Acylotropic tautomerism: XXXV. R?L-inversion of configuration of dipolar spyrocyclic and open-chain 2-arylaminotropone isomers

Article abstract of DOI:10.1023/A:1019619307779

R?L-Inversion of chiral spirocyclic and open-chain 2-arylaminotropone derivatives with varied heteroatom (O, S, N) has been studied. Kinetic relations holding in the R,L-permutation are discussed. Its mechanism includes formation and dissociation of spiro bonds and torsion stereodynamics.

Full text of DOI:10.1023/A:1019619307779

Russian Journal of Organic Chemistry, Vol. 38, No. 5, 2002, pp. 713 722. Translated from Zhurnal Organicheskoi Khimii, Vol. 38, No. 5, 2002,
pp. 751 759.
Original Russian Text Copyright
2002 by Olekhnovich, Budarina, Borodkin, Kurbatov, Vaslyaeva, Zhdanov.
Acylotropic Tautomerism: XXXV.* R L-Inversion
of Configuration of Dipolar Spyrocyclic and Open-Chain
2-Arylaminotropone Isomers
1
2
2
1
L. P. Olekhnovich , Z. N. Budarina , G. S. Borodkin , S. V. Kurbatov ,
1
1
G. S. Vaslyaeva , and Yu. A. Zhdanov
1
Rostov State University, ul. Zorge 7, Rostov-on-Don, 344090 Russia
2
Research Institute of Physical and Organic Chemistry, Rostov State University,
pr. Stachki 194/3, Rostov-on-Don, 344104 Russia
Received June 21, 2000
Abstract
R
L-Inversion of chiral spirocyclic and open-chain 2-arylaminotropone derivatives with varied
heteroatom (O, S, N) has been studied. Kinetic relations holding in the R,L-permutation are discussed. Its
mechanism includes formation and dissociation of spiro bonds and torsion stereodynamics.
Using the dynamic NMR technique, we recently
[2] revealed degenerate R L-inversion (Scheme 1)
of chiral spiro -complexes like Ia, which are stable
( 5.7 5.9 ppm; Fig. 1a). This indicates that -orbitals
of C5 and C6 do not participate in delocalization of
the negative charge and that the corresponding double
intermediates in intramolecular arylotropic tauto- bond is vinyl-like (structure A in Scheme 2). An ana-
merism Ib Ib [1, 3 5]. This process is analogous
to bimolecular nucleophilic substitution reactions at
the ipso-carbon atom (C*) of electron-deficient arenes
[6]. With the goal of studying kinetic features of the
logous C N fragment in 3,5-dinitropyridyl was
revealed [5] by X-ray analysis of spirocyclic com-
pound derived from 3,5-dinitropyridine and N,N -di-
methyl-2-amino-2,4,6-cycloheptatrieneimine (structure
B in Scheme 2).
R
L process we have synthesized a series of new
compounds II VII (see Experimental) containing
various nitroaryl fragments A D (Scheme 2) and
heteroatoms X (O, S, NR) in the aminotropone frag-
ment. Spirocyclic isomers a of compounds I VII
have zwitterionic structure due to delocalization of
the positive charge in the tropylium fragment, and
of the negative, over the nitroaryl moiety (Schemes 1
and 2). These isomers are insoluble in weakly polar
media, so that the corresponding NMR experiments
were carried out mainly with their solutions in
C6D5NO2 and DMSO-d6.
Figure 1b shows the evolution with temperature of
the AB quartet from the N-benzyl CH2 group of com-
pound VA, which can be regarded as diastereotopic
indicator of R,L-conversion [2, 7]. The kinetic and
activation parameters of the R,L-conversion for com-
pounds II VII were determined by computer simula-
tion of the shape of reference signals (Table 1). It is
seen that the R,L-conversion rate varies over a very
wide range, from extremely slow for compounds IID,
IVD, and VD to fairly fast for VID and VIIB. Let us
compare the data given in Table 1 for aminotropone
imine derivatives IIA VA, IIB, IID, IVD, and VD
with those of aminotropone VID and aminothio-
tropones VIIB VIID. First, spirocyclic compounds
IIA VA, IIB, IID, IVD, and VD, unlike their oxygen
and sulfur analogs (X = O, S) are characterized by
a high barrier to L R-inversion. Second, fusion of
a benzene ring to fragment A strongly suppresses
inversion (compounds IID, IVD, and VD; Table 1).
When their solutions were heated up to 180 200 C,
1
The H NMR spectra of spiro compounds IIA VA
are characterized by a considerable upfield shift of
the doublet 6 -H signal of the dinitroaryl fragment
____________
*
For communication XXXIV, see [1].
