Enantioselective synthesis of crotyl geminal bis(silane) and its usage for asymmetric Sakurai allylation of acetals

Article abstract of DOI:10.1016/j.tet.2017.05.011

Enantioselective synthesis of crotyl geminal bis(silane) 4 has been developed by an asymmetric [1, 5]-hydride shift of allylic hydrazine. SnCl₄-promoted Sakurai allylation of (R)-4 with acetals leads to chemoselective desilylation of SiMe₃

Full text of DOI:10.1016/j.tet.2017.05.011

Accepted Manuscript
Enantioselective synthesis of crotyl geminal bis(silane) and its usage for asymmetric
Sakurai allylation of acetals
Yang Chu, Qiang Pu, Zhixing Tang, Lu Gao, Zhenlei Song
PII:
S0040-4020(17)30477-5
10.1016/j.tet.2017.05.011
TET 28677
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 30 January 2017
Revised Date: 16 March 2017
Accepted Date: 2 May 2017
Please cite this article as: Chu Y, Pu Q, Tang Z, Gao L, Song Z, Enantioselective synthesis of crotyl
geminal bis(silane) and its usage for asymmetric Sakurai allylation of acetals, Tetrahedron (2017), doi:
10.1016/j.tet.2017.05.011.
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Enantioselective synthesis of crotyl geminal
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Sakurai allylation of acetals
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∗
Yang Chu, Qiang Pu, Zhixing Tang, Lu Gao, Zhenlei Song
Key Laboratory of Drug-Targeting of Education Ministry and Department of Medicinal Chemistry, West China
School of Pharmacy, Sichuan University, Chengdu, 610041, P. R. China

1
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Tetrahedron
journal homepage: www.elsevier.com
Enantioselective synthesis of crotyl geminal bis(silane) and its usage for asymmetric
Sakurai allylation of acetals
∗
Yang Chu, Qiang Pu, Zhixing Tang, Lu Gao, Zhenlei Song
Key Laboratory of Drug-Targeting of Education Ministry and Department of Medicinal Chemistry, West China School of Pharmacy, Sichuan University,
Chengdu, 610041, P. R. China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Enantioselective synthesis of crotyl geminal bis(silane) 4 has been developed by an asymmetric
[1, 5]-hydride shift of allylic hydrazine. SnCl -promoted Sakurai allylation of (R)-4 with acetals
, generating E-syn-(S, R)-5 in good yields with
4
leads to chemoselective desilylation of SiMe
3
high E/Z-, diastereo- and enantioselectivity.
Available online
2
009 Elsevier Ltd. All rights reserved.
Keywords:
Allyl silanes
Sakurai allylation
Acetals
Chirality transfer
[
1, 5]-hydride shift
1
. Introduction
a) Previous studies of chiral allyl 1,1-bimetallic reagents
Allyl metallic compounds are very important reagents in
1
H
H
organic synthesis. Allylation of aldehydes using these reagents
has become one of the most useful methods for controlling the
stereochemistry in acyclic systems. The resulting homoallylic
alcohols are vital building blocks in the synthesis of biologically
active molecules such as macrolides and polyether antibiotics.
Despite the typical allylation reagents are mono-metal-substituted,
bimetallic species appears being more attractive for rapid
increasing the structural complexity. In the allyl bimetal family, 1,
H
E2
1
E /E2
and
E1
Y
X
M
X
X
M
type-I (hetero)
type-II (homo)
type-I
H
H
H
(most studied)
Si
R
Sn
R
Si
R
B
B
Sn
B/Si
Yamamoto,[2a, 2c] Matteson,[2b] Shimizu Roush[3]
and Hiyama,[2d] Hall,[2e] Roush[2g]
Lautens[4]
B/Sn
Sn/Si
1
-bimetallic compound is a unique member. Distinct from 1, 2-
type-II (Si/Si)
very few examples)
H
Me
H
H
OR
and 1, 3-types (not shown), 1, 1-type contains two metals
attached into one carbon center. Because two C−M bonds share
with the same allylic moiety, 1, 1-type allyl bimetallic reagent
could play as a linchpin to assemble electrophiles E and E by
sequential functionalization at 3- and 1-positions (Scheme 1a, top
left). When two metal moieties are different, the carbon they
attached would be a stereogenic center. Thus, chemoselective
cleaving one of the C−M bonds becomes crucial for realizing
effective chirality transfer. To do so, previous studies have been
largely focused on hetero-bimetallic compounds possessing two
(R)
FMe2Si
Me3Si
(
i-Pr t-BuMe2Si
PhMe2Si
Me3Si
selectivity?
Me3Si
chemo-
E/Z-
diastereo-
enantio-
1
2
3
1
2
(non-racemic)
(racemic)
Lautens[7]
(racemic)
Song[8]
[
6]
Wetter
b) Present work
H
OP
RCH(OP)2 (1.2 equiv)
(R)
MePh Si
(R)
2
MePh2Si
Me3Si
SnCl4 (1.5 equiv)
(S)
R
Me
CH2Cl2, -78 oC, 1 h
Me
5
5-93% yield
(R)-4
E-syn-(S, R)-5
2
3
4
different metal centers such as B/Si, B/Sn and Sn/Si (Scheme
a, type-I). In the combination of B/Si, due to the C−B bond is
dr up to 95:5; er up to 97:3
1
weaker than the C−Si bond, chemoselective elimination of the
more reactive C−B bond could be achieved during the allylation
with aldehydes.
Scheme 1. (a) Previous studies on chiral allyl 1, 1-hetero- and homo-
bimetallic reagents; (b) asymmetric Sakurai allylation of acetals
using crotyl geminal bis(silane) (R)-4.
—
——
∗
Corresponding author. Tel.: +86-28-85501876; E-mail: zhenleisong@scu.edu.cn

2
Tetrahedron
a
Compared with allyl 1, 1-hetero-bimetals,
A
the
C
c
C
or
E
res
P
p
T
on
E
di
D
ng MATa
NU
bl
e 1
S
. S
C
cr
R
ee
I
ning of Mitsunobu reaction conditions.
