Intramolecular Diels - Alder reaction of chiral silatrienes: Synthesis of 4a,7,8,8a-tetrahydro-4-silaisochroman-1-ones

Article abstract of DOI:10.1002/1099-0690(200009)2000:17<3039::AID-EJOC3039>3.0.CO;2-X

Intramolecular Diels - Alder reactions of chiral 2-silahexa-3,5-dienyl α,β-unsaturated esters have been found to afford tetrahydro-4-silaisochroman-1-ones in moderate yields. The best diastereoselectivity was achieved in the reaction of silatriene 8c, in

Full text of DOI:10.1002/1099-0690(200009)2000:17<3039::AID-EJOC3039>3.0.CO;2-X

FULL PAPER
Intramolecular Diels؊Alder Reaction of Chiral Silatrienes: Synthesis of
4a,7,8,8a-Tetrahydro-4-silaisochroman-1-ones
Paulo J. Coelho*[a] and Luis Blanco[a]
Keywords: Intramolecular DielsϪAlder reaction / Cycloadditions / Chirality / Silicon / Tetrahydro-4-silaisochroman-1-ones
Intramolecular Diels−Alder reactions of chiral 2-silahexa-3,5-
dienyl α,β-unsaturated esters have been found to afford tetra-
hydro-4-silaisochroman-1-ones in moderate yields. The best
diastereoselectivity was achieved in the reaction of silatriene
8c, in which methyl and triisopropylsilyloxymethyl groups
are attached to the silicon atom, with an acrylate as the dien-
ophile under EtAlCl2-catalyzed conditions.
Introduction
lowed us to synthesize several optically active 2,2-disubsti-
tuted 2-silapropanes (ee
Յ 70%) in 50Ϫ80% yield
(Scheme 1).
Silicon compounds find wide application in organic syn-
thesis, for example as protective groups, as reagents for
functional group transformation or for carbonϪcarbon
bond formation.[1] More recently, silicon compounds have
been used with great success as a temporary tether between
two reacting groups in intramolecular reactions. Highly re-
gio- and stereoselective transformations have been reported
using this approach, specifically in radical additions,[2] hy-
drosilylations,[3] [2 ϩ 2] cycloadditions,[4] and DielsϪAlder
reactions.[5] Since SiϪO and SiϪC bonds can be selectively
cleaved, it is possible to perform chemical transformations
that are impossible by means of intermolecular reactions,
either due to a lack of reactivity of the reagents or to inher-
ently low selectivity.
Scheme 1. Transesterification of prochiral 2-silapropane-1,3-diols
Results and Discussion
Since the pioneering work of Sommer’s group on the syn-
thesis and reactions of optically active methylnaphthylphen-
ylsilyl compounds,[6] there have been only a few reports on
the use of Si-centered chiral compounds as chiral auxiliar-
ies.[7] This lack of interest is partially due to the low diaster-
eoselectivities hitherto observed. However, such studies
have been almost exclusively undertaken by using methyl-
naphthylphenylsilyl derivatives. In these systems, the select-
ivity stems mainly from the steric differentiation of the
methyl, naphthyl, and phenyl groups. Recently, Bienz and
Chapeaurouge[8] showed that high diastereoselectivity can
be achieved in the addition of organometallic compounds,
at very low temperatures, to chiral acylsilanes bearing alkyl-
oxymethyl groups at their silicon atoms.
The lack of available methods for the synthesis of optic-
ally active silicon compounds has also contributed to the
slow development of their application in asymmetric syn-
thesis. In this context, a new method for the synthesis of
these compounds has been developed in our laboratory. It
uses enzymes for the monotransesterification of esters with
prochiral 2-silapropane-1,3-diols.[9] This approach has al-
In this paper, we describe a study of the regio- and dias-
tereoselectivity of the intramolecular DielsϪAlder reaction
(IMDA) between a diene and a dienophile linked by a chiral
silicon atom through SiϪC bonds. The enantiomerically en-
riched silatrienes 8a؊g and 6c (ee Ն 34%) were prepared in
good yield in six or seven steps from (E)-1,4-dichlorobut-2-
ene (1) as shown in Scheme 2. Dehydrochlorination of 1 in
aqueous NaOH in the presence of the phase-transfer agent
Aliquat 336 at 50Ϫ60 °C under reduced pressure gave 1-
chlorobuta-1,3-diene (2) (E/Z ϭ 6:94) in good yield (86%).
The CuCN-catalyzed reaction of buta-1,3-dienylmagnesium
chloride with bis(chloromethyl)methylchlorosilane gave a
mixture of silabutadienes 3 (E/Z ϭ 1:2) in 79% yield.[10]
Viehe[11] showed that heating benzene solutions of 1-chloro-
buta-1,3-diene containing 1% iodine yielded an equilibrium
mixture of E and Z isomers [E/Z ϭ (70 Ϯ 5):(30 Ϯ 5)].
When applied to a mixture of silabutadienes, (Z)-3 and (E)-
3, this reaction gave rise to a mixture highly enriched in the
Z isomer (E/Z ϭ 97:3), which could be isolated in 88% yield
by distillation. Replacement of the chloro substituents by
acetate groups in the presence of the phase-transfer agent
n-Bu4NBr gave bis(acetoxy)silane, which was reduced to 2-
silapropanediol 4 with LiAlH4 in excellent yield (96%). This
compound was found to be rather unstable at room temper-
´
[a]
Laboratoire des Carbocycles (associe au CNRS), Institut de
´
ˆ
´
Chimie Moleculaire d’Orsay, Bat. 420, Universite de Paris-Sud,
F-91405 Orsay, France
E-mail: pcoelho@marao.utad.pt
Eur. J. Org. Chem. 2000, 3039Ϫ3046
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1434Ϫ193X/00/0917Ϫ3039 $ 17.50ϩ.50/0
3039

P. J. Coelho, L. Blanco
FULL PAPER
ature, but could be stored for months at Ϫ20 °C without to silatrienes, which incorporate a diene, a dienophile, and
noticeable decomposition.
a hydroxymethyl group amenable to further functionaliz-
ation. However, the silatrienes prepared in this way were
found to be formed with low ee. Thus, it was concluded
that the synthetic sequence leading to silatrienes with high
enantiomeric purity involves the transesterification of
methyl isobutyrate with subsequent introduction of the di-
enophile.
Table 1. LCR-catalyzed transesterification of methyl isobutyrate
and oximes 5b؊d with 2-silapropanediol 4
Ester
Time
(h)
Mono-
ester
ee
Yield
(%)
Diester
7a
Yield
(%)
(%)
Methyl
isobutyrate
5b
5c
5d
120
6a
62
70
8
44
28
48
6b
6c
6d
34
40
58
64
71
79
7b
7c
7d
12
9
10
It is noteworthy that the ee of monoester 6d (58%), pre-
pared by transesterification of methacrylate oxime 5d, was
superior to that of monoester 6c (40%) prepared by transes-
terification of acrylate oxime 5c, and very similar to that of
monoester 6a (62%). Hence, it would seem that the enanti-
oselectivity of the LCR-catalyzed transesterification is par-
Scheme 2. Synthesis of silatrienes 8a؊g, 6c
Transesterifications of methyl isobutyrate and acetoxime ticularly influenced by the presence of substituents α to the
esters 5b؊d with prochiral 2-silapropanediol 4 catalyzed by ester group. On the other hand, the degree of unsaturation
the lipase from Candida rugosa (LCR) gave rise to optically of the ester function is seen to have a strong effect on the
active 2-(hydroxymethyl)-2-silapropyl esters 6a؊d,[9] to- rate of the reaction but does not seem to modify its enanti-
gether with small amounts of the corresponding diesters oselectivity.
7a؊d. The transesterification of methyl isobutyrate was car-
The hydroxymethyl(butadienyl)silanes 6a؊d were then
ried out in the neat liquid, while the transesterifications of converted into compounds 8a؊g by one of two methods,
oximes 5b؊d were performed in diisopropyl ether. All en- namely introduction of the dienophile by esterification of
zymatic reactions were carried out at Ϫ20 °C[12] (Table 1). the hydroxymethyl function (compounds 6a,b) or, in the
The transesterifications of the α,β-unsaturated oximes led case of compounds 6c؊d that already incorporated the di-
Scheme 3. Synthesis of silatrienes 8a؊g.
3040
Eur. J. Org. Chem. 2000, 3039Ϫ3046

Intramolecular DielsϪAlder Reaction of Chiral Silatrienes
FULL PAPER
Table 2. Intramolecular DielsϪAlder reactions of silatrienes 8a؊f and 6c
[a] 41% of the acid 10 was also isolated. Ϫ [b] Decomposition. Ϫ [c] No reaction.
enophile function, by protection of the hydroxymethyl func-
tion (Scheme 3).
