Catalytic and highly enantioselective Friedel-Crafts type reactions of heteroaromatic compounds with trifluoropyruvate and glyoxylate by a dicationic palladium complex

Article abstract of DOI:10.1016/j.tetasy.2014.06.013

The highly enantioselective Friedel-Crafts alkylation of furan and thiophene derivatives with trifluoropyruvate, which have never provided the high level of asymmetric induction and yield until now, was achieved by using dicationic palladium complexes as Lewis acid catalysts. Moreover, glyoxylate instead of trifluoropyruvate as an electrophile led to complete change of regioselectivity with 2-trimethylsilylated furan, thiophene, and pyrrole derivatives to give the corresponding heteroarylated products in high yields and enantioselectivities. The respective products with trifluoropyruvate and glyoxylate could also be obtained via sequential catalytic reaction; intramolecular cyclization of alkynyldiols using cationic Au catalyst followed by Friedel-Crafts type reactions using dicationic Pd catalyst.

Full text of DOI:10.1016/j.tetasy.2014.06.013

Tetrahedron: Asymmetry 25 (2014) 1104–1115
Contents lists available at ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Catalytic and highly enantioselective Friedel–Crafts type reactions of
heteroaromatic compounds with trifluoropyruvate and glyoxylate by
a dicationic palladium complex
⇑
ꢀ
Kohsuke Aikawa, Yuya Asai, Yuta Hioki, Koichi Mikami
Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 May 2014
Accepted 12 June 2014
The highly enantioselective Friedel–Crafts alkylation of furan and thiophene derivatives with trifluoro-
pyruvate, which have never provided the high level of asymmetric induction and yield until now, was
achieved by using dicationic palladium complexes as Lewis acid catalysts. Moreover, glyoxylate instead
of trifluoropyruvate as an electrophile led to complete change of regioselectivity with 2-trimethylsilylat-
ed furan, thiophene, and pyrrole derivatives to give the corresponding heteroarylated products in high
yields and enantioselectivities. The respective products with trifluoropyruvate and glyoxylate could also
be obtained via sequential catalytic reaction; intramolecular cyclization of alkynyldiols using cationic Au
catalyst followed by Friedel–Crafts type reactions using dicationic Pd catalyst.
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
as a carbonyl compound, which is a versatile and commercially
available reagent for the CF3 building block method, can lead to
Organofluorine compounds, which are extremely rare in Nature,
have received considerable attention in the fields of pharmaceuti-
cals, agrochemicals, and organic materials due to their unique
chemical, biological, and physical properties.1 In modern medicinal
chemistry, trifluoromethyl-substituted compounds are widely
employed, because trifluoromethyl (CF3) groups can bring higher
metabolic stability, increased lipophilicity, and stronger dipole
moments to druglike compounds.1 Therefore, a variety of synthetic
methods to introduce the CF3 group into organic compounds have
been reported to readily produce the corresponding compounds,
optically active a-trifluoromethyl-substituted tertiary alcohols in
high yields and enantioselectivities.5–8 However, the high level of
asymmetric induction is limited to indole, pyrrole, and activated
aromatic derivatives as nucleophiles with higher reactivity,5 as
compared with furan and thiophene derivatives. Herein, we report
the highly enantioselective Friedel–Crafts alkylations of furan and
thiophene derivatives with trifluoropyruvate with high levels of
asymmetric induction and yield using dicationic palladium com-
plexes as Lewis acid catalysts (Scheme 1-1). We also report that
the combination of 2-trimethylsilylated furan, thiophene, and pyr-
role derivatives and glyoxylate leads to a complete change of reg-
ioselectivity to afford the heteroarylated products at the 2-position
along with high asymmetric induction (Scheme 1-2).9
even in optically active forms. Optically active
a-trifluoromethyl-
substituted tertiary alcohols prepared via catalytic asymmetric
synthesis have attracted widespread interest due to their
unique biological activities, as typically shown in the anti-HIV
agent (Efavirenz)2 and nonsteroidal glucocorticoid receptor (GR)
agonists.3
2. Results and discussion
Initially, the Friedel–Crafts type reaction of 2-trimethylsilyl
furan 4a as a nucleophile was examined in the presence of dicat-
ionic Pd-catalyst 1a (5 mol %) prepared in situ from the corre-
The Friedel–Crafts alkylation is one of the most fundamental
carbonAcarbon bond forming reactions in modern organic synthe-
sis.4 Chiral transition-metal catalysts as well as organocatalysts
have been developed for the Friedel–Crafts alkylations of (het-
ero)aromatic compounds with carbonyl and imine compounds.4
The Friedel–Crafts alkylations by treatment of trifluoropyruvate
10
sponding dichloride complex and two equivalents of AgSbF6
(Scheme 2). As shown in the literature,9 the reactions with ethyl
glyoxylate 3 proceeded regioselectively at the 2-position even at
ꢀ40 °C to give product 6a in excellent yield and enantioselectivity
after the desilylation of siloxy product 6a0 (Scheme 2, Eq. 2). In
sharp contrast to ethyl glyoxylate 3, it was found that the reaction
with ethyl trifluoropyruvate 2 provided the Friedel–Crafts product
⇑
Corresponding author. Tel.: +81 3 5734 2142; fax: +81 3 5734 2776.
E-mail address: mikami.k.ab@m.titech.ac.jp (K. Mikami).
http://dx.doi.org/10.1016/j.tetasy.2014.06.013
0957-4166/Ó 2014 Elsevier Ltd. All rights reserved.

K. Aikawa et al. / Tetrahedron: Asymmetry 25 (2014) 1104–1115
1105
1)
O
F3C OH
X
X
F3C
CO2Et
s-Bu
CO2Et
R
R
Ph2
P
Pd cat*
up to 95%, 99% ee
X = O, S, NR
2)
Pd2+
P
-
Ph2
O
2SbF6
H
OSi
CO2Et
H
CO2Et
X
Pd cat*
X
Si
R
Pd cat*
R
up to 96%, 99% ee
X = O, S, NR
Scheme 1. Regio- and enantioselective Friedel–Crafts type reactions with dicationic palladium catalyst.
O
F3C
CO2Et
F3C OH
2
O
1a (5 mol%)
CO2Et
TMS
(1)
(2)
CH2Cl2, -78 °C, 4 h
O
5a: 46%, 98% ee
OX
CO2Et
H
TMS
H
4a
O
1a (5 mol%)
H
Ref. 9
CH2Cl2, -40 °C, 6 h
O
6a' (X = TMS)
1M HCl/THF
H
CO2Et
3
6a (X = H): 95%, 99% ee
Scheme 2. Complete change of regioselectivity in reaction with 2-trimethylsilyl furan and carbonyl compounds.
Table 1
5a at the 5-position with high levels of enantioselectivity but mod-
erate yield, although 6a and 6a0 were not observed at all (Scheme 2,
Eq. 1). It is supposed that the complete change of regioselectivity
originates from the steric repulsion between the trimethylsilyl
and trifluoromethyl groups. The absolute configuration at the cre-
ated carbon center of 5a and 6a was determined to be the same (R)
by comparison with the specific rotation of the reported data.5b,9
Encouraged by the excellent enantioselectivity (98% ee)
obtained even with simple mono-substituted furan, we attempted
to optimize the Friedel–Crafts alkylation (Table 1). (S)-BINAP and
(S)-SEGPHOS exhibited excellent enantioselectivities, while the
yields were moderate (entries 1 and 2). The more sterically
demanding ligand, (S)-DTBM-SEGPHOS led to an almost racemic
product (entry 3). (R,R)-QuinoxP⁄11 also gave high levels of enanti-
oselectivity (entry 4). With the aim of enhancing the yield, we
investigated the effect of the co-solvent. The use of toluene as a
co-solvent did not increase the yield (entries 5 and 6). The combi-
nation of CH2Cl2 and the coordinating solvent Et2O, which gener-
ally lowers the reactivity of Lewis acid catalysts, catalyzed the
reaction to provide product 5a in high yields, while maintaining
excellent enantioselectivities (entries 7 and 8). Additionally, the
yield and enantioselectivity could be maintained even with a lower
catalyst loading of 1 and 2 mol % (90–93% yields, 99% ee) (entries 9
and 10). The use of THF or CH3CN provided no products (entries 11
and 12).
Catalytic asymmetric Friedel–Crafts alkylation of 2-trimethylsilyl furan with
trifluoropyruvatea
F3C OH
O
O
Pd cat* (X mol%)
conditions
H
TMS
O
CO2Et
+
TMS
F3C
X
CO2Et
5a
ee (%)c
4a
2
conditions
yield (%)b
entry
Pd cat*
1a
1b
1c
1d
1a
1d
1a
1d
1a
1a
1a
1a
1
5
5
5
5
5
5
5
5
2
1
5
5
CH2Cl2, -78 °C, 4 h
CH2Cl2, -78 °C, 4 h
CH2Cl2, -40 °C, 4 h
CH2Cl2, -40 °C, 4 h
46
52
92
76
48
55
92
83
93
90
trace
0
98
97
2
2
3
4
95d
94
96d
99
99d
99
99
-
5
CH2Cl2/toluene (1/1), -78 °C, 8 h
CH2Cl2/toluene (1/1), -78 °C, 8 h
CH2Cl2/Et2O (1/1), -78 °C, 8 h
CH2Cl2/Et2O (1/1), -78 °C, 8 h
CH2Cl2/Et2O (1/1), -78 °C, 8 h
CH2Cl2/Et2O (1/1), -40 °C, 8 h
CH2Cl2/THF (1/1), -20 °C, 24 h
CH2Cl2/MeCN (1/1), -20 °C, 24 h
6
7
8
9e
10e
11
12
-
a3 equivalents of 2 were used. bIsolated yield. cEnantiopurity was determined by chiral HPLC anlysis.
dOpposite enantiomer (S) was obtained. e1.2 equivalents of 2 were used.
tBu
Me
O
Ph2
P
Ar2
P
N
N
P
P
To extend the scope of the substrates, the Friedel–Crafts alkyl-
ation was further examined under the optimized reaction condi-
tions in hand (Table 2). Non-substituted furan 4b exhibited
excellent results (95% and 99% ee), although it was hard to attain
both high yield and enantioselectivity as in the previous reports.5a,b
Furans 4c–e bearing aliphatic and aromatic substituents at the
O
O
Pd2+
Pd2+
Pd2+
P
P
-
2SbF6
-
Ph2
-
Ar2
2SbF6
2SbF6
Me
tBu
O
1a
(S)-BINAP-Pd:
1b
1c
1d
(S)-SEGPHOS-Pd (Ar = Ph):
(S)-DTBM-SEGPHOS-Pd:
(Ar = 3,5-tBu2-4-OMe-C6H2)
(R,R)-QuinoxP*:

1106
K. Aikawa et al. / Tetrahedron: Asymmetry 25 (2014) 1104–1115
Table 2
Scope of substrates in the catalytic enantioselective Friedel–Crafts alkylation
F3C OH
O
X
1a
(2 mol%)
H
X
+
CO2Et
R
CH2Cl2/Et2O (1/1)
-78 °C, 8 h
F3C
CO2Et
R
4a-k
2
5a-k
(1.2 eq.)
O
O
O
TMS
O
Me
Ph
5a: 93%, 99% ee
5b: 95%, 99% ee
5c: 65%, 94% ee
5d: 70%, 99% ee
O
O
Ph
O
O
TBDPSO
EtO
Ph
5e: 89%, 99% ee
5f: 82%, 99% ee
5g: N.R.
