Protonation of 3-arylpropynoic acid derivatives in superacids

Article abstract of DOI:10.1007/s11178-005-0371-z

According to the ¹H and ¹³C NMR data, 3-arylpropynoic acids and their esters XC₆H_n-C≡C-CO₂R (R = H, Me, Et) having electron-withdrawing substituents in the benzene ring (X = NO₂, CN, COMe,

Full text of DOI:10.1007/s11178-005-0371-z

Russian Journal of Organic Chemistry, Vol. 41, No. 10, 2005, pp. 1485–1492. Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 10, 2005,
pp. 1516–1523.
Original Russian Text Copyright © 2005 by Walspurger, Vasil’ev, Sommer, Pale, Savechenkov, Rudenko.
Protonation of 3-Arylpropynoic Acid Derivatives
in Superacids
S. Walspurger1, A. V. Vasil’ev2, J. Sommer1, P. Pale1,
P. Yu. Savechenkov2, and A. P. Rudenko2
1 Universite L. Pasteur, rue B. Pascal 4, Strasbourg, 67000 France
2 St. Petersburg Academy of Forestry Engineering, Institutskii per. 5, St. Petersburg, 194021 Russia
e-mail: aleksvasil@hotmail.com
Received November 12, 2004
Abstract—According to the 1H and 13C NMR data, 3-arylpropynoic acids and their esters XC6Hn–CŁC–CO2R
(R = H, Me, Et) having electron-withdrawing substituents in the benzene ring (X = NO2, CN, COMe, CO2Me)
exist in HSO3F at –80 to 0°C as XC6Hn–CŁC–C+(OH)OR ions. Derivatives with other substituents (X = H, F,
Me, MeO) in HSO3F or CF3SO3H above –40°C undergo protonation at the acetylenic carbon atom neighboring
to the acid group to give unstable vinyl-type XC6Hn–C+=CH–CO2R cations which are then transformed into
mixtures of stereoisomeric (Z and E) fluorosulfonates or triflluoromethanesulfonates XC6Hn–CY=CH–CO2R
(Y = OSO2F, OSO2CF3), the E isomer prevailing.
We recently initiated studies on protonation and
subsequent transformations of acetylenic compounds
in superacidic media [1–6], which opened new pros-
pects in the application of superacids [7] in synthetic
organic chemistry. Stang [8, 9] and Olah [10] were the
first to report on the addition of superacids (HSO3F
and CF3SO3H) to alkyl- and dialkylacetylenes with
formation of the corresponding vinyl fluorosulfonates
and trifluoromethanesulfonates. The transformations in
HSO3F of acetylenic compounds with strong electron-
withdrawing substituents were studied using propyn-
oic, 2-butynoic, and 3-phenylpropynoic acids as ex-
amples [10]; however, the mechanism of formation of
fluorosulfonates thus obtained and their stereochemical
structure were not determined.
synthetic procedures on the basis of this reaction are
important for the preparation of fluorosulfonates and
trifluoromethanesulfonates [11]. Trifluoromethanesul-
fonates possessing various functional groups attract
specific interest from the viewpoint of their use in Pd-
catalyzed reactions leading to formation of new C–C
bonds [12–14]. In particular, access to such compounds
may be opened via addition of CF3SO3H to 3-aryl-
propynoic acid derivatives.
The present communication reports on the behavior
of 3-arylpropynoic acid derivatives in superacids
(HSO3F and CF3SO3H), reactivity of the O- and C-pro-
tonated species thus formed, and stereochemical
aspects of the addition of HSO3F and CF3SO3H at the
triple bond of the substrate.
1H and 13C NMR monitoring of the reactions of
3-arylpropynoic acids Ia–Ie and the corresponding
ethyl esters If–In with HSO3F at –80°C revealed
Despite apparent simplicity of processes involving
addition of superacids at a triple carbon–carbon bond,
study of the reaction mechanism and development of
Scheme 1.
O
OH
OR
OH
OR
HSO3F
3
2
1
C
C
C
C
C
C
C
C
C
X
OR
X
X
Ia–In
IIa–IIn
IIIa–IIIn
I, IIa–IIh, IIk–IIm, IIIa–IIIh, IIIk–IIIm, R = H, X = 3-O2N (a), 4-O2N (b), 4-NC (c), 4-F (d), 4-MeO-3-O2N (e); R = Et, X =
3-O2N (f), 4-O2N (g), 4-NC (h), 4-MeCO (i), 4-MeOCO (j), 3,4-(O2N)2 (k), 4-MeO-3-O2N (l), 2,5-Me2-4-O2N (m), 4-EtOCOCŁC (n);
IIi, IIj, IIn, IIIi, IIIj, IIIn, R = Et, X = 4-MeC+(OH) (i), 4-MeOC+(OH) (j), 4-EtOC+(OH)CŁC (o).