**
This study was financially supported by the Russian Founda-
tion for Basic Research (project no. 99-03-33496a) and
by the Program Universities of Russia. Basic Research
at Higher School in the Field of Natural Science and
Humanities (project no. 991440).
1
we observed in the H NMR spectra only uniform
1070-4280/02/3805-0713$27.00 2002 MAIK Nauka/Interperiodica

714
OLEKHNOVICH et al.
Scheme 1.
signal broadening and no collapse of the AB-quartet
from the CH2Ph group (Fig. 1c), which is typical of
the other compounds (Fig. 1b).
Table 1). However, in going from IID, IVD, and VD
to oxygen and sulfur analogs VID and VIID the rate
of the R,L-process increases very sharply, by a factor
of more than 1010 1013; Table 1). This means that
benzene ring fusion does not suppress R,L-conversion
of the tropone and thiotropone derivatives.
The presence of a methyl group in position 3 of
the 2,4,6-trinitrophenyl fragment (structure C in
Scheme 2) promotes torsions of the neighboring nitro
groups (in positions 2 and 4); therefore, the degree of
their participation in -delocalization of the negative
An analogous pattern is observed on variation of
substituent on the nitrogen atom in II V. The R L-
conversion of IIA VA is strongly accelerated (by
more than two orders of magnitude; Table 1) on
replacement of N-isopropyl or N-benzyl group by
bulkier N-tert-butyl group. The same replacement in
the series IID, IVD, and VD does not reduce the
activation threshold for R,L-dynamics (Fig. 1c,
Scheme 2.
II, R = R = CH2Ph; III, R = R = i-Pr; IV, R = CH2Ph, R = i-Pr; V, R = CH2Ph, R = t-Bu; VI, VII, R = CH2Ph.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 5 2002

ACYLOTROPIC TAUTOMERISM: XXXV.
715
Table 1. Kinetic and activation parameters of the R L-permutation of arylaminotropone derivatives II IV
Compound
no.
G298
kJ/mol
,
Temperature
range, K
1
1
Solvent
k
298, s
H , kJ/mol
S , J mol 1 K
9
IID
C6D5NO2
DMSO-d6
C6D5NO2
DMSO-d6
C6D5NO2
C6D5NO2
DMSO-d6
C6D5NO2
<10
<10
<10
<10
<10
>125.4
>125.4
>125.4
>125.4
>125.4
77.58
87.36
82.18
88.41
82.14
97.27
86.57
69.89
83.14
88.32
62.87
69.85
55.26
56.05
51.21
61.15
62.53
313 473
313 453
313 473
313 453
313 473
313 433
313 433
313 353
353 433
313 373
373 433
323 433
293 413
323 433
323 433
293 373
293 393
213 313
213 303
223 313
278 338
293 363
9
9
9
9
IVD
VD
IIA
1
4.46 10
2.80 10
2.29 10
1.83 10
2.30 10
5.08 10
3.86 10
3.29
45.57 0.59
94.47 0.46
82.72 0.46
122.89 0.54
82.14 0.50
157.29 0.54
87.19 0.42
72.65 0.46
43.47 0.50
52.33 0.46
77.46 0.75
80.76 0.88
46.11 1.42
48.11 0.30
51.21 0.96
61.15 0.67
55.97 0.59
104.08 1.38
23.83 1.17
11.88 1.30
115.66 1.42
0.00 1.12
3
2
3
2
5
3
IIIA
IVA
C6D5NO2
201.48 1.13
2.09 1.05
DMSO-d6
C6D5NO2
C6D5NO2
DMSO-d6
C6D5NO2
DMSO-d6
CDCl3
(CD3)2CO
CD3CN
C6D5NO2
DMSO-d6
VA
IIB
9.20 1.09
2
2.0 10
1.1 10
56.3
131.25 1.05
104.50 1.05
48.91 1.92
36.66 2.05
29.51 3.43
26.92 3.26
0.00 2.01
2
VIID
VID
3.34
1.2 103
9.2 102
VIIC
VIIB
6.29 103
1.13 102
0.00 1.71
23.41 1.34
64.5
charge decreases, and stabilization of the spiro isomer
of VIIC (a) weakens. Obviously, this is the reason
why the R,L conversion of VIIC is characterized by
the highest rate (Table 1).
The R L process includes three steps, two of
which require some energy (Scheme 1): dissociation
of the C* X bond (X = N, O, S), which accompanies
the transition from spiro isomers a or a to open-chain
isomers b or b ; proper R,L-conversion b-R b-L
(b -L b -R ) of isomers b via torsions about the
arene X (T1) and tropone X bonds (T2); and cycliza-
tion to give inverted spiro structure.
