Palladium-catalyzed insertion reactions of trimethylsilyldiazomethane

Article abstract of DOI:10.1016/S0040-4020(01)00363-5

Palladium(II) salts catalyze the Kirmse reaction of allylsulfides with trimethylsilyldiazomethane (TMSD) to give homoallylsulfides. Similarly, TMSD can intercept ArPdX intermediates generated during Stille couplings to give benzhydryl derivatives. The yie

Full text of DOI:10.1016/S0040-4020(01)00363-5

TETRAHEDRON
Pergamon
Tetrahedron 57 *2001) 5219±5225
Palladium-catalyzed insertion reactions of
trimethylsilyldiazomethane
Kevin L. Greenman, David S. Carter and David L. Van Vrankenp
Department of Chemistry, University of California, Irvine, CA 92697-2025, USA
Dedicated to Professor Barry M. Trost on the occasion of his 60th birthday
Received 12 February 2001; revised 6 March 2001; accepted 12 March 2001
AbstractÐPalladium*II) salts catalyze the Kirmse reaction of allylsul®des with trimethylsilyldiazomethane *TMSD) to give homoallyl-
sul®des. Similarly, TMSD can intercept ArPdX intermediates generated during Stille couplings to give benzhydryl derivatives. The yields of
this process are limited by overinsertion and b-elimination. Insertion and elimination can be harnessed to generate styrenes from benzylic
halides in the presence of palladium *0) catalysts. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
diazomethane *TMSD) to phenyl dimethallyl sul®de *1a)
by slow addition of TMSD to a solution of sul®de 1a,
10 mol% 2,6-di-tert-butyl-4-methylpyridine *DTBP), and
5 mol% PdCl2 *Scheme 1).17 The homoallylic sul®de
product was formed in only 4% yield and most of the start-
ing material *89%) was recovered.
Many metals catalyze useful reactions of diazo
compounds.1,2 Cationic palladium can effect ef®cient cyclo-
propanation of ole®ns with low lying LUMOs *e.g.
styrene,3,4 acrylates,5,6 and norbornenes7±9) or when the
diazo compound has a high lying HOMO *e.g. diazo-
methane).10,11 However, palladium is a poor catalyst for
intermolecular cyclopropanation of simple alkenes with
stabilized diazo compounds such as a-diazoesters.12
Palladium-catalyzed cyclopropanation is less general than
rhodium-catalyzed cyclopropanation, but the rich reactivity
of palladium makes it an attractive catalyst for exploring
new patterns of reactivity with diazo compounds.13,14 In this
manuscript, we describe three types of palladium catalyzed
reactions with trimethylsilyldiazomethane: *1) insertion/
rearrangement of allyl sul®des, *2) a low yielding Stille
insertion reaction, and *3) a unique halide homologation.
Since the reaction remained homogeneous, it seemed likely
that it might be possible to achieve turnover by increasing
the reaction temperature. While benzene is known to
undergo electrophilic substitution by palladium*II) in the
presence of thioethers *in the absence of diazo
compounds),18 it is still a suitable solvent for the palladium
chloride catalyzed process. When the same reaction was
carried out in benzene at 808C, the desired homoallylic
sul®de was obtained in 67% yield with 12% recovered start-
ing material. Not surprisingly, Pd*Ph3P)4 does not function
as a catalyst under these conditions. Dichloroethane gave
even better results with only 2% recovered starting material
*Table 1). Other palladium salts were inferior to palladium
2. Results and discussion
2.1. PdꢀII)-Catalyzed Kirmse reaction
Many of the metals that ef®ciently catalyze cyclopropana-
tion *e.g., rhodium, copper, cobalt) can also ef®ciently cata-
lyze addition/rearrangement reactions of allyl sul®des with
diazo compounds *the Kirmse reaction).1,2,15 Even though
thioethers bind to Pd*II) with high af®nity McCrindle has
shown that diazomethane inserts into the Pd±Cl and Pd±S
bonds of R2S±PdCl2 complexes.16 Recently, we reported
stoichiometric addition/rearrangement of trimethylsilyl-
Scheme 1. Insertion/rearrangement without turnover.
Table 1. Palladium *II) salts in the Kirmse reaction at re¯ux
Catalyst
Solvent
[2,3] Yield *%) Starting material *%)
PdCl2
PdCl2
Pd*O2CCF3)2
C6H6
67
83
22
8
12
2
55
75
ClCH2CH2Cl
ClCH2CH2Cl
Pd*O2CCH3)2 ClCH2CH2Cl
Keywords: insertion; carbenes; palladium.
