Reactions of fluorinated silanes with 2-nitrocinnamates

Article abstract of DOI:10.1016/j.jfluchem.2011.03.015

The interaction of 2-nitrocinnamates with silicon reagents Me ₃SiR_f (R_f = CF₃, C₂F ₅, and C₆F₅) promoted either by sodium acetate in DMF or by tetrabutylammonium aceta

Full text of DOI:10.1016/j.jfluchem.2011.03.015

Journal of Fluorine Chemistry 132 (2011) 378–381
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Reactions of fluorinated silanes with 2-nitrocinnamates
*
Artem A. Zemtsov, Vitalij V. Levin, Alexander D. Dilman , Marina I. Struchkova, Vladimir A. Tartakovsky
N.D. Zelinsky Institute of Organic Chemistry, 119991 Moscow, Leninsky Prospect 47, Russia
A R T I C L E I N F O
A B S T R A C T
Article history:
The interaction of 2-nitrocinnamates with silicon reagents Me3SiRf (Rf = CF3, C2F5, and C6F5) promoted
either by sodium acetate in DMF or by tetrabutylammonium acetate in dichloromethane has been
described. The reactions proceed as conjugate addition of fluorinated carbanion at the C55C bond and
afford 3-aryl-2-nitrobutanoates bearing a fluorinated substituent in good yields as diastereomeric
mixtures in ratio from 1:1 to 1.6:1.
Received 7 February 2011
Received in revised form 10 March 2011
Accepted 12 March 2011
Available online 30 March 2011
ß 2011 Elsevier B.V. All rights reserved.
Keywords:
The Ruppert–Prakash reagent
Silanes
Conjugate addition
Nitro alkenes
1. Introduction
2. Results and discussion
Silicon reagents bearing a fluorinated group have become
valuable reagents as synthetic equivalents of fluorinated carba-
nions [1]. While the major attention has been devoted to
trifluoromethylation reactions using Me3SiCF3 (the Ruppert–
Prakash reagent), silanes with other fluorinated or fluorine-
containing fragments have also been exploited due to convenience
of their handling and mild reaction conditions [2,3].
2-Nitrocinnamates 1 were obtained from aldehydes or their N-
phenylimines and methyl nitro acetate by Knoevenagel condensa-
tion [10] (Scheme 1). Compounds 1 were isolated as mixtures of
geometrical isomers.
Nitrocinnamate 1a (mixture of isomers 1.6:1) was selected as a
model substrate and its reaction with the Ruppert–Prakash reagent
was investigated (Table 1).
The reactions are typically carried out in the presence of Lewis
basic activator which interacts with the silane to generate five-
coordinate species followed by transfer of the fluorinated
carbanion from silicon to electrophile. The interaction of silanes
with C55O and C55N bonds is very well developed [1], whereas
addition of fluorinated group to C55C bond still has a limited scope
[4–8].
Thus, recently we have demonstrated that highly electrophilic
Michael acceptors such as arylidenemalononitriles [6] and
arylidene Meldrum’s acids [7], which bear two electron-with-
drawing substituents, serve as suitable substrates for the coupling
Performing the reaction in DMF with stoichiometric amount of
sodium acetate as basic activator provides desired product 2a in
reasonable yields as a 1:1 mixture of diastereoisomers (entries 1–
3). The variation of temperature and time had no effect on the
product yield. We also tested analogous substrate with the tert-
butyl instead of methyl ester group, that gave identical result (68%
yield). When the amount of Lewis base was decreased to 10 mol%,
virtually no product was formed, suggesting that the nitronate
anion, which is produced after the addition of CF3-carbanion at
C55C bond, cannot activate the silicon reagent. For the variation of
solvent, we used tetrabutylammonium acetate, which was
reported to be effective activator of the Ruppert–Prakash reagent
in different media [11]. Thus, we observed that the reaction of 1a
with Me3SiCF3 in tetrahydrofuran or toluene promoted by
Bu4NOAc (1.2 equiv.) occurs rapidly and exothermically, but
affords the product 2a in only 70% yield. However, decreasing
the reaction temperature significantly slowed down the process
(entries 8–11). Finally, the best result was obtained when reaction
was performed in dichloromethane at À20 8C furnishing 2a in 82%
isolated yield (entry 12).