As expected, the fumarate 8g proved to be the most react-
ive silatriene. The thermal reaction occurred at a lower tem-
perature (140 °C) and the EtAlCl2-catalyzed reaction re-
quired only 30 min for complete consumption of the start-
ing material. Under thermal conditions, the best diastere-
omeric ratio was observed in the cyclization of compound
8e (32:8:58:2). The diastereoselectivities observed in the cyc-
lizations of silatrienes 8a؊d, in which the hydroxymethyl
function is protected as an isobutyric ester, a phenylacetyl
ester, a trisopropylsilyl ether, and a triphenylmethyl ether,
respectively, were somewhat higher, but the nature of the
protective group did not have a marked influence on the
diastereoselectivity. The diastereoselectivities of the Et-
AlCl2-catalyzed IMDA reactions of silatrienes 8a؊c,g were
found to be significantly higher than those obtained under
thermal conditions. Under EtAlCl2-catalyzed conditions,
the best diastereoselectivities were observed in the cycliza-
tions of acrylates 8a and 8c, where the major diastereomers
of tetrahydro-4-silaisochromanones 9a,c constituted 68%
and 71%, respectively, of the product mixtures.
Intramolecular Diels؊Alder Reactions
The DA reactions of silatrienes 8a؊g and 6c were per-
formed under thermal conditions or by adding a Lewis acid
catalyst. The thermal reaction involved heating 0.02  tolu-
ene solutions of the silatrienes at 140Ϫ220 °C. This led to
almost complete consumption of the starting material in
1Ϫ2 days. The catalyzed reactions were run at room tem-
perature in CH2Cl2 using 4 equivalents of EtAlCl2. The re-
sults are presented in Table 2. The DA reactions of silatri-
enes 8a؊g and 6c gave 4-methyl-4a,7,8,8a-tetrahydro-4-si-
laisochroman-1-ones 9a؊h in 23Ϫ56% yield as mixtures of
four diastereomers (Scheme 4). The diastereomeric ratios
1
were determined by H NMR spectroscopy through integ-
ration of the CH3Si singlets. The EtAlCl2-catalyzed IMDA
of silatriene 8a gave a mixture of four diastereomers of the
tetrahydro-4-silaisochromanone 9a (23%), along with 41%
of the acid 10. Treatment of a CH2Cl2 solution of tetrahy-
dro-4-silaisochromanone 9a with EtAlCl2 at room temper-
ature for two days, followed by hydrolysis gave acid 10. This
result would seem to indicate that the acid 10, isolated after
treatment of the silatriene 8a with EtAlCl2, was formed by
reaction of the Lewis acid with the tetrahydro-4-silaisochro-
manone 9a.
Structure Elucidation
The reactions of all the silatrienes gave mixtures of the
four diastereomers of tetrahydro-4-silaisochroman-1-one 9,
which could not be separated by column chromatography,
except in the case of the diastereomeric alcohols 9h. The
major isomer and a mixture of the remaining 3 isomers
were resolved by preparative thin-layer chromatography.
1
Analysis of the H NMR spectra of the various mixtures
allowed us to determine the coupling constant JH4a-H8a
(Scheme 5). The two major isomers have JH4a-H8a Ͻ 7 Hz,
which is consistent with a cis configuration for these two
protons, while the other two isomers have JH4a-H8a ϭ 11 Hz,
indicating a trans configuration. The two major diastereo-
mers were thus formed through endo cyclization, while the
two minor diastereomers were formed through exo cycliza-
tion. This means that the endo cyclization is favored over
Scheme 4. DielsϪAlder reaction of silatrienes 8a؊g, 6c; reagents:
(a) DEAD, Ph3P, CH2CHCOOH; (b) DMAP, Et3N,
CH3O(O)CCHCHCOCl; (c) (iPr)3SiOTf, 2,6-dimethylpyridine; (d)
Ph3CCl, Et3N; (e) DEAD, Ph3P, (CH3)2CHCOOH
Eur. J. Org. Chem. 2000, 3039Ϫ3046
3041

P. J. Coelho, L. Blanco
FULL PAPER
the exo cyclization by a factor of 1.8, the diastereoselectivity
of the latter being rather low (9%).
Since the major diastereomers of tetrahydro-4-silaisoch-
romanone 9a,b,h have the same relative configuration, we
can suppose that they are formed through an endo trans-
ition state where the bulky silicon substituent, ROCH2, and
the dienophile are on opposite sides of the plane defined by
the diene (I). Further studies involving the use of more
bulky silicon substituents are currently in progress in our
laboratory and the results will be reported in due course.
Scheme 5
Experimental Section
Treatment of tetrahydro-4-silaisochromanone 9h with
isobutyryl chloride or phenylacetyl chloride in CH2Cl2 in
the presence of triethylamine gave tetrahydro-4-silaisochro-
manones 9a and 9b, respectively. 1H NMR analysis of these
products showed that the two major diastereomers had the
same configuration as the two major diastereomers ob-
tained in the cyclization of silatrienes 8a and 8b. Table 3
shows the endo/exo selectivity and the de of the endo cyc-
lization of silatrienes 6c, 8a, and 8b. The endo/exo stereo-
selectivity of the EtAlCl2-catalyzed IMDA reaction can be
seen to be superior to that obtained under thermal condi-
tions. The diastereoselectivity imposed by the chiral silicon
atom in the endo cyclization is also greater under EtAlCl2
catalysis. The diastereoselectivities observed in the cycliza-
tions of acrylates 8a,b, which have protected hydroxyl func-
tions, are higher than those achieved with the hydroxyme-
thylsilatriene 6c. However, this increase is rather slight,
probably because the silicon atom is too distant to exercise
a significant steric control.
General Remarks: 1H and 13C NMR spectra were recorded on
Bruker AC200 (200 MHz and 50.3 MHz, respectively) or Bruker
AC250 (250 MHz and 62.9 MHz, respectively) spectrometers. All
spectra were recorded from samples in CDCl3 solution. Chemical
shifts are given in ppm. Ϫ Mass spectra were obtained on a NER-
MAG R10Ϫ10 spectrometer using electron ionization at 70 eV. Ϫ
IR spectra were recorded on a PerkinϪElmer 682 spectrometer
(wavenumbers in cmϪ1). Ϫ The products were isolated by column
chromatography on silica gel (SDS 70Ϫ230 mesh). Ϫ TLC was
performed on 0.25 mm thick silica gel plates (Merck 60 F254). Ϫ
The enantiomeric excesses were determined by 1H NMR in the
presence of chiral Eu(hfc)3. Ϫ Chlorobis(chloromethyl)methylsil-
ane and lipase LCR were obtained from commercial sources
(ABCR and Sigma L1754, respectively).
(Z)-1-Chlorobuta-1,3-diene (2): NaOH (71.0 g, 1.78 mol), water
(105 mL), and Aliquat 336 (60 drops) were placed in a reaction
vessel equipped for distillation and maintained under reduced pres-
sure (10 Torr) at 50Ϫ60 °C. (E)-1,4-Dichlorobut-2-ene (1) (E/Z ϭ
97:3) (30 mL, 0.282 mol) was then added dropwise over a period
of 4 h. The diene collected in the collector flask, which was kept at
Ϫ78 °C, was then dried over Na2SO4 and redistilled to give 21.5 g
Table 3. endo/exo Selectivity and endo diastereoselectivity of the
IMDA
1
(86%) of 2 (Z/E ϭ 94:6). Ϫ Z-Isomer: H NMR: δ ϭ 5.32 (d, J ϭ
10.3 Hz, 1 H), 5.39 (dd, J ϭ 17.1, 0.9 Hz, 1 H), 6.04 (d, J ϭ 7.1 Hz,
1 H), 6.33 (dd, J ϭ 10.3, 6.1 Hz, 1 H), 6.77 (ddd, J ϭ 10.3, 10.3,
17.1 Hz, 1 H); E-Isomer: δ ϭ 5.15 (d, J ϭ 10.4 Hz, 1 H), 5.24 (d,
J ϭ 16.7 Hz, 1 H), 6.20 (m, 2 H), 6.48 (dd, J ϭ 10.5, 13 Hz, 1 H).
Silatriene
R1
endo/exo ratio
endo diastereoselectivity
Thermal Catalyzed Thermal
reaction reaction reaction
Catalyzed
reaction
(Buta-1,3-dienyl)bis(chloromethyl)methylsilane (3): A solution of
buta-1,3-dienylmagnesium chloride in THF was prepared as fol-
lows: magnesium turnings (5.00 g, 206 mmol) and zinc chloride
(1.50 g, 11.0 mmol) were placed in a reaction vessel under an argon
atmosphere and heated for 2Ϫ3 min with a flame. Once the flask
6c H
1.8:1
9
22
18
66
37
8a CH2COCHMe2 3.0:1
8b CH2COCH2Ph 4.0:1
4.6:1
8.1:1
The relative configurations of the tetrahydro-4-silaisoch- had cooled to room temperature, THF (7.0 mL) and dibromoe-
thane (0.300 mL) were added. After ethene evolution, the mixture
was diluted with THF (15 mL) and heated to 45Ϫ50 °C. A solution
of 1-chlorobuta-1,3-diene (2) (Z/E ϭ 94:6) (10 mL, 100 mmol) and
1,2-dibromoethane (0.800 mL) in THF (70 mL) was then added
dropwise over a period of 1.5 h so as to maintain a gentle reflux.
