Lewis Acid Catalyzed Friedel-Crafts Alkylation of Alkenes with Trifluoropyruvates

Article abstract of DOI:10.1021/acs.joc.6b00358

A Friedel-Crafts alkylation reaction of styrenes with trifluoropyruvates has been developed, which delivered allylic alcohols in excellent yields (up to 98%) using the Ni(ClO₄)₂·6H₂O/bipyridine complex as a catalyst. The asymmetric reaction was catalyzed by the chiral Cu(OTf)₂/bisoxazoline complex to afford the corresponding chiral allylic alcohols bearing trifluoromethylated quaternary stereogenic centers in moderate enantioselectivities (up to 75% ee).

Full text of DOI:10.1021/acs.joc.6b00358

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Note
Lewis Acid-Catalyzed Friedel-Crafts
Alkylation of Alkenes with Trifluoropyruvates
Bin Xiang, Teng-Fei Xu, Liang Wu, Ren-Rong Liu, Jian-Rong Gao, and Yi-Xia Jia
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b00358 • Publication Date (Web): 30 Mar 2016
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Lewis Acid-Catalyzed Friedel-Crafts Alkylation of Alkenes with
Trifluoropyruvates
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Bin Xiang, Teng-Fei Xu, Liang Wu, Ren-Rong Liu, Jian-Rong Gao, and Yi-Xia Jia*
College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
ABSTRACT. A Friedel-Crafts alkylation reaction of styrenes with trifluoropyruvates has been
developed, which delivered allylic alcohols in excellent yields (up to 98%) using
Ni(ClO4)2·6H2O/bipyridine complex as a catalyst. The asymmetric reaction was catalyzed by
chiral Cu(OTf)2/bisoxazoline complex to afford the corresponding chiral allylic alcohols bearing
trifluoromethylated quaternary stereogenic centers in moderate enantioselectivities (up to 75% ee).
In the past decades, asymmetric Friedel-Crafts alkylation reaction of aromatic
system has been extensively developed as an efficient approach to construct chiral
benzylic stereocenters.1 In contrast, Friedel-Crafts alkylation of alkenes that furnishes
allylic stereogenic centers has remained largely unexplored. In this context, only a
few electron-rich olefins, e.g. silyl enol ethers,2 enamides,3 allylidenehydrazine,4
4-vinylanlines,5 and 2-vinylphenols,6 were documented as nucleophilic substrates in
the enantioselective additions to C=O, C=N, or C=C bonds. Simple olefins were
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rarely involved in this reaction probably due to their lower nucleophilicity, although a
few recent examples have disclosed the additions of simple olefins to the C=C bonds
of ,-unsaturated ketones in their racemic versions.7 Therefore, the development of
efficient Friedel-Crafts alkylation of simple olefins, in particular in the asymmetric
version, to build allylic stereogenic centers is highly desirable.
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Enantioselective alkenylation of carbonyl compounds allows an efficient access to
chiral allylic alcohols, which are important building blocks in organic synthesis.
Among them, the transition-metal-catalyzed or chiral ligand-promoted
enantioselective addition of vinyl organometallic reagents to C=O bonds has being a
reliable approach for this purpose (Scheme 1a).8 In comparison, the direct
alkenylation reaction between simple olefins and carbonyl compounds via a
Friedel-Crafts alkylation process is more attractive in term of atom economy and
efficiency, however, to the best of our knowledge, it actually remained unexplored.9
As a continuous interest in the asymmetric Friedel-Crafts reactions,10 our group has
recently developed a Ni(ClO4)2·6H2O/(S)-BINAP-catalyzed enantioselective addition of
styrenes to cyclic N-sulfonyl -iminoesters to access chiral allylic amine
derivatives.11 This encouraged us to explore the Friedel-Crafts alkylation of simple
alkenes with ketones (Scheme 1b). We hence report the primary result of a
Ni(ClO4)2·6H2O/bipyridine-catalyzed Friedel-Crafts reaction between styrenes and
trifluoropyruvates in its racemic version and the corresponding asymmetric reaction
using chiral Cu(OTf)2/bisoxazoline complex as a catalyst, which delivered allylic
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alcohols bearing trifluoromethylated quaternary stereogenic centers in excellent yields
and moderate enantioselectivities.
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Scheme 1. Approaches for Alkenylation of C=O Bonds
At the outset, methyl 3,3,3-trifluoropyruvate (1a) and styrene (2a) were selected as
model substrates to identify the optimal conditions (Table 1). In the presence of a
catalytic amount of Cu(OTf)2 (10 mol%) with 2,2'-bipyridine (12 mol%) as a ligand,
the desired allylic alcohol 3aa was obtained in 60% yield in DCM at 100°C
(temperature of oil bath) for 40 h (entry 1). Without the addition of 2,2'-bipyridine
ligand, only trace amount of the product was isolated (entry 2). Other Lewis acids
were then tested and Ni(ClO4)2·6H2O was identified as the best catalyst to deliver 3aa
in 92% yield (entry 6). Followed solvent examination indicated that the reaction
worked favorably in chlorinated solvents, such as dichloromethane, chloroform, and
dichloroethane (entries 6−8), while it was completely suppressed in MeOH (entry 10).
Inferior result was obtained for the reactions with 1,10-phenanthroline as a ligand
(entry 11). Furthermore, lowering the temperature led to a decreased yield (entry 12).
As a comparison, slightly lower yield of product 3aa was obtained when a preformed
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complex of Ni(ClO4)2/2,2’-bipyridine was used as the catalyst (entries 6 vs 13).
Noteworthy is that the present reaction could be classified as Prins reaction, while no
other side products through Prins reaction pathway were isolated.
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Table 1. Condition Optimization of Racemic Reactiona
10 mol% M
12 mol% L
Solvent
100 oC, 40 h
O
HO CF3
CO2Me
Ph
2a
Ph
CO2Me
F3C
1a
3aa
Entry
1
M
L
Solvent
Y (%)
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7
Cu(OTf)2
Cu(OTf)2
Zn(OTf)2
2,2’-bpy
--
DCM
DCM
DCM
DCM
DCM
DCM
CHCl3
DCE
2
3
2,2’-bpy
2,2’-bpy
2,2’-bpy
2,2’-bpy
2,2’-bpy
2,2’-bpy
2,2’-bpy
2,2’-bpy
1,10-phen
2,2’-bpy
2,2’-bpy
31
54
66
92
81
85
45
NR
68
79
84
4
Cu(ClO4)2·6H2O
Zn(ClO4)2·6H2O
Ni(ClO4)2·6H2O
Ni(ClO4)2·6H2O
Ni(ClO4)2·6H2O
Ni(ClO4)2·6H2O
Ni(ClO4)2·6H2O
Ni(ClO4)2·6H2O
Ni(ClO4)2·6H2O
Ni(ClO4)2·6H2O
5
6
7
8
9
Toluene
MeOH
DCM
DCM
DCM
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11
12b
13c
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aReaction conditions: 1a (0.2 mmol), 2a (0.4 mmol), Lewis acid (10 mol%), and ligand (12 mol%)
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in solvent (2.0 mL) in oil bath at 100°C for 40 h; 2,2’-bpy = 2,2'-bipyridine, 1,10-phen =
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b
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1,10-phenanthroline. In oil bath at 70 C. Preformed complex of Ni(ClO4)2/2,2’-bpy (10
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mol%) was used.