with Me3SiCF3. We also showed that
a,b-unsaturated nitriles,
esters and ketones containing additional activating acetoxy group
(acylated Baylis–Hillman adducts) can be pentafluorophenylated
with the use of complicated silanes MenSi(C6F5)4Àn [8]. In
continuation of these studies, herein we report the reactions of
trimethylsilicon reagents Me3SiRf with 2-nitrocinnamates. The
products of this reaction can be considered as precursors to
a-
amino acids bearing a fluorinated group in
b-position [9].
Based on the optimization studies, two procedures were
selected for further investigation: method A involving NaOAc in
DMF, and method B involving Bu4NOAc in dichloromethane. The
* Corresponding author. Fax: +7 499 135 53 28.
E-mail address: adil25@mail.ru (A.D. Dilman).
0022-1139/$ – see front matter ß 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2011.03.015

A.A. Zemtsov et al. / Journal of Fluorine Chemistry 132 (2011) 378–381
379
O
ophenyl groups also were successfully employed smoothly leading
to the desired products 2g and h in high yields. All products 2 were
obtained as mixtures of diastereoisomers in ratio from 1:1 to 1.6:1.
This ratio does not depend on the isomeric composition of starting
nitrocinnamate as clearly demonstrated for substrate 1c, for which
the sample of 1c enriched with one geometrical isomer (dr 25:1)
gave product 2c with virtually no selectivity (dr 1.2:1, entry 3).
However, as evidenced from the reaction of substrate 1d (entries 4
and 5) the isomeric composition of the product can depend on
reaction conditions. The latter phenomenon may be associated
with the subtle change of reactivity of nitronate anion coupled
with either sodium counterion in DMF or tetrabutylammonium
counterion in dichloromethane.
MeO2C
MeO2C
NO2
NO2
+
+
Ar
TiCl4
CO2Me
NO2
Ar
Ph
N
1
Ac2O
Ar
Scheme 1.
Table 1
Trifluoromethylation of nitrocinnamate 1a.
The opportunity to transform compounds 2 to derivatives of
fluorine-containing amino acids was examplified by the reduction
of compound 2a under mild conditions (Scheme 2). The
hydrogenation was performed over palladium on carbon under
atmospheric pressure in the presence of acylating reagent
furnishing N-Boc protected product 3a. Interestingly, the isomeric
ratio of the product was different from that of starting compound
thereby suggesting the rapid epimerization of the C–H acidic chiral
center prior to the reduction.
In summary, a method for the conjugate addition of fluorinated
carbanions (CF3, C2F5, and C6F5) to alkenes bearing nitro and ester
groups using readily available silicon reagents has been described.
The reactions proceed under mild conditions and provide facile
Me3SiCF3 (1.5 equiv.)
CF3
NO2
Acitivator
NO2
Ph
1a
Ph
2a
CO2Me
then aq. HCl
CO2Me
Entry
Activator
Equiv.
Solv.
t, 8C
Time, h
Yield,a,b
%
1
2
NaOAc
1.5
1.5
1.2
0.1
1.2
1.2
1.5
1.25
1.25
1.1
1.2
1.2
DMF
DMF
DMF
DMF
DMF
DMF
MeCN
THF
50
3
18
3
(67)
(62)
67
NaOAc
r.t.
3
NaOAc
r.t.
50
4
NaOAc
3
n.r.
(57)
(50)
0
5
LiOAc
r.t.
16
2
6
NaOBz
50
7
NaOAc
r.t.
18
0.3
1
access to fluorinated
a-nitro propionates, which can be trans-
8
NBu4OAc
NBu4OAc
NBu4OAc
NBu4OAc
NBu4OAc
À20
À50
0
(66)
(8)c
68
formed to amino acid derivatives.
9
THF
10
11
12
THF
0.2
0.2
3
3. Experimental
Toluene
CH2Cl2
À20
À20
(72)
82
a
3.1. General experimental procedures
All reactions were performed under an argon atmosphere. DMF
In all cases product 2a is formed as isomeric mixture, dr 1:1.
b
c
In parenthesis – yield by NMR standard, without parenthesis – isolated yield.