In order to interpret the observed kinetic relations
in the R,L-conversion of compounds II VII, the
following questions should be answered: (1) What is
the geometry of the five-membered reactive entity
in the primary elementary step (disociation of the
C* X bond): is it planar (P) or envelope-like (E)?
(2) What bond, C* N, C* O, or C* S in oxygen
and sulfur derivatives is cleaved first? (3) Does fusion
of a benzene ring affect the strength of the spiro
bonds? (4) What are the contributions of spiro bond
dissociation and torsions T1 and T2 to the overall
R,L-inversion barrier?
Scheme 3 shows that the primary act, cleavage of
the C* X bond, requires either planar (P) or envelope
(Ea, Es; the superscript s stands for syn, and a, for
anti) geometry of the five-membered entity. Con-
formation Ea is possible for spiro compounds IIA
VIIA and IIB, whereas conformation Es for all com-
pounds II VII is unfavorable because of steric repul-
sion between the tropylium ring and NO2 group in the
ortho-position of the arene moiety. For compounds
having a dinitronaphthalene fragment (D), Ea con-
former is also unfavorable (Scheme 3). Clearly, if
cleavage of the spiro bond is possible only when the
reactive entity has envelope-like geometry (E), R,L-
enantiomerism of IID, IVD, and VD would be sup-
pressed. If planar geometry is necessary (Schemes 1
and 3), other, less obvious reasons for suppression of
the R,L-conversion should be sought for.
Using the PM3 method, we calculated the heats of
formation (Hf) of model anionic -complexes VIIIa
and IXa and transition states b for their dissociation
(Scheme 4). The difference between Hf(a) and Hf(b)
( Hf in Table 2) corresponds to the energy of activa-
tion for dissociation of the C* X bond. Table 3 con-
tains Hf values for spirocyclic and open-chain isomers
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 5 2002

716
OLEKHNOVICH et al.
(a)
(b)
(c)
1
Fig. 1. (a) H NMR spectrum (25 C) of spiro isomer VA and temperature evolution of the AB-quartet from the N-benzyl CH2
group of (b) compound VA and (c) VD.
of compounds II VII (Schemes 1 and 5) and activa-
tion barriers Hf to cleavage of the C* X bond (in
the calculations, NCH2Ph and NPr-i fragments were
replaced by NMe group).
The calculated activation barriers (Table 2) to
C* X bond cleavage in anionic -complexes VIII
and IX are much higher than for spiro compounds
II VII (Table 3). This difference is determined by
the nature of the leaving group X. In compounds
VIIIb and IXb (Scheme 4) X is an anion (NH2, HO ,
HS ); however, X is a neutral species in structures b
of II IV, where it goes away as a part of imino, keto,
or thioketone group (Scheme 1). The activation energy
Hf of the elementary step VIIIa, Xa VIIIb, IXb
(Scheme 4) decreases in the series X = N > O >> S
(Table 2). Compounds II VII give rise to the reverse
Hf series: S N > O (Table 3). Obviously, R,L-con-
version in the aminotropone derivatives involves
preferentially cleavage of the C* O bond, and in the
aminothiotropone compounds, the C* N bond.
According to the calculations of transition states
for C* X bond cleavage, the five-membered reactive
entity in II VII is planar (Scheme 5); therefore, the
difference in size of the arene fragments could not
affect this process. Also, fusion of a benzene ring in
anionic -complexes VIIIa and IXa does not change
the activation barriers Hf to C* X bond cleavage
(Table 2); as concerns compounds II VII, Hf
Scheme 3.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 5 2002

ACYLOTROPIC TAUTOMERISM: XXXV.
717
Scheme 4.
VIII, X = NH, Z = CH; X = O, Z = CH; X = S, Z = CH; X = NH, Z = N; X = O,
Z = N; X = S, Z = N; IX, X = NH, O, S.
Scheme 5.
increases by only 6.3 8.4 kJ/mol (Table 3). Such
a gain is clearly insufficient to suppress R,L-conver-
sion so strongly as it is observed experimentally
Benzene ring fusion increases the activation barrier
to R,L-conversion for compound VID by 4.2 kJ/mol
(Table 1), and for its thio analog VIID, by 12.5
20.9 kJ/mol relative to trinitro compound VIIC.
However, unlike aryl(hetaryl) aminotropone deriva-
tives VIA and VIB [8] and compound VIIC, naphtha-
lene derivatives VID and VIID give rise to ring chain
isomerism a b; spiro isomer a of VIID prevails
in the equilibrium mixture (Fig. 2). Obviously, energy
consumption for cleavage of the C* N bond in spiro
isomers rather than hindrance to T1 torsion of the
naphthalene system is the main factor determining
increased activation barrier to R,L-conversion in
(
G
42 kJ/mol; Fig. 1c, Table 1).
