Stereo- and Regioselectivity of Reactions of Siliranes with Aldehydes and Related Substrates

Article abstract of DOI:10.1021/jo970263k

Siliranes undergo stereoselective and regioselective insertions of benzaldehyde to provide oxasilacyclopentane products. The thermal reaction (>100°C) leads to more decomposition and side products, whereas the catalyzed variant (t-BuOK, <25°C) proceeds more cleanly with a high degree of inversion (>95%). Treatment of siliranes with enolizable aldehydes leads to silyl enol ethers. The reaction of a silirane at high temperatures with an imine leads to reductive dimerization, presumably by way of intermediate-free silylene. The mechanism for the catalyzed insertion of benzaldehyde is discussed.

Full text of DOI:10.1021/jo970263k

J . Org. Chem. 1997, 62, 4737-4745
4737
Ster eo- a n d Regioselectivity of Rea ction s of Silir a n es w ith
Ald eh yd es a n d Rela ted Su bstr a tes
Paul M. Bodnar, Wylie S. Palmer, Brian H. Ridgway, J ared T. Shaw,
J acqueline H. Smitrovich, and K. A. Woerpel*
Department of Chemistry, University of California, Irvine, California 92697-2025
Received February 12, 1997X
Siliranes undergo stereoselective and regioselective insertions of benzaldehyde to provide oxasi-
lacyclopentane products. The thermal reaction (>100 °C) leads to more decomposition and side
products, whereas the catalyzed variant (t-BuOK, <25 °C) proceeds more cleanly with a high degree
of inversion (>95%). Treatment of siliranes with enolizable aldehydes leads to silyl enol ethers.
The reaction of a silirane at high temperatures with an imine leads to reductive dimerization,
presumably by way of intermediate-free silylene. The mechanism for the catalyzed insertion of
benzaldehyde is discussed.
In tr od u ction
issues such as stereo- and regiochemistry of their ring-
opening reactions.
Organic chemists have long recognized that the strain
energy released upon cleavage of three-membered rings
can be harnessed to achieve many otherwise unattainable
goals.1 For example, cyclopropanes have seen numerous
We initiated our studies of silirane chemistry to
discover new reactions of these compounds and to evalu-
ate the stereo- and regiochemistry of their ring-opening
reactions. Our early experiments were motivated by a
report by Seyferth, who demonstrated that silirane 1
2
applications in synthesis, as have their counterparts the
3
4
oxiranes and aziridines. In contrast, siliranes have not
been recognized as useful reactive intermediates in
organic synthesis. This situation is paradoxical, since
the unique reactivity of silicon compounds has had a
tremendous impact on organic chemistry.5 Although
seminal contributions to silirane chemistry have been
undergoes insertion of aldehydes to afford oxasilacyclo-
pentanes 2 (eq 1).1
0,18
Boudjouk and Chrusciel’s efficient
reported by Seyferth,6 Ando, and others,
-11
12
13-16
the use
1
7
of these highly strained compounds poses particular
problems because of the difficulty in their synthesis, their
high air sensitivity, and the lack of information regarding
synthesis of siliranes 3 from di-tert-butyldichlorosilane
19
and alkenes permits the synthesis of various substi-
tuted siliranes that can be used to elucidate the stereo-
and regiochemistry of ring-opening reactions. We re-
cently reported the dichotomous stereochemical courses
of the thermal and catalyzed carbon-carbon bond-
X
Abstract published in Advance ACS Abstracts, J une 15, 1997.
(1) Hoz has argued that orbital effects and ground state destabiliza-
tion contribute to rate accelerations observed in reactions of strained
rings: (a) Sella, A.; Basch, H.; Hoz, S. J . Am. Chem. Soc. 1996, 118,
2
0,21
4
5
16-420. (b) Sella, A.; Basch, H.; Hoz, S. Tetrahedron Lett. 1996, 37,
forming reactions of siliranes 3 with benzaldehyde.
573-5576.
The ability to oxidize carbon-silicon bonds, even those
(2) Wong, H. N. C.; Hon, M.-Y.; Tse, C.-W.; Yip, Y.-C.; Tanko, J .;
of sterically hindered silicon species,22 led to the synthesis
Hudlicky, T. Chem. Rev. 1989, 89, 165-198.
2
0
(3) Padwa, A.; Murphree, S. S. In Progress in Heterocyclic Chemistry;
of 1,3-diols with three contiguous stereocenters. Other
reactions of siliranes have been developed in our labo-
Suschitzky, H., Scriven, E. F. V., Eds.; Pergamon: New York, 1994;
Vol. 6; pp 56-73.
2
3
(4) Tanner, D. Angew. Chem., Int. Ed. Engl. 1994, 33, 599-619.
(5) Langkopf, E.; Schinzer, D. Chem. Rev. 1995, 95, 1375-1408.
(6) Seyferth, D.; Annarelli, D. C.; Vick, S. V.; Duncan, D. P. J .
ratories, such as the thermal insertion of formamides
and palladium-catalyzed alkyne insertion and silylene
24
transfer reactions. Herein, we detail our investigations
Organomet. Chem. 1980, 201, 179-195.
7) Seyferth, D.; Annarelli, D. C.; Shannon, M. L.; Escudie, J .;
Duncan, D. P. J . Organomet. Chem. 1982, 225, 177-191.
8) Seyferth, D.; Annarelli, D. C.; Duncan, D. P. Organometallics
982, 1, 1288-1294.
9) Seyferth, D.; Duncan, D. P.; Shannon, M. L.; Goldman, E. W.
Organometallics 1984, 3, 574-578.
10) Seyferth, D.; Duncan, D. P.; Shannon, M. L. Organometallics
984, 3, 579-583 and references cited therein.
11) Seyferth, D.; Vick, S. C.; Shannon, M. L. Organometallics 1984,
(
of the reactions of siliranes with aldehydes and related
observations.
(
1
Resu lts
(
Meth a n olysis. The first issue that needed to be
addressed was the stereochemistry of silirane ring-
(
1
(
3
, 1897-1905.
(18) Bobbitt, K. L.; Gaspar, P. P. J . Organomet. Chem. 1995, 499,
17-26.
(19) Boudjouk, P.; Samaraweera, U.; Sooriyakumaran, R.; Chrusciel,
J .; Anderson, K. R. Angew. Chem., Int. Ed. Engl. 1988, 27, 1355-1356.
(20) Bodnar, P. M.; Palmer, W. S.; Shaw, J . T.; Smitrovich, J . H.;
Sonnenberg, J . D.; Presley, A. L.; Woerpel, K. A. J . Am. Chem. Soc.
1995, 117, 10575-10576.
(21) Fleming has provided insightful analysis of our data: Fleming,
I. Chemtracts-Org. Chem. 1996, 9, 121-125.
(22) Smitrovich, J . H.; Woerpel, K. A. J . Org. Chem. 1996, 61, 6044-
6046.
(23) Shaw, J . T.; Woerpel, K. A. J . Org. Chem. 1997, 62, 442-443.
(24) Palmer, W. S.; Woerpel, K. A. Organometallics 1997, 16, 1097-
1099.
(
12) Saso, H.; Ando, W.; Ueno, K. Tetrahedron 1989, 45, 1929-1940.
(13) Boudjouk, P.; Black, E.; Kumarathasan, R.; Samaraweera, U.;
Castellino, S.; Oliver, J . P.; Kampf, J . W. Organometallics 1994, 13,
715-3727.
14) Pae, D. H.; Xiao, M.; Chiang, M. Y.; Gaspar, P. P. J . Am. Chem.
Soc. 1991, 113, 1281-1288.
15) Zhang, S.; Conlin, R. T. J . Am. Chem. Soc. 1991, 113, 4272-
278.
16) Kroke, E.; Willms, S.; Weidenbruch, M.; Saak, W.; Pohl, S.;
Marsmann, H. Tetrahedron Lett. 1996, 37, 3675-3678.
17) The ring strain of the parent silirane has been calculated to be
3
(
(
4
(
(
4
1
4 kcal/mol: Gordon, M. S.; Nelson, W. Organometallics 1995, 14,
067-1069.
S0022-3263(97)00263-6 CCC: $14.00 © 1997 American Chemical Society

4
738 J . Org. Chem., Vol. 62, No. 14, 1997
Bodnar et al.
Ta ble 1. Ster eoselectivity of In ser tion of P h CHO in to
Silir a n es (eq 5)
yield
silirane
conditions
10a 10b 10c 10d (%)
trans-3 100 °C
75
48
3
7
6
1
8
32
13
10
14
83
50
26
54
73
opening reactions. The stereochemical course of silirane
protonolysis7 has not been determined, although the
cis-3
trans-3 25% KO-t-Bu/18-crown-6
cis-3
100 °C
,25
methanolysis of silirenes proceeds with retention of
10% KO-t-Bu/18-crown-6 69
30 <1 <1
alkene configuration.2
6,27
J ones demonstrated that the
addition of MeOD to adducts of trans-2-butene or cyclo-
hexene and photochemically generated dimethylsilylene
gave stereospecific incorporation of a deuterium atom;28
however, no direct evidence was given for the presence
of silirane intermediates.
signment of relative stereochemistry, these experiments
do provide valuable data: they support J ones’ argument
that siliranes are reactive intermediates in photolytic
experiments28 and that silirane ring-opening reactions
are stereospecific.
Deuterium-labeling experiments demonstrate that pro-
tonolysis of the Si-C bond of siliranes is a stereospecific
process. Treatment of trans-3 with MeOD in the pres-
ence of fluoride ions25 provided silane 4 with the deute-
rium in only one of the diastereotopic positions of the
methylene unit (eq 2), while deuteriomethanolysis of cis-3
The regioselectivity of methanolysis of unsymmetrical
siliranes was found to depend upon the conditions
employed (eq 4). The butylsilirane 7, prepared from di-
tert-butyldichlorosilane and 1-hexene in 85% yield, un-
derwent fluoride-catalyzed methanolysis to cleave the
less substituted C-Si bond. The regioselectivity was
placed the deuterium atom at the other position as
1
2
28,29
determined by H and H NMR spectroscopy.
Fur-
reversed upon thermal methanolysis, which occurred
preferentially at the more substituted carbon (eq 4).