Corresponding author. Tel.: 1949-824-5455; fax: 1949-824-8571;
e-mail: dlvanvra@uci.edu
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020*01)00363-5

5220
K. L. Greenman et al. / Tetrahedron 57 &2001) 5219±5225
Table 2. Effect of ligands on conversion and ee
1a the optimal balance was achieved using between 1.5 and
2 equiv. TMSD. The inclusion of molecular sieves generally
leads to a slightly higher yield. For example, in the case of
Ê
benzylic substrate 1e the yield with 4 A molecular sieves is
80%, versus 73% without molecular sieves.
A more pronounced effect arises on changing from the 3,3-
dimethallyl substrates 1a±e to other allylic groups *Table
4). The methallyl substrate 4a and the geranyl substrate 5a
give yields around 60%. However, the hindered cyclo-
hexenyl substrate 6a leaves almost a third of the starting
material un-reacted. In addition, only 24% of the starting
material is successfully converted to product. Since the
sulfur lone pairs of substrate 6a are diastereotopic, it is
possible that reaction of one lone pair leads to product 6b
while reaction of the other lone pair leads to other pathways
or un-reactive ylide. The successful reaction of the cinnamyl
substrate 7a is compromised by the formation of a [1,2]-
rearrangement product. [1,2]-Rearrangements of free ylides
are common when the p component can form stable
radicals. The results in Table 4 suggest that the palladium-
catalyzed Kirmse reaction will work best with 3,3-
dimethallyl and related substrates in which the sulfur lone
pairs on the starting material are relatively accessible, but
the lone pairs on the product are not.
Catalyst
2a
eea
1a
dppp1PdCl2
64%
40%
No rxn.
70%
±
6%
±
12%
41%
±
*R)-BINAP1PdCl2
trans-*Ph3P)2PdCl2
*S,S)-box1PdCl2
6%
6%
a
Eu*hfc)3 lanthanide shift study, 3a ortho protons.
chloride. Unfortunately, with ethyl diazoacetate, the most
common diazo compound, dimerization is the dominant
reaction pathway, even when the diazo partner is added
slowly to the reaction mixture using a syringe pump.
With a 20:1 excess of substrate to the initial catalyst
complex it is reasonable to expect that the thioether might
displace phosphine and nitrogen ligands in the course of the
catalytic cycle. Addition of 1,3-bis*diphenylphosphino)pro-
pane gave a decreased yield of 2a *Table 2). *R)-BINAP led
to a more substantial reduction in yield with low levels of
enantioselection. Although results with the *S,S)-box
complex more closely paralleled those with the ligandless
precursor, the enantiomeric excess of the product was
still low. Interestingly, the trans bis*triphenylphosphine)±
palladium chloride complex was not an effective catalyst
precursor for this reaction. From these observations, it is
unclear whether the ligands remain attached to the metal
under the reaction conditions.
In the Kirmse reaction using rhodium dimer catalysts, the
sul®de is required to react in a bimolecular fashion with the
coordinatively saturated metal±carbene moiety. In contrast,
copper, iron, and palladium catalysts with open coordina-
tion sites could potentially deliver a ligand internally
*Scheme 2) as previously proposed by Hubert and Noels
for cyclopropanation.20
2.2. Participation of TMSD in Stille coupling reactions
The conditions are fairly general for aryl and benzylic ethers
of the type 1a±e *Table 3). The products are thioethers, just
like the starting material, so there is a tradeoff between
consumption of starting material and the subsequent con-
version of the product to a homoallyl ylide that cannot
rearrange.
If palladium can deliver sul®de ligands to carbene ligands,
then ArPdX intermediates in the Stille coupling may be able
to deliver aryl groups to carbene ligands as rationalized in
Scheme 3.
To explore the potential for trimethylsilyldiazomethane to
participate in cross-coupling reactions 1 equiv. of TMSD
In support of this idea, the analogous Cu catalyzed reaction
of allylic aryl sul®des with 3±4 equiv. of ethyl diazoacetate
is known to proceed through the homoallylic sul®de which
undergoes a second diazo insertion followed by elimination
to generate the a,b,g,d-unsaturated ester.19 With substrate
Table 4. Palladium catalyzed Kirmse reaction of various allyl sul®des
Starting material
Product
Yield SM
Table 3. Variation of sulfur substituents
R
Equiv. TMSD
Yield *%)
1a
1a
1a
1a
1b
1c
1d
1e
4-MeOPh
4-MeOPh
4-MeOPh
4-MeOPh
Ph
4-ClPh
4-MeOBn
Bn
1.5
2
3
2
2
64
62
54
84
75
64
80
2
2

K. L. Greenman et al. / Tetrahedron 57 &2001) 5219±5225
5221
Scheme 2. A plausible mechanistic pathway.