The reaction mixture was heated under reflux for a further 3 h and
then left overnight at room temperature without stirring. De-
cantation of the resulting suspension provided an orange 0.55 
solution of butadienylmagnesium chloride.
romanones 9a,b,h could be established by analysis of the
chemical shifts of the H8a protons. For tetrahydro-4-silai-
sochromanones 9h, the two major diastereomers have
δ(H8a) ϭ 3.05 and 3.07. Protection of the hydroxyl group
as an isobutyric ester did not have a significant effect on
these chemical shifts. However, the chemical shift of this
proton was greatly affected when the hydroxyl function was
protected as a phenylacetyl ester. While one of the diastere-
omers exhibits almost the same chemical shift as tetrahy-
dro-4-silaisochromanones 9h and 9a, δ(H8a) ϭ 3.02, in the
major diastereomer this signal is shifted upfield to δ(H8a) ϭ
2.79. The fact that only one diastereomer of tetrahydro-4-
silaisochromanone 9b was affected by the presence of the
phenylacetyl group indicates that in this diastereomer the
H8a proton and the aromatic ring are on the same side of
the molecule (III) (Scheme 5).
Chlorobis(chloromethyl)methylsilane (5.60 mL, 33.6 mmol) was
added dropwise to a stirred mixture of CuCN (220 mg, 2.40 mmol)
and the aforementioned solution of buta-1,3-dienylmagnesium
chloride in THF (80 mL, 44 mmol) under argon at 0 °C. The reac-
tion mixture was stirred overnight, then quenched with aqueous
NH4Cl, and the resulting mixture was extracted with n-hexane. The
combined organic extracts were dried over anhydrous Na2SO4.
After evaporation of the solvent, the crude product was purified by
3042
Eur. J. Org. Chem. 2000, 3039Ϫ3046

Intramolecular DielsϪAlder Reaction of Chiral Silatrienes
FULL PAPER
distillation under reduced pressure (0.05 Torr) to yield 5.180 g
(79%) of (buta-1,3-dienyl)bis(chloromethyl)methylsilane 3 (E/Z ϭ
1:2).
Celite and the filtrate was washed several times with diethyl ether.
After evaporation of the solvent, the products were separated by
silica gel column chromatography (n-hexane/Et2O).
Isomerization Reaction: A solution of butadienylsilane 3 (E/Z ϭ
1:2) (5.18 g, 26.5 mmol) and iodine (0.340 g, 1.34 mmol, 5%) in
benzene (100 mL) was refluxed for 3.5 h under argon. The reaction
was then quenched with aqueous Na2S2O3, the resulting mixture
was extracted with n-hexane, and the combined organic extracts
were dried over anhydrous Na2SO4. After evaporation of the solv-
ent, the crude product was purified by distillation under reduced
(E)-[Buta-1,3-dienyl(hydroxymethyl)methylsilyl]methyl Isobutyrate
˜
(6a): Yield 70%. Ϫ IR (neat): ν ϭ 3450, 1740, 1575, 1250 cmϪ1. Ϫ
1H NMR: δ ϭ 0.21 (s, 3 H), 1.17 (d, J ϭ 6.9 Hz, 6 H), 2.0 (br. s,
1 H), 2.58 (sept., J ϭ 6.9 Hz, 1 H), 3.48 (d, J ϭ 14 Hz) and 3.56
(d, J ϭ 14 Hz) [AB system, 2 H], 3.98 (s, 2 H), 5.22 (d, J ϭ 9.9 Hz,
1 H), 5.31 (d, J ϭ 17.1 Hz, 1 H), 5.79 (d, J ϭ 18.5 Hz, 1 H), 6.36
(ddd, J ϭ 10.0, 9.9, 17.1 Hz, 1 H), 6.69 (dd, J ϭ 10.0, 18.5 Hz, 1
H). Ϫ 13C NMR: δ ϭ Ϫ7.9, 19.0, 33.0, 52.7, 55.1, 119.4, 126.1,
139.2, 148.3, 178.1. Ϫ MS: m/z (%) ϭ 213 (3), 197 (91), 175 (90),
109 (59), 43 (100).
pressure (0.05 Torr) to yield 4.55 g (88%) of butadienylsilane 3
˜
(E/Z ϭ 97:3). Ϫ IR (neat): ν ϭ 1630, 1580, 1260 cmϪ1. Ϫ 1H
NMR: δ ϭ 0.36 (s, 3 H), 2.99 (s, 4 H), 5.27 (dd, J ϭ 10.1, 1.1 Hz,
1 H), 5.35 (dd, J ϭ 17.1, 1.1 Hz, 1 H), 5.85 (d, J ϭ 18.5 Hz, 1 H),
6.12 (dd, J ϭ 18.5, 10.2 Hz, 1 H), 6.39 (ddd, J ϭ 10.1, 10.2,
17.1 Hz, 1 H). Ϫ 13C NMR: δ ϭ Ϫ7.4, 27.1, 120.3, 124.9, 139.0,
149.1. Ϫ MS: m/z (%) ϭ 196 (6.7), 194 (9.5), 147 (28), 145 (87),
79 (100).
(E)-[Buta-1,3-dienyl(isobutyryloxymethyl)methylsilyl]methyl
˜
Isobutyrate (7a): Yield 7.5%. Ϫ IR (neat): ν ϭ 1750, 1580, 1265
1
cmϪ1. Ϫ H NMR: δ ϭ 0.24 (s, 3 H), 1.15 (d, J ϭ 6.9 Hz, 12 H),
2.55 (sept., J ϭ 6.9 Hz, 2 H), 3.92 (s, 4 H), 5.21 (d, J ϭ 9.9 Hz, 1
H), 5.29 (d, J ϭ 17.0 Hz, 1 H), 5.77 (d, J ϭ 18.5 Hz, 1 H), 6.35
(ddd, J ϭ 9.9, 9.9, 17.0 Hz, 1 H), 6.65 (dd, J ϭ 10.1, 18.5 Hz, 1
H). Ϫ 13C NMR: δ ϭ Ϫ7.3, 19.1, 34.0, 54.4, 119.7, 125.7, 139.2,
148.5, 177.7. Ϫ MS: m/z (%) ϭ 284 (1.79), 283 (7.05), 245 (29), 197
(100), 109 (29).
(E)-(Buta-1,3-dienyl)bis(hydroxymethyl)methylsilane (4): A mixture
of bis(chloromethyl)silane 3 (3.39 g, 17.4 mmol), potassium acetate
(4.0 g, 41 mmol), tetrabutylammonium bromide (170 mg,
0.530 mmol), and titanium oxide (680 mg, 8.51 mmol) was stirred
under argon at 80Ϫ90 °C for 3 h. Once the mixture had cooled to
room temperature, silica gel (10 g) and diethyl ether (10 mL) were Enzymatic Transesterification of Oximes 5b؊d with (E)-(Buta-1,3-
added. The resulting suspension was stirred for 5 min, then filtered,
and the collected solid was washed 10 times with diethyl ether.
After evaporation of the solvent from the combined filtrate and
washings, the crude product was purified by column chromato-
dienyl)bis(hydroxymethyl)methylsilane (4): A mixture of bis(hyd-
roxymethyl)silane (0.100 g, 0.633 mmol), oxime 5b؊d
(0.633 mmol), lipase LCR (300 mg), and diisopropyl ether (2 mL)
was kept at Ϫ20 °C. The reaction was monitored by TLC and was
terminated after complete consumption of the oxime or diol. The
suspension was then filtered through Celite and the collected solid
4
graphy (n-hexane/Et2O) to yield 3.37 g (80%) of (E)-[acetoxyme-
˜
thyl(buta-1,3-dienyl)methylsilyl]methyl acetate: Ϫ IR (neat): ν ϭ
1
1740, 1630, 1290, 1220 cmϪ1. Ϫ H NMR: δ ϭ 0.25 (s, 3 H), 2.06 was washed several times with diethyl ether. After evaporation of
(s, 6 H), 3.92 (s, 4 H), 5.24 (d, J ϭ 9.8 Hz, 1 H), 5.32 (dd, J ϭ the solvent from the combined filtrate and washings, the products,
16.8, 0.9 Hz, 1 H), 5.78 (d, J ϭ 18.5 Hz, 1 H), 6.38 (ddd, J ϭ 10.1,
monoesters 6b؊d and diesters 7b؊d, were separated by silica gel
9.8, 16.8 Hz, 1 H), 6.67 (dd, J ϭ 18.5, 10.1 Hz, 1 H). Ϫ 13C NMR: column chromatography (n-hexane/Et2O).
δ ϭ Ϫ7.0, 20.7, 54.4, 119.8, 125.6, 139.2, 148.6, 171.7. Ϫ MS: m/z
(E)-[Buta-1,3-dienyl(hydroxymethyl)methylsilyl]methyl Phenylacet-
(%) ϭ 228 (1.09), 227 (6.14), 189 (25), 169 (61), 109 (100). Ϫ
C11H18O4Si: calcd. C 54.52, H 7.49; found C 54.28, H 7.26.
