Reactions of Trifluoroacetyl Alkynes Under Electrophilic Activation with Br?nsted Acids or Acidic Zeolites

Article abstract of DOI:10.1002/ejoc.201801645

The reaction of trifluoroacetyl alkynes [ArC≡C(C=O)CF₃] with H₂SO₄ or TfOH affords products of addition of the acids to the acetylene bond. Hydrolysis of these adducts results in the formation of the corresponding 1,3-dike

Full text of DOI:10.1002/ejoc.201801645

A Journal of
Accepted Article
Title: Reactions of trifluoroacetyl alkynes under electrophilic activation
with Brønsted acids or acidic zeolites
Authors: Selbi K. Nursahedova, Dmitry S. Ryabukhin, Vasily M.
Muzalevskiy, Roman O. Iakovenko, Irina A. Boyarskaya,
Galina L. Starova, Valentine G. Nenajdenko, and Aleksander
Viktorovich Vasilyev
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201801645
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
Reactions of trifluoroacetyl alkynes under electrophilic activation
with Brønsted acids or acidic zeolites
Selbi K. Nursahedova,a Dmitry S. Ryabukhin,a Vasily M. Muzalevskiy,b Roman O. Iakovenko,c
Irina A. Boyarskaya,c Galina L. Starova,# Valentine G. Nenajdenko,b * Aleksander V. Vasilyeva ,c
*
aDepartment of Chemistry, Saint Petersburg State Forest Technical University, Institutsky per., 5,
Saint Petersburg , 194021, Russia
bDepartment of Chemistry, Lomonosov Moscow State University, Leninskie Gory, 1, Moscow,
119899, Russia
cDepartment of Organic Chemistry, Institute of Chemistry, Saint Petersburg State University,
Universitetskaya nab., 7/9, Saint Petersburg , 199034, Russia
Corresponding Authors
* E-mail: nenajdenko@org.chem.msu.ru (Valentine G. Nenajdenko),
http://www.chem.msu.ru/rus/chair/org_w/os/welcome.html
* E-mails: aleksvasil@mail.ru, a.vasilyev@spbu.ru (Aleksander V. Vasilyev),
http://chem.spbu.ru/research/nauchnye-gruppy/237-scientific-activities/research-groups/951-
nauchnaya-gruppa-professora-a-v-vasileva.html
1
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
Keywords: trifluoromethyl group; alkynes; protonation, electrophilic addition, aromatic
substitution
Graphical abstract:
F3C
1. H2SO4 or TfOH
or TfOH-Py. 2. H2O
Ar'
Ar'H, TfOH or
HUSY zeolite
O
O
OX
Ar
R'
CF3
Ar
CF3
8 examples
15 examples
X = H or SO2CF3
up to 98%
Ar
up to 81%
TOC text:
Trifluoroacetyl alkynes add H2SO4 or TfOH to the acetylene bond affording the corresponding
vinyl sulfates or triflates. Reactions of these alkynes with arenes in TfOH or under the action of
acidic HUSY zeolites result in the formation of 1,3-diaryl-1-CF3-indenes.
Key topics: trifluoroacetyl alkynes, trifluoromethyl indenes
Abstract:
The reaction of trifluoroacetyl alkynes [ArCC(C=O)CF3] with H2SO4 or TfOH affords products of
addition of the acids to the acetylene bond. Hydrolysis of these adducts results in the formation of
the corresponding 1,3-diketones existing in form of enols [Ar(HO)C=CH(C=O)CF3] in up to 98%
yield. The application of less acidic TfOH-pyridine system permits transformation of these alkynes
into the corresponding vinyl triflates in up to 76% yield. Moreover, this reaction is totally
stereoselective to give only Z-configurated vinyl triflates. The reaction of trifluoroacetyl alkynes
with arenes in TfOH or under the action of acidic HUSY zeolites CBV-720 gives rise to 1,3-diaryl-
1-CF3-indenes in up to 81% yield. Electronic characteristics of initial intermediate mono- and
dicationic species derived from such alkynes in the highly acidic media were studied by DFT
calculations. Plausible cationic reaction mechanism was proposed.
2
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
Introduction
Organofluorine compounds are widely used in chemistry, medicine, agrochemistry and
material science.1-7 Among all other fluorinated organic compounds, trifluoroacetyl alkynes bearing
two synthetically important functional groups, acetylene and carbonyl ones, are versatile building
blocks for the synthesis of various trifluoromethyl substituted O-, N-, or S-heterocycles, and many
other compounds.8-15 Moreover, these acetylenes have highly polarized triple bond, since the
trifluoroacetyl group is one of the most strong electron withdrawing groups.
Based on our study on chemistry of trifluoroacetyl alkynes,16-18 we undertook a special
investigation of transformations of these compounds under highly acidic activation conditions. The
main goal of this work was study of reactions of trifluoroacetyl alkynes with Brønsted (super)acids
(H2SO4, FSO3H, CF3SO3H) or under the action of highly acidic zeolite HUSY. Starting
trifluoroacetyl alkynes 1a-k used in this study are presented in Figure 1.
O
O
O
MeO
n-C6H13
X
CF3
CF3
CF3
1h
1g
1a-f,i-k
X = H (a), 4-Cl (b), 4-Me (c), 3-F-4-MeO (d), 3,4-MeO2 (e),
4-t-Bu (f). 4-MeO (i), 4-Br (j), 2,3,5,6-Me4 (k)
Figure 1. Starting trifluoroacetyl alkynes 1a-k used in this study.
Results and discussion
A priori protonation of alkynes 1 can proceed in two steps. At the first step the protonation of
oxygen atom of the carbonyl group to give species A is more favorable (Scheme 1). Then
protonation of carbon atom of the triple bond takes place leading to the formation of dications B. To
estimate electrophilicity, electronic properties of cations A and B and thermodynamic possibility of
their formation (ΔG298 of protonation reactions), DFT calculations were carried out for parent
ketone as well as 4-chloro, 4-methyl and 4-methoxy substituted ynones 1a-c,i. Electronic
characteristics (energies of HOMO/LUMO, electrophilicity indices ω, charge distribution, and
contribution of atomic orbital into the LUMO) of species A and B were calculated (Table 1,
Scheme 1).
