One-step addition of sulfonic acids to acetylene derivatives: An alternative and stereoselective approach to vinyl triflates and fluorosulfonates

Article abstract of DOI:10.1002/ejoc.200700650

Acetylenic acids and esters as well as acetylenic ketones were efficiently and stereoselectively converted in one step to the corresponding vinyl triflates or fluorosulfonates in triflic or fluorosulfonic acids. Depending on the reaction conditions the E or the Z isomer can be obtained very conveniently in high isolated yields. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200700650

FULL PAPER
DOI: 10.1002/ejoc.200700650
One-Step Addition of Sulfonic Acids to Acetylene Derivatives: An Alternative
and Stereoselective Approach to Vinyl Triflates and Fluorosulfonates
Aleksander V. Vasilyev,[a,b] Stéphane Walspurger,[b] Stefan Chassaing,[b] Patrick Pale,*[c] and
Jean Sommer*[b]
Dedicated to G. Olah on the occasion of his 80th birthday
Keywords: Superacidic systems / Alkynes / Vinyl triflates / Sulfones / Carbocations
Acetylenic acids and esters as well as acetylenic ketones
were efficiently and stereoselectively converted in one step
to the corresponding vinyl triflates or fluorosulfonates in
triflic or fluorosulfonic acids. Depending on the reaction con-
ditions the E or the Z isomer can be obtained very conve-
niently in high isolated yields.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Introduction
Vinyl triflates are important building blocks in organic
synthesis,[1] especially as intermediates for C–C bond for-
mation by Pd-catalyzed coupling reactions.[1–2] Vinyl fluo-
rosulfonates have also been used as precursors for such
coupling reactions, although to a much less extent.[3]
Surprisingly enough, only two routes are used to prepare
these important intermediates and they are mainly obtained
from ketones.[4] Deprotonation of the ketone and further
trapping of the so-formed enolate by a triflating agent leads
to vinyl triflates (Scheme 1, route a).[1,4,5] They can also be
produced by direct triflation of the ketone to yield a gem-
bis(triflate) intermediate,[6] followed by elimination with a
bulky base (Scheme 1, route b).[7] The main problem associ-
ated with these methods is the regio- and stereocontrol. In
the former method, the regio- and stereoselectivity is due
to the first enolization step, whereas in the latter, almost no
control can be achieved. It should be noted that side reac-
tions have been reported to occur with these methods.[8]
Expanding the access to vinyl triflates and related rea-
gents, especially through a stereoselective route, is therefore
appealing. On the basis of our work on alkyne deriva-
tives[9–10] and from a pioneering investigation,[11] we rea-
Scheme 1. Usual preparation of vinyl triflates (Ar = Ph, pyridine,
or 5-chloropyridine).
soned that substituted propynones and propynoic acid de-
rivatives 1 could be used as precursors of vinyl triflates or
other sulfonates (e.g. 2, 3; Scheme 2). Protonation of such
compounds in strong acids[12] would regioselectively gener-
ate a vinyl cation[13–14] in situ (Scheme 2, A), which could be
trapped by sulfonic acid to afford the corresponding vinyl
sulfonates. Moreover, the resulting dicationic species A ex-
[a] On leave from Saint-Petersburg State Forest Technical Acad-
emy, Department of Organic Chemistry
Institutsky per. 5, Saint-Petersburg, 194021 Russia
[b] Laboratoire de Physico-Chimie des Hydrocarbures, Associé au
CNRS, Institut de Chimie, Université L. Pasteur,
67000 Strasbourg, France
[c] Laboratoire de Synthèse et Réactivité Organique, Associé au
CNRS, Institut de Chimie, Université L. Pasteur,
67000 Strasbourg, France
Scheme 2. Mechanistic hypothesis for an alternative route to vinyl
sulfonates (X = O, CH2).
E-mail: ppale@chimie.u-strasbg.fr
sommer@chimie.u-strasbg.fr
5740
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 5740–5748

One-Step Addition of Sulfonic Acids to Acetylene Derivatives
hibits a distinct environment at the vinylic cationic site was still observed (Table 1, Entry 5 vs. 4). The correspond-
(Scheme 3). With the protonated carbonyl group on one ing ethyl ester 1c mostly gave the same results, adducts 2c
side, this vinylic cation should be trapped on the other side and 3c exhibited the same stereoselection (Table 1, Entries 6
(anti addition), which would lead to the corresponding vinyl and 7). The stereochemistry of these compounds was deter-
sulfonate with E stereoselectivity.
mined by NOESY experiments, and spatial correlations
were characterized for each isomer (Figure 1).
Scheme 3. Basis for expected stereoselectivity.
Results and Discussion
To investigate this reaction, we prepared variously substi-
tuted propynoic acid derivatives and propynones
(Table 1).[15] Upon dissolution in either triflic acid or fluo-
Figure 1. NOESY and ROESY data for the isolated triflates.
To further look at possible electronic effects and to ex-
rosulfonic acid at –30 °C, the evolution of the starting mate- pand the scope of this method, propynoates bearing aro-
rials can easily be monitored by NMR spectroscopy. Disap- matic groups of various electron density were also prepared
pearance of the spectroscopic signals of the starting mate- and studied.
rial and the appearance of signals for the vinyl sulfonates
para-Fluorophenyl-substituted propiolic acid 1d reacted
as well as their relative E/Z ratio can indeed be easily deter- similarly to nonsubstituted product 1a. Both fluorosulfon-
1
mined by H NMR spectroscopy.
ates and triflates 2d and 3d were quantitatively obtained
The efficiency of the reaction was first investigated with with a similar selectivity for the fluorosulfonate and with a
phenyl-substituted propynoic acid 1a (Table 1, Entry 1). comparable selectivity for the triflate (Table 1, Entries 8 vs.
