Regio- and stereospecific cleavage of stannylepoxides with lithium phenylsulfide

Article abstract of DOI:10.1016/S0040-4039(01)01990-6

Unsubstituted and α or β C-substituted epoxystannanes react with lithium phenylsulfide to give regio- and stereodefined α-phenylthio-β-hydroxystannanes resulting from α-opening with inversion of configuration. On the other hand, α- or β-trans-silyl epoxys

Full text of DOI:10.1016/S0040-4039(01)01990-6

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 8993–8996
Regio- and stereospecific cleavage of stannylepoxides with
lithium phenylsulfide
Purificacio´n Cuadrado and Ana M. Gonza´lez-Nogal*
Departamento de Qu´ımica Orga´nica, Universidad de Valladolid, 47011 Valladolid, Spain
Received 9 October 2001; revised 19 October 2001; accepted 24 October 2001
Abstract—Unsubstituted and a or b C-substituted epoxystannanes react with lithium phenylsulfide to give regio- and stereodefined
a-phenylthio-b-hydroxystannanes resulting from a-opening with inversion of configuration. On the other hand, a- or b-trans-silyl
epoxystannanes afford stereospecific a- or b-silylated vinylsulfides formed by nucleophilic attack at the carbon which bears the tin
group and subsequent syn-elimination of HOSnBu3. Both types of products are interesting synthons in organic chemistry. © 2001
Elsevier Science Ltd. All rights reserved.
Although the behavior of silylepoxides toward nucle-
ophilic reagents has been widely studied,1 there are few
references concerning the reactivity of stannylepoxides.
We have only found reported their conversion in
ketones2 by cleavage with formic acid followed by
treatment with lithium hydroxide in aqueous THF,
their transformation in olefins3 by a reductive alkyla-
tion with alkyl lithium reagents, ring-opening with
metal hydrides4 and organocuprates5 and transmetala-
tion with an organolithium.6
The behavior of epoxystannanes toward lithium
phenylsulfide is different from that shown for epoxysi-
lanes.8 Unsubstituted or differently C-substituted stan-
nylepoxides 1a–d react at 0°C with lithium
phenylsulfide in THF11 to give in excellent yields regio-
and stereodefined a-phenylthio-b-hydroxystannanes 2a–
d formed by hydrolysis of the lithium b-oxido stan-
nanes resulting from a-opening with inversion of
configuration (Scheme 1).
All new compounds showed satisfactory spectroscopic
and analytical data.12
In previous papers, we have described the regio- and
stereospecific cleavage of epoxysilanes with lithium
diphenylphosphide7 and lithium phenylsulfide.8 In the
latter case we obtained vinyl sulfides resulting from
a-opening or silyl enol ethers, a-silylaldehydes and a-
hydroxy-b-phenylthiosilanes, all resulting from b-
opening.
These a-phenylthio-b-hydroxystannanes are very ver-
satile synthons. They experience acid-catalyzed anti
elimination of HOSnBu3 affording alkenylsulfides,
which are stereoisomers of those we had previously
obtained by reaction of trimethylsilyl- or dimethyl-
phenylsilylepoxides with the same reagent.8 Conversely,
they undergo thermal syn-elimination by heating at
reflux of xylene. Although both eliminations are
stereospecific, when the b-substituent is a phenyl group
the initial Z-alkenylsulfide was isomerized to the more
stable E isomer (Scheme 2).
We have now extended our research to the study of the
reactivity of stannylepoxides toward nucleophile
reagents and in this communication we report the
results obtained in the treatment of stannylepoxides
with lithium phenyl sulfide.
R3
R2
R3
R2
SPh
R1
1.PhS Li
The starting compounds are a and b C- and Si-substi-
tuted epoxystannanes prepared by reaction with
MCPBA of the corresponding vinylstannanes, obtained
by tributylstannyl cupration from alkynes9 or allenes.10
R1
SnBu3
2.NH4Cl+H2O
O H
O
SnBu3
1a;R1=R2=R3=H
2a (90%)
2b (85%)
2c (83%)
2d (86%)
1b;R1=R2=H,R3=Me
1c;R1=R3=H,R2=Ph
1d;R1=Me,R2=R3=H
Keywords: epoxystannanes; thiostannanes; vinylsulfides; vinylsilanes.