3
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
Scheme 1. Selected characteristics of cations Aa and Ba (q – natural charge; k – contribution of
atomic orbital into LUMO, %), and calculated Gibbs energies G298 of protonation.
Table 1. Selected calculated (DFT) electronic characteristics of compounds 1 and species A, B.
HO
O
H3O+(-H2O)
CF3
OH
H3O+(-H2O)
2
1
Ar
Ar
Ar
4
2
CF3
3 H
2
4
3
4
3
G
G
CF3
1
1
B
1
A
с
с
Species
EHOMO
,
ELUMO
,
ω,a q(C2),b q(C4),b k(C2)LUMO
,
k(C4)LUMO
,
ΔG,
eV
eV
eV
e
e
%
%
kcal/mol
O
2
-7.58
-2.83
2.9
0.46
0.46
0.16
0.32
21
33
25
24
3
4
CF3
1
1a
OH
2
3
4
-8.42
-9.43
-4.59
-5.39
5.5
6.8
-0.7
CF3
1
Aa
HO
CF3
0.63
0.57
8
48
15.8
2
1
4
3 H
Ba
O
Cl
Cl
2
-7.44
-8.13
-2.89
-4.60
2.9
5.7
0.46
0.46
0.15
0.31
19
30
25
24
3
4
CF3
1
1b
OH
-0.5
15
2
3
4
4
CF3
1
Ab
HO
CF3
-9.61
-5.32
6.5
0.63
0.54
14
15
2
1
Cl
3 H
Bb
4
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
O
Me
2
-7.31
-8.10
-2.77
-4.47
2.8
5.4
0.45
0.44
0.16
0.29
13
24
16
3
4
CF3
1
1c
OH
Me
18
12
-2.6
2
3
4
CF3
1
Ac
HO
CF3
-9.39
-5.62
6.5
0.62
0.54
16
11.2
2
1
Me
3 H
4
Bc
1i
O
MeO
2
-6.92
-7.69
-2.68
-4.27
2.7
5.2
0.45
0.41
0.16
0.26
22
29
25
23
3
4
CF3
1
OH
MeO
-5.2
7.2
2
3
4
CF3
1
Ai
HO
CF3
2
1
-9.28
-5.12
6.2
0.61
0.50
21
19
MeO
3 H
4
Bi
Notes. Global electrophilicity index ω = (EHOMO + ELUMO) 2/8(ELUMO - EHOMO); Natural charges;
a
b
cContribution of atomic orbital into the molecular orbital.
Accordingly DFT data, first protonation on the oxygen atom is more thermodynamically
favorable. The corresponding values of ΔG298 for the formation reactions of cations A are within -
0.5 – -5.2 kcal/mol. The second protonation step, which affords dications B, is rather unfavorable,
ΔG298 values are 7.2 – 15.8 kcal/mol (Table 1). However, the formation of dicationic species is
possible in Brønsted superacids due to their high protonation ability.19,20
Species B, as dications, have higher values of electrophilicity indices ω 6.2-6.8 eV compared
to monocations A with ω 5.2-5.7 eV (Table 1). Comparison of electrophilic properties of carbon
atoms C2 and C4 in species A reveals that carbon C2 bears slightly bigger positive charge 0.41-0.46
e and it has slightly bigger contribution of atomic orbital into the LUMO 24-33% in comparison
with the same characteristics for carbon C4. For example, charge on C4 is 0.26-0.32 e and LUMO
contribution is 18-24% (Table 1, as an example see data for Aa in Scheme 1). However, difference
in charge and orbital characteristics of carbons C2 and C4 for cations A is not significant, therefore,
both these carbons can play role of reactive electrophilic centers in cations A.
The same comparison of properties of the atoms C2 and C4 in dications B shows that the latter
has less charge 0.50-0.57 e (contrary to 0.61-0.63 e for C2), but it gives significantly bigger
contribution into the LUMO 12-48% (contrary to 8-21% for C2) (Table 1 as an example see data for
Ba in Scheme 1). Therefore, it can be expected that cabon C4 in species B may be a reactive
electrophilic center due to orbital factors.
5
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
Having in hand these theoretical predictions, we decided to study the protonation of 1 using
different Brønsted acids. First, the reaction of alkynes 1a-k with sulfuric acid was investigated. It
was found that treatment of acetylenes 1a-g with H2SO4 at room temperature for 24 h resulted in
smooth transformation into the corresponding 1,3-diketones existing as enols 2a-g. The reaction is
very efficient. The corresponding products 2 were isolated in up to 88% yield (Scheme 2).
O
OH
O
1. H2SO4, r.t., 24 h
2. H2O
R
CF3
2a-g (57-88%)
R
CF3
1a-g
Scheme 2. Formation of 2a-g in H2SO4.
Next, the reaction with much stronger superacid was studied, namely with TfOH having
Hammet acidity function H0 -14.19 Treatment of compounds 1a-c with neat TfOH at room
temperature for 1 h followed by quenching with water afforded enols 2a-c in 50-87% yields
(Scheme 3). However, the reaction with arylacetylenes bearing donating substituents in aryl ring
(1d-g, k) and alkylacetylene 1h under these conditions gave oligomeric products only. The
formation of such complex reaction products may be caused by extremely high reactivity of
intermediate cationic species, which may react with starting alkynes in low nucleophilic superacidic
media.
O
OH
O
1. TfOH, r.t., 1 h
2. H2O
Ar
CF3
2a-c (50-87%)
Ar
CF3
1a-c
Scheme 3. Formation of enols 2a-c in TfOH.
To overcome this obstacle, acidity of TfOH was decreased by addition of pyridine (30% vol.).
To our delight, this system worked very cleanly to give the corresponding vinyl triflates Z-3a-c by
treatment of 1a-c with the system TfOH-pyridine (Scheme 4). The reaction with alkyne 1c having
donating 4-methylphenyl ring gave mixture of vinyl triflate Z-3c and enol 2c. Alkyne 1d bearing
donating 4-MeO group in aryl ring afforded in almost quantitative yield (98%) enol 2d only. Taking
into account stability of vinyl triflates to hydrolysis,21,22 one may propose that enols 2c,d were
formed not as a results of aqueous treatment of triflates 3c,d, but in a different way under the
reaction conditions (see below). Z-Configuration of the carbon-carbon double bond in compounds 3
was determined by H-H and H-F NOESY correlations (see SI).
