Nitration of phenylpropiolic acid derivatives in HSO3F and reactions of vinyl type cations formed therefrom

Article abstract of DOI:10.1007/s11178-005-0070-9

Nitration of phenylpropiolic acid derivatives ArC≡CX (X=CN, CO ₂Me) in HSO₃F at -75...-50°C afforded mononitro compounds, for instance, m-O₂NC₆H₄C≡CX. Vinyl type cations generated in HSO₃F

Full text of DOI:10.1007/s11178-005-0070-9

Russian Journal of Organic Chemistry, Vol. 40, No. 11, 2004, pp. 1633 -1637. Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 11,
2004, pp. 1665-1677.
Original Russian Text Copyright Ó 2004 by Savechenkov, Rudenko, Vasil'ev.
Nitration of Phenylpropiolic Acid Derivatives in HSO3F
And Reactions of Vinyl Type Cations Formed Therefrom
P.Yu. Savechenkov, A.P. Rudenko, andA.V. Vasil'ev
St. Petersburg State Academy of Forestry Engineering, St. Petersburg, 194021Russia
Received February 20, 2004
Abstract-- Nitration of phenylpropiolic acid derivativesArCºCX (X=CN, CO2Me) in HSO3F at -75...–50°C afforded
mononitro compounds, for instance, m-O2NC6H4CºCX. Vinyl type cations generated in HSO3F from methyl 3-aryl-
propiolatesArC+=CHCO2Me react along two pathways. The first among them results in formation of fluorosulfonates
ArC(OSO2F)=CHCO2Me, and the second one after the attack of vinyl cation on the aryl moiety of the substrate
affords a dimer that on nitration is converted into a nitro product with conserved triple bond.
We report here on results of nitration of phenyl-
propiolonitrile and methyl arylpropiolates in a system
HNO3–HSO3F performed in the framework of investig-
ation on acetylene compounds reactions with electrophilic
agents [1. 2].
These facts should be taken into account in planning and
performing reactions of acetylene compounds with
electrophilic reagents.
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In a general case the interaction of a superacid and
an acetylene compound depends on the basicity of the
latter and may involve a simple solvation, a formation of
of variable strength hydrogen bonds, or a complete proton
transfer to one of the potential basicity sites of the
acetylene affording the corresponding ions.
+
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The analysis of nitration results of compounds I and
II in the system HNO3–HSO3F, 3:1, at –50°C (here and
hereinafter molar ratios HNO3–substance are given) has
demonstrated that in both cases the reaction does not
affect the triple bonds and the products contain exclusively
mixtures obtained by mononitration in the benzene ring,
compounds Ia–c and IIa–c. Therewith the mixture of
nitro compounds Ia–c (yield 30%) contains isomers in
1
As seen from H and 13C NMR spectra nitrile I
dissolved in the superacid at –80°C does not specifically
interact with HSO3F. In contrast, many among acetylene
esters under similar conditions first undergo the O-proton-
ation at the oxygen of the carbonyl group furnishing
hydroxycarbonium ions [1]. The stability of the latter and
their further transformations depend not only on the
temperature and the medium acidity but are crucially
governed by the number, mutual position, and the character
of the substituent in the aryl moiety. Ions with strong
electron-withdrawing groups are the most stable in
HSO3F at –80°C (the frontier case), but at increasing
number of alkyl and especially alkoxy substituents in the
benzene ring the reactivity of this type ions sharply grows.
Therewith irreversible changes are seen in the 1H NMR
spectra of the primary ions accompanied by appearance
of the characteristic signals of –CH= groups belonging
to the final products of the observed transformation.
the ratio o- : m- : p- ~1 : 3 : 6, and for compounds IIa–c
~
(yield 33%) this ratio is o- : m- : p- ~1 : 3 : 2.
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I, X = CN; II, X = COOMe; Y = o-NO2 (a), m –NO2(b), p-
NO2 (c).
Due to the strong deactivation of the benzene ring no
nitration of compounds IIa–c occurred even at increased
1070-4280/04/4011-1633Ó2004 MAIK “Nauka/Interperiodica”

SAVECHENKOV et al.