1070-4280/05/4110-1485 © 2005 Pleiades Publishing, Inc.

WALSPURGER et al.
1486
formation of stable cations IIa–IIn via protonation of
the carbonyl oxygen atom (Scheme 1). The 1H and 13C
NMR spectra of protonated acids IIa–IIe in HSO3F at
–80 and 0°C are given in Tables 1 and 2, and Tables 3
and 4 contain the 1H and 13C NMR data for protonated
ethyl 3-arylpropynoates IIf–IIn in HSO3F at –80°C.
For comparison, the NMR spectra of precursors Ia–Ic
and If–In in CDCl3 or CD3OD at 25°C are also given
structures IIa–IIc, IIe, IIf–IIh, and IIk–IIm, on the
one hand, and COMe and CO2Me groups in IIi and IIj,
on the other, are reflected in Scheme 1.
Insofar as HSO3F at –80°C is characterized by
a high viscosity, in most cases signals from aromatic
protons and protons in the CH2 and CH3 groups of the
ester fragment of ions IIf–IIn appeared in the 1H NMR
spectra as broadened singlets with unresolved fine
structure (Tables 1, 3). In the spectra recorded at 0°C
we observed well resolved multiplets typical of aro-
matic systems (Table 1).
13
in Tables 2 and 4. The C signals were assigned by
analysis of their multiplicity in the proton-coupled
spectra of ions IIa, IIg, and IIh and neutral com-
pounds Ia–Ic and If–In (Tables 2 and 4 contain only
proton-decoupled 13C NMR spectra of the latter).
The C1 signal in the 13C NMR spectra of ions
IIa–IIc and IIf–IIn in HSO3F is located at įC 165.7–
168.5 ppm, i.e., in a weaker field (by 11–13 ppm) than
the corresponding signal of neutral acids and esters
Ia–Ic and If–In in CDCl3 or CD3OD (Tables 2, 4).
Likewise, the spectra of protonated species IIa–IIc and
IIf–IIn are characterized by an appreciably more
downfield position of the C3 signal (įC 99–108 ppm in
HSO3F against įC 79–85 ppm in the spectra of Ia–Ic
and If–In in CDCl3 and CD3OD; įǻC = 17–24 ppm;
Tables 2, 4). These data suggest delocalization of the
positive charge over the arylethynyl fragment, i.e.,
a considerable contribution of canonical structures
IIIa–IIIn to the charge distribution (Scheme 1). The
position of the C1 signal in the 13C NMR spectra of
IIa–IIc and IIf–IIn in HSO3F (įC 165.7–168.5 ppm)
indicates formation of protonated species IIa–IIn
rather than the corresponding acylium (arylpropynoyl)
ions which are characterized by a C1 signal located at
įC 124 ppm [15].
Protonated esters IIf–IIn in HSO3F at –80°C
1
showed in the H NMR spectra a broadened singlet in
the į region 13.5–14.5 ppm from proton on the
carbonyl oxygen atom (Table 3). The corresponding
signal of protonated acids Ia–Ie was not detected even
at –80°C due to fast exchange with the acidic medium
(Table 1), while protonated esters If–In did not display
that signal at 0°C. Diester In in HSO3F undergoes pro-
tonation at both carbonyl groups to give dication IIn
(Scheme 1; Tables 3, 4).
1
In the examined H NMR spectra of IIa–IIc, IIe,
IIf–IIh, and IIk–IIm in HSO3F we observed no signal
from proton that added to electron-withdrawing groups
(X = NO2, CN) in the benzene ring; an analogous pat-
tern was typical of protonation of 1,3-diarylpropyn-
ones in superacids [2]. Compounds IIi and IIj (X =
4-COMe and 4-CO2Me) take up an additional proton
at the X substituent, and the corresponding signal is
present in the 1H NMR spectra (Table 3). The different
behaviors in HSO3F of the NO2 and CN groups in
NMR analysis of the protonation of 3-arylpropyn-
oic acid derivatives showed that compounds Ia–Ic, If–
Ik, Im, and In containing strong electron-withdrawing
substituents in the aromatic ring (X = NO2, CN,
COMe, CO2Me, etc.) in HSO3F exist as stable ions
1
Table 1. H NMR spectra of ions IIa–IIe generated from
3-arylpropynoic acids Ia–Ie in HSO3F
1
IIa–IIc, IIf–IIk, IIm, and IIn even at 0°C. Their H
Ion Tempera-
Chemical shifts į, ppm (J, Hz)
NMR spectra lacked signals in the į region 6–7 ppm,
which could be assigned to vinyl protons in products
of HSO3F addition at the triple bond.
no.
ture, °C
–80
7.97 s (1H), 8.41 s (1H), 8.74 s (1H),
8.89 s (1H)
IIa
Compounds Id, Ie, and Il (X = 4-F, 4-MeO-3-NO2)
in HSO3F at –80°C also give rise to the corresponding
O-protonated species IId, IIe, and IIl (Scheme 1).