P
T
chiral homo-bimetallic reagents (Scheme 1a, type-II) such as
allyl geminal bis(silanes) have been investigated in a very limited
scope. Both metal centers in these compounds are silicon, but
with different substitution modes. Imaginably, it would be
difficult to selectively cleavage one of the C−Si bonds if only by
differentiating the substituents on silicon. That would make the
5
chirality transfer more challenging than that using hybrid
combination such as B/Si. To the best of our knowledge, there is
only one successful example utilizing optically active 1 featuring
6
a SiMe /SiMe F combination. As reported by Wetter,
1
3
2
underwent asymmetric acylation with CH COCl through chirality
3
b
b
transfer enabled by chemoselective desilylation of SiMe F. There
entry
8
Ar
p-Me-C
solvent
THF
PR
3
(±)-4
11
2
are other two examples using racemic 2 (SiMe /SiMe t-Bu)
1
2
3
4
5
6
8a
8a
8a
8a
8a
8b
6
H
4
PPh
3
30%
11a(20%)
N. R.
3
2
7
reported by Lautens, and racemic 3 (SiMe /SiMe Ph) reported
p-Me-C H4
CH NO2 PPh3
N. R.
N. R.
N.R.
N. R.
43%
3
2
6
6
3
8a
by our group. Despite selective desilylation of SiMe3 was
observed in these two cases, no asymmetric chirality transfer was
involved since 2 and 3 are racemic. Overall, the potential values
of optically active allyl geminal bis(silanes) in organic synthesis
are still poorly unexplored. A series of selectivity issues have not
been fully understood in these reagents-involved allylation with
electrophiles.
p-Me-C H4
NMM
THF
THF
THF
PPh3
PPh
P(t-Bu)
PPh
NHNH
N. R.
o-NO
2
-C
6
H
4
3
N.R.
p-Me-C
p-Me-C
6
H
4
3
N. R.
6
H
4
3
11b(10%)
a
Reaction conditions: 8 (0.6 mmol), ArSO
2
2 3
(1.2 mmol), Ph P (1.2
mmol) and DIAD (1.2 mmol) in THF (6.0 mL) at 0 °C to 25 °C for 2 h; then
b
NaOAc (0.9 mmol) in MeOH (4.0 mL) at rt for 24 h. Isolated yields after
Herein we report the enantioselective synthesis of crotyl
purification by silica gel column chromatography.
geminal bis(silane) 4 by an asymmetric [1, 5]-hydride shift of
9
as solvent (entries 2 and 3), or switching the sulfonyl substituent
allylic hydrazine. SnCl -promoted Sakurai allylation of (R)-4
4
from Ts to Ns (entry 4), or replacing PPh with P(t-Bu) (entry 5).
3
3
with acetals leads to chemoselective desilylation of SiMe3,
generating E-syn-(S, R)-5 in good yields with high E/Z-,
diastereo- and enatioselectivity (Scheme 1b).
Compared with 8a, the approach using 8b increased the yield of
±)-4 to a useful level of 43% (entry 6). Formation of the by-
(
product 11b was suppressed in an acceptable 10% yield. The
increased efficiency might be explained by the different steric
effect of the Z-silyl group in 8a and 8b. Because 8b contains a
2
. Results and discussion
smaller Z-SiMe3 group, the S 2 substitution with hydrazine
should be easier to proceed than that of 8a containing a larger Z-
N
The key strategy for the synthesis of crotyl geminal bis(silane)
relies on a sigmatropic [1, 5]-hydride shift of allylic hydrazine.
4
SiPh Me group.
2
The requisite bis(silyl) allylic alcohols
8 were initially
synthesized in racemic form by the procedure shown in Scheme 2.
Propargyl alcohol 6 was reduced with Red-Al to afford the
corresponding Z-vinyl aluminum species, which was trapped
10
with iodine to afford Z-vinyl silane 7. Silylation of 7 followed
11
by t-BuLi-promoted retro-[1, 4]-Brook rearrangement delivered
allylic alcohols 8a and 8b, respectively, in 60% and 64% overall
yields by three steps. Allylic alcohol 8a contains E-SiMe and Z-
3
SiPh Me, while these two silyl groups in 8b are switched to each
2
other.
Scheme 2. Synthesis of racemic 8a and 8b.
Transformation of alcohol 8 into racemic crotyl geminal
bis(silane) (±)-4 involves Mitsunobu reaction to generate the
hydrazine intermediate 9 followed by NaOAc-promoted [1, 5]-
Scheme 3. Enantioselective synthesis of crotyl geminal bis(silane) 4.
12
hydride shift (10). The approach was first examined using 8a
and TsNHNH with DIAD/PPh in THF (Table 1, entry 1). The
With the optimal [1, 5]-hydride shift condition in hand, the
enantioselective synthesis of 4 was carried out (Scheme 3). The
preparation commenced with lipase-catalyzed kinetic resolution
2
3
initially formed allylic hydrazine 9 underwent clean [1, 5]-
hydride shift by treatment with NaOAc in MeOH. The desired
silane (±)-4 was obtained in 30% overall yield. The moderate
yield of the approach was attributed to the low efficiency of
Mitsunobu reaction. Besides some undefined side-paths, a based-
promoted elimination of the oxyphosphonium intermediate was
observed to generate the major by-product diene 11a in 20%
13
of 6b to provide (S)-6b in 50% yield with 99:1 er. The (R)-6b-
Ac was generated in 49% yield, and was directly reduced with
DIBAL-H to afford (R)-6b quantitatively with 98:2 er. Following
the same procedure as that used for racemic 6b, allylic alcohol
(S)-8b was obtained in 64% yield without loss of
enantioselectivity. The Mitsunobu reaction/[1, 5]-hydride shift
14
yield. No Mitsunobu reaction occurred using CH NO or NMM
3
2
process of (S)-8b subsequently delivered (R)-4 in 43% yield

3
with 99:1 er. The process was also applied to th
A
e s
C
yn
C
th
E
es
P
is
T
of
E
(S
D
)- MAal
N
ky
U
l ac
S
e
CRIPT
tal
.
4
from the corresponding (R)-6b. Both (R)- and (S)-4 are stable
Using FeCl as Lewis acid allowed us to realize a one-pot
acetalation/Sakurai allylation process (Scheme 4). The reaction
was performed simply by mixing (R)-4, t-BuCHO, MeOSiMe3
and FeCl in CCl at room temperature for 12 h. The desired
3
to moisture, and were prepared on gram scale and purified easily
by silica gel column.
15
a
Table 2. Asymmetric Sakurai Allylation of (R)-4 with Acetals.
3
4
Sakurai allylation product 5l was generated as a single syn-
diastereomer in 80% yield with a 90:10 er.