Conversion of 1a is 18%.
˚
was distilled under vacuum from P2O5 and stored over MS 4 A;
former procedure is more practical, while the latter gives higher
yields.
CF3
CF3
A variety of nitrocinnamates 1 were reacted with fluorinated
silanes (Table 2). As a rule, good yields of trifluoromethylated
products 2a–d can be achieved. Only substrate with the furyl
substituent gave decreased yields, despite complete conversion of
starting material. Silanes with pentafluoroethyl and pentafluor-
H2 (1 bar), Pd/C (10%)
Boc2O, MeOH, 20h
CO2Me
NO2
CO2Me
NHBoc
3a, dr = 1.7 : 1
Ph
Ph
79%
2a, dr = 1 : 1
Scheme 2.
Table 2
Reactions of nitrocinnamates 1 with silanes.
Rf
RfSiMe3 (1.5 equiv.)
CO2Me
CO2Me
NO2
Ar
Ar
NO2
2
1
Method A: NaOAc (1.2 equiv.), DMF, r.t., 3h
Method B: Bu4NOAc (1.2 equiv.), CH2Cl2, –20 °C, 3h
Entry
Ar
Starting
dr of 1
Rf
Product
Method
Yield (B),a
%
dr of 2b
1
2
4-MeOC6H4
1b
1.1:1
CF3
2b
A
B
B
A
B
A
B
B
A
A
67
82
84
32
68
<1
37
70
88
99
1:1
1:1
3
4-ClC6H4
2-Thienyl
1c
25:1
CF3
CF3
2c
1.2:1
1.6:1
1:1.2
4
1d
1.3:1
2d
5
6
2-Furyl
1e
1.2:1
CF3
2e
7
1.2:1
1:1
8
1-Naphthyl
1f
1.7:1
1.6:1
1.6:1
CF3
2f
9
Ph
Ph
1a
1a
C2F5
C6F5
2g
2h
1.4:1
1.2:1
10
a
Isolated yield.
b
Determined by NMR spectroscopy of crude product.

380
A.A. Zemtsov et al. / Journal of Fluorine Chemistry 132 (2011) 378–381
CH2Cl2 was freshly distilled from CaH2. Column chromatography
was carried out employing Merck silica gel (Kieselgel60, 230–400
mesh). Precoated silica gel plates F-254 were used for thin-layer
analytical chromatography visualizing with UV and/or acidic aq.
KMnO4 solution. NMR spectra were recorded on a Bruker AM-300
instrument. Microanalyses were performed on KarloErba 1106
instrument. Me3SiCF3 and Me3SiC2F5 were purchased from P&M.
Nitrocinnamates 1a–d [10a] and 1e and f [10b], as well as
Me3SiC6F5 [12], were obtained according to the literature
procedures.
162.4; minor isomer: 50.0 (q, J = 29.2), 54.0, 86.2, 124.4 (q,
J = 280.8), 127.0 (q, J = 1.4), 129.5, 131.1 (q, J = 1.4), 136.3, 161.5. 19
NMR (282 MHz, CDCl3),
: major isomer: À67.2 (d, 3F, J = 8.3, CF3);
minor isomer: À69.0 (d, 3F, J = 8.3, CF3). Anal. Calcd for
11H9ClF3NO4 (311.64): C, 42.39; H, 2.91; N, 4.49. Found: C,
F
d
C
42.30; H, 2.78; N, 4.32.