Scheme 3. Stille carbene insertion.
and 1 equiv. of tributylphenyltin were added by syringe
pump to a re¯uxing solution of iodoanisole in THF. The
desired insertion product 8a was obtained in 21% yield
along with the normal product, biphenyl, isolated in 10%
yield. Under the same conditions, p-iodoanisole reacts to
give 10% yield of the chiral benzhydryl derivative 8b.
The primary competing process in these reactions is the
continued reaction of intermediate c with TMSD, followed
by b-hydride or b-silyl elimination.
was detected by GCMS. No reaction occurred in the absence
of palladium.
We rationalize this result by the mechanism shown in
Scheme 4. Following benzyl migration to the carbene
ligand, b-hydride elimination could afford the b-silyl-
styrene as a complex with H±Pd±Br. The subsequent events
follow from Karabelas and Hallberg's mechanistic study of
the de-silylation of b-silylstyrenes21 and are closely
analogous to the mechanism proposed by Farina and
Hossain for the abnormal cine substitution that is observed
during Stille coupling of a-trimethylstannylstyrenes.22
2.3. Participation of TMSD in a homologation reaction
We decided to exploit this insertion/elimination process as a
unique method for generating styrene derivatives. We
envisioned that either an extra equivalent of TMSD or a
hindered amine base could convert the H±Pd±X species
back into Pd*0). Rather than adding 2 equiv. of TMSD to
an aryl iodide, the reaction was simpli®ed by starting with a
benzyl bromide, requiring only one insertion for styrene
formation. To our surprise, we found that when TMSD
was slowly added to bromide 9a in re¯uxing chloroform,
the corresponding styrene 10a was formed in 56% yield
*Table 5), but none of the corresponding b-silylstyrene
3. Conclusions
In conclusion, this work demonstrates for the ®rst time that
palladium can catalyze the addition and rearrangement of
trimethylsilyldiazomethane to allylic sul®des. This reaction
does not work with ethyl diazoacetate, a more common
reagent. Yields are best with dimethallyl substrates that
generate quaternary centers. Diastereoselection generally
falls in the range of 3±5:1, but enantioselection was poor.
The insertion concept can be extended to Stille reactions in
Table 5. Pd-catalyzed homologation of benzyl halides with TMSD
S.M.
X
R
Solvent
CHCl3
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
Time *h)
Yield *%)
9a
9a
9b
9c
Br
Br
Cl
Cl
4-MeO2C
4-MeO2C
4-O2N
12
1
1
56
60
57
54
3-MeO
1

5222
K. L. Greenman et al. / Tetrahedron 57 &2001) 5219±5225
Scheme 4. Palladium catalyzed benzyl homologation.
low yields. In contrast, the TMSD homologation of benzyl
halides appears quite promising and may be of greater utility
if applied to related aryl, vinyl and allyl halides.
in vacuo, diluted with ether *100 mL) and washed with 2N
sodium hydroxide *3£50 mL). The organic layer was dried
*MgSO4) and concentrated in vacuo. The resultant oils were
puri®ed by bulb to bulb distillation except for the solid 8a,
which was recrystallized from hexanes. Compounds 1a,24
1b,25 1c,26 1e,27 4a,28 5a,29 6a30 and 7a31 have been
previously reported. Compound 1d was obtained in 78%
yield following bulb to bulb distillation: Rfˆ0.15 *hexanes);
4. Experimental
4.1. General
1
IR*neat) 3030, 2912, 2834, 1610, 1510 cm21; H NMR
*500 MHz, CDCl3) d 7.22 *d, Jˆ8.5 Hz, 2H), 6.83 *d,
Jˆ8.5 Hz, 2H), 5.23 *t, Jˆ7.6 Hz, 1H), 3.78 *s, 3H), 3.63
*s, 2H), 3.03 *d, Jˆ7.6 Hz, 2H), 1.73 *s, 3H), 1.58 *s, 3H);
13C NMR *125 MHz, CDCl3) d 158.5, 135.2, 130.5, 130.0,
129.9, 120.5, 113.8, 55.2, 35.0, 29.0, 25.7, 17.8; LRMS *EI)
m/z 222 *50), 154 *50), 121 *100), 77 *80); HRMS*EI) calcd
for C13H18OS [M]1 222.1078, found: 222.1079; Anal. Calcd
for C13H18OS: C, 70.23; H, 8.16; Found: C, 70.20, H, 8.20.
