The Peterson olefination using the tert-butyldiphenylsilyl group: Stereoselective synthesis of di- and trisubstituted alkenes

Article abstract of DOI:10.1055/s-2000-6409

The reaction of α-tert-butyldiphenylsilyl carbonyl compounds with organometallics leads with a high diastereoselectivity to erythro-β-hydroxysilanes, which under acidic or basic elimination conditions give E or Z di- and trisubstituted alkenes.

Full text of DOI:10.1055/s-2000-6409

PAPER
1223
The Peterson Olefination Using the tert-Butyldiphenylsilyl Group:
Stereoselective Synthesis of Di- and Trisubstituted Alkenes
Asunción Barbero, Yolanda Blanco, Carlos García, Francisco J. Pulido*
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Valladolid, E-47011 Valladolid, Spain
Fax +34(83)423013; E-mail: pulido@qo.uva.es
Received 14 February 2000; revised 11 May 2000
nus. The mixed tert-butyldiphenylsilyl(butyl)cuprate
reacts in the same way with acetylenes 1 and 2 to give vi-
nylsilanes 3 and 4 in high yield. The reaction with hex-1-
yne (2) was only moderately regioselective leading to
both isomers 4a and 4b in a ratio of 6:1 which could not
be well separated (Scheme 1).
Abstract: The reaction of a-tert-butyldiphenylsilyl carbonyl com-
pounds with organometallics leads with a high diastereoselectivity
to erythro-b-hydroxysilanes, which under acidic or basic elimina-
tion conditions give E or Z di- and trisubstituted alkenes.
Key words: Peterson olefination, tert-butyldiphenylsilyl group,
stereoselective synthesis, alkenes, silicon
tBuPh2Si(Bu)Cu·CNLi2
t
SiPh2 Bu
a-Silyl carbonyl compounds are very important interme-
diates in organic synthesis as it has been well document-
ed.1 Several procedures have been described for their
synthesis involving enolate anion displacement of chlo-
rine from chlorosilanes,2 reaction of Grignard or lithium
reagents derived from a-halosilanes with acetic anhy-
drides, ethyl carboxylates or acid chlorides,3 oxidation of
vinylsilanes4 and more recently C-silylation of hydra-
zones.5 However, there are several difficulties associated
with their preparation mainly due to the lability of some
of these compounds.6 One of the most interesting applica-
tions of these compounds lies in their ability to get con-
verted into Z- and E-alkenes, through the stereospecific
syn- and anti-elimination reactions of the intermediate b-
hydroxysilane resulting from nucleophilic addition to the
carbonyl group.7 However, the diastereoselectivity asso-
ciated to the formation of the b-hydroxysilane is not al-
ways high and strongly depends on the nature of the silyl
group.8 Apart from a brief example9a that we have report-
ed some time ago, the tert-butyldiphenylsilyl group has
not been tested before in the Peterson reaction. Obviously,
its steric hindrance could promote highly Cram-selective
reactions. The tert-butyldiphenylsilyl group has been
widely used in our group for the preparation of vinylsi-
lanes.9b
R
+
1 R = Ph
2 R = Bu
O
R
5
R = Ph 95%
6a R = Bu 77%
tBuPh2Si
+
t
MCPBA, 60 °C
CH2Cl2, 24 h
SiPh2 Bu
+
R
tBuPh2Si
R
3 R = Ph 82%
4a+b R = Bu (79%+13%)
R
O
6b R = Bu 13%
tBuPh2Si
H2SO4
O
t
+
SiPh2 Bu
R
R
CHO
THF, 65 °C
7
R = Ph 95%
8a R = Bu 68% 8b R = Bu 12%
Scheme 1
Reaction of vinylsilanes 3 and 4 with MCPBA gave ep-
oxysilanes 5 and 6 in good yield (Scheme 1). Epoxysi-
lanes 6a and 6b were difficult to separate by
chromatography and the mixture was carried forward in
the next step. The acid-catalyzed rearrangement of 5 and
6 with protic acid provided cleanly a-silyl aldehydes 7 and
8a and a-silyl ketone 8b (Scheme 1). Contrarily to other
reported examples where the Stork-Colvin reaction oc-
curs predominantly,10 it should be noted that in our reac-
tion the a-silyl group is retained, as it has been observed
with other epoxides having bulky silyl groups.11 On the
other hand, the use of tert-butyldiphenylsilyl group is very
advantageous because it is known that only a-silyl alde-
hydes bearing crowded silyl groups are stable enough to
be isolated.12
We report here on the synthesis of a-silyl aldehydes and
ketones carrying the bulky tert-butyldiphenylsilyl group,
and their reaction with organolithium and Grignard re-
agents as an efficient and easy route to stereodefined b-
hydroxysilanes, which can be used in the stereoselective
synthesis of di- and trisubstituted olefins via Peterson ole-
fination. Preparation of the starting a-silyl carbonyl com-
pounds has been achieved using our silylcuprate
chemistry.9c We have recently described9a that silylcupra-
tion of acetylenes is an excellent method for the stereose-
lective synthesis of vinylsilanes with a wide substitution
pattern. As we have shown,9a monosubstituted acetylenes
react with bis(tert-butyldiphenylsilyl)cuprate to give vi-
nylsilanes in which the silyl group is placed at the termi-
The silyl aldehydes thus obtained arise from mechanisms
involving cleavage of either the a or b C-O bond of the
epoxide. Previous studies have shown that the cleavage a
to silicon is more probable,13 however, the formation of
ketone 8b by the acid-catalyzed rearrangement of ep-
oxysilane 6b, can be explained only if cleavage of the C-
O bond b to silicon takes place with migration of the silyl
group.14
Synthesis 2000, No. 9, 1223–1228 ISSN 0039-7881 © Thieme Stuttgart · New York

