Regio- and stereoselectivity in the Lewis acid- and NaH-induced reactions of thiocamphor with (R)-2-vinyloxirane

Article abstract of DOI:10.1002/hlca.200690046

The reaction of the enolizable thioketone (1R,4R)-thiocamphor (=(1R,4R)-l,7,7-trimethylbicyclo[2.2.1]heptane-2-thione: (1) with (R)-2-vinyloxirane (2) in the presence of a Lewis acid such as SnCl₄ or SiO₂ in anhydrous CH₂Cl₂ gave the spirocyclic 1,3-oxathiolane 3 with the vinyl group at C(4′), as well as the isomeric enesulfanyl alcohol 4. In the case of SnCl₄, an allylic alcohol 5 was obtained in low yield in addition to 3 and 4 (Scheme 2). Repetition of the reaction in the presence of ZnCl₂ yielded two diastereoisomeric 4-vinyl-1,3-oxathiolanes 3 and 7 together with an alcohol 4, and a '1:2 adduct' 8 (Scheme 3). The reaction of 1 and 2 in the presence of NaH afforded regioselectively two enesulfanyl alcohols 4 and 9, which, in CDCl ₃, cyclized smoothly to give the corresponding spirocyclic 1,3-oxathiolanes 3, 10, and 11, respectively (Scheme 4). In the presence of HCl, epimerization of 3 and 10 occurred to yield the corresponding epimers 7 and 11, respectively (Scheme 5). The thio-Claisen rearrangement of 4 in boiling mesitylene led to the allylic alcohol 12, and the analogous [3,3]-sigmatropic rearrangement of the intermediate xanthate 13, which was formed by treatment of the allylic alcohol 9 with CS₂ and MeI under basic conditions, occurred already at room temperature to give the dithiocarbonate 14 (Schemes 6 and 7). The presented results show that the Lewis acid-catalyzed as well as the NaH-induced addition of (R)-vinyloxirane (2) to the enolizable thiocamphor (1) proceeds stereoselectively via an S_N2-type mechanism, but with different regioselectivity.

Full text of DOI:10.1002/hlca.200690046

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Helvetica Chimica Acta – Vol. 89 (2006)
Regio- and Stereoselectivity in the Lewis Acid- and NaH-Induced Reactions
of Thiocamphor with (R)-2-Vinyloxirane
by Alexey Fedorov1), Changchun Fu, and Heinz Heimgartner*
Organisch-chemisches Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich
The reaction of the enolizable thioketone (1R,4R)-thiocamphor (=(1R,4R)-1,7,7-trimethylbicy-
clo[2.2.1]heptane-2-thione; 1) with (R)-2-vinyloxirane (2) in the presence of a Lewis acid such as
SnCl4 or SiO2 in anhydrous CH2Cl2 gave the spirocyclic 1,3-oxathiolane 3 with the vinyl group at
C(4’), as well as the isomeric enesulfanyl alcohol 4. In the case of SnCl4, an allylic alcohol 5 was obtained
in low yield in addition to 3 and 4 (Scheme 2). Repetition of the reaction in the presence of ZnCl2 yielded
two diastereoisomeric 4-vinyl-1,3-oxathiolanes 3 and 7 together with an alcohol 4, and a ‘1 :2 adduct’ 8
(Scheme 3). The reaction of 1 and 2 in the presence of NaH afforded regioselectively two enesulfanyl
alcohols 4 and 9, which, in CDCl3, cyclized smoothly to give the corresponding spirocyclic 1,3-oxathio-
lanes 3, 10, and 11, respectively (Scheme 4). In the presence of HCl, epimerization of 3 and 10 occurred
to yield the corresponding epimers 7 and 11, respectively (Scheme 5). The thio-Claisen rearrangement of
4 in boiling mesitylene led to the allylic alcohol 12, and the analogous [3,3]-sigmatropic rearrangement of
the intermediate xanthate 13, which was formed by treatment of the allylic alcohol 9 with CS2 and MeI
under basic conditions, occurred already at room temperature to give the dithiocarbonate 14 (Schemes 6
and 7). The presented results show that the Lewis acid-catalyzed as well as the NaH-induced addition of
(R)-vinyloxirane (2) to the enolizable thiocamphor (1) proceeds stereoselectively via an SN2-type mech-
anism, but with different regioselectivity.
1. Introduction. – 1,3-Oxathiolanes can be prepared by the Lewis acid-catalyzed
reaction of oxiranes not only with non-enolizable and enolizable thioketones, but
with enolized thioketones as well [1–8]. The latter reaction occurs in two steps via
an intermediate enesulfanyl alcohol [6]. In the cases of (R)-2-phenyl- and (R)-2-vinyl-
oxirane, the reactions proceed with high regio- and stereoselectivity via an SN2-type
mechanism (Scheme 1): the nucleophilic thiocarbonyl S-atom attacks preferentially
at C(2) of the Lewis acid-activated oxiranes, leading to the ‘direct’ or ‘indirect’ forma-
tion of 4-substituted 1,3-oxathiolanes with inversion of the configuration.
Enolizable thioketones exist predominantly in the enethiol form [9][10], which can
be deprotonated with a strong base such as NaH. The thio anion formed can cleave the
three-membered ring of oxiranes via an analogous SN2-type mechanism as under Lewis
acid catalysis, but the regioselectivity is different. The reactions afford enesulfanyl alco-
hols, which cyclize smoothly to give the corresponding ring-enlarged 1,3-oxathiolanes
as well [5][6].
1
)
Stay at the University of Zürich, 01.–04. 2005; Saint-Petersburg State University, Universitetskij pr.
26, 198504 Saint Petersburg, Russia; present address: Laboratorium für Organische Chemie, ETH-
Hönggerberg, CH-8093 Zürich.
© 2006 Verlag Helvetica Chimica Acta AG, Zürich