1634
reaction temperature. For instance, methyl 4-nitrophenyl-
propiolate (IIc) kept in the system HNO3–HSO3F at
–10°C for 0.5 h was recovered unchanged.
unsaturated fluorosulfonate III. We assigned the
stereochemical structure to compound III basing on a
close similarity of fluorosulfonate formation from
phenylpropiolic acid [3]. The nitration of fluorosulfonate
III in the system HNO3–HSO3F (1 h, –50°C) occurred
regioselectively affording a single meta-nitroisomer
IIIa.
The triple bond in unsubstituted ester II is more basic
than in nitro compounds IIa–c, therefore in HSO3F
already at –30°C after protonation at the acetylene C2
atom followed by nucleophile addition it is converted into
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Ar = Ph (II), 4-FC6H4 (IV).
In methyl 4-tolylpropiolate (V) the triple bond is more
prone to protonation at the acetylene C2 atom than in the
previously mentined propiolates, and thus its nitration
should be carried out at the temperature not exceeding
–75°C. Therewith the order of reagents mixing becomes
Methyl 4-fluorophenylpropiolate (IV) in HSO3F within
1 h at –30°C transformed into a mixture of isomeric
compounds IVa (yield 60%) and IVb (yield 10%), but
they did not undergo nitration in the system HNO3–
HSO3F (1 h, –30°C).
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RUSSIAN JOURNALOF ORGANIC CHEMISTRY Vol. 40 No. 11 2004

NITRATION OF PHENYLPROPIOLIC ACID DERIVATIVES IN HSO3F
1635
of a crucial importance. To perform efficient reaction
along the a pathway indicated on the scheme substrate
V should be gradually added to the nitrating system
HNO3–HSO3F cooled to –75°C.At this order of carrying
out the reaction the benzene ring nitration occurs faster
than the competing protonation of the triple bond into
cation A along the pathway b. By this procedure it was
possible to obtain nitro compound Va in 61% yield.
1H, 13C, and 19F NMR spectra were registered on
spectrometer Bruker AM-500 (operating frequencies
500, 125.76, and 470.7 MHz respectively) from solutions
in CDCl3. As internal references in the NMR spectra
we used the residual signal of CHCl3 (1H, dH 7.25 ppm),
signal of the solvent (13C, dC 77.0 ppm), and signal of
CFCl3 (19F, dF 0.0 ppm) respectively. Mass spectra were
measured on MKh-1321 instrument at the ionizing
electrons energy 70 eV.
Another order of reagents mixing led to reaction along
pathway c. In this case substrate V was first dissolved in
HSO3F cooled to –75°C. Then the cooled nitrating system
HNO3–HSO3F was added dropwise to the above solution.
As a result alongside the expected product Va (12%)
dimeric nitro compound VIa (17%) was isolated
containing a triple bond; its structure was established by
spectral data.
GC-MS analysis of mixtures of compounds Ia–c and
IIa–c was performed on Hewlett-Packard HP-5995
instrument equipped with a flame-ionization detector,
ionizing electrons energy 70 eV, separator temperature
240°C, ion source temperature 250°C. Quartz capillary
column 25000´0.32 mm, stationary phase Ultra-2 (95%
of methylsilicone, 5% of phenylmethylsilicone) 0.53 mm.
Oven temperature programmed from 100°C to 240°C,
heating rate 10–20 deg/min. Carrier gas helium, flow rate
1 ml/min. The volume of probe of 3–5% solution was
2 ml.
The purity of the initial [5, 6] and obtained compounds
was checked by TLC on Silufol UV-254 plates. The
preparative separation of the reaction mixtures was
carried out by column chromatography on silica gel
Chemapol (40–100 mm) at gradient elution with 2–10%
ethyl acetate solutions in hexane. Yields of the products
were determined as weight of fractions obtained by
chromatography.
The nontrivial course of the process along pathway c
is presumably caused by the protonation of acetylene
ester V giving rise to relatively stable vinyl-type cation A
that after the electrophilic attack of the aryl substituent
of initial ester V and deprotonation affords dimer VI which
is nitrated into the final reaction product VIa. To confirm
this pathway we dissolved acetylene ester V in HSO3F
at –75°C, left standing the solution at this temperature
for 0.5 h, and after treating with 20% H2SO4 at –60°C
isolated dimer VI in 64% yield [2]. The regioselective
nitration of only one of the two benzene rings of dimer
VI is due to deactivation of the other ring by two electron-
withdrawing groups whereas the ring undergoing nitration
is linked to a single such moiety –C(Ar)=CHCO2Me (cf.
with nitration of fluorosulfonate III).