1224
A. Barbero et al.
PAPER
The lack of methods for the synthesis and isolation of a- pyridinium chlorochromate (PCC). These ketones
trimethylsilyl aldehydes has lowered the potential of these showed to be very unstable, isomerizing to tert-butyl-
compounds in the stereospecific synthesis of olefins, al- diphenlsilyl enol ethers 12a,b after standing at room tem-
though in some cases they have been generated and perature for several hours. It is noteworthy that, the
trapped in situ with Grignard reagents.13,15 However, the rearrangement ocurred with high stereocontrol leading
bulky tert-butyldiphenylsilyl group allows the corre- exclusively to the E-isomers (Scheme 4). The high E-se-
sponding aldehydes to be stable, opening a potential gen- lectivity observed should be the result of the concerted in-
eral method for the stereospecific synthesis of alkenes. tramolecular migration of the silyl group via a four-
Thus, reaction of aldehydes 7 and 8a with organolithium membered transition state similar to the one proposed in
and Grignard reagents provides stereoselectively b-hy- the thermal isomerization of silylmethyl ketones.18
droxysilanes 9a-g in an addition reaction according to the
Felkin-Anh model16 (Scheme 2). The addition takes
tBuPh2Si
tBuPh2Si
R1
place with a high degree of diastereoselectivity to form al-
most exclusively erythro-b-hydroxysilanes (after chro-
matographic purification no threo-isomer could be
detected).
PCC
OH
O
R1
Hexane/CH2Cl2, r.t.
R2
R2
11a (75%)
11b (70%)
9a
9b
R
R
1 = Ph, R2 = Me
1 = Ph, R2 = Bu
t
OSiPh2 Bu
R1
tBuPh2Si
r.t.
tBuPh2Si
R2
R2M
OH
R1
12a (97%)
12b (94%)
R1
CHO
R1 = Ph
R1 = Ph
R1 = Ph
R1 = Ph
THF, -78 °C
R2
R2 = Me, M = Li
R2 = Bu, M = Li
R2 = Ph, M = Li
R2 = vinyl, M = MgBr
R2 = Me, M = Li
R2 = i-Pr, M = MgBr
R2 = Ph, M = Li
7
7
7
7
9a (87%)
9b (85%)
9c (90%)
9d (83%)
9e (72%)
Scheme 4
8a R1 = Bu
8a R1 = Bu
8a R1 = Bu
Nevertheless ketones 11a,b could be prepared, purified
and used within a short time. Thus, treatment of these silyl
ketones with organolithium reagents led to the corre-
sponding trisubstituted alkenes, without isolation of the b-
hydroxysilane intermediates, in a process where the b-
alkoxysilane seems to be sufficiently reactive to undergo
“in situ” a syn b-elimination giving 13 and 14 (Scheme 5).
The reaction of alkyllithium reagents with ketones 11a,b
is acceptably stereoselective following the Felkin-Anh
model. However, reaction with PhLi is not very selective,
as it was reported for similar ketones by Utimoto.19
9f
(60%)
9g (70%)
Scheme 2
Fortunately the bulky tert-butyldiphenylsilyl group is still
capable of taking part in a b-elimination step, under mild
conditions, using the standard acidic (BF3) or basic condi-
tions (KH).17 The so-called Peterson olefination can be
used in the stereoselective preparation of Z- or E-disubsti-
tuted alkenes by syn- or anti-elimination as shown in
Scheme 3. The Z to E ratio was determined by GC and/or
NMR (Scheme 3).
tBuPh2Si
R3Li
O
R2
R3
R2
R1
R1
R1
tBuPh2Si
+
THF, -78 °C
R2
R3
13a =14c (85:15) 14a = 13c (70%)
13b (55:45) 14b (75%)
3 = Me 13c =14a (80:20) 14c = 13a (71%)
3 = Ph
13d (60:40) 14d (90%)
KH
R1
OH
R1
11a R1 = Ph, R2 = Me R3 = Bu
(Z:E)
R2
THF, 30 °C
11a R1 = Ph, R2 = Me
11b R1 = Ph, R2 = Bu
11b R1 = Ph, R2 = Bu
R
R
R
3 = Ph
R2
9a R1 = Ph, R2 = Me
10a (92:8) 86%
10b (97:3) 90%
10c (85:15) 91%
10d (95:5) 93%
10b (96:4) 80%
9b
9c
9d
9g
R
1 = Ph, R2 = Bu
R
R
R
1 = Ph, R2 = Ph
1 = Ph, R2 = vinyl
1 = Bu, R2 = Ph
Scheme 5
Ph
BF3·OEt2
9b
R
1 = Ph, R2 = Bu
(E:Z = 99:1)
Bu
In summary, the tert-butyldiphenylsilyl group is a novel
and useful silyl goup to be utilized in Peterson reactions.
The corresponding a-silyl aldehydes undergo highly
diastereoselective organometallic addition leading to
erythro-b-hydroxysilanes which under typical Peterson
elimination conditions give E or Z disubstituted alkenes
with a high stereocontrol. The behaviour of the analogous
a-silyl ketones is less stereroselective but still favouring
CH2Cl2, 0 °C
10e 87%
Scheme 3
We have also explored the possibility of obtaining trisub-
stituted alkenes via reaction of b-tert-butyldiphenylsilyl
ketones with lithium reagents. Silyl ketones 11a,b were
prepared by oxidation of b-hydroxysilanes 9a and 9b with
Synthesis 2000, No. 9, 1223–1228 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Stereoselective Synthesis of Di- and Trisubstituted Alkenes
1225
MS (EI): m/z (%) = 358 (9, M), 301 (33, M – t-Bu), 239 (100, t-
BuPh2Si).
the trisubstituted alkenes expected according to the Fel-
kin-Anh model.
Anal. C24H26SiO (358.6): calcd C 80.40, H 7.31; found: C 80.68, H
7.50.
Melting points are uncorrected. All reagents were of commercial
quality from freshly opened containers or were purified before use.