Now let us consider the stereodynamics of torsions
T1 and T2 which are in fact responsible for the R,L-
conversion (Scheme 1) following the C* X bond
cleavage. We previously found [8] that N-aryl(hetaryl)
derivatives of aminotropones like VIA and VIB do
not form spiro isomers a, but their open-chain isomers
b are R ,L -chiral (Schemes 1 and 5), and their
inversion through conjugate T1,T2 torsions are charac-
terized by activation barriers of 45.1 to 46.8 kJ/mol.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 5 2002

718
OLEKHNOVICH et al.
Table 2. Calculated (PM3) activation energies for C* X bond cleavage in model anionic -complexes VIII and IX
Activation energy Ea ( Hf, kJ/mol) for cleavage of the C* X bond
-Complex
no.
NN (X = N)
ON (X = O)
ON (X = N)
SN (X = S)
SN (X = N)
VIIIa
VIIIb
IX
270.03
273.79
261.25
227.81
249.55
228.23
431.79
441.41
428.45
75.24
91.12
88.62
390.83
396.68
387.90
a
X = NH, Z = CH; X = S, Z = CH.
X = NH, Z = N; X = S; Z = N.
b
Table 3. Calculated (PM3) heats of formation (Hf, kJ/mol) of spiro -complexes IIa VIIa and open-chain conformers
IIb VIIb and energies of transition states ( Hf, kJ/mol) for C* X bond cleavagea
Compound no.
NO
Hf
NS
Hf
NN
Hf
VIA-a, VIIA-a, IIA-a
VIA-b, VIIA-b, IIA-b
212.55
(N) 235.25
(O) 234.50
Fo(N) 203.78
Fo(O) 165.57
290.72
(N) 324.41
(O) 320.94
Fo(N) 262.75
Fof(O) 165.57
204.44
420.84
(N) 446.22
(S) 475.52
Fo(N) 395.22
Ff(N) 405.21
510.63
334.15
(N) 387.74
Fo 203.78
Ff 165.57
22.70
21.95
25.33
53.73
53.59
VID-a, VIID-a, IID-a
VID-b, VIID-b, IID-b
423.56
(N) 480.11
470.79
8.06
7.23
(N) 540.89
(S) 571.11
(N) 510.04
30.26
61.32
56.56
70.06
Fof 478.86
VIB-a, VIIB-a, IIB-a
VIB-b, VIIB-b, IIB-b
428.91
(N) 470.84
340.54
(N) 410.64
Fo 369.85
Ff 384.43
(N) 249.84
(O) 240.31
Fo(O) 178.07
45.39
35.86
42.34
73.65
(S) 502.56
Fo(N) 431.00
Fo(S) 483.50
a
The X atom is given in parentheses.
these compounds. Therefore, the energy of activation
for T1, 2-torsions may be assumed to range from 46
to 54 kJ/mol for all compounds I VII, both those for
which the equilibrium a b is displaced completely
toward open-chain isomers b [8] and those stable in
spiro form a [2].
Nevertheless, the state of ring chain equilibrium
b (Scheme 1) for each compound of the series
II VII can be estimated by comparing the calculated
Hf values for spirocyclic isomer a and open-chain
conformers b (Scheme 5) corresponding to global or
local minima on the potential energy surface.
a
It is still impossible to estimate in terms of
the PM3 procedure the energy of activation of T1 and
T2 torsions because of their concerted conjugation [8]
in isomers b of II VII. Unlike Hessians of transition
states for a single elementary step, cleavage of spiro-
C* X bonds, Hessians of transition conformers for
open-chain isomers b are characterized by two vibra-
As follows from the data in Table 3, open-chain
isomers b of compounds II VII having a 2,4-dinitro-
phenyl (A) and 3,5-dinitropyridyl moieties (B)
(Scheme 2) exist mainly as flagpole (F) conformations
with an orthogonal (Fo) or frontal (Ff) mutual orienta-
tion of the arene and tropone moieties (Scheme 5).
Fusion of a benzene ring makes F-conformers un-
favorable: hybrid Fof-conformation of isomer b is
still feasible for compound VID, but all these (Fo, Ff,
and Fof) are thermodynamically unfavorable (Table 3)
for open-chain isomers of IID VD and VIIG. The
tions with negative frequencies corresponding to T1, 2
-
torsions. However, the known algorithms [9] allow
energy minimization of transition states to be per-
formed for only one elementary act (either T1 or T2).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 5 2002

ACYLOTROPIC TAUTOMERISM: XXXV.
L inversion (T1,2) in IIA, B VIIA, B begins after
719
R
relaxation of transition states for C* X bond cleavage
to F-conformers; but for naphthalene derivatives IID,
IVD, VD, and VID the inversion process directly
follows the C* X bond cleavage (Scheme 5).