H
RCH(OP)2 (1.2 equiv)
OP
(R)
Ph2MeSi
Ph2MeSi
Me3Si
Me
SnCl4 (1.5 equiv)
R
CH2Cl2, -78 oC, 1 h
Me
4
5b
OBn
OBn
OBn
Si
Si
Si
Si
Si
Me
Me
Me
Br
CF3
CN
c
5
a: 75%
5b: 90%
dr 95:5; er = 97:3
5c: 91%
dr 95:5; er = 96:4
d
e
dr 95:5; er = 96:4
OBn
OBn
OBn NO2
Si
Si
Me
Me
Me
CO2Me
NO2
5d: 93%
5e: 85%
dr 95:5; er = 96:4
5f: 92%
dr 95:5; er = 92:8
dr 95:5; er = 96:4
Scheme 5. Model analysis to explain the selectivity outcomes.
OBn
OBn
OMe
Si
Si
As shown in Table 2, our approach achieved four different
selectivities in a single transformation: elimination of SiMe over
Me
Me
Me
Me
3
SiMe Ph (chemoselectivity), E- over Z-vinyl silane (geometrical
5
g: 70%
5h:
5i: 55%
dr 95:5; er = 96:4
2
dr 95:5; er = 87:13
dr and er: N.D.
selectivity), syn- over anti-allylation (diastereoselectivity) and
S/R over R/S (enantioselectivity). A model in Scheme 5 was
proposed to rationalize the above selectivity outcomes. Firstly,
the reactive conformation of (R)-4 should be that which
minimizes allylic strain, and also benefits from a dual
hyperconjugation effect between the two C−Si bonds and alkene.
OBn
OBn
Si
Si
Me
Me
5
j: 83%
5k: 60%
dr 50:50; er: N.D.
dr 95:5; er = 97:3
Chemoselective elimination of the more reactive C−SiMe bond
3
would generate SiPh Me-substituted alkene with E-configuration.
2
a
Secondly, based on the classical anti-S ' mechanism, the
Reaction conditions: (R)-4 (0.15 mmol), acetal (0.18 mmol) and SnCl
4
(0.23
E
o
b
oxacarbenium should approach to the 3-position of (R)-4 by the
mmol) in CH
Cl
2 2
( 3.0 mL) at -78 C for 1 h. The syn-(S, R)-stereochemistry
1
6
of the product was assigned by transforming 5a to the known compound. See
orientation antiperiplanar to the eliminating C-SiMe bond. In
3
c
the resulted two “open” transition states 12-syn and 12-anti, 12-
syn appears being more favorable than 12-anti, which suffers
from a gauche interaction between Me and R groups. Thus,
reaction via 12-syn would generate E-syn-(S, R)-5
predominantly.
supporting information for details. Isolated yields after purification by silica
d
1
gel column chromatography. The ratios were determined by H NMR
e
spectroscopy of the crude products. The ratios were determined by HPLC
analysis using a chiral stationary phase.
The Sakurai allylation of (R)-4 with acetals was next
examined (Table 2). After screening a range of Lewis acids,
SnCl appears most effective to promote the reaction in CH Cl at
4
2
2
-78 °C. While chemoselective desilylation of the more reactive
SiMe occurred in all cases to give SiPh Me substituted E-alkene,
3
2
the nature of acetals has great impacts on the diastereo- and
enantioselectivity. Reaction of aryl acetals containing an
electron-withdrawing group gave rise to 5a-5f as a single syn-
diastereomer. Moreover, the chirality transfer from geminal
bis(silyl) moiety to the products proceeded reliably to give
excellent (S, R)-enantioselectivity. However, a severe decreasing
of er was observed when using phenyl acetals to form 5g. In
addition, substitution of an electron-donating Me group on the
phenyl ring inhibited the allylation to give the desired 5h. The
reaction was suitable for Cy- and t-Bu-substituted acetals, giving
Scheme 6. Transformation of ent-5b into E-enyne 14 and Z-enyne 16.
5
i and 5j in high dr and er. But, a poor dr of 50:50 was detected
The resulting E-vinyl silane moiety was utilized as the second
functionality of geminal bis(silane), leading to divergent
synthesis of E- and Z-enynes. As shown in Scheme 6, ent-5b,
generated from (S)-4, underwent Ag CO -promoted iodination
in the formation of 5k from less sterically demanding unbranched
2
3
1
7
with NIS to provide E-vinyl iodide 13 in 90% yield. The
18
subsequent Sonogashira cross-coupling with terminal alkyne
gave rise to E-enyne 14 in 70% yield. On the other hand,
Scheme 4. One-pot acetalation/Sakurai allylation to form 5l.
dibromination of ent-5b followed by elimination of MePh SiBr
2

4
Tetrahedron
19
with TBAF led to Z-vinyl bromide 15
A
inCC88
E
%
P
yie
T
E
ld
D
.
MAEt
NU
O
(3
S
×
C
2
R
00IP
mL). The combined layers were washed with sat
T
2
Sonogashira cross-coupling of 15 with terminal alkyne then
afforded Z-enyne 16 in 65% yield.
aq Na S O (20 mL), dried over anhydrous Na SO , filtered and
2
2
3
2
4
concentrated under reduced pressure. Purification of the crude
residue via silica gel column chromatography (gradient eluent: 0-
3
. Conclusion
1
.0% of EtOAc/petroleum ether) afforded vinyl iodine
intermediate (13.6 g, 85%) as a yellow oil. To a solution of the
In summary, we have described the enantioselective synthesis
above vinyl iodine (10.0 g, 25.4 mmol), Et N (10.5 mL, 76.2
3
of crotyl geminal bis(silane) 4 by an asymmetric [1, 5]-hydride
shift of allylic hydrazine. Chemoselective desilylation of SiMe3
was realized in the Sakurai allylation with acetals, leading to
mmol) and DMAP (310 mg, 2.6 mmol) in CH Cl (120 mL) was
2
2
added TMSCl (3.8 mL, 30.4 mmol) at 0 °C. After stirring for 1 h
at room temperature, the reaction was quenched with sat aq
NaHCO (50 mL) and extracted with CH Cl (3 × 50 mL). The
MePh Si-substituted E-syn-(S, R)-5 in good yields with high E/Z-
2
3
2
2
,
diastereo- and enatioselectivity. More applications of this new
allyl silane reagent in organic synthesis are underway.
