Intramolecular hydrogen bond in the push-pull CF3-aminoenones: DFT and FTIR study, NBO analysis

Article abstract of DOI:10.1016/j.tet.2013.12.061

Postulated conformers of trifluoromethylated β-aminoenones stabilized by intramolecular NHaO and NHO bonds were studied by IR and NMR spectroscopy and evaluated with quantum chemical calculations (B3LYP/6-311+G(d,p), MP2/6-311+G(d,p)//B3LYP/6-311+G(d,p) a

Full text of DOI:10.1016/j.tet.2013.12.061

Tetrahedron xxx (2014) 1e7
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Intramolecular hydrogen bond in the pushepull CF3-aminoenones:
DFT and FTIR study, NBO analysis
*
N.N. Chipanina , L.P. Oznobikhina, T.N. Aksamentova, A.R. Romanov, A.Yu. Rulev
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky Str. 1, RUS-664033 Irkutsk, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Postulated conformers of trifluoromethylated b-aminoenones stabilized by intramolecular NH/O and
Received 28 October 2013
Received in revised form 18 December 2013
Accepted 24 December 2013
Available online xxx
N/HO bonds were studied by IR and NMR spectroscopy and evaluated with quantum chemical calcu-
lations (B3LYP/6-311þG(d,p), MP2/6-311þG(d,p)//B3LYP/6-311þG(d,p) and MP2/6-31G(d,p)) and NBO
analysis. The influence of the nature of EWG, substituents at the nitrogen atom and double bond, and of
orbital interactions of heteroatoms and double bonds in these structures on the proton affinity of basic
and acid centers, strength of hydrogen bonds, and the energy of tautomeric transfers is discussed. The
theoretical results agree satisfactorily with the experimental observations.
Keywords:
Pushepull CF3-aminoenones
Hydrogen bonds
NMR/IR/DFT study
NBO analysis
Ó 2014 Published by Elsevier Ltd.
1. Introduction
NMR and IR spectroscopy, X-ray diffraction and, finally, quantum
chemistry.10,11 In general, the following tautomeric forms of
b-
Trifluoromethylated
b
-aminoenones belong to the class of
aminoenones could be presented: aminoketone A, iminoketone B
and iminoenol C (Chart 1).
pushepull alkenes, i.e., systems bearing electron donating (EDG)
and electron withdrawing (EWG) groups at the vicinal sp2-carbon
atoms. Such compounds are very useful building blocks and
widely used for the synthesis of analogs of natural substances1,2
and the assembly of various fluorinated heterocycles.3e8 More-
over, pushepull aminoenones are also of considerable interest
from a theoretical point of view because they can exist in several
stereoisomeric and tautomeric forms, especially for derivatives
bearing at least one hydrogen on the nitrogen atom. In the last
case the intramolecular hydrogen bond often determines the
preferable configuration of the molecule. Because the reactivity of
pushepull systems depends strongly on their structure and, par-
ticularly, geometry,9 it is important to understand the influence of
the nature of both EWG and EDG as well as the olefin substituent
on the electron distribution and the stereochemistry of these
compounds.
Chart 1. Possible tautomeric forms of b-aminoenones.
It has been previously shown that intramolecular hydrogen
bonding helps to stabilize some tautomers of substituted -ami-
b
noenones and related compounds.12e18 It is well known that N/O
plays a determinant role in protein folding and DNA pairing.10 The
compounds bearing such bonding are more stable than iso-
structural systems having hydrogen bond N/HO in spite of the fact
that the latter is generally stronger. However, it was found that 1,3-
enaminoketonatoboron difluorides in solution exist as a 1:1 mix-
ture of A and C tautomers, but in the solid state the amount of the
latter form increases.19 Similarly, two tautomeric forms of phos-
phorus bearing aminoenones were registered in the solid state.20 It
was reported that some tautomers self-associate into dimers with
the different type of H-bonds.21,22 Non-polar aprotic solvents favor
the imino-enol form C of the azomethyne derivatives obtained from
substituted ortho-hydroxy aromatic aldehydes, while the use of
The role of the hydrogen bond in the existence of different
conformers and tautomers of pushepull aminoenones, as well as
their equilibrium, which depends on the nature of substituents,
crystal structure and experimental conditions, such as temperature
and solvent polarity has been intensively studied for last decade by
* Corresponding author. Fax: þ7 3952 419346; e-mail address: nina_chipanina@
irioch.irk.ru (N.N. Chipanina).
0040-4020/$ e see front matter Ó 2014 Published by Elsevier Ltd.
http://dx.doi.org/10.1016/j.tet.2013.12.061
Please cite this article in press as: Chipanina, N.N.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2013.12.061

2
N.N. Chipanina et al. / Tetrahedron xxx (2014) 1e7
polar solvents shifts the equilibrium toward the tautomer A.11 The
barrier to such isomerization for these compounds is lowered with
increase of the solvent polarity and its proton acceptor ability.23 For
example, low-barrier O/H/N imine-oxo tautomeric form is
characteristic for such type compounds in acetonitrile due to sol-
vent/proton interaction.24 It has been recently reported that H-
bond donors lower the energy of the proton-transfer transition
state up to barrier-free tautomeric transformation.23,25 According
to quantum chemistry calculations and X-ray analysis, (Z)-4,4,4-
trifluoro-3-(2-hydroxyethylamino)-1-(2-hydroxyphenyl)-2-buten-
1-one forms three tautomeric forms bearing intramolecular hy-
drogen bonds OH/O and NH/O.26 Interestingly, the most stable
tautomer is one having the oxygen atom of the carbonyl moiety
participate in the formation of both these bonds while in-
termolecular bonds OH/O form a polymeric structure. Functional
groups bearing a mobile proton can also take part in H-bonding.
Thus, intermolecular bond ]CeH/O participates in CF3-amino-
enones self-association in both non-polar solvents and solid state.27
This is the first example of a strong hydrogen bonding formed by an
olefinic proton. Usually, the conformation analysis was carried out
for pushepull systems with general formula Me2NeCH]CHeC(O)
R, where R¼Me, CF3.28e32 The following factors were taken into
account: basicity of nitrogen and oxygen atoms in different con-
formers, the impact of environment polarity on molecule structure
and its interaction with proton- and electron-donating solvents,
formation of dimers with bonds CeHa/O]C and CeHa/FeC. The
study of conformational behavior of CF3-aminoenone bearing sec-
ondary amino group (NHMe) has shown that the solvents having
proton withdrawing groups (such as P]O, S]O, etc.) destroy
intramolecular bond NH/O in the Z,Z-isomer due to formation of
intermolecular H-bonds, which favor the E,E-configuration.33 Fi-
with the B3LYP/6-311þG(d,p), MP2/6-311þG(d,p)//B3LYP/6-
311þG(d,p), and MP2/6-31G(d,p) levels of theory and NBO analysis
for aminoenone conformers A with syn- and anti-planar arrange-
ment of Ca]Cb and C]O bonds as well as for syn- and anti-con-
formers of their imino-enol tautomeric form C (Chart 3).