(2-Nitrophenyl)propiolonitrile (Ia). mp 86–87°C.
–1
IR spectrum, cm : 1340, 1525, 2275. 1H, d, ppm: 7.69–
7.76 m (2Harom), 7.82–7.85 m (1Harom), 8.24–8.26 m
(1Harom). Mass spectrum, m/z (Irel , %): 172 (22) M+, 156
(11), 142 (11), 126 (13) [M–NO2]+, 119 (15), 114 (21),
104 (28), 100 (19), 99 (22), 90 (40), 76 (100), 63 (32), 50
(56), 44 (31). Calculated M 172.14.
The results reported here demonstrate the new
possibilities of functionalizing phenylpropiolic acid
derivatives under conditions of mild low-temperature
process in superacids where even in the presence of the
competing protonation of the triple bond and SE-nitration
of the aryl substituent the electrophilic reaction can be
efficiently directed into the desired path by varying the
experimental conditions. Detailed aspects of vinyl-type
cations with the “original” substrate-precursor [2]
“substitute” substrates [4], and also data on
regioselectivity and regiospecificity of these new reactions
will be published elsewhere within the framework of the
declared program [4].
(3-Nitrophenyl)propiolonitrile (Ib). mp 145–
–1
146°C. IR spectrum, cm : 1345, 1540, 2265, 2285. 1H
NMR spectrum, d, ppm: 7.65 t (1Harom, J 8.0 Hz), 7.92 d.t
(1Harom, J 7.7, 1.1 Hz), 8.38 d.d.d (1H arom, J 8.4, 2.1,
1.0 Hz), 8.47 t (1Harom, J 1.6 Hz). Mass spectrum, m/z
(Irel , %): 172 (68) M+, 126 (100) [M–NO2]+, 114 (19),
100 (39), 99 (39), 76 (18), 75 (28), 51 (35), 50 (26), 39
(11). Calculated M 172.14.
(4-Nitrophenyl)propiolonitrile (Ic). mp 140–142°C
(publ.: mp 139–141°C [7]). 1H NMR spectrum is
consistent with the published one [7].
EXPERIMENTAL
Methyl (2-nitrophenyl)propiolate (IIa). mp. 86–
–1
1
87°C. IR spectrum, cm : 1330, 1520, 1700, 2230. H
IR spectra were recorded on spectrophotometer
Specord 75 IR from solutions of compounds in CHCl3.
NMR spectrum, d, ppm: 3.86 s (3H, OMe), 7.61 t.d
RUSSIAN JOURNALOF ORGANIC CHEMISTRY Vol. 40 No. 11 2004

SAVECHENKOV et al.
1636
(1Harom, J 7.7, 1.3 Hz), 7.66 t.d (1Harom, J 7.3, 1.0 Hz),
7.77 d.d (1Harom, J 7.6, 1.5 Hz), 8.16 d (1Harom J 8.1 Hz).
Mass spectrum, m/z (Irel , %): 205 (2) M+, 174 (19) [M–
OMe]+, 147 (70), 104 (43), 102 (27), 91 (100), 89 (46),
76 (43), 74 (54), 63 (38), 59 (34). Calculated M 205.17.
d, ppm: 52.23 q (J 147.5 Hz), 113.12 d (J 166.2 Hz),
115.67 d.d.d (J 165.7, 22.5, 3.0 Hz), 125.50 m (J 3.0 Hz),
131.78 d.d.d (J 164.5, 8.9, 6.8 Hz), 158.60 m (J 6.0 Hz),
163.63 m (J 4.0 Hz), 164.57 d (J 253.9 Hz). 19F NMR
spectrum, d, ppm: –102.91 t.t (1Farom, J 8.3, 5.2 Hz), 46.29
s (1F, FSO3). Mass spectrum, m/z (Irel , %): 278 (65) M+,
247 (100) [M–OMe]+, 179 (23) [M–FSO3]+, 147 (79),
123 (95), 120 (30), 95 (53), 69 (26), 59 (23). Then Z-
(IVb) was isolated, Rf 0.10 (hexane–ethyl acetate, 9:1).