With the optimal conditions in hand, the scope of alkene was then investigated. As
shown in Scheme 2, a wide variety of styrenes bearing either electron-withdrawing or
electron-donating substituents on the phenyl ring reacted smoothly with 1a to produce
the corresponding allylic alcohols in moderate to excellent yields. Generally,
functionalities in the para-position on the benzene ring were well-tolerated, while
relatively lower yields of products 3ab-3ad were observed as the corresponding
styrenes bearing electron-donating substituents were unstable in the reaction system.12
Addition of these styrenes to reaction system in two batches led to improved yields,
which are also observed in the cases of 3ah, 3ak, and 3al. In addition, products 3am
and 3an were obtained in moderate yields. Electron-withdrawing groups were also
well-tolerated and led to the products (3ae-3ag and 3ai-3aj) in satisfactory yields
regardless of the steric effect. To our delight, 1,1’-diphenylethene and
(E)-buta-1,3-dien-1-ylbenzene were also successfully employed in the reactions to
afford the corresponding products 3ao and 3ap in 98% and 79% yields, respectively.
It’s noteworthy that no reaction occurred for the reaction of 1,2-diphenylethene and
aliphatic terminal alkene (e.g. 1-hexene) failed to deliver any desired product, which
implies the limitation of the scope of alkenes.
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Scheme 2. Scope of Alkene in the Racemic Reactiona
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aReaction conditions: 1a (0.2 mmol), 2a (0.4 mmol), Ni(ClO4)2·6H2O (0.02 mmol), and
2,2'-bipyridine (0.024 mmol) in DCM (2.0 mL) at 100°C (temperature of oil bath) for 40 h;
Styrenes bearing electron-donating groups (3ab-3ad, 3ah, 3ak, and 3al) were added to the
reaction system in two batches (the second batch of styrenes (0.2 mmol) were added after 24 h).
To further evaluate the scope of this reaction, other ketoesters were examined and
the results were shown in Scheme 3. Different trifluoropyruvates reacted well with
styrene 2a to deliver the corresponding allylic alcohols in moderate yields (74%, 60%,
and 78% for ethyl ester 3ba, isopropyl ester 3ca, and n-butyl ester 3da, respectively).
In addition, 2-oxomalonate was also applied in the reaction and led to product 3ea in
40% yield. However, other ketones, such as 2,2,2-trifluoro-1-phenylethanone,
acetophenone, and isatine, remained inert in this reaction.
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Scheme 3. Scope of Ketoester in the Racemic Reactiona
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aReaction conditions: 1 (0.2 mmol), 2a (0.4 mmol), Ni(ClO4)2·6H2O (0.02 mmol), and
2,2'-bipyridine (0.024 mmol) in DCM (2.0 mL) at 100°C (temperature of oil bath) for 40 h.
Encouraged by above success, we then moved our attention to the asymmetric
reaction. After systematic investigations of Lewis acids, chiral ligands, and the
solvents (See Table S1 in supporting information), the complex of Cu(OTf)2 with a
chiral bisoxazoline ligand L1 was defined as an optimal catalyst for the asymmetric
alkenylation of trifluoropyruvates, although only moderate ee value was obtained. A
series of styrenes were then examined to disclose the scope of the asymmetric
reactions (Scheme 4). All of the reactions afforded the corresponding products in
moderate enantioselectivities (64-75% ee). However, the yields were unfavorably
influenced by the electron-withdrawing substituents, which resulted in poor to
moderate yields for products 3ae-3ag and 3ai. In contract, styrenes bearing
electron-donating groups delivered the products (3aa-3ac, 3ah, 3al, 3aq, and 3ar) in
relatively higher yield and with the same level of enantioselectivity (around 70% ee).
Furthermore, product 3ao resulting from the reaction of 1,1’-diphenylethene with 1a
was also isolated in 56% yield and 68% ee.
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Scheme 4. Scope of the Asymmetric Reactiona
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aReaction conditions: 1 (0.2 mmol), 2a (0.4 mmol), Cu(OTf)2 (0.02 mmol), and L1 (0.024
mmol) in CHCl3 (2.0 mL) at 100 °C (temperature of oil bath) for 40 h; Ee was determined by
chiral HPLC.
In order to determine the absolute configuration of the product, 3ba was reduced to
compound 4 by the hydrogenation reaction in EtOH for 12 h using Pd/C catalyst
(Scheme 5). By comparing the optical rotation with the reported value for compound
4,13 the absolute configuration of product 3ba is conversely determined to be S. A
tentative model for asymmetric induction is then proposed, where trifluoropyruvate is
activated by the catalyst via a 1,4-chelation of two carbonyl oxygen atoms to Cu(II)
and hence facilitates the nucleophilic attack of styrene in a favored Si face to result in
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the S configuration of product 3ba. As shown in Scheme 6, synthetic transformations
of the products were then conducted. Product 3aa was readily converted to the
corresponding amide 5 in 72% yield and 70% ee via a three-step procedure including
protection of hydroxyl group, hydrolysis of the ester, and the condensation of acid
chloride with aniline. In addition, a Suzuki-coupling reaction of product 3ag with
PhB(OH)2 was realized in the presence of Pd(PPh3)4 catalyst, which gave compound 6
bearing a free hydroxyl group in 71% yield and 70% ee.
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Scheme 5. Determination of the Absolute Configuration and Proposed
Asymmetric Induction Model
Scheme 6. Synthetic Transformations of the Products
In summary, a catalytic Friedel-Crafts alkylation of styrenes with trifluoropyruvates
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has been developed as a straightforward access to allylic alcohols. Moderate to
excellent yields of the products were obtained in the racemic reactions catalyzed by
the complex of Ni(ClO4)2·6H2O with 2,2’-bypyridine. The asymmetric reactions were
established with chiral Cu(OTf)2/bisoxazoline complex as a catalyst, which furnished
the corresponding chiral allylic alcohols bearing trifluoromethylated quaternary
stereogenic centers in moderate enantioselectivities (up to 75% ee).
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EXPERIMENTAL SECTION
General Information. Column chromatography was carried out on silica gel
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(200-300 mesh). H NMR spectra were recorded on 500 MHz in CDCl3, C NMR
spectra were recorded on 125 MHz in CDCl3. Melting points were determined on a
microscopic apparatus and were uncorrected. All new products were further
characterized by HRMS obtained on a TOF LC/MS mass spectrometer equipped with
1
an ESI source; copies of their H NMR and 13C NMR spectra are provided.