Helvetica Chimica Acta – Vol. 89 (2006)
457
Scheme 1
In the present paper, the results of the reaction of (1R,4R)-thiocamphor
(=(1R,4R)-1,7,7-trimethylbicyclo[2.2.1]heptane-2-thione; 1) with (R)-2-vinyloxirane
(2) in the presence of Lewis acids and of NaH, respectively, are described.
2. Results. – 2.1. Reaction of (1R,4R)-Thiocamphor (1) with (R)-2-Vinyloxirane (2).
On dropping two equiv. of 2 into a solution of 1 and 0.5 equiv. of SnCl4 in anhydrous
CH2Cl2 at À788 during 20 min under an N2 atmosphere, the color of the yellow solution
turned slowly to light yellow. After stirring the mixture for an additional 5 min, the
reaction was quenched by addition of a saturated aqueous NaHCO3 solution. Chroma-
tographic separation of the mixture gave the spirocyclic 1,3-oxathiolane 3, the enesul-
fanyl alcohol 4, and camphor (6) in 49, 23, and 2% yield, respectively, as well as an
unexpected alcohol 5 in 3% yield. Repetition of the reaction with silica gel as catalyst
at 08 for 2 d led to 3, 4, and 6 in 39, 6, and 1% yield, respectively, but no alcohol 5 was
observed. In both cases, the reaction was almost complete, and the starting material 1
was recovered only in a small amount (Scheme 2 and Table).
Scheme 2
Table. SnCl4- and SiO2-Catalyzed Reactions of 1 with 2 in CH2Cl2
Lewis acid
Temp. [8]
Reaction time
Yield of products [%]
3
4
5
6
1
SnCl4
SiO2
À78
25 min
2 d
49
39
23
6
3
–
2
1
1
1
0

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Helvetica Chimica Acta – Vol. 89 (2006)
The reaction of 1 and 2 in a ratio of 1:2 was also repeated in the presence of 0.5
equiv. of ZnCl2 under an N2 atmosphere at À308 for 5 h, and the mixture was kept
at À208 for 18 h. Chromatographic separation of the mixture afforded two diastereo-
isomeric spirocyclic 1,3-oxathiolanes 3 and 7, and the alcohol 4 in 16, 32, and 4%
yield, respectively, as well as another unexpected product 8 in 13% yield (Scheme 3).
The latter contains two vinyl groups, indicating that two molecules of 2 have reacted,
but there are also two S-atoms in 8.
Scheme 3
The structures of 3, 4, 7, and 8 were assigned on the basis of their elemental analyses,
and 1H-, 13C-, and 2D-NMR, and mass spectra, and by comparison with those of similar
compounds described previously [3–7]. The configurations at C(2) and C(4’) of 3 and 7
were determined by means of NOESY spectra relative to the known absolute config-
uration of the bicyclic skeleton of thiocamphor (1). The examination of a Dreiding
model of 3 shows that the spatial distance between the methine H-atom of the vinyl
group and the MeÀC(1) group is small, in good agreement with the NOESY spectrum
(500 MHz, CDCl3) of 3, which shows one relevant cross-signal between CH=CH2 at
5.82 ppm and MeÀC(1) at 0.99 ppm. It is worth mentioning that the difference between
the chemical shifts of HendoÀC(6) at 2.15–2.10 ppm and HexoÀC(6) at 1.51–1.45 ppm is
Ddꢀ0.65 ppm due to the proximity of the electronegative O-atom, which means that
the O-atom is close to HendoÀC(6), i.e., in the endo-position (cf. [6]). These analyses
indicate that the absolute configuration of 3 is (1R,2R,4R,4’S). Similarly, the NOESY
spectrum of 7 (500 MHz, CDCl3) shows one relevant cross-signal between HÀC(4’)
at 3.95–3.90 ppm and MeÀC(1) at 0.91 ppm, but the signals of HendoÀC(6) and Hexo
À
C(6) overlap at 1.57–1.54 ppm, which implies that the O-atom is exo-oriented. There-
fore, it can be deduced that 7 possesses the (1R,2S,4R,4’S)-configuration, i.e., it is the
C(2)-epimer of 3.
The absolute configuration at C(2) in 4 has been assigned based on the knowledge
that ring opening of (R)-2-vinyloxirane (2) takes place via nucleophilic attack at C(2),
and the cleavage of the OÀC(2) bond occurs under inversion of the configuration at
C(2) [7]. The structure of compound 5, i.e., the product of a thio-Claisen rearrange-

Helvetica Chimica Acta – Vol. 89 (2006)
459
ment, followed by dethionation (cf. [11][12]), was proposed on the basis of its CI-MS,
1H-NMR, and IR data. The IR spectrum shows an intensive C=O absorption at 1739
cmÀ1 and a broad absorption for OH at 3425 cmÀ1. In the 1H-NMR spectrum, multiplets
for two olefinic H-atoms (5.8–5.2 ppm) and a CH2O group (4.15–4.05 ppm) are char-
acteristic. Furthermore, a set of six Me signals indicates a mixture of two isomers. The
formation of 8 and its configuration will be discussed in Sect. 3.
2.2. Reaction of 1 and 2 in the Presence of NaH. To a solution of 1 in anhydrous THF,
1.2 equiv. of NaH were poured at room temperature. After stirring the mixture for 30
min, 1.3 equiv. of 2 were added dropwise. The reaction was followed by TLC and was
completed after 6 h. Chromatographic separation of the mixture gave the secondary
alcohol 9 and the primary alcohol 4 in 70 and 22% yield, respectively (Scheme 4).
Scheme 4
The formation of 4 and 9 proceeded via nucleophilic attack of the enethiolate,
which is formed by deprotonation of the starting material 1, at C(2) and C(3) of (R)-
2-vinyloxirane (2), leading to 4 and 9 with inversion and retention of the configuration
at C(2), respectively. This proposal was confirmed by the structures of the cyclization
products 3, 10, and 11.
In CDCl3 at room temperature, the primary alcohol 4 cyclized quantitatively to give
the 4-vinyl-substituted 1,3-oxathiolane 3. The cyclization of the secondary alcohol 9
occurred also smoothly under the same conditions, leading to a mixture of the 5-
vinyl-substituted 1,3-oxathiolanes 10 and 11 in 86 and 14% yield, respectively (ratio
6.1:1; Scheme 4). Treatment of 9 with 1 equiv. of ZnCl2 in boiling THF under an N2
atmosphere for 2 h gave 47% of 10 and 36% of 11 (ratio of 1.3 :1).
Again, the structures of 9, 10, and 11 were assigned on the basis of their elemental
analyses and spectroscopic data, and by comparison with compounds described previ-