THF was distilled under N2 from purple solutions of sodium ben-
zophenone ketyl. IR spectra were recorded on a PU97400 or Matt-
son Cygnus-100 spectrophotometer. NMR spectra were obtained
with a Bruker AM-300 spectrometer. GC/MS were recorded on a
Hewlett-Packard 5988. Purification of products was performed by
flash chromatography on silica gel 60 (Merck, 230-400 mesh).
2-tert-Butyldiphenylsilyl-1,2-epoxyhexane (6b)
Colorless oil (13%); Rf (hexane/ Et2O, 20:1) 0.24.
IR (neat): n = 1110 cm-1 (Si-Ph).
1H NMR (300 MHz, CDCl3): d = 7.7-7.3 (m, 10 H, 2 î C6H5), 2.76
(d, J = 5.2 Hz, 1 H, CHHO), 2.61 (d, J = 5.2 Hz, 1 H, CHHO),
2.04-1.94 (m, 1H, CHHCSi), 1.73-1.55 (m, 1 H, CHHCSi), 1.45-
1.1 (m, 4 H, CH2CH2), 1.2 [s, 9 H, SiC(CH3)3], 0.8 (t, J = 7.2 Hz, 3
H, CH3).
13C NMR (75 MHz, CDCl3): d = 136.1, 136.0, 133.7, 133.2, 129.4,
129.2, 127.8, 127.6 (C6H5), 51.2 (SiCO), 48.7 (OCH2), 34.5 (CH2),
28.8 [C(CH3)3], 26.0 (CH2), 22.9 (CH2), 19.1 [C(CH3)3], 13.9
(CH3).
Silylcupration of Acetylenes; General Procedure
tert-Butyldiphenylsilyl choride (0.80 mL, 3 mmol) was stirred with
lithium shots (0.126 g, 18 mmol) under N2 in THF (10 mL) for 4 h
at 0 °C. The solution of tert-butyldiphenylsilyllithium9a thus formed
was added by a syringe to a suspension of CuCN (0.269 g, 3 mmol)
in THF (15 mL) at 0 °C, and then BuLi (1.9 mL, 3 mmol) was added
to the mixture which was stirred at this temperature for 45 min and
then cooled to -78 °C. A solution of the acetylene 1 or 2 (3 mmol)
in THF (1 mL) was added at -78 °C and the mixture stirred for 1 h.
The mixture was quenched with aq sat. basic NH4Cl solution
(20 mL) and allowed to warm to r.t. The residue was extracted with
Et2O (3 î 15 mL), the combined organic fractions washed with
brine, dried (MgSO4) and evaporated under reduced pressure to
give after chromatography the following vinylsilanes: for the silyl-
cupration of phenylacetylene (E)-1-tert-butyl(diphenyl)silyl-2-
phenylethene9a (3) (82%), and for the silylcupration of hex-1-yne
92% of a 6:1 mixture of (E)-1-tert-butyl(diphenyl)silylhex-1-ene9a
(4a) and 2-tert-butyl(diphenyl)silylhex-1-ene (4b). Componds 3
and 4a have been previously described.9a NMR data of 4b were
obtained from a mixture of 4a and 4b.
MS (EI): m/z (%) = 338 (0.5, M ), 281 (46, M - t-Bu), 199 (100,
Ph2SiOH).
Acid Rearrangement of Epoxysilanes; General Procedure
To a solution of the epoxide 5 or 6 (1.8 mmol) in THF (20 mL) was
added H2SO4 (1 mL) and heated at 65 °C for 5 h. The mixture was
quenched with aq NaHCO3 solution. The organic layer was washed
with brine (3 î 10 mL), dried (MgSO4) and evaporated under re-
duced pressure. The residue was chromatographed (SiO2, hexane/
Et2O, 10:1) to give the silyl carbonyl compounds 7 and 8a,b. The
silyl aldehyde 8a has been previously described.9a
2-tert-Butyldiphenylsilyl-2-phenylethanal (7)
Colorless crystals (95%); Rf (hexane/Et2O, 9:1) 0.24; mp 115-
116 °C (MeOH).
IR (KBr): d = 1700 (C=O), 1100 cm-1 (Si-Ph).
1H NMR (300 MHz, CDCl3): d = 9.9 (d, J = 3.5 Hz, 1 H, CHO),
7.68-6.96 (m, 15 H, 3 C6H5), 4.45 (d, J = 3.5 Hz, 1 H, CHPh), 0.97
[s, 9 H, SiC(CH3)3].
13C NMR (75 MHz, CDCl3): d = 200.1 (CO), 136.7, 134.1, 132.3,
131.5, 129.9, 129.8, 129.5, 128.4, 127.8, 127.6, 126.2 (C6H5), 53.7
(CHCHO), 27.7 [C(CH3)3], 19.6 [C(CH3)3].
2-tert-Butyl(diphenyl)silylhex-1-ene (4b)
Colorless oil (13%); Rf (hexane) 0.54.
1H NMR (300 MHz, CDCl3): d = 7.70-7.54 (m, 4 H, C6H5), 7.30-
7.20 (m, 6 H, C6H5), 6.04 (s with fine couplings, 1 H, H2C=), 5.67
(s with fine couplings, 1 H, H2C=), 2.2 (t with fine couplings, J = 7
Hz, 2 H, CH2C=), 1.45-1.21 (m, 4 H, CH2CH2) 1.20 [s, 9 H,
SiC(CH3)3], 0.85 (t, J = 7 Hz, 3 H, CH2CH3).
13C NMR (75 MHz, CDCl3): d = 146.8 (SiC=), 136.3, 135.0 (C6H5),
129.3 (=CH2), 128.9, 127.5 (C6H5), 36.5 (CH2C=), 30.7 (CH2), 28.7
[C(CH3)3], 22.5 (CH2), 18.5 [C(CH3)3], 13.9 (CH3).
MS (EI): m/z (%) = 301 (64, M – t-Bu), 239 (18, t-BuPh2Si), 199
(100, Ph2SiOH).
Anal. C24H26SiO (358.6): calcd C 80.40, H 7.31; found: C 80.62, H
7.42.