combined organic layers were dried over anhydrous Na SO ,
2
4
filtered and concentrated under reduced pressure to provide crude
silyl ether. To a solution of the above silyl ether (2.0 g, 4.3
mmol) in THF (50 mL) was added t-BuLi (6.6 mL of 1.3 M
solution in pentane, 8.6 mmol) dropwise via syringe at -78 °C
under argon atmosphere. The reaction was allowed to proceed for
4
. Experimental section
Commercial reagents were used without any purification. All
reactions were performed using common anhydrous, inert
atmosphere techniques. Reactions were monitored by thin-layer
chromatography (TLC) using aluminium-backed silica gel plates
3
0 min at -78 °C. The resultant solution was warmed to room
temperature and stirred for another 30 min before quenching with
(
HSGF-254). TLC spots were viewed under ultraviolet light and
by heating the plate after treatment with a staining solution of
stains, H PO ·12MoO /EtOH stains,
conc.)/anisaldehyde/EtOH stains. Product purifications were
sat aq NH Cl (20 mL) and extraction with ether (3 × 20 mL). The
4
combined organic layers were dried over anhydrous NaSO4,
filtered, and concentrated under reduced pressure. Purification of
the crude residue via silica gel column chromatography (gradient
eluent: 0-1.0% of EtOAc/petroleum ether) afforded (S)-8b (1.1 g,
KMnO4
3
4
3
2
H SO4
(
performing using Silica Gel (200-300 mesh) for column
1
chromatography. H NMR spectra were recorded at 400 MHz
6
4% for 3 steps) as a yellow oil. R = 0.51 (EtOAc-petroleum
f
13
(
Varian) and 600 MHz (Agilent), and C NMR spectra were
20
ether, 1:10) ; [α]D = -18.6 (c 1.0, CHCl ); The enantiomeric
3
recorded at 100 MHz (Varian) and 150 MHz (Agilent) using
ratio was determined to be 99:1 by HPLC analysis on Chiralpak
CDCl (except where noted) with TMS or residual solvent as
3
IA column (0.25% 2-propanol/n-hexane, 1.0 mL/min), UV 220
standard. Infrared spectra were obtained using KCl plates on a
VECTOR22. High-resolution mass spectral analyses performed
on Waters Q-TOF. In each case, enantiomeric ratio was
determined by HPLC analysis on a chiral column in comparison
with racemates, using a Daicel Chiralpak IA Column (250 × 4.6
mm) or Chiralpak IC Column (250 × 4.6 mm), Chiralpak OD-H
Column (250 × 4.6 mm). UV detection was monitored at 220 nm
1
nm, tminor = 21.95 min, tmajor = 30.63 min; H NMR (400 MHz,
CDCl ) δ 7.44-7.47 (m, 4H), 7.33-7.34 (m, 6H), 6.42 (d, J = 8.8
3
Hz, 1H), 4.62-4.69 (m, 1H), 1.24 (d, J = 6.4 Hz, 3H), 0.68 (s,
13
3
1
2
1
H); 0.05 (s, 9H); C NMR (150 MHz, CDCl ) δ 163.9, 138.1,
3
37.0 136.9, 135.0, 134.9, 129.1, 129.0, 127.7, 89.2, 22.7, 2.0, -
.3; IR (liquid film) cm 2960, 2919, 1568, 1428, 1262, 1249,
110, 1052, 1027, 941, 907, 837; HRMS (MALDI, m/z) calcd for
C H NaOSi (M+Na) : 363.1571, found 363.1575.
-1
or 254 nm. Optical rotation was examined in CHCl solution at
+
3
20
28
2
2
0 °C. Pentane, CH NO , NMM, CH Cl , CCl , Et NH and Et N
3 2 2 2 4 2 3
were distilled from CaH . Et O and THF were distilled from
4.3. Synthesis of (R)-4
2
2
sodium.
.1. Synthesis of (S)-6b
To a 0.5 M pentane solution of racemic 6b (20.6 g, 37.6
To a solution of Ph P (6.4 g, 34.1 mmol) in dry THF (100 mL)
was added diisopropoylazodicarboxylate (DIAD, 6.8 mL, 34.1
mmol) at 0 °C. A solution of (S)-8b (5.8 g, 17.1 mmol) in dry
3
4
THF (200 mL) and TsNHNH (6.35 g, 34.1 mmol) were then
2
mmol) was added Amano lipase AK (2.2 g, 18.8 mmol) and vinyl
acetate (58 mL, 188 mmol). The resulting suspension was stirred
at room temperature for 24 h under argon atomosphere. The
mixture was filtered via celite. The filtration was concentrated
and purified by silica gel chromatography (10%
EtOAc/petroleum ether) to provide (S)-6b (10.3 g, 50%) as a
added sequentially to the above mixture at 0 °C. The reaction was
warmed to room temperature and allowed to stand for 2 h. The
resultant solution was partitioned with Et O (50 mL) and H O (50
2
2
mL). The organic layers were washed with 50 mL of H O, dried
2
over anhydrous Na SO , filtered and concentrated under reduced
2 4
pressure. Filtration of the residue by silica gel column
chromatography provided the crude allylic hydrazine. To a
solution of the above allylic hydrazine (3.8 g, 7.5 mmol) in
MeOH (5 mL) was added NaOAc (1.23 g, 15 mmol) at room
temperature. After stirring for 24 h, MeOH was removed under
reduced pressure. The residue was purified by silica gel column
chromatography (100% petroleum ether) to afford (R)-4 (2.4 g,
20
colorless oil. R = 0.51 (EtOAc-petroleum ether, 1:10) ; [α] = -
f
D
1
9
3.9 (c 1.0, CHCl ); The enantiomeric ratio was determined to be
9:1 by HPLC analysis on Chiralpak IC column (1% 2-
3
propanol/n-hexane, 1.0 mL/min), UV 220 nm, t
= 18.33 min,
minor
1
tmajor = 19.77 min; H NMR (600 MHz, CDCl ), δ 7.65-7.66 (m,
3
4
H), 7.38-7.44 (m, 6H), 4.62 (q, J = 6.6 Hz, 1H), 2.11 (s, 1H,
13
43%) as a clear oil. R = 0.68 (EtOAc-petroleum ether, 0:1);
f
OH), 1.53 (d, J = 6.6 Hz, 3H), 0.72 (s, 3H); C NMR (150 MHz,
20
[
α]D = -36.4 (c 1.0, CHCl ); The enantiomeric ratio was
3
CDCl ) δ 134.9, 134.5 134.4, 129.7, 127.9, 110.9, 84.8, 58.8,
3
-
1
determined to be 99:1 by HPLC analysis on Chiralpak IG-RH
column (CH OH/H O = 90/10, 0.4 mL/min), UV 205 nm, t
2
1
4.1, -2.1. IR (liquid film) cm 3310, 3069, 2962, 2172, 1428,
=
major
3
2
370, 1325, 1259, 1113, 1042, 788; HRMS (MALDI, m/z) calcd
1
1
7
=
4.85 min, tminor = 16.60 min; H NMR (400 MHz, CDCl ) δ
+
3
for C H NaOSi (M+Na) : 289.1019, found 289.1021.