Boc
N
H
N
S
S
Me
2-
3-
5j: 73% (2-/3- = 3/2)a
5h: 89%, 94% eea
5i:
95%, 97% ee
b
c
5k:
89%, 37% ee
aConditions: 0 °C, 24 h. bConditions: -40 °C, 24 h. cConditions: -78 °C, 24 h.
5-position also gave the good results, but 4c decreased both the
yield and enantioselectivity. Furan 4f with a phenyl group at the
3,5-positions could be employed regardless of steric hindrance
(82% and 99% ee). The reaction of furan 4g with an electron-
withdrawing ester group did not proceed even under the reflux
conditions. Non- or methyl-substituted thiophenes 4h–i were
amenable to the highly enantioselective Friedel–Crafts reaction.
The tert-butoxycarbonyl (Boc) group of pyrrole 4j had a deteriorat-
ing effect on the regioselectivity and gave a mixture of a 3:2 ratio
in the 2- and 3-positions. Treatment of N-unprotected pyrrole 4k
led to a single product at the 2-position but the enantioselectivity
was low (89% and 37% ee).
excellent enantioselectivities (94–99% ee). The reaction of 2,3,5-tri-
substituted furans 11e provided the product in high yield, but the
enantioselectivity decreased with a deleterious effect on the steric
hindrance (95% and 82% ee). 2,4,5-Trisubstituted furans 11f facili-
tated the reactions to give excellent results (89% and 99% ee). Addi-
tionally, the reactions with mono- and disubstituted thiophenes
11g–j also gave high yields and enantioselectivites (85–93% and
98–99% ee). The combination of Boc-pyrroles 11k–n and 3 led to
complete regioselectivity at the 2-position and high enantioselec-
tivities (96–99% ee), while the regioisomers at the 2- and
3-positions were obtained in the Friedel–Crafts alkylation with
Boc-pyrrole 4j and 2.
In sharp contrast to a heteroaromatic system, the combination
of vinylsilane 7 as a nucleophile and ethyl trifluoropyruvate 2
afforded the alkenylated product 8 in 92% yield and with 98% ee
after desilylation, due to the smaller steric repulsion between 7
and the trifluoromethyl group compared to 4a (Scheme 3, Eq. 1).
Dienylsilane 9 also gave the dienylated product 10 in 82% and with
99% ee (Scheme 3, Eq. 2).
We also investigated the scope of the substrates in catalytic
asymmetric Friedel–Crafts type reactions of 2-trimethylsilylated
heteroaromatic compounds with ethyl glyoxylate 3 (Table 3). All
substrates gave products 6 bonded onto the trimethylsilylated car-
bon with high enantioselectivity. Not only mono-substituted furan
4a12 but also 2,5-disubstituted 11b–d provided with high to
With these positive results for a wide range of 5-membered het-
eroaromatic nucleophiles, we utilized the heteroarylated products
as chiral building blocks for the enantioselective synthesis of pyr-
anone13 (Scheme 4). Reduction14 with 6a followed by pivaloyl pro-
tection provided the corresponding alcohol 13 in good yield.
Reaction of NBS with 13 in the presence of NaOAc and NaHCO3
led to pyranone 14 via an Achmatowicz rearrangement.15 Finally,
Bz-protection of a hemiacetal proceeded to give the protected pyr-
anone 1513b in a 4:1 ratio of trans and cis-stereoisomer in 86% yield
for two steps.
The palladium-catalyzed methodology was then expanded for a
two-directional reaction (Scheme 5). Following the Friedel–Crafts
alkylation of furan 4a with trifluoropyruvate 2 in the presence of
O
F3C OX
1a
(5 mol%)
CH2Cl2, 0 °C, 24 h
6M HCl/THF
TMS
(1)
(2)
+
Ph
F3C
CO2Et
Ph
8'
CO2Et
7
2
(X = TMS)
8 (X = H): 92%, 98% ee
F3C OX
CO2Et
O
1a (5 mol%)
CO2Et CH2Cl2, 0 °C, 24 h
TMS
+
F3C
Ph
Ph
10'
9
2
(X = TMS)
6M HCl/THF
10 (X = H): 82%, 99% ee
Scheme 3. Catalytic asymmetric alkenylation and dienylation.

K. Aikawa et al. / Tetrahedron: Asymmetry 25 (2014) 1104–1115
1107
Table 3
Catalytic asymmetric Friedel–Crafts type reaction of 2-trimethylsilylated furan, thiophene, and pyrrole derivatives with ethyl glyoxylate
H
OH
CO2Et
O
X
1a (5 mol%)
TMS
X
+
R
CH2Cl2
0 °C, 24 h
then 1M HCl/THF
H
CO2Et
R
4a 11b-n
3
6a-n
or
O
O
O
O
Me
Ph
TBDPSO
6d:
89%, 99% ee
6a: 80%, 97% ee
95%, 99% eea
6b: 75%, 94% ee
6c: 86%, 97% ee
O
O
Ph
Ph
Ph
Ph
b
6e
: 95%, 82% ee
6f:
89%, 99% ee
S
S
S
S
Ph
Me
TBDPSO
c
c
6j: 87%, 99% eec
c
6h:
6i:
92%, 99% ee
93%, 99% ee
6g:
85%, 98% ee
Boc
Boc
N
Boc
N
Boc
N
N
Ph
Me
TBDPSO
6k: 92%, 99% eed
6l: 96%, 98% eee
6m: 91%, 96% eee
6n: 85%, 99% eee
aConditions: -40 °C, 6 h. bConditions: -40 °C, 12 h. cConditions: 0 °C, 12 h.
dConditions: -78 °C, 5 h. eConditions: -40 °C, 24 h.
H
OH
CO2Et
H
OH
NEt3
PivCl
H
OH
O
NaBH4
OH
O
OPiv
O
CH2Cl2
THF/MeOH
rt, 12 h
0 °C, 5 h
13
: 87%
6a (99% ee)
12: 90%
O
O
NEt3, BzCl
NBS, NaOAc
DMAP (cat.)
OPiv
NaHCO3
OPiv
O
O
CH2Cl2
THF/H2O
0 °C, 1 h
-40 °C, 1 h
OBz
OH
15
14
86% (2 steps)
trans:cis = 4:1
Scheme 4. Synthesis of a chiral pyranone from furan via an Achmatowicz rearrangement.
1a (2 mol %) under the optimized reaction conditions, the reaction
of glyoxylate 3 to intermediate 5a led to the two-directional
adduct 16 in 91% yield with 99% ee as a single diastereomer with-
out the formation of the undesired meso type product.
O
F3C
CO2Et
2
F3C OH
O
H
TMS
1a (2 mol%)
We also attempted to transform alkynyldiols, which can be
O
CO2Et
readily synthesized from
a-hydroxy ketones, to a-hydroxy esters
TMS
CH2Cl2/Et2O (1/1)
-78 °C, 8 h
by a one-pot operation (Scheme 6). Alkynyldiol 17 in toluene
was converted in situ to 2-trimethylsilylated furan 11f via intra-
molecular cyclization by a cationic Au catalyst 19a.16,17 After the
solution of ethyl glyoxylate 3 and dicationic Pd catalyst 1a in
dichloromethane was transferred to a solution of 17, the Friedel–
Crafts type reaction proceeded to produce the heteroarylated prod-
uct 6f in 57% yield and with 99% ee (Scheme 6, Eq. 1). In a similar
manner to the glyoxylate system, intramolecular cyclization with
alkynyldiol 18 by Au catalyst 19b followed by Friedel–Crafts reac-
tion with trifluoropyruvate 2 using Pd catalyst 1a led to product 5f
in 62% yield and with 99% ee (Scheme 6, Eq. 2).
4a
5a
O
H
CO2Et
F3C OH
HO
EtO2C
H
3
O
CO2Et
rt, 12 h
then 1M HCl/THF
16: 91%, 99% ee
Scheme 5. Two-directional reaction of furan 4a with ethyl trifluoropyruvate
followed by ethyl glyoxylate.

1108
K. Aikawa et al. / Tetrahedron: Asymmetry 25 (2014) 1104–1115
Glyoxylate
OH
Au(NTf2)
P
tBu2
TMS
O
Ph
TMS
19a (2.5 mol%)
Ph
(1)
Ph OH
toluene, rt, 3 h
Ph
17
11f
H
OH
CO2Et
O
O
1a
(5 mol%)
Ph
H
CO2Et
3
CH2Cl2/toluene (1/1)
0 °C, 24 h
Ph
6f: 57%, 99% ee
then 1N HCl/THF
Trifluoropyruvate
Au(SbF6)
P
tBu2
OH
Ph
O
Ph
H
19b
(2.5 mol%)
H
(2)
Ph OH
CH2Cl2, rt, 3 h
Ph
18
4f
F3C OH
O
O
1a (2 mol%)
CO2Et
F3C
CO2Et
Ph
2
CH2Cl2/Et2O (1/1)
-40 °C, 16 h
Ph
5f: 62%, 99% ee
Scheme 6. Sequential catalytic intramolecular cyclization by an Au catalyst followed by Friedel–Crafts type reactions by a Pd catalyst.
FT/IR-4200 spectrometer. High performance liquid chromatogra-
phy (HPLC) was conducted on JASCO PU-980, LG-980-02, DG-
3. Conclusion
980-50, MD-2010, and CO-966 instrument equipped with model
UV-975 spectrometers as an ultra violet light. Dichloromethane
(dehydrate), toluene (dehydrate), and diethyl ether (dehydrate)
were purchased from Kanto Chemical Co., Inc. Ethyl trifluoropyru-
vate was provided by Central Glass Co., Ltd. Silver hexafluoroan-
timonate and ethyl glyoxylate polymer form (ꢁ50 wt % in
toluene) were purchased from Aldrich. PdCl2[(S)-BINAP] was syn-
thesized according to the literature procedure.18 Heteroarylsilanes
4a,19 11b,20 11c,21 11g,22 11h,23 11k,24 vinylsilane 7,25 and die-
nylsilane 926 were also synthesized according to the literature
procedures.
In conclusion, we have reported on the highly enantioselective
Friedel–Crafts reactions of furan and thiophene derivatives with
trifluoropyruvate by using dicationic palladium complexes as
Lewis acid catalysts. Moreover, the Friedel–Crafts type reaction of
2-trimethylsilylated furan, thiophene, and pyrrole derivatives with
glyoxylate led to a complete change of regioselectivity to give the
heteroarylated products in high yields and enantioselectivities.
Additionally, the catalytic intramolecular cyclization of alkynyldi-
ols by a cationic gold catalyst followed by Friedel–Crafts type reac-
tions with trifluoropyruvate or glyoxylate by
a dicationic
palladium catalyst gave the corresponding products with high
enantioselectivities. The development of novel and practical reac-
4.2. General procedure for the catalytic asymmetric Friedel–
Crafts reaction with trifluoropyruvate (Table 2)
tions to provide optically active
tiary alcohols is currently ongoing in our laboratory.
a-fluoromethyl-substituted ter-
To a solution of PdCl2[(S)-BINAP] (3.2 mg, 0.004 mmol) in
CH2Cl2 (1.0 mL) was added AgSbF6 (3.0 mg, 0.0088 mmol) at room
temperature under an argon atmosphere. After stirring for 30 min,
4. Experimental
4.1. General
Et2O (1.0 mL), ethyl trifluoropyruvate 2 (32 lL, 0.24 mmol), and
heteroaryl compounds 4 (0.2 mmol) were added at ꢀ78 °C. The
reaction mixture was stirred at ꢀ78 °C for 8 h, and then loaded
directly onto a short silica-gel column (hexane/AcOEt = 1:1) to
remove the catalyst. Purification by a silica-gel chromatography
(hexane/AcOEt = 9:1) gave the corresponding alcohol product 5.