O
OH
O
OTf
O
1. TfOH-Py (30% vol.), r.t., 1 h
2. H2O
Ar
+
CF3
CF3
Ar
Ar
CF3
1a-d
Z-3a (76%),
b (71%),
c (66%)
2c (22%),
d (98%)
Scheme 4. Formation of vinyl triflates Z-3a-c and enols 2c,d in the system TfOH-pyridine.
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
Plausible pathways of formation of the compounds 2 and 3 are presented in Scheme 5. In
relatively low acidic H2SO4, the reaction proceeds through formation of monocations A. As a result,
vinyl sulfates C (X = H) were isolated accordingly addition of nucleophile (sulfate or triflate
anions) to A (mesomeric form A). Hydrolysis of the latter gives rise to trifluoroacetyl enols 2. The
same way is realized in the system TfOH-Py leading to O-protonated forms of vinyl triflates C (X =
CF3). Subsequent aqueous workup of the reaction mixture affords triflates 3 in this case (see also
formation of triflates from alkynes in the recent works23,24). However, most probably the reaction in
stronger triflic acid leads to the formation of dications B. These highly reactive electrophiles were
transformed into species C as well by addition of triflate. Subsequent protonation of intermediate C
in the superacid TfOH leads to dications D. Next, bis-traflates E were formed by addition of second
triflate as nucleophile. Quench of the reaction mixture with water leads to isolation of enols 2 as
well (see Scheme 3). Alkynes 1c,d bearing strong donating aryl substituents and having higher
basicity may be protonated onto acetylene carbon with formation of species D in the system TfOH-
Py (Scheme 5), that finally affords enols 2 (see Scheme 4).
O
R
CF3
1
H+(H2SO4 or
TfOH-Py)
HO
H+(TfOH)
OH
CF3
R
Ar
A
B
CF3
TfO-
OH
CF3
XO2SO-,
HO
XO2SO
H+(TfOH)
OH
H+
TfO
Ar
CF3
R
R
C
D
CF3
A'
H2O
X = CF3
H2O
TfO-
HO
X = OH
O
OH
R
O
OTf
H2O
TfO
TfO
CF3
CF3
CF3
R
- 2 TfOH,
- H+
2
3
E
Ar
Scheme 5. Plausible reaction mechanism of formation of 2 and 3 from alkynes 1 in various acids.
Very interesting direction of the reaction was found for alkyne 1h in H2SO4 (Scheme 6). The
corresponding phenalene 4a was isolated in yield of 57%. The formation of this compound can be
explained by Friedel-Crafts type cyclization of O-protonated form of vinyl sulfate Ch into
compound 4, hydrolysis of which affords 4a. Also highly electrophilic nature of trifluoroacetyl
group should be taken into account.
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
OH
CF3
HO
O
1. H2SO4, r.t., 24 h
2. H2O
MeO
CF3
1h
4a (57%)
OMe
H2O
H2SO4
OH
OH
CF3
HO3SO
HO3SO
CF3
-H+
Ch
4
OMe
OMe
Scheme 6. Formation of phenalene 4a from alkyne 1h in H2SO4.
Similar reaction was observed for transformation of alkyne 1e in the system TfOH-Py. The
corresponding hydroxy-CF3-indanone 4b was isolated in high yield (64%) (Scheme 7). The
formation of this indanone can be rationalized in terms of the formation of O-protonated form of
vinyl triflate Ce, which is cyclized into compound F due to higher aromatic ring nucleophilicity. As
a result, cyclization occurs to form intermediate F. The addition of triflic acid to F gives bis-triflate
G, and indanone 4b was isolated after hydrolysis.
OH
HO
O
1. H2SO4, r.t., 24 h
2. H2O
CF3
MeO
CF3
1h
4a (57%)
OMe
H2O
H2SO4
OH
OH
HO3SO
HO3SO
CF3
CF3
-H+
Ch
4
OMe
OMe
Scheme 7. Formation of indanone 4b from alkyne 1e in the system TfOH-pyridine.
Next, the reaction of alkynes 1 with arenes under the action of various Brønsted or Lewis
acids, and acidic zeolites was investigated (Table 2). Reaction of alkyne 1a with benzene in
Brønsted superacids (TfOH, FSO3H) at room temperature or -40°C furnished CF3-indene 5a in low
yield of 8-20% (entries 2-4, Table 1), due to significant oligomerization of starting material. A
similar reaction under the action of AlX3 (X = Cl, Br) at room temperature gave complex mixture of
8
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
oligomers as well. Better result was obtained when acidic HUSY zeolite CBV-720 was used as an
activator. In this case, indene 5a was isolated in 54% yield (entry 1). The reaction of other alkynes
1b,j,k with benzene under the action of zeolite CBV-720 afforded the corresponding indenes 5c-e
in up to 81% yield (entries 6, 7, 9). The same reactions in TfOH resulted in the formation of the
indenes in lower yields of 36-40% (entries 8, 10). Structure of the compound 5e was confirmed by
X-ray analysis data (see SI).
It was found that the reaction has some restrictions. Other alkynes 1 bearing donating
substituents or the use of arenes having electron donative groups (toluene, xylenes, anisole) led to
formation of oligomeric products, due to extremely high reactivity of electrophilic intermediates
generated from alkynes 1. Very reactive cations A and B (see Scheme 1) may attack aromatic ring
of both starting alkynes and arenes forming oligomeric products. However, tetramethyl substituted
alkyne 1k gave indene 5e both in TfOH and with zeolite (entries 9, 10). Apart from that, the
reaction of compound 1a with 1,2-dimethoxybenzene in TfOH resulted formation of indene 5b in
good yield of 75% (entry 5).
Table 2. Synthesis of CF3-indenes 5 under superacidic conditions.