Fluoride-catalyzed ring cleavage does not always occur
at the primary position: when benzaldehyde was em-
ployed as the electrophile, the ring opening occurred at
the more substituted carbon (vide infra). Regioselective
cleavage at the more hindered position by formamides
has been explained by consideration of postulated pen-
tacoordinate intermediates.23
thermore, ring opening of the bicyclic silirane 5 with
MeOD incorporated a deuterium atom into a single
1
2
position of 6, according to H and H NMR spectroscopy
eq 3). J ones assigned cis stereochemistry to the dimeth-
(
Ald eh yd e In ser tion . Since the insertion of methanol
was found to proceed stereoselectively and regioselec-
tively, the next step was to evaluate the formation of
carbon-carbon bonds. Considering the methanolysis
experiments, thermal aldehyde insertion was anticipated
to proceed with some memory of the stereochemistry of
the starting silirane. In fact, the reaction of trans-3 with
benzaldehyde at 100 °C occurred predominately with
retention of configuration, affording a mixture of oxasi-
lacyclopentanes 10a -d with the major product 10a
possessing the anti-anti stereochemistry (eq 5, Table 1).
yl analogue of 6 on the basis of the chemical shift of the
deuterium atom;28 a similar chemical shift was observed
for the deuterium atom of 6, suggesting that the stere-
1
ochemistry of 6 is cis. The similarities between the H
2
and H NMR spectral data of J ones’ dimethyl com-
pounds28 and the tert-butyl analogues described here
suggest similar stereochemical outcomes.
The relative stereochemistry of the deuterated silanes
4
and 6 could not be determined unambiguously. The
strategy for proof of relative stereochemistry rested on
the oxidation of these silanes to the deuterated alcohols.30
Extensive attempts failed to oxidize these silanes, even
2
2
under our modified conditions. Either starting materi-
als were recovered or no products with the 2-butyl or
cyclohexyl group were obtained. The volatility of the
desired products could complicate isolation if only small
amounts were formed. Even without unambiguous as-
(
25) Kumarathasan, R.; Boudjouk, P. Tetrahedron Lett. 1990, 31,
987-3990.
26) Conlin, R. T.; Gaspar, P. P. J . Am. Chem. Soc. 1976, 98, 3715-
716.
27) Ring opening of postulated silacyclopropene intermediates by
3
3
(
(
MeOH, MeCHO, and acetone has been reported: Lee, S. T.; Baek, E.
In contrast, insertion into cis-319 proceeded (albeit in low
K.; Shim, S. C. Organometallics 1996, 15, 2182-2184.
yield) with loss of stereochemistry, not with retention.
Because the reactions of cis- and trans-3 with benzalde-
hyde do not give the same distribution of products, the
reactions do not involve precisely the same reactive
intermediates. If these transformations proceed via
(28) Tortorelli, V. J .; J ones, M., J r.; Wu, S.-h.; Li, Z.-h. Organome-
tallics 1983, 2, 759-764.
29) Thermal deuteriomethanolysis proceeded with the same ster-
eochemical outcome, albeit with extensive decomposition.
30) For example, the 3-deuterio-2-butanols are known: Kabalka,
G. W.; Bowman, N. S. J . Org. Chem. 1973, 38, 1607-1608.
(
(

Stereo- and Regioselectivity of Reactions of Siliranes
diradical intermediates as was originally proposed for
hexamethylsilirane (1) (eq 1), the diradical must cyclize
more rapidly than bond rotation or inversion of stereo-
chemistry occurs.
J . Org. Chem., Vol. 62, No. 14, 1997 4739
1
0
The regiochemistry of the thermal insertion reaction
was probed using unsymmetrical silirane 7 (eq 6). The
catalyzed methanolysis, which cleaved the less substi-
tuted bond. This difference is not due to the use of
fluoride: insertion catalyzed by fluoride ion occurred with
similar regioselectivity and stereoselectivity, albeit in low
yield.
insertion occurred with poor regioselectively (71:29) and
yield (14%) and was attended with extensive decomposi-
tion. Three side products, the alkoxysilanes 12a -c, were
also obtained in these reactions (8%, 3%, and 1%,
respectively). The proposed mechanism for their forma-
tion involves coordination of the aldehyde to the silirane
followed by hydrogen-atom transfer from a carbon that
is â to the silicon atom. Related hydrogen-atom transfer
reactions to ketones were observed by Seyferth upon
irradiation of hexamethylsilirane (1) in the presence of
cyclohexanone.10
Ster eoch em istr y a n d Oxid a tion of Sila n es. Criti-
cal to the results presented above are the stereochemical
assignments of the oxasilacyclopentane products. Defini-
tive proof for the structure of oxasilacyclopentane 10d
was obtained by X-ray crystallography.20 Since C-Si
bonds can be oxidized to C-O bonds with retention of
configuration,3
3-35
oxidation of the oxasilacyclopentanes
10a -c provided 1,3-diols, whose stereochemistry could
be proven unambiguously. Exposure of oxasilacyclopen-
3
3
tane 10d to previously reported oxidation conditions
34
resulted in recovered starting material.
recently reported conditions (t-BuOOH, CsOH‚H
in DMF at 75 °C),22 however, the corresponding 1,3-diol
4d was obtained as a single isomer in 64% yield (eq 8).
Under our
2
O, TBAF
1
The fact that the reaction proceeded with retention of
configuration was confirmed by conversion of 14d to the
p-nitrobenzylidene acetal 15 and analysis by X-ray
Since siliranes are thermally sensitive,19 it is not
surprising that the elevated temperatures required for
aldehyde insertion produce significant amounts of de-
composition materials as well. For this reason, a catalyst
would be desirable to effect this transformation. On the
basis of observations of aldehyde insertions into silacy-
clobutanes,31 nucleophilic catalysts were investigated.
When a catalyst such as t-BuOK/18-crown-6 (10-25 mol
20
crystallography.
%
) was added to a solution of trans-3 and benzaldehyde
3
1
in THF at 22 °C, insertion ensued with >95% inversion
of stereochemistry (54% yield, eq 5, Table 1). Under
similar conditions, cis-3 also underwent nearly complete
inversion (73% yield), affording the anti-anti isomer 10a
as the dominant product. The preponderance of inversion
of stereochemistry contrasts with the stereochemical
outcome of the thermal reactions.32
A wide variety of nucleophilic catalysts effect the
insertion of benzaldehyde, including halide, azide, and
3
aryloxide ions as well as DMF, HMPA, PPh , and DMAP.
In all cases, the stereochemical outcome was similar to
that observed for t-BuOK (within 5-10% for each iso-
mer), but the yields were dramatically inferior (<20%).
The necessity of a strong base seriously limits the
generality of the insertion reaction, rendering only non-
enolizable aldehydes as suitable substrates (vide infra).
The milder conditions for the catalyzed insertion
proved amenable to the insertion of benzaldehyde into
the unsymmetrical silirane 7 (eq 7). The catalyzed
insertion of benzaldehyde proceeded with high regiose-
lection (85:15) for cleavage of the ring at the more
sterically hindered center, providing oxasilacyclopentanes
The stereochemical proof of the remaining oxasilacy-
clopentanes 10a -c was accomplished by oxidation to the
corresponding diols 14a -c. For each isomeric diol, the
relative stereochemistry between the hydroxyl groups
was confirmed by analysis of the derived acetonides by
13
36,37
C NMR spectroscopy.
Two-dimensional hetero-
nuclear correlation experiments were necessary to assign
the resonances of the acetonide methyl groups. To
determine the configuration of the remaining stereo-
center, reference materials were prepared by stereose-
38
39
lective aldol reactions (both syn and anti ) between
propiophenone and acetaldehyde (Scheme 1). As in other
aldol reactions,40 acetaldehyde showed diminished ste-
reoselectivity compared to other aldehydes. The aldol
adducts were then reduced stereoselectively by methods
that are known to proceed with the illustrated stereo-
chemical course.4
1-43
(
33) Tamao, K.; Ishida, N.; Tanaka, T.; Kumada, M. Organometallics
983, 2, 1694-1696.
34) J ones, G. R.; Landais, Y. Tetrahedron 1996, 52, 7599-7662.
(35) Fleming, I. Chemtracts-Org. Chem. 1996, 9, 1-64.
36) Rychnovsky, S. D.; Rogers, B.; Yang, G. J . Org. Chem. 1993,
8, 3511-3515.
37) Evans, D. A.; Rieger, D. L.; Gage, J . R. Tetrahedron Lett. 1990,
1
(
1
3 as a mixture of diastereomers. The regioselection of
(
this insertion is opposite to the outcome of fluoride-
5
(
(
31) These conditions were inspired by insertions of aldehydes into
31, 7099-7100.
silacyclobutanes: Takeyama, Y.; Oshima, K.; Utimoto, K. Tetrahedron
Lett. 1990, 31, 6059-6062.
(38) Hamana, H.; Sasakura, K.; Sugasawa, T. Chem. Lett. 1984,
1729-1732.
(32) Control experiments indicate that the products are formed
(39) Brown, H.; Dhar, R.; Bakshi, R.; Pandiarajan, P.; Singaram,
B. J . Am. Chem. Soc. 1989, 111, 3441-3442.
(40) Raimundo, B. C.; Heathcock, C. H. Synlett 1995, 1213.
kinetically and that no isomerization of the silirane occurred during
either the thermal or catalyzed insertions.

4
740 J . Org. Chem., Vol. 62, No. 14, 1997
Bodnar et al.
Sch em e 1a
a
C6H11)2BCl, Et3N, 81% ds. b PhBCl2, EtN(i-Pr)2, 94% ds. c TBSCl; LiAlH4, 70% ds (14b), 80% ds (14c). d Me4N(AcO)3BH, >95% ds.
(
e
EtB(OMe)2, NaBH4, >95% ds.
The structures of the products obtained from the
reactions of unsymmetrical silirane 7 were determined
using a similar strategy. The regioselectivity of aldehyde
insertion was evident by 1H NMR spectroscopy. The
stereochemistry was determined (and the regioselectivity
confirmed) by oxidation of the diastereomeric oxasilacy-
clopentanes 13 to the diols 17 and by comparison to
reference compounds (eqs 9 and 10). The latter were
prepared by reduction of the esters 18 and 19, obtained
by stereoselective syn44 and anti ester enolate aldol
reactions.