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ously (see [3–7] and Sect. 2.1). The configurations of the spirocyclic 1,3-oxathiolanes 10
and 11 were determined by means of NOESY spectra, relative to the known absolute
configuration of the bicyclic skeleton of the starting material 1: the examination of a
Dreiding model of 10 shows that the spatial distance between the methine H-atom of
the vinyl group and the MeÀC(1) group is small and in agreement with the NOESY
spectrum (600 MHz, CDCl3) of 10, which shows one cross-signal between CH=CH2
at 5.92 ppm and MeÀC(1) at 0.94 ppm, as well as two relevant cross-signals between
HÀC(5’) at 4.32–4.28 ppm, and HexoÀC(3) at 2.37 ppm and HendoÀC(3) at 1.75–
1.73 ppm. In addition, Dd of HendoÀC(6) at 2.17 ppm and HexoÀC(6) at 1.44 ppm is
0.73 ppm, which demonstrates that the O-atom is close to HendoÀC(6), i.e., the
O-atom is in the endo-position. Therefore, 10 has the (1R,2R,4R,5’R)-configuration.
The NOESY spectrum of 11 (600 MHz, CDCl3) shows one relevant cross-signal
between HÀC(5’) at 4.52–4.49 ppm and MeÀC(1) at 0.92 ppm, and the signals of
HendoÀC(6) and HexoÀC(6) overlap at 1.57–1.46 ppm, indicating an exo-oriented
O-atom. Therefore, 11 is the C(2)-epimer of 10 with the absolute configuration
(1R,2S,4R,5’R).
2.3. Epimerization of 3 and 10. Irradiation of a CDCl3 solution of 3 in an NMR tube
with sunlight at room temperature for 16 h afforded a mixture of 3 and 7 in a ratio of
1:15. Treatment of 3 with 1 equiv. of ZnCl2 in boiling THF under an N2 atmosphere for
1
45 min led to a 1:1 mixture of 3 and 7 according to an H-NMR analysis (Scheme 5).
However, no epimerization of 3 took place when it was treated with 0.5 equiv. of
ZnCl2 in CH2Cl2 at À208 for 26 h.
Scheme 5
Treatment of a solution of 10 in CHCl3 at room temperature with 10 drops of conc.
HCl for 14 h yielded 42% of 11, and 40% of the starting material 10 was recovered
(Scheme 5).
2.4. Thio-Claisen Rearrangement of 4. As it was proposed that the minor product 5
(Scheme 2) is the product of a [3,3]-sigmatropic rearrangement (thio-Claisen rearrange-
ment [11][12]) of 4 and subsequent dethionation, we examined the thermolysis of 4.

Helvetica Chimica Acta – Vol. 89 (2006)
461
Heating of a solution of 4 in mesitylene to reflux under an N2 atmosphere for 12 min
yielded stereospecifically 12 as a pink orange oil in 88% yield (Scheme 6). Treatment
of 4 in the presence of ZnCl2 in CH2Cl2 under an N2 atmosphere at À308 for 3 h
gave 5 in 30% yield2).
Scheme 6
The structure of 12 was assigned as described in the previous cases. The NOESY
spectrum (500 MHz, CDCl3) shows one relevant cross-peak between HÀC(3) at
2.67–2.63 ppm and MesynÀC(7) at 0.82 ppm. Furthermore, there are two relevant
cross-signals between 2 HÀC(4’) of the side chain at 4.13–4.07 ppm, and 2 HÀC(1’)
at 2.04–1.98 ppm and the H-atom of the OH group at 1.56–1.49 ppm, confirming
the (Z)-configuration. In addition, HexoÀC(3) appeared as a multiplet instead of a
ddd signal due to the W-coupling with HexoÀC(5). These analyses indicate an endo-ori-
ented side chain at C(3) and an absolute configuration of (1R,2S,4R,2’Z).
2.5. [3,3]-Sigmatropic Rearrangement of Intermediate Xanthate 13. A mixture of 9
and 5 equiv. of MeI in a two-phase system of 50% aq. NaOH containing 0.1 equiv. of
Bu4NHSO4 and 2.2 ml of CS2 was vigorously stirred overnight at room temperature.
After separation of the CS2 layer and workup, dithiocarbonate 14 was obtained as a yel-
low oil in 81% yield (Scheme 7). We propose that 14 was formed via a [3,3]-sigmatropic
rearrangement of the intermediate xanthate 13.
Scheme 7
a) CS2, MeI, NaOH, Bu4NHSO4, H2O, r.t., overnight.
The structure of 14 was assigned on the basis of its NMR and mass spectra. The con-
figuration of the side-chain double bond of 14 was determined by means of 1D-NOESY
and IR spectrum. The 1D-NOESY spectrum (300 MHz, CDCl3), on irradiation of 2 HÀ
C(1) at 3.62 ppm, showed no NOE signal for 2 HÀC(4) at 3.27 ppm, and vice versa. In
2
)
Unfortunately, this reaction was non-reproducible.