Enantiomeric excesses (ee) were determined by chiral high-performance liquid
chromatography (chiral HPLC). Optical rotation values were measured with
instruments operating at λ = 589 nm, corresponding to the sodium D line at the
temperatures indicated. Anhydrous THF, toluene, and ether were freshly distilled over
Na and benzophenone. Anhydrous methanol was freshly distilled over Mg.
Anhydrous CH2Cl2 and CHCl3 were freshly distilled over calcium hydride.
General procedure for the racemic reaction. To a dried Schlenk tube containing
Ni(ClO4)2·6H2O (7.2 mg, 0.02 mmol) and 2,2'-bipyridine (3.7 mg, 0.024 mmol) was
added 2.0 mL of anhydrous DCM. The Schlenk tube was sealed with a Teflon cap and
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the mixture was stirred at 80 °C for 1 h. After cooling to room temperature, ketoester
1 (0.2 mmol) and styrene 2 (0.4 mmol) was added under N2 atmosphere. The Schlenk
tube was sealed again and the mixture was stirred at 100 °C (temperature of oil bath)
for 40 h. The solvent was then removed under vacuum and the residue was purified by
chromatography on silica gel, eluting with ethyl/petroleum ether to afford the product
3. Styrenes bearing electron-donating groups (2b-2d, 2h, 2k, and 2l) were added in
two batches. The second batch of styrene (0.2 mmol) was added to the Schlenk tube
after 24 h under N2 atmosphere when the tube was cooled to room temperature.
(E)-Methyl 2-hydroxy-4-phenyl-2-(trifluoromethyl)but-3-enoate (3aa). Purified
by chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (v/v);
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1
white solid, 48.0 mg, 92% yield, m.p. 55–58 °C; H NMR (500 MHz, CDCl3): δ
7.45–7.47 (m, 2H), 7.35–7.39 (m, 2H), 7.30–7.34 (m, 1H), 7.13 (d, J = 16.0 Hz, 1H),
6.37 (d, J = 15.5 Hz, 1H), 4.12 (s, 1H), 3.97 (s, 3H). 13C{1H}NMR (125 MHz,
CDCl3): δ 169.5, 135.2, 134.9, 128.8, 128.7, 127.1, 122.8 (q, J = 285.0 Hz), 119.3,
77.2 (q, J = 30.0 Hz), 54.6. 19F{1H}NMR (376 MHz, CDCl3): δ –78.1 (s, 3F); HRMS
m/z (ESI+): Calculated for C12H11F3NaO3 ([M+Na]+): 283.0552, Found 283.0554.
(E)-Methyl 2-hydroxy-4-(p-tolyl)-2-(trifluoromethyl)but-3-enoate (3ab). Purified
by chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (v/v);
white solid, 44.2 mg, 81% yield, m.p. 71–73 °C; 1H NMR (500 MHz, CDCl3): δ 7.35
(d, J = 8.0 Hz, 2H), 7.17 (d, J = 6.5 Hz, 2H), 7.08 (d, J = 15.5 Hz, 1H), 6.31 (d, J =
16.0 Hz, 1H), 4.10 (s, 1H), 3.97 (s, 3H), 2.37 (s, 3H). 13C{1H}NMR (125 MHz,
CDCl3): δ 169.6, 138.8, 134.8, 132.4, 129.4, 127.1, 122.9 (q, J = 285.0 Hz), 118.2,
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77.2 (q, J = 30.0 Hz), 54.6, 21.2. F{1H}NMR (376 MHz, CDCl3): δ –78.2 (s, 3F);
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HRMS m/z (ESI+): Calculated for C13H17F3NO3 ([M+NH4]+): 292.1155, Found
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292.1152.
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(E)-Methyl
4-(4-(tert-butyl)phenyl)-2-hydroxy-2-(trifluoromethyl)but-3-enoate
(3ac). Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum
ether 1:10 (v/v); yellow oil, 51.4 mg, 81% yield; 1H NMR (500 MHz, CDCl3): δ 7.39
(s, 4H), 7.10 (d, J = 16.0 Hz, 1H), 6.33 (d, J = 15.5 Hz, 1H), 4.11 (s, 1H), 3.96 (s, 3H),
1.33 (s, 9H). 13C{1H}NMR (125 MHz, CDCl3): δ 169.6, 152.1, 134.6, 132.4, 126.9,
125.6, 122.9 (q, J = 285.0 Hz), 118.4, 77.2 (q, J = 31.3 Hz), 54.5, 34.7, 31.2.
19F{1H}NMR (376 MHz, CDCl3): δ –78.2 (s, 3F); HRMS m/z (ESI+): Calculated for
C16H19F3NaO3 ([M+Na]+): 339.1179, Found 339.1181.
(E)-Methyl 4-(4-acetoxyphenyl)-2-hydroxy-2-(trifluoromethyl)but-3-enoate (3ad).
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
1:5 (v/v); white solid, 38.0 mg, 60% yield, m.p. 98–101 C; 1H NMR (500 MHz,
o
CDCl3): δ 7.46 (d, J = 8.5 Hz, 2H), 7.09–7.12 (m, 3H), 6.33 (d, J = 15.5 Hz, 1H), 4.16
(s, 1H), 3.97 (s, 3H), 2.32 (s, 3H). C{1H}NMR (125 MHz, CDCl3): δ 169.4, 169.2,
13
151.0, 134.0, 133.0, 128.1, 122.8 (q, J = 285.0 Hz), 121.9, 119.6, 54.6, 21.0.
19F{1H}NMR (376 MHz, CDCl3): δ –78.1 (s, 3F); HRMS m/z (ESI+): Calculated for
C14H17F3NO5 ([M+NH4]+): 336.1053, Found 336.1054.
(E)-Methyl 4-(4-fluorophenyl)-2-hydroxy-2-(trifluoromethyl)but-3-enoate (3ae).
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
1:10 (v/v); white solid, 47.0 mg, 85% yield, m.p. 48–51 C; 1H NMR (500 MHz,
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CDCl3): δ 7.43 (dd, J = 9.0, 5.0 Hz, 2H), 7.09 (d, J = 15.5 Hz, 1H), 7.05 (t, J = 8.5 Hz,
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7
13
2H), 6.29 (d, J = 15.5 Hz, 1H), 4.11 (s, 1H), 3.97 (s, 3H). C{1H}NMR (125 MHz,
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CDCl3): δ 169.4, 163.0 (d, J = 246.3 Hz), 133.8, 131.4 (d, J = 3.8 Hz), 128.8 (d, J =
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8.8 Hz), 122.8 (q, J = 285.0 Hz), 119.0, 115.7 (d, J = 22.5 Hz), 54.6. F{1H}NMR
(376 MHz, CDCl3): δ –78.1 (s, 3F), –112.5 (s, 1F); HRMS m/z (ESI+): Calculated for
C12H10F4NaO3 ([M+Na]+): 301.0458, Found 301.0457.
(E)-Methyl 4-(4-chlorophenyl)-2-hydroxy-2-(trifluoromethyl)but-3-enoate (3af).