Epoxidation of Vinylsilanes; General Procedure
1-tert-Butyldiphenylsilylhexan-2-one (8b)
Colorless oil (12%); Rf (hexane/EtOAc, 13:1) 0.4.
IR (neat): n = 1720 (C=O), 1245 (C-Si), 1100 cm-1 (Ph-Si).
1H NMR (300 MHz, CDCl3): d = 7.65-7.25 (m, 10 H, 2 î C6H5),
2.75 (s, 2 H, CH2Si), 1.9 (t, J = 7.4 Hz, 2 H, CH2CO), 1.3-0.8 (m,
4 H, 2 î CH2), 1.1 [s, 9 H, SiC(CH3)3], 0.7 (t, J = 7.2 Hz, 3 H, CH3).
13C NMR (75 MHz, CDCl3): d = 209.8 (CO), 136.1, 133.1, 129.6,
127.8 (C6H5), 44.2 (SiCH2CO), 32.3 (CH2CO), 27.5 [C(CH3)3],
25.7 (CH2), 22.0 (CH2), 18.7 [C(CH3)3], 13.7 (CH3).
A solution of m-chloroperoxybenzoic acid (0.27 g, 1.31 mmol) in
anhyd CH2Cl2 (10 mL) was added to a stirred solution of the vinyl-
silane 3 or 4 (0.88 mmol) in anhyd CH2Cl2 (15 mL) containing solid
NaHCO3 (0.14 g, 1.75 mmol). The mixture was refluxed for 24 h,
until completion of the reaction and then allowed to cool down. The
solution was washed with aq NaHCO3 solution and brine, dried
(MgSO4), and concentrated. The residue was chromatographed
(hexane/Et2O) to give the epoxysilanes 5 and a mixture of 6a and
6b. Compound 6a had been previously described.9a
MS (EI): m/z (%) = 338 (9, M), 281 (100, M – t-Bu), 239 (4, t-
(E)-1-tert-Butyldiphenylsilyl-2-phenyl-1,2-epoxyethane (5)
BuPh2Si), 199 (83, Ph2SiOH).
Colorless oil (95%); Rf (hexane/Et2O, 35:1) 0.3.
IR (neat): n = 1110 cm-1 (Si-Ph).
1H NMR (300 MHz, CDCl3): d = 7.72-7.31 (m, 15 H, 3 î C6H5),
3.61 (d, J = 3.3 Hz, 1 H, CHPh), 2.9 (d, J = 3.3 Hz, 1 H, CHSi), 1.25
[s, 9 H, SiC(CH3)3].
13C NMR (75 MHz, CDCl3): d = 138.9, 136.1, 136.0, 132.3, 132.0,
129.73, 129.68, 128.5, 127.9, 127.8, 125.2 (C6H5), 55.7 (CHO),
54.7 (CHO), 27.8 [C(CH3)3], 18.7 [C(CH3)3].
Reaction of Silyl Aldehydes with Organometallic Reagents;
General Procedure
The organometallic reagent (1.0 mmol) was added to a stirred solu-
tion of the aldehyde 7 or 8a (0.65 mmol) in anhyd THF at -78 °C
under N2. After 1 h at this temperature the reaction was quenched
with MeOH (2 mL), allowing the mixture to warm up to r.t. Sat. aq
NH4Cl solution (15 mL) was added, and the aqueous layer extracted
Synthesis 2000, No. 9, 1223–1228 ISSN 0039-7881 © Thieme Stuttgart · New York

1226
A. Barbero et al.
PAPER
with Et2O (3 î 15 mL). The organic layers were combined, washed
with brine, dried (MgSO4), and evaporated under reduced pressure.
The residue was chromatographed (SiO2, hexane/Et2O, 9:1) to give
the alcohols 9a-g (Scheme 2). In the case of 9g, purification was
not desirable because much elimination occurred during column
elution. The crude 9g [70% yield, roughly determined; H NMR:
d = 5.1 (d, CHOH)] was directly treated with KH to give the alkene
10b.
J = 6.1, 4.1 Hz, 1 H, CHOH), 3.1 (d, J = 4.1 Hz, 1 H, CHSi), 1.3 (br
s, 1 H, OH), 0.9 [s, 9 H, SiC(CH3)3].
13C NMR (75 MHz, CDCl3): d = 140.8 (CH=), 138.4, 137.2, 136.9,
134.4, 134.0, 131.2, 129.5, 129.2, 128.2, 127.6, 127.4, 126.0
(C6H5), 114.2 (CH2=), 73.2 (CHOH), 40.2 (CHSi), 28.1 [C(CH3)3],
19.1 [C(CH3)3].
1
MS (EI): m/z (%) = 329 (3, M – t-Bu), 239 (3, t-BuPh2Si), 199 (100,
Ph2SiOH).
(1SR,2RS)-1-tert-Butyldiphenylsilyl-1-phenylpropan-2-ol (9a)
Colorless oil (87%); Rf (hexane/Et2O, 9:1) 0.2.
IR (neat): n = 3600 (OH), 1100 cm-1 (Si-Ph).
1H NMR (300 MHz, CDCl3): d = 7.8-7.1 (m, 15 H, 3 î C6H5), 4.37
(qd, J = 6.1, 5.9 Hz, 1 H, CHOH), 3.0 (d, J = 5.9 Hz, 1 H, CHPh),
1.29 (br s, 1 H, OH), 1.1 (d, J = 6.1 Hz, 3 H, CH3), 0.8 [s, 9 H,
SiC(CH3)3].
13C NMR (75 MHz, CDCl3): n = 139.3, 136.9, 136.7, 134.8, 133.9,
130.9, 129.5, 129.2, 128.4, 127.7, 127.4, 126.0 (C6H5), 68.7
(CHOH), 41.5 (CHSi), 27.9 [C(CH3)3], 23.8 (CH3), 19.1 [C(CH3)3].