17
18
.55-7.56 (m, 4H), 7.33-7.36 (m, 6H), 5.38 (dd, J = 11.2 Hz, J
1
2
14.8 Hz, 1H), 5.21 (dq, J = 6.4 Hz, J = 14.8 Hz, 1H), 1.72 (q,
4
.2. Synthesis of (S)-8b
1
2
J = 11.2 Hz, 1H), 1.63 (d, J = 6.4 Hz, 3H), 0.63 (s, 3H), -0.15 (s,
13
To a solution of (S)-6b (10.8 g, 40.6 mmol) in Et O (500 mL)
9H); C NMR (150 MHz, CDCl ) δ 137.9, 137.7, 135.0, 134.9,
2
3
was added Red-Al (11.9 mL, 60.9 mmol) dropwise at 0 °C. After
134.8, 128.9, 128.8, 127.6, 127.4, 124.2, 22.0, 18.2, 0.5, -3.3; IR
-
1
stirring for 8 h, I (15.5 g, 60.9 mmol) was added at –20 °C. The
(liquid film) cm 3010, 2955, 2915, 1427, 1248, 1105, 1052,
1024, 857, 770; HRMS (MALDI, m/z) calcd for C20H28NaSi
2
2
resultant mixture was stirred at room temperature overnight
+
(
M+Na) : 347.1622, found 347.1625.
before quenching with sat aq NH Cl (200 mL) and extracted with
4

5
1
4
.4. Synthesis of 5a
UV 220 nm, tm = 13.53 min, tmajor = 17.24 min; H NMR (400
inor
ACCEPTED MANUSCRI
PT
MHz, CDCl ) δ 7.63 (d, J = 8.0 Hz, 1H), 7.28-7.39 (m, 7H), 6.43
dd, J = 8.0 Hz, J = 14.4 Hz, 1H), 5.92 (d, J = 14.4 Hz, 1H),
3
To a solution of (R)-4 (50 mg, 0.15 mmol) and p-Br-
(
1 2
C H CH(OBn) (59 mg, 0.19 mmol) in anhydrous CH Cl (3.0
mL) was added SnCl (26 µL, 0.23 mmol) at –78 °C under argon
atmosphere. After stirring for 1 h, the reaction was quenched
with sat aq NaHCO (5 mL) and extract with CH Cl (3 × 5 mL).
The combined organic phases were dried over anhydrous
Na SO , filtered and concentrated under reduced pressure.
Purification of the crude residue via silica gel column
chromatography (gradient eluent: 0-0.5% of EtOAc/petroleum
ether) afforded 5a (61 mg, 75%) as a yellowish oil. R = 0.55
6
4
2
2
2
4
8
.49 (d, J = 12.0 Hz, 1H), 4.24 (d, J = 12.0 Hz, 1H), 4.23 (d, J =
13
4
.4 Hz, 1H), 2.53-2.61 ( m, 1H), 1.04 (d, J = 6.8 Hz, 3H);
C
NMR (150 MHz, CDCl ) δ 147.5, 144.0, 137.8, 128.4, 128.3,
3
3
2
2
1
7
1
27.8, 127.7, 127.6, 125.2 (CF , q, J = 3.8 Hz), 83.3, 76.1,
3 C-F
-1
0.8, 47.0, 14.6, -1.1; IR (liquid film) cm 2971, 2915, 2850,
2
4
455, 1325, 1251, 1215, 1166, 1128, 1067, 1018, 960, 842;
+
HRMS (ESI-TOF, m/z) calcd for C H F INaO (M+K) :
19
18 3
4
84.9986, found 484.9990.
f
20
4
.7. Synthesis of 14
(EtOAc-petroleum ether, 1:40); [α]D = -32.2 (c 1.0, CHCl3);
The enantiomeric ratio was determined to be 95:5 by HPLC
To a solution of 13 (65 mg, 0.15 mmol) in Et NH (2 mL) was
2
analysis on Chiralpak OD-H column (n-hexane, 1.0 mL/min),
1
added CuI (2.7 mg, 0.014 mmol), Pd(PPh ) (8.4 mg, 0.007
3 4
UV 220 nm, tmajor = 28.50 min, tminor = 36.08 min; H NMR (400
mmol). The solution was degassed by three-pump-taw cycles
followed by adding ethynyltrimethylsilane (82 µL, 0.83 mmol).
The resulting mixture was refluxed at 40 °C before complete
conversion of the starting material as monitored by TLC. The
MHz, CDCl ) δ 7.46 (d, J = 8.0 Hz, 2H), 7.26-7.38 (m, 15H),
3
7
5
1
.12 (d, J = 8.0 Hz, 2H), 5.90 (dd, J = 7.2 Hz, J = 18.4 Hz, 1H),
1 2
.77 (d, J = 18.4 Hz, 1H), 4.44 (d, J = 12.0 Hz, 1H), 4.22 (d, J =
2.0 Hz, 1H), 4.10 (d, J =7.2 Hz, 1H), 2.62-2.70 ( m, 1H), 1.15
13
reaction was quenched with sat aq NH Cl (2 mL) and extracted
4
(d, J = 7.2 Hz, 3H), 0.52 (s, 3H); C NMR (150 MHz, CDCl ) δ
3
with Et O (3 × 5 mL). The combined organic layers were dried
2
1
1
8
2
52.0, 139.8, 138.2, 136.6, 136.5, 134.7, 134.6, 131.3, 129.3,
29.2, 129.1, 128.3, 127.8, 127.7, 127.6, 127.5, 126.3, 121.3,
4.4, 70.6, 47.5, 16.0, -3.8; IR (liquid film) cm 2960, 2918,
over anhydrous Na SO , filtered and concentrated under reduced
2
4
-
1
pressure. Purification of the crude residue via silica gel column
chromatography (gradient eluent: 0-0.5% of EtOAc/petroleum
851, 1742, 1428, 1217, 1112, 1070, 1011, 754; HRMS (ESI-
+
ether) afforded 14 (42 mg, 70%) as a yellow oil. R
f
= 0.56
TOF, m/z) calcd for C H BrNaOSi (M+Na) : 549.1220, found
20
31
31
(
EtOAc-petroleum ether, 1:40); [α]D
= 1.9 (c 1.0 in CHCl3);
5
49.1226.