When 1a was dissolved in neat fluorosulfonic acid at 1 and 9 vs. 2, respectively). Corresponding ester 1e also
–80 °C, protonation of the acid group can easily be detected yielded expected adducts 2e and 3e, and the E selectivity
but no further reaction occurred. Upon gradual warming of was higher for the triflic acid addition (Table 1, Entry 11 vs.
the reaction mixture, two products were formed. At –40 °C, 10). It thus seems that an electron-withdrawing group does
NMR spectroscopic experiments cleanly showed the disap- not interfere much with the sulfonic acid addition across
pearance of protonated 1a and the gradual formation of the triple bond.
two series of signals; sharp 1H NMR signals at δ = 6.62 and
In sharp contrast, the presence of an electron-donating
6.71 ppm of unequal intensity were assigned to the expected group on the propynoate system dramatically changed its
isomeric vinyl fluorosulfonates 2a. Under these conditions, reactivity. para-Methyl-substituted 1f did not give the ex-
the isomeric ratio was 90:10, in favor of the E fluorosulfo- pected addition of fluorosulfonic acid, but instead yielded
nate as demonstrated by the typical shift of the vinylic pro- side products. Among them, dimers resulting from self-ad-
ton and confirmed by NOE.
dition were mostly isolated (Table 1, Entry 12).[16] In triflic
In triflic acid, 1a was also converted into the expected acid, the expected addition, however, did occur and af-
addition product 3a at low temperature (–30 °C) (Table 1, forded expected adducts 3f with very high E stereoselec-
Entry 2). Interestingly enough, the stereoselectivity was tivity and excellent isolated yield (Table 1, Entry 13). With
higher under these conditions, probably reflecting larger in- a more electron-donating methoxy group, 1g in triflic acid
teractions during the addition of a larger sulfonate.
gave expected adduct 3g, but surprisingly, an equivalent
Similar results were obtained from the corresponding amount of the hydrolysis product, β-keto ester 4g, was also
methyl ester 1b (Table 1, Entries 3–5). Fluorosulfonic acid isolated (Table 1, Entry 14). It seems that more electron-en-
and triflic acid added to 1b but at higher temperature (0 °C riched adducts were too sensitive to be isolated and that
instead of –30 °C). The expected mixtures of adducts 2b such vinyl triflates were subsequently hydrolyzed to the cor-
and 3b were obtained quantitatively, again in favor of the responding ketones. It is worth noting that unsubstituted or
E isomer but with different selectivities. The fluorosulfonic alkyl-substituted ynoates did not react with sulfonic acids
addition was surprisingly less stereoselective (Table 1, En- (e.g. 1h,i) and the starting material was recovered quantita-
try 3 vs. 1), whereas the trifluorosulfonic addition was tively (Table 1, Entries 15 and 16)
slightly better (Table 1, Entry 4 vs. 2). A preparative version
For comparison purposes, the addition reactions of
gave the vinyl triflate in high yield and high E selectivity ynones were also studied (Table 2). Hex-3-yn-2-one (5a)
without any problem (Table 1, Entry 5). Careful work up was used as a standard analog of nonreactive methyl oct-2-
allowed isolation of the product in high yields (95%) as a ynoate (1i), and but-3-yn-2-ones 5b-d carrying phenyl group
mixture of isomers without isomerization, as the same ratio of increasing electron-donating properties were used as ana-
Eur. J. Org. Chem. 2007, 5740–5748
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5741

A. V. Vasilyev, S. Walspurger, S. Chassaing, P. Pale, J. Sommer
FULL PAPER
Table 1. Synthesis of vinyl fluorosulfonates and vinyl trifluoromethylsulfonates (triflates) by the addition of triflic or fluorosulfonic acid
to the triple bond of propynoate derivatives.
[a] Yields and E/Z ratio determined by NMR spectroscopy. [b] Isolated yields.
5742
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 5740–5748

One-Step Addition of Sulfonic Acids to Acetylene Derivatives
Table 2. Synthesis of vinyl fluorosulfonates and vinyl trifluoromethylsulfonates (triflates) by the addition of triflic or fluorosulfonic acid
to the triple bond of ynone derivatives (isolated yields).
logs of 1b,f,g, respectively. As expected from the above-men- cross-peak correlations CH3Ar–Hmeta and Hvinyl–Hortho ob-
tioned results, 5a did not react, but surprisingly, phenyl de- served in (Z)-6c suggested a distance Hvinyl–Hortho roughly
rivative 5b also did not react (Table 2, Entries 1 and 2). around 3 Å, which is close to the literature data for a cis
Only the enriched para-methyl- and methoxy-substituted configuration of the vinyl proton and the protons in ortho
derivatives 5c and 5d cleanly gave the expected adducts. position of the neighboring aromatic ring (e.g. 2.423–
Fluorosulfonic and triflic acid treatment of 5c indeed 2.666 Å in Figure 3), whereas for the trans configuration the
yielded 6c and 7c, respectively, as the exclusive product distance is higher than 3.7 Å (e.g. 3.741–3.809 Å in Fig-
(Table 2, Entries 3 and 4). For para-methoxyphenyl-substi- ure 3).
tuted butyn-2-one 5d, the triflic acid adduct was not stable
enough, and as for its propynoate counterpart 1g, we could
only isolate the hydrolysis product, enol 8d (Table 2, En-
try 5).
Strikingly, these addition products exhibited a com-
pletely reverse in stereochemistry in comparison to the yno-
ate adducts; the Z isomer was the exclusive product. NOE
spectroscopic experiments allowed the unambiguous assign-
ment of proton signals in these addition products (Fig-
ure 2).
Figure 3. Basis for ROESY correlations and distance estimations.
Distances [Å]: H(5)–H(11) 2.475, H(10)–H(9) 2.423, H(2)–H(1)
2.666, H(10)–H(1) 3.741, H(2)–H(9) 3.809.
Figure 2. NOESY and ROESY data for isolated triflates.
