6.8%) of 30, 145 mg (80.6 %) of 31, and 21 mg (10.7%) of 32.
b) The reaction of 5b with 28 was performed at different temperatures, but no spirocyclic 1,3-oxathiolane or
1,3-dithiolane was observed. For instance, from the reaction of 5b (434 mg, 5.2 mmol) and 28 (188 mg,
0.96 mmol) at 788 (1 min), only 31 (63 mg, 36.4 %), 32 (60 mg, 31.9%), and 9,9'-bifluorenylidene (33) [28]
(6 mg, 3.8%) were obtained.
2.6. With Thiobenzophenone (34a). a) Reaction of 5a (665 mg, 6.7 mmol) with 34a (198 mg, 1 mmol),
10 min, 508; CC (hexane/AcOEt 30 : 1) yielded 12 mg (3.8%) of 8,8-diphenyl-7,9-dithiabicyclo[4.3.0]nonane
(36a), 15 mg (5.4%) of 8,8-diphenyl-7,9-dioxabicyclo[4.3.0]nonane (37a), and 122 mg (67.0%) of benzophe-
none (38a).
Data of 36a: Colorless crystals. M.p. 143 ± 145.58. IR (KBr): 2935m, 2921m, 2854m, 1590w, 1486m, 1441s,
1325w, 1316w, 1279m, 1150w, 1078m, 1032w, 862w, 756m, 742s, 696s. 1H-NMR: 7.65 ± 7.58 (m, 4 arom. H); 7.35 ±
7.20 (m, 6 arom. H); 3.45 ± 3.33 (m, H C(1), H C(6)); 2.30 ± 2.15, 2.00 ± 1.83 (2m, 2 CH2); 1.70 ± 1.20 (m,
2 CH2). 13C-NMR: 146.9 (s, 2 arom. C); 128.0, 127.9, 126.9 (3d, 10 arom. C); 72.8 (s, C(8)); 61.1 (d, C(1), C(6));
‡
29.8, 25.3 (2t, 4 CH2). CI-MS: 313 (100, [M ‡ 1] ), 213 (13), 199 (58), 183 (20), 102 (55).
Data of 37a: Colorless crystals. M.p. 138 ± 1398. IR (KBr): 2938m, 2860m, 1490w, 1447m, 1358w, 1318w,
1240m, 1226m, 1112s, 1082s, 1070s, 1030w, 965m, 944m, 910m, 782s, 760m, 700s. 1H-NMR: 7.60 ± 7.54 (m, 4 arom.
H); 7.38 ± 7.26 (m, 6 arom. H); 3.49 ± 3.40 (m, H C(1), H C(6)); 2.29 ± 2.22, 1.86 ± 1.82, 1.62 ± 1.54, 1.38 ± 1.21
(4m, 4 CH2). 13C-NMR: 143.8 (s, 2 arom. C); 127.9, 127.7, 126.0 (3d, 10 arom. C); 108.7 (s, C(8)); 80.9 (d, C(1),
‡
C(6)); 28.8, 23.6 (2t, 4 CH2). CI-MS: 281 (100, [M ‡ 1] ), 203 (14), 183 (6). Anal. calc. for C19H20O2 (280.37):
C 81.40, H 7.19; found: C 81.16, H 6.99.
Crystals of 37a suitable for X-ray crystal-structure determination were grown from CH2Cl2/i-PrOH.
An analogous experiment with 5a (770 mg, 7.9 mmol) and 34a (268 mg, 1.35 mmol), 1 min, 788; CC and
PLC (hexane/AcOEt 30 : 1) yielded 36 mg (9.0%) of 8,8-diphenyl-7-oxa-9-thiabicyclo[4.3.0]nonane (35a) in
addition to 36a, 37a, and 38a.
Data of 35a: Colorless crystals. M.p. 90 ± 928. IR (KBr): 2940m, 2860m, 1487m, 1447m, 1352w, 1260w,
1230w, 1207w, 1182w, 1060m, 1022m, 962w, 858w, 762m, 748m, 704m. 1H-NMR: 7.60 ± 7.55 (m, 2 arom. H); 7.46 ±
7.41 (m, 2 arom. H); 7.38 ± 7.20 (m, 6 arom. H); 3.58 (ddd, 3J ˆ 11.2, 9.7, 3.7, H C(6)); 3.23 (ddd, 3J ˆ 11.5, 9.7,
3.5, H C(1)); 2.36 ± 2.14, 1.95 ± 1.75 (2m, 2 CH2); 1.75 ± 1.22 (m, 2 CH2). 13C-NMR: 146.5, 146.0 (2s, 2 arom. C);
128.0, 127.9, 127.4, 127.3, 126.8, 126.5 (6d, 10 arom. C); 97.5 (s, C(8)); 87.2 (d, C(6)); 55.3 (d, C(1)); 30.5, 29.2,

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Helvetica Chimica Acta ± Vol. 82 (1999)
‡
25.5, 23.9 (4t, 4 CH2). CI-MS: 297 (12, [M ‡ 1] ), 200 (60), 183 (100). Anal. calc. for C19H20OS (296.43):
C 76.98, H 6.80; found: C 76.81, H 6.85.