The enantiomeric excess was determined by chiral HPLC analysis.
1H, 13C, and 19F NMR spectra were measured on Bruker AV300M
(300 MHz) spectrometers. The chemical shifts of 1H NMR are
expressed in parts per million relative to the singlet (d = 7.26) for
CDCl3. The chemical shifts of 13C NMR are expressed in parts per
million relative to the central line of the triplet (d = 77.0) for CDCl3.
The chemical shifts of 19F NMR are expressed in parts per million
relative to the singlet (d = ꢀ63.24) for benzotrifluoride (BTF) as
an internal standard. Optical rotations were measured on a JASCO
P-1020. Mass spectra were measured on a JEOL JMS-T100CS
(Accu-TOF) spectrometer. IR spectra were measured on a JASCO
4.2.1. (R)-Ethyl 3,3,3-trifluoro-2-hydroxy-2-(5-(trimethylsilyl)-
furan-2-yl)propanoate 5a
1H NMR (300 MHz, CDCl3) d 0.25 (s, 9H), 1.34 (t, J = 7.2 Hz, 3H),
4.36–4.44 (m, 2H), 4.37 (s, 1H), 6.57 (d, J = 3.3 Hz, 1H), 6.60 (d,

K. Aikawa et al. / Tetrahedron: Asymmetry 25 (2014) 1104–1115
1109
J = 3.3 Hz, 1H); 13C NMR (75 MHz, CDCl3) d ꢀ1.3, 13.9, 64.4, 75.3 (q,
JC–F = 31.5 Hz), 110.2, 120.2, 122.4 (q, JC–F = 284 Hz), 149.8, 162.5,
167.4; 19F NMR (282 MHz, CDCl3) d ꢀ76.2; FT-IR (KBr pellet,
cmꢀ1) 3479, 2963, 1744, 1300, 1253, 1176, 1111, 1020, 932, 842;
HRMS (ESI-TOF) calcd for C12H17F3NaO4Si [M+Na]+: 333.0746,
d ꢀ76.6; FT-IR (KBr pellet, cmꢀ1) 3479, 2957, 2932, 2858, 1745,
1428, 1308, 1178, 1111, 1019, 823, 703; HRMS (ESI-TOF) calcd
for C26H29F3KO5Si [M+K]+: 545.1373, found: 545.1355; [
a]
=
25
D
ꢀ19.0 (c 0.7, CHCl3), 99% ee; HPLC (column, CHIRALCEL OD-3,
Hexane/2-Propanol = 99:1, flow rate 0.6 mL/min, 20 °C, detection
UV 210 nm) tR of minor isomer 18.4 min, tR of major isomer
20.1 min. The absolute configuration was tentatively assigned by
analogy of the specific rotation.
found: 333.0749; [
a]
25 = ꢀ15.2 (c 1.3, CHCl3), 99% ee; HPLC (col-
D
umn, CHIRALPAK AD-3, Hexane/2-Propanol = 99:1, flow rate
0.6 mL/min, 20 °C, detection UV 210 nm) tR of minor isomer
11.8 min, tR of major isomer 19.2 min. The absolute configuration
was determined to be (R) in comparison with the specific rotation
of the reported data.5b
4.2.6. (R)-Ethyl 2-(3,5-diphenylfuran-2-yl)-3,3,3-trifluoro-2-
hydroxypropanoate 5f
1H NMR (300 MHz, CDCl3) d 1.05 (t, J = 7.2 Hz, 3H), 3.61–3.67
(m, 1H), 4.01–4.07 (m, 1H), 4.52 (s, 1H), 6.76 (s, 1H), 7.34–7.47
(m, 8H), 7.75 (d, J = 7.8 Hz, 2H); 13C NMR (75 MHz, CDCl3) d 13.4,
64.4, 75.3 (q, JC–F = 31.0 Hz), 108.3, 122.6 (q, JC–F = 284 Hz), 124.1,
127.9, 128.2 (2C), 128.8, 129.1, 129.4, 129.7, 132.3, 140.6, 153.7,
167.3; 19F NMR (282 MHz, CDCl3) d ꢀ74.3; FT-IR (KBr pellet,
cmꢀ1) 3465, 3059, 2985, 1743, 1299, 1221, 1167, 1143, 916, 760,
700, 691, 673; HRMS (ESI-TOF) calcd for C21H17F3NaO4 [M+Na]+:
4.2.2. (R)-Ethyl 3,3,3-trifluoro-2-(furan-2-yl)-2-hydroxypro-
panoate 5b
1H NMR (300 MHz, CDCl3) d 1.35 (t, J = 7.2 Hz, 3H), 4.37–4.46
(m, 2H), 4.39 (s, 1H), 6.42 (d, J = 3.0 Hz, 1H), 6.62 (d, J = 3.0 Hz,
1H), 7.46 (s, 1H); 13C NMR (75 MHz, CDCl3) d 13.8, 64.7, 75.3 (q,
JC–F = 30.5 Hz), 110.6, 110.7, 122.3 (q, JC–F = 284 Hz), 143.9, 145.9,
167.2; 19F NMR (282 MHz, CDCl3) d ꢀ76.4; FT-IR (KBr pellet,
cmꢀ1) 3473, 2992, 2946, 1746, 1372, 1308, 1249, 1189, 1155,
1015, 968, 751; HRMS (ESI-TOF) calcd for C9H9F3NaO4 [M+Na]+:
413.0977, found: 413.0991; [
a
]
D
25 = ꢀ23.3 (c 1.3, CHCl3), 99% ee;
HPLC (column, CHIRALPAK AD-3, Hexane/2-Propanol = 99:1, flow
rate 0.6 mL/min, 20 °C, detection UV 210 nm) tR of major isomer
33.9 min, tR of minor isomer 55.7 min. The absolute configuration
was tentatively assigned by analogy of the specific rotation.
261.0351, found: 261.0363; [
a
]
25 = ꢀ20.3 (c 0.80, CHCl3), 99% ee;
D
HPLC (column, CHIRALPAK AD-3, Hexane/2-Propanol = 99:1, flow
rate 0.6 mL/min, 20 °C, detection UV 210 nm) tR of minor isomer
32.2 min, tR of major isomer 46.4 min. The absolute configuration
was tentatively assigned by analogy of the specific rotation.
4.2.7. (R)-Ethyl 3,3,3-trifluoro-2-hydroxy-2-(thiophen-2-yl)-
propanoate 5h
4.2.3. (R)-Ethyl 3,3,3-trifluoro-2-hydroxy-2-(5-methylfuran-2-
yl)propanoate 5c
1H NMR (300 MHz, CDCl3) d 1.39 (t, J = 7.2 Hz, 3H), 4.38–4.48
(m, 2H), 4.63 (s, 1H), 7.05 (dd, J = 5.1, 3.6 Hz, 1H), 7.36–7.39 (m,
1H NMR (300 MHz, CDCl3) d 1.35 (t, J = 7.2 Hz, 3H), 2.29 (s, 3H),
4.35 (s, 1H), 4.35–4.46 (m, 2H), 5.99 (d, J = 3.0 Hz, 1H), 6.47 (d,
J = 3.0 Hz, 1H); 13C NMR (75 MHz, CDCl3) d 13.5, 13.8, 64.5, 75.1
(q, JC–F = 30.5 Hz), 106.7, 111.4, 122.4 (q, JC–F = 284 Hz), 143.9,
153.9, 167.4; 19F NMR (282 MHz, CDCl3) d ꢀ76.3; FT-IR (KBr pellet,
cmꢀ1) 3474, 2988, 2929, 1749, 1371, 1305, 1261, 1178, 1113, 1021,
791; HRMS (ESI-TOF) calcd for C10H11F3NaO4 [M+Na]+: 275.0507,
2H); 13C NMR (75 MHz, CDCl3)
d 13.8, 64.8, 76.7 (q, JC–
F = 31.2 Hz), 122.4 (q, JC–F = 284 Hz), 127.2, 127.3, 127.5, 135.9,
168.0; 19F NMR (282 MHz, CDCl3) d ꢀ78.0; FT-IR (KBr pellet,
cmꢀ1) 3469, 2988, 2942, 1743, 1306, 1236, 1190, 1166, 1011,
856, 711; HRMS (ESI-TOF) calcd for C9H9F3NaO3S [M+Na]+:
277.0122, found: 277.0116; [
a
]
25 = ꢀ14.5 (c 1.4, CHCl3), 94% ee;
D
HPLC (column, CHIRALPAK AD-3, Hexane/2-Propanol = 99:1, flow
rate 0.6 mL/min, 20 °C, detection UV 210 nm) tR of minor isomer
17.2 min, tR of major isomer 22.8 min. The absolute configuration
was tentatively assigned by analogy of the specific rotation.
found: 275.0495; [
a
]
25 = ꢀ10.7 (c 0.7, CHCl3), 94% ee; HPLC (col-
D
umn, CHIRALPAK AD-3, Hexane/2-Propanol = 99:1, flow rate
0.6 mL/min, 20 °C, detection UV 210 nm) tR of minor isomer
20.7 min, tR of major isomer 22.7 min. The absolute configuration
was tentatively assigned by analogy of the specific rotation.
4.2.8. (R)-Ethyl 3,3,3-trifluoro-2-hydroxy-2-(5-methylthiophen-
2-yl)propanoate 5i
4.2.4. (R)-Ethyl 3,3,3-trifluoro-2-hydroxy-2-(5-phenylfuran-2-
yl)propanoate 5d
1H NMR (300 MHz, CDCl3) d 1.39 (t, J = 7.2 Hz, 3H), 2.47 (s, 3H),
4.38–4.47 (m, 2H), 4.55 (s, 1H), 6.69 (d, J = 3.6 Hz, 1H), 7.16 (d,
J = 3.6 Hz, 1H); 13C NMR (75 MHz, CDCl3) d 13.8, 16.1, 64.6, 76.6
(q, JC–F = 32.4 Hz), 122.4 (q, JC–F = 284 Hz), 125.5, 127.5, 132.9,
141.9, 168.2; 19F NMR (282 MHz, CDCl3) d ꢀ78.0; FT-IR (KBr pellet,
cmꢀ1) 3475, 2987, 2928, 1741, 1372, 1301, 1242, 1188, 1131, 1014,
805, 671; HRMS (ESI-TOF) calcd for C10H11F3NaO3S [M+Na]+:
1H NMR (300 MHz, CDCl3) d 1.37 (t, J = 7.2 Hz, 3H), 4.42–4.50
(m, 2H), 4.43 (s, 1H), 6.65 (d, J = 3.6 Hz, 1H), 6.69 (d, J = 3.6 Hz,
1H), 7.29–7.39 (m, 3H), 7.66 (d, J = 5.4 Hz, 2H); 13C NMR
(75 MHz, CDCl3) d 13.9, 64.7, 75.1 (q, JC–F = 32.0 Hz), 105.7, 112.5,
122.4 (q, JC–F = 284 Hz), 124.0, 128.1, 128.7, 130.0, 145.2, 155.3,
167.3; 19F NMR (282 MHz, CDCl3) d ꢀ76.2; FT-IR (KBr pellet,
cmꢀ1) 3475, 2986, 2933, 1745, 1486, 1371, 1304, 1179, 1115,
1017, 760, 691; HRMS (ESI-TOF) calcd for C15H13F3NaO4 [M+Na]+:
291.0279, found: 291.0270; [
a]
D
25 = ꢀ10.6 (c 0.8, CHCl3), 97% ee;
HPLC (column, CHIRALPAK AD-3, Hexane/2-Propanol = 99:1, flow
rate 0.6 mL/min, 20 °C, detection UV 210 nm) tR of minor isomer
18.6 min, tR of major isomer 23.0 min. The absolute configuration
was tentatively assigned by analogy of the specific rotation.