Alkyne Arene
Conditions
Products, yield (%)
F3C
Ph
benzene
HUSY zeolite CBV-720,
130°C, 1 h
1a
Ph
5a (54%)
benzene
benzene
benzene
TfOH, r.t., 1 h
5a (17%)
5a (20%)
5a (8%)
1a
1a
1a
1a
TfOH, CH2Cl2, -40°C, 1 h
FSO3H, CH2Cl2, -40°C, 1 h
TfOH, r.t., 1 h
OCH3
OCH3
F3C
H3CO
H3CO
Ph
5b (75%)
F3C
Ph
benzene
HUSY zeolite CBV-720,
130°C, 1 h
1b
5c (71%)
Cl
9
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
F3C
benzene
HUSY zeolite CBV-720,
130°C, 1 h
1j
Ph
5d (44%)
Br
benzene
benzene
TfOH, r.t., 1 h
5d (40%)
1j
F3C
HUSY zeolite CBV-720,
130°C, 1 h
1k
Ph
Me
Me
5e (81%)
Me
Me
X-ray of 5e
benzene
TfOH, r.t., 1 h
5e (36%)
1k
One may propose plausible reaction mechanism for formation of 5 including intermediate
formation of both cation A and dication B. It was previously reported that weak Brønsted acid
catalyzed reactions of alkynes 1 with electron-rich indoles gave rise to the corresponding CF3-
bis(indolyl)butynes.15 In this case, only carbonyl carbon C2 of substrates 1 was involved in the
reaction, no participation of acetylene fragment at all was observed under this conditions. Taking
into account these data, plausible reaction mechanism of the formation of indenes 5 through species
A can be proposed (Scheme 8). The reaction of cations A with arenes results in the information of
compounds H. The latter afford propargyl type cations I, subsequent Friedel-Crafts alkylation of
one more arene molecule led to compounds J. Next, protonation of acetylene bond in compounds J
gives highly reactive vinyl cations K. This protonation step is not realized in weaker acids,
CF3CO2H, PhCO2H (see ref.15). Finally, intermediates K are cyclized into indenes 5.
H+
O
OH
OH
Ar'
CF3
Ar'
H+
Ar'H
-H+
Ar
Ar
Ar
Ar
-H2O
CF3
CF3
CF3
1
A
H
I
Ar'H
-H+
R'
F3C
Ar'
Ar'
Ar'
CF3
H+
Ar'
CF3
K
Ar
R'
-H+
Ar
J
5
Ar
Scheme 8. Plausible mechanism of the formation of CF3-indenes 5.
However, the formation of dications B from alkynes 1 in the superacidic media can not be
excluded. These species have electrophilic reactive center on carbon C4 (see discussion on DFT
10
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
calculations above). Their reaction with arenes gives monocations L (Scheme 9). The latter are
cyclized into compounds M, and then, through formation of cations N, gives indenes 5.
R'
HO
O
CF3
2H+
Ar'H
-H+
OH
CF3
Ar
Ar
CF3
B
1
Ar
L
- H+
HO
F3C
CF3
Ar
Ar'
CF3
H+
-H2O
Ar'H
-H+
R'
R'
R'
Ar
M
Ar
N
5
Scheme 9. Plausible reaction mechanism of the formation of CF3-indenes 5 from alkynes 1 in
TfOH through an intermediate formation of dications B.
Conclusion
In conclusion, the reaction of trifluoroacetyl alkynes with Brønsted (super)acids or acidic
zeolite HUSY was investigated. As a result various valuable fluorinated products can be prepared
efficiently depending on the acidic activation system. It was found, that trifluoroacetyl enols,
trifluoroacetyl vinyl triflates or trifluoromethyl indenes can be synthesized to open new
opportunities for the synthesis of various CF3-containing compounds.
Experimental part
NMR spectra of solutions of compounds in CDCl3 were recorded on Bruker AVANCE 500
1
19
13
spectrometer (at 500, 470 and 125 MHz for H, F and C NMR spectra respectively) at 25 °C.
1
The solvent residual signals CDCl3 (δ 7.26 ppm) for H NMR spectra and the carbon signal of
CDCl3 (δ 77.0 ppm) for 13C NMR spectra were used as references. 19F NMR spectra were indirectly
referred to the signal of CFCl3 (δ 0.0 ppm). IR spectra of compounds were taken with FSM-1201
spectrometer. HRMS was carried out at instrument Bruker maXis HRMS-ESI-QTOF and by
matrix-assisted laser desorption ionization (MALDI-MS) using Fourier Transform (Ion Cyclotron
Resonance) Mass Spectrometer (Varian 902-MS) equipped with MALDI and 9.4 T magnet
(FTMS). Chromato-mass spectrometry analysis was done with machine G 2570A GC/MSD Agilent
Technologies. The preparative reactions were monitored by thin-layer chromatography carried out
on silica gel plates (Silufol UV-254), using UV light for detection. Preparative column
chromatography was performed on silica gel, Merk company. HUSY zeolite CBV-720 was
purchased from the company Zeolyst Int., it was activated at 550°C under air for 4h before
reactions.
11
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
X-ray diffraction study. Single crystal X-ray analysis was performed at single crystal
diffractometer Agilent Technologies (Oxford Diffraction) «Supernova». A suitable crystal was
selected and studied on the diffractometer. The crystal was kept at 100(2) K during data collection.
Using Olex225 the structure was solved with the ShelXS26 structure solution program using Direct
Methods and refined with the ShelXL refinement package using Least Squares minimization.
CCDC 1875535 – (5e) contains the supplementary crystallographic data, which can be obtained
free of charge at www.ccdc.cam.ac.uk/conts/retrieving.htmL or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: (internat.) + 44-
1223-336-033; E-mail: deposit@ccdc.cam.ac.uk.
DFT calculations. All computations were carried out at the DFT/HF hybrid level of theory
using hybrid exchange functional M06 by using GAUSSIAN 2009 program packages.27 The
geometries optimization were performed using the 6-311+G(2d,2p) basis set (standard 6-311 basis
set added with polarization (d, p) and diffuse functions). Optimizations were performed on all
degrees of freedom and solvent-phase optimized structures were verified as true minima with no
imaginary frequencies. The Hessian matrix was calculated analytically for the optimized structures
in order to prove the location of correct minima and to estimate the thermodynamic parameters.
Solvent-phase calculations used the Polarizable Continuum Model (PCM).