2.7. With 4,4'-Dimethoxythiobenzophenone (34b). Reaction of 5a (528 mg, 5.4 mmol) with 34b (200 mg,
0.77 mmol), 30 s, 788; CC and PLC (hexane/AcOEt 10 : 1) yielded 145 mg (77.5%) of 4,4'-dimethoxybenzo-
phenone (38b) and 55 mg (20.1%) of 8,8-bis(4-methoxyphenyl)-7-oxa-9-thiabicyclo[4.3.0]nonane (35b).
Colorless crystals. M.p. 140 ± 1428. IR (KBr): 2932s, 2857m, 1636s, 1604s, 1505m, 1448w, 1416w, 1306m,
1294m, 1255s, 1172m, 1150m, 1097w, 1027s, 967w, 930m, 852s, 838s, 765s. 1H-NMR: 7.52 ± 7.46 (m, 2 arom. H);
7.36 ± 7.30 (m, 2 arom. H); 6.91 ± 6.85 (m, 2 arom. H); 6.83 ± 6.77 (m, 2 arom. H); 3.82, 3.78 (2s, 2 MeO); 3.57
(ddd, 3J ˆ 11.2, 9.7, 3.7, H C(6)); 3.24 (ddd, 3J ˆ 11.5, 9.7, 3.4, H C(1)); 2.33 ± 2.16, 1.95 ± 1.78, 1.74 ± 1.58,
1.50 ± 1.25 (4m, 4 CH2). 13C-NMR: 158.8, 158.7, 139.0, 138.2 (4s, 4 arom. C); 128.2, 127.9, 113.2, 113.1 (4d, 8
arom. C); 97.2 (s, C(8)); 87.0 (d, C(6)); 55.4 (d, C(1)); 55.2 (q, 2 MeO); 30.6, 29.3, 25.5, 21.0 (4t, 4 CH2). CI-MS:
‡
357 (100, [M ‡ 1] ), 243 (50), 135 (9).
3. Control Experiments. 3.1. Reaction of 7 with 1,2-Epithiocyclohexane (11). According to the General
Procedure in Sect. 2, the reaction of 7 (105 mg, 0.52 mmol) with 11 (212 mg, 1.9 mmol) at r.t. (14 h) yielded
142 mg (85.9%) of 9.
3.2. Decomposition of 8. A soln. of 8 (31 mg, 0.10 mmol) and 1.1 equiv. of BF3 ´ Et2O in 7 ml of CH2Cl2 was
stirred at r.t. After 4 d, no 8 could be detected (TLC). After workup and CC (hexane/AcOEt 20 : 1), 17 mg
(87.7%) of 10 were isolated.
3.3. Attempted Reaction of 10 with 11. According to the General Procedure in Sect. 2, a soln. of 380 mg
(2.0 mmol) of 10, 1.1 equiv. of BF3 ´ Et2O, and 950 mg (8.3 mmol) of 11 was stirred at r.t. Even after 2 d, no 8
could be detected by TLC. After usual workup, only 10 could be isolated (367 mg (96.6%)).
3.4. Reaction of 5a with 38a. According to the General Procedure in Sect. 2, 5a (686 mg, 7 mmol) was added
to a CH2Cl2 soln. of 38a (364 mg, 2 mmol) and 1.1 equiv. of BF3 ´ Et2O. The mixture was stirred at r.t. for 2 h. The
usual workup gave 33 mg (5.9%) of 37a.
4. X-Ray Crystal-Structure Determination of 8, 9, 16, cis-22a, 23, 25, 26, and 37a (see Table 2 and Figs. 1 ±
6) ). All measurements were made on a Rigaku-AFC5R diffractometer using graphite-monochromated MoKa
17
radiation (l ˆ 0.71069 Š) and a 12-kW rotating-anode generator. The w/2q scan mode was employed for data
collection. The intensities were corrected for Lorentz and polarization effects. An empirical absorption
correction was applied in the case of 26 [35]. Data collection and refinement parameters are given in Table 2,
views of the molecules are shown in Figs. 1 ± 6. The structures were solved by direct methods with SHELXS86
[36]. For each structure, all non-H-atoms were refined anisotropically and the H-atoms were treated as
described below.