Anal. C26H30SiO (386.6): calcd C 80.78, H 7.82; found: C 81.12, H
8.08.
(2RS,3SR)-3-tert-Butyldiphenylsilylheptan-2-ol (9e)
Colorless oil (72%); Rf (hexane/Et2O, 8:1) 0.32.
IR (neat): n = 3540 (OH), 1255 (Si-C), 1100 cm-1 (Si-Ph).
1H NMR (300 MHz, CDCl3): d = 7.8-7.2 (m, 10 H, 2 î C6H5), 4.3
(dq, J = 7.1, 6.4 Hz, 1 H, CHOH), 1.69-1.23 (m, 8 H, 3 î CH2 +
CHSi + OH), 1.2 (d, J = 6.4 Hz, 3 H, CH3CHOH), 1.1 [s, 9 H,
SiC(CH3)3], 0.84 (t, J = 7 Hz, 3 H, CH3CH2).
13C NMR (75 MHz, CDCl3): d = 136.5, 136.4, 135.1, 134.9, 129.1,
129.0, 127.7, 127.5 (C6H5), 68.1 (CHOH), 35.7 (CH2), 32.2 (CHSi),
28.9 [C(CH3)3], 24.7 (CH2), 23.9 (CH3CHOH), 23.2 (CH2), 18.9
[C(CH3)3], 14.0 (CH3).
MS (EI): m/z (%) = 317 (2, M – t-Bu), 239 (2, t-BuPh2Si), 199 (100,
Ph2SiOH).
Anal. C25H30SiO (374.6): calcd C 80.16, H 8.07; found: C 80.41, H
8.29.
MS (EI): m/z (%) = 336 (3, M - H2O), 279 (64, M - H2O – t-Bu), 239
(56, t-BuPh2Si), 199 (22, Ph2SiOH).
(1SR,2RS)-1-tert-Butyldiphenylsilyl-1-phenylhexan-2-ol (9b)
Colorless oil (85%); Rf (hexane/Et2O, 11:1) 0.22.
IR (neat): n = 3600 (OH), 1100 cm-1 (Si-Ph).
1H NMR (300 MHz, CDCl3): d = 7.8-7.1 (m, 15 H, 3 î C6H5),
4.25-4.15 (m, 1 H, CHOH), 3.1 (d, J = 3.5 Hz, 1 H, CHPh), 1.4-
1.1 (m, 7 H, 3 î CH2 and OH), 0.9-0.75 (m, 3 H, CH3), 0.8 [s, 9 H,
SiC(CH3)3].
Anal. C23H34SiO (354.6): calcd C 77.90, H 9.66; found: C 78.29, H
9.95.
(3RS,4SR)-4-tert-Butyldiphenylsilyl-2-methyloctan-3-ol (9f)
Colorless oil (60%); Rf (hexane/Et2O, 8:1) 0.3.
IR (neat): n = 3580 (OH), 1255 (Si-C), 1100 cm-1 (Si-Ph).
1H NMR (300 MHz, CDCl3): d = 7.7-7.3 (m, 10 H, 2 î C6H5), 3.6
(br d, J = 9.4 Hz, 1 H, CHOH), 1.8-1.2 [m, 9 H, 3 î CH2 +
CH(CH3)2 + CHSi + OH], 1.1 [s, 9 H, SiC(CH3)3], 0.9 [d J = 6.6 Hz,
6 H, CH(CH3)2], 0.8 (t, J = 7.2 Hz, 3 H, CH3CH2).
13C NMR (75 MHz, CDCl3): d = 139.1, 137.0, 136.8, 134.6, 134.3,
131.2, 129.4, 128.2, 127.7, 127.4, 125.8 (C6H5), 72.0 (CHOH), 39.3
(CHSi), 36.9 (CH2CHOH), 28.5 (CH2), 28.0 [C(CH3)3], 22.5 (CH2),
19.1 [C(CH3)3], 14.0 (CH3).
13C NMR (75 MHz, CDCl3): d = 136.6, 136.5, 135.2, 134.6, 129.1,
129.0, 127.6, 127.4 (C6H5), 78.1 (CHOH), 35.2 (CH2), 32.3 (CHSi),
28.9 [C(CH3)3], 26.8 [CH(CH3)2], 24.2 (CH2), 23.4 (CH2), 20.1
[CH(CH3)2], 19.9 [CH(CH3)2], 19.0 [C(CH3)3], 13.9 (CH3).
MS (EI): m/z (%) = 399 (0.2, M - OH), 359 (3, M – t-Bu), 239 (2,
t-BuPh2Si), 199 (100, Ph2SiOH).
Anal. C28H36SiO (416.7): calcd C 80.71, H 8.71; found: C 80.96, H
8.82.
MS (EI): m/z (%) = 325 (2, M – t-Bu), 281 (2, M – t-Bu – i-Pr), 239
(3, t-BuPh2Si), 199 (100, Ph2SiOH).
(1RS,2SR)-2-tert-Butyldiphenylsilyl-1,2-diphenylethan-1-ol (9c)
Colorless crystals (90%); Rf (hexane/Et2O, 10:1) 0.3; mp 124.4-
125.1 °C (MeOH).
IR (neat): n = 3580 (OH), 1100 cm-1 (Si-Ph).
Anal. C25H38SiO (382.7): calcd C 78.47, H 10.01; found: C 78.23,
H 9.92.
1H NMR ( 300 MHz, CDCl3): d = 7.9-6.9 (m, 20 H, 4 î C6H5), 5.5
(dd, J = 4.3, 1.9 Hz, 1 H, CHOH), 3.2 (d, J = 1.9 Hz, 1 H, CHSi),
1.68 (d, J = 4.3 Hz, 1 H, OH), 0.9 [s, 9 H, SiC(CH3)3].
13C NMR (75 MHz, CDCl3): d = 144.5, 137.3, 137.1, 136.9, 134.4,
134.2, 131.9, 129.6, 129.3, 127.8, 127.6, 126.7, 125.8, 125.6
(C6H5), 73.5 (CHOH), 42.0 (CHSi), 28.0 [C(CH3)3], 19.1
[C(CH3)3].