The enantiomeric ratio was determined to be 95:5 by HPLC
4
.5. Synthesis of 5l
analysis on Chiralpak OD-H column (n-hexane, 1.0 mL/min),
UV 220 nm, tminor = 11.79 min, tmajor = 12.56 min; H NMR (400
1
To a solution of (R)-4 (50 mg, 0.15 mmol), trimethyl
MHz, CDCl ) δ 7.62 (d, J = 8.0 Hz, 2H), 7.40 (d, J = 8.0 Hz,
3
acetaldehyde (20 µL, 0.18 mmol) and MeOTMS (0.18 mL, 0.77
mmol) in CCl (0.5 mL) was added anhydrous FeCl (25 mg,
0
reaction was quenched with sat aq NaHCO3 (10 mL) and
extracted with CH Cl (3 × 10 mL). The combined organic layers
were dried over anhydrous Na SO , filtered and concentrated
under reduced pressure. Purification of the crude residue via
silica gel column chromatography (gradient eluent: 0-0.5% of
EtOAc/petroleum ether) afforded 5l (43 mg, 80 %) as a yellow
2
5
1
H), 7.28-7.37 (m, 5H), 6.08 (dd, J = 7.6 Hz, J = 16.0 Hz, 1H),
.41 (d, J = 16.0 Hz, 1H), 4.46 (d, J = 12.0 Hz, 1H), 4.25 (d, J =
1 2
4
3
.15 mmol) at room temperature. After stirring for 12 h, the
2.0 Hz, 1H), 4.24 (d, J = 6.4 Hz, 1H), 2.57-2.66 ( m, 1H), 1.05
13
(d, J = 6.4 Hz, 3H), 0.17 (s, 9H); C NMR (150 MHz, CDCl ) δ
3
2
2
1
46.3, 144.2, 138.0, 128.4, 127.7, 127.6, 127.5, 125.2 (CF , q, J
3 C-
2
4
=
3.8 Hz), 110.5, 103.7, 93.7, 83.8, 70.9, 44.0, 15.0, -0.07; IR
-1
F
(
liquid film) cm 2969, 2916, 2848, 1455, 1325, 1250, 1165,
1
127, 1066, 841, 757; HRMS (ESI-TOF, m/z) calcd for
+
20
D
C H F NaOSi (M+Na) : 439.1675, found 439.1677.
oil. R = 0.50 (EtOAc-petroleum ether, 1:40); [α] = -5.4 (c =
24 27 3
f
1
9
0
.0 in CHCl ); The enantiomeric ratio was determined to be
3
4
.8. Synthesis of 15
0:10 by HPLC analysis on Chiralpak OD-H column (n-hexane,
1
.7 mL/min), UV 220 nm, tmajor = 6.01 min tminor = 6.28 min; H
To a solution of ent-5b (100 mg, 0.19 mmol) in anhydrous
NMR (400 MHz, CDCl ) δ 7.50-7.51 (m, 4H), 7.34-7.39 (m,
6
Hz, 1H), 3.36 (s, 3H), 2.75 (d, J = 4.0 Hz, 1H), 2.56-2.62 (m,
1
NMR (100 MHz, CDCl ) δ 157.7, 137.0, 136.9, 134.8, 129.7,
1
3
CH Cl (5.0 mL) was added Br (11 µL, 0.20 mmol) at –78 °C
under argon atmosphere. After stirring for 30 min, the reaction
was quenched with sat aq Na S O (5 mL) and extracted with
CH Cl (3 × 5 mL). The combined organic layers were dried over
anhydrous Na SO , filtered and concentrated under reduced
pressure. The crude product was used in the next step without
further purification. To a solution of the above crude product in
THF (5 mL) was added TBAF (0.25 mL, 0.25 mmol, 1.0 M
solution in THF) at –78 °C under argon atmosphere. After
stirring for 30 min, the reaction was quenched with sat aq
NaHCO (5 mL) and extracted with Et O (3 × 5 mL). The
2
2
2
H), 6.21 (dd, J = 6.8 Hz, J = 18.4 Hz, 1H), 5.92 (d, J = 18.4
1 2
13
2
2
3
H), 1.09 (d, J = 6.8 Hz, 3H), 0.92 (s, 9H); 0.60 (s, 3H);
C
2
2
3
2
4
27.7, 122.5, 92.5, 61.5, 42.2, 36.9, 27.0, 15.5, -3.7; IR (liquid
-1
film) cm 2956, 2927, 2859, 1615, 1428, 1260, 1216, 1106,
082, 1030, 797; HRMS (ESI-TOF, m/z) calcd for C H NaOSi
1
23
32
+
(
M+Na) : 375.2115, found 375.2111.
.6. Synthesis of 13
To a solution of ent-5b (100 mg, 0.19 mmol) in anhydrous
4
3
2
combined organic layers were dried over anhydrous Na SO ,
2
4
HFIP (5.0 mL) were added Ag CO (16 mg, 0.058 mmol) and
NIS (52 mg, 0.23 mmol) under argon atmosphere at room
temperature. After stirring for 2 h, the reaction was quenched
with sat aq Na S O (5.0 mL) and extracted with CH Cl (3 × 20
mL). The combined organic layers were dried over anhydrous
Na SO , filtered and concentrated under reduced pressure.