˜
ate (6b): Yield 64%. Ϫ IR (neat): ν ϭ 3450, 1735, 1575, 1250 cmϪ1
.
Ϫ 1H NMR: δ ϭ 0.14 (s, 3 H), 1.6 (br. s, 1 H), 3.38 (d, J ϭ 13.8 Hz)
and 3.45 (d, J ϭ 13.8 Hz) [AB system, 2 H], 3.64 (s, 2 H), 4.00 (s,
2 H), 5.22 (d, J ϭ 9.8 Hz, 1 H), 5.29 (d, J ϭ 16.8 Hz, 1 H), 5.71
(d, J ϭ 18.5 Hz, 1 H), 6.32 (ddd, J ϭ 9.8, 10, 16.8 Hz, 1 H), 6.62
(dd, J ϭ 10, 18.5 Hz, 1 H), 7.20Ϫ7.40 (m, 5 H). Ϫ MS: m/z (%) ϭ
262 (0.44), 261 (2.88), 246 (22), 245 (100), 223 (8), 109 (50), 91 (93).
In the next step, a 1  LiAlH4 solution in diethyl ether (37 mL,
37 mmol) was added dropwise to a stirred solution of (E)-[acetoxy-
methyl(buta-1,3-dienyl)methylsilyl]methyl acetate (3.34 g, 13.8
mmol) in diethyl ether at Ϫ20 °C. The resulting suspension was
stirred for 30 min at room temperature, then hydrated Na2SO4
(2Ϫ3 g) was slowly added in small portions (violent reaction!) fol-
lowed by water (10 mL). After decantation, the aqueous phase was
extracted 4 times with diethyl ether. The combined organic extracts
were dried over Na2SO4, and then the solvent was removed under
(E)-[(Buta-1,3-dienyl)methyl(phenylacetoxymethyl)silyl]methyl
˜
Phenylacetate (7b): Yield 12%. Ϫ IR (neat): ν ϭ 1735, 1605, 1575,
1
1235 cmϪ1. Ϫ H NMR: δ ϭ 0.11 (s, 3 H), 3.60 (s, 4 H), 3.88 (s, 4
H), 5.22 (d, J ϭ 9.8 Hz, 1 H), 5.27 (d, J ϭ 16.8 Hz, 1 H), 5.63 (d,
J ϭ 18.5 Hz, 1 H), 6.30 (ddd, J ϭ 9.8, 10.0, 16.8 Hz, 1 H), 6.54
(dd, J ϭ 10.0, 18.5 Hz, 1 H), 7.2Ϫ7.4 (m, 10 H). Ϫ 13C NMR: δ ϭ
Ϫ7.5, 41.3, 54.9, 119.8, 125.3, 127.1, 128.5, 129.2, 134.0, 139.1,
148.6, 172.1. Ϫ MS: m/z (%) ϭ 379 (7.2), 342 (5), 341 (18), 245
(100), 109 (21), 91 (60).
reduced pressure to leave the pure bis(hydroxymethyl)silane 4
˜
(2.09 g, 96%). Ϫ IR (neat): ν ϭ 3450, 1575, 1265 cmϪ1. Ϫ 1H
NMR: δ ϭ 0.23 (s, 3 H), 1.81 (br. s, 2 H), 3.72 (d, J ϭ 13.9 Hz)
and 3.63 (d, J ϭ 13.9 Hz, AB system, 4 H], 5.22 (d, J ϭ 9.8 Hz, 1
H), 5.31 (d, J ϭ 16.8 Hz, 1 H), 5.84 (d, J ϭ 18.5 Hz, 1 H), 6.38
(ddd, J ϭ 9.8, 10.1, 16.8 Hz, 1 H), 6.72 (dd, J ϭ 18.5, 10.1 Hz, 1
H). Ϫ 13C NMR: δ ϭ Ϫ7.9, 54.5, 119.3, 126.8, 139.3, 148.2. Ϫ
MS: m/z (%) ϭ 143 (0.88), 127 (22), 109 (21), 61 (100). Ϫ
C7H14O2Si: calcd. C 53.12, H 8.92; found C 53.01, H 8.95.
(E)-[Buta-1,3-dienyl(hydroxymethyl)methylsilyl]methyl
Acrylate
˜
(6c): Yield 71%. Ϫ IR (neat): ν ϭ 3420, 1730, 1575, 1255 cmϪ1. Ϫ
1H NMR: δ ϭ 0.24 (s, 3 H), 1.6 (br. s, 1 H), 3.57 (d, J ϭ 14 Hz)
and 3.50 (d, J ϭ 14 Hz) [AB system, 2 H], 4.08 (s, 2 H), 5.23 (d,
J ϭ 9.7 Hz, 1 H), 5.32 (d, J ϭ 17.3 Hz, 1 H), 5.81 (d, J ϭ 18.5 Hz,
1 H), 5.85 (dd, J ϭ 10.3, 1.1 Hz, 1 H), 6.15 (dd, J ϭ 10.3, 17.1 Hz,
1 H), 6.35 (ddd, J ϭ 9.8, 10.0, 17.3 Hz) and 6.40 (dd, J ϭ 1.1,
17.1 Hz) (2 H), 6.70 (dd, J ϭ 9.8, 18.5 Hz, 1 H). Ϫ 13C NMR: δ ϭ
Ϫ8.1, 52.3, 55.1, 119.2, 126.0, 127.9, 130.6, 139.1, 148.1, 167.1. Ϫ
Enzymatic Transesterification of Methyl Isobutyrate with (E)-(Buta-
1,3-dienyl)bis(hydroxymethyl)methylsilane (4):
A mixture of 4
(0.318 g, 2.00 mmol), methyl isobutyrate (3 mL), and lipase LCR
(1.2 g) was kept at Ϫ20 °C for 5 days. The reaction was monitored
by TLC and was terminated when the amounts of the diester and
diol were approximately equal. The suspension was filtered through
Eur. J. Org. Chem. 2000, 3039Ϫ3046
3043

P. J. Coelho, L. Blanco
FULL PAPER
MS: m/z (%) ϭ 198 (0.49), 197 (3.41), 182 (17), 181 (100), 159 (12),
(E)-[(Buta-1,3-dienyl)methyl(triphenylmethoxymethyl)methylsilyl]-
109 (62).
methyl Acrylate (8d): A mixture of triethylamine (200 µL,
143 mmol), hydroxymethylsilane 6c (200 mg, 0.943 mmol), triphen-
ylmethyl chloride (316 mg, 1.13 mmol), and CH2Cl2 (20 mL) was
stirred under argon. After 2 days at room temperature, the reaction
was quenched with saturated aqueous NH4Cl and the resulting
mixture was extracted with CH2Cl2. The combined organic extracts
were dried over anhydrous Na2SO4, concentrated, and the residue
was purified by column chromatography (n-hexane/Et2O) to yield
(E)-[(Acryloxymethyl)(buta-1,3-dienyl)methylsilyl]methyl Acrylate
˜
(7c): Yield 8.5%. Ϫ IR (neat): ν ϭ 1735, 1645, 1260 cmϪ1. Ϫ H
NMR: δ ϭ 0.28 (s, 3 H), 4.04 (s, 4 H), 5.24 (d, J ϭ 10.0 Hz, 1 H),
5.31 (d, J ϭ 17.3 Hz, 1 H), 5.75Ϫ5.90 (m, 2 H), 6.13 (dd, J ϭ 10.3,
16.9 Hz, 1 H), 6.38 (ddd, J ϭ 10.0, 10.1, 17.3 Hz) and 6.40 (dd,
J ϭ 16.9, 1.7 Hz) (2 H), 6.69 (dd, J ϭ 10.1, 18.5 Hz, 1 H). Ϫ 13C
NMR: δ ϭ Ϫ7.3, 54.6, 119.8, 125.3, 128.1, 130.5, 139.1, 148.7,
166.8. Ϫ MS: m/z (%) ϭ 252 (1.06), 251 (6.16), 213 (24), 181 (100),
109 (67). Ϫ C13H18O4Si: calcd. C 58.62, H 6.81; found C 58.63,
H 6.88.
1
˜
1
8d (415 mg, 97%). Ϫ IR (neat): ν ϭ 1735, 1260, 1185 cmϪ1. Ϫ H
NMR: δ ϭ 0.27 (s, 3 H), 2.87 (s, 2 H), 4.08 (s, 2 H), 5.20 (d, J ϭ
10.0 Hz, 1 H), 5.26 (d, J ϭ 17.0 Hz, 1 H), 5.79 (dd, J ϭ 10.3,
1.6 Hz, 1 H), 5.84 (d, J ϭ 18.5 Hz, 1 H), 6.11 (dd, J ϭ 10.3,
17.2 Hz, 1 H), 6.36 (dd, J ϭ 1.6, 17.2 Hz) and 6.37 (ddd, J ϭ 10,
10, 17.0 Hz, 2 H), 6.64 (dd, J ϭ 9.9, 18.5 Hz, 1 H), 7.45Ϫ7.20 (m,
15 H). Ϫ 13C NMR: δ ϭ Ϫ7.1, 52.7, 55.5, 88.5, 119.1, 126.6, 128.3,
130.2, 139.2, 120.8, 127.6, 128.8, 143.7, 148.1, 167.4. Ϫ MS: m/z
(%) ϭ 244 (29), 243 (100), 181 (91), 166 (20), 165 (97), 109 (20). Ϫ
CI-MS (NH3): m/z (%) ϭ 244 (63), 243 (100), 181 (6).