Discussions and Mechanism
Moreover, a ROESY experiment allowed us to confirm
this stereochemistry and even to estimate the Hvinyl–Hortho Although ynones seem less reactive than ynoates under
distance between the vinyl proton and the aromatic ortho the same conditions, some similarities were observed in
protons (Figure 2).
each series. Unsubstituted or alkyl-substituted derivatives
did not reacted with sulfonic acid, whereas an aryl group
According to X-ray literature data, the distance CH3Ar
–
Hmeta is around 2.5 Å (e.g. 2.465–2.475 Å in Figure 3).[17] usually induced fast addition. The results obtained from the
With this distance as a reference, the relative intensities of ynoates and ynones clearly reflected the reactivity differ-
Eur. J. Org. Chem. 2007, 5740–5748
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5743

A. V. Vasilyev, S. Walspurger, S. Chassaing, P. Pale, J. Sommer
To address this point, we studied the stability and the
FULL PAPER
ences of the triple bond, which can be correlated to the
HOMO levels: the more conjugated the substituent, the possible isomerization of some adducts. We carried out re-
higher the HOMO.[18] However, under more acidic condi- actions at different temperatures and with prolonged reac-
tions (mixtures of CF3SO3H/SbF5 having H0 ≈ –20), the tion times (Table 3). Such a study could also shed some
initially nonreactive ynoates and ynones eventually under- light on the mechanism of these reactions. Adduct equili-
went sulfonic acid additions (Scheme 4). This clearly high- bration as well as reversibility of sulfonate addition to con-
lighted the key role of protonation in the reaction mecha- jugated acetylene carbonyl compounds could indeed be en-
nism.
visaged in superacids.
In fluorosulfonic acid, phenylpropynoic acid (1a) gave
the corresponding vinylic fluorosulfonate, and the E isomer
was the major adduct (Table 3, Entry 1; E/Z, 90:10) below
–30 °C but at 0 °C, the proportion of Z isomer started to
increase (Table 3, Entry 2; 76:24). Similar results were ob-
tained with para-fluorophenylpropiolic acid (1d) (Table 3,
Entries 3, 4 vs. 1, 2) as well as with methyl tolylpropynoate
(1f) and triflic acid (Table 3, Entries 5, 6 vs. 1, 2). Interest-
ingly, after 6 d at –20 °C in triflic acid, the isomer distribu-
tion of the 1f adducts was found to be completely reversed
(E:Z, 9:91). An increase in both the reaction time and the
temperature thus plays a key role on the isomeric ratio of
sulfonic acid addition. In contrast, Z isomers did not evolve
further under similar conditions.
Scheme 4. Reactions of ynoates and ynones in a superacidic me-
dium.
Interestingly enough, under such superacidic conditions
It is thus clear that equilibration occurred. These results
(H0 ≈ –20), the addition stereoselectivity is always in strong may be interpreted by kinetic versus thermodynamic con-
favor of the Z isomer (the E was not detected), whereas siderations. E isomers appear as kinetic products that are
in triflic or fluorosulfonic acids, the stereoselectivity seems favored at low temperatures and short reaction times. They
dependent on the structure: the ynoates give E adducts and would be generated by the addition of the sulfonate group
the ynones give Z adducts. These results suggest that adduct on the less-hindered face of a dicationic intermediate, anti
equilibration could occur depending on the acidity of the to the protonated carbonyl (Scheme 5, A). It is worth not-
medium.
ing that the stereoselectivity is always better for the triflate
Table 3. Isomerization of vinyl fluorosulfonates and vinyl trifluoromethylsulfonates in triflic or fluorosulfonic acids.
5744
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 5740–5748

One-Step Addition of Sulfonic Acids to Acetylene Derivatives
addition in comparison to the fluorosulfonate addition
Because no intermediate could be detected in the ad-
(Table 1), which is in agreement with what could be ex- dition to ynones, the isomerization process is probably very
pected from the addition of a larger group. Such a stereose- fast with vinyl sulfonates derived from ynones and much
lectivity was reported earlier for the fluorosulfonation of slower with vinyl sulfonates derived from ynoates.
propiolic acid and explained by electronic repulsion.[11] Be-
Accordingly, PM3 calculations[20] on protonated vinyl
cause Z isomers are the major product in the case of propy- triflates in the gas phase revealed important differences in
noates after prolonged reaction times, they probably are the stabilities and properties. Table 4 summarizes the calculated
more stable compounds.
results obtained for energy minima (enthalpies of forma-
tion) for various geometries and isomers. The protonation
of the carbonyl group offers the possibility of an intramo-
lecular hydrogen bond between the newly introduced pro-
ton and either the vinylic oxygen atom of the sulfonate
group or with the phenyl ring itself. This hydrogen bond
significantly participates to the stabilization of these struc-
tures (Table 4, Entries 1,3 vs. 2, 4 and 6, 8 vs. 7, 9). As
expected, the H–OTf interaction is stronger than the H–Ph
interaction, which stabilizes the Z isomers more (Table 4,
Entry 1 vs. 3 and 6 vs. 8).
Table 4. Thermodynamic stabilities of protonated vinyl triflates es-
ters and ketones calculated at the PM3 level.
Scheme 5. Mechanistic proposal for sulfonic acid additions to
ynones and ynoates.
Isomerization from the E to the Z isomer could be sim-
ply envisaged through the mesomeric form B in Scheme 5
or possibly through prototropic shift, but such a simple
phenomenon would not reflect the reactivity differences ob-
served. Isomerization may rather take place by a further
protonation[14] (Scheme 5, C) followed by rotation, in agree-
ment with our observations in stronger acidic media
(Scheme 4). The addition of a second sulfonate to yield in-
termediate D (Scheme 5) followed by elimination can also
be envisaged. Such a gem-disulfonate species, analog to C,
were characterized and are indeed prone to fast elimi-
nation;[6] they also were detected in superacid solutions.[11]
We thus tried to detect transient species by NMR spec-
Calculations also revealed a significant difference in the
troscopy, either dication C or gem-bistriflate D, but without stabilities between the protonated triflates derived from es-
success. Their lifetimes could render them undetectable on ters and ketones. Triflyl esters are indeed much more stable
the NMR timescale.
than their keto analogs (35–40 kcalmol–1 in the gas phase;
It is worth noting that initial “anti addition” to the triple Table 4, Entries 1–5 vs. 6–9). The relative stability of the
bond followed by isomerization to “syn addition” products protonated vinyl triflate derived from esters may most prob-
is known for some reactions of acetylenic compounds in ably be at the origin of the slower isomerization rate ob-
superacids.[19]
served in superacids. Furthermore, the comparison of the
Eur. J. Org. Chem. 2007, 5740–5748
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5745

A. V. Vasilyev, S. Walspurger, S. Chassaing, P. Pale, J. Sommer
FULL PAPER
(75 MHz, CDCl3, 25 °C): δ = 14.0 (OCH2CH3), 62.1 (OCH2CH3),
free enthalpies of formation between the protonated E and
Z isomers confirms that the Z isomers are thermodynami-
cally favored in both the ester and ketone series (Table 4,
Entry 1 vs. 3 and 6 vs. 8).