However, raising the temperature to –40°C leads to
rearrangement into C-protonated vinyl-type cations
Ar–C+=CH–CO2R which are then converted into mix-
tures of isomeric E- and Z-fluorosulfonates IVd, IVe,
and IVl (Scheme 2). Likewise, 3-phenylpropynoic acid
(Io), its methyl ester Ip, and para-fluoro-substituted
ester Iq in HSO3F above –40°C are converted into
–00
7.94 t (1H, J = 8.1), 8.35 d (1H, J = 8.1),
8.70 d (1H, J = 8.1), 8.84 s (1H)
–80
–00
–80
–00
–80
–80
8.20 s (2H), 8.58 s (2H)
IIb
IIc
8.17 d (2H, J = 8.6), 8.55 d (2H, J = 8.6)
8.17 d (2H, J = 6.6), 8.31 d (2H, J = 6.6)
8.13 d (2H, J = 7.3), 8.20 d (2H, J = 7.3)
7.35 s (2H), 8.00 s (2H)
IId
IIe
4.49 s (3H, OMe), 7.71 d (1H, J = 6.5),
8.52 d (1H, J = 6.5), 9.09 s (1H)
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PROTONATION OF 3-ARYLPROPYNOIC ACID DERIVATIVES IN SUPERACIDS
1487
Table 2. 13C NMR spectra of 3-arylpropynoic acids Ia–Ic in CDCl3 or CD3OD (25°C) and ions IIa–IIc generated therefrom
in HSO3F (–80 and 0°C)
Chemical shifts į, ppm (J, Hz)
Comp.
no.
Tempera-
ture, °C
Solvent
C1=Oa
C2
C3
Ci
Co
Cm
Cp
CDCl3
HSO3Fb
–25
–80
156.62 s 81.58 s 084.89 121.08 d
127.86, 138.47
148.14, 129.90
125.57
Ia
168.03 s 76.86 s 106.73 s 118.23 d
(9.2)
131.61 d (175.0),
144.40 d.t (168.0, 6) 132.49 d (171.2)
146.45 m (4.0),
131.01 d
(171.0)
IIa
–00
168.47 s 76.86 s 108.04 t 118.36 d 131.38 d.t (174.5, 5.6), 147.39 m (4.8), 130.98 d.m
(5.6) (9.6) 143.71 d.t (169.7, 6) 132.54 d (171.3) (170.1, 3.6)
CD3OD
HSO3F
–25
–80
156.76 s 86.34 s 084.84 121.08 d
167.93 s 78.05 s 105.68 124.61 d
168.37 s 78.27 s 106.86 124.45 d
135.81
125.58
125.67
134.59
136.29
135.78
125.84
137.25
137.20
134.59
136.38
136.35
150.97
149.03
149.98
116.01
108.36
111.03
Ib
IIb
–00
c
CD3OD
HSO3F
25c 156.82 s 85.90 s 084.65 126.88 d
d–80d 168.04 s 78.25 s 105.40 125.29 d
e–00e 168.48 s 78.33 s 107.01 124.47 d
Ic
IIc
a
In HSO3F, signal from the protonated carboxy group.
Proton-coupled spectrum.
įC CN 119.85 ppm.
b
c
d
e
įC CN 106.83 ppm.
įC CN 110.24 ppm.
Table 3. 1H NMR spectra of ions IIf–IIn generated from ethyl 3-arylpropynoates If–In in HSO3F at –80°C
Chemical shifts, į, ppm (J, Hz)
Ion no.
+C1–OH
a
a
OCH2CH3 CH2CH3
Harom, X
5.07
5.08
5.06
5.09
5.07
5.09
5.05
5.09
5.05
1.66
1.66
1.65
1.66
1.65
1.65
1.64
1.66
1.64
7.97 s (1H), 8.39 s (1H), 8.73 s (1H), 8.87 s (1H)
8.16 s (2H), 8.56 s (2H)
13.6 s
13.7 s
13.9 s
14.46 s
13.5 s
14 s
IIf
IIg
IIh
IIib
IIjc
IIk
IIl
8.13 s (2H), 8.25 s (2H)
3.45 s (3H, Me), 8.18 s (2H), 8.63 s (2H)
4.69 s (3H, OMe), 8.17 s (2H), 8.32 s (2H)
8.25 d (1H, J = 8.2), 8.41 d (1H, J = 8.2), 8.61 s (1H)
4.52 s (3H, OMe), 7.73 d (1H, J = 8.2), 8.52 d (1H, J = 8.2), 9.02 s (1H)
2.71 s (3H, Me), 2.75 s (3H, Me), 8.02 s (1H), 8.73 s (1H)
8.01 s (4H)
13.6 s
13.8 s
13.52 s
IIm
IIn
a
b
c
The CH2 and CH3 signals appeared as singlets (for details, see text).