2
0 (62:14:14:10 for R ) OMe, 61:14:14:11 for R ) CF
3
4
)
6
are similar to those obtained for benzaldehyde (Table 1).
45
Competition experiments between the different alde-
hydes establish a reactivity order of p-CF CHO >
CHO > p-CH OC CHO.
3
6 4
C H
C
6
H
5
3
6 4
H
The catalyzed reactions of substituted benzaldehydes
proceed in significantly higher yield than the thermal
reactions, and no hydride-transfer side products were
obtained. The stereochemistries of the major products
(
20d ) were proven unambiguously by methods analogous
4
7
to those for 10d . As was observed for benzaldehyde,
the catalyzed processes occurred with predominately
inversion of stereochemistry. As was observed for the
Oth er Ar yl Ald eh yd es: Electr on ic Effects u p on
In ser tion . If the assumption is made that the insertion
reactions involve the silirane as nucleophile and aldehyde
as electrophile, it is logical that electron-poor aldehydes
should be better substrates for insertion than electron-
rich ones. This straightforward analysis does not apply
to other carbonyl compounds, however: formamides,
notoriously poor electrophiles, undergo thermal insertion
reactions whereas alkyl aldehydes do not.23 To provide
insight into the relationship between the aldehyde and
formamide insertions, we examined the reactions of
substituted aryl aldehydes with silirane trans-3 under
the thermal and catalyzed reaction conditions.
thermal insertions, the order of reactivity was p-CF
3 6
C -
H
4
CHO > C CHO > p-CH OC CHO (eq 12). There-
6
H
5
3
6 4
H
fore, for both the thermal and catalyzed insertions, more
electrophilic aldehydes undergo insertions faster.
Heating trans-3 with p-anisaldehyde or p-(trifluoro-
methyl)benzaldehyde at 110 °C afforded mixtures of
insertion products 20 along with hydride transfer prod-
ucts 21 and 22, favoring insertion over hydride transfer
by a ratio of 65:35 by GC/MS in both cases (eq 11). The
stereoselectivities observed for the oxasilacyclopentanes
E n oliza b le Ald eh yd es a n d Ket on es. Because
strongly basic catalysts proved optimal for the insertion
of benzaldehyde, it was expected that problems would
be encountered upon attempted insertion of enolizable
substrates. In accord with this prediction, treatment of
silirane trans-3 with crotonaldehyde and catalytic amounts
of alkoxide (eq 13) provided the unstable dienol ether 23
(
41) TBSCl/LiAlH
Lett. 1988, 29, 1021-1024.
42) Me N(AcO) BH: Evans, D. A.; Chapman, K. T.; Carreira, E.
M. J . Am. Chem. Soc. 1988, 110, 3560-3578.
43) EtB(OMe) /NaBH : Chen, K.; Goetz, E. H.; Prasad, K.; Repic,
O.; Shapiro, M. J . Tetrahedron Lett. 1987, 28, 155-158.
44) Evans, D. A.; McGee, L. R. Tetrahedron Lett. 1980, 21, 3975-
978.
45) Heathcock, C. H.; Pirrung, M. C.; Montgomery, S. H.; Lampe,
J . Tetrahedron 1981, 37, 4087-4095.
4
: Bloch, R.; Gilbert, L.; Girard, C. Tetrahedron
1
in 37% yield as a single alkene isomer (by H NMR
(
4
3
(
2
4
(46) The stereochemistries of the major isomers are assigned on the
basis of the comparable selectivity and the striking similarities of the
1
(
H NMR spectra of the major isomers 20a of the two substituted
3
systems compared to that of 10a . Because the reactions were low-
yielding, no further attempts were made to prove the stereochemistry.
(47) The details are provided as Supporting Information.
(

Stereo- and Regioselectivity of Reactions of Siliranes
J . Org. Chem., Vol. 62, No. 14, 1997 4741
coupling of aldehydes by an isolable silylene was recently
reported.5
4,55
Discu ssion
Although the mechanism of aldehyde insertion has not
been elucidated in any detail, the stereochemical data
presented here allows a working mechanism to be gener-
ated. The mechanistic picture for the thermal reaction
is more difficult to evaluate because of the lack of
stereochemical fidelity and low yields; the formation of
products may occur by several different mechanisms
operating simultaneously. The catalyzed insertion of
aldehydes is a cleaner reaction and consequently lends
itself more favorably to analysis.21
spectroscopy).10 Similar products were observed with
fluoride and chloride catalysis, although the yields were
lower. Attempts to effect insertion under thermal condi-
tions failed: heating siliranes with enolizable aldehydes
such as crotonaldehyde and isobutyraldehyde led to
decomposition and no insertion. When the catalyzed
insertion was attempted with 3-pentanone (eq 14), the
Because the insertion is catalyzed by Lewis bases, we
favor a mechanism that involves the silirane as a Lewis
acid. Gas phase experiments56 demonstrate that the ring
strain of silacyclobutanes renders the silicon atom elec-
trophilic, because strain is released upon coordination of
a fifth group to silicon.5
6-58
Similar (and possibly en-
silyl enol ether 24 was isolated as the Z stereoisomer
hanced) Lewis acidity would be expected for siliranes
because they are even more strained. We believe that
an interaction occurs between the nucleophilic catalyst
1
(
>95:5 by H NMR spectroscopy). Isomerization occurred
17
in CDCl
3
solution, resulting in a 1:1 mixture of (E)- and
(Z)-alkenes, which allowed the stereochemical assign-
and the silirane as shown in eq 16 to provide pentaco-
ment of the kinetic enol ether 24 from spectroscopic
59
ordinate intermediate 28.
No interaction has been
data.48 This result may be rationalized as attack of the
4
9
thermodynamically preferred (Z)-enolate to the silirane
followed by protonation of the ring, in analogy to the
methanolysis reactions (eq 2).
Rea ction w ith Im in es. Since aldehyde insertion
lacked generality, the insertion of imines was investi-
gated. Reactions of several imines such as PhCHNCH
2
Ph
(
25) with siliranes 3 and various catalysts failed to
observed between the silirane trans-3 and carbonyl
provide any identifiable products. Thermal conditions,
however, led to a new product: heating the silirane
trans-3 and imine 25 to 150 °C (eq 15) afforded the
silylene-protected diamine 26 (28-55% yield) in 90%
diastereoselectivity (as determined by H NMR spectro-
scopy). The stereochemistry of this product was tenta-
60
1
13
compounds such as crotonaldehyde and DMF by H, C,
29
and Si NMR spectroscopy from -80 to 25 °C. Because
of the severe steric constraints imposed by the two tert-
butyl groups and the incoming tert-butoxide catalyst,
formation of the pentacoordinate siliconate 28 is more
likely than that of a hexacoordinate siliconate.
1
The next step in the mechanism is the formation of a
new carbon-carbon bond, setting two stereogenic centers
in the process. The nucleophilicity of the carbon atoms
of the ring is enhanced in the ate complex 28 compared
to the neutral silirane,59 so this intermediate is the one
that would attack the electrophilic carbonyl group of the
aldehyde. Competition experiments demonstrated that
electron-deficient aldehydes react faster than electron-
rich ones, suggesting that the silirane behaves as a
nucleophile in (or before) the rate-determining step. The
insertion could proceed by prior coordination of the
aldehyde or direct nucleophilic attack on free aldehyde.
The prior-coordination manifold would require a six-
coordinate intermediate such as 29, which would suffer
tively assigned as trans because 1H and 13C NMR
spectroscopy indicated that the two tert-butyl groups
were equivalent. To confirm this stereochemical assign-
ment, the silyl group was removed with HF to afford the
known 1,2-diamine 27.5
0-52
The mechanism for the
formation of this product most likely involves the libera-
8
,19
tion of di-tert-butylsilylene
followed by reductive cou-
from significant steric destabilization. Alternatively,
pling of the imines.53 A similar stereoselective reductive
61
E
back-side S 2 attack upon free aldehyde (as shown for
(
48) Heathcock, C. H.; Buse, C. T.; Kleschick, W. A.; Pirrung, M.
C.; Sohn, J . E.; Lampe, J . J . Org. Chem. 1980, 45, 1066-1081.
49) Fataftah, Z.; Kopka, I. E.; Rathke, M. W. J . Am. Chem. Soc.
980, 102, 3959-3960.
50) Mangeney, P.; Tejero, T.; Alexakis, A.; Grosjean, F.; Normant,
J . Synthesis 1988, 255-257.
51) Enholm, E. J .; Forbes, D. C.; Holub, D. P. Synth. Commun.
990, 20, 981-987.
52) Further confirmation of the stereochemistry of 27 was obtained
(54) J utzi, P.; Eikenberg, D.; Bunte, E.-A.; M o¨ hrke, A.; Neumann,
B.; Stammler, H.-G. Organometallics 1996, 15, 1930-1934.
(55) Belzner, J .; Ihmels, H.; Pauletto, L.; Noltemeyer, M. J . Org.
Chem. 1996, 61, 3315-3319.
(
1
(
(56) Sullivan, S. A.; DePuy, C. H.; Damrauer, R. J . Am. Chem. Soc.
1981, 103, 480-481.
(
(57) Myers, A. G.; Kephart, S. E.; Chen, H. J . Am. Chem. Soc. 1992,
114, 7922-7923.
1
(
(58) Denmark, S. E.; Griedel, B. D.; Coe, D. M. J . Org. Chem. 1993,
58, 988-990.
by reductive amination of the corresponding primary diamine with
benzaldehyde.
(59) For a review covering penta- and hexacoordinate silicon com-
pounds, see: Chuit, C.; Corriu, R. J . P.; Reye, C.; Young, J . C. Chem.
Rev. 1993, 93, 1371-1448.
(
53) For reactions of silylenes with imines, see: (a) Weidenbruch,
M.; Piel, H.; Peters, K.; von Schnering, H. G. Organometallics 1993,
2, 2881-2882. (b) Belzner, J .; Ihmels, H.; Pauletto, L.; Noltemeyer,
M. J . Org. Chem. 1996, 61, 3315-3319.
1
(60) Childs, R. F.; Mulholland, D. L.; Nixon, A. Can. J . Chem. 1982,
60, 801-808.