Chart 3. The equilibria for b-aminoenones bearing secondary amino group.
2. Results and discussion
2.1. Synthesis of aminoenones 9e11
The reaction of ynones 12a,b with 1 equiv of primary (iso-
propylamine) or secondary (pyrrolidine) amines as well as diamine
bearing primary amino groups (o-phenylenediamine) under very
mild conditions (room temperature, benzene or acetonitrile,
3e24 h) affords the corresponding aminoenones 9e11 in high
yields (Chart 4).
nally, it has been found that in contrast to
a
-unsubstituted tri-
fluoromethylated -aminoenones their
b
a-bromo substituted
analogs have unusual configuration due to the stabilizing effect of
a weak NH/Br bond.34 Here, we describe the dependence of the
strength of intramolecular hydrogen bond in pushepull CF3-ami-
noenones on the nature of the nitrogen and olefin substituent and
its role in the tautomeric equilibrium. The research was carried out
by IR and NMR spectroscopy and quantum chemistry calculations
for the enones 1e10 (Chart 2). In spite of the fact that two geometric
isomers are possible for each tautomeric form of aminoenones, we
have studied Z-isomers because they are stabilized by hydrogen
bond and therefore are more favored. The calculations are done
Chart 4. The synthesis of b-aminoenones 9e11.
According to NMR spectroscopy, these enones were isolated as
a single geometric isomer. Their configuration was assigned on the
basis of 1He1H 2D homonuclear NOESY experiment (Chart 5). For
example, in the spectrum of enone 9 there is one NOE peak be-
tween the resonance of the olefinic proton and the ortho-protons of
the aromatic ring. At the same time no correlation has been ob-
served between the protons of CH] and isopropylamino groups.
Similarly, the olefinic proton of aminoenone 10 has only one cross
peak with the
in the NOESY spectrum of enone 10 only one cross peak between
olefinic and -methylene protons is observed. Moreover, in both
a-methylene protons of the hexyl moiety. Similarly,
a
Chart 2. The studied
b-aminoenones.
Chart 5. Main NOESY correlations for aminoenones 9e11.
Please cite this article in press as: Chipanina, N.N.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2013.12.061

N.N. Chipanina et al. / Tetrahedron xxx (2014) 1e7
3
Table 1
Total (Et) and relative (
energy
cases the peak of the amino proton is shifted (
d
¼11e12 ppm in
D
E) syn- and anti-conformers of enamino-ketones 1a,be8a,b
CDCl3) due to the formation of the hydrogen bond between C]O
and NH. For the latter compound 10 the protons of the primary
amino group resonate at w3.8 ppm. These data undoubtedly con-
firm the (Z)-configuration of aminoenones 9 and 10. In contrast,
aminoenone 11 bearing a tertiary amino group has the (E)-config-
uration: the olefinic proton has a cross peak only with the methy-
lene protons of pyrrolidine moiety in the NOE spectra.
Entry Molecule B3LYP/6-311þG**
MP2/6-311þG**//B3LYP/6-311þG**
ꢀEt (ZPE)a,
ꢀ
D
E (ZPE)a, ꢀEt, a.u.
ꢀDE, kcal/mol
a.u.
kcal/mol
1
2
3
4
5
6
7
8
1a
1b
2a
2b
3a
3b
4a
4b
5a
5b
6a
6b
7a
7b
8a
8b
854.751739
0
852.7350365
852.7196861
555.482248
555.468223
852.736633
852.720254
555.484220
555.468589
907.970949
907.954567
610.718840
610.703737
661.518739
661.506044
364.265311
364.249590
0
9.84
0
8.80
0
10.28
0
9.81
0
10.28
0
9.48
0
7.97
0
854.734654 10.70
556.913525
556.896534 10.66
854.756908
854.739082 11.19
556.919402
556.901725 11.09
910.118004
910.100424 11.03
612.280282
612.262901 10.91
663.025978
663.014872 6.97
365.187395
365.169434 11.27
0
The additional confirmation of this assignment has been ob-
tained by the analysis of their IR spectra: the ratio of intensities
0
observed for the C]O (1608e1657 cmꢀ1
)
and C]C
(1530e1585 cmꢀ1) stretching vibration bands strongly suggests a s-
0
cis-conformation of the C]CeC]O moiety.35,36
9
0
The pushepull aminoenones bearing a trifluoromethyl group
have a very polar double bond. It is well known that the 13C
chemical shifts difference between adjacent olefinic carbon atoms
can serve as reliable parameter of double bond polarization.37
These values achieve 79.7, 85.7, and 78.1 ppm for aminoenones 9,
10, and 11, respectively, and are much higher than for non-
fluorinated analogs (w55e65 ppm).38 In contrast to non-
fluorinated aminoenones39 their trifluoromethylated analogs as
classical pushepull systems have a low-barrier to rotation about
the carbonecarbon double bond and therefore can readily undergo
the Z,E-isomerization.40 Taking into account this fact we assume
that the stereoselective formation of aminoenones 9e11 proceeds
by the same pathway but further isomerization occurs leading to
a more stable isomer. The similar E,Z-isomerization for polar acrylic
systems, such as enammonium salts of captodative formyl- and
carbonyl(amino)alkenes and their derivatives was reported.41e44
Interestingly, the aminoenone 10 undergoes further trans-
formations after standing in CDCl3 solution at room temperature
for a week. Careful analysis of the 1H and 13C NMR spectra allows us
to conclude that a new compound has the structure of 1,4-
diazepine 13 (Chart 6).
10
11
12
13
14
15
16
0
0
0
9.86
a
Calculations corrected by zero-point energy.