Purification of the crude residue via silica gel column
chromatography (gradient eluent: 0-0.5% of EtOAc/petroleum
ether) afforded 13 (78 mg, 90%) as a yellow oil. R = 0.55
2
3
filtered and concentrated under reduced pressure. Purification of
the crude residue via silica gel column chromatography (gradient
eluent: 0-0.5% of EtOAc/petroleum ether) afforded 15 (66 mg,
88%) as a yellowish oil. R = 0.55 (EtOAc-petroleum ether,
1
determined to be 95:5 by HPLC analysis on Chiralpak OD-H
column (n-hexane, 1.0 mL/min), UV 220 nm, t = 10.57 min,
tmajor = 13.15 min; H NMR (400 MHz, CDCl ) δ 7.63 (d, J = 7.6
Hz, 2H), 7.46 (d, J = 7.6 Hz, 2H), 7.31-7.38 (m, 5H), 6.08 (d, J =
7.2 Hz, 1H), 6.02 (dd, J = 7.2 Hz, J = 8.8 Hz, 1H), 4.51 (d, J =
1
2
2
3
2
2
f
20
:40); [α]D = 92.8 (c 1.0 in CHCl ); The enantiomeric ratio was
3
2
4
minor
1
3
f
20
(
EtOAc-petroleum ether, 1:40); [α]D = 12.6 (c 1.0 in CHCl3);
1
2
The enantiomeric ratio was determined to be 94:6 by HPLC
analysis on Chiralpak OD-H column (n-hexane, 1.0 mL/min),
2.0 Hz, 1H), 4.38 (d, J = 6.4 Hz, 1H), 4.28 (d, J = 12.0 Hz, 1H),

6
Tetrahedron
TE(150 MANUSCRIPT
1
C
3
8
985; (f) Jiménez-Aquino, A.; Flegeau, E. F.; Schneider, U.;
3
.06-3.11 ( m, 1H), 1.07 (d, J = 6.8 Hz, 3H
A
);
C
CENM
P
R
D
Kobayashi, S. Chem. Commun. 2011, 47, 9456-9458; (g) Chen,
M.; Roush, W. R. Org. Lett. 2013, 15, 1662-1665; (h) Zuo, Z. Q.;
Yang, J.; Huang, Z. Angew. Chem. Int. Ed. 2016, 55, 10839-
MHz, CDCl ) δ 144.4, 138.0, 136.6, 128.4, 127.7, 127.6, 127.5,
3
1
25.2 (CF , q, J = 3.8 Hz), 107.9, 83.1, 71.1, 41.5, 14.4; IR
3 C-F
-1
(liquid film) cm 2971, 2919, 2867, 1619, 1454, 1418, 1323,
1
0843.
1
261, 1163, 1123, 1066, 1017, 834; HRMS (ESI-TOF, m/z)
3. (a) Chen, M.; Roush, W. R. J. Am. Chem. Soc. 2011, 133, 5744-
5747; (b) Chen, M.; Roush, W. R. J. Am. Chem. Soc. 2012, 134,
+
calcd for C H BrF KO (M+K) : 437.0125, found 437.0120.
19
18
3
3
925-3931; (c) Chen, M.; Roush, W. R. J. Org. Chem. 2013, 78,
4
.6. Synthesis of 16
To a solution of 15 (65 mg, 0.16 mmol) in Et NH (2 mL) was
3-8.
4
5
.
.
(a) Lautens, M.; Huboux, A. H.; Chin, B.; Downer, J.
Tetrahedron Lett. 1990, 131, 5829-5832; (b) Lautens, M.; Ben,
R. N.; Delanghe, P. H. M. Tetrahedron. 1996, 52, 7221-7234.
(a) Panek, J. S.; Yang, M. J. Am. Chem. Soc. 1991, 113, 6594-
2
added CuI (3 mg, 0.016 mmol), Pd(PPh ) (9.4 mg, 0.08 mmol).
3
4
The solution was degassed by three-pump-taw cycles followed
by adding ethynyltrimethylsilane (92 µL, 0.65 mmol). The
resulting mixture was refluxed at 40 °C before complete
conversion of the starting material as monitored by TLC. The
6
1
1
2
600; (b) Panek, J. S.; Xu, F. J. Am. Chem. Soc. 1995, 117,
0587-10588; (c) Panek, J. S.; Zhu, B. J. Am. Chem. Soc.
997, 119, 12022-12023; (d) Lowe, J. T.; Panek, J. S. Org. Lett.
005, 7, 1529-1532; (e) Wu, J.; Chen, Y.; Panek, J. S. Org. Lett.
reaction was quenched with sat aq NH Cl (2 mL) and extracted
2010, 12, 2112-2115; (f) Wu, J.; Zhu, K. C.; Yuan, P. W.; Panek,
J. S. Org. Lett. 2012, 14, 3624-3627; (g) Chen, M.; Roush, W. R.
Org. Lett. 2013, 15, 7, 1662-1665.
4
with Et O (3 × 5 mL). The combined organic layers were dried
2
over anhydrous Na SO , filtered and concentrated under reduced
2
4
6
.
(a) Wetter, H.; Scherer, P.; Schweizer, W. B. Helv. Chim. Acta.
pressure. Purification of the crude residue via silica gel flash
column chromatography (gradient eluent: 0-0.5% of
EtOAc/petroleum ether) afforded 16 (44 mg, 65%) as a yellow
1
1
979, 62, 1987-1989; (b) Wetter, H.; Paul, S. Helv. Chim. Acta.
983, 66, 118-122.
7. Lautens, M.; Delanghe, P. H. M. Angew. Chem. Int. Ed. 1994,
06, 2557-2559.
20
D
1
oil. R = 0.55 (EtOAc-petroleum ether, 1:40); [α] = 78.4 (c 1.0
f
8
.
Li, L. J.; Ye, X. C.; Wu, Y.; Gao, L.; Song, Z. L.; Yin, Z. P.; Xu
Y. J. Org. Lett. 2013, 15, 1068-1071. For selected advances of
geminal bis(silane) chemistry, see: (b) Luo, Q.; Wang, C.; Li, Y.
X.; Ouyang, K. B.; Gu, L; Uchiyama, M; Xi, Z. F. Chem.
Sci. 2011, 2, 2271-2274; (c) Groll, K.; Manolikakes, S. M.; du
Jourdin, X. M.; Jaric, M.; Bredihhin, A.; Karaghiosoff, K.;
Carell, T.; Knochel, P. Angew. Chem. Int. Ed. 2013, 52, 6776-
in CHCl ); The enantiomeric ratio was determined to be 94:6 by
3
HPLC analysis on Chiralpak OD-H column (n-hexane, 1.0
1
mL/min), UV 220 nm, tminor = 6.94 min, tmajor = 8.88 min; H
NMR (600 MHz, CDCl ) δ 7.61 (d, J = 8.4 Hz, 2H), 7.46 (d, J =
3
8
5
6
.4 Hz, 2H), 7.29-7.37 (m, 5H), 5.83 (dd, J = J = 10.2 Hz, 1H),
1 2
.41 (d, J = 10.2 Hz, 1H), 4.50 (d, J = 12.0 Hz, 1H), 4.36 (d, J =
.0 Hz, 1H), 4.29 (d, J = 12.0 Hz, 1H), 3.16-3.22 ( m, 1H), 1.09
6
2
780; (d) Cui, H. Y.; Zhang, J. Y.; Cui, C. M. Organometallics
013, 32, 1-4; (e) Bai, X. F.; Deng, W. H.; Xu, Z.; Li, F. W.;
13
(d, J = 7.2 Hz, 3H), 0.21 (s, 9H); C NMR (150 MHz, CDCl ) δ
3
Deng, Y.; Xia, C. G.; Xu, L.W. Chem. Asian J. 2014, 9, 1108-
1112. (f) Liu, Z. X.; Tan, H. C.; Fu, T. R.; Xia, Y.; Qiu, D.;
Zhang, Y.; Wang, J. B. J. Am. Chem. Soc. 2015, 137, 12800-
12803; (g) Liu, Z. J.; Lin, X. L.; Yang, N.; Su, Z. S.; Hu, C. W.;
Xiao, P. H.; He, Y. Y.; Song, Z. L. J. Am. Soc. Chem. 2016, 138,
1
46.5, 147.8, 138.1, 128.4, 127.7, 127.6, 127.5, 125.1 (CF , q, J
3 C-
=
3.8 Hz), 109.6, 101.6, 99.1, 84.0, 71.2, 41.8, 15; IR (liquid
F
-1
film) cm 2963, 2920, 2848, 1325, 1261, 1215, 1166, 1066,
017, 805; HRMS (ESI-TOF, m/z) calcd for C H F NaOSi
M+Na) : 439.1675, found 439.1677.