3.2.2.4. Methyl 4,4,4-trifluoro-2-nitro-3-(thiophen-2-yl)butanoate
(2d). Mixture of isomers 1.6:1. Mp 80–81 8C. Rf 0.20 (hexane/EtOAc,
10:1). 1H NMR (300 MHz, CDCl3),
d: major isomer: 3.92 (s, 3H, CH3),
4.86 (dq, 1H, J = 10.1, 8.4, CHCF3), 5.66 (d, 1H, J = 10.1, CHNO2), 7.05
(dd, 1H, J = 5.0, 4.1, S–CH55CH), 7.16 (d, 1H, J = 4.1, S–CH), 7.38 (d,
1H, J = 5.0, S–C55CH); minor isomer: 3.59 (s, 3H, CH3), 4.98 (dq, 1H,
J = 10.1, 8.3, CHCF3), 5.66 (d, 1H, J = 10.1, CHNO2), 7.03 (dd, 1H,
J = 5.0, 4.1, S–CH55CH), 7.14 (d, 1H, J = 4.1, S–CH), 7.40 (d, 1H, J = 5.0,
3.2. General procedures for perfluoroalkylation
3.2.1. Method A
Sodium acetate (98 mg, 1.2 mmol) was added to a solution of
nitrocinnamate 1 (1.0 mmol) and Me3SiRf (1.5 mmol) in DMF
(2 mL) at room temperature. The resulting suspension was stirred
for 3 h and quenched with aq. HCl (4 mL, 0.5 M). The aqueous
phase was extracted with Et2O (3 Â 5 mL), the combined organic
layer was filtered through Na2SO4, concentrated under reduced
pressure, and the residue was purified by column chromatography.
S–C55CH). 13C NMR (75 MHz, CDCl3),
d: major isomer: 46.4 (q,
J = 29.9), 54.5, 87.5, 123.8 (q, J = 280.8), 127.4, 128.0, 129.3 (q,
J = 1.7), 129.8, 162.3; minor isomer: 45.9 (q, J = 30.3), 54.0, 86.4,
124.2 (q, J = 281.0), 127.8, 128.3 (q, J = 1.7), 130.1, 130.1, 161.5. 19
F
NMR (282 MHz, CDCl3),
d
: major isomer: À68.2 (d, 3F, J = 8.4, CF3);
minor isomer: À69.9 (d, 3F, J = 8.3, CF3). Anal. Calcd for C9H8F3NO4S
(283.22): C, 38.17; H, 2.85; N, 4.95. Found: C, 38.14; H, 2.91; N 4.87.
3.2.2. Method B
Tetrabutylammonium acetate (361 mg, 1.2 mmol) was added
to a stirred solution of nitrocinnamate 1 (1.0 mmol) and Me3SiCF3
(0.22 mL, 1.5 mmol) in CH2Cl2 (2 mL) at À20 8C. The resulting
homogeneous solution was kept at À20 8C for 3 h, then warmed to
room temperature and quenched with aq. HCl (4 mL, 0.5 M), and
worked-up similar to the method A.
3.2.2.5. Methyl
(2e). Mixture of isomers 1.2:1. Oil. Rf 0.23 (hexane/EtOAc, 6:1).
1H NMR (300 MHz, CDCl3),
: major isomer: 3.66 (s, 3H, CH3), 4.86
4,4,4-trifluoro-3-(furan-2-yl)-2-nitrobutanoate
d
(dq, 1H, J = 10.1, 8.3, CHCF3), 5.73 (d, 1H, J = 10.1, CHNO2), 6.41 (dd,
1H, J = 3.7, 1.6, O–CH55CH), 6.49 (d, 1H, J = 3.7, O–CH), 7.45 (d, 1H,
J = 1.6, O–C55CH); minor isomer: 3.92 (s, 3H, CH3), 4.75 (dq, 1H,
J = 10.1, 8.3, CHCF3), 5.70 (d, 1H, J = 10.1, CHNO2), 6.40 (dd, 1H,
J = 3.7, 1.6, O–CH55CH), 6.50 (d, 1H, J = 3.7, O–CH), 7.44 (d, 1H,
3.2.2.1. Methyl 4,4,4-trifluoro-2-nitro-3-phenylbutanoate (2a). Mix-
ture of isomers 1:1. Mp 77–79 8C. Rf 0.23 (hexane/EtOAc, 6:1). 1H
J = 1.6, O–C55CH). 13C NMR (75 MHz, CDCl3),
d: major isomer: 44.8
NMR (300 MHz, CDCl3),
(dq, 1H, J = 10.6, 8.4, EHCF3), 4.64 (dq, 1H, J = 10.6, 8.4, EHCF3), 5.75
(d, 2H, J = 10.6, CHNO2 of both isomers), 7.30–7.45 (m, 10H, 2Ph).