337.0664, found: 337.0654; [
a
]
25 = ꢀ35.2 (c 1.2, CHCl3), 99% ee;
D
HPLC (column, CHIRALPAK AD-3, Hexane/2-Propanol = 99:1, flow
rate 0.6 mL/min, 20 °C, detection UV 210 nm) tR of minor isomer
29.4 min, tR of major isomer 42.4 min. The absolute configuration
was tentatively assigned by analogy of the specific rotation.
4.2.9. tert-Butyl 2-(3-ethoxy-1,1,1-trifluoro-2-hydroxy-3-oxo-
propan-2-yl)-1H-pyrrole-1-carboxylate 5j
1H NMR (300 MHz, CDCl3) 2-substituted product: d 1.28 (t,
J = 7.2 Hz, 3H), 1.58 (s, 9H), 4.26–4.33 (m, 2H), 4.27 (s, 1H), 6.43
(m, 1H), 6.56 (m, 1H), 7.48 (t, J = 2.1 Hz, 1H); 3-substituted prod-
uct: d 1.38 (t, J = 7.2 Hz, 3H), 1.61 (s, 9H), 4.38–4.46 (m, 2H), 5.18
(s, 1H), 6.19 (t, J = 3.6 Hz, 1H), 7.22–7.26 (m, 2H); 13C NMR
(75 MHz, CDCl3) a mixture of 2- and 3-substituted products: d
13.84, 13.88, 27.8, 27.9, 63.2, 64.2, 75.3 (q, JC–F = 31.5 Hz), 76.4
(q, JC–F = 31.3 Hz), 84.3, 85.4, 110.4, 110.9, 116.2, 119.6, 120.2,
120.5, 122.9 (q, JC–F = 284 Hz), 123.1 (q, JC–F = 286 Hz), 148.3,
4.2.5. (R)-Ethyl 2-(5-(((tert-butyldiphenylsilyl)oxy)methyl)-
furan-2-yl)-3,3,3-trifluoro-2-hydroxypropanoate 5e
1H NMR (300 MHz, CDCl3) d 1.04 (s, 9H), 1.31 (t, J = 7.2 Hz, 3H),
4.32 (s, 1H), 4.32–4.47 (m, 2H), 4.62 (s, 2H), 6.17 (d, J = 3.3 Hz, 1H),
6.52 (d, J = 3.3 Hz, 1H), 7.36–7.44 (m, 6H), 7.68 (d, J = 7.5 Hz, 4H);
13C NMR (75 MHz, CDCl3) d 13.9, 19.2, 26.6, 58.7, 64.6, 75.1 (q,
JC–F = 32.0 Hz), 108.2, 111.2, 122.3 (q, JC–F = 284 Hz), 127.7, 129.8,
133.1, 135.6, 145.2, 155.6, 167.3; 19F NMR (282 MHz, CDCl3)

1110
K. Aikawa et al. / Tetrahedron: Asymmetry 25 (2014) 1104–1115
149.9, 167.4, 168.8; 19F NMR (282 MHz, CDCl3) 2-substituted prod-
uct: d ꢀ78.4, 3-substituted product: d ꢀ74.0; FT-IR (KBr pellet,
cmꢀ1) 3482, 2984, 2938, 1749, 1371, 1231, 1175, 1141, 978, 846,
772; HRMS (ESI-TOF) calcd for C14H18F3KNO5 [M+K]: 376.0774,
found: 376.0764.
CHIRALCEL OD-H, Hexane/2-Propanol = 97:3, flow rate 0.6 mL/
min, 20 °C, detection UV 254 nm) tR of minor isomer 19.8 min, tR
of major isomer 27.1 min. The absolute configuration was tenta-
tively assigned by analogy of the specific rotation.10d
4.4. Synthesis of 2-trimethylsilylated heteroarylsilanes
4.2.10. (R)-Ethyl 3,3,3-trifluoro-2-hydroxy-2-(1H-pyrrol-2-yl)-
propanoate 5k
General procedure A: To a solution of the corresponding hetero-
aryl compound (5.0 mmol) in THF (20 mL) was slowly added
n-BuLi in hexane (1.6 M) (3.44 mL, 5.5 mmol) at ꢀ78 °C. The mix-
ture was then allowed to warm up slowly to room temperature
1H NMR (300 MHz, CDCl3) d 1.40 (t, J = 7.2 Hz, 3H), 4.41–4.47
(m, 2H), 6.24 (d, J = 3.3 Hz, 1H), 6.48 (s, 1H), 6.83 (s, 1H), 8.79
(br, 1H); 13C NMR (75 MHz, CDCl3) d 13.8, 64.6, 75.1 (q, JC–
F = 32.5 Hz), 108.9, 109.3, 118.8, 121.7, 122.5 (q, JC–F = 284 Hz),
168.0; 19F NMR (282 MHz, CDCl3) d ꢀ78.4; FT-IR (KBr pellet,
cmꢀ1) 3435, 3367, 3123, 2991, 1738, 1265, 1226, 1182, 817, 746;
HRMS (ESI-TOF) calcd for C9H9F3NO3 [MꢀH]ꢀ: 236.0535, found:
and stirred for 1 h, after which chlorotrimethylsilane (694 lL,
5.5 mmol) was added to the reaction mixture at ꢀ78 °C. The reac-
tion mixture was allowed to warm slowly to room temperature,
stirred for 4 h, and then quenched with saturated aqueous NH4Cl.
The organic layer was separated, and the aqueous layer was
extracted with ether. The combined organic layer was washed with
brine, dried over Na2SO4, and evaporated under reduced pressure.
The residue was purified by column chromatography on silica gel
to afford the corresponding heteroarylsilane products.
236.0528; [
a
]
25 = ꢀ8.6 (c 0.8, CHCl3), 37% ee; HPLC (column, CHIR-
D
ALPAK AD-3, Hexane/2-Propanol = 97:3, flow rate 0.6 mL/min,
20 °C, detection UV 210 nm) tR of minor isomer 38.9 min, tR of
major isomer 45.7 min. The absolute configuration was tentatively
assigned by analogy of the specific rotation.
General procedure B: Freshly distilled diisopropylamine
(0.94 mL, 6.6 mmol, 1.1 equiv) in THF (10 mL) was cooled to
ꢀ78 °C. Next, n-BuLi in hexane (1.6 M) (4.12 mL, 6.6 mmol,
1.1 equiv) was slowly added to the THF solution at ꢀ78 °C, and
the mixture was allowed to warm up to 0 °C. The mixture was stir-
red for 1 h at 0 °C before recooling to ꢀ78 °C. A solution of 1-tert-
butyl pyrrole carboxylate derivative (6.0 mmol, 1.0 equiv) in THF
(20 mL) was cooled to ꢀ78 °C. The LDA solution was added via can-
nula over 20 min at ꢀ78 °C. The mixture was stirred at ꢀ78 °C for a
further 6 h before trimethylsilylchloride (1.0 mL, 7.2 mmol,
1.2 equiv) was added. The reaction mixture was allowed to warm
up slowly to 0 °C and stirred for 10 h. The reaction mixture was
poured into ice cold water. The organic layer was separated, and
the aqueous layer was extracted with ethyl acetate. The combined
organic layer was washed with brine, dried over MgSO4, and evap-
orated under reduced pressure. The residue was purified by col-
umn chromatography on silica gel to afford the corresponding
heteroarylsilane products.
4.3. Procedure for the catalytic asymmetric alkenylation and
dienylation with trifluoropyruvate (Scheme 3)
To a solution of PdCl2[(S)-BINAP] (8.0 mg, 0.01 mmol) in CH2Cl2
(2.0 mL) was added AgSbF6 (7.6 mg, 0.022 mmol) at room temper-
ature under an argon atmosphere. After stirring for 30 min, ethyl
trifluoropyruvate 2 (53 lL, 0.4 mmol) and vinylsilane 8 or dienylsi-
lane 9 (0.2 mmol) were added at 0 °C. The reaction mixture was
stirred at 0 °C for 24 h, and then loaded directly onto a short sil-
ica-gel column (hexane/AcOEt = 1:1) to remove the catalyst. To a
solution of the crude product in THF (1.0 mL) was added 6 M HCl
(1.0 mL). After stirring for 4 h at room temperature, saturated
aqueous NaHCO3 (2.0 mL) was added, and then the mixture was
extracted with ether. The organic layer was washed with brine,
dried over Na2SO4, and evaporated under reduced pressure. Purifi-
cation by a short silica-gel chromatography (hexane/AcOEt = 5:1)
gave the corresponding alcohol products. The enantiomeric excess
was determined by chiral HPLC analysis.
4.4.1. tert-Butyldiphenyl((5-(trimethylsilyl)furan-2-yl)- meth-
oxy)silane 11d
4.3.1. (E,R)-2-Hydroxy-4-phenyl-2-trifluoromethyl-but-3-enoic
acid ethyl ester 8
The title compound was synthesized from 4e according to gen-
eral procedure A (yield 60%). 1H NMR (300 MHz, CDCl3) d 0.29 (s,
9H), 1.10 (s, 9H), 4.73 (s, 2H), 6.18 (d, J = 3.3 Hz, 1H), 6.56 (d,
J = 3.0 Hz, 1H), 7.38–7.70 (m, 10H); 13C NMR (75 MHz, CDCl3) d
ꢀ1.6, 19.3, 26.7, 59.1, 107.2, 120.1, 127.6, 129.6, 133.5, 135.6,
158.2, 159.7; FT-IR (neat, cmꢀ1) 3074, 2962, 2936, 2857, 1476,
1427, 1250, 1115, 908, 833, 735; HRMS (ESI-TOF) calcd for C24H32-
NaO2Si2 [M+Na]+: 431.1838, found: 431.1822.
1H NMR (300 MHz, CDCl3) d 1.36 (t, J = 7.2 Hz, 3H), 4.14 (s, 1H),
4.30–4.51 (m, 2H), 6.35 (d, J = 15.9 Hz, 1H), 7.12 (d, J = 15.9 Hz, 1H),
7.30–7.38 (m, 3H), 7.43–7.45 (m, 2H); 13C NMR (75 MHz, CDCl3) d
13.9, 64.4, 77.1 (q, JC–F = 31.0 Hz), 119.3, 122.8 (q, JC–F = 286 Hz),
127.1, 128.69, 128.72, 134.8, 135.2, 168.9; 19F NMR (282 MHz,
CDCl3) d ꢀ78.07; FT-IR (neat, cmꢀ1) 3484, 3063, 3024, 2988,
2932, 1741, 1650, 1448, 1368, 1305, 1166, 1043, 856; HRMS
(ESI-TOF) calcd for
C
13H13F3NaO3 [M+Na]+: 297.0715, found:
297.0710; [
a
]
D
23 = ꢀ68.6 (c 1.6, CHCl3), 98% ee; HPLC (column,
4.4.2. (3,5-Diphenylfuran-2-yl)trimethylsilane 11e
CHIRALPAK AD-H, Hexane/2-Propanol = 97:3, flow rate 0.6 mL/
min, 20 °C, detection UV 254 nm) tR of major isomer 21.2 min, tR
of minor isomer 25.6 min. The absolute configuration was tenta-
tively assigned by analogy of the specific rotation.10d
The title compound was synthesized from 4f according to gen-
eral procedure A (yield 82%). 1H NMR (300 MHz, CDCl3) d 0.33 (s,
9H), 6.83 (s, 1H), 7.28–7.49 (m, 8H), 7.77 (d, J = 2.4 Hz, 2H); 13C
NMR (75 MHz, CDCl3) d ꢀ1.6, 114.0, 123.9, 126.3, 126.9, 127.4,
128.3, 128.5, 128.6, 131.5, 134.7, 152.4, 159.2; FT-IR (neat, cmꢀ1
)
4.3.2. (R,3E,5E)-Ethyl 2-hydroxy-6-phenyl-2-(trifluoromethyl)-
hexa-3,5-dienoate 10
3059, 2957, 1604, 1502, 1446, 1269, 1246, 942, 840, 761, 698;
HRMS (ESI-TOF) calcd for C19H21OSi [M+H]+: 293.1361, found:
293.1348.