1
(
24
27 3
1
877-1883.
+
9
.
For seminal works, see: (a) Hosomi, A.; Endo, M.; Sakurai, H.
Chem. Lett. 1976, 941-942; (b) Hosomi, A.; Sakurai, H.
Tetrahedron Lett. 1976, 1295-1298; (c) Sakurai, H.; Sasaki, K.;
Hosomi, A. Tetrahedron Lett. 1981, 22, 745-748. For selected
reviews, see: (d) Fleming, I.; Dunogues, J.; Smithers, R. Org.
React. 1989, 37, 57-575; (e) Overman, L. E.; Blumenkopf, T. A.
Chem. Rev. 1986, 86, 857-873; (f) Hosomi, A. Acc. Chem. Res.
1988, 21, 200-206. For the latest advances, see: (g) Orimoto, K.;
Oyama, H. Namera, Y.; Niwa, T.; Nakada, M. Org. Lett. 2013,
Acknowledgments
We are grateful for financial support from the NSFC
21290180, 21622202, 21502125). The authors thank Prof. Qin
(
Ouyang in Third Military Medical University for his invaluable
help in computational works. The authors also thank Prof. Cheng
Yang in Chemical Department at Sichuan University for his
invaluable help in circular dichroism spectroscopy.
1
5
2
5, 768-771; (h) List, B.; Gandhi, S. Angew. Chem. Int. Ed. 2013,
2, 2573-2576; (i) Chaskar, A.; Murugan, K. Catal. Sci. Technol.
014, 4, 1852-1868; (j) MacDonald, J. P.; Shupe, B. H.;
Schreiber, J. D.; Franz, A. K. Chem. Commun. 2014, 50, 5242-
5244; (k) Sai, M.; Yamamoto, H. J. Am. Chem. Soc. 2015, 137,
Supplementary Material
7
091-7094; (l) Zhao, S.; Zhang, X. L.; Zhang, Y. W.; Yang, H.
H.; Huang, Y.; Zhang, K.; Du, T. New J. Chem. 2015, 39, 7734-
737; (m) Kaib, P. S., Schreyer, L., Lee, S., Properzi, R., List, B.
Angew. Chem. Int. Ed. 2016, 55, 13200-13203.
1
13
Supplementary data ( H NMR, C NMR, IR, HRMS spectra
of new compounds) related to this article can be found online.
7
1
0. (a) Corey, E. J.; Katzenellenbogen, J. A.; Posner, G. H. J. Am.
Chem. Soc. 1967, 89, 4245-4247; (b) Denmark, S. E.; Jones T. K.
J. Org. Chem., 1982, 47, 4595-4597.
References and notes
1
1
1. Kim, K. D.; Wagriotis, P. A. Tetrahedron Lett. 1990, 131, 6137-
1
.
(a) Yamamoto, Y.; Asao, N.; Chem. Rev. 1993, 93, 2207-2293;
b) Chemler, S. R; Roush, W. R. Modern Carbonyl Chemistry;
Otera, J., Ed.; WILEY-VCH: New York, 2000; Chapter 11, p
6
140.
2. (a) Myers, A. G.; Zheng, Bin Tetrahedron Lett. 1996. 37, 4841-
844; (b) Sammis, G. M.; Flamme, E. M.; Xie, H.; Ho, D. M.;
(
4
4
9
9
03. (c) Fleming, I.; Barbero, A.; Walter, D. Chem. Rev. 1997,
7, 2063-2192; (d) Langkopf, E.; Schinzer, D. Chem. Rev. 1995,
5, 1375-1406. (e) Hall, D. G.; Lachance, H. Allylboration of
Sorensen, E. J. J. Am. Chem. Soc. 2005, 127, 8612-8613; (c)
Movassaghi, M.; Ahmad, O. K. J. Org. Chem. 2007, 72, 1838-
1
841; (d) Qi, W.; McIntosh, M. C. Org. Lett. 2008, 10, 357-359.
3. (a) Panek, J. S.; Clark, T. D. J. Org. Chem. 1992, 57, 4323-4326;
b) Ogawa, J.; Xie, S. X.; Shimizu, S. Appl. Microbiol. Biot.
999, 51, 53-57; (c) Denmark, S. E.; Werner, N. J. Am. Chem.
Carbonyl Compounds; Wiley: Hoboken, NJ, 2012. (f) Fleming, I.
Allylsilanes, allylstannanes and related systems. In
Comprehensive Organic Synthesis; Trost, B. M.; Fleming, I.
Eds.; Pergamon Press: Oxford, 1991; Vol. 6, pp 563-593.
1
1
(
1
Soc. 2010, 132, 3612-3620.
2
.
(a) Yamamoto, Y.; Yatagai, H.; Maruyama, K. J. Am. Chem. Soc.
4. The R-configuration of (R)-4 was assigned by comparing its
circular dichroism spectroscopy with the computational results.
See Supporting Information for details. This assignment can be
also supported by the following well-known stereochemical
course. Mitsunobu reaction of (S)-8b with hydrazine would give
1
981, 103, 3229-3231; (b) Tsai, D. J. S.; Matteson, D. S.
Organometallics. 1983, 2, 236-241; (c) Yamamoto, Y.;
Maruyama, K.; Komatsu, T.; Ito, W. J. Org. Chem. 1986, 51,
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(
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