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Helvetica Chimica Acta – Vol. 89 (2006)
the IR spectrum of 14, a strong absorption band at 963 cmÀ1 indicates the (2E)-config-
uration3).
3. Discussion and Conclusions. – The results presented show that 1,3-oxathiolanes
can be prepared not only by the Lewis acid-catalyzed reaction of an enolizable thioke-
tone with 2-vinyloxirane, but also under basic conditions. Thiocamphor (1) reacts with
(R)-vinyloxirane (2) in the presence of a Lewis acid to yield spirocyclic 1,3-oxathiolanes
3 and 7, as well as the enesulfanyl alcohol 4, with high regio- and stereoselectivity
(Schemes 2 and 3). The reaction proceeds via an SN2-type mechanism, whereby the
nucleophilic thiocarbonyl S-atom preferentially attacks the more hindered C(2)-atom
of the activated 2 (OÀC(2) cleavage), leading to products with inversion of the config-
uration, in analogy to the reaction of 1 with (R)-2-phenyloxirane [5].
In contrast, the reaction of thiocamphor (1) with 2 under basic conditions, i.e., the
reaction of the enethiolate anion with 2, afforded two enesulfanyl alcohols 4 and 9 with
low regioselectivity (Scheme 4). We propose that this reaction proceeds also via an SN2-
type mechanism, in which the preferred nucleophilic attack of the enethiolate anion
occurs at C(3) (OÀC(3) cleavage) to give 9 with retention of the configuration, whereas
the formation of the minor product 4 takes place via OÀC(2) cleavage with inversion of
the configuration at C(2) of the oxirane 2.
The enesulfanyl alcohols 4 and 9 isomerize smoothly via the mechanism reported in
[5] to give the corresponding spirocyclic 1,3-oxathiolanes in the presence of traces of
DCl that is formed during the storage of CDCl3 (Scheme 4). The observed epimeriza-
tions at the spiro-centre in the cases of 3/7 and 10/11 (Scheme 5) can be explained by the
mechanism described earlier [5], i.e., an acid-catalyzed ring-opening/ring-closure reac-
tion of the S/O acetal.
A likely mechanism of the formation of adduct 8 is proposed in Scheme 8. The
ZnCl2-catalyzed reaction of 1 and 2 leads to two spirocyclic diastereoisomers 3 and
7, which then decompose to give camphor 6 and (S)-2-vinylthiirane (15) via the ring-
opening of the 1,3-oxathiolanes and the subsequent nucleophilic attack of the S-atom
at C(5’). The analogous decomposition reaction of 1,3-oxathiolanes in the presence
of Lewis acids was described in the previous work [1][14]. Then, the thiirane ring is
cleaved by nucleophilic attack of the S-atom of 1 at the less hindered C(3)-atom (SÀ
C(3) cleavage) of 15 with retention of the configuration at C(2) of 15, which leads to
the intermediate enesulfanyl thiol 16. Finally, OÀC(2) cleavage of oxirane 2 by nucle-
ophilic attack of the SH group of 16 with inversion of configuration affords the unex-
pected adduct 8. As a result of this reaction mechanism, we propose that the configu-
ration of 8 is (S,S). This cascade reaction demonstrates the influence of the heteroatom
upon the regioselectivity of the ring opening of three-membered rings. In contrast to
oxiranes, the ring opening of thiirane 15 proceeds via nucleophilic attack of the thiocar-
bonyl S-atom at the less hindered C(3)-atom (SÀC(3) cleavage). Because the differ-
ence of the electronegativities of S- and C-atom is small, the partial positive charges
at C(2) and C(3) of thiiranes are much lower than those of oxiranes, so that the steric
1
3
)
In addition, the (2E)-configuration was supported by a computer simulation of the H-NMR spec-
trum [13].

Helvetica Chimica Acta – Vol. 89 (2006)
463
Scheme 8
hindrance dominates the ring opening of thiiranes in favour of the SÀC(3) cleavage
(Scheme 8).
The rearrangement of allylic xanthates is known to proceed thermally (ca. 1008) via
a concerted reaction mechanism ([3,3]-sigmatropic rearrangement) [15]. It can be
accelerated by catalysis with b-cyclodextrin, in which case the reaction occurs in an
inclusion complex at 2–58 [16]. The formation of the dithiocarbonate 14 via the inter-
mediate 13 occurs stereospecifically and smoothly in situ at room temperature. A con-
certed mechanism, i.e., a [3,3]-sigmatropic rearrangement is postulated via the transi-
tion state A, in which a neighboring group participation is responsible for the acceler-
ation of the reaction (Scheme 9).
Scheme 9
We thank the analytical services of our institute for NMR and mass spectra, and elemental analyses,
and F. Hoffmann-La Roche AG, Basel, for financial support. A. F. also thanks Prof. M. Kuznetsov, Saint-
Petersburg State University, for useful discussions, and Anna and Masha Brouwer for kind support during
residence in Zurich.