From comparison of the experimental (Table 1;
Figs. 1, 2) and calculated data (Table 3) it follows
that the R L-dynamics in the series of compounds
II VII can formally be represented as potential energy
surface sections shown in Fig. 3. Figure 3a illustrates
the situation when spirocyclic isomers a occupy local
minima, and their open-chain isomers b appear in
global minima. An alternative state of the equilibrium
a
b is given in Fig. 3b. The PES section shown
in Fig. 3c looks like a funnel with compounds IID,
IVD, VD at the bottom; this section clearly illustrates
inhibition of the R,L-inversion. Open-chain isomers
b of IID, IVD, and VD do not populate effectively
the corresponding areas on the PES, for their heats of
formation ( Hf = 1.2 9.2 kJ/mol; Table 3) are com-
Fig. 2. Electron absorption spectra of compounds (1) VID
and (2) VIID in DMSO (c = 5 10 M).
5
(a)
parable with the energies of transition states for C*
bond cleavage (Scheme 5).
N
As noted above, the activation energies for T1,2-
dynamics of open-chain isomers of all compounds
II VII fall into a narrow range ( 46 54 kJ/mol).
The calculated geometries of compounds IID VD and
VIIG are similar (Scheme 5) both in transition states
corresponding to extension of the C* X bond (r =
2.07, 1.92 ) and after its cleavage (r = 2.57,
2.75 ) when T1,2 torsions (proper R L-conversion)
become possible. Just the difference in the heats of
formation (Table 3) of isomers b is responsible for
suppression of R,L-dynamics in IID, IVD, and VD
(b)
( G
125.4 kJ/mol) and for the reverse situation
with compound VIID ( G = 68.6 kJ/mol; Table 1).
Thus the overall activation barrier to R,L-permuta-
tion of IID, IVD, and VD is high since it includes
energy expenses for both cleavage of the spiro bond
and T1,2 torsions (Fig. 3c). In the R L-conversion
of IIA VA, IIB, and VIID, the activation barrier to
T1,2-torsions is increased only by the energy difference
(Table 3) between states a and b (Fig. 3b). The R ,L -
permutation of VID and VIIC depends only on the
energy of T1,2-dynamics in F-conformers of their
stable isomers b (Fig. 3a; Scheme 5).
(c)
EXPERIMENTAL
1
The dynamic H NMR spectra were recorded on
a Varian VXR-300 spectrometer (300 MHz) (Table 1).
The electron absorption spectra were measured on
a Specord UV-Vis instrument in toluene and DMSO.
The rate constants for R,L-permutation were deter-
Fig. 3. Potential energy surface sections corresponding to
R,L-permutation of (a) compounds VID, VIIB, and VIIC;
(b) IIA VA, IIB, and VIID; and (c) IID, IVD, and VD.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 5 2002

720
OLEKHNOVICH et al.
Table 4. Melting points, yields, and elemental analyses of compounds II VII
Found, %
Calculated, %
H
Comp.
no.
Yield,
%
mp, C (solvent)
Formula
C
H
N
C
N
IIA
235 (CHCl3)
265 (ethanol)
220 (ethanol)
210 (ethanol)
260 (benzene)
290 (ethanol)
270 (ethanol)
280 (ethanol)
160 (ethanol)
150
65
74
56
70
76
90
66
78
94
70
80
92
69.15
61.46
66.24
66.43
66.44
71.84
69.36
69.53
70.28
57.93
56.53
65.19
4.45
5.79
5.41
5.37
4.69
4.21
5.28
5.21
4.21
3.68
3.72
3.61
12.30
15.23
13.48
12.68
14.67
10.71
12.17
11.48
10.14
14.37
12.54
9.64
C27H22N4O4
C19H22N4O4
C23H22N4O4
C24H24N4O4
C26H21N5O4
C31H24N4O4
C27H24N4O4
C28H26N4O4
C24H17N3O5
C19H14N4O4S
C21H16N4O6S
C24H17N3O4S
69.52
61.60
66.01
66.65
66.80
72.08
69.21
69.61
70.06
57.86
55.74
65.00
4.75
5.98
5.29
5.59
4.53
4.68
5.16
5.43
4.16
3.57
3.56
3.86
12.01
15.12
13.39
12.95
14.98
10.85
11.96
11.61
10.21
14.21
12.38
9.48
IIIA
IVA
VA
IIB
IID
IVD
VD
VID
VIIBa
VIICb
VIIDc
175
210
a
b
c
Found S, %: 8.25; calculated S, %: 8.13.
Found S, %: 7.21; calculated S, %: 7.08.