1H NMR (300 MHz, CDCl3) d 1.37 (t, J = 7.2 Hz, 3H), 4.07 (s, 1H),
4.32–4.46 (m, 2H), 5.96 (d, J = 4.1 Hz, 1H), 6.67–7.00 (m, 3H), 7.23–
7.43 (m, 5H); 13C NMR (75 MHz, CDCl3) d 13.9, 64.3, 76.3 (q, JC–
F = 33.8 Hz), 122.7, 122.9 (q, JC–F = 282 Hz), 126.6, 126.7, 128.2,
128.7, 134.9, 135.9, 136.6, 168.9; FT-IR (neat, cmꢀ1) 3490, 2919,
2845, 1731, 1634, 1589, 1453, 1311, 1283, 1011; HRMS (APCI-
4.4.3. Trimethyl(5-phenylthiophen-2-yl)silane 11i
The title compound was synthesized from 2-phenylthiophene
according to general procedure A (yield 83%). 1H NMR (300 MHz,
CDCl3) d 0.31 (s, 9H), 7.18 (d, J = 3.3 Hz, 1H), 7.23 (d, J = 4.8 Hz,
1H), 7.31–7.37 (m, 3H), 7.59 (d, J = 7.5 Hz, 2H); 13C NMR
(75 MHz, CDCl3) d ꢀ0.09, 124.4, 126.0, 127.4, 128.8, 134.4, 135.0,
TOF) calcd for
C
15H15NaF3NaO3 [M+Na]+: 323.0871, found:
323.0866; [
a
]
D
25 = ꢀ33.7 (c 2.16, CHCl3), 99% ee; HPLC (column,

K. Aikawa et al. / Tetrahedron: Asymmetry 25 (2014) 1104–1115
1111
140.1, 149.6; FT-IR (neat, cmꢀ1) 3059, 2954, 2894, 1596, 1483,
1430, 1246, 1078, 995, 840, 754, 690, 637; HRMS (ESI-TOF) calcd
for C13H17SSi [M+H]+: 233.0820, found: 233.0824.
123.9, 126.3, 126.9, 127.4, 128.3, 128.5, 128.6, 131.5, 134.7,
152.4, 159.2; FT-IR (neat, cmꢀ1) 3059, 2957, 1604, 1502, 1446,
1269, 1246, 942, 840, 761, 698; HRMS (ESI-TOF) calcd for
C
19H21OSi [M+H]+: 293.1361, found: 293.1348.
4.4.4. tert-Butyldiphenyl((5-(trimethylsilyl)thiophen-2-yl)-
meth oxy)silane 11j
4.5. General procedure for the catalytic asymmetric Friedel–
Crafts type reaction with glyoxylate (Table 3)
The title compound was synthesized from tert-butyldiphe-
nyl(thiophen-2-ylmethoxy)silane according to general procedure
A (yield 89%). 1H NMR (300 MHz, CDCl3) d 0.33 (s, 9H), 1.10 (s,
9H), 4.92 (s, 2H), 6.92 (d, J = 3.3 Hz, 1H), 7.09 (d, J = 3.3 Hz, 1H),
7.37–7.44 (m, 6H), 7.71 (d, J = 7.5 Hz, 4H); 13C NMR (75 MHz,
CDCl3) d ꢀ0.01, 19.3, 26.8, 61.5, 125.1, 127.7, 129.7, 133.3, 133.6,
135.6, 139.3, 144.9; FT-IR (neat, cmꢀ1) 3074, 2954, 2857, 1743,
1472, 1427, 1371, 1250, 1111, 995, 836, 704; HRMS (ESI-TOF) calcd
for C24H32NaOSSi2 [M+Na]+: 447.1610, found: 447.1606.
To a solution of PdCl2[(S)-BINAP] (8.0 mg, 0.01 mmol) in CH2Cl2
(2.0 mL) was added AgSbF6 (7.6 mg, 0.022 mmol) at room temper-
ature under an argon atmosphere. After stirring for 30 min, freshly
distilled ethyl glyoxylate 3 (61.3 mg, 0.6 mmol) and 2-trimethylsi-
lylated heteroaromatic compound 4a or 11 (0.2 mmol) were added
at ꢀ78 to 0 °C. The reaction mixture was stirred at ꢀ78 to 0 °C for
5–24 h, and then directly loaded onto a silica-gel column (hexane/
AcOEt = 1:1) to remove the catalyst. To a solution of the crude
product in THF (2.0 mL) was added 1 M HCl (1.0 mL). After stirring
for 1 h at room temperature, the mixture was extracted with ether.
The organic layer was washed with brine, dried over Na2SO4, and
evaporated under reduced pressure. Purification by silica-gel chro-
matography (hexane/AcOEt = 4:1) gave the corresponding alcohol
products 6. The enantiomeric excess was determined by chiral
HPLC analysis.
4.4.5. tert-Butyl 2-methyl-5-(trimethylsilyl)-1H-pyrrole-1-car-
boxylate 11l
The title compound was synthesized from tert-butyl 2-methyl-
1H-pyrrole-1-carboxylate according to general procedure B (yield
52%). 1H NMR (300 MHz, CDCl3) d 0.25 (s, 9H), 1.60 (s, 9H), 2.38
(s, 3H), 5.96 (d, J = 3.0 Hz, 1H), 6.34 (d, J = 3.0 Hz, 1H); 13C NMR
(75 MHz, CDCl3) d 0.06, 16.6, 27.9, 83.5, 112.9, 122.1, 134.8,
135.8, 150.8; FT-IR (neat, cmꢀ1) 2984, 2901, 1727, 1570, 1468,
1351, 1239, 1111, 916, 848, 735; HRMS (ESI-TOF) calcd for C13H24-
NNaO2Si [M+Na]+: 254.1576, found: 254.1566.
4.5.1. (R)-Ethyl 2-(furan-2-yl)-2-hydroxyacetate 6a9
1H NMR (300 MHz, CDCl3) d 1.27 (t, J = 7.2 Hz, 3H), 3.33 (d,
J = 6.6 Hz, 1H), 4.25–4.33 (m, 2H), 5.17 (d, J = 5.7 Hz, 1H), 6.35–
6.38 (m, 2H), 7.40 (dd, J = 1.8, 0.9 Hz, 1H); 13C NMR (75 MHz,
CDCl3) d 14.0, 62.4, 66.9, 108.5, 110.5, 142.9, 151.0, 171.5; FT-IR
(KBr pellet, cmꢀ1) 3422, 2976, 2954, 2359, 1737, 1589, 1495,
1456, 1363, 1292, 1133, 1001, 892, 831; HRMS (APCI-TOF) calcd
4.4.6. tert-Butyl 2-phenyl-5-(trimethylsilyl)-1H-pyrrole-1-car-
boxylate 11m
The title compound was synthesized from tert-butyl 2-phenyl-
1H-pyrrole-1-carboxylate according to general procedure B (yield
80%). 1H NMR (300 MHz, CDCl3) d 0.33 (s, 9H), 1.21 (s, 9H), 6.24
(d, J = 3.3 Hz, 1H), 6.50 (d, J = 3.3 Hz, 1H), 7.30–7.37 (m, 5H); 13C
NMR (75 MHz, CDCl3) d ꢀ0.14, 27.2, 83.2, 114.2, 122.0, 126.9,
127.6, 128.9, 135.5, 137.1, 138.8, 150.8; FT-IR (neat, cmꢀ1) 3063,
2976, 2901, 1739, 1457, 1337, 1242, 1149, 1054, 998, 848, 757,
for C8H11O4 [M+H]+: 171.0657, found: 171.0651; [
a]
D
25 = ꢀ108.3 (c
0.80, CHCl3), 99% ee; HPLC (column, CHIRALCEL OD-H, Hexane/2-
Propanol = 96:4, flow rate 1.0 mL/min, 20 °C, detection UV
210 nm) tR of minor isomer 11.2 min, tR of major isomer
14.1 min. The absolute configuration was determined to be (R) in
comparison with the specific rotation of the reported data.9
701; HRMS (ESI-TOF) calcd for
338.1552, found: 338.1552.
C
18H25NNaO2Si [M+Na]+:
4.5.2. (R)-Ethyl 2-hydroxy-2-(5-methylfuran-2-yl)acetate 6b
1H NMR (300 MHz, CDCl3) d 1.27 (t, J = 7.2 Hz, 3H), 2.27 (s, 3H),
3.32 (br s, 1H), 4.25–4.33 (m, 2H), 5.11 (s, 1H), 5.93 (d, J = 2.4 Hz,
1H), 6.24 (d, J = 3.0 Hz, 1H); 13C NMR (75 MHz, CDCl3) d 13.5,
14.0, 62.4, 66.9, 106.4, 109.6, 149.1, 152.9, 171.7; FT-IR (KBr pellet,
cmꢀ1) 3466, 2984, 2924, 1743, 1563, 1266, 1216, 1074, 1022, 791;
HRMS (ESI-TOF) calcd for C9H13O4 [M+H]+: 185.0814, found:
4.4.7. tert-Butyl 2-(((tert-butyldiphenylsilyl)oxy)methyl)-5-
(trimethylsilyl)-1H-pyrrole-1-carboxylate 11n
The title compound was synthesized from tert-butyl 2-(((tert-
butyldiphenylsilyl)oxy)methyl)-1H-pyrrole-1-carboxylate accord-
ing to general procedure B (yield 27%). 1H NMR (300 MHz, CDCl3)
d 0.26 (s, 9H), 1.10 (s, 9H), 1.36 (s, 9H), 4.80 (s, 2H), 6.40 (d,
J = 3.3 Hz, 1H), 6.44 (d, J = 3.3 Hz, 1H), 7.35–7.42 (m, 6H), 7.68 (d,
J = 5.4 Hz, 4H); 13C NMR (75 MHz, CDCl3) d ꢀ0.02, 19.3, 26.8,
27.7, 62.1, 83.8, 111.7, 122.4, 127.7, 129.7, 133.5, 135.6, 136.2,
138.5, 150.2; FT-IR (neat, cmꢀ1) 3048, 2958, 2857, 1731, 1476,
1341, 1262, 1167, 1111, 844, 739, 701; HRMS (ESI-TOF) calcd for
185.0808; [
a
]
25 = ꢀ42.3 (c 1.1, CHCl3), 94% ee; HPLC (column, CHI-
D
RALCEL OD-H, Hexane/2-Propanol = 96:4, flow rate 1.0 ml/min,
20 °C, detection UV 210 nm) tR of minor isomer 12.5 min, tR of
major isomer 14.7 min. The absolute configuration was tentatively
assigned by analogy of the specific rotation.