4
742 J . Org. Chem., Vol. 62, No. 14, 1997
Bodnar et al.
except that MeOD was employed in place of MeOH:25 1H NMR
(
7
7
500 MHz, CDCl
3
) δ 3.58 (s, 3H), 1.20 (m, 1H), 1.13 (d, J )
.0, 3H), 1.05 (s, 9H), 1.04 (s, 9H), 1.02 (m, 1H), 0.97 (d, J )
2
13
.2, 3H); H NMR (77 MHz, CHCl
3
1
) δ 1.83; C NMR (125 MHz,
CDCl
1
2
3
) δ 52.2, 29.1, 29.0, 25.1 (t, J CD ) 19.4), 22.2, 22.0, 20.4,
+
4.6, 14.0; HRMS (CI) m/ z calcd for C13
32.2208, found 232.2207.
3-Deu ter io-sec-bu tyl)d i-ter t-bu tylm eth oxysila n e (4′).
H30DOSi (M + H)
(
Boudjouk’s procedure was employed, starting with cis-3, except
3
0, eq 17) with inversion of configuration at the migrating
that MeOD was employed in place of MeOH:25 H NMR (300
1
carbon (C-1) would explain the observed stereochemistry
at this stereocenter. The oxygen-bearing stereocenter,
although set with only modest selectivity (2-6:1), is
controlled by the distal stereocenter (C-2), not the
proximal one (C-1, eq 17). The major products obtained
MHz, CDCl
3
) δ 3.58 (s, 3H), 1.80 (m, 1H), 1.13 (d, J ) 6.9,
3
3
H), 1.05 (s, 9H), 1.04 (s, 9H), 1.02 (m, 1H), 0.97 (d, J ) 7.3,
2
1
3
H); H NMR (77 MHz, CHCl
3
) δ 1.17; C NMR (125 MHz,
1
CDCl
14.5, 14.0.
3
) δ 52.2, 29.1, 29.0, 25.0 (t, J CD ) 19.7), 22.2, 22.0, 20.4,
(
2-Deu ter iocycloh exyl)d i-ter t-bu tylm eth oxysila n e (6).
Boudjouk’s procedure was employed, starting with 5, except
that MeOD was employed in place of MeOH:25 H NMR (500
1
MHz, CDCl
m, 1H), 1.18 (m, 4H), 1.05 (s, 18H); H NMR (77 MHz, CHCl
δ 1.42.
,1-Di-ter t-bu tyl-2-(1-bu tyl)silir a n e (7). To a cooled (-78
C) slurry of lithium powder (obtained by washing a 30%
lithium dispersion with 3 × 10 mL of hexanes to give 0.77 g,
11 mmol) in 10 mL of THF were added 1-hexene (10.0 mL,
3
) δ 3.59 (s, 3H), 1.90 (m, 2H), 1.74 (m, 3H), 1.42
2
(
3
)
1
°
1
from both cis- and trans-3 bear a 1,3-syn relationship
175 mmol) and di-tert-butyldichlorosilane (3.8 mL, 18 mmol).
The reaction mixture was stirred at 25 °C for 12 h. The
supernatant was decanted, and the residual solids were
washed with 2 × 10 mL of hexanes. The combined solutions
were concentrated in vacuo to give an impure oil. Purification
by bulb-to-bulb distillation afforded the product as a clear
liquid (3.47 g, 86%): bp 72-73 °C (0.05 Torr); IR (thin film)
(Table 1), indicating that the staggered transition states
leading to the major products minimize interaction
between the aryl moiety and the methyl group on C-2,
as shown for 30.2 The final step involves cyclization of
the alkoxide 31, providing the observed product 10d and
regenerating the nucleophilic catalyst, or 31 could itself
act as the catalyst in these reactions. The latter situation
would explain why the stereoselectivity of insertion is
roughly independent of catalyst employed.
1
-
1 1
2958, 1470, 1364 cm ; H NMR (500 MHz, CDCl
3
) δ 1.63 (m,
1H), 1.56 (m, 1H), 1.43 (m, 1H), 1.33 (m, 3H), 1.13 (s, 9H),
1
1
.04 (s, 9H), 0.90 (t, J ) 7.1, 3H), 0.75 (m, 1H), 0.66 (dd, J )
2.1, 10.4, 1H), 0.05 (dd, J ) 10.1, 8.8, 1H); 13C NMR (125
MHz, CDCl
3.9, 3.2; HRMS (CI) m/ z calcd for C14
244.2462, found 244.2458.
3
) δ 34.7, 31.8, 30.7, 29.8, 22.6, 18.9, 18.1, 14.3,
+
+
4
(M + NH )
1
H
30SiNH
4
Con clu sion
Di-ter t-bu tyl(2-h exyl)m eth oxysila n e (8). To a 25 °C
solution of 7 (0.33 g, 1.5 mmol) in 3 mL of THF were added
KF (8 mg, 0.15 mmol) and MeOH (0.30 mL, 7.4 mmol). The
reaction mixture was stirred at 25 °C for 7 h and then
concentrated in vacuo. Purification by flash chromatography
In conclusion, siliranes undergo stereoselective and
regioselective insertions of benzaldehyde to provide ox-
asilacyclopentane products. Whereas the thermal reac-
tion (>100 °C) leads to extensive decomposition and
sideproducts, the catalyzed variant (t-BuOK, <25 °C)
proceeds more cleanly and with a high degree of inver-
sion. Treatment with enolizable aldehydes leads to clean
silyl enol ether formation. The working mechanism for
the catalyzed insertion process entails addition of the
catalyst to form a pentacoordinate siliconate intermediate
followed by back-side electrophilic attack on the C-Si
bond.
25
(
0:100-2:98 EtOAc:hexanes) afforded a clear oil (0.25 g, 65%)
1
as a 93:7 ratio of 8 and 9 (as determined by H NMR
spectroscopy): IR (thin film) 2934, 1470, 1386, 1190, 1105
-
1 1
cm ; H NMR (500 MHz, C
1
3
6
D
6
) δ 3.44 (s, 3H), 1.83 (m, 1H),
.55 (m, 1H), 1.30 (m, 4H), 1.165 (m, 1H), 1.160 (d, J ) 2.6,
13
H), 1.13 (s, 18H), 0.93 (t, J ) 7.3, 3H); C NMR (125 MHz,
CDCl ) δ 52.2, 32.2, 31.6, 29.2, 29.1, 22.8, 22.2, 22.1, 18.2, 15.1,
3
+
14.2; HRMS (CI) m/ z calcd for C15
found 259.2469. Anal. Calcd for C15
3.26. Found: C, 69.43; H, 13.09.
Di-ter t-bu tyl(1-h exyl)m eth oxysilan e (9). Silirane 7 (0.64
H
35OSi (M + H) 259.2458,
H
34OSi: C, 69.69; H,
1
Exp er im en ta l Section
g, 2.8 mmol) and methanol (2.0 mL, 49 mmol) were added to
a clean flame-dried bomb, which was then cooled to -78 °C
and evacuated. The bomb was sealed under vacuum, and the
reaction mixture was heated in a 95 °C oil bath for 32 h. The
mixture was cooled, and 1H NMR spectroscopy of the unpu-
rified mixture indicated an 87:13 ratio of 9:8. Purification by
flash chromatography (hexanes) afforded the product as a clear
Gen er a l. General experimental details are provided as
Supporting Information. Microanalyses were performed by
Atlantic Microlab, Atlanta, GA. Analytical gas-liquid chro-
matography (GLC) was performed on a Hewlett-Packard 5890
Level 4 chromatograph, equipped with a split-mode capillary
injection system and a flame ionization detector. Fused silica
capillary columns (30 × 0.32 mm) wall-coated with DB-1 or
DB-1701 (J &W Scientific) were used with helium as the carrier
gas. All reactions were carried out under an atmosphere of
nitrogen in glassware which had been flame-dried under a
stream of nitrogen. Siliranes were stored and handled in an
Innovative Technologies nitrogen atmosphere drybox. Sol-
vents were dried and distilled prior to use.
-
1
oil (0.22 g, 30%): IR (thin film) 2931, 1470, 1189, 1107 cm
;
1
H NMR (500 MHz, C
m, 6H), 1.10 (s, 18H), 0.92 (t, J ) 6.5, 3H), 0.77 (m, 2H); H
NMR (CDCl , 500 MHz) δ 3.58 (s, 3H), 1.48 (m, 1H), 1.30 (m,
H), 1.00 (m, 6H), 1.00 (s, 18H), 0.89 (t, J ) 6.9, 3H), 0.73 (m,
H); 13C NMR (125 MHz, CDCl
) δ 52.6, 34.1, 31.5, 28.3, 24.5,
2.7, 21.4, 14.1, 10.6; HRMS (CI) m/ z calcd for C15 35OSi (M
H) 259.2458, found 259.2458. Anal. Calcd for C15 34OSi:
C, 69.69; H, 13.26. Found: C, 69.47; H, 13.24.
,4-Dim eth yl-5-p h en yl-2,2-d i-ter t-bu tyl-1-oxa -2-sila cy-
6 6
D ) δ 3.45 (s, 3H), 1.57 (m, 2H), 1.32
1
(
3
1
2
2
3
H
+
+
H
(
3-Deu ter io-sec-bu tyl)d i-ter t-bu tylm eth oxysila n e (4).
Boudjouk’s procedure was employed, starting with trans-3,
3
clop en ta n e (10a -d ) fr om cis-3: Rep r esen ta tive P r oce-
d u r e for Ca ta lyzed In ser tion . To a cooled (-78 °C) solution
of cis-3 (425 mg, 2.14 mmol) in 3 mL of THF was added
benzaldehyde (0.435 mL, 4.30 mmol) followed by potassium
tert-butoxide (24 mg, 0.21 mmol) and 18-crown-6 (58 mg, 0.22
(
61) Electrophilic attack of pentacoordinate silanes with electro-
philes can occur with either retention or inversion of configuration:
Tamao, K.; Yoshida, J .-i.; Yamamoto, H.; Kakui, T.; Matsumoto, H.;
Takahashi, M.; Kurita, A.; Murata, M.; Kumada, M. Organometallics
1
982, 1, 355-368.