(E)-[Buta-1,3-dienyl(hydroxymethyl)methylsilyl]methyl Methacryl-
˜
ate (6d): Yield 79%. Ϫ IR (neat): ν ϭ 3500, 1735, 1645, 1200 cmϪ1
.
1
Ϫ H NMR: δ ϭ 0.24 (s, 3 H), 1.6 (br. s, 1 H), 1.95 (s, 3 H), 3.57
(d, J ϭ 14 Hz) and 3.50 (d, J ϭ 14 Hz) [AB system, 2 H], 4.06 (s,
2 H), 5.23 (d, J ϭ 10.0 Hz, 1 H), 5.31 (d, J ϭ 17.2 Hz, 1 H),
5.54Ϫ5.60 (m, 1 H), 5.81 (d, J ϭ 18.5 Hz, 1 H), 6.11 (s, 1 H), 6.37
(ddd, J ϭ 10.0, 10.1, 17.2 Hz, 1 H), 6.70 (dd, J ϭ 10.1, 18.5 Hz, 1
H). Ϫ 13C NMR: δ ϭ Ϫ7.9, 16.3, 52.7, 55.4, 119.4, 125.6, 126.1,
136.1, 139.1, 148.4, 168.4. Ϫ MS: m/z (%) ϭ 196 (15), 195 (83),
173 (12), 109 (56), 41 (100).
(E)-[Buta-1,3-dienyl(isobutyryloxymethyl)methylsilyl]methyl
Methacrylate (8e) : Diethyl azodicarboxylate (DEAD) (105 µL,
0.660 mmol) was added dropwise to a stirred solution of (hydroxy-
methyl)silane 6d (0.439 mmol), triphenylphosphane (0.660 mmol),
and isobutyric acid (0.527 mmol) in THF (20 mL) at Ϫ78 °C under
argon. The reaction mixture was stirred for 20 min at room temper-
ature. After evaporation of the solvent, the crude product was puri-
fied by chromatography (n-hexane/Et2O). Yield: 74%. Ϫ IR (neat):
(E)-[Buta-1,3-dienyl(methacryloxymethyl)methylsilyl]methyl
˜
Methacrylate (7d): Yield: 10%. Ϫ IR (neat): ν ϭ 1730, 1645, 1260
1
cmϪ1. Ϫ H NMR: δ ϭ 0.29 (s, 3 H), 1.94 (s, 6 H), 4.01 (s, 4 H),
˜
1
ν ϭ 1735, 1670, 1240 cmϪ1. Ϫ H NMR: δ ϭ 0.27 (s, 3 H), 1.15
5.23 (d, J ϭ 10.0 Hz, 1 H), 5.31 (d, J ϭ 17.0 Hz, 1 H), 5.52Ϫ5.58
(m, 2 H), 5.81 (d, J ϭ 18.5 Hz, 1 H), 6.08 (s, 2 H), 6.37 (ddd, J ϭ
10.0, 10.0, 17.0 Hz, 1 H), 6.67 (dd, J ϭ 10.0, 18.5 Hz, 1 H). Ϫ 13C
NMR: δ ϭ Ϫ7.2, 18.4, 54.7, 119.8, 125.4, 125.5, 136.2, 139.2,
148.7, 168.1. Ϫ MS: m/z (%) ϭ 279 (7.6), 241 (26), 195 (93), 109
(40), 69 (100). Ϫ C15H22O4Si: calcd. C 61.19, H 7.53; found C
61.11, H 7.42.
(d, J ϭ 7.0 Hz, 6 H), 1.94 (d, J ϭ 1.5 Hz, 3 H), 2.55 (sept., J ϭ
7.0 Hz, 1 H), 3.94 (s, 2 H), 4.00 (s, 2 H), 5.22 (d, J ϭ 9.7 Hz, 1 H),
5.30 (d, J ϭ 16.9 Hz, 1 H), 5.52Ϫ5.58 (m, 1 H), 5.78 (d, J ϭ
18.6 Hz, 1 H), 6.09 (d, J ϭ 1.5 Hz, 1 H), 6.37 (ddd, J ϭ 9.7, 9.9,
16.9 Hz, 1 H), 6.67 (dd, J ϭ 9.9, 18.6 Hz, 1 H). Ϫ 13C NMR: δ ϭ
Ϫ7.3, 18.3, 19.0, 33.9, 54.3, 54.6, 119.6, 125.2, 125.5, 136.6, 139.1,
148.5, 168.0, 177.5. Ϫ MS: m/z (%) ϭ 281 (12.8), 243 (64), 197
(100), 195 (95), 109 (64). Ϫ C15H24O4Si: calcd. C 60.78, H 8.16;
found C 60.56, H 8.27.
Synthesis of Silatrienes 8a,b: Diethyl azodicarboxylate (DEAD)
(105 µL, 0.660 mmol) was added dropwise to a stirred solution of
(hydroxymethyl)silane 6a,b (0.439 mmol), triphenylphosphane
(0.660 mmol), and acrylic acid (0.527 mmol) in THF (20 mL) at
Ϫ78 °C under argon. The reaction mixture was stirred for 20 min
(E)-[Buta-1,3-dienyl(isobutyryloxymethyl)methylsilyl]methyl
Methyl Fumarate (8g): 3-(Methoxycarbonyl)acryloyl chloride
at room temperature. After evaporation of the solvent, the crude (0.56 mmol) was added dropwise to a stirred solution of (hydroxy-
product was purified by chromatography (n-hexane/Et2O).
methyl)silane 6a (0.37 mmol), triethylamine (0.56 mmol), and
DMAP (10 mg) in CH2Cl2 (10 mL) at 0 °C under argon. The reac-
tion mixture was stirred for 30 min at room temperature, then
quenched with saturated aqueous NH4Cl and the resulting mixture
was extracted with CH2Cl2. The combined organic extracts were
dried over anhydrous Na2SO4. After evaporation of the solvent, the
(E)-[Buta-1,3-dienyl(isobutyryloxymethyl)methylsilyl]methyl
˜
Acrylate (8a): Yield 73%. Ϫ IR (neat): ν ϭ 1730, 1640, 1250 cmϪ1
.
Ϫ
1H NMR: δ ϭ 0.27 (s, 3 H), 1.16 (d, J ϭ 7.0 Hz, 6 H), 2.56
(sept., J ϭ 7.0 Hz, 1 H), 3.93 (s, 2 H), 4.02 (s, 2 H), 5.23 (d, J ϭ
10.0 Hz, 1 H), 5.30 (d, J ϭ 17.3 Hz, 1 H), 5.79 (d, J ϭ 18.5 Hz, 1
H), 5.83 (dd, J ϭ 10.2, 1.6 Hz, 1 H), 6.13 (dd, J ϭ 10.2, 17.3 Hz,
1 H), 6.37 (ddd, J ϭ 10, 10, 17.3 Hz, 1 H), 6.40 (dd, J ϭ 1.6,
17.3 Hz, 2 H), 6.67 (dd, J ϭ 18.5, 10.0 Hz. 1 H). Ϫ 13C NMR: δ ϭ
Ϫ7.3, 19.0, 33.9, 54.3, 54.7, 119.7, 125.5, 128.2, 130.5, 139.1, 148.6,
166.1, 177.6. Ϫ MS: m/z (%) ϭ 267 (13), 230 (24), 229 (65), 198
(31), 197 (91), 182 (36), 181 (100), 110 (20), 109 (71).
crude product was purified by column chromatography (n-hexane/
˜
Et2O) to give 8g (88 mg, 70%). Ϫ IR (neat): ν ϭ 1740, 1280 cmϪ1
Ϫ
.
1H NMR: δ ϭ 0.27 (s, 3 H), 1.16 (d, J ϭ 7.0 Hz, 6 H), 2.56
(sept., J ϭ 7.0 Hz, 1 H), 3.82 (s, 3 H), 3.92 (s, 2 H), 4.08 (s, 2 H),
5.24 (d, J ϭ 10.0 Hz, 1 H), 5.32 (d, J ϭ 17.3 Hz, 1 H), 5.76 (d, J ϭ
18.5 Hz, 1 H), 6.37 (ddd, J ϭ 10.0, 10.0, 17.3 Hz, 1 H), 6.67 (dd,
J ϭ 18.5, 10.0 Hz, 1 H), 6.86 (s, 2 H). Ϫ 13C NMR: δ ϭ Ϫ7.4,
19.0, 33.9, 52.2, 54.2, 55.7, 119.9, 125.0, 133.1, 133.9, 139.0, 149.0,
165.3, 165.4, 177.5. Ϫ MS: m/z (%) ϭ 282 (19.7), 287 (100), 239
(9), 199 (29), 197 (16), 189 (23). Ϫ C16H24O6Si: calcd. C 56.45, H
7.11; found C 56.41, H 7.29.