4.5.3. (R)-Ethyl 2-hydroxy-2-(5-phenylfuran-2-yl)acetate 6c
1H NMR (300 MHz, CDCl3) d 1.29 (t, J = 7.2 Hz, 3H), 3.41 (d,
J = 7.8 Hz, 1H), 4.26–4.35 (m, 2H), 5.22 (d, J = 7.8 Hz, 1H), 6.45 (d,
J = 3.3 Hz, 1H), 6.61 (d, J = 3.3 Hz, 1H), 7.24–7.40 (m, 3H), 7.65 (d,
J = 5.4 Hz, 2H); 13C NMR (75 MHz, CDCl3) d 14.0, 62.6, 67.0,
105.7, 110.7, 123.9, 127.7, 128.7, 130.4, 150.4, 154.4, 171.5; FT-IR
(KBr pellet, cmꢀ1) 3462, 2981, 2927, 1739, 1484, 1448, 1263,
1211, 1074, 1023, 758, 695; HRMS (ESI-TOF) calcd for C14H14NaO4
C
29H41NNaO3Si2 [M+Na]+: 530.2522, found: 530.2518.
4.4.8. (4,5-Diphenylfuran-2-yl)trimethylsilane 11f
To a solution of the neutral Au chloride complex (3.9 mg,
0.005 mmol), which can lead to the corresponding cationic com-
plex 19a, and AgNTf2 (1.9 mg, 0.005 mmol) in toluene (1.0 mL)
was added diol 17 (62.0 mg, 0.20 mmol) at room temperature
and the reaction mixture was stirred for 3 h. The reaction mixture
was directly loaded onto a short silica-gel column (hexane/
AcOEt = 1:1) to remove the catalyst. Purification by silica-gel col-
umn chromatography (hexane/AcOEt = 20:1) gave the product
(85% yield). 1H NMR (300 MHz, CDCl3) d 0.38 (s, 9H), 6.79 (s, 1H),
7.30–7.61 (m, 10H); 13C NMR (75 MHz, CDCl3) d ꢀ1.6, 114.0,
[M+Na]+: 269.0790, found: 269.0803; [
a]
25 = ꢀ44.4 (c 0.86, CHCl3),
D
97% ee; HPLC (column, CHIRALCEL OD-H, Hexane/2-Propa-
nol = 96:4, flow rate 1.0 mL/min, 20 °C, detection UV 210 nm) tR
of minor isomer 15.9 min, tR of major isomer 22.4 min. The abso-
lute configuration was tentatively assigned by analogy of the spe-
cific rotation.

1112
K. Aikawa et al. / Tetrahedron: Asymmetry 25 (2014) 1104–1115
4.5.4. (R)-Ethyl 2-(5-(((tert-butyldiphenylsilyl)oxy)methyl)-
furan-2-yl)-2-hydroxyacetate 6d
[M+Na]+: 223.0405, found: 223.0394; [
a]
25 = ꢀ59.7 (c 1.16, CHCl3),
D
99% ee; HPLC (column, CHIRALPAK AD-3, Hexane/2-Propa-
nol = 97:3, flow rate 0.6 mL/min, 20 °C, detection UV 210 nm) tR
of minor isomer 35.2 min, tR of major isomer 39.6 min. The abso-
lute configuration was tentatively assigned by analogy of the spe-
cific rotation.
1H NMR (300 MHz, CDCl3) d 1.05 (s, 9H), 1.26 (t, J = 7.2 Hz, 3H),
3.30 (br s, 1H), 4.21–4.33 (m, 2H), 4.62 (s, 1H), 5.14 (s, 2H), 6.12 (d,
J = 3.3 Hz, 1H), 6.29 (d, J = 3.3 Hz, 1H), 7.38–7.70 (m, 10H); 13C NMR
(75 MHz, CDCl3) d 14.1, 19.2, 26.7, 58.9, 62.5, 67.0, 108.2, 109.3,
127.6, 129.7, 133.2, 135.6, 150.3, 154.6, 171.5; FT-IR (KBr pellet,
cmꢀ1) 3488, 2959, 2931, 2857, 1739, 1428, 1219, 1110, 1073,
1015, 823, 701, 610; HRMS (ESI-TOF) calcd for C25H30NaO5Si
4.5.9. (R)-Ethyl 2-hydroxy-2-(5-phenylthiophen-2-yl)acetate 6i
1H NMR (300 MHz, CDCl3) d 1.33 (t, J = 7.2 Hz, 3H), 3.58 (d,
J = 6.0 Hz, 1H), 4.30–4.35 (m, 2H), 5.41 (d, J = 4.8 Hz, 1H), 7.08 (d,
J = 3.9 Hz, 1H), 7.20 (d, J = 3.6 Hz, 1H), 7.28–7.42 (m, 3H), 7.40
(dd, J = 7.2, 1.5 Hz, 2H); 13C NMR (75 MHz, CDCl3) d 14.0, 62.7,
69.2, 122.8, 125.7, 126.3, 127.7, 128.9, 134.1, 140.6, 144.7, 172.6;
FT-IR (KBr pellet, cmꢀ1) 3454, 2980, 2932, 1727, 1460, 1382,
1213, 1196, 1083, 1022, 751, 685; HRMS (ESI-TOF) calcd for C14-
[M+Na]+: 461.1760, found: 461.1772; [
a
]
D
25 = ꢀ35.6 (c 1.1, CHCl3),
99% ee; HPLC (column, CHIRALCEL OD-H, Hexane/2-Propa-
nol = 96:4, flow rate 1.0 mL/min, 20 °C, detection UV 210 nm) tR
of minor isomer 17.2 min, tR of major isomer 20.6 min. The abso-
lute configuration was tentatively assigned by analogy of the spe-
cific rotation.
H14NaO3S [M+Na]+: 285.0561, found: 285.0573; [
a
]
D
25 = ꢀ13.6 (c
4.5.5. (R)-Ethyl 2-(3,5-diphenylfuran-2-yl)-2-hydroxyacetate 6e
1H NMR (300 MHz, CDCl3) d 1.25 (t, J = 7.2 Hz, 3H), 3.60 (d,
J = 6.0 Hz, 1H), 4.25–4.33 (m, 2H), 5.35 (d, J = 6.0 Hz, 1H), 6.83 (s,
1H), 7.28–7.49 (m, 6H), 7.58 (d, J = 2.4 Hz, 2H), 7.59 (d, J = 2.4 Hz,
2H); 13C NMR (75 MHz, CDCl3) d 14.0, 62.6, 65.5, 106.8, 124.0,
127.6, 127.89, 127.94, 128.2, 128.7, 128.8, 130.1, 132.5, 145.5,
153.5, 171.6; FT-IR (KBr pellet, cmꢀ1) 3481, 3059, 2980, 1739,
1486, 1451, 1264, 1222, 1071, 758, 696; HRMS (ESI-TOF) calcd
1.00, CHCl3), 99% ee; HPLC (column, CHIRALCEL OD-H, Hexane/2-
Propanol = 96:4, flow rate 1.0 mL/min, 20 °C, detection UV
210 nm) tR of minor isomer 18.1 min, tR of major isomer
22.0 min. The absolute configuration was tentatively assigned by
analogy of the specific rotation.
4.5.10. (R)-Ethyl 2-(5-(((tert-butyldiphenylsilyl)oxy)- methyl)-
thiophen-2-yl)-2-hydroxyacetate 6j
for C20H18KO4 [M+K]+: 361.0842, found: 361.0830; [
a]
25 = ꢀ19.5
1H NMR (300 MHz, CDCl3) d 1.08 (s, 9H), 1.31 (t, J = 7.2 Hz, 3H),
3.46 (d, J = 6.6 Hz, 1H), 4.26–4.34 (m, 2H), 4.83 (s, 2H), 5.36 (d,
J = 6.3 Hz, 1H), 6.70 (d, J = 3.6 Hz, 1H), 6.92 (d, J = 3.6 Hz, 1H),
7.37–7.44 (m, 6H), 7.69 (d, J = 7.8 Hz, 4H); 13C NMR (75 MHz,
CDCl3) d 14.0, 19.2, 26.7, 61.6, 62.5, 69.2, 123.3, 124.9, 127.7,
D
(c 1.05, CHCl3), 82% ee; HPLC (column, CHIRALCEL OD-H, Hexane/
2-Propanol = 96:4, flow rate 1.0 mL/min, 20 °C, detection UV
210 nm) tR of major isomer 25.8 min, tR of minor isomer
37.6 min. The absolute configuration was tentatively assigned by
analogy of the specific rotation.
129.7, 133.1, 135.6, 140.3, 145.4, 172.5; FT-IR (KBr pellet, cmꢀ1
)
3487, 3068, 2934, 2856, 1739, 1428, 1268, 1211, 1107, 1076,
4.5.6. (R)-Ethyl 2-(4,5-diphenylfuran-2-yl)-2-hydroxyacetate 6f
1H NMR (300 MHz, CDCl3) d 1.32 (t, J = 7.2 Hz, 3H), 3.40 (br s,
1H), 4.27–4.40 (m, 2H), 5.25 (s, 1H), 6.53 (s, 1H), 7.30–7.52 (m,
10H); 13C NMR (75 MHz, CDCl3) d 14.1, 62.7, 67.0, 112.8, 123.0,
126.3, 127.3, 127.8, 128.4, 128.63, 128.64, 130.7, 133.9, 148.9,
149.8, 171.4; FT-IR (KBr pellet, cmꢀ1) 3390, 2920, 2853, 1743,
1671, 1446, 1252, 1188, 764, 697; HRMS (ESI-TOF) calcd for C20-
826, 705; HRMS (ESI-TOF) calcd for C25H30NaO4SSi [M+Na]+:
477.1532, found: 477.1544; [
a]
D
25 = ꢀ24.5 (c 1.12, CHCl3), 99% ee;
HPLC (column, CHIRALCEL OD-H, Hexane/2-Propanol = 96:4, flow
rate 1.0 mL/min, 20 °C, detection UV 210 nm) tR of minor isomer
19.5 min, tR of major isomer 43.2 min. The absolute configuration
was tentatively assigned by analogy of the specific rotation.
H18NaO4 [M+Na]+: 345.1103, found: 345.1116; [
a
]
D
25 = ꢀ36.1 (c
4.5.11. (R)-tert-Butyl 2-(2-ethoxy-1-hydroxy-2-oxoethyl)-1H-
pyrrole-1-carboxylate 6k9
0.88, CHCl3), 99% ee; HPLC (column, CHIRALCEL OD-H, Hexane/2-
Propanol = 96:4, flow rate 1.0 mL/min, 20 °C, detection UV
210 nm) tR of minor isomer 18.2 min, tR of major isomer
26.2 min. The absolute configuration was tentatively assigned by
analogy of the specific rotation.