13C NMR (75 MHz, CDCl3),
54.4, 86.5, 87.0, 124.4 (q, J = 280.4), 124.9 (q, J = 280.8), 129.2, 129.3,
129.8 (q, J = 0.8), 129.87, 129.90, 161.7, 162.7. 19F NMR (282 MHz,
d
: 3.49 (s, 3H, CH3), 3.93 (s, 3H, CH3), 4.54
(q, J = 30.7), 54.2, 84.7, 111.1, 112.3, 123.6 (q, J = 281.2), 141.8 (q,
J = 2.0), 144.3, 162.3; minor isomer: 45.2 (q, J = 30.3), 54.5, 85.0,
111.1, 112.0, 123.3 (q, J = 281.0), 142.3 (q, J = 2.1), 144.2, 161.6. 19
F
d: 50.6 (q, J = 20.8), 51.0 (q, J = 28.2), 53.8,
NMR (282 MHz, CDCl3),
d
: major isomer: À69.3 (d, 3F, J = 8.3, CF3);
minor isomer: À67.8 (d, 3F, J = 8.3, CF3). Anal. Calcd for C9H8F3NO5
(267.16): C, 40.46; H, 3.02; N, 5.24. Found: C, 40.27; H, 2.94; N,
5.07.
CDCl3),
d
: À67.1 (d, 3F, J = 8.4, CF3), À68.9 (d, 3F, J = 8.4, CF3). Anal.
Calcd for C11H10F3NO4 (277.20): C, 47.66; H, 3.64; N, 5.05. Found: C,
47.61; H, 3.59; N 5.11.
3.2.2.6. Methyl 4,4,4-trifluoro-3-(naphthalen-1-yl)-2-nitrobutanoate
(2f). Mixture of isomers 1:1. Mp 62–94 8C. Rf 0.22 (hexane/EtOAc,
3.2.2.2. Methyl 4,4,4-trifluoro-3-(4-methoxyphenyl)-2-nitrobutano-
6:1). 1H NMR (300 MHz, CDCl3),
d: 3.31 (s, 3H, CH3), 3.99 (s, 3H,
ate (2b). Mixture of isomers 1:1. Oil. Rf 0.22 (hexane/EtOAc, 6:1). 1H
CH3), 5.60 (dq, 1H, J = 11.1, 8.3, EHCF3), 5.69 (dq, 1H, J = 11.0, 8.3,
CHCF3), 5.98 (d, 1H, J = 11.1, CHNO2), 5.99 (d, 1H, J = 11.0, CHNO2),
7.42–7.75 (m, 8H, 4CHNaph of both isomers), 7.92 (d, 4H, J = 7.7,
2CHNaph of both isomers), 8.24 (d, 2H, J = 8.5, CHNaph of both
isomers). 13C NMR (75 MHz, CDCl3),
d: 44.0 (q, J = 29.0), 44.4 (q,
J = 28.4), 53.8, 54.6, 87.3, 87.4, 122.5, 122.7, 124.5 (q, J = 280.3),
124.8, 124.9 (q, J = 281.0), 125.0, 125.4 (q, J = 1.4), 125.6, 126.5,
126.6, 126.7, 127.7, 127.8, 129.3, 130.7, 132.0, 132.3, 134.1, 134.2,
NMR (300 MHz, CDCl3), d: 3.52 (s, 3H, CO2Me), 3.80 (s, 3H, OMe),
3.82 (s, 3H, OMe), 3.92 (s, 3H, CO2Me), 4.48 (dq, 1H, J = 10.5, 8.6,
CHCF3), 4.58 (dq, 1H, J = 10.5, 8.6, CHCF3), 5.69 (d, 1H, J = 11.0,
CHNO2), 5.70 (d, 1H, J = 10.5, CHNO2), 6.90 (d, 4H, J = 8.7, 2CHAr of
both isomers), 7.25 (d, 2H, J = 8.7, 2CHAr), 7.29 (d, 2H, J = 8.7,
2CHAr). 13C NMR (75 MHz, CDCl3),
d: 49.9 (q, J = 29.0), 50.3 (q,
J = 28.4), 53.8, 54.4, 55.4, 86.5, 87.2, 114.6, 114.7, 120.1, 120.8,
124.5 (q, J = 280.4), 124.8 (q, J = 280.6), 130.5, 131.1, 160.6, 160.7,
161.5, 163.1. 19F NMR (282 MHz, CDCl3),
CF3), À66.9 (d, 3F, J = 8.3, CF3). Anal. Calcd for C15H12F3NO4
(327.26): C, 55.05; H, 3.70; N, 4.28. Found: C, 55.09; H, 3.64; N,
4.17.