4
2
80.6, 84.9, 115.7 (d, JC,F = 3.8 Hz, Ar), 116.0 (d, JC,F = 22.0 Hz,
3
1
Ar), 135.1 (d, JC,F = 9.5 Hz, Ar), 153.9 (C=O), 163.86 (d, JC,F
=
252 Hz, Ar) ppm.
Procedure for the Preparation of Vinyl Triflates and Vinyl Fluorosul-
fonates in NMR Tubes:[10a] An NMR tube was loaded with HSO3F
(0.8–1 mL) and cooled down to –78 °C (dry ice/acetone), and the
acetylenic compound (5–20 mg) was then added. The temperature
was increased up to –40 °C, and a thin Teflon capillary was entered
to the bottom of the NMR tube, passing through it a weak flow
of argon during 5–10 min to homogenize the solution. The capil-
lary was then removed and CH2Cl2 as an internal standard was
Together, experiments and calculations demonstrate that
the stereoselectivity of the compound can be chosen in this
synthesis of vinyl fluorosulfonates and triflates. Starting
from acetylenic esters, “playing” with the experimental con-
ditions allowed full control over whether the E or the Z
isomer would be formed.
This method offers a single step efficient synthesis of the
E or Z isomer of vinyl sulfonates through fluorosulfonic
acid addition to acetylenes. Contrary to what was expected
with “superacids”, the reaction is very convenient, easy to
perform, and easily worked up.
1
added. H NMR spectra of the in situ obtained vinyl fluorosulfo-
nates were recorded at –40, –30, or 0 °C in the HSO3F solution.
The same procedure was used for the in situ preparation of vinyl
triflates from acetylenic compounds in CF3SO3H. In this case, the
1
reaction solutions were homogenized at –30 °C, and the H NMR
spectra of vinyl triflates were taken at –30 or 0 °C.
Conclusions
3-Fluorosulfonyloxy-3-phenyl-2-propenoic Acid (2a): E and Z iso-
mers were observed in superacid with an E:Z ratio of 90:10. Pro-
tonated 2a: 1H NMR (400 MHz, FSO3H, –40 °C): δ = 6.65/6.72 (s,
1 H, E/Z -CH), 7.67 (m, 2 H, Ph), 7.76 (m, 2 H, Ph), 7.83 (m, 1
H, Ph) ppm.
We developed an efficient and highly stereoselective
method for the synthesis of vinyl sulfonates by the stereose-
lective addition of sulfonic acids to alkynoic acid derivatives
and alkynones. Moreover, the stereoselectivity can be com-
pletely reversed from E to Z by controlling the reaction
time and temperature for the ynoates derivatives. Therefore,
this one-pot reaction offers an easy and innovative alterna-
tive to the two-step procedures commonly used to prepare
these important intermediates for C–C formations by coup-
ling reactions.
Methyl 3-Fluorosulfonyloxy-3-phenyl-2-propenoate (2b): E and Z
isomers were observed in superacid with an E:Z ratio of 78:22.
1
Protonated 2b: H NMR (400 MHz, FSO3H, 0 °C): δ = 4.34/4.65
(s, O-CH3) 6.64/6.71 (s, 1 H, E/Z -CH), 7.65–7.83 (m, 5 H, Ph)
ppm.
Ethyl 3-Fluorosulfonyloxy-3-phenyl-2-propenoate (2c): E and Z iso-
mers were observed in superacid with an E:Z ratio of 79:21. Pro-
1
tonated 2c: H NMR (400 MHz, FSO3H, 0 °C): δ = 1.70 (m, 3 H,
OCH2CH3), 5.12 (m 2 H, OCH2CH3) 6.64/6.71 (s, 1 H, E/Z -CH),
7.64–7.85 (m, 5 H, Ph) ppm.
Experimental Section
3-(4-Fluorophenyl)-3-fluorosulfonyloxy-2-propenoic Acid (2d): E and
Z isomers were observed in superacid with an E:Z ratio of 87:13.
Protonated 2d: 1H NMR (400 MHz, FSO3H, –40 °C): δ = 6.58/
6.65 (s, 1 H, E/Z -CH), 7.34 (m, 2 H, Ph Z+E), 7.82 (m, 2 H, Ph
E isomer), 7.98 (m, 2 H, Ph Z isomer) ppm.
General Remarks: Phenylpropiolic acid, methyl phenylpropiolate,
ethyl phenylpropiolate, ethyl propiolate, 3-hexyn-2-one, and methyl
2-octynoate were purchased from Aldrich and used without further
purification. Other starting materials, namely, acids,[10a,15a] es-
ters,[10a,15a] and ketones,[15b] were prepared according to previously
reported procedures. The reactions were monitored by thin-layer
chromatography carried out on silica plates (silica gel 60 F254,
Merck) by using UV light for detection. Column chromatography
was performed on silica gel 60 (0.040–0.063 mm, Merck). Melting
points (m.p.) were determined with a Bibby-Stenlin Stuart SMP3
melting point apparatus and are uncorrected. 1H, 13C, and 19F
NMR spectra were recorded with a Bruker AC-300 spectrometer
at 300, 75, and 300 MHz, respectively. The residual proton solvent
peak CHCl3 (δ = 7.26 ppm) for 1H NMR spectra, the signal of
CDCl3 (δ = 77.0 ppm) for 13C NMR spectra, and the signal of
CFCl3 (δ = 0.0 ppm) for 19F NMR spectra were used as references.