All reactions were run under an atmosphere of dry nitrogen
unless otherwise noted. Trimethylsilyldiazomethane in
hexanes and anhydrous 1,2-dichloroethane were purchased
from Sigma±Aldrich. PdCl2 and *MeCN)2PdCl2 were
purchased from Strem Chemical. Deuterated NMR solvents
with a 0.05% by volume tetramethylsilane standard were
obtained from Cambridge Isotope Labs. All other reagents
and solvents were purchased from Fisher Scienti®c.
Dichloromethane was dried by passage over alumina as
described by Grubbs.23 Commercial reagents and solvents
were used without further puri®cation except as indicated.
Chromatography solvents were prepared as volume to
volume mixtures. Analtech 1.5 and 2.0 mm GF silica plates
were used for preparative thin layer chromatography.
Reverse phase HPLC was preformed on a C18 microsorb
column with 1 mL/min *analytical) and 10 mL/min
*preparative) ¯ow rates. HPLC grade water and acetonitrile
were ®ltered and degassed prior to use. All NMR spectra
were taken with Bruker 500 or 400 MHz spectrometers.
Mass spectra were obtained from a Micromass Analytica
7070E *LRMS/HRMS), Micromass Autospec *HRMS/
LRMS), or a Perspective Biosystems Voyager DESTR
*LCMS) using the indicated ionization method. Combustion
analyses were performed by Atlantic Micro Labs, Atlanta,
GA. Uncorrected melting points were determined in open
capillary tubes.
4.1.2. General procedure for [2,3]-sigmatropic rearrange-
Ê
ment. A two-necked ¯ask with 4 A molecular sieve spheres
and a magnetic stir bar was ¯ame dried under vacuum. The
vessel was then charged with 2,6-di-tert-butyl-4-methyl-
pyridine *0.10 equiv.), PdCl2 *0.05 equiv.) and purged
with nitrogen. The corresponding allyl sul®de *1.0 equiv.)
was added to the ¯ask along with 1,2-dichloroethane
*10 mL). The solution was then heated to re¯ux. Trimethyl-
silyldiazomethane in hexanes *2.0 equiv.) was added over
12 h by syringe pump. The resulting brown solution was
cooled to room temperature, ®ltered through a pad of Celite,
and concentrated in vacuo.
4.1.3. [1-ꢀ4-Methoxyphenylsulfanyl)-2,2-dimethylbut-3-
enyl]trimethylsilane ꢀ2a). Following the above procedure,
puri®cation by preparative thin layer chromatography *98:2
hexanes/ether) afforded 2a as a clear, colorless oil *169 mg,
64%): Rfˆ0.36 *98:2 hexanes/ether); IR *neat) 3082, 2960,
2835, 1634, 1593, 1284 cm21; 1H NMR *500 MHz, CDCl3)
d 7.34 *dt, Jˆ8.8, 2.4 Hz, 2H), 6.81 *dt, Jˆ8.8, 2.4 Hz, 2H),
5.89 *dd, Jˆ17.5, 10.7 Hz, 1H), 4.97 *dd, Jˆ17.5, 1.0 Hz,
1H), 4.91 *dd, Jˆ10.7, 1.0 Hz, 1H), 3.79 *s, 3H), 2.27 *s,
1H), 1.13 *s, 3H), 1.10 *s, 3H), 0.18 *s, 9H); 13C NMR
*125 MHz, CDCl3) d 158.3, 148.3, 132.1, 131.6, 114.5,
110.9, 55.4, 50.4, 42.7, 28.3, 26.3, 1.0; LRMS *EI) m/z
294 *16), 225 *56), 212 *86), 197 *64), 182 *68), 167 *30),
139 *24), 135 *22), 117 *14), 73 *100); HRMS *CI/NH3)
4.1.1. General procedure for preparation of allylic
sul®des 1a±e and 4a±7a. A ¯ame dried ¯ask with a
magnetic stir bar was charged with methanol *50 mL) and
cooled to 08C. One equivalent of sodium metal was added to
the ¯ask. Upon complete reaction of the metal, 1.2 equiv. of
the appropriate thiol was added and the solution maintained
for 1 h. One equivalent of the corresponding allylic bromide
was then added and the solution warmed to room tempera-
ture. After an additional 1 h, the solution was concentrated

K. L. Greenman et al. / Tetrahedron 57 &2001) 5219±5225
5223
calcd for C16H26OSSi [M]1 294.1474, found 294.1472.