Stereo- and Regioselectivity of Reactions of Siliranes
J . Org. Chem., Vol. 62, No. 14, 1997 4743
mmol). The reaction mixture was stirred for 30 min at -78
NMR (125 MHz, CDCl
122.0, 66.0, 36.9, 30.9, 28.1, 22.2, 20.8, 13.9; HRMS (CI) m/ z
3
) δ 151.0, 141.8, 128.1, 126.6, 125.7,
°
C and then 12 h at 22 °C. To the mixture was added 2 mL of
+
MeOH, and the mixture was concentrated in vacuo. GC of
the unpurified product showed a mixture of four diastereomers
calcd for C17
Anal. Calcd for C21
75.62; H, 10.84.
H
27OSi (M - C
4
H
9
)
275.1831, found 275.1836.
H36OSi: C, 75.84; H, 10.91. Found: C,
(10a -d ) in the ratio of 69.2:29.6:0.3:0.8. Purification by flash
chromatography (5:95 CH Cl :hexanes) yielded the products
as a clear oil (477 mg, 73%). The diastereomeric oxasilacy-
clopentanes were separated by careful flash chromatography.
2
2
4-(1-Bu t yl)-5-p h en yl-2-d i-ter t-b u t yl-1-oxa -2-sila cyclo-
p en ta n e (13). To a cooled (-78 °C) solution of silirane 7 (0.17
g, 0.76 mmol) in 2 mL of THF were added benzaldehyde (0.24
mL, 2.3 mmol), potassium tert-butoxide (8.0 mg, 0.07 mmol),
and 18-crown-6 (0.02 g, 0.08 mmol). The mixture was stirred
at 25 °C for 16 h, and then 0.5 mL of MeOH was added. The
mixture was concentrated in vacuo and purified by flash
chromatography (3:97 EtOAc:hexanes) to afford the product
as a clear oil (0.14 g, 55%) as a mixture of four isomers (two
pairs of diastereomers anti-13/syn-13 and two others in the
ratio 38:47:9:6, respectively, determined by GC analysis).
3
,4-Dim eth yl-5-p h en yl-2,2-d i-ter t-bu tyl-1-oxa -2-sila cy-
clop en ta n e (10a -d ) fr om tr a n s-3: Rep r esen ta tive P r o-
ced u r e for Th er m a l In ser tion . To a solution of trans-3 (68
mg, 0.34 mmol) in 5 mL of THF was added benzaldehyde (70.0
µL, 0.69 mmol). The reaction mixture was brought to reflux
for 16 h. To the reaction mixture was added 2 mL of MeOH,
and the mixture was concentrated in vacuo. GC of the
unpurified product showed a mixture of four diastereomers
a n ti-13: IR (thin film) 3031, 1470, 1364, 1004 cm ; 1
H
-
1
(
10a -d ) in the ratio of 77.1:6.1:8.3:8.5. Purification by flash
chromatography (5:95 CH Cl :hexanes) yielded a diastereo-
2
2
NMR (500 MHz, CDCl ) δ 7.39-7.21 (m, 5H), 4.29 (d, J ) 10.2,
3
meric mixture of products as a clear oil (52 mg, 50%).
Oxa sila cyclop en ta n e 10a : IR (thin film) 3117, 1492,
1H), 1.78 (m, 1H), 1.36 (m, 2H), 1.19 (dd, J ) 14.8, 7.2, 1H),
1.14 (s, 9H), 1.09 (m, 4H), 1.07 (s, 9H), 0.81 (t, J ) 7.1, 3H),
1
7
(
(
1
472, 1386, 1363, 1063 cm-1; H NMR (500 MHz, CDCl
1
3
) δ
0.53 (dd, J ) 14.8, 11.9, 1H); C NMR (125 MHz, CDCl ) δ
13
3
.38-7.25 (m, 5H), 4.24 (d, J ) 10.0, 1H), 1.62 (m, 1H), 1.25
143.6, 128.2, 127.4, 126.8, 86.5, 47.8, 33.0, 30.0, 27.8, 27.7, 22.7,
20.8, 20.2, 14.1, 13.3; HRMS (EI) m/ z calcd for C H OSi (M )
+
d, J ) 7.4, 3H), 1.19 (s, 9H), 1.09 (s, 9H), 1.05 (m, 1H), 0.88
2
1
36
1
3
d, J ) 6.1, 3H); C NMR (125 MHz, CDCl
3
) δ 143.3, 128.2,
21
332.2537, found 332.2527. Anal. Calcd for C H36OSi: C,
75.84; H, 10.91. Found: C, 75.78; H, 11.00.
syn -13: IR (thin film) 3025, 1471, 1364, 1021 cm-1; 1H NMR
27.4, 126.6, 86.7, 49.4, 28.2, 27.9, 26.0, 21.5, 21.4, 15.2, 12.7;
+
HRMS (EI) m/ z calcd for C15
H
23OSi (M - C H ) 247.1517,
4 9
found 247.1522. Anal. Calcd for C19H32OSi: C, 74.93; H,
(
3
500 MHz, CDCl ) δ 7.32-7.26 (m, 4H), 7.20 (m, 1H), 5.17 (d,
1
0.59. Found: C, 74.69; H, 10.68.
J ) 6.3, 1H), 2.40 (m, 1H), 1.21 (m, 1H), 1.13 (s, 9H), 1.08 (s,
Oxa sila cyclop en ta n e 10b: IR (thin film) 3117, 1473,
9H), 1.07 (m, 2H), 0.93 (m, 4H), 0.82 (dd, J ) 15.5, 2.8, 1H),
1
7
7
7
1
387, 1363, 1072 cm-1; H NMR (500 MHz, CDCl
1
3
) δ 7.29-
0.74 (t, J ) 7.3, 3H); C NMR (125 MHz, CDCl ) δ 142.5, 127.8,
13
3
.20 (m, 5H), 5.26 (d, J ) 8.8, 1H), 2.40 (m, 1H), 1.26 (d, J )
126.5, 126.2 , 83.3, 42.0, 30.4, 30.2, 28.6, 28.1, 22.4, 21.7, 19.7,
+
.4, 3H), 1.17 (s, 9H), 1.15 (s, 9H), 1.15 (m, 1H), 0.61 (d, J )
14.0, 10.7; HRMS (EI) m/ z calcd for C H OSi (M - C H )
275.1832, found 275.1830. Anal. Calcd for C H OSi: C,
21 36
1
7
27
4
9
1
3
.1, 3H); C NMR (125 MHz, CDCl
3
) δ 142.8, 127.7, 127.5,
26.9, 83.4, 44.0, 29.1, 28.6, 24.2, 22.6, 20.6, 17.5, 14.2; HRMS
75.84; H, 10.91. Found: C, 75.66; H, 10.84.
Oxid a tion of Oxa sila cyclop en ta n es: Gen er a l P r oce-
d u r e. To a cooled (0 °C) slurry of KH (0.066 g, 1.65 mmol,
+
4 9
H ) 247.1517, found
(EI) m/ z calcd for C15
H
23OSi (M - C
2
47.1517. Anal. Calcd for C19 32OSi: C, 74.93; H, 10.59.
H
Found: C, 74.86; H, 10.64.
Oxa sila cyclop en ta n e 10c: IR (thin film) 2962, 1471, 1387,
3
0% dispersion washed with 3 × 1 mL of hexanes prior to use)
in 1.9 mL of DMF was added tert-butyl hydroperoxide (0.193
g, 90%, 1.93 mmol) dropwise by syringe. After the solution
was warmed to 25 °C, a solution of 10a (0.042 g, 0.140 mmol)
in 1 mL of DMF was added dropwise by syringe followed by
TBAF (0.180 g, 0.690 mmol, hydrate, lyophilized from ben-
zene). The reaction mixture was heated at 70 °C for 8 h. After
the solution was cooled to 25 °C, Na S O (0.60 g) was added.
-
1 1
1
5
(
3
8
363, 1004 cm ; H NMR (500 MHz, CDCl
3
) δ 7.21-7.40 (m,
H), 4.38 (d, J ) 10.5, 1H), 2.04 (m, 1H), 1.54 (m, 1H), 1.19
d, J ) 8.1, 3H), 1.15 (s, 9H), 1.14 (s, 9H), 0.78 (d, J ) 6.8,
1
3
H); C NMR (125 MHz, CDCl
3
) δ 143.7, 128.2, 127.4, 126.6,
4.5, 45.4, 28.7, 28.4, 22.1, 20.8, 20.6, 12.3, 11.0; HRMS (EI)
m/ z calcd for C15
Anal. Calcd for C19
+
4 9
H ) 247.1517, found 247.1513.
H
23OSi (M - C
32SiO: C, 74.93; H, 10.59. Found: C,
2
2
3
H
After 0.5 h, the solvent was removed in vacuo. The resultant
7
1
4.93; H, 10.56.
oily solid was partitioned between 5 mL of 0.5 M Na S O and
2
2
3
Oxa sila cyclop en ta n e 10d : mp 63-64 °C; IR (KBr) 2942,
10 mL of Et O. The layers were separated, and the aqueous
2
476, 1388, 1364, 1102, 1056, 1019 cm-1; 1H NMR (300 MHz,
layer was extracted with 3 × 5 mL of Et O. The combined
2
CDCl
quintet, J ) 5.0, 7.5, 1H), 1.89 (q, J ) 7.9, 1H), 1.22, (d, J )
.8, 3H), 1.17 (s, 9H), 1.10 (s, 9H), 0.48 (d, J ) 7.5, 3H); 13
NMR (125 MHz, CDCl ) δ 142.7, 127.9, 126.3, 125.6, 81.9, 42.7,
9.1, 28.4, 22.8, 22.3, 20.7, 12.2, 10.8. Anal. Calcd for
32SiO: C, 74.93; H, 10.59. Found: C, 74.68; H, 10.50.
-(Ben zyloxy)-1-(2-h exen yl)di-ter t-bu tylsilan e (12a): IR
3
) δ 7.17-7.34 (m, 5H), 5.09 (d, J ) 5.0, 1H), 4.43 (d-
organic layers were washed with 3 × 1 mL of H O and 2.5 mL
2
of brine, dried (MgSO ),and concentrated in vacuo to afford a
4
7
C
yellow oil. The oil was purified by flash chromatography (15:
85 EtOAc:hexanes) to yield the product as a white solid (17
mg, 68%). All physical and spectroscopic data were identical
to those of the reference compound.