1H NMR spectrum, d, ppm: 3.84 C (3H, OMe), 6.24 s
,
Methyl (3-nitrophenyl)propiolate (IIb). Oily
–1
substance. IR spectrum, cm : 1345, 1535, 1710, 2245.
1H NMR spectrum, d, ppm: 3.86 s (3H, OMe), 7.59 t
(1Harom, J 8.0 Hz), 7.88 d.t (1Harom, J 7.7, 1.7 Hz),
8.30 d.d.d (1H arom, J 8.3, 2.3, 1.0 Hz), 8.43 t (1Harom
,
J 1.8 Hz). Mass spectrum, m/z (Irel , %): 205 (41) M+,
174 (100) [M-OMe]+, 147 (62), 128 (82), 116 (40), 105
(18), 101 (36), 88 (36), 77 (26), 74 (90), 50 (26). Calculated
M 205.17.
(1H, HC=), 7.17 t (2Harom, J 8.5 Hz), 7.63 d.d (2H arom
,
J 8.8, 5.2 Hz). 19F NMR spectrum, d, ppm: –102.44 t.t
(1Farom, J 8.2, 5.0 Hz), 50.43 s (1F, FSO3). Mass
spectrum, m/z (Irel , %): 278 (55) M+, 247 (100) [M–
OMe]+, 179 (15) [M-FSO3]+, 147 (65), 123 (87), 120 (20),
109 (15), 108 (15), 107 (15), 95 (58), 75 (29), 69 (25), 59
(18), 50 (15). Found for isomer mixture, % : C 43.30,
H 3.07. C10H8F2O5S. Calculated, %: C 43.17, H 2.90.
M 278.23.
Methyl (4-nitrophenyl)propiolate (IIc). mp 111 –
–1
112°C (publ.: mp 108–111°C [8]). IR spectrum, cm :
1345, 1520, 1710, 2240. 1H NMR spectrum, d, ppm:
3.86 s (3H, OMe), 7.74 d (2Harom, J 8.6 Hz), 8.24 d
(2Harom, J 8.6 Hz). Mass spectrum, m/z (Irel , %): 205
(49) M+, 174 (100) [M–OMe]+, 147 (65), 128(73), 116
(47), 101 (20), 100 (36), 99 (13), 98 (20), 88 (31), 77 (25),
74 (69), 62 (22), 50 (25). Calculated M 205.17.
Methyl (4-methyl-3-nitrophenyl)propiolate (Va).
A solution of 26 mg (0.257 mmol) of KNO3 in 0.5 ml of
HSO3F was cooled to –75°C, and thereto at vigorous
stirring was added within 5 min 30 mg (0.172 mmol) of
ester V. After 20 min the reaction mixture was quickly
poured into 5 ml of 20% H2SO4 cooled to –50°C. After
the usual workup [4] the residue was subjected to
chromatography on silica gel. Yield 61%, mp 58–59°C.
E-Methyl 3-(3-nitrophenyl)-3-(fluorosulfonyl-
oxy)propenoate (IIIa). Oily substance. IR spectrum,
–1
cm : 1210, 1235, 1350, 1555, 1665, 1730. 1H NMR
spectrum, d, ppm: 3.73 s (3H, OMe), 6.41 s (1H, HC=),
7.67 t (1Harom, J 8.0 Hz), 7.89 d.t (1Harom, J 7.8, 1.2 Hz),
8.38 d.d.d (1Harom, J 8.4, 2.3, 1.1 Hz), 8.44 t (1Harom,
–1
IR spectrum, cm : 1345, 1430, 1515, 1700 (C=O), 2215,
1
2245 (CºC). H NMR spectrum, d, ppm: 2.63 s (3H,
J 1.7 Hz). 13C NMR spectrum (CDCl3), d, ppm: 52.57 q
(J 148.3 Hz), 115.14 d (J 166.6 Hz), 124.65 d.t (J 170.4,
5.3 Hz), 126.27 d.t.d (J 170.8, 6.6, 1.0 Hz), 129.60 d
(J 167.0 Hz), 131.06 m (J 6.8 Hz), 135.03 d.t (J 164.9,
6.0 Hz), 147.97 m (J 7.2 Hz), 156.62 m (J 5.5 Hz),
163.09 q (J 3.8 Hz). 19F NMR spectrum, d, ppm: 46.49 s
(1F, FSO3). Mass spectrum, m/z (Irel , %): 305 (6) M+,
288 (18), 274 (45) [M–OMe]+, 206 (19) [M–FSO3]+, 191
(31), 174 (40), 150 (58), 104 (31), 101 (24), 89 (47), 77
(77), 76 (68), 69 (100), 63 (66), 59 (80). Found, %:
C 39.15, H 2.71, N 4.30. C10H8FNO7S. Calculated, %:
C 39.35, H 2.64, N 4.59. M 305.24.