The protonated acetyl group in the benzene ring gave a singlet at į 14.4 ppm.
The protonated methoxycarbonyl group in the benzene ring gave a singlet at į 13.7 ppm.
E/Z-fluorosulfonates IVo–IVq. Isomeric trifluoro-
methanesulfonates Vo and Vp are formed From com-
pounds Io and Ip in CF3SO3H at 0°C (Scheme 2).
The addition of superacids to compounds Id, Ie, Il,
and Io–Iq was monitored, and the E/Z-isomer ratios in
products IVd, IVe, IVl, IVo–IVq, Vo, and Vp were
determined, by NMR spectroscopy (the reactions were
carried out in NMR ampules). The results are collected
in Table 5. No vinyl-type cations were detected,
though they should be formed as unstable interme-
diates via protonation of the triple carbon–carbon bond
in the substrates by HSO3F or CF3SO3H. The isomer
structure of compounds IVd, IVe, IVl, IVo–IVq, Vo,
and Vp was assigned by analysis of the 1H NMR spec-
tra of the isomer mixtures. Comparison of the 1H NMR
spectrum of E-IVo [10] with that of isomer mixture
E-IVo/Z-IVo showed that signal from the vinyl proton
in the E isomer is located in a stronger field than the
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WALSPURGER et al.
1488
Table 4. 13C NMR spectra of ethyl 3-arylpropynoates If–In (CDCl3, 25°C) and ions IIf–IIn derived therefrom in fluorosul-
fonic acid at –80°C
Chemical shifts įC, ppm (J, Hz)
Comp.
Solvent
no.
C1
C2
C3
Carom
OCH2
CH3
X
CDCl3 153.03
82.13 082.22 121.28, 124.97, 127.32, 129.71, 138.10, 62.27
147.89
13.80
If
HSO3F 166.02
CDCl3 153.05
81.97 102.96 118.64, 130.58, 131.32, 132.41, 144.27, 78.32
146.30
12.78
13.89
IIf
84.04 082.52 123.58, 126.10, 133.51, 148.34
62.39
Ig
HSO3Fa 166.00 s s 82.04 s 102.46 s 125.31 s, 125.70 d (173.7), 136.98 d t 78.33 t q 12.74 q
IIg
(171.3), 148.61 s
(152.40) (129.59)
CDCl3 153.10
83.51 082.89 113.8, 124.21, 132.06, 133.05
62.29 13.82 117.61 (CN)
Ih
HSO3Fa 165.90 s s 81.79 s 102.00 s 109.30 s, 124.78 s, 135.64 d.d (173.0, t 77.98 t q 12.66 q 108.28 s (CN)
IIh
10.0), 135.78 d.d (173.3, 10.4)
(130.39) (127.58)
CDCl3 153.26
HSO3F 165.98
CDCl3 153.48
HSO3F 166.07
82.62 084.06 123.85, 128.01, 132.70, 137.75
62.01
78.59
62.14
78.60
13.76 26.33 (CH3),
Ii
196.61 (C=O)
79.21 101.55 129.54, 132.49, 135.96
82.56 084.30 123.98, 129.46, 131.53, 132.62
82.28 102.49 126.36, 132.03, 136.28
12.64 26.28 (CH3),
222.73 (C=OH+)
IIi
Ij
13.90 52.24 (CH3),
165.85 (C=O)
12.76 64.03 (CH3),
181.85 (C=OH+)
IIj
CDCl3 152.56
HSO3F 165.93
85.47 079.69 125.53, 125.95, 128.76, 137.11, 142.77 62.85
13.87
12.76
Ik
78.24 099.06 123.26, 127.84, 132.46, 141.55, 142.56, 79.08
144.57
IIk
CDCl3 153.47
HSO3F 165.74
CDCl3 153.29
HSO3F 165.99
81.15 083.04 111.74, 113.87, 130.04, 138.36, 139.37, 62.16
154.28
13.92 56.73 (OMe)
12.73 61.43 (OMe)
Il
81.89 101.39 112.28, 118.09, 131.42, 137.21, 151.11, 78.34
164.06
IIl
Im
IIm
86.66 081.90 124.37, 125.32, 130.70, 137.99, 140.79, 62.25
149.39
13.89 19.42 (CH3),
19.49 (CH3)
82.80 099.95 129.16, 129.81, 140.64, 140.89, 145.16, 78.83
145.96
12.76 19.51 (CH3),
21.63 (CH3)
CDCl3 153.45
HSO3F 166.05
82.78 084.19 121.66, 132.73
81.62 104.94 121.57, 135.86
62.14
78.06
13.90
12.78
In
IIn
a
Proton-coupled spectrum.