(E)-[(Buta-1,3-dienyl)methyl(phenylacetoxymethyl)silyl]methyl
˜
Acrylate (8b): Yield 85%. Ϫ IR (neat): ν ϭ 1735, 1265 cmϪ1. Ϫ 1H
NMR: δ ϭ 0.20 (s, 3 H), 3.62 (s, 2 H), 3.96 (s, 4 H), 5.23 (d, J ϭ
10.2 Hz, 1 H), 5.29 (d, J ϭ 17.0 Hz, 1 H), 5.72 (d, J ϭ 18.6 Hz, 1
H), 5.82 (dd, J ϭ 1.5, 10.3 Hz, 1 H), 6.11 (dd, J ϭ 10.3, 17.3 Hz,
1 H), 6.33 (ddd, J ϭ 10.0, 10.2, 17.0 Hz, 1 H), 6.39 (dd, J ϭ 1.5,
Synthesis of Silatrienes 8c,f: Triisopropylsilyl trifluoromethanesul-
fonate (405 µL, 1.5 mmol) was added to a solution of (hydroxyme-
17.3 Hz, 1 H), 6.61 (dd, J ϭ 10.0, 18.6 Hz, 1 H), 7.40Ϫ7.20 (m, 5 thyl)silane 6a (1.0 mmol) and 2,6-dimethylpyridine (240 µL,
H). Ϫ MS: m/z (%) ϭ 316 (3.14), 315 (4.31), 277 (38), 245 (18),
182 (24), 181 (75), 109 (21), 91 (96), 55 (100).
2.0 mmol) in CH2Cl2 (20 mL) under argon. After stirring for
15 min, the reaction was quenched with saturated aqueous
3044
Eur. J. Org. Chem. 2000, 3039Ϫ3046

Intramolecular DielsϪAlder Reaction of Chiral Silatrienes
FULL PAPER
NaHCO3 and the resulting mixture was extracted with CH2Cl2.
The combined organic extracts were dried over anhydrous Na2SO4,
concentrated, and the product was purified by column chromato-
graphy (n-hexane/Et2O).
H), 1.75Ϫ2.60 (m, 5.21 H), 2.78 (ddd, J ϭ 12, 12, 2 Hz, 0.13 H),
2.97Ϫ3.13 (m, 0.66 H), 3.50Ϫ3.65 (m, 2 H), [3.88 (d, J ϭ 15.3 Hz)
and 4.23 (d, J ϭ 15.3 Hz) (AB system); 3.98 (d, J ϭ 15.3 Hz) and
4.26 (d, J ϭ 15.3 Hz) (AB system); 4.06 (d, J ϭ 15.3 Hz) and 4.18
(d, J ϭ 15.3 Hz) (AB system); 4.10 (d, J ϭ 15.3 Hz) and 4.24 (d,
J ϭ 15.3 Hz) (AB system)] (2 H), 5.55Ϫ5.75 (m, 2 H). Ϫ 13C NMR:
δ ϭ Ϫ8.6, Ϫ6.7, 11.7, 17.7, 18.0, 20.1, 22.5, 24.0, 24.1, 39.2, 39.0,
51.8, 53.2, 58.7, 123.1, 124.0, 125.8, 175.7. Ϫ MS: m/z (%) ϭ 370
(9), 369 (24), 368 (18), 326 (11), 325 (12), 147 (50), 133 (23), 119
(100). Ϫ C19H36O3Si2: calcd. C 61.98, H 9.78; found C 62.17, H
9.86.
(E)-[(Buta-1,3-dienyl)methyl(triisopropylsilyloxymethyl)silyl]-
˜
methyl Acrylate (8c): Yield 94%. Ϫ IR (neat): ν ϭ 1740, 1255 cmϪ1
.
Ϫ 1H NMR: δ ϭ 0.22 (s, 3 H), 1.15Ϫ1.00 (m, 21 H), 3.58 (s, 2 H),
4.03 (s, 2 H), 5.19 (d, J ϭ 10.0 Hz, 1 H), 5.27 (d, J ϭ 16.8 Hz, 1
H), 5.80 (dd, J ϭ 10.2, 1.8 Hz, 1 H), 5.82 (d, J ϭ 18.6 Hz, 1 H),
6.13 (dd, J ϭ 10.2, 17.2 Hz, 1 H), 6.37 (ddd, J ϭ 10.0, 10.0,
16.8 Hz, 1 H), 6.38 (dd, J ϭ 17.2, 1.8 Hz, 1 H), 6.70 (dd, J ϭ 10.0,
18.6 Hz, 1 H). Ϫ 13C NMR: δ ϭ Ϫ7.8, 11.8, 18.0, 53.5, 54.7, 118.9,
127.1, 128.5, 130.2, 139.5, 147.0, 167.0. Ϫ MS: m/z (%) ϭ 326
(0.88), 325 (1.91), 315 (2), 181 (100), 109 (13). Ϫ C19H36O3Si2:
calcd. C 61.90, H 9.84; found C 62.08, H 10.03.
4-Methyl-4-(triphenylmethoxymethyl)-4a,7,8,8a-tetrahydro-4-sila-
˜
isochroman-1-one (9d): IR (neat): ν ϭ 1750, 1650, 1500, 1260 cmϪ1
.
1
Ϫ H NMR: δ ϭ 0.21, 0.25, 0.31, and 0.37 (4 s, 3 H), 1.60Ϫ2.50
(m, 5 H), 2.75Ϫ3.12 (m, 3 H), [3.41 (d, J ϭ 15.3 Hz) and 4.25 (d,
J ϭ 15.3 Hz) (AB system); 4.02 (d, J ϭ 15.3 Hz) and 4.22 (d, J ϭ
15.3 Hz) (AB system); 4.08 (d, J ϭ 15.3 Hz) and 4.18 (d, J ϭ
15.3 Hz) (AB system)] (2 H), 5.50Ϫ5.80 (m, 2 H), 7.15Ϫ7.48 (m,
15 H). Ϫ 13C NMR: δ ϭ Ϫ9.6, Ϫ8.1, Ϫ6.5, Ϫ6.0, 15.2, 20.3, 22.4,
22.6, 22.9, 23.7, 24.0, 24.2, 24.7, 38.5, 39.0, 39.2, 51.0, 52.2, 52.3,
58.7, 58.9, 59.0, 88.4, 123.1, 123.7, 123.9, 125.5, 125.9, 126.6, 127.0,
127.7, 127.8, 128.7, 175.5, 176.4, 176.6. Ϫ MS: m/z (%) ϭ 244 (24),
243 (100), 165 (100), 79 (13), 77 (14). Ϫ C29H30O3Si: calcd. C 76.61,
H 6.65; found C 76.36, H 6.85.
(E)-[Buta-1,3-dienyl(triisopropylsilyloxymethyl)methylsilyl]methyl
˜
Methacrylate (8f): Yield 86%. Ϫ IR (neat): ν ϭ 1735, 1650, 1260
1
cmϪ1. Ϫ H NMR: δ ϭ 0.23 (s, 3 H), 1.15Ϫ1.00 (m, 21 H), 1.94
(d, J ϭ 1.1 Hz, 3 H), 3.58 (s, 2 H), 4.01 (s, 2 H), 5.18 (d, J ϭ
9.9 Hz, 1 H), 5.27 (d, J ϭ 16.8 Hz, 1 H), 5.50Ϫ5.56 (m, 1 H), 5.84
(d, J ϭ 18.5 Hz, 1 H), 6.08 (br. s, 1 H), 6.36 (ddd, J ϭ 9.9, 9.9,
16.8 Hz, 1 H), 6.70 (dd, J ϭ 9.9, 18.5 Hz, 1 H). Ϫ 13C NMR: δ ϭ
Ϫ7.8, 11.8, 18.0, 18.4, 53.5, 54.6, 118.8, 125.0, 127.1, 136.4, 139.5,
147.9, 168.1. Ϫ MS: m/z (%) ϭ 340 (0.95), 339 (2.94), 329 (0.8),
195 (100).
(4,8a-Dimethyl-1-oxo-4a,7,8,8a-tetrahydro-4-silaisochroman-4-yl)-
˜
methyl Isobutanoate (9e): IR (solution in CCl4): ν ϭ 1740, 1260
Intramolecular Diels؊Alder Reaction
cmϪ1. Ϫ 1H NMR: δ ϭ 0.17, 0.23, 0.26, and 0.32 (4 s, 3 H),
1.10Ϫ1.20 (m, 6 H), 1.26, 1.30, 1.37, and 1.39 (4 s, 3 H), 1.45Ϫ1.55
(m, 1 H), 1.83Ϫ1.85 (m, 1 H), 2.00Ϫ2.30 (m, 3 H), 2.49Ϫ2.68 (m,
1 H), 3.65Ϫ4.10 (m, 2 H), 4.10Ϫ4.45 (m, 2 H), 5.50Ϫ5.80 (m, 2
H). Ϫ 13C NMR: δ ϭ Ϫ7.0, Ϫ5.2, 19.0, 21.7, 21.9, 25.1, 25.2, 28.4,
30.2, 31.5, 31.7, 33.8, 33.8, 42.1, 53.9, 55.7, 59.7, 60.0, 123.5, 124.3,
124.6, 125.0, 177.1, 177.2, 177.9, 178.2. Ϫ MS: m/z (%) ϭ 296 (4),
281 (3), 253 (4), 230 (25), 229 (62), 161 (37), 159 (51), 158 (100),
143 (40).