Found S, %: 7.07; calculated S, %: 7.23.
mined with an accuracy of 10% by computer simula-
tion of signals from reference diastereotopic protons
[8] and visual adjustment to the experimental signal
shape at a given temperature. The activation param-
eters for R,L-dynamics (Table 1) were calculated by
the standard linearization procedure (lnk 1/T) with
regression coefficients no less than 0.98.
1-Benzylamino-7-benzylimino-1,3,5-cyclohepta-
triene (II). 1,2-Diethoxytropylium tetrafluoroborate,
1.6 g, was added in portions to 2 ml of benzylamine
with stirring and cooling in an ice bath. A thick
material was obtained, which was kept for 12 16 h at
room temperature. It was diluted with water, and the
precipitate was filtered off, washed with water, and
dried in air. The product was purified by chromatog-
raphy on Al2O3 (eluent CHCl3), followed by recrystal-
lization from ethanol. Yield 1.7 g (94%). Yellow
crystals, mp 82 C; published data [14]: yield 90%,
mp 82 C.
1-Isopropylamino-7-isopropylimino-1,3,5-cyclo-
heptatriene (III) was synthesized in a similar way.
The yellow product was recrystallized from methanol
or light petroleum ether. Yield 80%, mp 66 C; pub-
lished data [14]: yield 18%, bp 104 106 C (0.35 mm).
Quantum-chemical calculations were performed
using Hyper-Chem
program kindly provided by
Full Member of the Russian Academy of Sciences
N.S. Zefirov and Prof. Yu.A. Ustynyuk.
The initial reactants, aryl halides, 1-fluoro-2,4-di-
nitronaphthalene, 1-chloro-3-methyl-2,4,6-trinitro-
benzene, and the others, were synthesized by proce-
dures analogous to those given in [10]; tropolone was
prepared as described in [11].
1,2-Diethoxytropylium tetrafluoroborate (I) as
starting compound for preparation of aminotropones
was synthesized by improved procedure [12]. Tropo-
lone sodium salt, 5 g, was added with stirring to
a solution of 13.2 g of triethyloxonium tetrafluoro-
borate [13] in 20 ml of dry methylene chloride, cooled
with an ice salt bath. The mixture was kept for
12 16 h at room temperature and filtered, the precip-
itate was washed with methylene chloride on a filter,
and the filtrate was poured into 200 ml of cold dry
diethyl ether. The precipitate was filtered off, washed
with ether on a filter, and recrystallized from ethanol.
Yield 8 g (77%), mp 116 C; published data [12]:
yield 63%, mp 115 116 C.
7-Benzylimino-1-tert-butylamino-1,3,5-cyclo-
heptatriene (V). A mixture of 1 g of 2-benzylamino-
tropone [15] and 2 g of freshly distilled dimethyl
sulfate was heated to 110 C and was kept for 10 min
at 110 C and for 12 16 h at room temperature. Excess
dimethyl sulfate was removed by shaking with several
5-ml portions of benzene or toluene. 1-Benzylamino-
2-methoxytropylium methyl sulfate thus obtained was
dissolved in methanol, triethylamine was added until
the mixture became alkaline, and 2 ml of tert-butyl-
amine was added. The mixture was kept for several
days at room temperature (until the reaction was
complete, TLC), the precipitate was filtered off, the
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 5 2002

ACYLOTROPIC TAUTOMERISM: XXXV.
Table 5. 1H NMR spectra of compounds II VIIa
721
Compound
no.