d
: À68.6 (d, 3F, J = 8.3,
161.8, 162.8. 19F NMR (282 MHz, CDCl3),
CF3), À69.3 (d, 3F, J = 8.6, CF3). Anal. Calcd for C12H12F3NO5
(307.22): C, 46.91; H, 3.94; N, 4.56. Found: C, 46.77; H, 3.98; N,
4.54.
d
: À67.5 (d, 3F, J = 8.6,
3.2.2.7. Methyl
(2g). Mixture of isomers 1.4:1. Oil. Rf 0.22 (hexane/EtOAc, 10:1).
1H NMR (300 MHz, CDCl3),
: major isomer: 3.41 (s, 3H, CH3), 4.75
(ddd, 1H, J = 25.8, 10.1, 3.5, CHCF3), 5.84 (d, 1H, J = 10.1, CHNO2),
7.30–7.44 (m, 5H, CHAr); minor isomer: 3.92 (s, 3H, CH3), 4.62 (ddd,
1H, J = 26.8, 10.5, 3.5, CHCF3), 5.83 (d, 1H, J = 10.5, CHNO2), 7.30–
7.44 (m, 5H, CHAr). 13C NMR (75 MHz, CDCl3),
d: major isomer: 48.3
(t, J = 19.3), 53.7, 85.7, 161.9; minor-isomer: 48.7 (q, J = 18.7), 54.4,
87.0, 162.8; both isomers: 127.8 (d, J = 6.3), 128.2 (d, J = 6.9), 129.1,
129.2, 129.8 (br), 130.0 (d, J = 2.3), 130.4 (d, J = 2.3). 19F NMR
4,4,5,5,5-pentafluoro-2-nitro-3-phenylpentanoate
3.2.2.3. Methyl 3-(4-chlorophenyl)-4,4,4-trifluoro-2-nitrobutanoate
(2c). Mixture of isomers 1.2:1. Mp 89–90 8C. Rf 0.21 (hexane/EtOAc,
d
12:1). 1H NMR (300 MHz, CDCl3),
d: major isomer: 3.93 (s, 3H, CH3),
4.53 (dq, 1H, J = 10.5, 8.3, CHCF3), 5.70 (d, 1H, J = 10.5, CHNO2),
7.25–7.42 (m, 4H, 2CHAr of both isomers); minor isomer: 3.55 (s,
3H, CH3), 4.63 (dq, 1H, J = 10.5, 8.3, CHCF3), 5.72 (d, 1H, J = 10.5,
CHNO2), 7.25–7.42 (m, 4H, 2CHAr of both isomers). 13C NMR
(75 MHz, CDCl3),
d: major isomer: 50.4 (q, J = 28.2), 54.6, 86.8,
124.1 (q, J = 280.8), 127.5 (q, J = 1.5), 129.6, 130.6 (q, J = 1.3), 136.3,

A.A. Zemtsov et al. / Journal of Fluorine Chemistry 132 (2011) 378–381
381
(282 MHz, CDCl3),
d
: major isomer: À82.4 (s, 3F, CF3), À113.8 (dd,
CO2Me), minor isomer: 3.63 (s, 3H, CO2Me); both isomers: 1.41 (s,
9H, t-Bu), 3.85–4.04 (m, 1H, CHCF3), 4.80–4.95 (m) and 5.18–5.26
(m) (2H, NH + CHNO2), 7.26–7.42 (m, 5H, CHAr). 13C NMR (75 MHz,
1F, J = 273.4, 3.5, CFAFB), À122.9 (dd, 1F, J = 273.4, 25.8, CFAFB);
minor isomer: À82.2 (s, 3F, CF3), À111.0 (dd, 1F, J = 271.3, 3.5,
CFAFB), À122.1 (dd, 1F, J = 271.3, 26.8, CFAFB). Anal. Calcd for
CDCl3), d: both isomers: 28.3, 51.6 (q, J = 26.3), 51.9 (q, J = 26.3),
C12H10F5NO4 (327.20): C, 44.05; H, 3.08; N, 4.28. Found: C, 44.04;
52.6, 52.9, 54.4, 80.5–80.7 (m), 125.7 (q, J = 280.5), 125.8 (q,
J = 281.2), 128.9, 129.0, 129.1, 129.4, 129.5, 130.4 (q, J = 1.8), 131.6
(q, J = 1.8), 154.7–155.0 (m), 170.4, 170.6. 19F NMR (282 MHz,
H, 2.97; N, 4.19.