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Helvetica Chimica Acta – Vol. 89 (2006)
Experimental Part
1. General. See [7][17]. Optical rotations were recorded on a Perkin-Elmer-241 polarimeter (c=1, in
THF). IR Spectra: film, cmÀ1. NMR Spectra: at 500 or 600 (1H) and 125.8 or 150.9 MHz (13C) in CDCl3 or
C6D6 if not otherwise stated. Assignment of signals based on 2D-NMR spectra.
2. General Procedures for the Reactions of (1R,4R)-Thiocamphor (=(1R,4R)-1,7,7-Trimethylbicy-
clo[2.2.1]heptane-2-thione; 1) with (R)-2-Vinyloxirane (=2-Ethenyloxirane; 2). General Procedure 1
(GP 1). To a soln. of 1 (ca. 1 mmol) in anh. CH2Cl2 (10–15 ml) under N2, SnCl4 (0.5 equiv.) was added
at À788. This led to little change in the color of the soln. After stirring the mixture for 15 min at
À788, ca. 2 equiv. of 2 were added dropwise within 20 min, whereby the color of the soln. changed to
pale yellow. After stirring the mixture for an additional 5 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 products were separated by chromatography (SiO2; hex-
ane/Et2O; CC or prep. TLC (PLC)).
General Procedure 2 (GP 2). To a soln. of 1 (ca. 1 mmol) and 2 (ca. 2 mmol) in anh. CH2Cl2 (10–15
ml) under N2, 4.5 g of silica gel were added at r.t. After stirring the suspension for 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 as described in GP 1.
General Procedure 3 (GP 3). To a soln. of 1 (ca. 2 mmol) in anh. CH2Cl2 (15 ml) under N2, 0.5 equiv.
of ZnCl2 was added at À308. After stirring the mixture for 15 min at À308, ca. 2 equiv. of 2 were added
dropwise. Then, the mixture was stirred for 5 h at À308, kept for 18 h at À208, and the reaction was
quenched by addition of H2O. The mixture was washed with sat. aq. NaCl soln. (3×). The combined
org. layers were dried (MgSO4) and evaporated in vacuo. The products were separated by CC (SiO2; hex-
ane/Et2O).
General Procedure 4 (GP 4). To the soln. of 1 (ca. 5 mmol) in anh. THF (25 ml), 1.2 equiv. of NaH
(95% purity) were added at 258. After stirring the mixture for 30 min, 1.3 equiv. of 2 were added dropwise
to the almost colorless soln. The reaction was controlled by TLC and was completed after 6 h. After aq.
workup, the products were separated by CC (SiO2; hexane/Et2O).
3. Reactions of 1 with 2. 3.1. Lewis Acid-Catalyzed Reaction of 1 and 2. Reaction of 1 (168 mg,
1 mmol) with 2 (140 mg, 2 mmol) and 0.5 equiv. of SnCl4 (or 4.5 g of SiO2) at À788 or 08 (CC, prep.
TLC (PLC) hexane/Et2O) according to GP 1 yielded 117 mg (49%) (or 93 mg, 39%) of (1R,2R,4R,
4’S)-4’-ethenyl-1,7,7-trimethylspiro[bicyclo[2.2.1]heptane-2,2’-[1,3]oxathiolane] (3), 55 mg (23%) (or
15 mg, 6%) of (2S)-2-[(1’R,4’R)-(1’,7’,7’-trimethylbicyclo[2.2.1]hept-2’-en-2’-yl)sulfanyl]but-3-en-1-ol
(4), 7 mg (3%) of (1R,3S,4R)-3-[(2’Z)-4’-hydroxybut-2’-en-1’-yl]-1,7,7-trimethylbicyclo[2.2.1]heptane-2-
one (5) and 2 mg (1%) of camphor (6) (Table).
Data of 3. Colorless oil. [a]2D3 =À146.8. IR: 3081w, 2954s, 2869m, 1636m, 1476m, 1453m, 1418w,
1389m, 1372m, 1305w, 1272w, 1250w, 1194w, 1113m, 1083s, 1044m, 1017m, 987m, 958w, 914m, 882m,
819m, 809m, 701w. 1H-NMR (500 MHz, CDCl3): 5.82 (ddd, J=16.9, 9.9, 7.9, CH=CH2); 5.10 (ddd,
J=17.0, 1.4, 0.9, 1 H of =CH2); 4.97 (ddd, J=9.8, 1.4, 0.5, 1 H of =CH2); 4.02–3.98 (m, HÀC(4’));
3.96 (dd, J=9.2, 2.5, 1 HÀC(5’)); 3.87 (dd, J=9.2, 5.2, 1 HÀC(5’)); 2.37 (ddd, J=13.9, 4.7, 3.2, Hexo
À
C(3)); 2.15–2.10 (m, HendoÀC(6)); 1.74–1.67 (m, HÀC(4), HexoÀC(5)); 1.70 (d, J=13.8, HendoÀC(3));
1.51–1.45 (m, HexoÀC(6)); 1.26–1.20 (m, HendoÀC(5)); 0.99 (s, MeÀC(1)); 0.93 (s, Mesyn); 0.88 (s, Meanti).
13C-NMR (125.8 MHz, CDCl3): 138.8 (d, CH=CH2); 114.5 (t, CH=CH2); 105.1 (s, C(2)); 73.6 (t, C(5’));
53.9 (s, C(1)); 52.6 (d, C(4’)); 50.1 (t, C(3)); 48.5 (s, C(7)); 46.2 (d, C(4)); 30.2 (t, C(6)); 27.4 (t, C(5)); 21.0
(q, Mesyn), 20.2 (q, Meanti); 14.1 (q, MeÀC(1)). ESI-MS (MeOH+NaI): 277 (28, [M+K]+), 263 (14), 262
(18), 261 (100, [M+Na]+), 245 (24), 229 (7), 207 (11). Anal. calc. for C14H22OS (238.39): C 70.54, H 9.30;
found: C 70.24, H 9.16.
Data of 4. Colorless oil. [a]2D3 =+0.27. IR: 3375m (br., OH), 3083w, 2984m, 2953s, 2871m, 1637w,
1561w, 1472w, 1456w, 1440w, 1416w, 1385m, 1375w, 1365w, 1297w, 1184w, 1134w, 1106m, 1062m,
1
1043m, 1025m, 983m, 921m, 875w, 819w, 783w, 715w. H-NMR (300 MHz, CDCl3): 5.88–5.77 (m, HÀ
C(3)); 5.73 (d, J=3.3, HÀC(3’)); 5.33 (d, J=17.1, 1 HÀC(4)); 5.25 (d, J=10.9, 1 HÀC(4)); 3.71–3.65
(m, 2 HÀC(1), HÀC(2)); 2.36 (t, J=3.5, HÀC(4’)); 1.93–1.83 (m, OH, HexoÀC(5’)); 1.55–1.45 (m,
HexoÀC(6’)); 1.10–0.96 (m, HendoÀC(5’), HendoÀC(6’)); 1.01 (s, MeÀC(1)); 0.81 (s, Mesyn); 0.78 (s, Meanti).