Elimination Reactions of b-Hydroxysilanes; General Proce-
dures (Scheme 3)
Basic Conditions: KH (0.103 g of a 50% slurry in oil, 1.25 mmol)
was stirred with hexane (3 î 4 mL), and the supernatant layer was
removed by syringe. To the residue was added anhyd THF (5 mL),
and a solution of the b-hydroxysilane 9a-d,g (0.4 mmol) in anhyd
THF (2 mL). After stirring for 1 h at r.t., the mixture was added to
cold 10% NH4Cl solution and Et2O. The Et2O layer was separated
and dried (MgSO4).
MS (EI): m/z (%) = 379 (1, M – t-Bu), 239 (5, t-BuPh2Si), 199 (100,
Ph2SiOH).
Acidic conditions: To an ice-cooled solution of the b-hydroxysilane
9b (0.32 mmol) in anhyd CH2Cl2 (7 mL) was added BF3•OEt2
(4 mmol). The mixture was stirred for 1 h at 0 °C, then added to
aq sat. NaHCO3 and extracted with Et2O. The Et2O layer was
separated and dried (MgSO4).
Anal. C30H32SiO (436.7): calcd C 82.52, H 7.39; found: C 82.61, H
7.44.
(1SR,2RS)-1-tert-Butyldiphenylsilyl-1-phenylbut-3-en-2-ol (9d)
Colorless oil (83%); Rf (hexane/Et2O, 10:1) 0.17.
IR (neat): n = 3580 (OH), 1255 (Si-C), 1100 cm-1 (Si-Ph).
1H NMR (300 MHz, CDCl3): d = 7.8-7.1 (m, 15 H, 3 î C6H5), 5.8
(ddd, J = 16.9, 10.4, 6.1 Hz, 1 H, CHOHCH=), 5.1 (dt, J = 16.9, 1.5
Hz, 1 H, CHH=), 4.9 (dt, J = 10.4, 1.5 Hz, 1 H, CHH=), 4.8 (dd,
(Z)-1-Phenylprop-1-ene (10a)20
1H NMR (300 MHz, CDCl3): d = 7.5-7.2 (m, 5 H, C6H5), 6.5 (dq,
J = 11.6, 1.8 Hz, 1 H, CHPh), 5.8 (dq, J = 11.6, 7.1 Hz, 1 H,
CHCH3), 1.9 (dd, J = 7.1, 1.8 Hz, 3 H, CH3).
Synthesis 2000, No. 9, 1223–1228 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Stereoselective Synthesis of Di- and Trisubstituted Alkenes
1227
(Z)-1-Phenylhex-1-ene (10b)21
The silyl ketones 11a,b on standing at r.t., easily isomerized in high
yield to the following silyl enol ethers (Scheme 4).
1H NMR (300 MHz, CDCl3): d = 7.5-7.2 (m, 5 H, C6H5), 6.4 (br d,
J = 11.6 Hz, 1 H, CHPh), 5.7 (dt, J = 11.6, 7.2 Hz, 1 H, CHCH2),
2.4-2.3 (m, 2 H, CH2C= ), 1.5-1.3 (m, 4 H, 2 î CH2), 0.9 (t, J = 7.2
Hz, 3 H, CH3).
(E)-2-tert-Butyldiphenylsilyloxy-1-phenylprop-1-ene (12a)24
Colorless oil (97% conversion); Rf (hexane/EtOAc, 20:1) 0.6.
IR (neat): n = 1650 (C=C), 1240 and 1180 (SiOC=), 1100 cm-1 (Si-
(E)-1-Phenylhex-1-ene (10e)21
Ph).
1H NMR (300 MHz, CDCl3): d = 7.5-7.3 (m, 5 H, C6H5), 6.38 (br
d, J = 15 Hz, 1 H, CHPh), 6.24 (dt, J = 15, 7.1 Hz, 1 H, CHCH2),
2.3-2.2 (m, 2 H, CH2C= ), 1.5-1.3 (m, 4 H, 2 î CH2), 0.89 (t,
J = 7.2 Hz, 3 H, CH3).
1H NMR (300 MHz, CDCl3): d = 7.87-7.43 (m, 10 H, 2 î C6H5Si),
7.28-7.0 (m, 5 H, C6H5), 5.78 (s, 1 H, CH=), 2.04 (s, 3 H, CH3C=),
1.17 [s, 9 H, SiC(CH3)3].
13C NMR (75 MHz, CDCl3): d = 151.2 (=C-O), 137.5, 135.5,
133.3, 129.8, 128.4, 128.0, 127.7, 125.2 (C6H5), 111.0 (CH=), 26.6
[C(CH3)3], 19.5 (CH3), 19.4 [C(CH3)3].
(Z)-1,2-Diphenylethene (10c)22
1H NMR (300 MHz, CDCl3): d = 7.4-7.2 (m, 10 H, 2 î C6H5), 6.7
(s, 2 H, 2 î CH).
MS (EI): m/z (%) = 372 (8, M), 315 (61, M – t-Bu), 237 (100, M –
t-BuPh), 199 (5, Ph2SiOH).
(Z)-1-Phenylbuta-1,3-diene (10d)23
1H NMR (300 MHz, CDCl3): d = 7.8-7.7 (m, 5 H, C6H5), 6.8 (ddd,
J = 16.8, 11.0, 10.1 Hz, 1 H, CH=CH2), 6.5 (d, J = 11.3 Hz, 1 H,
CHPh), 6.3 (dd, J = 11.3, 11.3 Hz, 1 H, CHC= ), 5.4 (dd, J = 16.8,
2.0 Hz, 1 H, =CHH), 5.2 (dd, J = 10.1, 2.0 Hz, 1 H, =CHH).
(E)-2-tert-Butyldiphenylsilyloxy-1-phenylhex-1-ene (12b)
Colorless oil (94% conversion); Rf (hexane) 0.4.