Solvent
(temperature, C)
1H NMR spectrum, , ppm (J, Hz)
IIA
DMSO-d6 (20)
8.40 d (1H, 3 -H, J3 , 5 = 2.7), 7.72 7.31 m (12H, Harom, 4-H, 6-H), 7.12 d.d (1H, 5 -H,
J5 , 6 = 8.3), 7.01 t (1H, 5-H, J5, 6 = J4, 5 = 8.6), 6.88 d (2H, 3-H, 7-H, J3, 4 = J6, 7
9.0), 5.82 d (1H, 6 -H), 4.85 4.63 q (4H, 2CH2, JH, H = 17)
=
DMSO-d6 (160) 8.47 d (1H, 3 -H, J3 , 5 = 2.7), 7.69 7.27 m (12H, Harom, 4-H, 6-H), 7.13 d.d (1H,
5 -H, J5 , 6 = 8.3), 7.01 t (1H, 5-H, J5, 6 = J4, 5 = 8.6), 6.92 d (1H, 3-H, 7-H, J3, 4
J6, 7 = 9.0), 5.61 d (1H, 6 -H), 4.73 s (4H, 2CH2)
=
IIIA
IVA
VA
C6D5NO2 (20)
DMSO-d6 (20)
C6D5NO2 (20)
9.24 s (1H, 3 -H), 7.65 d.d (1H, 5 -H), 5.64 d (1H, 6 -H), 4.06 m [1H, CH(CH3)2],
1.59 1.46 q (6H, 2CH3, JH, H = 7)
8.45 s (1H, 3 -H), 7.15 d.d (1H, 5 -H), 5.71 d (1H, 6 -H), 4.72 4.51 q (2H, CH2,
JH, H = 17), 3.76 m [1H, CH(CH3)2], 1.39 1.24 q (6H, 2CH3, J = 7)
9.09 s (1H, 3 -H), 7.3 7.4 m (2H, 5 -H, 6 -H), 4.82 4.60 q (1H, CH2, JH, H = 17), 1.75 s
(9H, 3CH3)
IIID
IVD
DMSO-d6 (40)
DMSO-d6 (40)
8.81 s (1H, 3 -H), 4.72 4.39 q (2H, CH2, JH, H = 18)
8.77 s (1H, 3 -H), 4.70 4.48 q (2H, CH2, JH, H = 17), 3.89 m [1H, CH(CH3)2], 1.49
1.35 q (6H, 2CH3, J = 7)
VD
DMSO-d6 (40)
CDCl3 (20)
8.75 s (1H, 3 -H), 4.48 4.15 q (2H, CH2, JH, H = 17), 1.2 s (9H, 3CH3)
8.55 s (1H, 3 -H), 5.05 s (2H, CH2)
VID
VIIB
VIIC
VIID
DMSO-d6 (30)
CD3CN (20)
8.48 s (1H, 3 -H), 8.4 s (1H, 5 -H), 5.28 5.0 collapsing q (2H, CH2)
8.42 s (1H, 3 -H), 5.0 s (2H, CH2), 2.43 s (3H, CH3)
8.83 s (1H, 3 -H), 4.89 4.64 q (2H, CH2, JH, H = 17)
DMSO-d6 (20)
a
Signals from protons in the cycloheptatriene ring, phenyl ring of the N-benzyl group, and unsubstituted benzene ring in 2,4-dinitro-
naphthalene derivatives are similar for all compounds; therefore, they are given only for compound IIA.
filtrate was evaporated, and the residue was subjected
to chromatography on Al2O3 (eluent CHCl3). The
solvent was removed from the eluate, and the residue
was combined with the previously obtained precipitate
and was recrystallized from light petroleum ether.
Yield 66%. Light yellow crystals, mp 75 C.
7-Benzylimino-1-isopropylamino-1,3,5-cyclo-
heptatriene (IV) was synthesized as described above
for compound V by reaction of 1-benzylamino-2-
methoxytropylium methyl sulfate with isopropyl-
amine. Oily substance. Yield 60%.
2-Benzylamino-2,4,6-cycloheptatrienethione
(VII). To a solution of 2 g of 1-benzylamino-2-
methoxytropylium methyl sulfate (see above) in 8 ml
of ethanol we added with stirring 5 g of of sodium
sulfide and 20 ml of water in small portions. After
12 16 h, the precipitate was filtered off, washed with
water, dried in air, and recrystallized from ethanol
or methanol. Yield 89%. Orange crystals, mp 142 C;
published data [14]: mp 138 C.
1 mmol of 2-aminotropone imine (or 2-aminotropone),
and 0.5 mmol of aryl halide (1-fluoro-2,4-dinitroben-
zene or 1-fluoro-2,4-dinitronaphthalene) in 3 ml of
chloroform was heated to the boiling point and was
kept for 6 8 h at 70 80 C until the solvent was
removed completely. The remaining melt was dis-
solved in chloroform and subjected to chromatography
on Al2O3. The solution was evaporated, and the
residue was washed with petroleum ether and recrys-
tallized from ethanol. Spiro -complexes were
isolated as bright red crystalline substances. Their
melting points, yields, and elemental analyses are
given in Table 4, and 1H NMR spectra, in Table 5.
1,3-Dibenzyl-3 (5 )-nitro-2,2 ,3,5 (3 )-tetrahydro-
1H-cyclohepta[d]imidazolium-2-spiro-2 -pyridine-
5 (3 )-nitronate (IIB). A solution of 1 mmol of
1-benzylamino-7-benzylimino-1,3,5-cycloheptatriene
and 0.5 mmol of 2-chloro-3,5-dinitropyridine [16] in
5 ml of dry benzene was refluxed for 3 h. The mixture
was filtered, the filtrate was evaporated, and the
residue was subjected to chromatography on Al2O3
using CHCl3 as eluent. Yellow crystals, yield 76%.
2-Aminotropone imine and 2-aminotropone
derivatives IIA,D VA,D and VID. A mixture of
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 5 2002

722
OLEKHNOVICH et al.