3
2
19
C H
1
(1R*,2R*,3R*)-1-P h en yl-2-m eth yl-1,3-bu ta n ed iol (14a ).
A solution of anti-16 (0.305 g, 1.71 mmol) in 10 mL of DMF
was treated with tert-butyldimethylsilyl chloride (0.39 g, 2.57
mmol) and imidazole (0.23 g, 3.4 mmol) for 12 h. The reaction
mixture was diluted with 20 mL of ether, washed with 4 × 5
mL of water, reduced to an oil, and redissolved in CH Cl . The
-
1
1
(
thin film) 3026, 1470, 1384, 1110 cm ; H NMR (300 MHz,
CDCl ) δ 7.35-7.21 (m, 5H), 5.55 (m, 1H), 5.35 (m, 1H), 4.91
3
(
)
s, 2H), 1.93 (q, J ) 7.1, 2H), 1.78 (d, J ) 7.0, 2H), 1.32 (q, J
7.4, 2H), 1.06 (s, 18H), 0.86 (t, J ) 7.3, 3H); 13C NMR (125
) δ 141.7, 129.9, 128.1, 126.7, 126.4, 125.8, 66.1,
5.0, 28.2, 22.8, 21.7, 16.8, 13.8; HRMS (CI) m/ z calcd for
MHz, CDCl
3
2
2
3
C
resultant solution was filtered through a cotton plug and
+
1
21
H
35OSi (M - H) 331.2457, found 331.2465. Anal. Calcd
36OSi: C, 75.84; H, 10.91. Found: C, 75.91; H, 10.84.
-(Ben zyloxy)-2-(1-h exen yl)di-ter t-bu tylsilan e (12b): IR
reduced in vacuo to yield a clear oil: H NMR (500 MHz,
for C21
H
CDCl ) δ 7.96 (m, J ) 6.3, 2H), 7.59-7.43 (m, 3H), 4.11 (m,
3
1
1H), 3.48 (m, 1H), 1.21 (d, J ) 7.0, 3H), 1.08 (d, J ) 7.0, 3H),
0.68 (s, 9H), 0.01 (s, 3H), -0.16 (s, 3H). The major alcohol
isomer underwent quantitative conversion to the silyl ether.
The silylated intermediate was dissolved in 10 mL of ether
and cooled to -78 °C before being treated with lithium
aluminum hydride (100 mg, 2.57 mmol).41 The reaction
mixture was slowly warmed to 22 °C over a period of 2 h before
being treated with water (4 drops), KOH (4 drops, 4 N,
aqueous), and water (12 drops). The resultant white precipi-
tate was filtered, and the ether solution was stirred with HCl
(3 N, aqueous) to cleave the silyl ether. The organic layer was
recovered and the aqueous layer extracted twice with ether.
Reduction in vacuo and purification by flash chromatography
(40:60 EtOAc:hexanes) yielded the desired product as the
-
1
1
(
thin film) 3061, 1470, 1382, 1114 cm ; H NMR (500 MHz,
CDCl ) δ 7.39-7.33 (m, 4H), 7.24 (m, 1H), 5.76 (s, 1H), 5.48
s, 1H), 4.98 (s, 2H), 2.18 (t, J ) 7.9, 2H), 1.48 (m, 2H), 1.30
m, 2H), 1.09 (s, 18H), 0.88 (t, J ) 7.3, 3H); C NMR (125
) δ 147.8, 141.6, 128.1, 126.7, 126.4, 125.6, 66.0,
5.8, 30.7, 28.6, 22.8, 21.2, 14.0; HRMS (CI) m/ z calcd for
3
(
(
1
3
MHz, CDCl
3
3
+
C
21
H
35OSi (M - H) 331.2457, found 331.2449. Anal. Calcd
36OSi: C, 75.84; H, 10.91. Found: C, 75.93; H, 10.98.
-(Ben zyloxy)-1-(1-h exen yl)di-ter t-bu tylsilan e (12c): IR
for C21
H
1
-
1
1
(
thin film) 3065, 1615, 1469, 1382, 1110 cm ; H NMR (500
MHz, CDCl ) δ 7.38-7.32 (m, 4H), 7.25 (m, 1H), 6.22 (dt, J )
8.7, 6.4, 1H), 5.57 (d, J ) 19.1, 1H), 4.91 (s, 2H), 2.16 (q, J )
.8, 2H), 1.35 (m, 4H), 1.04 (s, 18H), 0.90 (t, J ) 7.2, 3H); 13
3
1
6
C

4
744 J . Org. Chem., Vol. 62, No. 14, 1997
Bodnar et al.
major isomer (0.237 g, 77%, mixture of isomers, 70% 14a ): IR
) 8.8, 2H), 7.39-7.26 (m, 5H), 5.82 (s, 1H), 5.12 (d, J ) 1.8,
-
1
(
KBr) 3383, 3033, 1454, 1376, 1314, 1230, 1128, 1089 cm
;
1H), 4.33 (qd, J ) 6.2, 2.1, 1H), 1.85 (m, 1H), 1.33 (d, J ) 6.6,
1
13
H NMR (500 MHz, CDCl
3
) δ 7.38-7.28 (m, 5H), 4.52 (d, J )
.4, 1H), 3.90 (m, 1H) 3.71 (bs, 1H), 3.46 (bs, 1H), 1.83 (m,
H), 1.24 (d, J ) 6.0, 3H), 0.54 (d, J ) 7.2, 3H); 13C NMR (125
) δ 143.3, 128.5, 128.0, 127.1, 81.2, 73.3, 46.4, 21.8,
2 2
3H), 0.77 (d, J ) 7, 3H); C NMR (125 MHz, CD Cl ) δ 148.6,
7
1
145.9, 140.7, 128.5, 127.8, 127.4, 125.6, 123.7, 100.3, 82.5, 77.3,
+
38.5, 18.9, 5.8; HRMS (CI) m/ z calcd for C18
314.1392, found 314.1407. Anal. Calcd for C18
69.00; H, 6.11. Found: C, 68.96; H, 6.17.
H
20NO
4
(M + H)
19 4
MHz, CDCl
1
1
3
H O N: C,
+
3.5; HRMS (FAB) m/ z calcd (M + H) 181.1228, found
81.1225. Anal. Calcd for C11 C, 73.30; H 8.95.
H
16
O
2
:
(1R*,2S*)-1-P h en yl-2-(1-bu tyl)-1,3-p r op a n ed iol (syn-17).
To a cooled (-78 °C) solution of 18 (0.34 g, 1.4 mmol) in 4 mL
of THF was added LiAlH (85 mg, 2.2 mmol), and the mixture
4
Found: C, 73.17; H, 8.92.
(
1S*,2R*,3R*)-1-P h en yl-2-m eth yl-1,3-bu ta n ed iol (14b).
To a mixture of acetic acid (2 mL) and acetonitrile (2 mL,
freshly distilled) was added tetramethylammonium triacetoxy-
borohydride (0.875 g, 3.33 mmol). The solution was stirred
at 25 °C for 1.5 h. The mixture was cooled to -40 °C before a
solution of anti-16 (0.075 g, 0.42 mmol) in acetonitrile (0.5 mL)
was added. The solution was stirred and for 18 h at -40 °C.4
The mixture was treated with 5 mL of sodium potassium
tartrate solution (saturated aqueous), warmed to 22 °C, and
was stirred for 12 h at 25 °C. The reaction was then quenched
with 5 mL of sodium potassium tartrate solution (saturated
aqueous), then 20 mL of water was added, the organic layer
was separated, and the aqueous layer was washed with ether
(2 × 20 mL). The combined organic layers were washed with
2
2 4
saturated aqueous NaCl (20 mL), dried over Na SO , and
concentrated in vacuo to give an impure yellow liquid. Puri-
fication by flash chromatography (40:60 EtOAc:hexanes) af-
forded a clear viscous oil (0.27 g, 92%): IR (thin film) 3355,
partitioned between H
organic layer was recovered, and the aqueous layer was
Cl . The combined organic
2 2 2
O (10 mL) and CH Cl (10 mL). The
-
1
1
3063, 1454, 1026 cm ; H NMR (500 MHz, CDCl ) δ 7.35-
3
extracted with 2 × 10 mL of CH
2
2
7.33 (m, 4H), 7.28 (m, 1H), 5.00 (t, J ) 3.5, 1H), 3.72 (t, J )
4.6, 2H), 3.00 (d, J ) 3.7, 1H), 2.41 (t, J ) 4.6, 1H), 1.93 (m,
layers were filtered through a cotton plug and reduced in vacuo
to a clear oil. Flash chromatography yielded the product as a
white solid (0.037 g, 61% based on 81:19 mixture of anti-16:
syn-16): mp 110-111 °C; IR (KBr) 3406, 3301, 2968, 1459,
1
3
1H), 1.24 (m, 6H), 0.83 (t, J ) 7.2, 3H); C NMR (125 MHz,
CDCl
3
) δ 142.4, 128.2, 127.3, 126.2, 77.2, 64.1, 46.1, 29.6, 24.6,
+
22.8, 13.9; HRMS (CI) m/ z calcd for C13
found 208.1468. Anal. Calcd for C13
Found: C, 74.76; H, 9.67.
H
O
20
O
2
(M ) 208.1464,
-
1
1
1
7
6
6
1
348, 1205, 1125, 1096 cm ; H NMR (500 MHz, CDCl
3
) δ
H
20
2
: C, 74.96; H, 9.68.
.26-7.36 (m, 5H), 5.12 (d, J ) 1.8, 1H), 3.83 (quintet, J )
.3, 1H) 3.15 (bs, 1H), 2.56 (bs, 1H), 1.84 (m, 1H), 1.31 (d, J )
(1R*,2R*)-1-P h en yl-2-(1-bu t yl)-1,3-p r op a n ed iol (anti-
17). This compound was prepared in a manner similar to that
of syn-17: mp 39.0-40.0 °C; IR (thin film) 3337, 3030, 1454,
.2, 3H), 0.82 (d, J ) 7.0, 3H); 13C NMR (125 MHz, CDCl
) δ
3
42.6, 128.0, 127.0, 126.1, 75.0, 70.9, 45.5, 21.9, 11.5; HRMS
+
-1
1
(
1
CI) m/ z calcd for C11
98.1499. Anal. Calcd for C11
H
20NO
2
(M + NH
4
)
198.1494, found
C, 73.30; H 8.95.