* Corresponding author. Tel.: 34-983-423213; fax: 34-983-423013;
e-mail: agn@qo.uva.es
Scheme 1.
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01990-6

8994
P. Cuadrado, A. M. Gonza´lez-Nogal / Tetrahedron Letters 42 (2001) 8993–8996
us8 in the opening of epoxysilanes with lithium phenyl-
sulfide and those obtained now in the reactions of
epoxystannanes with the same reagent, the intermediate
6g should undergo Peterson-elimination to give the
corresponding a-stannylated vinylsulfide. Surpris-
ingly,14 the product isolated was in all conditions (0°C,
rt, neutral, acid or basic hydrolysis) exclusively the
a-silylated vinylsulfide 3g resulting from elimination of
HOSnBu3 (Scheme 5).
R1
R2
SPh
H
R2
R1
SnBu3
SPh
E-3b (94%)
Z-3c (23%)+E-3c (69%)
O H
H
R1
H
2b; R1=H,R2=Me
2c;R1=Ph,R2=H
R2
SPh
Z-3b (92%)
E-3c (91%)
The a-silyl epoxystannane 1h bearing a hindered tert-
butyldiphenylsilyl group was recovered untransformed
even after prolonged heating with lithium phenylsulfide
in THF at reflux (12 h). It was necessary to add
aluminum chloride in order for the reaction to take
place. After 21 h at rt, the corresponding a-tert-
butyldiphenylsilyl vinylsulfide 3h resulting from a-open-
ing was obtained in low yield (8%). However, when the
reaction was heated at reflux of THF for 3 h, 2,3-bis-
tert-butyldiphenylsilylbuta-1,3-diene 7h was isolated in
good yield. The compound 7h is probably obtained by
thermal dimerization from the initially formed vinyl-
sulfide 3h (Scheme 6).
Scheme 2.
Moreover, the presence of a tributylstannyl group gem
to the phenylthio makes the compounds 2 synthetic
equivalents of stereodefined a-phenylthio-stabilized car-
banions capable of being trapped by electrophiles to
provide a route to interesting synthons. In fact, 2b was
stereoselectively transmetalated by treatment with BuLi
and the intermediate 4b was quenched with ethyl chlo-
roformate to give the b-hydroxyester derivative 5b as
the sole diastereomer13 (verified by H NMR and TLC
1
of the reaction mixture) (Scheme 3).
We have also studied the behavior of silylated epoxy-
stannanes with the aim of knowing which of the two
metalated groups controlled the regiochemistry of the
ring opening as this will determine the nature of the
reaction products.
This strong tendency for nucleophilic attack at the
carbon a to the tin group contrasts with the acid-cata-
lyzed b-opening observed by us8 in the reactions of
tert-butyldiphenylsilylepoxides with the same reagent.
Moreover, the reactivity of the tin and silicon dimeta-
The b-silylated epoxystannanes 1e and 1f were exclu-
sively attacked by phenylsulfide at the carbon a to the
tin group giving an intermediate lithium a-phenylthio-
b-silyl-b-oxido stannanes 6e or 6f, which was
hydrolyzed to the corresponding b-hydroxystannane 2e
or underwent spontaneous syn-elimination of
HOSnBu3 affording the b-silyl vinylsulfide 3f (Scheme
4).
The different behavior of cis and trans b-silyl epoxy-
stannanes 1e and 1f may depend on the stability of the
conformation necessary for the syn-elimination of
HOSnBu3. Probably, the intermediate 6e does not
undergo elimination due to the fact that in this confor-
mation two bulky groups (dimethylphenylsilyl and
phenylthio) should be eclipsed (Scheme 4).
On the other hand, the a-silylepoxystannane 1g is
opened by nucleophilic a-attack to give the intermedi-
ate 6g. According to the results previously described by
Scheme 4.