As for enone 7, its syn-conformer 7a stability is 2e4 kcal/mol
lower than for its non-fluorinated analog 8a. The E values be-
tween syn- and anti-conformers for the imino-enol form increase
by 1.5e2 times for compounds bearing either aryl (1, 2) or methyl
D
(7, 8) substituents at the b-carbon atom (Table 2). syn-Conformers
1c and 7c are more stable by 2e3 kcal/mol due to the electron
withdrawing effect of the CF3-group. The aryl moiety at nitrogen
atom (for imino-enols 3e6) provides the same electronic effect that
results in
DE decreasing. At the same time syn-conformers of tau-
tomeric forms of non-fluorinated enones 4c and 6c proved to be
insignificantly more stable than their CF3-bearing analogs 3c and
5c. The study of the dependence of DE on substituent nature in both
tautomeric forms is possible with the estimation of factors that
contribute to syn-conformers stabilization, such as intramolecular
bond strength and degree of electron density delocalization in the
formed cyclic systems.
Table 2
Total (Et) and relative (DE) syn- and anti-conformers of imino-enols 1c,de8c,d
energy
Chart 6. Cyclization of aminoenone 10.
Entry Molecule B3LYP/6-311þG**
MP2/6-311þG**//B3LYP/6-311þG**
ꢀEt (ZPE)a,
ꢀ
D
E (ZPE)a, ꢀEt , a.u.
ꢀDE,
This heterocycle was obtained by a separate experiment from
ynone 12b and o-phenylenediamine in acetonitrile with good yield.
This result allowed us to suggest a hypothesis that both formation
of heterocycle 13 and enamino-ketoneeimino-enol tautomeriza-
tion of pushepull aminoenones bearing electron withdrawing
substituents at both amino and carbonyl functional groups pass
through the same transition state.
a.u.
kcal/mol
kcal/mol
1
2
3
4
5
6
7
8
1c
1d
2c
2d
3c
3d
4c
4d
5c
5d
6c
6d
7c
7d
8c
8d
854.738507
0
852.725659
852.698811
555.475208
555.451510
852.731328
852.711310
555.481427
555.460654
907.966335
907.946976
610.716883
610.695618
661.509079
661.480500
364.258137
364.233407
0
854.711078 17.21
556.902870
556.879631 14.58
854.746715
854.727698 11.93
556.912148
556.892058 12.60
910.107748
910.090351 10.92
612.273218
612.252666 12.90
663.012464
662.983591 18.12
365.176689
365.152794 14.99
16.85
0
14.87
0
12.56
0
13.03
0
12.15
0
13.34
0
17.93
0
15.52
0
0
0
2.2. Theoretical calculations: energies, geometry, proton
affinities
9
0
10
11
12
13
14
15
16
0
The theoretical analysis was performed for compounds 1e8
bearing substituents at both nitrogen and olefinic carbon atoms,
which have different electronic and steric parameters. syn-Con-
formers of both tautomeric forms A and C are stabilized by intra-
molecular hydrogen bonds NeH/O or N/HeO, respectively. The
calculations, which were performed at the B3LYP/6-311þG(d,p) and
MP2/6-311þG(d,p)//B3LYP/6-311þG(d,p) level of theory indicate
that formation energy for syn-conformers of aminoenones 1ae6a
and 8a is lower for 9e11 kcal/mol than its anti-conformers 1be6b
and 8b regardless of the nature of EWG or a substituent at the
olefinic carbon atom (Table 1).
0
0
a
Calculations corrected by zero-point energy.
Calculated values of the intramolecular hydrogen bond NeH/O
length and the frequency shifts Dn(NeH) for syn-conformers
(1ae8a) versus their anti-conformers (1be8b) change symbatically
and therefore can serve as a bond strength measure (Table 3).
Please cite this article in press as: Chipanina, N.N.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2013.12.061

4
N.N. Chipanina et al. / Tetrahedron xxx (2014) 1e7
Table 3
Bond distance NeH/O (dH/O), frequency shift Dn(NeH) and second-order perturbation energy E(2) for orbital interactions in syn-conformers of enamino-ketones 1ae8aa
Dn (NeH), cmꢀ1
E
(2), kcal/mol
nO/
ꢀ
Entry
Molecule
dH/O, A
s
*
nN/
p
*
Ca
]
nN/p*C]C(Ar)
pC ] /p*C]O
a Cb
NeH
Cb
1
2
3
4
5
6
7
8
1a
2a
3a
4a
5a
6a
7a
8a
1.844
1.813
1.808
1.773
1.835
1.802
1.844
1.835
249
301
314
393
290
339
237
287
12.48
14.66
14.77
17.67
13.11
15.52
12.51
13.38
65.37
61.93
61.74
57.49
62.07
58.35
66.72
63.04
38.42
32.26
38.17
31.73
38.52
32.15
38.90
32.11
18.51
23.89
5.61
6.11
a
Calculated using B3LYP/6-311þG**.
When the CF3 group is replaced with methyl, the H-bond length
decreases for 0.01e0.03 A. As expected the presence of substituents
In enamino-ketones bearing aryl (1a, 2a) or methyl (7a, 8a) as
ꢀ
the olefinic substituent the PA value for the deprotonated nitrogen
atom is higher than for the protonated oxygen atom for
132e139 kcal/mol. According to Hammond’s postulate, the de-
of the same type in enones 3ae6a results in formation of shorter H-
bonds due to the electron withdrawing effect of the aryl substituent
at nitrogen that increases NeH group acidity. The shortest H-bond
corresponds to the highest value of Dn(NeH) for these conformers.
In contrast to aminoenones, imino-enols bearing a CF3-group
have a shorter intramolecular bond OeH/N than their methyl-
bearing analogs (Table 4). It is not surprising that this bond
crease of
D
PA for acidic and basic centers favors tautomeric tran-
sition.45,46 The value of
D
PA for aminoenones 3ae6a lowers up to
122e126 kcal/mol because of reduction of nitrogen atom PA with
the length of H-bond decrease and corresponds to a lower TS en-
ergy. Interestingly, the introduction of more electron withdrawing
CF3 instead of the methyl one into tautomeric form A decreases the
ꢀ
length increases up to 1.630e1.654 A when the N-methyl moiety is
replaced with N-phenyl. Low-frequency shift
n
(OeH) in imino-
PA of both heteroatoms in equal extent. As a result, the value of DPA
enols significantly exceeds shift (NeH) in aminoenones and cor-
n
is not changed. Similar relations are observed for imino-enols C.