IR (neat): n = 1640 (C=C), 1240 and 1180 (SiOC=), 1100 cm-1 (Si-
Ph).
1H NMR (300 MHz, CDCl3): d = 7.81-7.38 (m, 10 H, 2 î C6H5Si),
7.21-6.87 (m, 5 H, C6H5), 5.51 (s, 1H, CH=), 2.37 (t, J = 7.7 Hz, 2
H, CH2C=), 1.72, (quintet, J = 7.7 Hz, 2 H, CH2CH2C=), 1.49-1.26
(m, 2 H, CH3CH2), 1.09 [s, 9 H, SiC(CH3)3], 0.92 (t, J = 7.4 Hz, 3
H, CH3CH2).
13C NMR (75 MHz, CDCl3): d = 154.6 (=C-O), 137.4, 135.5,
133.0, 129.7, 128.3, 127.9, 127.6, 125.1 (C6H5), 110.3 (CH=), 31.9
(CH2), 29.5 (CH2), 26.6 [C(CH3)3], 22.5 (CH2), 19.4 [C(CH3)3],
14.0 (CH3).
Oxidation of b-Hydroxysilanes; General Procedure
To a suspension of PCC/aluminum oxide (2.54 g, 2.1 mmol) in hex-
ane/CH2Cl2 (50%) was added a solution of the b-hydroxysilane 9a,b
(0.6 mmol) in hexane/CH2Cl2, and the mixture stirred for 16 h at r.t.
The solution was filtered and the solid residue washed with Et2O
(3 î 10 mL). The combined filtrates were evaporated and the crude
product was chromatographed (hexane/Et2O).
1-tert-Butyldiphenylsilyl-1-phenylpropan-2-one (11a)
Colorless crystals (75%); Rf (hexane/EtOAc, 20:1) 0.3; mp 119-
120 °C (hexane).
IR (KBr): n = 1700 (C=O), 1255 (Si-C), 1100 cm-1 (Si-Ph).
MS (EI): m/z (%) = 414 (8, M ), 357 (98, M – t-Bu), 279 (100, M –
t-Bu-Ph), 199 (19, Ph2SiOH).
1H NMR (300 MHz, CDCl3): d = 7.72-7.11 (m, 15 H, 3 î C6H5),
4.52 (s, 1 H, CHPh), 2.07 (s, 3 H, CH3CO), 0.96 [s, 9 H, SiC(CH3)3].
Reaction of the a-Silyl Ketones with Organolithium Reagents;
General Procedure
To a stirred solution of the a-silyl ketone 11a,b (0.11 mmol) in an-
hyd THF (3 mL) was added the appropriate organolithium reagent
(0.22 mmol) ) at -78 °C under N2. After 2 h at this temperature, the
reaction was quenched with MeOH (2 mL) at -78 °C, allowing the
mixture to warm up to r.t. Aq satd NH4Cl solution (15 mL) was add-
ed, and the aqueous layer extracted with Et2O (3 î 15mL). The or-
ganic layers were combined, washed with brine, dried (MgSO4),
and evaporated under reduced pressure. The residue was chromato-
graphed (SiO2, pentane) to give the alkenes 13a-d and 14a-d in the
ratio shown in Scheme 5. The ratio was determined by 1H NMR and
GC.
13C NMR (75 MHz, CDCl3): d = 206.5 (CO), 137.0, 136.9, 136.2,
133.4, 132.2, 130.2, 129.6, 129.5, 128.1, 127.4, 126.1 (C6H5), 53.2
(CHSi), 32.2 (CH3CO), 28.2 [C(CH3)3], 19.6 [C(CH3)3].
MS (EI): m/z (%) = 372 (8, M ), 315 (51, M – t-Bu), 237 (100, M –
t-BuPh), 199 (10, Ph2SiOH).
Anal. C25H28SiO (372.6): calcd C 80.59, H 7.57; found: C 80.72, H
7.66.
1-tert-Butyldiphenylsilyl-1-phenylhexan-2-one (11b)
Colorless crystals (70%); Rf (hexane/EtOAc, 25:1) 0.6; mp 72-
73 °C (MeOH).
IR (KBr): n = 1700 (C=O), 1100 cm-1 (Si-Ph).
From silyl ketone 11a and PhLi, a mixture of (E)- and (Z)-1,2-
diphenylprop-1-enes24 (75%) was obtained.
1H NMR (300 MHz, CDCl3): d = 7.89-7.06 (m, 15 H, 3 î C6H5),
4.45 (s, 1 H, CHPh), 2.42-2.29 (m, 2 H, CH2CO). 1.44-1.02 (m, 4
H, 2 î CH2), 0.96 [s, 9 H, SiC(CH3)3], 0.75 (t, J = 7.2 Hz, 3 H,
CH3CH2).
(E)-1,2-Diphenylprop-1-ene (14b)25
1H NMR (300 MHz, CDCl3): d = 7.63-6.98 (m, 10 H, 2 î C6H5),
6.87 (br s, 1 H, CHPh), 2.33 (d, J = 1.3 Hz, 3 H, CH3).
13C NMR (75 MHz, CDCl3): d = 208.7 (CO), 137.1, 136.9, 136.2,
133.3, 132.4, 130.0, 129.3, 128.0, 127.3, 125.9 (C6H5), 52.3 (CHSi),
44.3 (CH2CO), 28.3 [C(CH3)3], 25.8 (CH2), 22.0 (CH2), 19.5
[C(CH3)3], 13.7 (CH3).
(Z)-1,2-Diphenylprop-1-ene (13b)25
1H NMR ( 300 MHz, CDCl3): d = 7.63-6.98 (m, 10 H, 2 î C6H5),
6.5 (br s, 1 H, CHPh), 2.25 (d, J = 1.5 Hz, 3 H, CH3).
From silyl ketone 11b and PhLi, a mixture of (E)- and (Z)-1,2-
diphenylhex-1-enes25 (90%) was obtained.