Anal. Calcd for C16H26OSSi: C, 65.25; H, 8.90. Found: C,
65.25, H, 8.93.
HRMS *CI/NH3) calcd for C16H26SSi [M1H]1 279.1603,
found 279.1599. Anal. Calcd for C16H26SSi: C, 69.00; H,
9.41. Found: C, 68.88, H, 9.41.
4.1.4. ꢀ2,2-Dimethyl-1-phenylsulfanylbut-3-enyl)trimethyl-
silane ꢀ2b). Following the above procedure, puri®cation by
preparative thin layer chromatography *hexanes) afforded
the previously reported17 2b as a clear, colorless oil
4.1.8. ꢀ1-Benzylsulfanyl-3-methylbut-3-enyl)trimethyl-
silane ꢀ4b). Following the above procedure, puri®cation
by preparative thin layer chromatography *hexanes)
afforded 4b as a clear, colorless oil *155 mg, 60%):
Rfˆ0.25 *hexanes); IR*neat) 3072, 3028, 2955, 1648,
1
*179 mg, 84%): Rfˆ0.57 *pentane); H NMR *500 MHz,
1
CDCl3) d 7.38±7.36 *m, 2H), 7.26±7.23 *m, 2H), 7.14±
7.13 *m, 1H), 5.94 *dd, Jˆ17.4, 10.7 Hz, 1H), 5.00 *dd,
Jˆ17.4, 1.2 Hz, 1H), 4.93 *dd, Jˆ10.7, 1.2 Hz, 1H), 2.46
*s, 1H), 1.15 *s, 3H), 1.12 *s, 3H), 0.19 *s, 9H); 13C NMR
*125 MHz, CDCl3) d 147.8, 140.6, 128.7, 128.6, 125.3,
111.0, 47.9, 42.7, 28.5, 26.5, 1.2.
1248 cm21; H NMR *500 MHz, CDCl3) d 7.33±7.28 *m,
4H), 7.24±7.21 *m, 1H), 4.86 *d, Jˆ1.0 Hz, 1H), 4.83 *d,
Jˆ1.0 Hz, 1H), 3.77 *d, Jˆ13.0 Hz, 1H), 3.75 *d,
Jˆ13.0 Hz, 1H), 2.41 *dd, Jˆ14.3, 5.8 Hz, 1H), 2.32 *dd,
Jˆ14.3, 9.0 Hz, 1H), 1.93 *dd, Jˆ9.0, 5.8 Hz, 1H), 1.70 *s,
3H), 0.04 *s, 9H); 13C NMR *125 MHz, CDCl3) d 144.7,
138.7, 129.3, 128.4, 126.9, 112.6, 41.1, 37.48, 28.1, 22.3,
22.3; LRMS *EI) m/z 264 *4), 209 *8), 181 *14), 173 *66),
99 *40), 91 *74) 73 *100); HRMS *EI) calcd for C15H24SSi
[M]1 264.1368, found 264.1363. Anal. Calcd for
C15H24SSi: C, 68.12; H, 9.15. Found: C, 67.72, H, 9.05.