Helvetica Chimica Acta – Vol. 89 (2006)
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13C-NMR (150.9 MHz, CDCl3): 141.2 (s, C(2’)); 135.2 (d, C(3)); 128.8 (d, C(3’)); 118.2 (t, C(4)); 63.8 (t,
C(1)); 56.8 (s, C(1’)); 56.0 (s, C(7’)); 52.3 (d, C(4’)); 50.5 (d, C(2)); 31.5 (t, C(6’)); 26.3 (t, C(5’)); 19.6 (q,
Meanti); 19.4 (q, Mesyn); 11.4 (q, MeÀC(1)). CI-MS (NH3): 241 (6), 240 (16), 239 (100, [M+H]+), 221 (7),
169 (5).
Data of 5. Colorless oil. IR (film): 3425m (br.), 2960s, 2873m, 1739s, 1447m, 1392m, 1372m, 1324w,
1093m, 1016m, 971m. 1H-NMR (300 MHz, CDCl3): 5.80–5.60 (m, 2 H); 4.15–4.05 (m, CH2O);
2.65–2.40 (m, ca. 1 H); 2.10–1.85 (m, ca. 3 H); 1.80–1.25 (m, ca. 4 H); 0.93, 0.87, 0.84, 0.83, 0.80, 0.78
(6s, 3 Me). CI-MS (NH3): 240 (28, [M+NH4]+), 206 (16), 205 (100, [MÀH2O+H]+).
Repetition of the reaction of 1 (336 mg, 2 mmol), 2 (280 mg, 4 mmol), and 0.5 equiv. of ZnCl2 accord-
ing to GP 3 afforded 52 mg (11%) of 3, 176 mg (37%) of (1R,2S,4R,4’S)-4’-ethenyl-1,7,7-trimethylspiro-
[bicyclo[2.2.1]heptane-2,2’-[1,3]oxathiolane] (7), 9.5 mg (4%) of 4, and 84.2 mg (13%) of (2S)-2-[1’-(1’S)-
({[((1’’R,4’’R)-1’’,7’’,7’’-trimethylbicyclo[2.2.1]hept-2’’-en-2’’-yl)sulfanyl]methyl}prop-2’-en-1’-yl)sulfa-
nyl]but-3-en-1-ol (8).
Data of 7. Colorless oil. [a]2D3 =À131.1. IR: 3083w, 2956s, 2884m, 1636w, 1480m, 1453m, 1417w,
1389m, 1370m, 1306w, 1248w, 1201w, 1161w, 1138w, 1110m, 1086s, 1052m, 1016w, 986m, 943w, 917m,
873w, 837m, 804w, 736w. 1H-NMR (500 MHz, CDCl3): 5.74 (ddd, J=16.9, 9.9, 7.9, CH=CH2); 5.19
(dd, J=16.9, 1.3, 1 H of =CH2); 5.05 (dd, J=9.8, 1.2, 1 H of =CH2); 4.19 (dd, J=9.3, 5.9, 1 HÀC(5’));
3.95–3.90 (m, HÀC(4’)); 3.66 (dd, J=9.2, 8.2, 1 HÀC(5’)); 2.37 (ddd, J=13.5, 4.5, 3.2, HexoÀC(3));
2.00 (d, J=13.5, HendoÀC(3)); 1.77 (t, J=4.5, HÀC(4)); 1.75–1.67 (m, HexoÀC(5)); 1.57–1.54 (m, 2
HÀC(6)); 1.23–1.18 (m, HendoÀC(5)); 1.01 (s, Mesyn); 0.91 (s, MeÀC(1)); 0.87 (s, Meanti). 13C-NMR
(125.8 MHz, CDCl3): 136.5 (d, CH=CH2); 116.8 (t, CH=CH2); 106.9 (s, C(2)); 74.7 (t, C(5’)); 53.8 (s,
C(1)); 51.7 (d, C(4’)); 51.6 (t, C(3)); 48.3 (s, C(7)); 45.9 (d, C(4)); 34.7 (t, C(6)); 27.1 (t, C(5)); 21.1 (q,
Meanti); 20.7 (q, Mesyn); 10.0 (q, MeÀC(1)). ESI-MS (MeOH+NaI): 278 (18), 277 (83, [M+K]+), 261
(25, [M+Na]+), 229 (7), 207 (7), 173 (14). Anal. calc. for C14H22OS (238.39): C 70.54, H 9.30, S 13.45;
found: C 70.40, H 9.18, S 13.57.
Data of 8. Colorless oil. [a]2D3 =+30. IR: 3406m (br., OH), 3081w, 2953s, 2870m, 1635w, 1561w,
1456m, 1416m, 1386m, 1296m, 1068m, 1042m, 985m, 918m, 794w, 715w. 1H-NMR (600 MHz, C6D6):
5.64 (ddd, J=17.0, 10.1, 8.5, HÀC(2’)); 5.60 (d, J=3.3, HÀC(3’’)); 5.54 (ddd, J=17.2, 10.2, 8.5, HÀ
C(3)); 5.04 (dt-like, Jꢀ17.0, 2.1, 1 HÀC(3’)); 4.96–4.90 (m, 2 HÀC(4), 1 HÀC(3’)); 3.64 (ddd, J=8.9,
8.6, 5.2, HÀC(1’)); 3.46 (br. m, 2 HÀC(1)); 3.21–3.17 (m, HÀC(2)); 2.84 (dd, J=13.1, 5.1, 1 H of
CH2S); 2.63 (dd, J=13.1, 9.1, 1 H of CH2S); 2.26 (t, J=3.4, HÀC(4’’)); 1.81–1.76 (m, HexoÀC(5’’));
1.53 (br. m, OH); 1.43 (ddd, J=12.0, 5.2, 3.5, HexoÀC(6’’)); 1.16 (ddd, J=11.9, 5.5, 3.8, HendoÀC(6’’));
1.08 (s, MeÀC(1’’)); 0.99 (ddd, J=11.6, 5.9, 3.5, HendoÀC(5’’)); 0.92 (s, Mesyn); 0.69 (s, Meanti). 13C-
NMR (150.9 MHz, C6D6): 142.8 (s, C(2’’)); 137.6 (d, C(3)); 136.8 (d, C(2’)); 128.4 (d, C(3’’), assigned
by means of HSQC and HSQC-TOCSY spectra); 117.5 (t, C(4)); 117.2 (t, C(3’)); 64.4 (t, C(1)); 57.4
(s, C(1’’)); 56.3 (s, C(7’’)); 53.1 (d, C(4’’)); 52.8 (d, C(2)); 49.0 (d, C(1’)); 34.9 (t, CH2S); 31.9 (t, C(6’’));
27.4 (t, C(5’’)); 20.1 (q, Meanti, Mesyn); 12.0 (q, MeÀC(1’’)). CI-MS (NH3): 327 (10), 326 (19), 325 (87,
[M+H]+), 221 (15), 169 (11), 159 (10), 157 (100).
3.2. NaH-Activated Reaction of 1 and 2. Reaction of 1 (840 mg, 5 mmol), NaH (151 mg, 6.3 mmol)
and 2 (455 mg, 6.5 mmol) in anh. THF at r.t. (6 h, CC, hexane/Et2O) according to GP 4 gave 830 mg
(70%) of (2R)-1-[(1’R,4’R)-(1’,7’,7’-trimethylbicyclo[2.2.1]hept-2’-en-2’-yl)sulfanyl]but-3-en-2-ol (9) and
260 mg (22%) of 4.
Data of 9. Colorless oil. [a]2D3 =+2.76. IR: 3382m (br., OH), 3081w, 3059w, 2984m, 2953s, 2871m,
1644w, 1561m, 1471m, 1452m, 1440m, 1420m, 1385m, 1375m, 1365m, 1297m, 1290m, 1279m, 1254w,
1185w, 1106m, 1045m, 985m, 925m, 875w, 820w, 781w, 714w. 1H-NMR (600 MHz, C6D6): 5.73 (ddd,
J=17.1, 10.5, 5.5, HÀC(3)); 5.43 (d, J=3.4, HÀC(3’)); 5.23 (dt-like, Jꢀ17.2, 1.5, 1 HÀC(4)); 4.98 (dt-
like, Jꢀ10.5, 1.5, 1 HÀC(4)); 4.12–4.09 (m, HÀC(2)); 2.68 (dd, J=13.3, 4.5, 1 HÀC(1)); 2.57 (dd,
J=13.3, 8.0, 1 HÀC(1)); 2.23 (t, J=3.5, HÀC(4’)); 1.92 (d, J=3.8, OH); 1.81–1.76 (m, HexoÀC(5’));
1.43 (ddd, J=12.1, 5.2, 3.5, HexoÀC(6’)); 1.15 (ddd, J=12.1, 5.4, 3.8, HendoÀC(6’)); 1.06 (s, MeÀC(1));
0.98 (ddd, J=12.3, 5.7, 3.6, HendoÀC(5’)); 0.88 (s, Mesyn); 0.68 (s, Meanti). 13C-NMR (150.9 MHz, C6D6):
144.3 (s, C(2’)); 139.9 (d, C(3)); 125.7 (d, C(3’)); 115.5 (t, C(4)); 70.8 (d, C(2)); 57.2 (s, C(1’)); 56.6 (s,