1026 cm ; H NMR (500 MHz, CDCl ) δ 7.36-7.24 (m, 5H),
3
H
16
O
2
:
4.61 (dd, J ) 7.0, 2.6, 1H), 3.91 (d, J ) 3.3, 1H), 3.73 (m, 1H),
3.59 (m, 2H), 1.75 (m, 1H), 1.19 (m, 6H), 0.80 (t, J ) 6.9, 3H);
Found: C, 73.03 ; H, 8.86.
1S*,2S*,3R*)-1-P h en yl-2-m eth yl-1,3-bu ta n ed iol (14c).
The procedure described for 14a was employed to provide
1
3
(
3
C NMR (125 MHz, CDCl ) δ 143.5, 128.2, 127.4, 126.4, 79.0,
64.5, 46.1, 29.1, 27.7, 22.7, 13.8; HRMS (CI) m/ z calcd for
+
1
1
4c: IR (thin film) 3342, 2972, 2894, 1455, 1380, 1305, 1202,
C
13
H
21
O
H
2
(M + H) 209.1542, found 209.1542. Anal. Calcd
20 2
-1 1
105, 1072, 1021, 926, 891, 757, 702 cm ; H NMR (500 MHz,
) δ 7.26-7.36 (m, 5H), 4.71 (d, J ) 6.6, 1H), 4.04 (m,
H) 3.14 (bs, 1H), 2.75 (bs, 1H), 1.95 (m, 1H), 1.22 (d, J ) 6.6,
for C13
O : C, 74.96; H, 9.68. Found: C, 74.73; H, 9.65.
CDCl
3
Ca ta lyzed In ser tion of An isa ld eh yd e: 2,2-Di-ter t-bu -
tyl-3,4-d im eth yl-5-(4-m eth oxyp h en yl)-1-oxa -2-sila cyclo-
p en ta n e (20d , Ar ) 4-MeOC H ). Anisaldehyde (530 mg,
1
3
1
1
3
H), 0.83 (d, J ) 7.2, 3H); C NMR (125 MHz, CDCl
3
) δ 143.7,
6
4
28.4, 127.6, 126.4, 78.1, 69.2, 44.5, 19.4, 12.1; HRMS (EI) m/ z
3.9 mmol) was added to trans-3 (515 mg, 2.60 mmol) and 18-
crown-6 (79 mg, 0.30 mmol) in 10 mL of THF at -78 °C.
Potassium tert-butoxide (67 mg, 0.60 mmol) was added. The
reaction mixture was stirred for 12 h at 22 °C. The reaction
mixture was reduced in vacuo, yielding a turbid orange-brown
oil. GC-MS of the unpurified product gave a diastereomeric
distribution of oxasilacyclopentanes as 5:10:22:63. Purification
by flash chromatography (3:97 EtOAc:hexane) gave the major
+
calcd for C11
Calcd for C11
.03.
1R*,2S*,3R*)-1-P h en yl-2-m eth yl-1,3-bu ta n ed iol (14d ).
H
16
O
2
(M ) 180.1150, found 180.1156. Anal.
H
16
O
2
: C, 73.30; H, 8.95. Found: C, 73.23; H,
9
(
To a stirred solution of syn-16 (199 mg, 1.12 mmol) in 20%
MeOH/THF (11 mL total, cooled to -78 °C) was added
diethylmethoxyborane (0.612 mL, 1.23 mmol). After 20 min,
sodium borohydride (0.047 g, 1.2 mmol) was added and the
product47 (20d , Ar ) 4-MeOC
mixture of the three other isomers as an oil (20d , Ar )
4-MeOC , 201 mg; mixture, 275 mg, 55% combined). 20d ,
Ar ) 4-MeOC : mp 97-98 °C; IR (KBr) 2857, 1612, 1513
cm ; H NMR (500 MHz, CDCl ) δ 7.21 (d, J ) 8.8, 2H), 6.86
6
4
H ) as a white solid and a
4
3
mixture was stirred at -78 °C for 3 h. The reaction was
quenched with HOAc (1 mL), warmed to 25 °C, diluted in 20
6 4
H
mL of ether, and washed with 4 × 10 mL of NaHCO
saturated aqueous). The ether layer was reduced in vacuo
and the resultant material was dissolved in CH Cl before
3
6 4
H
-
1 1
(
3
2
2
(d, J ) 8.7, 2H), 5.05 (d, J ) 4.8, 1H), 3.79 (s, 3H), 2.38 (tq, J
) 7.6, 5.1, 1H), 1.88 (q, J ) 7.9, 1H), 1.21 (d, J ) 7.6, 3H),
being filtered through a cotton plug. Reduction in vacuo and
purification by flash chromatography (12:88 EtOAc:hexanes)
yielded the product as a clear oil (0.012 g, 60%, >95% isomeric
1
3
1.17 (s, 9H), 1.10 (s, 9H), 0.48 (d, J ) 7.6, 3H); C NMR (125
MHz, CDCl
3
) δ 158.1, 134.9, 126.6, 113.3, 81.6, 55.2, 42.8, 29.1,
1
purity by GC and H NMR): IR (thin film) 3355, 2975, 1453,
28.4, 22.8, 22.3, 20.7, 12.3, 10.8; HRMS (CI) m/ z calcd for
-
1
1
+
1
7
3
0
1
380, 1199, 1072 cm ; H NMR (500 MHz, CDCl
3
) δ 7.36-
C
C
20
20
H
H
34
34
O
O
2
2
Si (M ) 334.2328, found 334.2320. Anal. Calcd for
Si: C, 71.80; H, 10.24. Found: C, 71.65; H, 10.17.
.24 (m, 5H), 5.04 (d, J ) 1.7, 1H), 3.83 (quintet, J ) 6.3, 1H),
.15 (bs, 1H), 2.56 (bs, 1H), 1.84 (m, 1H), 1.31 (d, J ) 6.2, 3H),
Ca ta lyzed In ser tion of 4-(Tr iflu or om eth yl)ben za ld e-
.82 (d, J ) 7.0, 3H); 13C NMR (125 MHz, CDCl
) δ 142.6,
3
h yd e. 4-(Trifluoromethyl)benzaldehyde (820 mg, 4.71 mmol)
was added to trans-3 (623 mg, 3.14 mmol) and 18-crown-6 (82
mg, 0.31 mmol) in 12.5 mL of THF at -78 °C. To the mixture
was added potassium tert-butoxide (89 mg, 0.79 mmol). The
reaction mixture was stirred for 12 h at 22 °C. The reaction
mixture was reduced in vacuo, yielding a turbid, colorless oil.
GC of the unpurified product gave a diastereomeric distribu-
28.0, 127.0, 126.1, 75.0, 70.9, 45.5, 21.9, 11.5; HRMS (CI) m/ z
+
calcd for C11
Calcd for C11
.04.
p-Nitr oben zylid en e Aceta l 15. To a solution of diol 14d
0.028 g, 0.16 mol) in 1.6 mL of benzene was added p-
H
17
O
2
(M + H) 181.1228, found 181.1225. Anal.
H
16
O : C, 73.30; H, 8.95. Found: C, 73.09; H,
2
9
(
nitrobenzaldehyde (0.026 g, 0.171 mmol) followed by 4 Å
molecular sieves. The mixture was heated to reflux for 12 h
before being cooled, filtered, and reduced in vacuo. Purifica-
tion by flash chromatography (4:96-5:95 EtOAc:hexanes)
yielded the product as a colorless crystalline solid. Crystals
tion of 1:8:21:70. Purification by flash chromatography (0:
:hexane) gave the major product4 as a white
7
100-5:95 CH
2
Cl
2
solid and a mixture of the three other isomers as an oil (20d ,
Ar ) 4-(CF )C , 554 mg; minor isomers, 272 mg, 71%
combined). 20d , Ar ) 4-(CF )C : mp 55-57 °C; IR (thin
3
film) 2969, 1619, 1475, 1126 cm ; H NMR (500 MHz, CDCl )
3
6 4
H
3
6 4
H
2
0
-1 1
suitable for X-ray crystallography were obtained by slow
crystallization from 10-20% CH Cl in hexanes: mp 125-127
C; IR (KBr) 2978, 1609, 1529, 1396, 1350, 1158, 1066 cm
2
2
δ 7.58 (d, J ) 8.1, 2H), 7.42 (d, J ) 8.0, 2H), 5.12 (d, J ) 4.9,
-
1
°
;
1H), 2.49 (m, 1H), 1.92 (quintet, J ) 7.8, 1H), 1.22 (d, J ) 7.7,
1
13
H NMR (500 MHz, CDCl
3
) δ 8.26 (d, J ) 8.1, 2H), 7.79 (d, J
3H), 1.17 (s, 9H), 1.10 (s, 9H), 0.46 (d, J ) 7.5, 3H); C NMR

Stereo- and Regioselectivity of Reactions of Siliranes
J . Org. Chem., Vol. 62, No. 14, 1997 4745
Z:E by H NMR spectroscopy): IR (thin film) 2968, 1674, 1194,
) δ 147.1, 128.7 (q, 2J CF ) 33), 125.9, 124.4
q, J CF ) 271), 124.9, 81.4, 42.6, 29.0, 28.3, 22.9, 22.3, 20.7,
2.1, 10.7. Anal. Calcd for C20 OSi: C, 64.48; H, 8.39.
Found: C, 64.44; H, 8.41.
1
(
(
1
125 MHz, CDCl
3
1
-1 1
6 6
1069 cm ; H NMR (500 MHz, C D ) δ 4.41 (m, 1H), 2.1 (m,
H
30
F
3
2H), 1.96 (m, 1H), 1.71 (d, J ) 6.7, 3H), 1.23 (m, 1H), 1.18 (d,
J ) 7.6, 3H), 1.16 (s, 9H), 1.14 (s, 9H), 1.08 (m, 1H), 0.98 (td,
1
3
Th er m a l In ser tion of An isa ld eh yd e (eq 11). To a bomb
were added trans-3 (135 mg, 0.680 mmol) and THF (1 mL).