4.1.5. [1-ꢀ4-Chlorophenylsulfanyl)-2,2-dimethylbut-3-
enyl]trimethylsilane ꢀ2c). Following the above procedure,
puri®cation by preparative thin layer chromatography
*hexanes) afforded 2c as a clear, colorless oil *222 mg,
75%): Rfˆ0.56 *hexanes); IR*neat) 3082, 2965, 2897,
1
1636, 1475, 1250 cm21; H NMR *500 MHz, CDCl3) d
4.1.9. ꢀ1-Benzylsulfanyl-2,6-dimethyl-2-vinylhept-5-enyl)-
trimethylsilane ꢀ5b). Following the above procedure, puri-
®cation by preparative thin layer chromatography *hexanes)
afforded the clear, colorless oil 5b as an inseparable mixture
of diastereomers *112 mg, 65%): Rfˆ0.25 *hexanes);
7.29 *d, Jˆ8.6 Hz, 2H), 7.21 *d, Jˆ8.6 Hz, 2H), 5.89 *dd,
Jˆ17.4, 10.7 Hz, 1H), 4.98 *d, Jˆ17.4 Hz, 1H), 4.92 *d,
Jˆ10.7 Hz, 1H), 2.37 *s, 1H), 1.13 *s, 3H), 1.10 *s, 3H),
0.17 *s, 9H); 13C NMR *125 MHz, CDCl3) d 147.8, 139.5,
131.3, 130.3, 128.9, 111.3, 48.5, 42.5, 28.2, 26.3, 0.9;
LRMS *EI) m/z 298 *16), 229 *40), 216 *60), 201 *86),
165 *60), 73 *100); HRMS *EI) calcd for C15H23ClSSi
[M]1 298.0978, found 298.0974. Anal. Calcd for
C15H23ClSSi: C, 60.27; H, 7.75. Found: C, 60.37, H, 7.73.
IR*neat) 3082, 3062, 3028, 2967, 1634, 1494, 1248 cm21
;
1H NMR indicated a 5:1 mixture of diastereomers; 1H NMR,
major diastereomer *500 MHz, CDCl3) d 7.31±7.20 *m,
5H), 5.85 *dd, Jˆ17.5, 11.0 Hz, 1H), 5.08±5.04 *m, 2H),
4.97 *d, Jˆ17.5 Hz, 1H), 3.77 *d, Jˆ12.3 Hz, 1H), 3.66 *d,
Jˆ12.3 Hz, 1H), 1.88±1.85 *m, 2H), 1.74 *s, 1H), 1.71 *s,
3H), 1.60 *s, 3H), 1.50 *m, 2H), 1.30 *s, 3H), 0.03 *s, 9H);
13C NMR, major diastereomer *125 MHz, CDCl3) d 146.0,
138.2, 131.0, 129.3, 128.3, 126.8, 124.8, 112.5, 45.6, 44.2,
41.6, 40.5, 26.1, 23.4, 21.3, 18.1, 1.1; LRMS *EI) m/z 346
*5), 255 *45), 209 *38), 181 *55), 149 *36), 107 *40), 91
*100), 73 *80); HRMS *EI) calcd for C21H34SSi [M]1
346.2151, found 346.2148. Anal. Calcd for C21H34SSi: C,
72.76; H, 9.89. Found: C, 73.04, H, 9.97.
4.1.6. [1-ꢀ4-Methoxybenzylsulfanyl)-2,2-dimethylbut-3-
enyl]trimethylsilane ꢀ2d). Following the above procedure,
puri®cation by preparative thin layer chromatography *99:1
hexanes/ether) afforded 2d as a clear, colorless oil *162 mg,
64%): Rfˆ0.21 *99:1 hexanes/ether); IR*neat) 3080, 2957,
2835, 1634, 1610, 1301 cm21; 1H NMR *500 MHz, CDCl3)
d 7.19 *d, Jˆ8.6 Hz, 2H), 6.83 *d, Jˆ8.6 Hz, 2H), 5.94 *dd,
Jˆ17.5, 10.7 Hz, 1H), 4.97 *d, Jˆ17.5 Hz), 4.93 *d,
Jˆ10.7 Hz, 1H), 3.79 *s, 3H), 3.75 *d, Jˆ12.4 Hz, 1H),
3.62 *d, Jˆ12.4 Hz, 1H), 1.65 *s, 1H), 1.15 *s, 3H), 1.13
*s, 3H), 0.02 *s, 9H); 13C NMR *125 MHz, CDCl3) d 158.7,
148.6, 130.6, 130.5, 113.9, 110.7, 55.4, 44.0, 42.2, 40.9,
27.8, 26.4, 0.7; LRMS *EI) m/z 308 *2), 239 *46), 187
*64), 121 *100), 113 *66), 73 *88); HRMS *EI) calcd
for C17H28OSSi [M]1 308.1630, found 308.1636. Anal.
Calcd for C17H28OSSi: C, 66.18; H, 9.15. Found: C,
66.14, H, 9.17.