SPh
Me
Me
SiMe3
SPh
SPh
H
H
H
PhS Li
0 °C or r.t.
BuLi ( 4 eq.)
SiMe3
SnBu3
O
-78 -40 °C
SnBu3
H
SnBu3
O H
LiO
LiO
Li
1g
2b
4b
6g
Me
SPh
H
SiMe3
SPh
ClCO2Et ( 4 eq.)
H2O
ClNH4 or HCO3Na
-40 0 °C
H
EtO2CO
CO2Et
3g (79%)
5b (43%)
Scheme 5.
Scheme 3.

P. Cuadrado, A. M. Gonza´lez-Nogal / Tetrahedron Letters 42 (2001) 8993–8996
8995
5. Chong, J. M.; Mar, E. K. J. Org. Chem. 1992, 57, 46–49.
6. Lautens, M.; Delanghe, P. H. M.; Goh, J. B.; Zhang, C.
H. J. Org. Chem. 1995, 60, 4213–4227.
7. Cuadrado, P.; Gonza´lez-Nogal, A. M. Tetrahedron Lett.
1997, 38, 8117–8120.
8. Cuadrado, P.; Gonza´lez-Nogal, A. M. Tetrahedron Lett.
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9. (a) Barbero, A.; Cuadrado, P.; Fleming, I.; Gonzalez-
Nogal, A. M.; Pulido, F. J. J. Chem. Soc., Chem. Com-
mun. 1992, 351–353; (b) Barbero, A.; Cuadrado, P.;
Fleming, I.; Gonza´lez-Nogal, A. M.; Pulido, F. J. J.
Chem. Soc., Perkin Trans. 1 1993, 1657–1662; (c) Bar-
bero, A.; Cuadrado, P.; Fleming, I.; Gonza´lez-Nogal, A.
M.; Pulido, F. J.; Sa´nchez, A. J. Chem. Soc., Perkin
Trans. 1 1995, 1525–1532.
10. (a) Barbero, A.; Cuadrado, P.; Fleming, I.; Gonza´lez-
Nogal, A. M.; Pulido, F. J. J. Chem. Soc., Chem. Com-
mun. 1990, 1030–1031; (b) Barbero, A.; Cuadrado, P.;
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Chem. Soc., Perkin Trans. 1 1992, 327–331.
Scheme 6.
lated epoxides is dominated by the stannyl group. The
nucleophilic attack always takes place in the carbon
bearing the stannyl group and the evolution of the
resulting intermediate is also controlled and directed by
this group. In contrast to what was observed in the
reactions of epoxysilanes with lithium phenylsulfide,8
the lithium b-oxido stannanes 6f and 6g intermediates
containing also an a-alkoxy and b-alkoxysilane moiety
respectively, do not undergo Brook rearrangement or
Peterson-elimination. They afford the corresponding 1-
or 2-silylated vinylsulfide 3f and 3g resulting from
syn-elimination of HOSnBu3.
11. General procedure. To a stirred THF solution of lithium
phenylsulfide [prepared from benzenethiol (0.1 mL, 1
mmol) and butyllithium (0.625 mL, 1.6 M solution in
hexane, 1 mmol) in THF (5 mL) at −78°C under N2 for
10 min] was added dropwise a solution of epoxystannane
(1 mmol) in THF (5 mL). The resulting mixture was
allowed to warm up to 0°C for 1a–d and 1g or to room
temperature for 1e and 1f and stirred at these tempera-
tures until TLC indicated complete reaction. Ammonium
chloride solution was added and the mixture was
extracted with ether, washed with sodium hydroxide solu-
tion, dried (MgSO4) and chromatographed.