However, despite the shortest H-bond in trifluoromethylated con-
responds to formation of a stronger H-bond. The greatest shift
Dn(OeH) (1310 cmꢀ1) is observed in conformer 7c, which has the
former 7c,
DPA values for its nitrogen and oxygen atoms as well as
ꢀ
shortest H-bond (1.568 A).
in methyl substituted conformer 8c are the highest (134.05 and
Table 4
Bond distance NeH/O (dH/N), frequency shift Dn(OeH) and second-order perturbation energy E(2) for orbital interactions in syn-conformers of imino-enols 1ce8ca
Dn(OH), cmꢀ1
E
(2), kcal/mol
ꢀ
Entry
Molecule
dH/N, A
nN/s
*
OeH
nO/
p*
]
C
nN/p*C]C(Ar)
pC ] /p*C]N
a Cb
Ca
b
1
2
3
4
5
6
7
8
1c
2c
3c
4c
5c
6c
7c
8c
1.578
1.611
1.630
1.643
1.637
1.654
1.568
1.595
1236
1141
1043
962
1032
977
db
54.38
53.78
53.99
53.74
52.37
52.36
55.52
54.64
20.83
25.45
20.74
25.60
20.60
25.67
21.85
26.48
41.21
37.53
35.41
36.74
33.99
48.68
43.36
10.52
11.46
8.34
10.31
1310
1202
a
Calculated using B3LYP/6-311þG**.
High polarization of OeH bond.
b
Enamino-ketone tautomeric form 1ae8a is more stable by
4.4e8.5 kcal/mol (according to B3LYP/6-311þG(d,p)) and by
1.2e6.5 kcal/mol (according to MP2/6-311þG(d,p)//B3LYP/6-
311þG(d,p) and MP2/6-31G(d,p)) (Table 5). In the case of tri-
fluoromethylated aminoenones this difference is higher. At the
same time it is lower for molecules 3 and 5, which contain a phenyl
substituent at nitrogen atom and increases a tautomeric transition
Table 5
Relative total energy
tautomeric transition
states (TS)
D
D
E (kcal/mol) for tautomers 1ae8a and 1ce8c, free energy for
G
# (kcal/mol) and bond distance dN/H and dO/H in transition
probability. Transition state (TS) energy
(D
G#) for tri-
Entry Molecule
ꢀ
D
E (ZPE)a
ꢀ
D
Eb
ꢀD
Ec TSc
d(N/H), A d(O/H), A
fluoromethylated molecules is higher than for non-fluorinated
ones but decreases for compounds 3 and 5 and therefore corre-
sponds to a lesser distance for N/H and to a greater distance for
D
G#
ꢀ
ꢀ
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
8.30
6.69
6.40
4.55
6.44
4.43
8.48
6.72
6.09
4.42
3.33
1.75
2.90
1.23
6.06
4.50
6.28
5.14
4.11
3.02
3.52
2.29
6.50
5.30
1.311
dd
1.160
dd
7.18
dd
O/H in transition state. Both D DE parameters decrease with
G# and
1.281
1.261
1.279
1.256
1.312
1.285
1.184
1.200
1.184
1.203
1.157
1.177
5.73
2.33
5.01
4.58
7.29
6.74
the replacement of the CF3-substituent with methyl and are the
lowest for compound 4 (2.33 kcal/mol). The length of the H-bond in
its enamino-ketone 4a form is the least and serves as a criterion for
the easiest tautomeric transformation A/C.10
Proton affinity (PA) of oxygen and nitrogen atoms in syn-con-
formers of both tautomers defines the strength of intramolecular
hydrogen bonds and capacity of molecules for tautomeric trans-
formation (Table 6).
a
b
c
Calculated using B3LYP/6-311þG**,
DE corrected by zero-point energy.
Calculated using MP2/6-311þG**//B3LYP/6-311þG**.
Calculated using MP2/6-31G**.
Tautomer 2a is formed.
d
Please cite this article in press as: Chipanina, N.N.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2013.12.061

N.N. Chipanina et al. / Tetrahedron xxx (2014) 1e7
5
Table 6
Total energy (Et) for syn-conformers of enamino-ketones 1ae8a and imino-enols 1ce8c, proton affinity (PA)a of corresponding nitrogen and oxygen
Entry
Molecule
ꢀEt (ZPE)b a.u.
PA kcal/mol
D
PAc
Molecule
ꢀEt (ZPE)b a.u.
PA kcal/mol
D
PAd
1
2
3
4
5
6
7
8
1a, Nꢀ
854.198303
855.094920
556.337841
557.277492
854.215882
855.096914
556.357400
557.280367
909.580203
910.460788
611.722004
612.642926
662.466999
663.363118
364.604771
365.548077
347.28
215.35
361.24
228.39
339.49
213.35
352.66
226.51
337.47
215.10
350.32
227.56
350.76
211.56
365.60
226.33
131.93
132.85
126.14
126.15
122.37
122.76
139.20
139.27
1c, Oꢀ
854.198302
855.079188
556.337841
557.263357
854.215882
855.079825
556.357384
557.265181
909.580203
910.441404
611.722004
612.626310
662.466999
663.344297
364.604771
365.531188
338.98
213.78
354.56
226.20
333.10
209.03
348.11
221.53
331.03
209.37
345.89
221.57
342.28
208.23
358.88
222.45
125.20
128.36
124.07
126.58
121.66
124.32
134.05
136.43
1a, OHþ
2a, Nꢀ
1c, NHþ
2c, Oꢀ
2a, OHþ
3a, Nꢀ
2c, NHþ
3c, Oꢀ
3a, OHþ
4a, Nꢀ
3c, NHþ
4c, Oꢀ
4a, OHþ
5a, Nꢀ
4c, NHþ
5c, Oꢀ
9
10
11
12
13
14
15
16
5a, OHþ
6a, Nꢀ
5c, NHþ
6c, Oꢀ
6a, OHþ
7a, Nꢀ
6c, NHþ
7c, Oꢀ
7a, OHþ
8a, Nꢀ
7c, NHþ
8c, Oꢀ
8a, OHþ
8c, NHþ
a
Calculated using B3LYP/6-311þG** as energy of protonation and deprotonation of molecules.
b
c
Total energy corrected by zero-point energy.
D
PA¼PA(1ae8a), NꢀꢀPA(1ae8a), OHþ.
d
D
PA¼PA(1ce8c), OꢀꢀPA(1ce8c), NHþ.
136.43 kcal/mol). They correspond to the highest TS energy values
(Table 5). The lowest PA value (121.66 kcal/mol) refers to con-
former 5c having the most acidic OeH and basic C]N moieties.