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Helvetica Chimica Acta – Vol. 89 (2006)
C(7’)); 52.8 (d, C(4’)); 39.1 (t, C(1)); 32.2 (t, C(6’)); 27.3 (t, C(5’)); 20.08, 20.05 (2q, Meanti, Mesyn); 11.9 (q,
MeÀC(1)). CI-MS (NH3): 241(6), 240 (16), 239 (100, [M+H]+). Anal. calc. for C14H22OS (238.39): C
70.54, H 9.30, S 13.45; found: C 70.20, H 9.14, S 13.41.
4. Isomerization of 4 to 3, and of 9 to 10 and 11. The cyclization of 4 (ca. 15 mg) to 3 proceeded quan-
titatively in CDCl3 (0.5 ml, NMR tube) in 15 min at r.t. The cyclization of 9 (50 mg) under the same con-
ditions (10 min) led to 86% of (1R,2R,4R,5’R)-5’-ethenyl-1,7,7-trimethylspiro[bicyclo[2.2.1]heptane-2,2’-
[1,3]oxathiolane] (10) and 14% of (1R,2S,4R,5’R)-5’-ethenyl-1,7,7-trimethylspiro[bicyclo[2.2.1]heptane-
2,2’-[1,3]oxathiolane] (11).
Data of 10. Colorless oil. [a]2D3 =À27.1. IR: 3083w, 2985s, 2952s, 2873s, 1647w, 1477m, 1453m, 1389m,
1371w, 1318w, 1272w, 1195w, 1159w, 1113m, 1071s, 1027m, 1003w, 986m, 960w, 925m, 887w, 834w, 808w.
1H-NMR (600 MHz, CDCl3): 5.92 (ddd, J=17.3, 10.5, 6.4, CH=CH2); 5.38 (dd, J=17.3, 1.3, 1 H of =
CH2); 5.21 (dd, J=10.5, 1.3, 1 H of =CH2); 4.32–4.28 (m, HÀC(5’)); 2.94 (dd, J=10.0, 4.5, 1 HÀ
C(4’)); 2.50 (t-like, Jꢀ10.2, 1 HÀC(4’)); 2.37 (ddd, J=13.9, 4.8, 3.1, HexoÀC(3)); 2.17 (ddd, J=13.1,
5.5, 3.7, HendoÀC(6)); 1.75–1.73 (m, HendoÀC(3), HÀC(4)); 1.72–1.66 (m, HexoÀC(5)); 1.44 (ddd,
J=12.3, 7.9, 4.9, HexoÀC(6)); 1.28–1.23 (m, HendoÀC(5)); 0.94 (s, MeÀC(1), Mesyn); 0.88 (s, Meanti).
13C-NMR (150.9 MHz, CDCl3): 136.1 (d, CH=CH2); 117.0 (t, CH=CH2); 103.1 (s, C(2)); 81.4 (d,
C(5’)); 54.0 (s, C(1)); 50.7 (t, C(3)); 48.1 (s, C(7)); 46.4 (d, C(4)); 39.3 (t, C(4’)); 30.2 (t, C(6)); 27.0 (t,
C(5)); 21.0 (q, Mesyn); 20.2 (q, Meanti); 12.4 (q, MeÀC(1)). CI-MS (isobutane): 240 (14), 239 (67,
[M+H]+), 238 (24, M+C), 237 (12), 184 (11), 154 (17), 153 (100), 143 (18), 129 (19), 127 (8), 125 (11),
108 (7). CI-MS (NH3): 240 (7), 239 (36, [M+H]+), 238 (24), 171 (11), 170 (100), 108 (6).
Data of 11. Colorless oil. [a]2D3 =À33.0. IR: 3083w, 3016w, 2955s, 2885m, 1646w, 1481m, 1454m,
1
1389m, 1369w, 1306w, 1165w, 1110m, 1071s, 1050m, 1004m, 986m, 925m, 875w, 843w, 801w. H-NMR
(600 MHz, CDCl3): 5.89 (ddd, J=17.1, 10.6, 6.4, CH=CH2); 5.31 (dd, J=17.2, 1.3, 1 H of =CH2); 5.14
(dd, J=10.4, 1.4, 1 H of =CH2); 4.52–4.49 (m, HÀC(5’)); 2.94 (dd, J=10.6, 4.5, 1 HÀC(4’)); 2.71 (t-
like, Jꢀ10.2, 1 HÀC(4’)); 2.45 (dt-like, Jꢀ13.7, 4.1, HexoÀC(3)); 1.97 (d, J=13.7, HendoÀC(3)); 1.73 (t,
J=4.5, HÀC(4)); 1.69–1.66 (m, HexoÀC(5)); 1.57–1.46 (m, 2 HÀC(6)); 1.20–1.15 (m, HendoÀC(5));
1.05 (s, Mesyn); 0.92 (s, MeÀC(1)); 0.86 (s, Meanti). 13C-NMR (150.9 MHz, CDCl3): 137.1 (d, CH=CH2);
116.3 (t, CH=CH2); 105.4 (s, C(2)); 85.4 (d, C(5’)); 54.8 (s, C(1)); 52.0 (t, C(3)); 48.6 (s, C(7)); 45.4 (d,
C(4)); 37.6 (t, C(4’)); 33.3 (t, C(6)); 26.8 (t, C(5)); 21.2 (q, Meanti); 20.7 (q, Mesyn); 10.4 (q, MeÀC(1)).
CI-MS (isobutane): 305 (16), 241 (9), 240 (25), 239 (93, [M+H]+), 238 (52, M+C), 237 (22), 184 (13),
169 (11), 154 (15), 153 (100), 143 (23), 129 (29), 127 (12), 125 (16), 109 (10), 108 (13), 95 (7).
Treatment of 9 (100 mg, 0.42 mmol) with 1 equiv. of ZnCl2 in THF (5 ml) under N2 (2 h, reflux, PLC
(hexane)) gave 47 mg (47%) of 10 and 36 mg (36%) of 11, respectively.
5. Epimerization of 3 to 7, and of 10 to 11. Irradiation of 3 in CDCl3 (NMR tube) at r.t. with sunlight
(16-h irradiation, workup after 56 h) afforded a mixture of 3 and 7 in a ratio of 1:15. Treatment of 3 (100
mg, 0.42 mmol) with 1 equiv. of ZnCl2 in THF (5 ml) under N2 (45 min, reflux) and aq. workup gave 3 and
1
7 in a ratio of 1:1 according to H-NMR. However, no epimerization of 3 to 7 took place, when 3 was
treated with 0.5 equiv. of ZnCl2 in CH2Cl2 (5 ml) at À208 for 26 h.
Treatment of 10 (100 mg, 0.42 mmol) in CHCl3 (15 ml) at r.t. with 10 drops of conc. HCl (14 h, PLC
(hexane)) yielded 42 mg (42%) of 11, and 40 mg (40%) of the starting material 10 was recovered.
5. Thio-Claisen Rearrangement of 4. Heating of a soln. of 4 (150 mg, 0.63 mmol) in mesitylene (15
ml) under N2 to reflux (12 min, PLC (hexane/Et2O 1:1)) led to 132 mg (88%) of (1R,3S,4R)-3-[(2’Z)-
4’-hydroxybut-2’-en-1’-yl]-1,7,7-trimethylbicyclo[2.2.1]heptane-2-thione
(12).
Pink
orange
oil.
[a]2D3 =+254.3. IR: 3345m (br., OH), 2960s, 2870m, 1669w, 1485w, 1444m, 1390m, 1375m, 1294m,
1
1267m, 1254m, 1231w, 1125m, 1099m, 999m, 970m, 832w. H-NMR (500 MHz, CDCl3): 5.73–5.71 (m,
HÀC(2’), HÀC(3’)); 4.13–4.07 (m, 2 HÀC(4’)); 2.98–2.93 (m, 1 HÀC(1’)); 2.67–2.63 (m, Hexo
À
C(3)); 2.12 (t-like, Jꢀ4.1, HÀC(4)); 2.04–1.98 (m, 1 HÀC(1’)); 1.83–1.71 (m, HexoÀC(5), 1 HÀC(6));
1.56–1.49 (m, HendoÀC(5), OH); 1.16–1.09 (m, 1 HÀC(6)); 1.08 (s, MeÀC(1)); 1.07 (s, Meanti); 0.82 (s,
Mesyn). 13C-NMR (125.8 MHz, CDCl3): 274.8 (s, C=S); 130.5 (d, C(2’), C(3’)); 70.4 (s, C(1)); 63.6 (t,
C(4’)); 60.0 (d, C(3)); 48.1 (s, C(7)); 47.6 (d, C(4)); 34.9 (t, C(6)); 34.1 (t, C(1’)); 20.3 (t, C(5)); 19.9
(q, Meanti); 19.3 (q, Mesyn); 13.7 (q, MeÀC(1)). CI-MS (isobutane): 238 (8, M+C), 223 (6), 222 (15), 221
(100, [MÀH2O+H]+).