The solution was cooled to -78 °C, and anisaldehyde (102 mg,
J ) 7.5, 0.9, 3H), 0.95 (t, J ) 7.2, 3H); C NMR (125 MHz,
C
6
D
6
) δ 153.4, 98.9, 29.5, 29.4, 29.3, 26.0, 24.2, 22.8, 22.4, 14.9,
14.2, 12.0, 11.3; HRMS (FAB) m/ z calcd for C17
H) 285.2613, found 285.2611. Anal. Calcd for C17
71.76; H, 12.75. Found: C, 71.88; H, 12.85.
H
37OSi (M +
36OSi: C,
+
0
.750 mmol) was added. The solution was degassed (freeze,
H
pump, thaw ×2) and then heated at 110 °C for 24 h. The
reaction mixture was reduced in vacuo, and then purified by
2,5-Diben zyl-3,4-d ip h en yl-2,5-d ia za -1,1-d i-ter t-bu tyl-1-
sila cyclop en ta n e (26). To a bomb were added trans-3 (200
mg, 1.0 mmol) and N-benzylphenylimine 2562 (430 mg, 2.2
mmol). The reaction mixture was degassed (freeze, pump,
thaw ×2) and heated to 150 °C for 20 h, yielding a yellow oil.
The reaction mixture was purified by flash chromatography
2 2
flash chromatography (30:70 CH Cl :hexane), yielding the four
oxasilacyclopentane isomers (66 mg, 29%) and two isomeric
silanes 21 and 22 (61 mg, 27%). GC-MS of the unpurified
product gave a mixture (62:14:14:10) of oxasilacyclopentanes
2
0. GC-MS indicated a diastereomeric mixture (82:18) of
). Because of the difficulty
alkenes (21:22, Ar ) 4-MeOC
in isolating pure stereoisomers of oxasilacyclopentanes, the
stereochemistry of the products was assigned by analogy to
6
H
4
(5:95 CH
2 2
Cl :hexane), yielding a yellow oil (150 mg, 28%, anti:
1
syn >10:1 by H NMR spectroscopy): IR (thin film) 3062, 1602,
-
1
1
1069 cm ; H NMR (500 MHz, CDCl
(m, 6H), 6.89 (m, 4H), 4.23 (s, 2H), 4.19 (d, J ) 15.5, 2H), 4.11
(d, J ) 15.5, 2H), 1.37 (s, 18H); 13C NMR (125 MHz, CDCl
) δ
140.5, 140.4, 129.1, 128.2, 127.4, 127.2, 126.5, 125.5, 74.2, 51.3,
3
) δ 7.0 (m, 10H), 6.98
4
6
the benzaldehyde experiments.
,4-Di-ter t-bu tyl-6-(4-m eth oxyp h en yl)-3-m eth yl-4-sila -
-oxa -1-h exen e (21, Ar ) 4-MeOC ): IR (thin film) 3075,
614, 1513, 1247, 1096 cm-1; H NMR (500 MHz, CDCl
) δ
.28 (d, J ) 9.6, 2H), 6.88 (d, J ) 9.6, 2H), 6.21 (m, 1H), 4.91
4
3
5
1
7
6 4
H
1
+
3
29.4, 24.2; HRMS (CI) m/ z calcd for C36
533.3352, found 533.3332. Anal. Calcd for C36
H
45
N
2
Si (M + H)
44 2
H N
Si: C,
(
m, 4H), 3.79 (s, 3H), 2.27 (m, 1H), 1.29 (d, J ) 6.4, 3H), 1.10
81.15; H, 8.32; N, 5.26. Found: C, 81.16; H, 8.36; N, 5.19.
N,N′-Diben zyl-1,2-d ip h en yleth ylen ed ia m in e (27). To
a stirring solution of 26 (76 mg, 0.14 mmol) in 3 mL of THF
was added excess HF (2 mL, 48% aqueous solution). The
solution was stirred at 22 °C for 4 h, followed by dropwise
addition of 1 M NaOH (aq) until pH > 7 was achieved. The
1
3
(s, 18H); C NMR (125 MHz, CDCl
3
) δ 158.5, 142.0, 133.7,
1
27.0, 113.6, 110.9, 65.5, 55.2, 28.9, 28.6, 26.0, 22.7, 21.0, 14.4;
+
HRMS (CI) m/ z calcd for C20
3
H
33
O
2
Si (M - H) 333.2249, found
33.2243. Anal. Calcd for C20
H O Si: C, 71.80; H, 10.24.
34 2
Found: C, 71.65; H, 10.15.
Th er m a l In ser tion of 4-(Tr iflu or om eth yl)ben za ld e-
h yd e. A similar procedure was used as described above.
Because of the difficulty in isolating pure stereoisomers of
oxasilacyclopentanes, the stereochemistry of the products was
assigned by analogy to the benzaldehyde experiments.46 The
reaction mixture was partitioned between CH
NaOH (1 M aqueous, 50 mL). After separation, the aqueous
layer was washed 3 × 50 mL of CH Cl . The organic fractions
were combined, filtered through Na SO /glass wool, and
reduced in vacuo, yielding a turbid oil. Purification by flash
chromatography (5:1:94 EtOAc:Et N:hexane) yielded a clear
oil (32 mg, 58%). The product was identical to a reference
2 2
Cl (50 mL) and
2
2
2
4
side product 21, Ar ) 4-(CF
reaction mixture: 1H NMR (500 MHz, CDCl
.0, 2H), 7.48 (m, 2H), 6.17 (ddd, J ) 17.3, 10.4, 6.9, 1H), 5.03
3
)C
6
H
4
, was isolated from the
3
3
) δ 7.60 (d, J )
sample and comparison to literature data:5
MHz, CDCl ) δ 7.24 (m, 4H), 7.21 (m, 5H), 7.11 (m, 6H), 7.04
(m, 5H), 3.70 (s, 2H), 3.65 (d, J ) 13.1, 2H), 3.48 (d, J ) 13.5,
0,51
1
H NMR (500
8
(
(
(
s, 2H), 4.95 (m, 2H), 2.28 (m, 1H), 1.29 (d, J ) 7.6, 3H), 1.11
3
s, 9H), 1.08 (s, 9H); HRMS (CI) m/ z calcd for C20
H
31OSiF
2
+
13
M - F) 353.2112, found 353.2108.
3
2H), 2.40 (bs, 2H); C NMR (125 MHz, CDCl ) δ 141.1, 140.6,
128.3, 128.2, 128.1, 127.9, 126.9, 126.7, 68.4, 51.3.
Di-ter t-bu tyl-sec-bu tyl-1,3-(bu ta d ien yloxy)sila n e (23).
To a solution of trans-3 (200 mg, 1.0 mmol), 18-crown-6 (66
mg, 0.25 mmol), and 2 mL of THF was added crotonaldehyde
Ack n ow led gm en t. This research was supported by
the National Institutes of Health (GM-54909) and by
the University of California Cancer Research Coordi-
nating Committee funds. Acknowledgment is also made
to the donors of the Petroleum Research Fund, admin-
istered by the American Chemical Society, for support
of this research. K.A.W. is a recipient of the Presiden-
tial Early Career Award for Scientists and Engineers
and the American Cancer Society J unior Faculty Re-
search Award. The U.S. Department of Education is
thanked for support in the form of a GAANN fellowship
to J .T.S. We thank Dr. J ohn Greaves and J ohn Mudd
for mass spectrometric data and Dr. J oseph Ziller for
crystallographic analyses.
(90.0 µL, 1.1 mmol) followed by potassium tert-butoxide (11
mg, 0.1 mmol) at -78 °C. The solution was stirred at -78 °C
for 3 h, allowed to warm to 22 °C, and stirred for 17 h. The
reaction mixture was concentrated in vacuo and then parti-
tioned between CH
aqueous layer was washed with 2 × 50 mL of CH
combined organic layers were filtered through Na
2
Cl
2
(30 mL) and water (10 mL). The
Cl . The
SO /glass
2
2
2
4
wool and reduced in vacuo to yield a brown, turbid oil.
Purification by flash chromatography (hexane) yielded a clear,
1
colorless oil (100 mg, 37%, >95:5 E:Z by H NMR spectros-
-
1
1
copy): IR (thin film) 2965, 1645, 1195, 1012 cm ; H NMR
(
1
(
500 MHz, CDCl
0.7, 1H), 5.74 (t, J ) 11.4, 1H), 4.98 (m, J ) 16.7, 1H), 4.80
dd, J ) 10.3, 1.1, 1H), 1.84 (m, 1H), 1.27 (m, 1H), 1.15 (d, J
7.3, 3H), 1.073 (s, 9H), 1.071 (s, 9H), 1.11 (m, 1H), 0.98 (t,
3
) δ 6.69 (d, J ) 11.6, 1H), 6.25 (td, J ) 16.9,
)
1
3
J ) 8.0, 3H); C NMR (125 MHz, CDCl
3
) δ 146.2, 133.6, 113.6,
Su p p or tin g In for m a tion Ava ila ble: A listing of full
spectral and experimental details for stereochemical proof (9
pages). This material is contained in libraries on microfiche,
immediately follows this article in the microfilm version of the
journal, and can be ordered from the ACS; see any current
masthead page for ordering information.
1
11.3, 28.8, 28.7, 25.4, 22.1, 22.0, 20.9, 14.4, 14.0; HRMS (CI)
+
m/ z calcd for C16H32OSi (M ) 268.2222, found 268.2227.
Di-ter t-b u t yl-sec-b u t yl-3-et h yl-2-(p r op en yloxy)sila n e
24). To a cooled (-78 °C), stirring solution of trans-3 (120
(
mg, 0.60 mmol), 18-crown-6 (40.0 mg, 0.15 mmol), and 1.2 mL
of THF was added 3-pentanone (96 µL, 0.90 mmol) followed
by potassium tert-butoxide (7 mg, 0.06 mmol). The solution
was stirred for 18 h at 22 °C and then reduced in vacuo. The
resulting turbid oil was purified by flash chromatography
J O970263K
(62) Ishihara, K.; Miyata, M.; Hattori, K.; Tada, T.; Yamamoto, H.
(hexane), yielding a clear, colorless oil (115 mg, 67%, >95:5
J . Am. Chem. Soc. 1994, 116, 10520-10524.