In the case of imino-enols 1ce8c the value E(2) for the
D
nN/s*
*
orbital interaction exceeds significantly the energy of
interaction in enamino-ketones 1ae8a (Table 4). As in
OeH
nO/s
NeH
the amino-ketone form it varies in accordance with H-bond length
and its highest value (48.68 kcal/mol) corresponds to molecule 7c
having the shortest bond OH/N. Moreover, E(2) values increase if
the hydroxyl proton becomes more acidic (in the case of CF3-
enones). On the contrary, the presence of the NeAr moiety in
molecules 3ce6c results in a decreasing of stability of these con-
formers due to weakening of the H-bonds (Table 2). In this case, the
2.3. NBO Analysis
Donoreacceptor interactions of lone electronic pairs (LEP) of
heteroatoms and double bonds in the studied molecules were es-
timated with the NBO method within the limits of second-order
perturbation theory. The energy of electron delocalization E(2)
reflecting interactions between the oxygen LEP and antibonding
energy of nN/p*C]C(Ar) interaction (8e11 kcal/mol) is less de-
pendent on the effect of the substituent in the benzene ring due to
interaction energy decreasing for imino-enols 5c and 6c (up to
27.99 and 26.49 kcal/mol, respectively) in comparison with amino-
enones 5a and 6a (32.03 and 30.62 kcal/mol, respectively). The
higher stability of syn-conformers of imino-enols 1c and 7c (Table
2) bearing a trifluoromethyl substituent refers to the presence of
strong H-bonds in these molecules. But in the case of the phenyl
substituent on nitrogen, the less stability of conformers 3c and 5c in
comparison with their methyl bearing analogs 4c and 6c (Table 2,
entries 5, 7, 9, 11) does not correspond to the strength of the H-
bonds. Therefore, the stabilization of conformers 4c and 6c is
s
*-orbital of bond NeH nO/s*NeH was evaluated (Tables 3 and 4).
In fact, as evident from Table 3, for aminoenones 1ae8a there is
a close relationship between E(2) and the length H-bond values. The
biggest values of the energy were obtained for aminoenones 4a and
6a (Table 3, entries 4, 6), which are stabilized by a strong hydrogen
bond, while this parameter is the smallest for aminoenones 1a and
7a bearing the longest NH/O distance (Table 3, entry 1, 7). It ap-
pears that a high value of E(2) for aminoenone 4a might be
explained by the influence of the N-phenylamino moiety. Indeed, in
this case the electron withdrawing effect of an aryl substituent is
reflected in energy of the nitrogen LEP interaction with antibonding
caused mainly by the interaction energy pC
] /p*C]N, which is
p
*-orbital of benzene ring nN/p*C]C(Ar). Its values are signifi-
a
Cb
higher for the methyl substituent (Table 4).
cantly higher for enones 3a and 4a (18.51 and 23.89 kcal/mol) than
for their analogs 5a and 6a (5.61 and 6.11 kcal/mol) bearing sub-
stituent NH2 in the benzene ring.
The presence of the CF3-group weakens this interaction as well
but to a less extent. Conjugation in cycles formed with H-bonds is
characterized by an energy of interaction between the nitrogen LEP
2.4. FTIR spectra
Aminoenones 9 and 10 are analogs of model compounds 1 and 5
used in calculations where substituents i-Pr and Hex were replaced
with a methyl group for simplicity. In the solid state (IR spectra
data) and in CDCl3 solution (NMR data) these compounds have an
and antibonding
nN/ b and an energy of interaction between the bonding
orbital of double bond and the carbonyl group antibonding
bital pC *C]O. Higher energy values should correspond to
p*-orbital of the ethylene double bond
p*
]
C
p-
Ca
p*-or-
] /
p
enamino-ketone structure. The stretching vibration bands n(NeH)
a
Cb
simultaneous increase of oxygen atom basicity and nitrogen atom
acidity and therefore to H-bond strength increase. However, de-
spite the energy increase no changes in hydrogen bond strength is
observed. It is due to oxygen atom PA reduction (s.o.) because of the
electron withdrawing effect of the trifluoromethyl substituent. As
a result, there is no any formation energy dependence of amino-
(3200e3250 cmꢀ1) of solid substances are weak and broad. In the
spectra of their diluted solutions (CCl4 or cyclohexane) these bands
remain weak but have clear peaks (3205 (9) and 3184 cmꢀ1 (10),
respectively) and refer to NeH groups participating in forming
strong intramolecular H-bonds. This type of hydrogen bond is
discussed and explained by either resonance assistance47 or de-
enone syn-conformers (DE) on the substituent nature (Table 1).
localization of charges.48 A lower frequency band
n(NeH) in spec-
Symbate E and H-bond strength change with the replacement of
D
trum of the compound 10 indicates a higher strength of its H-bond
as compared with compound 9. This result agrees with a calculated
strength of hydrogen bond in model aminoenones 5a and 1a
(Table 3).
the methyl group with the CF3-group in molecule 7a only with the
absence of phenyl substituent, which influences the electronic
distribution in the cycle.
Please cite this article in press as: Chipanina, N.N.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2013.12.061

6
N.N. Chipanina et al. / Tetrahedron xxx (2014) 1e7
It is well known that the oxygen of the carbonyl group is the
solvents were dried by standard procedures and freshly distilled
prior to use.
only protonation center in pushepull aminoenones.32,49 Consider-
ing that the strength of the H-bond depends on the properties of
the basic center, we estimated the relative basicity of compounds 9
and 10. To this end phenol was used as standard proton donor in
CCl4 solutions.50 The relative basicity was evaluated with the low-
frequency shift Dn(OeH) of its associated hydroxyl group. The
Dn(OeH) for compounds 9 (167 cmꢀ1) and 10 (190 cmꢀ1) showed
that the latter has a stronger intramolecular H-bond. The second
peak Dn(OeH) (260 cmꢀ1) in the case of 10 refers to the formation
of a hydrogen bond between PhOH and free NH2 group. It should be
noted that when the proton donor was added, compounds 9 and 10
underwent easy tautomeric transformation into the imino-enol
form.23,25 The appearance of a shoulder at 3300e3320 cmꢀ1 on
4.2. General procedure for preparation of aminoenones 9e11
A mixture of the appropriate enone 12 (1 mmol) and amine
(1.0 mmol) in benzene (2 mL) was stirred at room temperature for
3 h. Volatiles were evaporated in vacuo, the residue was pure target
adduct (9 and 11) or purified (in the case of 10) by column chro-
matography [silica gel, ether/hexane (2:1)]. The following amino-
enones were obtained by this method.