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6. [3,3]-Sigmatropic Rearrangement of Intermediate Xanthate 13. To a two-phase system of 50% aq.
NaOH (2.2 ml) containing 61.2 mg (0.189 mmol) of Bu4NHSO4 and 2.2 ml of CS2, 9 (450 mg, 1.89 mmol)
and MeI (1.342 g, 9.45 mmol) were added. The mixture was vigorously stirred overnight at r.t. The CS2
layer was separated, and the aq. layer was extracted 3× with CS2. The combined org. layers were washed
with H2O, dried (MgSO4), and filtered. Removing the solvent in vacuo and drying the residue in high vac-
uum (48 h) gave 500 mg (81%) of pure S-methyl S-(2E)-4-[(1’R,4’R)-(1’,7’,7’-trimethylbicyclo[2.2.1]hept-
2’-en-2’-yl)sulfanyl]but-2-en-1-yl dithiocarbonate (14). Yellow oil. [a]2D3 =À28.5. IR: 2952vs, 2870s,
1647vs, 1560m, 1471m, 1452m, 1439m, 1385m, 1374m, 1364m, 1298m, 1253w, 1219m, 1186w, 1134w,
1
1105w, 1044m, 963s, 874vs, 820w, 780m, 714m. H-NMR (600 MHz, CDCl3): 5.76–5.69 (m, HÀC(3));
5.67–5.62 (m, HÀC(2)); 5.51 (d, J=2.3, HÀC(3’)); 3.62 (d, J=6.2, 2 HÀC(1)); 3.27 (d, J=6.3, 2 HÀ
C(4)); 2.43 (s, MeS); 2.42 (br. s, HÀC(4’)); 1.90–1.81 (m, 1 H); 1.52–1.45 (m, 1 H); 1.09–0.91 (m, 2
H); 0.98 (s, Me); 0.82 (s, Me); 0.78 (s, Me). 13C-NMR (75.5 MHz, CDCl3): 189.3 (s, C=O); 143.1 (s,
C(2’)); 129.5, 127.4 (2d, CH=CH); 125.5 (d, C(3’)); 56.5, 56.1 (2s, C(1’), C(7’)); 52.2 (d, C(4’)); 32.8,
32.3, 31.5, 26.5 (4t, 4 CH2); 19.5, 19.4, 12.9, 11.1 (4q, 4 Me). CI-MS (NH3): 331 (16), 330 (20), 329 (100,
[M+H]+), 169 (41).
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1
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Received October27, 2005