In conclusion, the opening of epoxystannanes with
lithium phenylsulfide is an easy method for preparing
new diastereomerically pure alcohols 2 bearing synthet-
ically versatile functionality in fixed regiospecific rela-
tionships. Furthermore, these erythro or threo
b-hydroxy stannanes undergo stereospecific syn or anti-
elimination of HOSnBu3. This has allowed us to pre-
pare Z or E vinyl sulfides.15 Especially interesting are
the 1- and 2-silylated vinylsulfides 3f–h which among
other applications,16–18 have been used for synthesizing
thiophenyl-functionalized cyclopentenones via Nazarov
cyclizations.19 Finally, the 2,3 disilylated diene 7h is a
potentially attractive reaction partner in [4+2] cycload-
ditions since the adducts are expected to be prone to
various functionalizations of the disilylated vinylic unit.
1
12. Selected spectroscopy data: 2b; H NMR (CDCl3) l 7.40
(dd, J=7.2 and 1.4 Hz, 2H), 7.27 (t, J=7.2 Hz, 2H), 7.15
(dd, J=7.2 and 1.4 Hz, 1H), 4.10 (ddq, J=5.8, 5.1 and
6.2 Hz, 1H), 3.08 (d J=5.8 Hz, JSn-H=53 Hz, 1H), 2.33
(d, J=5.1 Hz, 1H), 1.54 (m, 6H), 1.35 (m, 6H), 1.23 (d,
J=6.2 Hz, 3H), 1.03 (m, 6H), and 0.91 (t, J=7.3 Hz,
9H); 13C NMR (CDCl3) l 139.29, 128.79, 128.49, 125.75,
70.32, 39.04, 29.06, 27.39, 23.03, 13.67, and 10.50; MS
(EI) m/z 401 (M+−Bu, 6%), 265 (22), 150 (34), 135 (17),
109 (13), 71 (52), and 41 (100). Anal. calcd for
C21H38OSSn: C, 55.15; H, 8.38. Found: C, 55.32; H, 8.46.
1
Z-3b; H NMR (CDCl3) l 7.37–7.16 (m, 5H), 6.22 (dq,
Acknowledgements
J=9.2 and 1.6 Hz, 1H), 5.89 (dq, J=9.2 and 6.7 Hz, 1H),
1.85 (dd, J=6.7 and 1.6 Hz, 3H). E-3b; 1H NMR
(CDCl3) l 7.30 (m, 5H), 6.14 (dq, J=14.8 and 1.3 Hz,
1H), 6.00 (dq, J=14.8 and 6.5 Hz, 1H), and 1.84 (dd,
We thank the Ministerio de Ciencia y Tecnolog´ıa of
Spain for supporting this work (Grant BQU2000-0943).
J=6.5 and 1.3 Hz, 3H). 5b; IR (CCl4) 1735 cm−1 1H
;
NMR (CDCl3) l 7.47–7.19 (m, 5H), 5.10 (dq, J=9.1 and
6.3 Hz, 1H), 4.15 (q, J=7.1 Hz, 2H), 4.14 (q, J=7.0 Hz,
2H), 3.75 (d, J=9.1 Hz, 1H), 1.52 (d, J=6.3 Hz, 3H),
1.27 (t, J=7.1 Hz, 3H), and 1.19 (t, J=7.0 Hz, 3H); 13C
NMR (CDCl3) 169.58, 153.93, 133.27, 132.42, 129.10,
128.40, 73.70, 64.04, 61.35, 55.63, 17.58, 14.14, and 13.92.
Anal. calcd for C15H20O5S: C, 57.67; H, 6.45. Found: C,
57.79; H, 6.38. 2e; 1H NMR (CDCl3) l 7.53–7.14 (m,
10H), 3.88 (dd, J=7.9 and 4.1 Hz, 1H), 3.38 (d, J=4.1
Hz, JSn-H=50 Hz, 1H), 2.04 (d, J=7.9 Hz, 1H), 1.44 (m,
6H), 1.29 (m, 12H), 0.87 (t, J=7.1 Hz, 9H), 0.37 (s, 3H),
and 0.28 (s, 3H); 13C NMR (CDCl3) l 138.74, 137.52,
134.12, 129.04, 128.69, 127.81, 127.44, 127.12, 69.15,
37.40, 29.03, 27.39, 13.67, 10.68, −3.50, and −4.06. Anal.
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