4.1.10. ꢀBenzylsulfanylcyclohex-2-enylmethyl)trimethyl-
silane ꢀ6b). Following the above procedure, puri®cation by
preparative thin layer chromatography *hexanes) afforded
the clear colorless oil 6b as an inseparable mixture of
diastereomers *67.7 mg, 24%): Rfˆ0.33 *hexanes); IR*neat)
1
3061, 3025, 2931, 1602, 1248 cm21; H NMR indicated a
1
1:1 mixture of diastereomers; H NMR *400 MHz, CDCl3)
d 7.31±7.23 *m, 10H), 5.80±5.76 *m, 1H), 5.72±5.68 *m,
1H), 5.57 *dd, Jˆ10.4, 2.0 Hz, 1H), 5.46 *dt, Jˆ10.4,
2.0 Hz, 1H), 3.76±3.66 *m, 4H), 2.78±2.50 *m, 2H),
4.1.7. ꢀ1-Benzylsulfanyl-2,2-dimethylbut-3-enyl)trimethyl-
silane ꢀ2e). Following the above procedure, puri®cation by
preparative thin layer chromatography *hexanes) afforded
2e as a clear, colorless oil *244 mg, 80%): Rfˆ0.43
*hexanes); IR*neat) 3083, 3028, 2962, 1635, 1602,
1
2.03±2.00 *m, 4H), 1.86±1.79 *m, H and d, Jˆ2.8 Hz,
2H), 1.74 *d, Jˆ3.2 Hz, 2H), 1.62±1.51 *m, 5H), 0.01 *s,
18H); 13C NMR *100 MHz, CDCl3) d 138.8, 138.6, 132.4,
131.6, 129.5, 128.4, 128.2, 126.9, 39.2, 39.1, 38.7, 38.6,
29.1, 27.8, 25.4, 25.0, 22.9, 22.7; LRMS *EI) m/z 209
*60), 199 *65), 181 *60), 91 *100), 73 *90); HRMS *EI)
calcd for C17H26SSi [M1H]1 291.1603, found 291.1610.
Anal. Calcd for C17H26SSi: C, 70.28; H, 9.02. Found: C,
70.51, H, 9.04.
1
1248 cm21; H NMR *500 MHz, CDCl3) d 7.35±7.25 *m,
5H), 5.94 *dd, Jˆ17.5, 10.7 Hz, 1H), 5.00 *dd, Jˆ17.6,
1.2 Hz, 1H), 4.96 *dd, Jˆ10.7, 1.2 Hz, 1H), 3.78 *d,
Jˆ12.0 Hz, 1H), 3.65 *d, Jˆ12.0 Hz, 1H), 1.66 *s, 1H),
1.15 *s, 3H), 1.13 *s, 3H), 0.00 *s, 9H); 13C NMR
*125 MHz, CDCl3) d 148.6, 138.5, 129.5, 128.5, 127.0,
110.8, 44.0, 42.2, 41.5, 27.8, 26.4, 0.7; LRMS *CI/NH3)
m/z 296 *2), 279 *100), 226 *37), 209 *90), 90 *32);
4.1.11. ꢀ2-Phenyl-1-phenylsulfanylbut-3-enyl)trimethyl-
silane ꢀ7b). Following the above procedure, puri®cation

5224
K. L. Greenman et al. / Tetrahedron 57 &2001) 5219±5225
by preparative thin layer chromatography *hexanes)
afforded previously reported17 clear, colorless oil 7b as an
inseparable mixture of diastereomers *371 mg, 54%):
Acknowledgements
We thank the National Science Foundation and Eli Lilly for
generous support of this work. D. L. V. V. is a Research
Fellow of the Alfred P. Sloan Foundation.
1
Rfˆ0.24 *hexanes); H NMR indicated a 3:1 mixture of
1
diastereomers; H NMR, major diastereomer *500 MHz,
CDCl3) d 7.27±7.24 *m, 2H), 7.21±7.17 *m, 2H),
7.14±7.09 *m, 1H), 7.09±7.05 *m, 2H), 7.04±7.00
*m, 1H), 6.98±6.96 *m, 2H), 6.31 *ddd, Jˆ17.0, 10.2,
9.1 Hz, 1H), 5.15±5.09 *m, 2H), 3.79 *dd, Jˆ9.1, 5.1 Hz,
1H), 2.74 *d, Jˆ5.1 Hz, 1H), 0.07 *s, 9H); 13C NMR,
major diastereomer *125 MHz, CDCl3) d 144.0, 139.8,
138.8, 129.4, 128.3, 128.2, 128.1, 126.5, 125.4, 116.3,
51.6, 43.2, 21.6.
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