NMR experiments in superacids HSO3F and CF3SO3H were per-
formed with a Bruker AC-400 spectrometer at 400 MHz for 1H
Ethyl-3-(4-Fluorophenyl)-3-fluorosulfonyloxy-2-propenoate (2e):
E
and Z isomers were observed in superacid with an E:Z ratio of
87:15. Protonated 2e: 1H NMR (400 MHz, FSO3H, –30 °C): δ =
1.73 (m, 3 H, OCH2CH3), 5.07 (m, 2 H, OCH2CH3) 6.60/6.70 (s,
1 H, E/Z -CH), 7.65–7.92 (m, 4 H, Ph) ppm.
3-Phenyl-3-trifluoromethylsulfonyloxy-2-propenoic Acid (3a): E and
Z isomers were observed in superacid with an E:Z ratio of 93:7.
1
Protonated 3a: H NMR (400 MHz, CF3SO3H, –30 °C): δ = 6.61/
6.70 (s, 1 H, E/Z -CH), 7.67–7.83 (m, 5 H, Ph) ppm.
3-(4-Fluorophenyl)-3-fluorosulfonyloxy-2-propenoic Acid (3d): E and
Z isomers were observed in superacid with an E:Z ratio of 85:15.
1
Protonated 3d: H NMR (400 MHz, CF3SO3H, –30 °C): δ = 6.52/
1
NMR spectra. H NMR spectra in superacids were referenced to
6.60 (s, 1 H, E/Z -CH), 7.4 (m, 2 H, Ph Z+E), 7.8 (m, 2 H, Ph E
isomer), 8.0 (m, 2 H, Ph Z isomer) ppm.
the signal of CH2Cl2 added as an internal standard (δ = 5.32 ppm).
Low- and high-resolution mass spectra were obtained with a
Bruker micro-TOF instrument (ESI).
General Preparative Procedure: Fluorosulfonic acid, HSO3F, or
triflic acid, CF3SO3H (12.5 mmol), was added dropwise over 5 min
to a solution of the acetylenic compound (1.25 mmol) in dichloro-
methane (10 mL) while stirring vigorously at the temperature
shown in Table 1. After stirring for 0.25–1 h (see Table 1), the solu-
Ethyl 3-(4-Fluorophenyl)propynoate (1e): Prepared by Sonogashira
coupling from 1-fluoro-4-iodobenzene and ethyl propiolate accord-
ing to the literature.[21] Slightly yellow crystals. Yield: 0.98 g (17%).
M.p. 54–56 °C (ref.[21] oil). H NMR (300 MHz, CDCl3, 25 °C): δ tion was poured into an ice–water mixture. The aqueous phase was
1
= 1.33 (t, J = 7.2 Hz, 3 H, OCH2CH3), 4.25 (q, J = 7.2 Hz, 2 H,
extracted three times with dichloromethane, and the organic layer
OCH2CH3), 7.05 (m, 2 H, Ar), 7.56 (m, 2 H, Ar) ppm. 13C NMR was washed with saturated NaHCO3, water, and brine and then
5746
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 5740–5748

One-Step Addition of Sulfonic Acids to Acetylene Derivatives
dried with Na2SO4. After solvent evaporation under reduced pres-
sure, vinyl sulfonates are obtained in pure form. Yields of the pure
isolated compounds are given in Table 1.
25 °C): δ = 1.21 (t, J = 7.1 Hz, 3 H, OCH2CH3), 4.15 (q, J =
7.1 Hz, 2 H, OCH2CH3), 6.19 (s, 1 H), 7.13 (m, 2 H, Ar), 7.58
(m, 2 H, Ar) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 13.9
2
(OCH2CH3), 61.4 (OCH2CH3), 113.8, 115.6 (d, JC,F = 22.2 Hz),
Preparation of Vinyl Triflates in CF3SO3H/SbF5 Mixtures: Acetyle-
nic compound (0.5 mmol) was added with vigorous stirring to the
CF3SO3H/SbF5 mixture (1 mL) with value H0 ≈ –18 or –20 at 0 or
25 °C (see Table 2). After 0.5 h stirring, the solution was poured
into an ice–water mixture. The aqueous phase was extracted three
times with dichloromethane, and the organic layer was washed with
saturated NaHCO3, water, and brine and then dried with Na2SO4.
After solvent evaporation under reduced pressure, vinyl triflates
were obtained. Yields of the pure isolated compounds are given in
Scheme 4.
1
4
118.3 (q, JC,F = 323 Hz, CF3), 126.7 (d, JC,F = 3.1 Hz), 131.7 (d,
3JC,F = 9.0 Hz), 157.9, 163.2 (C=O), 164.4 (d, 1JC,F = 252 Hz) ppm.
19F NMR (300 MHz, CDCl3, 25 °C): δ = –107.1 (1 F, ArF), –74.2
(3 F, SO2CF3) ppm. For the Z isomer: 1H NMR (300 MHz, CDCl3,
25 °C): δ = 1.35 (t, J = 7.1 Hz, 3 H, OCH2CH3), 4.31 (q, J =
7.1 Hz, 2 H, OCH2CH3), 6.21 (s, 1 H), 7.10–7.16 (m, 2 H, Ar),
7.56–7.61 (m, 2 H, Ar) ppm. MS (ESI+): m/z (%) = 349 (100) [M
+ Na]+. HRMS: calcd. for C12H10F4O5S [M + Li]+ 349.0345; found
349.0340.