found for the major component (E-Vp, į 6.62 ppm in
HSO3F; Table 5). The existence of such correlation in
the NOESY spectrum indicates spatially close location
of the corresponding structural fragments, which is
possible only in the Z isomer.
corresponding signal of the Z isomer (Table 5). An ad-
ditional support to the above assignment was obtained
by NOESY experiment (CDCl3, 25°C) performed for
isomer mixture E-Vp/Z-Vp which was isolated in
a preparative amount by addition of trifluoromethane-
sulfonic acid to methyl 3-phenylpropynoate (Ip) (see
Experimental). The minor isomer (Z-Vp), though its
fraction in the mixture was as small as 5% (Table 5,
run no. 9), showed a strong correlation between the
vinyl proton (į 6.73 ppm in HSO3F) and ortho-protons
in the benzene ring. No analogous correlation was
As follows from the data in Table 5, isomer mix-
tures IVd, IVe, IVl, IVo–IVq, Vo, and Vp contain
mainly the E isomers whose fraction reaches 95%;
they result from syn-addition of superacids HSO3F and
CF3SO3H at the triple carbon–carbon bond. The E/Z-
isomer ratio depends on the temperature: raising the
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PROTONATION OF 3-ARYLPROPYNOIC ACID DERIVATIVES IN SUPERACIDS
1489
Scheme 2.
FSO2O
H
FSO2O
Ar
COOR
H
HSO3F
+
C
C
C
C
C
Ar
COOR
O
E
IVd, IVe, IVl, IVo–IVq
Z
Ar
C
C
C
OR
CF3SO2O
Ar
H
CF3SO2O
COOR
CF3SO3H
Id, Ie, Il, Io–Iq
+
C
C
C
COOR
Ar
H
E
Vo, Vp
Z
R = H, Ar = 4-FC6H4 (d), 4-MeO-3-O2NC6H3 (e), C6H5 (o); R = Et, Ar = 4-MeO-3-O2NC6H3 (l); R = Me, Ar = C6H5 (p), 4-FC6H4 (q).
temperature to 0°C (the reaction was performed at
–40°C) induces E–Z isomerization (cf. run nos. 1, 2
and 5, 6 in Table 5). Isomer mixtures IVe and IVl,
which were obtained in HSO3F at 0°C, contained the
corresponding Z isomers as the major components;
presumably, the reason is the presence of an electron-
donor methoxy group in the para-position with respect
to the double C=C bond, which facilitates isomeriza-
tion. Furthermore, when a mixture of trifluoromethane-
sulfonates E-Vp and Z-Vp (initial isomer ratio 95:5;
Table 5, run no. 9) was stored for three months without
a solvent at room temperature, the isomer ratio
changed to 21:79. The data on E–Z isomerization of
compounds IVd, IVo, and Vp indicate that addition of
HSO3F and CF3SO3H to 3-arylpropynoic acid deriva-
tives initially gives the corresponding E isomers as
kinetically controlled products (syn-addition at the
triple bond) which are then transformed into thermo-
dynamically more stable Z isomers (anti-addition prod-
ucts). Olah and Spear [10] postulated that addition of
HSO3F to acetylenecarboxylic acids initially gives
anti-adducts (Z isomers) which then undergo fast
isomerization into syn-adducts (E isomers).
The known methods for the synthesis of vinyl
trifluoromethanesulfonates are based on reactions of
carbonyl compounds with trifluoromethanesulfonic
anhydride in the presence of bases [9, 11]. The main
disadvantage of these procedures is low regio- and
stereoselectivity. The addition of HSO3F and CF3SO3H
to 3-arylpropynoic acid derivatives, described in the
present article, can be regarded as a simple, effective,
and selective synthetic route to fluorosulfonates and
trifluoromethanesulfonates like IV and V.
EXPERIMENTAL
1
The H, 13C, and 19F NMR spectra of solutions in
CDCl3 and CD3OD were recorded on Bruker AM-500
(500, 125.76, and 470 MHz, respectively) and Bruker
AVANCE 300 spectrometers (300, 75, and 300 MHz,
respectively). The chemical shifts were measured rela-
tive to the solvent signals (1H: CHCl3, į 7.25 ppm;
Table 5. Addition of fluorosulfonic and trifluoromethanesulfonic acids to compounds Id, Ie, Il, and Io–Iqa
Initial
compound no.
Run no.