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
1:10 (v/v); white solid, 53.3 mg, 90% yield, m.p. 72–74 C; 1H NMR (500 MHz,
o
CDCl3): δ 7.38 (d, J = 8.5 Hz, 2H), 7.33 (d, J = 8.5 Hz, 2H), 7.08 (d, J = 16.0 Hz, 1H),
6.35 (d, J = 15.5 Hz, 1H), 4.13 (s, 1H), 3.97 (s, 3H). 13C{1H}NMR (125 MHz,
CDCl3): δ 169.3, 134.6, 133.8, 133.8, 128.9, 128.4, 122.8 (q, J = 285.0 Hz), 120.0,
77.2 (q, J = 31.3 Hz), 54.6. 19F{1H}NMR (376 MHz, CDCl3): δ –78.1 (s, 3F); HRMS
m/z (ESI+): Calculated for C12H10ClF3NaO3 ([M+Na]+): 317.0163, Found 317.0164.
(E)-Methyl 4-(4-bromophenyl)-2-hydroxy-2-(trifluoromethyl)but-3-enoate (3ag).
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
1:10 (v/v); white solid, 59.9 mg, 88% yield, m.p. 80–82 C; 1H NMR (500 MHz,
o
CDCl3): δ 7.49 (d, J = 8.5 Hz, 2H), 7.32 (d, J = 8.4 Hz, 2H), 7.06 (d, J = 15.8 Hz, 1H),
6.36 (d, J = 15.8 Hz, 1H), 4.13 (s, 1H), 3.97 (s, 3H). 13C{1H}NMR (125 MHz,
CDCl3): δ 169.3, 134.2, 133.8, 131.9, 128.6, 122.8, 122.7 (q, J = 285.0 Hz), 120.1,
77.2 (q, J = 30.0 Hz), 54.6. 19F{1H}NMR (376 MHz, CDCl3): δ –78.1 (s, 3F); HRMS
m/z (ESI-): Calculated for C12H9BrF3O3 ([M-H]-): 336.9693, Found 336.9684.
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(E)-Methyl 2-hydroxy-4-mesityl-2-(trifluoromethyl)but-3-enoate (3ah). Purified
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by chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (v/v);
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9
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white solid, 57.0 mg, 94% yield, m.p. 67–69 C; 1H NMR (500 MHz, CDCl3): δ 7.17
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(d, J = 16.0 Hz, 1H), 6.92 (s, 2H), 5.96 (d, J = 16.0 Hz, 1H), 4.18 (s, 1H), 3.99 (s, 3H),
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2.32 (s, 3H), 2.28 (s, 6H). C{1H}NMR (125 MHz, CDCl3): δ 169.7, 137.1, 135.9,
19
133.3, 132.2, 128.7, 124.5, 122.9 (q, J = 285.0 Hz), 54.4, 20.9, 20.5. F{1H}NMR
(376 MHz, CDCl3): δ –78.2 (s, 3F); HRMS m/z (ESI+): Calculated for C15H17F3NaO3
([M+Na]+): 325.1022, Found 325.1025.
(E)-Methyl 4-(2-fluorophenyl)-2-hydroxy-2-(trifluoromethyl)but-3-enoate (3ai).
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
o
1:10 (v/v); white solid, 46.0 mg, 83% yield, m.p. 33–34 C; 1H NMR (500 MHz,
CDCl3): δ 7.48 (td, J = 8.0, 1.5 Hz, 1H), 7.28–7.34 (m, 1H), 7.26 (d, J = 16.0 Hz, 1H),
7.05–7.17 (m, 2H), 6.51 (d, J = 16.0 Hz, 1H), 4.17 (s, 1H), 3.98 (s, 3H).
13C{1H}NMR (125 MHz, CDCl3): δ 169.4, 160.7 (d, J = 250.0 Hz), 130.1 (d, J = 7.5
Hz), 128.5 (d, J = 3.8 Hz), 128.0 (d, J = 2.5 Hz), 124.2 (d, J = 3.8 Hz), 123.1 (d, J =
11.3 Hz), 122.8 (q, J = 285.0 Hz), 122.0 (d, J = 6.3 Hz), 116.0 (d, J = 22.5 Hz), 77.3
19
(q, J = 31.3 Hz), 54.7. F{1H}NMR (376 MHz, CDCl3): δ –78.1 (s, 3F), –116.2 (s,
1F); HRMS m/z (ESI+): Calculated for C12H10F4NaO3 ([M+Na]+): 301.0458, Found
301.0468.
(E)-Methyl
4-(3-bromo-4-fluorophenyl)-2-hydroxy-2-(trifluoromethyl)but-3-enoate
(3aj).
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
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1:10 (v/v); yellow solid, 46.2 mg, 65% yield, m.p. 86–87 C; 1H NMR (500 MHz,
CDCl3): δ 7.65 (dd, J = 6.5, 2.0 Hz, 1H), δ 7.33–7.36 (m, 1H), 7.11 (t, J = 8.5 Hz, 1H),
7.03 (d, J = 15.5 Hz, 1H), 6.31 (d, J = 16.0 Hz, 1H), 4.17 (s, 1H), 3.98 (s, 3H).
13C{1H}NMR (125 MHz, CDCl3): δ 169.2, 159.2 (d, J = 236.3 Hz), 133.0 (d, J = 3.75
Hz), 132.7, 131.9, 127.8 (d, J = 7.5 Hz), 122.7 (q, J = 285.0 Hz), 120.6, 116.7 (d, J =
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22.5 Hz), 109.5 (d, J = 22.5 Hz), 54.7. F{1H}NMR (376 MHz, CDCl3): δ –78.1 (s,
19
3F), –106.9 (s, 1F); HRMS m/z (ESI+): Calculated for C12H9BrF4NaO3 ([M+Na]+):
378.9563, Found 378.9568.
(E)-Methyl
2-hydroxy-4-(3-methoxyphenyl)-2-(trifluoromethyl)but-3-enoate
(3ak). Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum
ether 1:10 (v/v); yellow oil, 30.2 mg, 53% yield; 1H NMR (500 MHz, CDCl3): δ
7.27–7.31 (m, 1H), 7.10 (d, J = 15.5 Hz, 1H), 7.06 (d, J = 7.5 Hz, 1H), 6.97–7.01 (m,
1H), 6.86–6.91 (m, 1H), 6.37 (d, J = 15.5 Hz, 1H), 4.16 (s, 1H), 3.97 (s, 3H), 3.85 (s,
3H). 13C{1H}NMR (125 MHz, CDCl3): δ 169.4, 160.0, 136.6, 134.9, 129.7, 122.8 (q,
J = 285.0 Hz), 119.7, 119.7, 114.5, 112.6, 77.2 (q, J = 30.0 Hz), 55.3, 54.6.
19F{1H}NMR (376 MHz, CDCl3): δ –78.1 (s, 3F); HRMS m/z (ESI+): Calculated for
C13H14F3O4 ([M+H]+): 291.0839, Found 291.0844.