Starting trifluoroacetyl alkynes 1 were obtained as reported previously.28,29 Properties of
compounds 1a-j have been given in works.28,30
General procedures for synthesis of trifluoroacetyl alkynes 1. Preheated 500 mL three-
necked round-bottom flask equipped with thermometer, dropping funnel (with rubber septum) and
argon inlet was purged with argon and then charged with 200 mL of dry THF and 0.1 mol of
corresponding terminal acetylene. Thus, obtained solution was cooled to −60 °C and 0.11 mol of n-
BuLi (44 mL, 2.5 M solution in hexane) was added dropwise. The reaction mixture was allowed to
warm up to −20 °C and then was cooled to −60 °C. Next, CF3CO2Et was added slowly at
temperature lower than −50 °C. The reaction mixture was allowed to warm up to room temperature
(15−20 °C) and then quenched with 100 mL of 2 M HCl. Organic layer was separated and water
phase was extracted with CH2Cl2 (3 × 30 mL). Combined extracts were washed with water (50
mL), dried with Na2SO4 and concentrated in vacuum. The residue was purified by column
chromatography on silica gel using hexanes-ethyl acetate mixtures as eluent to purify reaction
product 1.
1
1,1,1-Trifluoro-4-(2,3,5,6-tetramethylphenyl)but-3-yn-2-one (1k). H NMR (CDCl3, 500
MHz) δ, ppm: 2.25 s (6Н, 2СН3), 2.42 s (6Н, 2СН3), 7.11 s (1Нarom.). 13CNMR (CDCl3, 125 MHz)
δ, ppm: 17.7 (2СН3), 19.8 (2СН3), 91.3 (С3), 101.2 (С4), 115.3 q (СF3, J = 284 Hz), 118.7, 134.5,
136.0, 140.2, 167.3 q (С=О, J = 36 Hz). 19F NMR (CDCl3, 470 MHz) δ, ppm: -78.3 s (CF3). HRMS
(ESI): calculated for C14H14F3O [М+Н] 255.0991, found 255.0989.
12
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
General procedures for synthesis of trifluoroacetyl enols 2a-g and compound 4a from
trifluoroacetyl alkynes 1a-g in H2SO4 and for synthesis of trifluoroacetyl enols 2a-c from
alkynes 1a-c in TfOH. Solution of trifluoroacetyl alkyne 1 (0.22 mmol) in acid, H2SO4 or TfOH,
(1 mL) was magnetically stirred at room temperature for 24 h (for H2SO4) or 1 h (for TfOH), then
poured into the water (50 mL). After extraction with CH2Cl2 (3 × 30 mL), the combined extracts
were consequently washed with water (50 mL), saturated aqueous solution of Na2CO3 (30 mL),
water (50 mL), dried with anhydrous Na2SO4 and evaporated in vacuum to give pure reaction
product 2 or 4a.
(Z)-1,1,1-Trifluoro-4-hydroxy-4-phenylbut-3-en-2-one (2a). Yield of 87%. Yellow solid,
1
m.p. 84-86°C. H NMR (CDCl3, 500 MHz) δ, ppm: 6.58 s (1Н, =СН), 7.52 t (2Нarom., J = 8.1 Hz),
13
7.62-7.65 m (1Нarom.), 7.95-7.97 m (2Нarom.), 15.15 broad s (ОН). CNMR (CDCl3, 125 MHz) δ,
ppm: 92.5 q (C3, J = 2 Hz), 117.3 q (СF3, J = 281 Hz), 127.8, 129.2, 133.1, 134.2, 177.4 q (С=О, J
19
= 35 Hz), 186.4 (C4). F NMR (CDCl3, 470 MHz) δ, ppm: -77.3 s (CF3). IR, ν, cm-1: 3400 (OH),
1727 (C=O). HRMS (ESI), negative mode: calculated for C10H6F3O2 [М-Н] 215.0320, found
215.0314.
(Z)-4-(4-Chlorophenyl)-1,1,1-trifluoro-4-hydroxybut-3-en-2-one (2b). Yield of 75%.
Yellow solid, m.p. 64-66°C. 1H NMR (CDCl3, 500 МHz) δ, ppm: 6.54 s (1Н, =СН), 7.49 d (2Нarom.
,
J = 8.5 Hz), 7.89 d (2Нarom., J = 8.5 Hz), 15.00 broad s (ОН). 13C NMR (CDCl3, 125 МHz) δ, ppm:
92.5 q (С3, J = 2 Hz), 117.8 q (СF3, J = 281 Hz), 129.1, 129.6, 131.5, 140.8, 173.9 q (С=О, J = 34.5
19
Hz), 185.1 (C4). F NMR (CDCl3, 470 МHz) δ, ppm: -77.3 s (СF3). IR, ν, cm-1: 3110 (OH), 1686
(C=O). HRMS (ESI), negative mode: calculated for C10H5ClF3O2 [M-H] 248.9930, found 248.9925.
(Z)-1,1,1-Trifluoro-4-hydroxy-4-(4-methylphenyl)-but-3-en-2-one (2c). Yield of 88%.
1
Yellow solid, m.p. 49-51°C. H NMR (CDCl3, 500 MHz) δ, ppm: 2.45 s (3Н, CH3), 6.55 s (1Н,
=СН), 7.31 d (2Нarom., J = 8 Hz), 7.85 d (2Нarom., J = 8 Hz), 15.24 broad s (ОН). 13C NMR (CDCl3,
125 MHz) δ, ppm: 21.9 (CH3), 92.1 q (C3, J = 2 Hz), 117.3 q (СF3, J = 276 Hz), 127.9, 129.9,
130.4, 145.5, 176.9 q (С=О, J = 40 Hz), 186.5 (C4).19F NMR (CDCl3, 470 МHz) δ, ppm: -77.3 s
(CF3). IR, ν, cm-1: 3400 (OH), 1668 (C=O). HRMS (ESI), negative mode: calculated for C11H8F3O2
[M-H] 229.0476, found 229.0471.
(Z)-1,1,1-Trifluoro-4-(3-fluoro-4-methoxyphenyl)-4-hydroxybut-3-en-2-one (2d). Yield of
1
87%. Yellow solid, m.p. 82-84°C. H NMR (CDCl3, 500 МHz) δ, ppm: 3.99 s (3Н, OCH3), 6.48 s
(1Н, =СН), 7.05 t (1Нarom., J = 8.4 Hz), 7.69 dd (1Нarom., J =2.0, 12.0 Hz), 7.75 d (1Нarom., J = 8.5
Hz), 12.67 broad s (ОН). 13C NMR (CDCl3, 125 МHz) δ, ppm: 56.6 (OCH3), 92.1 q (C3, J = 2 Hz),
113.1, 115.5, 115.6, 117.4 q (СF3, J = 280 Hz), 125.3, 151.4, 153.1, 175.9 q (С=О, J = 37 Hz),
185.4 (C4). 19F NMR (CDCl3, 470 МHz) δ, ppm: -77.1 s (CF3), 133.8 t (F, J = 10 Hz). HRMS
(ESI), negative mode: calculated for C11H7F4O3 [M-H] 263.0331, found 263.0326.