Thermal Reaction: The silatriene (0.40 mmol), phenothiazine
(2 mg), and toluene (20 mL) were placed in a degassed vial, which
was sealed and heated for 1Ϫ2 days (see Table 2). The vial was then
opened, the solvent was evaporated, and the residue was purified
by silica gel column chromatography (n-hexane/Et2O).
Lewis Acid Catalyzed Reaction: A 1  EtAlCl2 solution in CH2Cl2
(4 mL, 4.0 mmol) was added to a solution of silatriene 8 (1.0 mmol)
in CH2Cl2 (20 mL) under argon. After complete consumption of
the silatriene (TLC), the reaction was quenched with saturated
aqueous NH4Cl and the resulting mixture was extracted with
CH2Cl2. The combined organic extracts were dried over anhydrous
Na2SO4, concentrated, and the residue was purified by silica gel
column chromatography (n-hexane/Et2O).
4,8a-Dimethyl-4-(triisopropylsilyloxymethyl)-4a,7,8,8a-tetrahydro-4-
˜
silaisochroman-1-one (9f): IR (neat): ν ϭ 1740, 1270 cmϪ1. Ϫ 1H
NMR: δ ϭ 0.21, 0.23, 0.34, and 0.36 (4 s, 3 H), 0.90Ϫ1.20 (m, 21
H), 1.32, 1.33, 1.41, and 1.42 (4 s, 3 H), 1.43Ϫ1.60 (m, 1 H),
1.92Ϫ2.00 and 2.00Ϫ2.08 (2 m, 1 H), 2.10Ϫ2.45 (m, 3 H),
3.45Ϫ3.60 (m, 2 H), 4.05Ϫ4.35 (m, 2 H), 5.50Ϫ5.75 (m, 2 H). Ϫ
13C NMR: δ ϭ Ϫ5.6 and Ϫ7.6, 11.7, 15.3, 17.7, 18.0, 21.7, 22.0,
25.3, 27.4, 30.2, 31.6, 32.1, 42.1, 53.5 and 52.7, 59.2 and 59.3, 124.0,
124.9, 124.9, 126.8, 127.7, 128.9, 177.6. Ϫ MS: m/z (%) ϭ 384
(2.87), 383 (6.22), 362 (7.76), 368 (15.8), 367 (23), 340 (1.44), 339
(2.6), 147 (40), 133 (42), 131 (25), 119 (100).
(4-Methyl-1-oxo-4a,7,8,8a-tetrahydro-4-silaisochroman-4-yl)methyl
˜
Isobutanoate (9a): IR (neat): ν ϭ 1735, 1650, 1255 cmϪ1. Ϫ 1H
NMR: δ ϭ 0.18, 0.23, 0.30, and 0.35 (4 s, 3 H), 1.10Ϫ1.30 (m, 6
H), 1.5Ϫ2.5 (m, 5 H), 2.54 (sept., J ϭ 7.0 Hz, 1 H), 2.98Ϫ3.12 (m,
1 H), 3.70Ϫ4.30 (m, 4 H), 5.50Ϫ5.80 (m, 2 H). Ϫ 13C NMR: δ ϭ
Ϫ9.3, Ϫ8.0, Ϫ7.3, Ϫ6.2, 15.2, 18.0, 19.0, 21.1, 22.6, 23.0, 23.2, 24.0,
24.3, 33.8, 30.7, 39.3, 43.6, 53.6, 54.4, 54.9, 55.0, 59.6, 60.1, 122.1,
123.6, 123.2, 126.1, 127.1, 130.1, 175.5, 176.9, 178.3. Ϫ MS: m/z
(%) ϭ 284 (2.06), 283 (6.76), 282 (26), 281 (22), 267 (8), 175 (19),
161 (19), 158 (19), 143 (27), 43 (100).
(8-Methoxycarbonyl-4-methyl-1-oxo-4a,7,8,8a-tetrahydro-4-silaiso-
˜
chroman-4-yl)methyl Isobutanoate (9g): IR (neat): ν ϭ 1740, 1265
cmϪ1. Ϫ 1H NMR: δ ϭ 0.16, 0.20, 0.23, and 0.33 (4 s, 3 H),
1.10Ϫ1.23 (m, 6 H), 1.77Ϫ2.95 (m, 4.35 H), 3.20Ϫ3.30 (m, 0.80
H), 3.35Ϫ3.45 (m, 0.85 H), 3.72 and 3.73 (2 s, 3 H), 3.75Ϫ4.32 (m,
4 H), 5.55Ϫ5.75 (m, 2 H). Ϫ 13C NMR: δ ϭ Ϫ9.3, Ϫ8.6, Ϫ6.6,
14.5, 18.2, 19.0, 20.2, 22.7, 23.4, 23.6, 28.5, 33.7, 33.8, 39.0, 39.5,
40.6, 40.7, 52.1, 52.2, 52.8, 54.7, 59.1, 59.5, 60.4, 122.5, 123.2,
124.0, 124.8, 173.8, 174.1, 176.8, 178.0, 178.2. Ϫ MS: m/z (%) ϭ
345 (1.44), 340 (3.25), 325 (2), 309 (2), 281 (55), 175 (26), 43 (100).
Ϫ C16H24O6Si: calcd. C 56.45, H 7.11; found C 56.24, H 7.29.
(4-Methyl-1-oxo-4a,7,8,8a-tetrahydro-4-silaisochroman-4-yl)methyl
1
Phenylacetate (9b): H NMR: δ ϭ 0.10, 0.16, 0.21, and 0.28 (4 s, 3
H), 2.5Ϫ1.5 (m, 5 H), 2.79 (ddd, J ϭ 3, 7, 7 Hz, 0.6 H), 3.02 (ddd,
J ϭ 4, 7, 7 Hz, 0.4 H), 3.55Ϫ3.70 (m, 2 H), 3.80Ϫ4.20 (m, 4 H),
5.40Ϫ5.80 (m, 2 H), 7.20Ϫ7.40 (m, 5 H). Ϫ 13C NMR: δ ϭ Ϫ8.3.
Ϫ6.4, 20.5, 22.2, 22.6, 22.8, 23.9, 39.2, 38.6, 41.2, 53.5, 55.3, 59.1,
122.7, 123.2, 126.3, 127.3, 128.7, 129.1, 133.7, 172.5, 175.3.
4-(Hydroxymethyl)-4-methyl-4a,7,8,8a-tetrahydro-4-silaisochroman-
˜
4-Methyl-4-(triisopropylsilyloxymethyl)-4a,7,8,8a-tetrahydro-4-sila-
1-one (9h): IR (solution in CCl4): ν ϭ 3640, 3450, 1750, 1265 cmϪ1
.
˜
isochroman-1-one (9c): IR (neat): ν ϭ 1740, 1650, 1255 cmϪ1. Ϫ 1H
Ϫ H NMR: δ ϭ 0.20, 0.23, 0.32, and 0.33 (4 s, 3 H), 1.40Ϫ2.40
1
NMR: δ ϭ 0.09, 0.12, 0.30, and 0.32 (4 s, 3 H), 0.95Ϫ1.20 (m, 21 (m, 5 H), 2.52 (ddd, J ϭ 12, 12, 2 Hz, 0.24 H), 2.75 (ddd, J ϭ 12,
Eur. J. Org. Chem. 2000, 3039Ϫ3046 3045

P. J. Coelho, L. Blanco
FULL PAPER
J. Am. Chem. Soc. 1986, 108, 6826Ϫ6828. Ϫ [2d] G. Stork, Bull.
12, 2 Hz, 0.14 H), 3.01Ϫ3.13 (m, 0.62 H), 3.65Ϫ3.50 (m, 2 H),
[3.92 (d, J ϭ 15.3 Hz) and 4.28 (d, J ϭ 15.3 Hz) (AB system); 4.03
(d, J ϭ 15.3 Hz) and 4.30 (d, J ϭ 15.3 Hz) (AB system); 4.08 (d,
J ϭ 15.3 Hz) and 4.20 (d, J ϭ 15.3 Hz) (AB system); 4.11 (d, J ϭ
15.3 Hz) and 4.23 (d, J ϭ 15.3 Hz) (AB system)] (2 H), 5.85Ϫ5.50
(m, 2 H). Ϫ 13C NMR: δ ϭ Ϫ10.2, Ϫ8.7, Ϫ6.8, 15.5, 19.9, 22.2,
22.5, 22.8, 23.7, 23.9, 24.0, 24.3, 24.3, 24.7, 38.7, 39.0, 39.2, 39.3,
51.3, 51.4, 52.3, 52.4, 58.5, 58.6, 58.7, 59.0, 123.0, 123.7, 123.2,
123.9, 125.9, 126.2, 126.8, 127.3, 175.6, 175.7. Ϫ MS: m/z (%) ϭ
212 (16), 153 (16), 91 (29), 77 (100).