(E)-Methyl 2-hydroxy-4-(m-tolyl)-2-(trifluoromethyl)but-3-enoate (3al). Purified
by chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (v/v);
1
yellow oil, 43.8 mg, 80% yield; H NMR (500 MHz, CDCl3): δ 7.28 (s, 1H),
7.24–7.27 (m, 2H), 7.13–7.19 (m, 1H), 7.10 (d, J = 16.0 Hz, 1H), 6.36 (d, J = 16.0 Hz,
1H), 4.12 (s, 1H), 3.97 (s, 3H), 2.38 (s, 3H). 13C{1H}NMR (125 MHz, CDCl3): δ
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169.5, 138.3, 135.1, 135.0, 129.6, 128.6, 127.7, 124.4, 122.8 (q, J = 285.0 Hz), 119.0,
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77.2 (q, J = 30.0 Hz), 54.6, 21.3. F{1H}NMR (376 MHz, CDCl3): δ –78.1 (s, 3F);
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HRMS m/z (ESI+): Calculated for C13H17F3NO3 ([M+NH4]+): 292.1155, Found
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292.1163.
(E)-Methyl
4-(4-bromo-3,5-dimethoxyphenyl)-2-hydroxy-2-(trifluoromethyl)but-3-enoate
(3am). Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum
ether 1:10 (v/v); white solid, 39.0 mg, 49% yield, m.p. 132–134 C; 1H NMR (500
o
MHz, CDCl3): δ 7.07 (d, J = 16.0 Hz, 1H), 6.64 (s, 2H), 6.35 (d, J = 15.5 Hz, 1H),
4.14 (s, 1H), 3.99 (s, 3H), 3.94 (s, 6H). C{1H}NMR (125 MHz, CDCl3): δ 169.2,
13
157.3, 135.5, 134.8, 122.7 (q, J = 285.0 Hz), 120.0, 103.7, 101.9, 56.6, 54.7.
19F{1H}NMR (376 MHz, CDCl3): δ –78.0 (s, 3F); HRMS m/z (ESI+): Calculated for
C14H15BrF3O5 ([M+H]+): 399.0049, Found 399.0052.
(E)-Methyl 2-hydroxy-4-(naphthalen-2-yl)-2-(trifluoromethyl)but-3-enoate (3an).
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
1:10 (v/v); white solid, 30.8 mg, 50% yield, m.p. 89–91 C; 1H NMR (500 MHz,
o
CDCl3): δ 7.84 (t, J = 8.0 Hz, 4H), 7.64 (d, J = 9.5 Hz, 1H), 7.48–7.53 (m, 2H), 7.29
(d, J = 17.5 Hz, 1H), 6.50 (d, J = 15.5 Hz, 1H), 4.19 (s, 1H), 4.00 (s, 3H).
13C{1H}NMR (125 MHz, CDCl3): δ 169.5, 135.1, 133.5, 133.5, 132.7, 128.4, 128.2,
127.8, 127.7, 126.5, 126.1, 123.6, 122.9 (q, J = 283.8 Hz), 119.6, 54.6. 19F{1H}NMR
(376 MHz, CDCl3): δ –78.0 (s, 3F); HRMS m/z (ESI+): Calculated for C16H13F3NaO3
([M+Na]+): 333.0709, Found 333.0731.
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(E)-Methyl
2-hydroxy-4,4-diphenyl-2-(trifluoromethyl)but-3-enoate
(3ao).
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7
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
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1:10 (v/v); colorless oil, 65.9 mg, 98% yield; H NMR (500 MHz, CDCl3): δ
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7.35–7.42 (m, 3H), 7.29–7.34 (m, 3H), 7.24–7.26 (m, 2H), 7.19–7.21 (m, 2H), 6.35 (s,
1H), 3.88 (s, 1H), 3.59 (s, 3H). 13C{1H}NMR (125 MHz, CDCl3): δ 169.3, 150.0,
141.5, 137.9, 129.8, 128.5, 128.3, 128.2, 127.9, 127.6, 123.4 (q, J = 285.0 Hz), 119.4,
76.5 (q, J = 28.8 Hz), 53.9. 19F{1H}NMR (376 MHz, CDCl3): δ –78.9 (s, 3F); HRMS
m/z (ESI+): Calculated for C18H16F3O3 ([M+H]+): 337.1046, Found 337.1055.
(E)-Methyl
2-hydroxy-6-phenyl-2-(trifluoromethyl)hexa-3,5-dienoate
(3ap).
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
o
1:10 (v/v); yellow solid, 45.5 mg, 79% yield, m.p. 60–63 C; 1H NMR (500 MHz,
CDCl3): δ 7.40–7.45 (m, 2H), 7.35 (t, J = 7.0 Hz, 2H), δ 7.26–7.29 (m, 1H), δ
6.81–6.92 (m, 2H), 6.71 (d, J = 15.0 Hz, 1H), 5.97 (d, J = 14.5 Hz, 1H), 4.06 (s, 1H),
13
3.96 (s, 3H). C{1H}NMR (125 MHz, CDCl3): δ 169. 5, 136.6, 136.1, 135.0, 128.7,
19
128.2, 126.7, 126.6, 122.5, 122.8 (q, J = 285.0 Hz), 54.5. F{1H}NMR (376 MHz,
CDCl3): δ –78.2 (s, 3F); HRMS m/z (ESI+): Calculated for C14H13F3NaO3 ([M+Na]+):
309.0709, Found 309.0720.
(S,E)-Ethyl 2-hydroxy-4-phenyl-2-(trifluoromethyl)but-3-enoate (3ba).14 Purified
by chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (v/v);
yellow oil, 40.4 mg, 74% yield; 1H NMR (500 MHz, CDCl3): δ 7.43–7.49 (m, 2H),
7.37 (t, J = 8.0 Hz, 2H), 7.32 (t, J = 7.5 Hz, 1H), 7.13 (d, J = 15.5 Hz, 1H), 6.38 (d, J
= 15.5 Hz, 1H), 4.42 (m, 2H), 4.15 (s, 1H), 1.39 (t, J = 7.0 Hz, 3H).
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(E)-Isopropyl 2-hydroxy-4-phenyl-2-(trifluoromethyl)but-3-enoate (3ca). Purified
by chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (v/v);
yellow oil, 40.1 mg, 60% yield; 1H NMR (500 MHz, CDCl3): δ 7.44–7.47 (m, 2H),
7.37 (t, J = 7.0 Hz, 2H), 7.32 (t, J = 7.5 Hz, 1H), 7.12 (d, J = 16.0 Hz, 1H), 6.37 (d, J
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= 16.0 Hz, 1H), 5.22 (m, 1H), 4.17 (s, 1H), 1.37 (t, J = 6.5 Hz, 6H). C{1H}NMR
(125 MHz, CDCl3): δ 168.4, 135.4, 134.7, 128.7, 128.7, 127.1, 122.9 (q, J = 285.0
Hz), 119.6, 72.9, 21.5, 21.3. 19F{1H}NMR (376 MHz, CDCl3): δ –78.0 (s, 3F);
HRMS m/z (ESI+): Calculated for C14H15F3NaO3 ([M+Na]+): 311.0866, Found
311.0866.