Superacid, temperature
Products
E/Z-Isomer ratio
į2-H, ppm
01
02
03
04
05
06
07
08
09
10
HSO3F, –40°C
HSO3F, 0°C
E-IVd/Z-IVd
E-IVd/Z-IVd
Z-IVe
87:13
65:35
100
6.58/6.65
6.57/6.61
6.85
Id
Id
Ie
Il
HSO3F, 0°C
HSO3F, 0°C
E-IVl/Z-IVl
E-IVo/Z-IVo
E-IVo/Z-IVo
E-Vo/Z-Vo
20:80
90:10
76:24
93:70
78:22
95:50
89:11
6.78/6.87
6.65/6.72
6.62/6.71
6.61/6.70
6.64/6.71
6.62/6.73
6.60/6.70
HSO3F, –40°C
HSO3F, 0°C
Io
Io
Io
Ip
Ip
Iq
CF3SO3H, 0°C
HSO3F, 0°C
E-IVp/Z-IVp
E-Vp/Z-Vp
E-IVq/Z-IVq
CF3SO3H, 0°C
HSO3F, –30°C
a
In an NMR ampule (see Experimental).
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WALSPURGER et al.
1490
CD3OD, į 3.31 ppm; 13C: CDCl3, įC 77.0 ppm;
CD3OD, įC 49.0 ppm) or CFCl3 (19F: įF 0.0 ppm). The
7.81 d.d.d (1H, Harom, J = 7.7, 1.4, 1.1 Hz), 8.22 d.d.d
(1H, Harom, J = 8.3, 2.2, 1.1 Hz), 8.31 d.d (1H, Harom
,
13
1H and C NMR spectra of cationic species in super-
J = 2.2, 1.4 Hz). Mass spectrum, m/z (Irel, %): 219 (13)
[M]+, 174 (75) [M – OEt]+, 147 (100), 128 (55), 101
(23), 100 (21), 74 (34). Found, %: C 60.15; H 4.09;
N 6.44. C11H9NO4. Calculated, %: C 60.28; H 4.14;
N 6.39.
acids (HSO3F and CF3SO3H) were recorded on a Bruker
AVANCE 400 spectrometer at 400 and 100 MHz,
respectively, using methylene chloride as internal
reference (į 5.32 ppm, įC 77.0 ppm). The IR spectra
were obtained from solutions in CHCl3 on a Specord
75IR spectrophotometer. The mass spectra (electron
impact, 70 eV) were run on MKh-1321 and TSQ 700
Finigan MAT instruments. NOESY experiment was
performed with a solution of 50 mg of isomer mixture
E-Vp/Z-Vp in 1 ml of CDCl3 at 25°C using a Bruker
AVANCE 400 instrument.
Ethyl 3-(4-nitrophenyl)propynoate (Ig). mp 124–
126°C; published data: mp 120–122°C [20]. IR spec-
trum, Ȟ, cm–1: 1350, 1520, 1710 (C=O), 2230 (CŁC).
1H NMR spectrum (500 MHz, CDCl3), į, ppm: 1.30 t
(3H, Me, J = 7.1 Hz), 4.26 q (2H, CH2, J = 7.1 Hz),
7.68 d (2H, Harom, J = 8.9 Hz), 8.18 d (2H, Harom
J = 8.9 Hz).
,
Initial ethyl 3-arylpropynoates If–In were synthe-
sized by the procedures reported in [16, 17]. 3-Aryl-
propynoic acids Ia–Ie were obtained by hydrolysis of
the corresponding ethyl esters in the system KOH–
EtOH–H2O. Methyl 3-arylpropynoates Ip and Iq were
prepared by methylation of the corresponding 3-aryl-
propynoic acids with dimethyl sulfate according to
[18]. The properties of compounds Il, Ip, and Iq were
reported by us previously [17].
Ethyl 3-(4-cyanophenyl)propynoate (Ih). mp 67–
68°C; published data [20]: mp 66–68°C. IR spectrum,
Ȟ, cm–1: 1710 (C=O); 2220, 2235 (CŁC, CŁN).
1H NMR spectrum (500 MHz, CDCl3), į, ppm: 1.29 t
(3H, Me, J = 7.2 Hz), 4.25 q (2H, CH2, J = 7.2 Hz),
7.60 d (2H, Harom, J = 8.6 Hz), 7.63 d (2H, Harom
J = 8.6 Hz).
,
Ethyl 3-(4-acetylphenyl)propynoate (Ii). mp 82.0–
82.5°C. IR spectrum, Ȟ, cm–1: 1690, 1710 (C=O);
1
2220, 2250 (CŁC). H NMR spectrum (500 MHz,
3-(3-Nitrophenyl)propynoic acid (Ia). mp 145–
147°C; published data [19]: mp 141–142°C.
CDCl3), į, ppm: 1.24 t (3H, Me, J = 7.1 Hz), 2.49 s
(3H, Me), 4.19 q (2H, CH2, J = 7.1 Hz), 7.53 d (2H,
Harom, J = 8.5 Hz), 7.83 d (2H, Harom, J = 8.5 Hz).