Methyl 3-(4-Methylphenyl)-3-trifluoromethylsulfonyloxy-2-propeno-
ate (3f): E and Z isomers were obtained as a yellow oily mixture
in 91% yield (368 mg) with an E:Z ratio of 96:4. Stereochemical
configurations were confirmed by NMR NOESY experiments car-
ried out on the crude mixture. 1H, 13C, and 19F NMR spectroscopic
data for individual isomers were obtained from the spectra of the
crude mixture. For the E isomer: 1H NMR (300 MHz, CDCl3,
25 °C): δ = 2.41 (s, 3 H, OCH2CH3), 3.70 (s, 3 H, OCH2CH3), 6.14
(s, 1 H), 7.25 (m, 2 H, Ar), 7.46 (m, 2 H, Ar) ppm. 13C NMR
(75 MHz, CDCl3, 25 °C): δ = 21.6 (OCH2CH3), 52.1 (OCH2CH3),
3-Phenyl-3-(trifluoromethylsulfonyloxy)propenoic Acid (3a): For the
1
E isomer: H NMR (300 MHz, CDCl3): δ = 6.17 (s, 1 H, =CH-),
7.41–7.57 (m, 5H arom.), 9.2 (br. s, 1 H, -COOH) ppm. 13C NMR
(75 MHz, CDCl3): δ = 112.5 (=CH), 118.3 (q, JC,F = 318 Hz, CF3),
128.4 (CAr, meta-), 129.3 (CAr, ortho-), 130.2 (CAr, ipso-), 132.0 (CAr
,
para-), 160.8 (=COTf), 168.4 (C=O) ppm. 19F NMR (300 MHz,
CDCl3): δ = –74.2 (s, CF3) ppm. For the Z isomer: 1H NMR
(300 MHz, CDCl3): δ = 6.25 (s, 1 H, =CH-), 7.41–7.56 (m, 5 H,
arom.), 9.2 (br. s, 1 H, -COOH) ppm. MS: m/z (%) = 296 (32)
[M]+, 231 (23), 149 (8), 105 (13), 102 (100), 77 (17).
1
112.4, 118.3 (q, JC,F = 318 Hz, CF3), 127.6, 129.0, 129.1, 142.4,
159.5, 164.0 (C=O) ppm. 19F NMR (300 MHz, CDCl3, 25 °C): δ
= –74.2 ppm. The Z isomer was prepared from methyl (E)-3-(4-
methylphenyl)propynoate (1f) after leaving it in pure CF3SO3H at
–20 °C for 6 d. The reaction mixture was worked up in the general
manner described above, and the compound was then recrystallized
from MeOH. Brownish solid. M.p. 73–75 °C. 1H NMR (300 MHz,
CDCl3, 25 °C): δ = 2.40 (s, 3 H, OCH2CH3), 3.83 (s, 3 H,
OCH2CH3), 6.22 (s, 1 H), 7.26 (m, 2 H, Ar), 7.47 (m, 2 H, Ar)
ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 21.5 (OCH2CH3),
Methyl 3-Phenyl-3-trifluoromethylsulfonyloxy-2-propenoate (3b): E
and Z isomers were obtained as a yellow oily mixture in 90% yield
(349 mg) with an E:Z ratio of 95:5. Stereochemical configurations
were confirmed by NMR NOESY experiments carried out on the
1
crude mixture. H, 13C, and 19F NMR spectroscopic data for the
individual isomers were obtained from the spectra of the crude
1
mixture. For the E isomer: H NMR (300 MHz, CDCl3, 25 °C): δ
= 3.69 (s, 3 H, OCH3), 6.19 (s, 1 H), 7.41–7.57 (m, 5 H, Ph) ppm.
13C NMR (75 MHz, CDCl3, 25 °C): δ = 52.1 (OCH3), 113.1, 118.3
1
1
(q, JC,F = 318 Hz, CF3), 128.2, 129.1, 130.4, 131.6, 159.1, 163.8
52.1 (OCH2CH3), 110.1, 118.3 (q, JC,F = 319 Hz, CF3), 126.5,
(C=O) ppm. 19F NMR (300 MHz, CDCl3, 25 °C): δ = –74.2 ppm.
For the Z isomer: 1H NMR (300 MHz, CDCl3, 25 °C): δ = 3.84 (s,
3 H, OCH3), 6.25 (s, 1 H), 7.36–7.58 (m, 5 H, Ph) ppm. MS (ESI+):
m/z (%) = 317 (100) [M + Li]+. HRMS: calcd. for C11H9F3LiO5S
[M + Li]+ 317.0283; found 317.0277.
128.9, 129.8, 142.6, 155.6, 163.4 (C=O) ppm. 19F NMR (300 MHz,
CDCl3, 25 °C): δ = –74.1 ppm. MS (ESI+): m/z (%) = 347 (100)
[M + Na]+. HRMS: calcd. for C12H11F3NaO5S [M + Na]+
347.0177; found 347.0172.
Methyl
3-(4-Methoxyphenyl)-3-trifluoromethylsulfonyloxy-2-pro-
penoate (3g): E and Z isomers were obtained as an oily mixture
in 39% yield (166 mg) with an E:Z ratio of 93:7. Stereochemical
configurations were confirmed by NMR NOESY experiments car-
ried out on the crude mixture. 1H, 13C, and 19F NMR spectroscopic
data for individual isomers were obtained from the spectra of the
crude mixture. For the E isomer: 1H NMR (300 MHz, CDCl3,
25 °C): δ = 3.79 (s, 3 H), 3.83 (s, 3 H), 6.13 (s, 1 H), 6.93 (m, 2 H,
Ar), 7.50 (m, 2 H, Ar) ppm. For the Z isomer: 1H NMR (300 MHz,
CDCl3, 25 °C): δ = 3.82 (s, 3 H), 3.85 (s, 3 H), 6.23 (s, 1 H), 6.84
(m, 2 H, Ar), 7.15 (m, 2 H, Ar) ppm. MS (ESI+): m/z (%) = 363
(100) [M + Na]+. HRMS: calcd. for C12H11F3NaO6S [M + Na]+
363.0126; found 363.0121.