(E)-Butyl 2-hydroxy-4-phenyl-2-(trifluoromethyl)but-3-enoate (3da). Purified by
chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:20 (v/v);
colorless oil, 47.1 mg, 78% yield; 1H NMR (500 MHz, CDCl3): δ 7.45–7.47 (m, 2H),
7.36–7.39 (m, 2H), 7.32–7.34 (m, 1H), 7.14 (d, J = 16.0 Hz, 1H), 6.39 (d, J = 16.0 Hz,
1H), 4.40–4.45 (m, 1H), 4.29–4.34 (m, 1H), 4.19 (s, 1H), 1.71–1.77 (m, 2H),
1.41–1.47 (m, 2H), 0.98 (t, J = 7.5 Hz, 3H). 13C{1H}NMR (125 MHz, CDCl3): δ
169.1, 135.3, 134.8, 128.7, 128.7, 127.1, 122.9 (q, J = 285.0 Hz),119.5, 68.1, 30.3,
18.8, 13.5. 19F{1H}NMR (376 MHz, CDCl3): δ –78.0 (s, 3F); HRMS m/z (ESI–):
Calculated for C15H16F3O3 ([M–H]–): 301.1057, Found 301.1060.
(E)-Diethyl 2-hydroxy-2-styrylmalonate (3ea). Purified by chromatography on
silica gel, eluting with ethyl acetate/petroleum ether 1:10 (v/v); yellow oil, 22.0 mg,
40% yield; 1H NMR (500 MHz, CDCl3): δ 7.46 (d, J = 7.5 Hz, 2H), 7.35 (t, J = 7.0 Hz,
2H), 7.29 (d, J = 8.0 Hz, 1H), 6.98 (d, J = 15.5 Hz, 1H), 6.62 (d, J = 16.0 Hz, 1H),
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4.28–4.38 (m, 4H), 4.10 (s, 1H), 1.33 (t, J = 7.0 Hz, 6H). C{1H}NMR (125 MHz,
CDCl3): δ 169.6, 136.1, 131.5, 128.6, 128.1, 127.0, 123.9, 78.6, 62.9, 14.0. HRMS
m/z (ESI+): Calculated for C15H19O5 ([M+H]+): 279.1227, Found 279.1226.
General procedure for the asymmetric reaction. To a dried Schlenk tube
containing Cu(OTf)2 (7.2 mg, 0.02 mmol) and L1 (8.6 mg, 0.024 mmol) was added
2.0 mL of anhydrous CHCl3 and the mixture was stirred for 1 h at room temperature.
Subsequently, trifluoropyruvate 1 (0.2 mmol) and alkene 2 (0.4 mmol) was added and
the Schlenk tube was sealed with a Teflon cap. The reaction mixture was stirred at
100 °C (temperature of oil bath) for 40 h. The solvent was then removed under
vacuum and the residue was purified by chromatography on silica gel, eluting with
ethyl/petroleum ether to afford the product 3.
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(E)-Methyl 2-hydroxy-4-phenyl-2-(trifluoromethyl)but-3-enoate (3aa). Purified
by chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (v/v);
46.0 mg, 88% yield; [α]D20 = +28.0 (c 0.5, CH2Cl2), 70% ee [Daicel Chiralpak AD-H
column (25 cm × 0.46 cm ID), n-hexane/i-PrOH = 90/10, 0.8 mL/min, 254 nm; tmajor
= 8.9 min, tminor = 17.2 min].
(E)-Methyl 2-hydroxy-4-(p-tolyl)-2-(trifluoromethyl)but-3-enoate (3ab). Purified
by chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (v/v);
45.8 mg, 84 % yield; [α]D20 = +27.0 (c 0.5, CH2Cl2), 67% ee [Daicel Chiralpak AD-H
column (25 cm × 0.46 cm ID), n-hexane/i-PrOH = 90/10, 0.8 mL/min, 254 nm; tmajor
= 10.1 min, tminor = 30.8 min].
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(E)-Methyl
4-(4-(tert-butyl)phenyl)-2-hydroxy-2-(trifluoromethyl)but-3-enoate
6
7
8
(3ac). Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum
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ether 1:10 (v/v); 52.4 mg, 83% yield; [α]D = +30.4 (c 0.5, CH2Cl2), 71% ee [Daicel
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Chiralpak AD-H column (25 cm × 0.46 cm ID), n-hexane/i-PrOH = 90/10, 0.8
mL/min, 254 nm; tmajor = 9.4 min, tminor = 19.2 min].
(E)-Methyl 4-(4-fluorophenyl)-2-hydroxy-2-(trifluoromethyl)but-3-enoate (3ae).
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
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1:10 (v/v); 38.5 mg, 68% yield; [α]D = +31.0 (c 0.5, CH2Cl2), 69% ee [Daicel
Chiralpak AD-H column (25 cm × 0.46 cm ID), n-hexane/i-PrOH = 90/10, 0.8
mL/min, 254 nm; tmajor = 10.3 min, tminor = 28.8 min].
(E)-Methyl 4-(4-chlorophenyl)-2-hydroxy-2-(trifluoromethyl)but-3-enoate (3af).
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
20
1:10 (v/v); 20.1 mg, 34% yield; [α]D = +31.8 (c 0.5, CH2Cl2), 75% ee [Daicel
Chiralcel AS-H column (25 cm × 0.46 cm ID), n-hexane/i-PrOH = 90/10, 0.8 mL/min,
254 nm; tminor = 9.1 min, tmajor = 10.3 min].
(E)-Methyl 4-(4-bromophenyl)-2-hydroxy-2-(trifluoromethyl)but-3-enoate (3ag).
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
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1:10 (v/v); white solid, 21.0 mg, 31% yield; [α]D = +21.8 (c 0.5, CH2Cl2), 71% ee
[Daicel Chiralcel AS-H column (25 cm × 0.46 cm ID), n-hexane/i-PrOH = 90/10, 0.8
mL/min, 254 nm; tminor = 9.4 min, tmajor = 10.8 min].
(E)-Methyl 2-hydroxy-4-mesityl-2-(trifluoromethyl)but-3-enoate (3ah). Purified
by chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (v/v);
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52.4 mg, 87% yield; [α]D = +8.1 (c 0.5, CH2Cl2), 75% ee [Daicel Chiralcel AS-H
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(E)-Methyl 4-(2-fluorophenyl)-2-hydroxy-2-(trifluoromethyl)but-3-enoate (3ai).
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
20
1:10 (v/v); 15.6 mg, 28% yield; [α]D = +28.0 (c 0.5, CH2Cl2), 71% ee [Daicel
Chiralpak AD-H column (25 cm × 0.46 cm ID), n-hexane/i-PrOH = 90/10, 0.8
mL/min, 254 nm; tmajor = 8.4 min, tminor = 9.7 min].