Found, %: C 72.14; H 5.61. C13H12O3. Calculated, %:
C 72.21; H 5.59.
3-(4-Nitrophenyl)propynoic acid (Ib). mp 198–
200°C; published data [19]: mp 198°C. 1H NMR spec-
trum (500 MHz, CD3OD), į, ppm: 7.81 d (2H, Harom
,
J = 8.8 Hz), 8.28 d (2H, Harom, J = 8.8 Hz).
Ethyl 3-(4-methoxycarbonylphenyl)propynoate
3-(4-Cyanophenyl)propynoic acid (Ic). Sublimes
(Ij). mp 46–48°C [20]. IR spectrum, Ȟ, cm–1: 1710,
1
at 200°C. H NMR spectrum (500 MHz, CD3OD), į,
1
1730 (C=O); 2215, 2250 (CŁC). H NMR spectrum
ppm: 7.74 d (2H, Harom, J = 8.3 Hz), 7.79 d (2H, Harom
,
(500 MHz, CDCl3), į, ppm: 1.30 t (3H, Me, J =
7.1 Hz), 3.87 s (3H, OMe), 4.25 q (2H, CH2, J =
7.1 Hz), 7.58 d (2H, Harom, J = 8.5 Hz), 7.97 d (2H,
J = 8.3 Hz). Mass spectrum: m/z 171 [M]+. Found, %:
C 69.97; H 3.09; N 8.00. C10H5NO2. Calculated, %:
C 70.18; H 2.94; N 8.18.
Harom, J = 8.5 Hz).
3-(4-Fluorophenyl)propynoic acid (Id). mp 155–
157°C. 1H NMR spectrum (500 MHz, CDCl3), į, ppm:
7.01–7.07 m (2H, Harom), 7.54–7.59 m (2H, Harom),
~13 br.s (1H, OH). Found, %: C 65.89; H 3.11.
C9H5FO2. Calculated, %: C 65.86; H 3.07.
Ethyl 3-(3,4-dinitrophenyl)propynoate (Ik).
mp 72–73°C. IR spectrum, Ȟ, cm–1: 1360, 1550, 1710
1
(C=O), 2245 (CŁC). H NMR spectrum (500 MHz,
CDCl3), į, ppm: 1.34 t (3H, Me, J = 7.1 Hz), 4.30 q
(2H, CH2, J = 7.1 Hz), 7.91 d.d (1H, Harom, J = 8.4,
1.6 Hz), 7.95 d (1H, Harom, J = 8.4 Hz), 8.06 d (1H,
3-(4-Methoxy-3-nitrophenyl)propynoic acid (Ie).
mp 189–191°C. Mass spectrum: m/z 221 [M]+. Found,
%: C 54.18; H 3.02; N 6.47. C10H7NO5. Calculated, %:
C 54.31; H 3.19; N 6.33.
H
arom, J = 1.6 Hz). Found, %: C 49.88; H 3.00; N 10.43.
C11H8N2O6. Calculated, %: C 50.01; H 3.05; N 10.60.
Ethyl 3-(4-methoxy-3-nitrophenyl)propynoate
(Il). mp 86–87°C. IR spectrum, Ȟ, cm–1: 1355, 1525,
1700 (C=O), 2220 (CŁC). 1H NMR spectrum (500 MHz,
CDCl3), į, ppm: 1.31 t (3H, Me, J = 7.1 Hz), 3.96 s
(3H, OMe), 4.25 q (2H, CH2, J = 7.1 Hz), 7.08 d
(1H, Harom, J = 8.7 Hz), 7.70 d.d (1H, Harom, J = 8.7,
Ethyl 3-(3-nitrophenyl)propynoate (If). Oily sub-
stance. IR spectrum, Ȟ, cm–1: 1350, 1525, 1710 (C=O),
2220 (CŁC). 1H NMR spectrum (500 MHz, CDCl3), į,
ppm: 1.29 t (3H, Me, J = 7.1 Hz), 4.24 q (2H, CH2,
J = 7.1 Hz), 7.55 d.d (1H, Harom, J = 8.3, 7.7 Hz),
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 41 No. 10 2005

PROTONATION OF 3-ARYLPROPYNOIC ACID DERIVATIVES IN SUPERACIDS
1491
2.1 Hz), 8.00 d (1H, Harom, J = 2.1 Hz). Found, %:
C 57.69; H 4.41; N 5.74. C12H11NO5. Calculated, %:
C 57.83; H 4.45; N 5.62.
cooled to –30°C, 1.1 ml (12.5 mmol) of CF3SO3H was
added dropwise over a period of 5 min under vigorous
stirring, and the mixture was allowed to warm up to
0°C and was stirred for an additional 0.5 h. When the
reaction was complete, the mixture was added drop-
wise to a suspension of KHCO3 in MeOH, cooled to
–20°C. The resulting mixture was diluted with water
and extracted with diethyl ether. The extract was
washed with water and dried over Na2SO4, and the
solvent was distilled off to obtain 230 mg (59%) of
a mixture of isomeric trifluoromethanesulfonates E-Vp
and Z-Vp (95:5) as a light yellow oily material. Com-
pounds E-Vp and Z-Vp decomposed on attempted
chromatographic separation in a column charged with
silica gel. On storage at room temperature without
a solvent, isomer E-Vp was gradually converted into
Z-Vp. The spectral parameters of particular isomers
E-Vp and Z-Vp were derived from the spectra of their
mixture.