Ethyl 3-Phenyl-3-trifluoromethylsulfonyloxy-2-propenoate (3c): E
and Z isomers were obtained as a yellow oily mixture in 94% yield
(381 mg) with an E:Z ratio of 94:6. Stereochemical configurations
were confirmed by NMR NOESY experiments carried out on the
1
crude mixture. H, 13C, and 19F NMR spectroscopic data for the
individual isomers were obtained from the spectra of the crude
1
mixture. For the E isomer: H NMR (300 MHz, CDCl3, 25 °C): δ
= 1.92 (t, J = 7.1 Hz, 3 H, OCH2CH3), 4.14 (q, J = 7.1 Hz, 2 H,
OCH2CH3), 6.18 (s, 1 H), 7.41–7.57 (m, 5 H, Ph) ppm. 13C NMR
(75 MHz, CDCl3, 25 °C): δ = 13.8 (OCH2CH3), 61.3 (OCH2CH3),
1
113.6, 118.3 (q, JC,F = 318 Hz, CF3), 128.2, 129.1, 130.6, 131.6,
159.9, 163.3 (C=O) ppm. 19F NMR (300 MHz, CDCl3, 25 °C): δ
= –74.2 ppm. For the Z isomer: 1H NMR (300 MHz, CDCl3,
25 °C): δ = 1.35 (t, J = 7.1 Hz, 3 H, OCH2CH3), 4.32 (q, J =
7.1 Hz, 2 H, OCH2CH3), 6.25 (s, 1 H), 7.41–7.57 (m, 5 H, Ph) ppm.
MS (ESI+): m/z (%) = 347 (100) [M + Na]+. HRMS: calcd. for
C12H11F3NaO5S [M + Na]+ 347.0177; found 347.0171.
Methyl 3-(4-Methoxyphenyl)-3-oxopropanoate (4g): Was obtained
as the major product from methyl 3-(4-methoxyphenyl)propynoate
(1g) after purification by column chromatography of the crude mix-
1
ture. Slightly yellow oil (ref.[6] oil). Yield: 109 mg (42%). H NMR
(300 MHz, CDCl3, 25 °C): δ = 3.75 (s, 3 H), 3.87 (s, 3 H), 3.96 (s,
2 H), 6.94 (m, 2 H, Ar), 7.92 (m, 2 H, Ar) ppm. 13C NMR
(75 MHz, CDCl3, 25 °C): δ = 45.5, 52.4, 55.5, 114.0, 129.0, 130.9,
164.0, 168.1 (C=O), 190.8 (C=O) ppm. MS (ESI+): m/z (%) = 215
(100) [M + Li]+. HRMS: calcd. for C11H12LiO4 [M + Li]+
215.0896; found 215.0890.
Ethyl 3-(4-Fluorophenyl)-3-trifluoromethylsulfonyloxy-2-propenoate
(3e): E and Z isomers were obtained as an orange oily mixture
in 90% yield (385 mg) with an E:Z ratio of 91:9. Stereochemical
configurations were confirmed by NMR NOESY experiments car-
ried out on the crude mixture. 1H, 13C, and 19F NMR spectroscopic
data for individual isomers were obtained from the spectra of the
crude mixture. For the E isomer: 1H NMR (300 MHz, CDCl3,
(Z)-4-Fluorosulfonyloxy-4-(4-methylphenyl)-3-buten-2-one (6c): Yel-
low oil. Yield: 258 mg (80%). 1H NMR (300 MHz, CDCl3, 25 °C):
Eur. J. Org. Chem. 2007, 5740–5748
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5747

A. V. Vasilyev, S. Walspurger, S. Chassaing, P. Pale, J. Sommer
FULL PAPER
150, Chem. Abstr. 2004, 140, 339090; M. Alami, F. Ferri, G.
Linstrumelle, Tetrahedron Lett. 1993, 34, 6403–6406.
[5] D. Comins, A. Dehghani, Tetrahedron Lett. 1992, 33, 6299–
6302.
[6] M. E. Wright, S. R. Pulley, J. Org. Chem. 1989, 54, 2886–2889.
[7] a) P. J. Stang, W. Treptow, Synthesis 1980, 283–284; b) D.
Crich, J. Picione, M. Smith, Q. Yao, Synthesis 2001, 323–326.
[8] T. Netscher, P. Bohrer, Tetrahedron Lett. 1996, 37, 8359–8362.
[9] A. Vasilyev, S. Walspurger, P. Pale, J. Sommer, Tetrahedron Lett.
2004, 45, 3379–3381.
[10] a) S. Walspurger, A. Vasilyev, J. Sommer, P. Pale, P. Y. Savech-
enkov, A. P. Rudenko, Russ. J. Org. Chem. 2005, 41, 1485–1492;
b) A. Vasilyev, S. Walspurger, P. Pale, J. Sommer, M. Haouas,
A. P. Rudenko, Russ. J. Org. Chem. 2004, 40, 1769–1778; A.
Vasilyev, S. Walspurger, P. Pale, J. Sommer, M. Haouas, A. P.
Rudenko, Russ. J. Org. Chem. 2004, 40, 1819–1828.
[11] a) P. J. Stang, R. Summerville, J. Am. Chem. Soc. 1969, 91,
4600–4601; b) R. H. Summerville, P. v. R. Schleyer, J. Am.
Chem. Soc. 1974, 96, 1110–1120; c) G. A. Olah, R. J. Spear, J.
Am. Chem. Soc. 1975, 97, 1845–1851.
δ = 2.40 (s, 6 H), 6.47 (s, 1 H), 7.27 (m, 2 H, Ar), 7.52 (m, 2 H,
Ar) ppm. C11H11FO4S (258.27): calcd. C 51.16, H 4.29; found C
51.30, H 4.36.
(Z)-4-(4-Methylphenyl)-4-trifluoromethylsulfonyloxy-3-buten-2-one
(7c): Brownish oil. Yield: 335 mg (87%). 1H NMR (300 MHz,
CDCl3, 25 °C): δ = 2.38 (s, 3 H), 2.41 (s, 3 H), 6.48 (s, 1 H), 7.25
(m, 2 H, Ar), 7.48 (m, 2 H, Ar) ppm. 13C NMR (75 MHz, CDCl3,
25 °C): δ = 21.5, 31.7, 116.4, 118.3 (q, 1JC,F = 319 Hz, CF3), 126.6,
129.8, 133.1, 142.7, 152.6, 194.2 (C=O) ppm. 19F NMR (300 MHz,
CDCl3, 25 °C): δ = –74.1 ppm. MS (ESI+): m/z (%) = 331 (100)
[M + Na]+. HRMS: calcd. for C12H11F3NaO4S [M + Na]+
331.0228; found 331.0221.