Me), 3.85 s (3H, OMe), 7.37 d (1Harom, J 7.9 Hz), 7.67
d.d (1Harom, J 7.9, 1.7 Hz), 8.17 d (1Harom, J 1.7 Hz).
Mass spectrum, m/z (Irel , %): 219 (38) M+, 202 (100)
[M–OH]+, 188 (34) [M–OMe]+, 142 (40), 130 (12), 114
(30), 102 (16), 88 (15), 77 (12), 63 (23), 51 (12). Found,
% : C 60.13; H 4.31. C11H9NO4. Calculated, % : C 60.27;
H 4.14. M 219.19.
E-Methyl-3-(4-methyl-3-nitrophenyl)-3-(2-
methyl-5-methoxycarbonylethynyl phenylpropeno-
ate (VIa). Yield 17%, viscous oily substance. IR spectrum,
–1
cm : 895, 1120, 1170, 1345, 1425, 1515, 1620 (C=C),
1
1705, 1720 (C=O), 2225 (CºC). H NMR spectrum, d,
E- and Z-Methyl 3-(fluorosulfonyloxy)-3-(4-
fluorophenyl)propenoates (IVa, b). Oily substances
that were separated by column chromatography on silica
gel. First E-(IVa) was eluted, Rf 0.20 (hexane–ethyl
ppm: 2.12 s (3H, Me), 2.61 s (3H, Me), 3.69 s (3H,
OMe), 3.83 s (3H, MeO2CCº), 6.08 s (1H, HC=), 7.20
d (1Harom, J 7.9 Hz), 7.30 d (1H arom, J 8.0 Hz), 7.37 d.d
(1Harom, J 8.0, 1.7 Hz), 7.41 d (1H arom, J 1.6 Hz), 7.48
d.d (1Harom, J 7.9, 1.6 Hz), 7.84 d (1Harom, J 1.7 Hz).
Mass spectrum, m/z (Irel , %): 393 (17) M+, 376 (100)
[M–OH]+, 375 (26), 362 (65) [M–OMe]+, 361 (23), 346
(39), 330 (19), 310 (15), 302 (21), 287 (21), 226 (21), 215
–1
acetate, 9:1). IR spectrum, cm : 1010, 1200, 1445, 1495,
1645, 1725. 1H NMR spectrum, d, ppm: 3.70 s (3H,
OMe), 6.26 s (1H, HC=), 7.14 t (2Harom, J 8.6 Hz), 7.58
d.d (2Harom, J 8.9, 5.2 Hz). 13C NMR spectrum (CDCl3),
RUSSIAN JOURNALOF ORGANIC CHEMISTRY Vol. 40 No. 11 2004

NITRATION OF PHENYLPROPIOLIC ACID DERIVATIVES IN HSO3F
1637
3. Olah, G.A. and Spear, R. J., J. Am. Chem. Soc., 1975, p. 1845.
4. Rudenko, A.P., Cavechenkov, P. Yu., and Vasil’ev, A.V., Zh.
Org. Khim., 2004, vol. 40, p. 1424.
5. Cavechenkov, P. Yu., Vasil’ev, A.V., and Rudenko, A.P., Zh.
Org. Khim., 2004, vol. 40, p. 1329.
(19), 213 (19), 202 (23), 115 (20), 59 (32). Found, %:
C 66.93; H 5.01. C22H19NO6. Calculated, % : C 67.17;
H 4.87. M 393.39.
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