4.2.1. (Z)-1,1,1-Trifluoro-4-isopropylamino-4-phenylbut-3-en-2-one
9. Light yellow solid (236 mg, 92% 254 mg, 81% yield): mp 33 ꢁC; 1H
NMR (CDCl3): 1.19, 1.21 (s, 6H, 2CH3); 3.60e3.78 (m, 1H, NCH); 5.31
(s, 1H, CH]); 7.22e7.50 (m, 5H, Ph); 11.11 (s, 1H, NH). 13C NMR
(CDCl3): 23.9 ((CH3)2); 47.2 (NCH2); 90.0 (CH]); 116.4 (q, J¼292.6,
CF3); 127.1, 128.9, 130.4, 134.3 (Ph); 169.7 (NC]); 175.8 (q, J¼32.6,
the low-frequency wing of the n(OeH) band can serve as a sign of
such isomerization. Its value Dn(OH) (280e300 cmꢀ1) characterizes
the interaction between phenol and the nitrogen atom of the C]N
group of the corresponding imino-enols. The decrease in temper-
ature of the solutions results in shoulder disappearance and the
bands of H-complexes of phenol with more stable tautomer A are
observed. The appearance of the second tautomer of 10 in the
presence of the proton donor confirms our scheme on azepine
formation through the same transition state as the tautomerization
A/C.
C]O). 19F NMR (CDCl3): ꢀ76.7. 15N NMR (CDCl3): ꢀ235.7. IR (
n,
cmꢀ1) (CDCl3): 1142, 1195, 1216 (CeF), 1571, 1583, 1607 (C]C, Ph,
C]O), 3205 (NeH). Calcd for C13H14F3NO: C 60.70; H 5.49; N 5.44.
Found: C 60.81; H 5.68; N 5.27. MS, m/z (%): 257 (48, Mþ); 188 (100),
146 (70), 104 (73).
4.2.2. (Z)-4-[(2-Aminophenyl)amino]-1,1,1-trifluorodec-3-en-2-one
10. Light yellow solid (254 mg, 81% yield): mp 73 ꢁC; 1H NMR
(CDCl3): 0.81 (t, J¼7, 3H, CH3); 1.05e1.25 (m, 6H, (CH2)3); 1.40e1.55
(m, 2H, CH2); 2.25e2.35 (m, 2H, CH2); 3.79 (br s, 2H, NH2); 5.56 (s,
1H, CH]); 6.70e7.15 (m, 4H, C6H4); 12.07 (br s, 1H, NH). 13C NMR
(CDCl3): 14.0 (CH3); 22.4, 27.8, 28.9, 31.2, 32.4 (CH2); 89.5 (CH]);
116.4 (q, J¼288.4, CF3); 116.3, 118.7, 128.0, 129.5 (CHAr); 122.4
3. Conclusion
The hydrogen bonding in the pushepull CF3-aminoenones
substituted by various electron donating/withdrawing groups at
nitrogen and olefinic carbon atoms was successfully predicted by
quantum chemical calculations using B3LYP/6-311þG(d,p), MP2/6-
311þG(d,p)//B3LYP/6-311þG(d,p), MP2/6-31G(d,p) levels of theory
and NBO analysis. It was shown that syn-conformers of these
compounds are more stable by 9e11 kcal/mol than anti-conformers
regardless of the nature of the substituents at the nitrogen or
double bond. In contrast, the energy of formation of syn-con-
formers of the imino-enol tautomeric form depends on the amino
moiety and decreases if a ArNH group is present. In all cases the
barrier of tautomeric equilibrium is higher for trifluoromethylated
aminoenones as compared with non-fluorinated analogs due to the
electron withdrawing properties of CF3 group and decreases for N-
aryl substituted derivatives. As a consequence, CF3-aminoenones
bearing EWG at nitrogen can undergo a very easy condensation
leading to nitrogen heterocycles. The conformer stability is
explained with the superposition of orbital interaction of the het-
eroatom lone-pairs and double bonds. The theoretical study of
hydrogen bonding in pushepull CF3-aminoenones showed a good
agreement with experimental results.
(CeNH); 142.5 (CeNH2); 175.1 (NC]); 177.0 (q, J¼33.0, C]O). 19
F
NMR (CDCl3): ꢀ76.4. IR (KBr,
n
, cmꢀ1): 1124, 1136, 1182 (CeF), 1587,
1609, 1629 (C]C, Ph, C]O), 3356, 3456 (NeH). Calcd for
C
16H21F3N2O: C 61.13; H 6.73; N 8.91. Found: C 60.82; H 6.89; N 8.73.
MS, m/z (%): 239 (15, MþꢀCF3); 226 (100).
4.2.3. (E)-1,1,1-Trifluoro4-phenyl-4-pyrrolidin-1-ylbut-3-en-2-one
11. Light yellow solid (259 mg, 96% yield): mp 52 ꢁC; 1H NMR
(CDCl3): 1.80e1.95 (m, 2H, CH2); 2.05e2.15 (m, 2H, CH2); 3.15e3.25
(m, 2H, NCH2); 3.45e3.55 (m, 2H, NCH2); 5.34 (s, 1H, CH]);
7.25e7.55 (m, 5H, Ph). 13C NMR (CDCl3): 24.7, 25.0 ((CH2)2); 49.1,
50.6 (N(CH2)2); 87.4 (CH]); 117.9 (q, J¼293.0, CF3); 126.5, 128.2,
128.7, 136.4 (Ph); 165.5 (NeC]); 173.9 (q, J¼32.4, C]O). 19F NMR
(CDCl3): ꢀ76.9. 15N NMR (CDCl3): ꢀ249.3. IR (KBr,
n
, cmꢀ1): 1139,
1150, 1192 (CeF), 1530 (C]C), 1579 (Ph), 1657 (C]O). Calcd for
C
14H14F3NO: C 62.45; H 5.24; N 5.20, F 21.17. Found: C 62.81; H 4.96;
N 5.26, F 20.98. MS, m/z (%): 270 (48, Mþþ1); 200 (100).
4. Experimental section
4.2.4. 2-Hexyl-4-trifluoromethyl-3H-benzo[b][1.4]-diazepine 13. Oil;
1H NMR (CDCl3): 0.90 (t, J¼7.0, 3H, CH3); 1.20e1.45 (m, 6H, CH2);
1.70e1.80 (m, 2H, CH2); 2.55e1.65 (m, 2H, CH2); 2.96 (s, 2H, CH2);
7.30e7.55 (m, 4H, Ph). 13C NMR (CDCl3): 14.2 (CH3); 22.7, 26.2, 29.0,
31.7, 40.4, 35.7 (CH2); 119.2 (q, J¼276.8, CF3); 125.6, 127.6, 128.3,
129.1, 137.2, 141.2 (C6H4); 144.3 (q, J¼35.7, eC]N); 161.3 (eC]N).