1H NMR (300 MHz, CDCl3) d 1.24 (t, J = 7.2 Hz, 3H), 1.57 (s, 9H),
4.04 (d, J = 8.1 Hz, 1H), 4.18–4.26 (m, 2H), 5.37 (d, J = 7.5 Hz, 1H),
6.12 (dd, J = 3.6, 3.3 Hz, 1H), 6.25 (dd, J = 3.3, 1.5 Hz, 1H), 7.38
(dd, J = 3.6, 1.5 Hz, 1H); 13C NMR (75 MHz, CDCl3) d 14.2, 27.9,
61.6, 67.8, 84.8, 110.4, 115.5, 122.5, 131.7, 149.8, 171.6; FT-IR
(neat, cmꢀ1) 3491, 3154, 2982, 2938, 1739, 1478, 1423, 1395,
1350, 1240, 1145, 1053, 950, 847; HRMS (ESI-TOF) calcd for C13-
4.5.7. (R)-Ethyl 2-hydroxy-2-(thiophen-2-yl)acetate 6g9
1H NMR (300 MHz, CDCl3) d 1.29 (t, J = 7.2 Hz, 3H), 3.54 (d,
J = 6.3 Hz, 1H), 4.21–4.36 (m, 2H), 5.40 (d, J = 6.3 Hz, 1H), 6.99
(dd, J = 5.1, 3.6 Hz 1H), 7.10 (d, J = 3.6 Hz, 1H), 7.28 (dd, J = 5.1,
1.2 Hz 1H); 13C NMR (75 MHz, CDCl3) d 14.0, 62.6, 69.1, 125.3,
125.6, 126.9, 141.5, 172.6; FT-IR (neat, cmꢀ1) 3453, 3012, 2961,
2912, 1751, 1685, 1512, 1399, 1328, 1249, 1188, 1090, 1032,
918, 873; HRMS (APCI-TOF) calcd for C8H10NaO3S [M+Na]+:
H19NNaO5 [M+Na]+: 292.1161, found: 292.1160; [
a]
25 = ꢀ50.7 (c
D
0.96, CHCl3), 99% ee; HPLC (column, CHIRALPAK AD-H, Hexane/2-
Propanol = 97:3, flow rate 1.0 mL/min, 20 °C, detection UV
254 nm) tR of minor isomer 18.0 min, tR of major isomer
22.6 min. The absolute configuration was tentatively assigned by
analogy of the specific rotation.
209.0248, found: 209.0250; [
a
]
25 = ꢀ73.8 (c 0.55, CHCl3), 98% ee;
D
HPLC (column, CHIRALPAK AD-H, Hexane/2-Propanol = 96:4, flow
rate 1.0 mL/min, 20 °C, detection UV 210 nm) tR of minor isomer
15.8 min, tR of major isomer 17.7 min. The absolute configuration
was tentatively assigned by analogy of the specific rotation.
4.5.12. (R)-tert-Butyl 2-(2-ethoxy-1-hydroxy-2-oxoethyl)-5-
methyl-1H-pyrrole-1-carboxylate 6l
1H NMR (300 MHz, CDCl3) d 1.26 (t, J = 7.2 Hz, 3H), 1.58 (s, 9H),
4.05 (d, J = 9.3 Hz, 1H), 4.18–4.25 (m, 2H), 5.27 (d, J = 9.3 Hz, 1H),
5.87 (d, J = 3.3 Hz, 1H), 6.12 (dd, J = 3.3 Hz, 1H); 13C NMR
(75 MHz, CDCl3) d 14.2, 16.7, 28.0, 61.6, 68.6, 85.0, 110.1, 114.3,
131.8, 132.9, 151.0, 171.9; FT-IR (neat, cmꢀ1) 3504, 2978, 2931,
1739, 1392, 1347, 1259, 1129, 1071, 850, 788; HRMS (ESI-TOF)
4.5.8. (R)-Ethyl 2-hydroxy-2-(5-methylthiophen-2-yl)acetate 6h
1H NMR (300 MHz, CDCl3) d 1.29 (t, J = 7.2 Hz, 3H), 2.45 (s, 3H),
3.42 (d, J = 6.6 Hz, 1H), 4.21–4.35 (m, 2H), 5.30 (d, J = 6.6 Hz, 1H),
6.62 (d, J = 3.6 Hz, 1H), 6.87 (d, J = 3.6 Hz, 1H); 13C NMR (75 MHz,
CDCl3) d 14.0, 15.3, 62.4, 69.1, 124.9, 125.4, 138.8, 140.5, 172.6;
FT-IR (neat, cmꢀ1) 3480, 2982, 2923, 1735, 1448, 1367, 1267,
1213, 1072, 1022, 799; HRMS (ESI-TOF) calcd for C9H12NaO3S
calcd for
C
14H21NNaO5 [M+Na]+: 306.1317, found: 306.1317;
[a]
25 = ꢀ40.3 (c 0.86, CHCl3), 98% ee; HPLC (column, CHIRALPAK
D
AD-H, Hexane/2-Propanol = 97:3, flow rate 1.0 mL/min, 20 °C,
detection UV 210 nm) tR of minor isomer 13.5 min, tR of major

K. Aikawa et al. / Tetrahedron: Asymmetry 25 (2014) 1104–1115
1113
isomer 15.5 min. The absolute configuration was tentatively
assigned by analogy of the specific rotation.
27.0, 38.8, 66.2, 66.3, 107.1, 110.2, 142.3, 153.2, 178.6.
An Achmatowicz rearrangement was attempted in this step
according to O’Doherty’s procedure.13b To
solution of 13
a
(212 mg, 1.0 mmol), NaOAcꢂ3H2O (149 mg, 1.1 mmol), and
NaHCO3 (167 mg 2.0 mmol) in THF (2.0 mL) and H2O (1.0 mL)
was added NBS (195 mg, 1.1 mmol) at 0 °C. After stirring for 1 h,
the mixture was quenched by saturated aqueous NaHCO3 and
extracted with ether. The organic layer was washed with brine,
dried over Na2SO4, and evaporated under reduced pressure. Crude
14 was obtained and used for the next step without further purifi-
cation. trans-14: 1H NMR (300 MHz, CDCl3) d 1.19 (s, 9H), 4.41–
4.49 (m, 2H), 4.73 (dd, J = 4.2, 4.2 Hz, 1H), 5.61 (d, J = 7.5 Hz, 1H),
6.08 (d, J = 10.9 Hz, 1H), 6.91 (dd, J = 10.9, 7.5 Hz, 1H). To a solution
of 14 (without purification) and DMAP (cat.) in CH2Cl2 (5.0 mL)
4.5.13. (R)-tert-Butyl 2-(2-ethoxy-1-hydroxy-2-oxoethyl)-5-
phenyl-1H-pyrrole-1-carboxylate 6m
1H NMR (300 MHz, CDCl3) d 1.17 (s, 9H), 1.29 (t, J = 7.2 Hz, 3H),
4.17–4.30 (m, 3H), 5.37 (d, J = 9.0 Hz, 1H), 6.12 (d, J = 3.3 Hz, 1H),
6.27 (d, J = 3.3 Hz, 1H), 7.27–7.35 (m, 5H); 13C NMR (75 MHz,
CDCl3) d 14.2, 27.1, 61.7, 68.4, 84.8, 112.6, 113.9, 127.2, 127.7,
128.8, 133.0, 134.8, 136.7, 150.9, 171.7; FT-IR (neat, cmꢀ1) 3488,
2979, 2928, 1738, 1370, 1313, 1145, 848, 758, 700; HRMS (ESI-
TOF) calcd for C19H23KNO5 [M+K]+: 384.1213, found: 384.1214;
[
a
]
25 = ꢀ15.2 (c 0.64, CHCl3), 96% ee; HPLC (column, CHIRALPAK
D
AD-H, Hexane/2-Propanol = 97:3, flow rate 1.0 mL/min, 20 °C,
detection UV 210 nm) tR of minor isomer 15.1 min, tR of major iso-
mer 17.4 min. The absolute configuration was tentatively assigned
by analogy of the specific rotation.
were added triethylamine (277
lL, 2.0 mmol) and benzoyl chloride
(127
lL, 1.1 mmol) at ꢀ78 °C under an argon atmosphere. After
stirring for 1 h at ꢀ40 °C, saturated aqueous NaHCO3 was added.
The organic layer was separated, and the aqueous layer was
extracted with ether. The combined organic layer was washed with
brine, dried over Na2SO4, and evaporated under reduced pressure.
Purification by silica-gel chromatography (hexane/AcOEt = 5:1)
gave pyranone 1513b (86% yield, trans/cis 4:1, 2 steps). trans-15:
1H NMR (300 MHz, CDCl3) d 1.19 (s, 9H), 4.50–4.55 (m, 2H), 4.82
(dd, J = 5.7, 5.7 Hz, 1H), 6.31 (d, J = 10.5 Hz, 1H), 6.83 (d,
J = 6.6 Hz, 1H), 7.02 (dd, J = 10.5, 6.6 Hz, 1H), 7.41–7.50 (m, 2H),
7.61–7.67 (m, 1H), 8.01 (dd, J = 8.7, 1.5 Hz, 2H); 13C NMR
(75 MHz, CDCl3) d 27.0, 38.7, 62.2, 74.5, 87.3, 128.6, 128.8, 128.9,
129.9, 133.8, 142.2, 164.8, 177.9, 192.3.; FT-IR (neat, cmꢀ1) 3433,
2951, 2911, 2833, 1721, 1600, 1438, 1361, 1203, 1003, 882; HRMS
4.5.14. (R)-tert-Butyl 2-(((tert-butyldiphenylsilyl)oxy)methyl)-
5(2-ethoxy-1-hydroxy-2-oxoethyl)-1H-pyrrole-1-carboxylate
6n
1H NMR (300 MHz, CDCl3) d 1.09 (s, 9H), 1.27 (t, J = 7.2 Hz, 3H),
4.03 (d, J = 9.0 Hz, 1H), 4.22 (q, J = 7.2 Hz, 2H), 4.75 (s, 2H), 5.31 (d,
J = 9.0 Hz, 1H), 6.22 (d, J = 3.3 Hz, 1H), 6.28 (d, J = 3.3 Hz, 1H), 7.35–
7.43 (m, 6H), 7.64–7.68 (m, 4H); 13C NMR (75 MHz, CDCl3) d 14.2,
19.3, 26.8, 27.6, 61.6, 61.8, 68.5, 85.3, 110.2, 114.7, 127.7, 129.7
132.4, 133.3, 135.5, 136.3, 150.4, 171.7; FT-IR (neat, cmꢀ1) 3530,
3070, 2931, 2857, 1736, 1427, 1371, 1335, 1256, 1111, 704; HRMS
(ESI-TOF) calcd for C30H39NNaO5Si [M+Na]+: 560.2444, found:
(APCI-TOF) calcd for
C
13H11NaO4 [M+Na]+: 254.0555, found:
254.0553; [
a
]
D
25 = ꢀ82.1 (c 1.25, CHCl3).
560.2437; [
a
]
25 = ꢀ25.6 (c 1.03, CHCl3), 99% ee; HPLC (column,
D
CHIRALPAK AD-H, Hexane/2-Propanol = 97:3, flow rate 1.0 mL/
min, 20 °C, detection UV 210 nm) tR of minor isomer 12.4 min, tR
of major isomer 14.9 min. The absolute configuration was tenta-
tively assigned by analogy of the specific rotation.