3.2.2.8. Methyl
2-nitro-3-(perfluorophenyl)-3-phenylpropanoate
CDCl3),
minor isomer: À64.9 (br), À65.1 (d, 3F, J = 8.5, CF3). Anal. Calcd for
16H20F3NO4 (347.33): C, 55.33; H, 5.80; N, 4.03. Found: C, 55.31;
d
: major isomer: À67.0 (br), À67.3 (d, 3F, J = 8.5, CF3);
(2h). Mixture of isomers 1.2:1. Oil. Rf 0.24 (hexane/EtOAc, 12:1).
1H NMR (300 MHz, CDCl3),
: major isomer: 3.67 (s, 3H, CH3), 5.43
d
C
(d, 1H, J = 12.1, CHCF3), 6.23 (d, 1H, J = 12.1, CHNO2), 7.28–7.42 (m,
5H, CHAr); minor isomer: 3.79 (s, 3H, CH3), 5.41 (d, 1H, J = 12.5,
H, 5.87; N, 3.95.
CHCF3), 6.30 (d, 1H, J = 12.5, CHNO2), 7.28–7.42 (m, 5H, CHAr). 13
C
NMR (75 MHz, CDCl3), d: major isomer: 42.6, 53.9, 88.0 (t, J = 4.0),
minor isomer: 42.2, 54.2, 88.3 (t, J = 4.3); both isomers: 127.6 (t,
J = 1.7), 128.2 (t, J = 1.7), 128.97, 129.01, 129.6, 134.6, 135.2, 163.1,
Acknowledgments
This work was supported by Russian Foundation for Basic
Research (project 10-03-91159), the Ministry of Science (project
MD-1151.2011.3), and the Federal program ‘‘Scientific and
163.2. 19F NMR (282 MHz, CDCl3),
d
: major isomer: À142.4 (ddd,
2F, J = 21.2, 21.2, 8.5, meta), À154.4 (t, F, J = 21.2, para), À161.2 (dd,
J = 21.2, 8.5, ortho); minor isomer: À141.5 (ddd, 2F, J = 21.2, 21.2,
8.1, meta), À154.5 (t, F, J = 21.2, para), À161.0 (dd, J = 21.2, 8.5,
ortho). Anal. Calcd for C16H10F5NO4 (375.25): C, 51.21; H, 2.69; N,
3.73. Found: C, 51.19; H, 2.69; N, 3.64.
educational
personnel
of
innovative
Russia’’
(project
02.740.11.0258).
References
3.2.2.9. tert-Butyl 4,4,4-trifluoro-2-nitro-3-phenylbutanoate. Mix-
ture of isomers 2.2:1. Obtained according to method A using
tert-butyl 2-nitro-3-phenylacrylate (mixture of isomers 1.3:1).
Yield 68%. Mp 100–102 8C. Rf 0.20 (hexane/EtOAc, 20:1). 1H NMR
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Palladium on carbon (35 mg, 10% of Pd) and Boc2O (3.0 mmol,
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stirring was discontinued, the liquid phase was decanted and the
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3.3.1. Methyl 2-((tert-butoxycarbonyl)amino)-4,4,4-trifluoro-3-
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9 (1967)
6:1). 1H NMR (300 MHz, CDCl3),
d: major isomer: 3.73 (s, 3H,