4.1. General
1H and 13C NMR spectra were recorded with a Bruker AVANCE
400 MHz spectrometer with solutions in CDCl3. Chemical shifts (d)
in parts per million are reported with use of the residual chloroform
(7.25 for 1H and 77.20 for 13C) as internal references. The coupling
constants (J) are given in Hertz (Hz). The IR spectra of solid com-
pounds were taken on an ATR/FTIR Varian 3100 spectrometer. The
GC/MS analyses were performed with a Shimadzu GCMS-QP5050A
instrument (EI, 70 eV). The spectra of the H-bonded complexes
with phenol were registered on a FTIR Varian 3100 spectrometer in
CCl4 solution with concentration of phenol of 0.02 mol/l and con-
centration of the substrate of 0.1 mol/l. The silica gel used for flash
chromatography was 230e400 mesh. All reagents were of reagent
grade and were either used as such or distilled prior to use. All the
19F NMR (CDCl3): ꢀ71.5. 15N NMR (CDCl3): ꢀ71.0, ꢀ56.4. IR (film,
n,
cmꢀ1): 1116, 1130, 1143 (CeF), 1640 (C]N), 1598 (Ar). Calcd for
C
16H19F3N2: C 64.85; H 6.46; N 9.45. Found: C 64.71; H 6.11; N 9.04.
MS, m/z (%): 296 (2, Mþ), 239 (19), 226 (100).
4.3. Computational details
Calculations were performed by the B3LYP/6-311þG(d,p), MP2/
6-311þG(d,p)//B3LYP/6-311þG(d,p), and MP2/6-31G(d,p) methods
as implemented in the Gaussian03 program package.51 All calcu-
lated structures correspond to minima on the potential energy
Please cite this article in press as: Chipanina, N.N.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2013.12.061

N.N. Chipanina et al. / Tetrahedron xxx (2014) 1e7
7
24. Pyta, K.; Przybylski, P.; Schilf, W.; Ko1odziej, B.; Szady-Che1mieniecka, A.; Grech,
E.; Brzezinski, B. J. Mol. Struct. 2010, 967, 140e146.
surface (PES) as proved by positive eigenvalues of the corre-
sponding Hessian matrices. The DFT energies were calculated with
the ZPE correction. The NBO analysis52,53 as implemented into the
Gaussian03 package was performed using the 6-311þG** basis set
on the previously DFT optimized structures. The search and local-
ization of transition states were performed with the synchronous
transit approach QST2.54
25. Alkorta, I.; Elguero, J. Theor. Chem. Acc. 2011, 128, 563e567.
ꢁ
26. Hidalgo, A.; Jimenez, L. P. A.; Ramos, L. A.; Mroginski, M. A.; Jios, J. L.; Ulic, S. E.;
Echeverria, G. A.; Piro, O. E.; Castellano, E. J. Phys. Chem. A 2012, 116, 1110e1118.
27. Wojcik, J.; Kamienska-Trela, K.; Pecul, M.; Bartoszak-Adamska, E.; Vdovienko, S.
I.; Gerus, I. I. ChemPhysChem 2004, 5, 209e215.
28. Vdovenko, S. I.; Vdovenko, I. I.; Kukhar, V. P. 2010, 52, 144e153.
29. Vdovenko, S. I.; Vdovenko, I. I.; Fedorenko, H. A.; Kukhar, V. P. Spectrochim. Acta,
Part A 2013, 103, 368e377.
30. Vdovenko, S. I.; Gerus, I. I.; Fedorenko, H. A.; Kukhar, V. P. ISRN Spectrosc. 2013,
13 640896, 13p.
31. Vdovenko, S. I.; Gerus, I. I.; Fedorenko, H. A. Spectrochim. Acta, Part A 2009, 74A,
1010e1015.
32. Vdovenko, S. I.; Gerus, I. I.; Fedorenko, H. A.; Kukhar, V. P. J. Mol. Struct. 2010,
977, 237e242.
33. Vdovenko, S. I.; Gerus, I. I.; Gorbunova, M. G. J. Chem. Soc., Perkin Trans. 2 1993,
559e562.
34. Fedorov, S. V.; Rulev, A. Y.; Chipanina, N. N.; Shulunova, A. M.; Nenajdenko, V.
G.; Balenkova, E. S.; Tyurin, D. A.; Turchaninov, V. K. Izv. Akad. Nauk, Ser. Khim.
2005, 102e106 (Russ.); (Engl. Transl.: Russ. Chem. Bull. 2005, 54, 103e107).
35. Kucklander, U. Enaminones as Synthones. In The Chemistry of Enamines; Rap-
poport, Z., Ed.; ; John Wiley & Sons: New York, NY, 1994; pp 523e636.
36. Bellamy, L. J. Advances in Infrared Group Frequencies; Methuen: London, UK,
1968; (Russ. Transl.: Bellamy, L. J. New Data on IR Spectra of Complex Mole-
cules, Mir: Moscow, 1971).
Acknowledgements
Authors thank Dr. Igor Ushakov for assistance with the NOESY
experiments. Authors also thank Prof. Valentin Nenajdenko (Mos-
cow State University) for the kind gift of the samples of ynones
12a,b. This work was supported by the Russian Foundation for the
Basic Research (Grant no 13-03-00063-a).
Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2013.12.061.
37. See, for example: Rulev, A. Y.; Mokov, A. S.; Krivdin, L. B.; Keiko, N. A.; Voronkov,
M. G. Magn. Reson. Chem. 1997, 35, 533e537 and references therein.
ꢁ
ꢁ
38. Chiara, J. L.; Gomez-Sanchez, A. NMR Spectra. In The Chemistry of Enamines;
Rappoport, Z., Ed.; ; John Wiley & Sons: New York, NY, 1994; pp 279e404.
39. Hamed, E. A.; Sharaf, S. M.; Abdel-Baky, S. A.; Ibrahim, M. F.; Youssef, A.-H. A. J.
Phys. Org. Chem. 1990, 3, 627e634.