Refinement of each structure was carried out on F using full-matrix least-squares procedures, which
minimized the function S w(j Fo j j Fc j )2. A correction for secondary extinction was applied in the case of 8, 9,
16, 23, and 25. Neutral-atom scattering factors for non-H-atoms were taken from [37a] and the scattering factors
for H-atoms from [38]. Anomalous dispersion effects were included in Fc [39]. The values for f' and f'' were
those of [37b]. The values of the mass-attenuation coefficients were those of [37c]. The calculations were
performed with the TEXSAN crystallographic software package [40].
In the case of 8, the cyclohexane ring is disordered over two orientations, which result from alternative
chair conformations of the cyclohexane ring and a twist of the adjacent five-membered ring. The cyclohexane C-
atoms bonded to the S- and O-atoms are disordered, as well as the two C-atoms opposite to these: two positions
18
were refined for C(4), C(5), C(11), and C(12), while C(10) and C(13) ) occupy common positions in each
conformation. The site-occupation factors of the disordered atoms were initially refined and then held fixed.
The major conformation has 60% occupancy. All of the H-atoms, except those bonded to the disordered
cyclohexane ring, were placed in the positions indicated by a difference electron-density map, and their positions
were allowed to refine together with individual isotropic displacement parameters. The cyclohexane H-atoms
were fixed in geometrically calculated positions with d(C H) ˆ 0.95 Š and they were assigned fixed isotropic
displacement parameters with a value equal to 1.2 Ueq of the parent C-atom.
17
)
Crystallographic data (excluding structure factors) for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data Centre as deposition No. CCDC-133972 ± 133979 for
8, 9, 16, cis-22a, 23, 25, 26, and 37a, respectively. Copies of the data can be obtained, free of charge, on
application to the CCDC, 12 Union Road, Cambridge CB2EZ, UK (fax: ‡ 44-(0)1223-336033 or e-mail:
deposit@ccdc.cam.ac.uk).
18
)
Arbitrary numbering of the crystal-structure determination.

Helvetica Chimica Acta ± Vol. 82 (1999)
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Helvetica Chimica Acta ± Vol. 82 (1999)
In the case of 9, there are three independent molecules in the asymmetric unit, but no additional
crystallographic symmetry could be found. In each molecule, the cyclohexane ring is disordered over two
orientations. The disorder is similar to that found in 8 and was treated in an analogous fashion. The major
conformation in each molecule has ca. 58% occupancy.
In the case of 26, the cyclohexane ring is again similarly disordered. Two positions were defined for C(2)
and C(4), while C(3)18) occupies a common position in each conformation; the remaining atoms in this ring are
generated by the crystallographic C2 symmetry. The major conformation has ca. 80% occupancy.
The same sort of disorder is also displayed by the cyclohexane ring of 37a. Two positions were defined for
C(4) and C(5)18). While C(18) and C(21) occupy common positions in each conformation, the atoms C(19) and
C(20) are also disordered, but it was not possible to successfully refine any disordered positions for these atoms.
Instead, they have been treated as ordered atoms in the model, although the elongation of the displacement
ellipsoids clearly shows the presence of the disorder. The major conformation has ca. 79% occupancy.
For 16, C(4) and C(5) at the junction of the fused five-membered rings are disordered over two
orientations, which result from alternative half-chair twists of these rings. The disorder was treated analogously
to that in the structures described above. The major conformation has ca. 53% occupancy.
For cis-22a, there are two independent molecules in the asymmetric unit. There is some indication of
potential conformational disorder of the five- and six-membered rings in this structure as well. The elevated R
factors, small peaks of residual electron density, the slight elongation of some atomic displacement ellipsoids and
the unduly short lengths of some C C bonds are indicators of this. However, attempts to model any disorder
were unsuccessful.
For 9, 16, cis-22, 26, and 37a, all of the H-atoms were fixed in geometrically calculated positions with
d(C H) ˆ 0.95 Š, and they were assigned fixed isotropic displacement parameters with a value equal to 1.2 Ueq
of the parent atom. For 23 and 25, all of the H-atoms were located in difference electron-density maps, and their
positions were allowed to refine together with individual isotropic displacement parameters.
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Received September 1, 1999