6. Knyazev, V.N. and Drozd, V.N., Russ. J. Org.
2-Benzylamino-2,4,6-cycloheptatrienethione
Chem., 1995, vol. 31, no. 1, pp. 1 26; Terrier, F.,
Chem. Rev., 1982, vol. 82, no. 2, pp. 77 152;
Strauss, M.J., Chem. Rev., 1970, vol. 70, no. 3,
pp. 667 712.
derivatives VIIB VIID. A solution of 0.5 mmol
of 2-benzylamino-2,4,6-cycloheptatrienethione,
0.25 mmol of aryl halide (2-chloro-3,5-dinitropyri-
dine, 1-chloro-3-methyl-2,4,6-trinitrobenzene, or
1-chloro-2,4-dinitronaphthalene) in chloroform was
applied to a plate with a layer of Al2O3. After 15
20 h, the Al2O3-immobilized mixture was transferred
to a column charged with Al2O3 to a height of about
7 cm. The column was eluted with chloroform, the
eluate was evaporated, the residue was dispersed in
a minimal amount of benzene, and the precipitate
was filtered off and washed with benzene and diethyl
ether. The yields, melting points, elemental analyses,
7. Eaton, S.S. and Holm, R.H., Inorg. Chem., 1970,
vol. 10, pp. 1446 1452.
8. Olekhnovich, L.P., Kurbatov, S.V., Lesin, A.V.,
Budarina, Z.N., Zhdanov, Yu.A., and Minkin, V.I.,
Zh. Org. Khim., 1991, vol. 27, no. 1, pp. 6 13.
9. Tsai, C.J. and Jordan, K.D., J. Phys. Chem., 1993,
vol. 97, no. 8, pp. 1127 1137.
10. Weygand Hilgetag organisch-chemische Experi-
mentierkunst, Hilgetag, G. and Martini, A., Eds.,
Leipzig: Johann Ambrosius Barth, 1964, 3rd ed.
Translated under the title Metody eksperimenta
v organicheskoi khimii, Moscow: Khimiya, 1968,
pp. 197, 230.
1
and H NMR spectra of compounds IIB and VIIB
VIID are given in Tables 4 and 5.
REFERENCES
11. Minus, R.A., Elliot, A.J., and Sheppard, W.A., Org.
Synth., 1977, vol. 57, no. 1, pp. 117 121.
1. Kurbatov, S.V., Budarina, Z.N., Borisenko, N.I.,
Vaslyaeva, G.S., Knyazev, A.P., Olekhnovich, L.P.,
and Zhdanov, Yu.A., Russ. J. Org. Chem., 1999,
vol. 35, no. 11, pp. 1683 1688.
12. Forbes, C.E. and Holm, R.H., J. Am. Chem. Soc.,
1968, vol. 90, no. 12, p. 6884.
13. Fieser, L.F. and Fieser, M., Reagents for Organic
Synthesis, New York: Wiley Intersci., vol. 1, 1967.
Translated under the title Reagenty dlya organiche-
skogo sinteza, Moscow: Mir, 1970, vol. 3, p. 459.
2. Olekhnovich, L.P., Budarina, Z.N., Lesin, A.V.,
Kurbatov, S.V., Borodkin, G.S., and Minkin, V.I.,
Mendeleev Commun., 1994, no. 2, pp. 162 165.
3. Furmanova, N.G., Olekhnovich, L.P., Minkin, V.I.,
Struchkov, Yu.T., Kompan, O.E., and Budarina, Z.N.,
Zh. Org. Khim., 1982, vol. 18, no. 3, pp. 474 484.
14. Soma, N., Nakazawa, G., Watanabe, T., Sato, Y.,
and Sunagawa, G., Chem. Pharm. Bull., 1965,
vol. 13(4), no. 3, pp. 457 464.
4. Olekhnovich, L.P., Kurbatov, S.V., Budarina, Z.N.,
Minkin, V.I., and Zhdanov, Yu.A., Zh. Org. Khim.,
1985, vol. 21, no. 12, pp. 2550 2555.
15. Soma, N., Nakazawa, G., Watanabe, T., Sato, Y.,
and Sunagawa, G., Chem. Pharm. Bull., 1965,
vol. 13(7), no. 5, pp. 819 828.
5. Kurbatov, S.V., Budarina, Z.N., Olekhnovich, L.P.,
Furmanova, N.G., Lesin, A.V., Kompan, O.E., Min-
kin, V.I., and Zhdanov, Yu.A., Zh. Org. Khim., 1988,
vol. 24, no. 5, pp. 913 922.
16. Metody polucheniya khimicheskikh reaktivov i pre-
paratov (Methods of Synthesis of Chemical Reagents
and Preparations), Moscow: IREA, 1971, vol. 23,
pp. 150 152.
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