13
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(Z)-4-(3,4-Dimethoxyphenyl)-1,1,1-trifluoro-4-hydroxybut-3-en-2-one (2e). Yield of 81%.
1
Yellow solid, m.p. 74-76°C. H NMR (CDCl3, 500 МHz) δ, ppm: 3.97 s (3Н, OCH3), 3.98 s (3H,
OCH3), 6.53 s (1Н, =СН), 6.94 d (1Нarom., J = 9 Hz), 7.48 s (1Нarom.), 7.60 dd (1Нarom., J = 2.0, 9.0
13
Hz), 15.43 broad s (ОН). C NMR (CDCl3, 125 МHz) δ, ppm: 56.3, 56.4, 92.1 q (C3, J = 2 Hz),
110.0, 110.8, 117.7 q (СF3, J = 262 Hz), 122.7, 149.6, 154.6, 177.4 q (С=О, J = 26 Hz), 186.9 (C4).
19F NMR (CDCl3, 470 МHz) δ, ppm: -77.4 s (CF3). IR, ν, cm-1: 3439 (OH), 1704 (C=O). HRMS
(ESI), negative mode: calculated for C12H10F3O4 [M-H] 275.0531, found 275.0526.
(Z)-4-(4-Tert-butylphenyl)-1,1,1-trifluoro-4-hydroxybut-3-en-2-one (2f). Yield of 76%.
1
Reddish solid, m.p. 63-65°C. H NMR (CDCl3, 500 МHz, from mixture of compounds) δ, ppm:
1.36 s (9Н, -CH3), 6.55 s (1Н, =СН), 7.53 d (2Нarom., J = 8.5 Hz), 7.89 d (2Нarom., J = 8.5 Hz), 15.30
broad s (ОН).13C NMR (CDCl3, 125 МHz, from mixture of compounds) δ, ppm: 31.2 (СН3), 49.4,
92.1 q (C3, J = 3 Hz), 111.9, 125.3 q (СF3, J = 285 Hz), 126.2, 127.7, 129.5, 169.7 q (С=О, J = 46
19
Hz), 177.0 (C4). F NMR (CDCl3, 470 МHz) δ, ppm: -77.7 s (CF3). HRMS (ESI), negative mode:
calculated for C14H14F3O2 [M-H] 271.0946, found 271.0940.
(Z)-1,1,1-Trifluoro-4-hydroxydec-3-en-2-one (2g). Yield of 67%. Yellow solid, m.p. 54-
56°C. 1H NMR (CDCl3, 500 МHz) δ, ppm: 0.87-0.90 m (3Н, CH3), 1.25-1.30 m (8Н), 1.64 q (1Н,
J = 7.6 Hz), 2.43 t (1Н, J = 7.6 Hz), 5.91 s (1Н, =СН), 14.45 broad s (ОН).13C NMR (CDCl3, 125
МHz) δ, ppm: 14.1, 22.5, 25.6, 28.8, 31.5, 38.5, 95.8, 128.0 q (СF3, J = 284 Hz), 169.2 q (С=О, J =
19
48 Hz), 186.1. F NMR (CDCl3, 470 МHz) δ, ppm: -77.9 s (CF3). IR, ν, cm-1: 3400 (OH), 1716
(C=O). HRMS (ESI), negative mode: calculated for C10H14F3O2 [M-H] 223.0946, found 223.0940.
General procedures for synthesis of trifluoroacetyl vinyl triflates Z-3a-b and
trifluoroacetyl enols 2c,d from trifluoroacetyl alkynes 1a-d and for synthesis of
trifluoromethyl indanon 4b from alkynes 1e in the system TfOH-pyridine. Solution of
trifluoroacetyl alkyne 1 (0.22 mmol) in the mixture of TfOH (0.7 mL) and pyridine (0.3 mL) was
magnetically stirred at room temperature for 1 h, then poured into the water (50 mL). After
extraction with CH2Cl2 (3 × 30 mL), the combined extracts were consequently washed with water
(50 mL), saturated aqueous solution of Na2CO3 (30 mL), water (50 mL), dried with anhydrous
Na2SO4 and evaporated in vacuum, that gave pure reaction products.
(Z)-1,1,1-Trifluoro-3-oxo-1-phenylbut-1-enyl trifluoromethanesulfonate (3a). Yield of
1
76%. Colorless oil. H NMR (CDCl3, 500 МHz) δ, ppm: 6.79 s (1Н, =СН), 7.53 t (2Нarom., J = 7.6
Hz), 7.62 t (1Нarom., J = 7.6 Hz), 7.70 d (2Нarom., J = 7.6 Hz). 13C NMR (CDCl3, 125 МHz) δ, ppm:
92.5 q (C3, J = 2 Hz), 108.1, 115.7 q (СF3, J = 289 Hz), 118.4 q (OTf, J = 318 Hz) 127.4, 129.6,
133.7, 176.5 q (С=О, J = 37 Hz), 186.4. 19F NMR (CDCl3, 470 МHz) δ, ppm: -77.7 s (OTf), -79.0 s
(CF3). HRMS (ESI): calculated for C11H7F6O4S [M+H]+348.9964, found 348.9964.
(Z)-1-(4-Chlorophenyl)-4,4,4-trifluoro-3-oxobut-1-enyl trifluoromethanesulfonate (3b).
Yield of 71%. Colorless oil. 1H NMR (CDCl3, 500 MHz) δ, ppm: 6.77 s (1Н, =СН), 7.51 d (2Нarom.
,
14
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10.1002/ejoc.201801645
European Journal of Organic Chemistry
J = 8.6 Hz), 7.64 d (2Нarom., J = 8.6 Hz). 13C NMR (CDCl3, 125 МHz) δ, ppm: 92.4 q (C3, J = 2 Hz),
108.4, 115.6 q (СF3, J = 289 Hz), 118.4 q (OTf, J = 319 Hz), 128.6, 130.0, 140.4, 176.4 q (С=О, J
= 37 Hz), 197.5 (C4). 19F NMR (CDCl3, 470 МHz) δ, ppm: -74.0 s (OTf), -79.7 s (CF3).