MS (EI): m/z (%) = 414 (4, M ), 357 (85, M - t-Bu), 199 (15,
Ph2SiOH).
Anal. C28H34SiO (414.7): calcd C 81.10, H 8.26; found: C 80.98, H
8.20.
(E)-1,2-Diphenylhex-1-ene (14d)26
1H NMR (300 MHz, CDCl3): d = 7.89-7.39 (m, 10 H, 2 î C6H5),
6.77 (s, 1 H, CHPh), 2.79 (t, J = 7 Hz, 2 H, CH2C=), 1.52-1.1 (m,
4 H, 2 î CH2), 0.92 (t, J = 7 Hz, 3 H, CH3).
Synthesis 2000, No. 9, 1223–1228 ISSN 0039-7881 © Thieme Stuttgart · New York

1228
A. Barbero et al.
PAPER
(Z)-1,2-Diphenylhex-1-ene (13d)26
(7) (a) Hudrlik, P. F.; Peterson, D. Tetrahedron Lett. 1974, 1133.
(b) Weber, W. P. Silicon Reagents for Organic Synthesis;
Springer: Heidelberg, 1983.
(8) (a) Obayashi, M; Utimoto, K.; Nonaki, H. Bull Chem. Soc.
Jpn. 1979, 52, 1760.
(b) Hudrlik, P. F.; Peterson, D. Tetrahedron Lett. 1972, 1785.
(9) (a) Barbero, A.; Cuadrado, P.; Fleming, I.; Gonzalez, A. M.;
Pulido, F. J.; Sanchez, A. J. Chem. Soc., Perkin Trans. 1 1995,
1525.
1H NMR (300 MHz, CDCl3): d = 7.89-7.39 (m, 10 H, 2 î Ph), 6.51
(s, 1 H, CHPh), 2.56 (t, J = 7 Hz, 2 H, CH2C=), 1.52-1.1 (m, 4 H, 2
î CH2), 0.92 (t, J = 7 Hz, 3 H, CH3).
From silyl ketone 11a and BuLi and from silyl ketone 11b and Me-
Li, a mixture of (E)- and (Z)-2-methyl-1-phenylhex-1-enes26 in 71-
75% yield was obtained.
(E)-2-Methyl-1-phenylhex-1-ene (14a = 13c)27
(b) Blanco, F. J.; Cuadrado, P.; González, A. M.; Pulido, F. J.
Synthesis 1996, 42.
(c) Barbero, A.; Pulido, F. J. Recent Research Developments
in Synthetic Organic Chemistry, Vol. 2; Pandalai, S. G., Ed.;
T.R.N: Trivandrum, 1999; pp 1-22.
1H NMR (300 MHz, CDCl3): d = 7.34-7.19 (m, 5 H, C6H5), 6.29 (s,
1 H, CHPh), 2.24 (t J = 7 Hz, 2 H, CH2C=), 1.89 (s, 3 H, CH3C=),
1.52-1.2 (m, 4 H, 2 î CH2), 0.91 (t, J = 7 Hz, 3 H, CH3).
(Z)-2-Methyl-1-phenylhex-1-ene (13a = 14c)27
(10) Stork, G.; Colvin, E. J. Am. Chem. Soc. 1971, 93, 2080.
(11) Muchowski, M.; Naef, R.; Maddox, M. L. Tetrahedron Lett.
1985, 26, 5375.
(12) Hudrlik, P. F.; Kulkarni, A. K. J. Am. Chem. Soc. 1981, 103,
6251.
1H NMR (300 MHz, CDCl3): d = 7.34-7.19 (m, 5 H, C6H5), 6.29 (s,
1 H, CHPh), 2.24 (t, J = 7 Hz, 2 H, CH2C=), 1.82 (s, 3 H, CH3C=),
1.52-1.2 (m, 4 H, 2 î CH2), 0.87 (t, J = 7 Hz, 3 H, CH3).
(13) Hudrlik, P. F.; Hudrlik, A. M.; Misra, R. N.; Peterson, D.;
Withers, G. P.; Kulkarni, A. K. J. Org. Chem. 1980, 45, 4444.
(14) The assumption that 8b comes from 6b is based on the fact
that the acid-catalyzed rearrangement of a pure sample of 6a
yields 8a without contamination of 8b.
Acknowledgement
We gratefully acknowledge financial support from the Ministry of
Education and Culture of Spain (DGES PB96/0357 project) and
from the "Junta de Castilla y León" (VA43/98 project).
(15) Sato, T.; Abe, T.; Kuwajima, I. Tetrahedron Lett. 1978, 19,
259.
(16) (a) Cherest, M.; Felkin, H.; Prudent, N. Tetrahedron Lett.
1968, 2119.
(b) Anh, N. T.; Eisenstein, O. Nouv. J. Chim. 1977, 1, 61.
(17) (a) Peterson, D. J. J. Org. Chem. 1968, 33, 780.
(b) Hudrlik, P. F.; Peterson, D. J. Am. Chem. Soc. 1975, 97,
1464.
(18) (a) Brook, A. G.; MacRae, D. M.; Bassindale, A. R. J.
Organometal. Chem. 1975, 86, 185.
(b) Bassindale, A. R.; Brook, A. G.; Chen, P.; Lennon, J. J.
Organometal. Chem. 1975, 94, C21.
(19) Utimoto, K.; Obayashi, M.; Nozaki, H. J. Org. Chem. 1976,
41, 2940.
(20) Davidson, A. H.; Fleming, I.; Grayson, J. Y.; Pearce, A.;
Snowden, R. L.; Warren, S. J. Chem. Soc., Perkin Trans. 1
1977, 550.
(21) Fleming, I.; Newton, T. W. J. Chem. Soc., Perkin Trans. I
1984, 119.
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Article Identifier:
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Synthesis 2000, No. 9, 1223–1228 ISSN 0039-7881 © Thieme Stuttgart · New York