(Z)-4-Hydroxy-4-(4-methoxyphenyl)-3-buten-2-one (8d): Stereo-
chemical configuration was confirmed by NMR NOESY experi-
ments. Slightly yellow crystals. Yield: 218 mg (91%) after column
purification. M.p. 52–54 °C (ref.[7] 55–56 °C). 1H NMR (300 MHz,
CDCl3, 25 °C): δ = 2.17 (s, 3 H), 3.87 (s, 3 H), 6.11 (s, 1 H), 6.94
(m, 2 H, Ar), 7.86 (m, 2 H, Ar) ppm. 13C NMR (75 MHz, CDCl3,
25 °C): δ = 25.3, 55.4, 95.8, 113.9, 127.5, 129.1, 163.1, 184.1, 196.9
(C=O) ppm.
[12] G. A. Olah, G. K. S. Prakash, J. Sommer, Superacids, Wiley,
New York, 1985.
[13]
a) H.-U. Siehl, F.-P. Kaufman, K. Hori, J. Am. Chem. Soc.
1992, 114, 9343–9349; b) A. Vasilyev, S. Walspurger, M.
Haouas, P. Pale, J. Sommer, A. P. Rudenko, Org. Bio. Chem.
2004, 2, 3483–3489.
Acknowledgments
[14] Similar processes of O,C diprotonation of enone systems were
previously investigated, see: a) S. Walspurger, A. Vasilyev, J.
Sommer, P. Pale, Tetrahedron 2005, 61, 3559–3564; b) K. Y.
Koltunov, I. B. Repinskaya, Russ. J. Org. Chem. 1994, 30, 97–
100; c) K. Y. Koltunov, G. K. S. Prakash, G. Rasul, G. A. Olah,
J. Org. Chem. 2002, 67, 8943–8951, and references therein.
[15] a) Yu. P. Savechenkov, A. V. Vasilyev, A. P. Rudenko, Russ. J.
Org. Chem. (Engl.) 2004, 40, 1279–1283; b) S. A. Aristov, A. P.
Rudenko, A. V. Vasilyev, Russ. J. Org. Chem. (Engl.) 2006, 42,
66–72.
[16] a) Yu. P. Savechenkov, A. P. Rudenko, A. V. Vasilyev, Russ. J.
Org. Chem. (Engl.) 2004, 40, 1065–1066; b) Savechenkov, P.
Yu, A. P. Rudenko, A. V. Vasilyev, G. K. Fukin, Russ. J. Org.
Chem. (Engl.) 2005, 41, 1316–1328.
[17] G. Casalone, A. Gavezzotti, C. Mariani, A. Mugnoli, M. Si-
monetta, Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst.
Chem. 1970, 26, P.1.
[18] I. Fleming, Frontier Orbitals and Organic Chemical Reactions,
Wiley, Chichester, 1976.
[19] a) I. Kondolff, H. Doucet, M. Santelli, Tetrahedron Lett. 2003,
44, 8487–8491; b) Savechenkov, P. Yu, A. P. Rudenko, A. V.
Vasilyev, G. K. Fukin, Russ. J. Org. Chem. (Engl.) 2005, 41,
1316–1328; c) S. A. Aristov, A. V. Vasilyev, G. K. Fukin, A. P.
Rudenko, Russ. J. Org. Chem. (Engl.) 2007, 43, 691–705.
[20] Performed with CAChe and Hyperchem softwares.
[21] V. V. Rao, S. Ravikanth, G. V. Reddy, D. Maitraie, R. Yadla,
P. S. Ra o, Synth. Commun. 2003, 33, 1523–1529.
A. V. thanks the NATO for a postdoctoral fellowship and ULP
for an invited professor position. S. W. and S. C. thank the Loker
Hydrocarbon Institute, U.S.C., Los Angeles for financial support.
P. P. and J. S. thank the CNRS and the French Ministry of Re-
search for financial support.
[1] K. Ritter, Synthesis 1993, 735–762.
[2] a) U. Halbes-Letinois, P. Pale, P., “Palladium Catalyzed Syn-
thesis of Enynes” in Leading Edge Organometallic Chemistry
Research, (Ed.: M. A. Cato), Nova Publishers, New York,
2006, pp. 93–131; b) Tsuji, J., Palladium Reagents and Catalysts,
Wiley, New York, 2004; c) E-i. Negishi, A. De Meijere, Hand-
book of Organopalladium Chemistry for Organic Synthesis,
Wiley, New York, 2002; d) V. Farina in Comprehensive Organo-
metallic Chemistry II, (Eds.: E. W. Abel, F. G. A. Stone, G. Wil-
kinson), Pergamon, Oxford, 1995, vol. 12, pp. 222–225; e) K.
Sonogashira, in Comprehensive Organic Chemistry (Eds.: I.
Fleming, B. M. Trost), Pergamon, Oxford, 1991, vol. 3, pp.
521–549.
[3] a) G. P. Roth, C. E. Fuller, J. Org. Chem. 1991, 56, 3493–3496;
b) L. N. Pridgen, G. K. Huang, Tetrahedron Lett. 1998, 39,
8421–8424.
[4] They can also be obtained from amides, see: T. Okita, M.
Isobe, Synlett 1994, 589–591; C. J. Foti, D. L. Comins, J. Org.
Chem. 1995, 60, 2656–2657 or from conjugated enones, see: N.
Miyazawa, H. Nagata, K. Hanada, A. Tosaka, K. Ogasawara,
Tennen Yuki Kagobutsu Toronkai Koen Yoshishu 2001, 43, 145–
Received: July 14, 2007
Published Online: October 2, 2007
5748
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 5740–5748