(Z)-4,4,4-Trifluoro-3-oxo-1-p-tolylbut-1-enyl trifluoromethanesulfonate (3c) was obtained
1
in a mixture with compound 2c. Yield of 69%. Colorless oil. H NMR (CDCl3, 500 МHz, from
mixture of compounds) δ, ppm: 2.44 s (3H, CH3), 6.75 s (1Н, =СН), 7.31 d (2Нarom., J = 8Hz), 7.59
d (2Нarom., J = 8Hz). 13C NMR(CDCl3, 125 МHz, from mixture of compounds) δ, ppm: 21.8 (CH3),
92.1 q (C3, J=3Hz), 107.0, 115.7 q (СF3, J = 289 Hz), 118.4 q (OTf, J = 311 Hz), 127.4, 130.4,
134.2, 176.4 q (С=О, J = 36 Hz), 196.4 (C4). 19F NMR (CDCl3, 470 МHz, from mixture of
compounds) δ, ppm: -74.0 s (OTf), -79.6 s (CF3). HRMS (ESI): calculated for C12H9F6O4S [M+H]+
363.0120, found 363.0120.
6-Methoxy-1-(trifluoromethyl)-1H-phenalene-1,3-diol (4a).Yield of 57%. Yellow solid,
1
m.p. 115-117°C. H NMR (CDCl3, 500 МHz) δ, ppm: 4.13 s (3Н, OCH3), 7.09 s (1H. =CH), 7.09-
7.11 m (1Нarom.), 7.61 t (1Нarom., J = 8.4 Hz), 8.12 d (1Нarom., J = 7.2 Hz), 8.52 d (1Нarom., J = 8.4
Hz), 8.63 d (1Нarom., J = 8.4 Hz). 13C NMR (CDCl3, 125 МHz) δ, ppm: 56.5, 106.5, 122.4, 122.9 q
(CF3, J = 270 Hz), 124.2, 125.5, 127.5, 128.2 q (J = 5 Hz), 129.1, 130.2, 131.3, 134.3, 138.5, 162.9,
19
182.9. F NMR (CDCl3, 470 МHz) δ, ppm: -62.2 s (CF3). IR, ν, cm-1: 3400 (OH), 1645 (C=O).
HRMS (ESI), negative mode: calculated for C15H10F3O3 [M-H] 295.0582, found 295.0577.
3-Hydroxy-5,6-dimethoxy-3-(trifluoromethyl)-2,3-dihydro-1H-inden-1-one (4b). Yield of
1
94%. Colorless oil. H NMR (CDCl3, 500 MHz) δ, ppm: 2.83 d (1Н, CH, J = 19 Hz), 3.21 d (1H,
CH, J = 19 Hz), 3.94 s (3H, OCH3), 4.02 s (3H, OCH3), 6.23 s (OH), 7.18 s (1Нarom.), 7.20 s
(1Нarom.). 13C NMR (CDCl3, 125 MHz) δ, ppm: 47.3, 56.5, 56.7, 104.2, 106.2, 124.3, 126.5, 143.5 q
(СF3, J = 287 Hz), 143.6, 152.4, 156.1, 180.4 q (С=О, J = 46 Hz). 19F NMR (CDCl3, 470 MHz) δ,
ppm: -81.0 s (CF3). IR, ν, cm-1: 3404 (OH), 1706 (C=O). HRMS (MALDI): calculated for
C12H12F3O4 [M+H]+ 277.0682, found 277.0684.
General procedure for synthesis of trifluoromethyl indenes 5a-e from trifluoroacetyl
alkynes 1a,b,j,k and benzene under the action of HUSY zeolite CBV-720. The activated zeolite
(at 550°C under air for 4h) (0.45 g), alkyne 1 (0.2 mmol) and benzene (5 mL) were loaded in 15 ml
high pressure glass tube. The resulting suspension was magnetically stirred at 130°C for 1 h. After
cooling, reaction mixture was filtered to remove zeolite. Zeolite was boiling with MeOH (3 × 10
mL) and filtered off. The combined organic phases were concentrated in vacuum to provide a
residue, which was subjected to column chromatography on silica gel with eluation by hexanes-
ethyl acetate mixtures to purify reaction product 5.
General procedure for synthesis of trifluoromethyl indenes 5a,b,d,e from
trifluoroacetyl alkynes 1a,j,k and arenes in TfOH or FSO3H. The mixture alkyne 1 (0.22 mmol),
benzene (0.5 mL) or 1,2-dimethoxybenzene (2.3 mmol) with acid, TfOH or FSO3H, (1 mL) and
15
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European Journal of Organic Chemistry
with/without CH2Cl2 (0.5 mL) was magentacally stirred at room temperature (for TfOH) or -40°C
(for TfOH and FSO3H, see Table 2) for 1 h. Then reaction mixture was poured into the water (50
mL) and extracted with CHCl3 (2 × 40 mL). ). The combined extracts were consequently washed
with water (50 mL), saturated aqueous solution of Na2CO3 (25 mL), water (50 mL), dried with
anhydrous Na2SO4 and evaporated in vacuum. The obtained residue was subjected to column
chromatography on silica gel with eluation by hexanes-ethyl acetate mixtures to purify reaction
product 5.
1
1-(Trifluoromethyl)-1,3-diphenyl-1H-indene (5a). Yield of 54%. Yellow oil. H HMR
(CDCl3, 500 MHz) δ, ppm: 6.70 s (1Н, =СН), 7.32-7.39 m (4Harom.), 7.43-7.46 m (2Harom.), 7.49 t
(2Harom., J = 7.2 Hz), 7.59 d (3Harom., J = 7.6 Hz), 7.64 d (2Harom., J = 7.2 Hz), 7.69 d (1Harom., J =
13
7.6 Hz). C NMR (CDCl3, 125 MHz) δ, ppm: 64.0 q (J = 26.8 Hz), 121.6, 125.4, 126.5, 126.6 q
(CF3, J = 281 Hz), 127.78, 127.82, 128.0, 128.56, 128.63, 128.7, 130.0, 132.0, 134.3, 134.5, 143.5,
19
143.8, 147.3. F NMR (CDCl3, 470 MHz) δ, ppm: -67.4 s (CF3). MS (GC-MS, EI), (Irel.,%): 336
М+ (100), 267 (80), 252 (20), 239 (15), 189 (10). HRMS (MALDI): calculated for C22H16F3 [M+H]+
337.1199, found 337.1203.