[2e]
Chem. Soc. Jpn. 1988, 61, 149Ϫ154. Ϫ
R. V. Bonnert, M.
J. Davies, J. Howarth, P. R. Jenkins, J. Chem. Soc., Chem. Com-
mun. 1990, 148Ϫ149. Ϫ [2f] K. Tamao, K. Maeda, T. Yamagu-
chi, Y. Ito, J. Am. Chem. Soc. 1989, 111, 4984Ϫ4985. Ϫ [2g] M.
Koreeda, I. A. George, J. Am. Chem. Soc. 1986, 108,
8098Ϫ8100. Ϫ [2h] A. G. Myers, D. Y. Gin, K. L. Widdowson,
J. Am. Chem. Soc. 1991, 113, 9661Ϫ9663.
[3a] S. Anwar, A. P. Davis, Tetrahedron 1988, 44, 3761Ϫ3770. Ϫ
[3]
[3b]
K. Tamao, T. Nakajima, R. Sumiya, H. Arai, N. Higuchi,
Y. Ito, J. Am. Chem. Soc. 1986, 108, 6090Ϫ6093. Ϫ [3c] M. R.
Hale, A. H. Hoveyda, J. Org. Chem. 1992, 57, 1643Ϫ1645. Ϫ
[3d]
S. Anwar, G. Bradley, A. P. Davis, J. Chem. Soc., Perkin
Trans. 1 1991, 1383Ϫ1389. Ϫ [3e] K. Tamao, T. Tohma, N. Inui,
O. Nakayama, Y. Ito, Tetrahedron Lett. 1990, 31, 7333Ϫ7336.
[4a] K. Nakanishi, K. Mizuno, Y. Otsuji, J. Chem. Soc., Chem.
Commun. 1991, 90Ϫ92. Ϫ [4b] S. A. Fleming, S. C. Ward, Tetra-
hedron Lett. 1992, 33, 1013.
2-[(Chloromethyl)(isobutyryloxycarbonylmethyl)methylsilyl]cyclo-
˜
hex-3-enecarboxylic Acid (10): IR (neat): ν ϭ 3700Ϫ3300, 1735,
[4]
1
1255 cmϪ1. Ϫ H NMR: δ ϭ 0.25 (s, 3 H), 1.16 (d, J ϭ 7.1 Hz, 6
H), 1.74Ϫ1.94 (m, 1 H), 1.94Ϫ2.09 (m, 1 H), 2.09Ϫ2.12 (m, 2 H),
2.32Ϫ2.44 (m, 1 H), 2.56 (sept, J ϭ 7.0 Hz, 1 H), 2.89Ϫ3.04 (m)
and 2.97 (s) (3 H), 3.96 (s, 2 H), 5.63Ϫ5.78 (m, 2 H). Ϫ 13C NMR:
δ ϭ Ϫ7.0, 19.0, 23.7, 24.0, 25.2, 28.1, 34.0, 40.6, 54.2, 125.2, 125.9,
177.7, 181.2. Ϫ MS: m/z (%) ϭ 284 (1.03), 283 (4.87), 282 (20.9),
281 (18), 268 (1.54), 267 (3.85), 184 (26), 175 (40), 161 (26), 158
(27), 147 (53), 144 (23), 143 (38), 77 (100). Ϫ CI-MS (NH3): m/z
(%) ϭ 338 (1.08), 336 (1.89), 300 (19), 283 (100).
[5] [5a]
K. Tamao, K. Kobayashi, Y. Ito, J. Am. Chem. Soc. 1989,
111, 6478Ϫ6480. Ϫ [5b] J. W. Gillard, R. Fortin, E. L. Grimm,
M. Maillard, M. Tjepkema, M. A. Bernstein, R. Glaser, Tetra-
hedron Lett. 1991, 32, 1145Ϫ1148. Ϫ [5c] D. Craig, J. C. Reader,
[5d]
Tetrahedron Lett. 1990, 31, 6585Ϫ6588. Ϫ
D. Craig, J. C.
[5e]
Reader, Tetrahedron Lett. 1992, 33, 4073Ϫ4076. Ϫ
S. M.
Sieburth, L. Fensterbank, J. Org. Chem. 1992, 57, 5279Ϫ5281.
[5f]
Ϫ
G. Stork, T. Y. Chan, G. A. Breault, J. Am. Chem. Soc.
[5g]
1992, 114, 7578Ϫ7579. Ϫ
K. J. Shea, K. S. Zandi, A. J.
[5h]
Staab, R. Carr, Tetrahedron Lett. 1990, 31, 5885Ϫ5888. Ϫ
K. J. Shea, A. J. Staab, K. S. Zandi, Tetrahedron Lett. 1991,
32, 2715Ϫ2718.
Treatment of 10 (20 mg) with a CH2N2 solution in diethyl ether
afforded
[6]
L. H. Sommer, C. L. Frye, J. Am. Chem. Soc. 1959, 81, 1013.
Methyl 2-[(Chloromethyl)(isobutyryloxycarbonylmethyl)methylsilyl]-
cyclohex-3-enecarboxylate. Ϫ IR (neat): ν ϭ 1740, 1255 cmϪ1. Ϫ
[7] [7a]
R. G. Daniels, L. A. Paquette, Organometallics 1982, 1,
˜
1449Ϫ1453. Ϫ [7b] A. G. Brook, W. W. Limburg, J. Am. Chem.
[7c]
1H NMR: δ ϭ 0.22 (s, 3 H), 1.16 (d, J ϭ 6.8 Hz, 6 H), 1.72Ϫ1.89
(m, 1 H), 1.90Ϫ2.04 (m, 1 H), 2.06Ϫ2.17 (m, 2 H), 2.30Ϫ2.38 (m,
1 H), 2.55 (sept, J ϭ 7.0 Hz, 1 H), 2.91 (ddd, J ϭ 3.2, 5.5, 8.7 Hz,
1 H), 2.95 (s, 2 H), 3.72 (s, 3 H), 3.95 (s, 2 H), 5.63Ϫ5.75 (m, 2 H).
Soc. 1963, 85, 832Ϫ833. Ϫ
Am. Chem. Soc. 1971, 93, 6224Ϫ6227.
A. G. Brook, J. D. Pascoe, J.
[8] [8a]
A. Chapeaurouge, S. Bienz, Helv. Chim. Acta 1993, 76,
[8b]
1876Ϫ1889. Ϫ
Acta 1991, 74, 1477Ϫ1488.
S. Bienz, A. Chapeaurouge, Helv. Chim.
13C NMR: δ ϭ Ϫ7.0, 19.1, 23.9, 24.2, 25.4, 28.2, 34.1, 40.8, 51.8,
[9] [9a]
Ϫ
A. Djerourou, L. Blanco, Tetrahedron Lett. 1991, 32,
6325Ϫ6326. Ϫ [9b] A. Djerourou, L. Blanco, Phosphorus, Sulfur
and Silicon 1999, 149, 107.
54.2, 125.4, 125.8, 176.1, 177.7. Ϫ MS: m/z (%) ϭ 319 (0.29), 317
(0.77), 283 (5.65), 231 (14), 195 (33), 193 (100). Ϫ CI-MS (NH3):
m/z (%) ϭ 352 (24), 351 (17), 350 (64), 333 (21), 245 (18), 195 (35),
193 (100).
[10] The preparation of buta-1,3-dienylmagnesium chloride from a
mixture of (E)- and (Z)-chlorobutadiene (E/Z ϭ 3:7) has been
reported (see T. Ishii, N. Kawamura, S. Matsubara, K. Utim-
oto, S. Kozima, T Hitomi, J. Org. Chem. 1987, 52, 4416Ϫ4418).
Treatment of isobutyraldehyde with this reagent gave a mixture
of dienyl alcohols with a 3:7 E/Z ratio. This would seem to
have been a fortuitous stereospecific reaction as these dienyl
alcohols with the same E/Z ratio (3:7) were obtained starting
from a mixture of chlorobutadienes with E/Z ϭ 6:94.
[11] H. G. Viehe, Angew. Chem. Int. Ed. Engl. 1963, 75, 793Ϫ794.
[12] Transesterifications of methyl acrylate, phenyl acetate and fum-
arate with 2-silapropanediol 4 proved to be too slow at Ϫ20
°C. When these reactions were performed at room temperature,
the monoesters 6b؊d were isolated in low yields (15Ϫ46%) and
with very low ee (0Ϫ16%).
Acknowledgments
We wish to thank the JNICT for awarding a Ph.D. grant to
P. Coelho.
´
[1]
R. J. P. Corriu, C. Guerin, J. J. E. Moreau, in Topics In Stereo-
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Received December 9, 1999
[2c]
Chem. Soc. 1985, 107, 500Ϫ501. Ϫ
G. Stork, M. J. Sofia,
[O99665]
3046
Eur. J. Org. Chem. 2000, 3039Ϫ3046