References and notes
1. Filler, R.; Kobayashi, Y.; Yagupolski, L. M. Organofluorine Compounds in Medical
Chemistry and Biochemical Applications; Elsevier: Amsterdam, The Netherlands,
1993; pp 1e386.
40. Yakimovich, S. I. In Vopr. Phys. Org. Khim; Yakimovich, S. I., Zerova, I. V., Eds.; ;
LSU: Leningrad, Russia, 1980; pp 45e70.
2. Lyutenko, N. V.; Gerus, I. I.; Kacharov, A. D.; Kukhar, V. P. Tetrahedron 2003, 59,
1731e1738.
41. Rulev, A. Russ. Chem. Rev. 2002, 71, 195e221.
42. Fedorov, S. V.; Rulev, A. Y.; Chipanina, N. N.; Sherstyannikova, L. V.; Turchani-
nov, V. K. J. Mol. Struct. 2004, 697, 51e57.
43. Rulev, A. Y.; Zinchenko, S. V. Mendeleev Commun. 2001, 70e72.
44. Rulev, A. Y.; Mokov, A. S.; Voronkov, M. G. Mendeleev Commun. 1995, 53e55.
45. Chan, B.; Del Bene, J. E.; Elguero, J.; Radom, L. J. Phys. Chem. A 2005, 109,
5509e5517.
3. Fluorinated Heterocyclic Compounds: Synthesis, Chemistry, and Applications;
Petrov, V. A., Ed.; Wiley: New Jersey, NJ, 2009; pp 1e515.
4. Fluorinated Heterocycles; Gakh, A. A., Kirk, K. L., Eds.; ACS Symposium Series
1003; Oxford University/American Chemical Society: Washington, DC, 2009;
pp 1e384.
5. Nenajdenko, V. G.; Sanin, A. V.; Balenkova, E. S. Molecules 1997, 7, 186e232.
6. Druzhinin, S. V.; Balenkova, E. S.; Nenajdenko, V. G. Tetrahedron 2007, 63,
7753e7808.
7. Kumar, V.; Aggarwal, R.; Singh, S. P. Heterocycles 2008, 75, 2893e2929.
8. Nenajdenko, V. G.; Balenkova, E. S. Arkivoc 2011, i, 246e328.
9. Vdovenko, S. I.; Gerus, I. I.; Kukhar, V. P. J. Phys. Org. Chem. 2007, 20, 190e200.
10. Sobczyk, L.; Grabowski, S. J.; Krygowski, T. M. Chem. Rev. 2005, 105, 3513e3560.
46. Pross, A.; Radom, L. J. Am. Chem. Soc. 1981, 103, 6049e6053.
47. Bertolasi, V.; Gilli, P.; Ferretti, V.; Gilli, G.; Vaughan, K. New J. Chem. 1999, 23,
1261e1267.
ꢁ
48. Gora, R. W.; Maj, M.; Grabowski, S. J. Phys. Chem. Chem. Phys. 2013, 15,
2514e2522.
49. Greenhill, J. V. Chem. Soc. Rev. 1977, 6, 277e294.
50. Laurence, C.; Gal, J.-F. Lewis Basicity and Affinity Scales: Data and Measurement;
John Wiley & Sons: Chichester, UK, 2010.
ꢁ
ꢁ
ꢁ
11. Raczynska, E. D.; Kosinska, W.; Osmia1owski, B.; Gawinecki, R. Chem. Rev. 2005,
105, 3561e3612.
51. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;
Cheeseman, J. R.; Montgomery, J. A.; Vreven, T.; Kudin, K. N.; Burant, J. C.;
Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.;
Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.;
Toyota, K.; Fukuda, R.; Nasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.;
Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.;
Farkas, O.; Malik, D. K.; Rabuk, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J.
V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Lia-
shenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.;
Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision B.03;
Gaussian: Pittsburg, PA, 2003.
ꢁ
ꢁ
12. Raczynska, E. D.; Kolczynska, K.; Ste˛pniewski, T. M. J. Mol. Model. 2012, 18,
3523e3533.
13. Rybarczyk-Pirek, A. J.; Grabowski, S. J.; Malecka, M.; Nawrot-Modranka., J. J.
Phys. Chem. A 2002, 106, 11956e11962.
14. Kadkin, O. N.; Han, H.; Galyametdinov, Y. G. J. Organomet. Chem. 2007, 692,
5571e5582.
ꢁ
15. Dobosz, R.; Osmia1owski, B.; Gawinecki, R. Struct. Chem. 2010, 21, 1037e1041.
16. Raissi, H.; Jalbout, A. F.; Yoosefian, M.; Fazli, M.; Nowroozi, A.; Shahinin, M.; de
Leon, A. Int. J. Quantum Chem. 2010, 110, 821e830.
17. Sigalov, M. V.; Lemcoff, N. G.; Shainyan, B. A.; Chipanina, N. N.; Aksamentova, T.
N. Eur. J. Org. Chem. 2010, 2800e2811.
18. Sigalov, M. V.; Shainyan, B. A.; Chipanina, N. N.; Oznobikhina, L. P. J. Phys. Chem.
A 2013, http://dx.doi.org/10.1021/jp4072179
19. Itoh, K.; Okazaki, K.; Fujimoto, M. Aust. J. Chem. 2003, 56, 1209e1214.
20. Gilli, P.; Bertolasi, V.; Ferretti, V.; Gilli, G. J. Am. Chem. Soc. 2000, 122,
10405e10417.
21. Podolyan, Y.; Lipkowski, P.; Leszczynski, J. J. Mol. Struct. 2006, 792-793, 9e15.
22. Szyc, q.; Guo, J.; Yang, M.; Dreyer, J.; Tolstoy, P. M.; Nibbering, E. T. J.; Czarnik-
52. Weinhold, F.; Landis, C. R. Valency and Bonding: A Natural Bond Orbital Donor-
acceptor Perspective; Cambridge University: Cambridge, 2005.
53. Glendening, E. D.; Reed, A. E.; Carpenter, J. E.; Weinhold, F. NBO Version 3.1;
Gaussian: Pittsburg, PA, CT, 2003.
Matusewicz, B.; Elsaesser, T.; Limbach, H.-H. J. Phys. Chem.
7749e7760.
A 2010, 114,
54. Peng, C.; Ayala, P. Y.; Schlegal, H. B.; Frisch, M. J. J. Comput. Chem. 1996, 17,
49e56.
23. Tezer, N.; Karakus, N. J. Mol. Model. 2009, 15, 223e232.
Please cite this article in press as: Chipanina, N.N.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2013.12.061