(E)-Methyl 2-hydroxy-4-(m-tolyl)-2-(trifluoromethyl)but-3-enoate (3al). Purified
by chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (v/v);
34.8 mg, 63% yield; [α]D20 = +35.2 (c 0.5, CH2Cl2), 71% ee [Daicel Chiralpak AD-H
column (25 cm × 0.46 cm ID), n-hexane/i-PrOH = 90/10, 0.8 mL/min, 254 nm; tmajor
= 7.4 min, tminor = 8.3 min].
(E)-Methyl 4-(4-bromo-3,5-dimethoxyphenyl)-2-hydroxy-2-(trifluoromethyl)but-
3-enoate (3am). Purified by chromatography on silica gel, eluting with ethyl
acetate/petroleum ether 1:10 (v/v); 39.6 mg, 50% yield; [α]D20 = +20.7 (c 0.5, CH2Cl2),
68% ee [Daicel Chiralpak AD-H column (25 cm × 0.46 cm ID), n-hexane/i-PrOH =
90/10, 0.8 mL/min, 254 nm; tmajor = 17.0 min, tminor = 23.9 min].
(E)-Methyl 2-hydroxy-4-(naphthalen-2-yl)-2-(trifluoromethyl)but-3-enoate (3an).
Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
20
1:10 (v/v); 44.6 mg, 72% yield; [α]D = +15.5 (c 0.5, CH2Cl2), 69% ee [Daicel
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Chiralpak AD-H column (25 cm × 0.46 cm ID), n-hexane/i-PrOH = 90/10, 0.8
mL/min, 254 nm; tmajor = 12.4 min, tminor = 23.9 min].
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(S)-Methyl
2-hydroxy-4,4-diphenyl-2-(trifluoromethyl)but-3-enoate
(3ao).
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Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum ether
20
1:10 (v/v); 37.6 mg, 56% yield; [α]D = +29.0 (c 0.5, CH2Cl2), 68% ee [Daicel
Chiralpak AD-H column (25 cm × 0.46 cm ID), n-hexane/i-PrOH = 90/10, 0.8
mL/min, 254 nm; tminor = 8.0 min, tmajor = 9.1 min].
(E)-Methyl
2-hydroxy-4-(4-methoxyphenyl)-2-(trifluoromethyl)but-3-enoate
(3aq). Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum
ether 1:10 (v/v); white solid, 49.3 mg, 85% yield, m.p. 77–79 oC; [α]D20 = +27.2 (c 0.5,
CH2Cl2), 68% ee [Lux 5u Cellulose-3 column (25 cm×0.46 cm ID), n-hexane/i-PrOH
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= 90/10, 0.8 mL/min, 254 nm; tmajor = 21.5 min, tminor = 23.4 min]; H NMR (500
MHz, CDCl3): δ 7.39 (d, J = 8.5 Hz, 2H), 7.05 (d, J = 15.5 Hz, 1H), 6.89 (d, J = 9.0
Hz, 2H), 6.22 (d, J = 16.0 Hz, 1H), 4.10 (s, 1H), 3.96 (s, 3H), 3.84 (s, 3H).
13C{1H}NMR (125 MHz, CDCl3): δ 169.7, 160.12, 134.3, 128.5, 127.9, 122.9 (q, J =
285.0 Hz), 116.8, 114.1, 55.3, 54.6. 19F{1H}NMR (376 MHz, CDCl3): δ –78.2 (s, 3F);
HRMS m/z (ESI+): Calculated for C13H14F3O4 ([M+H]+): 291.0839, Found 291.0837.
(E)-Methyl
2-hydroxy-4-(2-methoxyphenyl)-2-(trifluoromethyl)but-3-enoate
(3ar). Purified by chromatography on silica gel, eluting with ethyl acetate/petroleum
ether 1:10 (v/v); yellow oil, 46.5 mg, 80% yield; [α]D20 = +15.5 (c 0.5, CH2Cl2), 69%
ee [Lux 5u Cellulose-1 column (25 cm × 0.46 cm ID), n-hexane/i-PrOH = 90/10, 0.8
mL/min, 254 nm; tmajor = 13.2 min, tminor = 16.6 min]; 1H NMR (500 MHz, CDCl3): δ
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7.47 (dd, J = 7.5, 1.5 Hz, 1H), 7.42 (d, J = 16.0 Hz, 1H), 7.30 (t, J = 8.5 Hz, 1H), 6.96
(t, J = 7.5 Hz, 1H), 6.91 (d, J = 8.5 Hz, 1H), 6.45 (d, J = 16.0 Hz, 1H), 4.12 (s, 1H),
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3.96 (s, 3H), 3.88 (s, 3H). C{1H}NMR (125 MHz, CDCl3): δ 169.7, 157.3, 130.0,
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129.9, 127.8, 124.1, 122.9 (q, J = 285.0 Hz), 120.6, 119.7, 111.0, 77.4 (q, J = 30.0
Hz), 55.4, 54.5. 19F{1H}NMR (376 MHz, CDCl3): δ –78.1 (s, 3F); HRMS m/z (ESI+):
Calculated for C13H14F3O4 ([M+H]+): 291.0839, Found 291.0842.
(S,E)-Ethyl 2-hydroxy-4-phenyl-2-(trifluoromethyl)but-3-enoate (3ba). Purified
by chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (v/v);
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38.3 mg, colorless oil, 70% yield; [α]D = +31.2 (c 0.5, CH2Cl2), 64% ee [Daicel
Chiralpak AD-H column (25 cm × 0.46 cm ID), n-hexane/i-PrOH = 90/10, 0.8
mL/min, 254 nm; tmajor = 9.0 min, tminor = 17.0 min].
Transformation of 3ba to (S)-ethyl 2-hydroxy-4-phenyl-2-(trifluoromethyl)-
butanoate 4.13 The mixture of 3ba (25.8 mg, 0.1 mmol, 1.0 eq) and Pd/C (2.6 mg,
0.0025 mmol, 10 mol%) in 2.0 mL of EtOH was stirred at room temperature for 12 h
under hydrogen balloon. The resulting mixture was filtered off and washed with
EtOH. The crude mixture was purified by flash silica gel column chromatography,
eluting with ethyl acetate/petroleum ether 1:10 (v/v), to give compound 4 as a
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colorless oil. 23.6 mg, 86% yield; [α]D = +8.5 (c 1.0, CHCl3), 64% ee [Daicel
Chiralcel AS-H column (25 cm × 0.46 cm ID), n-hexane/i-PrOH = 98/2, 0.75 mL/min,
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254 nm; tminor = 7.5 min, tmajor = 9.4 min]; H NMR (500 MHz, CDCl3): δ 7.30–7.33
(m, 2H), 7.19–7.24 (m, 3H), 4.21–4.37 (m, 2H), 3.98 (s, 1H), 2.85–2.90 (ddd, J = 5.0
Hz, 11.5Hz, 14.0 Hz, 1H), 2.44–2.50 (ddd, J = 5.5 Hz, 11.0 Hz, 13.5 Hz, 1H),
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2.32–2.38 (m,1H), 2.21–2.27 (ddd, J = 5.0 Hz, 11.5 Hz, 14.0 Hz, 1H), 1.34 (t, J = 7.5
Hz, 3H).