Ethyl 3-(2,5-dimethyl-4-nitrophenyl)propynoate
(Im). mp 68–69°C. IR spectrum, Ȟ, cm–1: 1350, 1520,
1710 (C=O), 2230 (CŁC). 1H NMR spectrum (500 MHz,
CDCl3), į, ppm: 1.31 t (3H, Me, J = 7.1 Hz), 2.45 s
(3H, Me), 2.47 s (3H, Me), 4.25 q (2H, CH2, J =
7.1 Hz), 7.43 s (1H, Harom), 7.76 s (1H, Harom). Found,
%: C 63.21; H 5.32; N 5.74. C13H13NO4. Calculated,
%: C 63.15; H 5.30; N 5.66.
Ethyl 3-[(4-ethoxycarbonylethynyl)phenyl]-
propynoate (In). mp 92–94°C. IR spectrum, Ȟ, cm–1:
1
1700 (C=O), 2215, 2250 (CŁC). H NMR spectrum
(500 MHz, CDCl3), į, ppm: 1.30 t (3H, Me, J =
7.1 Hz), 4.25 q (2H, CH2, J = 7.1 Hz), 7.52 s (4H,
H
arom). Found, %: C 71.26; H 5.20. C16H14O4. Cal-
culated, %: C 71.10; H 5.22.
General procedure for generation of ions IIa–IIn
in HSO3F and preparation of E/Z-isomeric fluoro-
sulfonates IVd, IVe, IVl, and IVo–IVq in HSO3F
and trifluoromethanesulfonates Vo and Vp in
CF3SO3H in situ. An NMR ampule was charged with
0.8–1 ml of HSO3F (mp –89°C) and cooled to approxi-
mately –110°C (using ethanol–liquid nitrogen), and 5–
30 mg of compound Ia–In was added. The tempera-
ture was raised to –78°C, and a Teflon capillary (1 mm
i.d.) was immersed into the ampule till its bottom.
A slight stream of argon was passed through the capil-
lary over a period of 5–15 min to obtain a homo-
geneous solution. The capillary was withdrawn, and
methylene chloride (internal reference) was added. The
1H and 13C NMR spectra of ionic species IIa–IIn were
Methyl (E)-3-phenyl-3-trifluoromethylsulfonyl-
oxy-2-propenoate (E-Vp). H NMR spectrum
1
(300 MHz, CDCl3), į, ppm: 3.69 s (3H, OMe), 6.19 s
(1H, =CH–), 7.41–7.57 m (5H, Harom). 13C NMR spec-
trum (75 MHz, CDCl3), įC, ppm: 52.06 (OMe), 113.07
(=C2), 118.25 q (CF3, JCF = 318 Hz), 128.19 (Cm),
129.07 (Co), 130.42 (Ci), 131.60 (Cp), 159.12 (C3),
163.75 (C=O). 19F NMR spectrum (300 MHz, CDCl3):
įF –74.17 ppm, s (CF3).
Methyl (Z)-3-phenyl-3-trifluoromethylsulfonyl-
1
oxy-2-propenoate (Z-Vp). H NMR spectrum
(300 MHz, CDCl3), į, ppm: 3.84 s (3H, OMe), 6.25 s
(1H, =CH–), 7.36–7.58 m (5H, Harom).
Mass spectrum of isomer mixture E/Z-Vp, m/z
(Irel, %): 310 (82) [M]+, 279 (45), 245 (14), 215 (28),
177 (27), 149 (89), 121 (62), 105 (97), 77 (100).
Found, %: C 43.05; H 3.31. C11H9F3O5S. Calculated,
%: C 42.58; H 2.92.
1
recorded at –80 and 0°C (Tables 1–4). The H NMR
spectra of isomeric fluorosulfonates IVd, IVe, IVl, and
IVo–IVq were recorded in HSO3F at –40 and 0°C
(Table 5). Solutions of E/Z-isomeric trifluoromethane-
sulfonates Vo and Vp in CF3SO3H were prepared in
a similar way, by adding 5–30 mg of substrate Io or
Ip to 0.8–1 ml of CF3SO3H (mp –34°C) placed in
an NMR ampule and frozen at –78°C, followed by
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