1-Trifluoromethyl-5,6-dimethoxy-1-(3,4-dimethoxyphenyl)-3-phenylindene (5b). Yield of
75%. Yellow oil. 1H NMR (CDCl3, 300 MHz) δ, ppm: 3.83 s (3H, OCH3), 3.86 s (3H, OCH3), 3.91
s (3H, OCH3), 3.95 s (3H, OCH3), 6.55 s (1H), 6.83 d (2Harom., J = 8.5 Hz), 7.05-7.13 m (3Harom.),
13
7.21 s (1Harom.), 7.41-7.50 m (3Harom.), 7.60-7.62 m (2Harom.). C NMR (CDCl3, 75 MHz) δ, ppm:
55.89 (OCH3), 55.95 (OCH3), 56.2 (OCH3), 56.5 (OCH3), 63.9 q (J = 27 Hz), 106.5, 109.9, 111.5,
111.9, 120.8, 127.3, 127.8 q (CF3, J = 234 Hz), 128.0, 128.9, 129.2, 131.6, 135.0, 136.6, 136.8,
19
147.1, 148.6, 149.2, 149.3, 150.1. F NMR (CDCl3, 470 MHz) δ, ppm: -68.74 s (CF3). MS (GC-
MS, EI), m/z, (Irel., %): 456 M+ (100), 387 [M-CF3]+ (10). HRMS (MALDI): calculated for
C26H24F3O4 [M+H]+ 457.1621, found 457.1625.
3-(4-Chlorophenyl)-1-(trifluoromethyl)-1-phenyl-1H-indene (5c). Yield of 71%. Yellow
oil. 1H NMR (CDCl3, 500 MHz) δ, ppm: 6.70 s (1Н, =СН), 7.34-7.36 m (3Harom.), 7.39 t (1Harom., J
= 7.6 Hz), 7.44-7.47 m (3Harom.), 7.53 d (1Harom., J = 7.6 Hz), 7.56-7.58 m (4Harom.), 7.70 d (1Harom.
,
J = 7.6 Hz). 13C NMR (CDCl3, 125 MHz) δ, ppm: 64.1 q (J = 26.8 Hz), 121.4, 125.8, 126.7, 126.4 q
(CF3, J = 281 Hz), 127.8, 128.1, 128.6, 128.7, 128.9, 129.0, 132.3, 132.6, 134.1, 134.4, 143.1,
143.6, 146.1. 19F NMR (CDCl3, 470 MHz) δ, ppm: - 68.4 s (CF3). MS (GC-MS, EI), m/z, (Irel., %):
370 M+ (100), 301 [M-CF3]+ (95). HRMS (MALDI): calculated for C22H15ClF3 [M+H]+ 371.0801,
found 371.0804.
3-(4-Bromophenyl)-1-(trifluoromethyl)-1-phenyl-1H-indene (5d). Yield of 44%. Yellow
oil. 1H NMR (CDCl3, 500 MHz) , ppm: 6.67 s (1H, =CH), 7.32-7.33 m (3Harom.), 7.37 t (1Harom., J
= 7.4 Hz), 7.43 t (1Harom., J = 7.4 Hz), 7.48-7.55 m (5Harom.), 7.60-7.61 m (2Harom.), 7.67 d (1Harom.
,
J = 7.4 Hz). 13C NMR (CDCl3, 125 MHz) , ppm: 64.4 q (J = 27 Hz), 122.8, 123.0, 126.0, 126.6 q
16
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European Journal of Organic Chemistry
(CF3, J = 280 Hz), 126.9, 128.0, 128.3, 128.8, 128.9, 129.5, 132.1, 132.6, 133.3, 134.3, 143.2,
19
143.8, 146.4. F NMR (CDCl3, 470 MHz) , ppm: -68.5 s (CF3). MS (GC-MS, EI), (Irel.,%): 414
(100) [M+], 345 (63), 265 (86), 239 (13), 207 (7), 189 (18), 157 (10), 132 (38). HRMS (MALDI):
calculated for C22H15BrF3 [M+H]+ 415.0304, found 415.0299.
1-(Trifluoromethyl)-3-(2,3,5,6-tetramethylphenyl)-1-phenyl-1H-indene (5e). Yield of
1
81%. Yellow oil. H NMR (CDCl3, 500 MHz) , ppm: 1.95 s (3H, CH3), 2.07 s (3H, CH3), 2.26 s
(3H, CH3), 2.29 s (3H, CH3), 6.43 s (1Н, =СН), 6.90-6.91 m (1Harom.), 7.03 s (1Harom.), 7.32-7.36 m
13
(5Harom.), 7.61-7.62 m (2Harom.), 7.68-7.69 m (1Harom.). C NMR (CDCl3, 125 MHz) δ, ppm: 16.6,
16.9, 20.1, 20.2, 64.8 q (J = 27 Hz), 121.6, 125.4, 126.6, 127.0 q (CF3, J = 284 Hz), 127.9, 128.2,
19
128.8, 128.9, 131.3, 132.4, 132.8, 133.0, 133.5, 133.8, 134.0, 135.0, 143.3, 145.4, 148.3. F NMR
(CDCl3, 470 MHz) , ppm: - 68.2 s (CF3). MS (GC-MS, EI), m/z, (Irel., %): 392 M+ (100), 377 [M-
CH3]+ (45), 299 (45). HRMS (MALDI): calculated for C26H24F3 [M+H]+ 393.1825, found 393.1827.
Supporting Information
13
19
Experimental details, compounds characterization, copies of 1H, C, F NMR spectra, X-ray data,
and details of DFT calculations.
Acknowledgment
This work was supported by Russian Scientific Foundation: grant no. 18-13-00008 – study on
electrophilic reactions of trifluoroacetyl alkynes, and 18-13-00136 – synthesis of starting
trifluoroacetyl alkynes and discussion (VMM and VGN). Part of studies on HRMS of the obtained
compounds was performed at Center for Chemical Analysis and Materials Research of Saint
Petersburg State University, Saint Petersburg , Russia.
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