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Transformation of 3aa to (S,E)-2-methoxy-N,4-diphenyl-2-(trifluoromethyl)
but-3-enamide 5. Step 1: To a solution of 3aa (52 mg, 0.2 mmol) in acetone (2.0 mL)
was added MeI (37.5 μL, 0.6 mmol) and K2CO3 (33.1 mg, 0.24 mmol). The resulting
mixture was refluxed for 30 h. After cooling to room temperature, the mixture was
then filtered and the solvent was removed under vacuum; the obtained residue was
used for the next step without purification. Step 2: The residue was dissolved in an
ethanolic solution of KOH (5%, 3.0 mL) and the resulting mixture was stirred at
60 °C for 3 h. After removing the solvent, the mixture was treated with cold 2N HCl
and extracted by ethyl acetate. The combined organic layers was washed with brine
and dried over anhydrous Na2SO4. After filtration and concentration under vacuum,
the crude intermediate was obtained and used for the next step without purification.
Step 3: To a solution of the crude intermediate obtained in step 2 in dry hexane (2.0
mL) was added oxalyl chloride (23.7 μL, 0.28 mmol) dropwise and DMF (15.4 μL,
0.2 mmol) in 10 min at 0 °C under N2. After which, the mixture was stirred at room
temperature for 2 h and then evaporated under vacuum to give the acid chloride as a
yellow solid. The resulting acid chloride was dissolved in CH2Cl2 (2.0 mL) and to the
solution were added NEt3 (44.3 μL, 0.32 mmol) and aniline (18.2 μL, 0.2 mmol). The
mixture was stirred at room temperature for 1 h. After diluting with CH2Cl2, the
mixture was washed subsequently with 1N HCl, saturated NaHCO3, and brine, and
then dried over Na2SO4. The solvent was evaporated under vacuum after filtration to
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afford the crude product, which was purified by flash column chromatography on
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silica gel (ethyl acetate/petroleum ether 1:5 (v/v)) to give compound 5 as a yellow
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solid. 48.2 mg, 72% yield for 3 steps, m.p. 97–99 C; [α]D = –8.3 (c 0.5, CH2Cl2),
70% ee [Daicel Chiralpak OD-H column (25 cm × 0.46 cm ID), n-hexane/i-PrOH =
90/10, 0.8 mL/min, 254 nm; tminor = 14.0 min, tmajor = 18.8 min];1H NMR (500 MHz,
CDCl3): δ 8.52 (s, 1H), 7.64 (d, J = 8.0 Hz, 2H), 7.50 (d, J = 7.5 Hz, 2H), 7.35–7.41
(m, 5H), 7.20 (t, J = 7.5 Hz, 1H), 7.02 (d, J = 16.5 Hz, 1H), 6.51 (d, J = 16.5 Hz, 1H),
3.62 (s, 3H). 13C{1H}NMR (125 MHz, CDCl3): δ 163.5, 137.8, 136.7, 135.1, 129.1,
129.1, 128.7, 127.1, 125.1, 123.4 (q, J = 287.5 Hz), 119.9, 118.0, 82.6 (q, J = 27.5
Hz), 54.4. 19F{1H}NMR: (376 MHz, CDCl3): δ –73.8 (s, 3F); HRMS m/z (ESI–):
Calculated for C18H15F3NO2 ([M–H]–): 334.1060, Found 334.1048.
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Transformation of 3ag to (S,E)-methyl 4-([1,1'-biphenyl]-4-yl)-2-hydroxy-2-(tri-
fluoromethyl)but-3-enoate compound 6. To a solution of 3ag (33.9 mg, 0.1 mmol)
in THF/H2O (1.0 mL, 9:1) were added Pd(PPh3)4 (11.6 mg, 0.01 mmol),
phenylboronic acid (36.6 mg, 0.3 mmol), and Na2CO3 (15.9 mg, 0.15 mmol). The
resulting mixture was stirred at 80 °C for 4 h under N2. After dilution with water and
extraction by CH2Cl2, the combined organic solvent was dried over Na2SO4 and
concentrated under vacuum. The residue was then purified by flash column
chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (v/v), to
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give compound 6 as a white solid. 23.9 mg, 71% yield, m.p. 187–189 C; [α]D
=
+28.4 (c 0.5, CH2Cl2), 70% ee [Daicel Chiralpak AD-H column (25 cm × 0.46 cm ID),
n-hexane/i-PrOH = 80/20, 0.8 mL/min, 254 nm; tmajor = 14.1 min, tminor = 40.8 min];
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1H NMR (500 MHz, CDCl3): δ 7.61–7.63 (m, 4H), 7.54 (d, J = 8.0 Hz, 2H), 7.47 (t, J
= 7.5 Hz, 2H), 7.38 (t, J = 7.5 Hz, 1H), 7.17 (d, J = 16.0 Hz, 1H), 6.42 (d, J = 16.0 Hz,
1H), 4.16 (s, 1H), 3.99 (s, 3H). 13C{1H}NMR (125 MHz, CDCl3): δ 169.5, 141.6,
140.4, 134.5, 134.2, 128.8, 127.6, 127.6, 127.4, 127.0, 122.8 (q, J = 285.0 Hz), 119.2,
77.2 (q, J = 30.0 Hz), 54.7. 19F{1H}NMR (376 MHz, CDCl3): δ –78.1 (s, 3F); HRMS
m/z (ESI–): Calculated for C18H14F3O3 ([M–H]–): 335.0901, Found 335.0898.
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AUTHOR INFORMATION
Corresponding Author
E-mail: yxjia@zjut.edu.cn
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We are grateful for the generous financial support by the National Natural Science
Foundation of China (Nos. 21372202 and 21522207), the Program for New Century
Excellent Talents in University (NCET-12-1086), and the Natural Science Foundation
of Zhejiang Province (LR14B020001).
Supporting Information
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Characterization data, including H, C, and F NMR for all the new compounds,
chiral HPLC spectra for the chiral products are available free of charge via the
Internet at http://pubs.acs.org.
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(12) 4-Methylstyrene 2b and 4-acetyloxystyrene 2d were unstable and consumed in
10 h under the optimal reaction conditions (10 mol% of Ni(ClO4)2·6H2O and 12
mol% of 2,2’-bipyridine in DCM at 100 oC).
(13) Ohshima, T.; Kawabata, T.; Takeuchi, Y.; Kakinuma, T.; Iwasaki, T.; Yonezawa,
T.; Murakami, H.; Nishiyama, H.; Mashima, K. Angew. Chem., Int. Ed. 2011, 50,
6296.
(14) Aikawa, K.; Asai, Y.; Hioki, Y.; Mikami, K. Tetrahedron: Asymmetry 2014, 25,
1104.
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