4.7. Two-directional reaction (Scheme 5)
To a solution of PdCl2[(S)-BINAP] (3.2 mg, 0.004 mmol) in CH2-
Cl2 (1.0 mL) was added AgSbF6 (3.0 mg, 0.0088 mmol) at room
temperature under an argon atmosphere. After stirring for
4.6. Synthesis of pyranone (Scheme 4)
30 min, Et2O (1.0 mL), ethyl trifluoropyruvate 2, (32
lL,
0.24 mmol) and 4a (32 L, 0.2 mmol) were added to the mixture
l
To a solution of 6a (851 mg, 5.0 mmol, 99% ee) in THF (30 mL)
and MeOH (5.0 mL) at 0 °C was added NaBH4 (605 mg, 16 mmol)
under an argon atmosphere, and the reaction mixture was warmed
up to room temperature. After stirring for 12 h, saturated aqueous
NH4Cl was added. The organic layer was separated, and the aque-
ous layer was extracted with ether. The combined organic layer
was washed with brine, dried over Na2SO4, and evaporated under
reduced pressure. Purification by silica-gel chromatography (hex-
ane/AcOEt = 1:1) gave the diol 12 (90% yield). 1H NMR (300 MHz,
CDCl3) d 3.54 (br, 1H), 3.76–3.80 (br s, 2H), 3.95 (br, 1H), 4.75 (d,
J = 5.9 Hz, 1H), 6.23 (dd, J = 4.0, 0.6 Hz, 1H), 6.27 (dd, J = 4.0,
1.8 Hz, 1H), 7.30 (dd, J = 1.8, 0.6 Hz, 1H); 13C NMR (75 MHz, CDCl3)
d 65.0, 68.3, 106.9, 110.3, 142.2, 153.6.
at ꢀ78 °C. The reaction mixture was stirred at ꢀ78 °C for 8 h, and
then freshly distilled ethyl glyoxylate (61.3 mg, 0.6 mmol) was
added at ꢀ78 °C. After stirring for 12 h at room temperature, the
reaction mixture was directly loaded onto a short silica-gel column
(hexane/AcOEt = 1:1) to remove the catalyst. To a solution of the
crude product in THF (2.0 mL) was added 1 M HCl (1.0 mL). After
stirring for 1 h at room temperature, the mixture was extracted
with ether. The combined organic layer was washed with brine,
dried over Na2SO4, and evaporated under reduced pressure.
Purification by
a silica-gel column chromatography (hexane/
AcOEt = 2:1) gave the corresponding (R,R)-diol 16 (91% yield).
The enantiomeric excess was determined by chiral HPLC
analysis (99% ee). 1H NMR (300 MHz, CDCl3) d 1.25 (t, J = 7.2 Hz,
3H), 1.33 (t, J = 7.2 Hz, 3H), 3.48 (s, 1H), 4.24 (q, J = 7.2 Hz, 2H),
4.37–4.46 (m, 2H), 4.44 (s, 1H), 5.16 (s, 1H), 6.39 (d, J = 3.3 Hz,
1H), 6.57 (d, J = 3.3 Hz, 1H); 13C NMR (75 MHz, CDCl3) d 13.8,
13.9, 62.7, 64.6, 66.7, 75.0 (q, JC–F = 32 Hz), 109.4, 111.4, 122.1 (q,
JC–F = 284 Hz), 146.2, 152.4, 166.9, 171.0; 19F NMR (282 MHz,
CDCl3) d ꢀ76.4; FT-IR (KBr pellet, cmꢀ1) 3500, 3055, 2984, 1739,
1423, 1266, 1224, 1017, 896, 742, 704; HRMS (ESI-TOF) calcd for
To a solution of diol 12 (256 mg, 2.0 mmol) in CH2Cl2 (10 mL)
were added triethylamine (554
lL, 4.0 mmol) and pivaloyl chloride
(270
lL, 2.2 mmol) at ꢀ78 °C under an argon atmosphere. After the
reaction mixture was allowed to slowly warm to 0 °C and stirred
for 5 h, saturated aqueous NaHCO3 was added. The organic layer
was separated, and the aqueous layer was extracted with ether.
The combined organic layer was washed with brine, dried over
Na2SO4, and evaporated under reduced pressure. Purification by
silica-gel chromatography (hexane/AcOEt = 5:1) gave the piv-pro-
tected product 13 (87% yield). 1H NMR (300 MHz, CDCl3) d 1.14
(s, 9H), 3.07 (br, 1H), 4.30 (dd, J = 5.7, 4.8 Hz, 1H), 4.33 (dd,
J = 5.7, 4.8 Hz, 1H), 4.90 (dd, J = 5.7, 5.7 Hz, 1H), 6.26–6.32 (m,
2H), 7.34 (dd, J = 1.8, 0.9 Hz, 1H); 13C NMR (75 MHz, CDCl3) d
C
13H15F3NaO7 [M+Na]+: 363.0667, found: 363.0663; [
a
]
25 = ꢀ52.3
D
(c 0.72, CHCl3), 99% ee; HPLC (column, CHIRALPAK AD-3,
Hexane/2-Propanol = 90:10, flow rate 0.6 mL/min, 20 °C, detection
UV 210 nm) tR of major isomer 35.2 min, tR of minor isomer
41.6 min. The absolute configuration was tentatively assigned by
analogy.

1114
K. Aikawa et al. / Tetrahedron: Asymmetry 25 (2014) 1104–1115
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4.8. Sequential catalytic reactions (Scheme 6)
4.8.1. Sequential catalytic reaction with glyoxylate by Au and Pd
catalysts
To a solution of the neutral Au chloride complex (3.9 mg,
0.005 mmol), which can lead to the corresponding cationic com-
plex 19a, and AgNTf2 (1.9 mg, 0.005 mmol) in toluene (1.0 mL)
was added diol 17 (62.0 mg, 0.20 mmol) at room temperature
and the reaction mixture was stirred for 3 h. At the same time, a
solution of PdCl2[(S)-BINAP] (8.0 mg, 0.01 mmol), AgSbF6 (7.6 mg,
0.022 mmol), and ethyl glyoxylate 3 (61.3 mg, 0.6 mmol) in CH2Cl2
(1.0 mL) was prepared according to the general procedure. The
solution of glyoxylate 3 was then transferred to a solution of diol
17 with a syringe at ꢀ20 °C. After stirring for 24 h at 0 °C, the reac-
tion mixture was loaded directly onto a short silica-gel column
(hexane/AcOEt = 1:1) to remove the catalyst. To a solution of the
crude product in THF (2.0 mL) was added 1 M HCl (1.0 mL). After
stirring for 1 h at room temperature, the mixture was extracted
with ether. The organic layer was washed with brine, dried over
Na2SO4, and evaporated under reduced pressure. Purification by
silica-gel chromatography (hexane/AcOEt = 5:1) gave the corre-
sponding alcohol product 6f (57% yield). The enantiomeric excess
was determined by chiral HPLC analysis (99% ee).
4. For reviews, see: (a) Bandini, M.; Melloni, A.; Umani-Ronchi, A. Angew. Chem.,
Int. Ed. 2004, 43, 550; (b) Bandini, M.; Melloni, A.; Umani-Ronchi, A. Synlett
2005, 1199; (c) Tsogoeva, S. B. Eur. J. Org. Chem. 2007, 1701; (d) Poulsen, T. B.;
Jørgensen, K. A. Chem. Rev. 2008, 108, 2903; (e) You, S.-L.; Cai, Q.; Zeng, M.
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5. For catalytic asymmetric Friedel–Crafts alkylation using trifluoropyruvate, see:
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Biomol. Chem. 2005, 3, 3284; (g) Zhao, J.-L.; Liu, L.; Sui, Y.; Liu, Y.-L.; Wang, D.;
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L.; Gu, C.-L.; Wang, D.; Chen, Y.-J. Tetrahedron Lett. 2008, 49, 1476; (k) Nie, J.;
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2012, 23, 209.
4.8.2. Sequential catalytic reaction with trifluoropyruvate by Au
and Pd catalysts
To a solution of the neutral Au chloride complex (3.9 mg,
0.005 mmol), which can lead to the corresponding cationic com-
plex 19a, and AgSbF6 (1.7 mg, 0.005 mmol) in CH2Cl2 (0.5 mL)
was added diol 18 (47.6 mg, 0.2 mmol) at room temperature and
the reaction mixture was stirred for 1 h. At the same time, a solu-
tion of PdCl2[(S)-BINAP] (8.0 mg, 0.010 mmol), AgSbF6 (7.6 mg,
6. Catalytic asymmetric Friedel–Crafts alkylation using fluoral, see: Ishii, A.;
Soloshonok, V. A.; Mikami, K. J. Org. Chem. 2000, 65, 1597.
7. Catalytic asymmetric Friedel–Crafts alkylation using trifluoromethyl ketones,
see: Blay, G.; Fernández, I.; Monleón, A.; Pedro, J. R.; Vila, C. Org. Lett. 2009, 11,
441.
8. Catalytic asymmetric Friedel–Crafts alkylation using glyoxylate, see: (a) Yuan,
Y.; Wang, X.; Li, X.; Ding, K. J. Org. Chem. 2004, 69, 146; (b) Li, H.; Wang, Y.-Q.;
Deng, L. Org. Lett. 2006, 8, 4063; (c) Majer, J.; Kwiatkowski, P.; Jurczak, J. Org.
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Mikami, K. Eur. J. Org. Chem. 2007, 1730.
0.022 mmol), and trifluoropyruvate 2 (32 lL, 0.24 mmol) in CH2Cl2
(0.5 mL) was prepared according to the general procedure. Ether
(1.0 mL) and a solution of trifluoropyruvate 2 were added to the
solution of diol 18 via a syringe at ꢀ40 °C. After stirring for 16 h
at ꢀ40 °C, the reaction mixture was loaded directly onto a short sil-
ica-gel column (hexane/AcOEt = 1:1) to remove the catalyst. Purifi-
cation by a silica-gel chromatography (hexane/AcOEt = 5:1) gave
the corresponding alcohol product 5f (62% yield). The enantiomeric
excess was determined by chiral HPLC analysis (99% ee).
9. Aikawa, K.; Hioki, Y.; Mikami, K. Chem. Asian J. 2010, 5, 2346.
10. (a) Aikawa, K.; Kainuma, S.; Hatano, M.; Mikami, K. Tetrahedron Lett. 2004, 45,
183; (b) Mikami, K.; Kawakami, Y.; Akiyama, K.; Aikawa, K. J. Am. Chem. Soc.
2007, 129, 12950; (c) Aikawa, K.; Hioki, Y.; Mikami, K. J. Am. Chem. Soc. 2009,
131, 13922; (d) Aikawa, K.; Hioki, Y.; Mikami, K. Org. Lett. 2010, 12, 5716; (e)
Aikawa, K.; Mimura, S.; Numata, Y.; Mikami, K. Eur. J. Org. Chem. 2011, 62; (f)
Aikawa, K.; Honda, K.; Mimura, S.; Mikami, K. Tetrahedron Lett. 2011, 52, 6682;
(g) Mikami, K.; Aikawa, K.; Aida, J. Synlett 2011, 2719; (h) Aikawa, K.; Hioki, Y.;
Shimizu, N.; Mikami, K. J. Am. Chem. Soc. 2011, 133, 20092.
11. QuinoxP⁄: Imamoto, T.; Sugita, K.; Yoshida, K. J. Am. Chem. Soc. 2005, 127,
11934.
Acknowledgments
12. See, Ref. 9; Even in the presence of 0.005 and 0.002 mol % Pd complex,
the Friedel–Crafts type reaction with 4a proceeded to give product 6a in
75%, 98% ee and 46%, 98% ee, respectively (reaction conditions: toluene, 0 °C,
72 h).
This research was supported by JST (ACT-C), JSPS KAKENHI
Grant Number 25410036, Mizuho Foundation for the Promotion
of Sciences, and The Noguchi Institute. We thank Central Glass
Co., Ltd for the gift of ethyl trifluoropyruvate. We also thank Takas-
ago International Co. for providing (S)-BINAP and (S)-SEGPHOS
derivatives. We are grateful to Professor T. Imamoto for the gift
of QuinoxP⁄.
13. (a) Harris, J. M.; Karanen, M. D.; O’Doherty, G. A. J. Org. Chem. 1999, 64, 2982;
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