E/Z(C=C)-Isomerization of enamines of 3-formyl-4-hydroxycoumarin induced by organic solvents

Article abstract of DOI:10.1007/s11172-010-0284-z

According to ¹H and ¹³C NMR data, enamines of 3-formyl-4-hydroxycoumarin exist in the keto enamine tautomeric form and undergo Z/E-isomerization around the C=C bond in CDCl₃, DMSO-d₆, and CD₃OD at room temperature. The activation energies of E/Z-isomerization were measured experimentally and calculated by the B3LYP/6-311++G(d,p) method. An X-ray diffraction study showed that 3-(benzyliminomethyl)chromane-2,4-dione in the crystalline state exists as a mixture of two keto enamine isomers.

Full text of DOI:10.1007/s11172-010-0284-z

Russian Chemical Bulletin, International Edition, Vol. 59, No. 8, pp. 1605—1611, August, 2010
1605
E/Z(C=C)ꢀIsomerization of enamines of 3ꢀformylꢀ4ꢀhydroxycoumarin
induced by organic solvents
V. F. Traven,a I. V. Ivanov,a V. S. Lebedev,a T. A. Chibisova,a B. G. Milevskii,a N. P. Solov´eva,a
V. I. Polshakov,b G. G. Alexandrov,c O. N. Kazheva,d and О. A. Dyachenkod
aD. Mendeleev University of Chemical Technology of Russia,
9 Miusskaya pl., 125147 Moscow, Russian Federation.
Eꢀmail: valerii.traven@gmail.com; ivanvi@yandex.ru
bCenter for Drug Chemistry,
7 Zubovskaya ul., 119815 Moscow, Russian Federation
cInstitute of Problems of Chemical Physics, Russian Academy of Sciences,
1 prosp. Akad. Semenova, 142432 Chernogolovka, Moscow Region, Russian Federation
dN. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
31 Leninsky prosp., 119991 Moscow, Russian Federation
According to 1Н and 13С NMR data, enamines of 3ꢀformylꢀ4ꢀhydroxycoumarin exist in
the keto enamine tautomeric form and undergo Z/Eꢀisomerization around the C=C bond in
CDCl3, DMSOꢀd6, and CD3OD at room temperature. The activation energies of Е/Zꢀisomerꢀ
ization were measured experimentally and calculated by the B3LYP/6ꢀ311++G(d,p) method.
An Xꢀray diffraction study showed that 3ꢀ(benzyliminomethyl)chromaneꢀ2,4ꢀdione in the
crystalline state exists as a mixture of two keto enamine isomers.
Key words: imines, isomerization, tautomerism, keto enamines, hydroxy imines, coumarin
derivatives.
Scheme 1
Noncovalent interactions play an important role in
organic chemistry, in the formation of supramolecular
systems, and in interactions of biological substrates.1—3 In
particular, these interactions are responsible for isomerꢀ
izations of solvatochromic compounds used for the deꢀ
sign of various types of sensors, elements of molecular
electronics devices, and information recording and storꢀ
age systems.4,5
Aromatic and heteroaromatic imines are particularly
prone to isomerization.6—8 Earlier, we have reported
on solvatochromism in imines derived from 8ꢀformylꢀ
7ꢀhydroxyꢀ4ꢀmethylcoumarin.9 It was found that these
compounds mainly exist in the enol form and no ketoꢀ
enol tautomerism was observed. Some compounds of this
series (in particular, imines containing strong electronꢀ
withdrawing groups in the paraꢀposition of the phenyl
ring) can undergo E/Zꢀisomerization around the C=N
bond (Scheme 1).
In the present work, we have synthesized imines of
3ꢀformylꢀ4ꢀhydroxycoumarin 2—4 and studied their
isomerization in organic solvents.
Like other derivatives of 4ꢀhydroxycoumarin, imines
2—4 can potentially undergo tautomeric transformations.
Scheme 2 presents selected tautomeric forms. Nevertheꢀ
1
less, we inferred from our studies of Н NMR spectra of
4ꢀHydroxycoumarins representing the enol forms of
2,4ꢀdiketochromone are also prone to tautomerism. Tauꢀ
tomeric transformations of derivatives of 4ꢀhydroxyꢀ
coumarin and 3ꢀacylꢀ4ꢀhydroxycoumarins (1) are induced
by changes in the solvent polarity and are sometimes
accompanied by changes in both electronic absorption
spectra and fluorescence spectra.10,11
imines 2—4 that all of them exist in solution in the same
tautomeric form, namely, as a mixture of two Eꢀ and
Zꢀisomers of the keto enamine form (Scheme 2). The rate
of equilibration between isomers depends strongly on the
solvent polarity and on the imine structure.
The isomerization of imine 2b was studied in most
detail. For this compound, an equilibrium between the
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1565—1570, August, 2010.
1066ꢀ5285/10/5908ꢀ1605 © 2010 Springer Science+Business Media, Inc.

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Russ.Chem.Bull., Int.Ed., Vol. 59, No. 8, August, 2010
Traven et al.
2
1
14.0 13.0 12.0
11.0 10.0
9.0 δ
1
Fig. 1. Н NMR spectra recorded immediately (1) and 24 h (2)
after dissolution of imine 2b in chloroformꢀd.
mers (Table 1). The signal for the С(4) atom of the major
isomer at δ 181.6 is shifted downfield compared to the
signal of the minor isomer at δ 178.5. The reverse is
observed for the signal for the С(2) atom. This can
be explained by the effect of the С(2)=O...H—N and
C(4)=O...H—N hydrogen bond in the Zꢀ and Eꢀketo
enamine, respectively. The signal for the С(2) atom is a
doublet owing to the spinꢀspin coupling between this atom
and the Н(9) proton. The constant of heteronuclear spinꢀ
spin coupling C—H for the minor isomer is much larger
than for the major isomer, namely, JС(2)Н(9) = 9.94 and
3.07 Hz, respectively. These values suggest that the minor
isomer is the Zꢀketo enamine with a transꢀorientation of
the bonds C(2)—C(3) and C(9)—H and, correspondingly,
large JС(2)Н(9). Thus, the major isomer is the Eꢀisomer.
The chemical shifts in the 13С NMR spectrum (CDCl3) of
compound 2b are listed in Table 1.
X = H (a), Me (b), OMe (c), Br (d), NO2 (e)
Scheme 2
Hydroxy imine
According to our B3LYP/6ꢀ311++G(d,p) calculations
using the GAUSSIANꢀ98 program,12 the energy of forꢀ
Table 1. Chemical shifts (δ) in the 13С NMR
spectrum (CDCl3) of imine 2b
(E)ꢀ(Keto)enamine
(Z)ꢀ(Keto)enamine
Atom, group
EꢀIsomer
ZꢀIsomer
2
3
163.60
98.37
165.30
98.39
Eꢀ and Zꢀisomers is established almost immediately after
dissolution in methanol, 4 h after dissolution in DMSO,
and 24 h after dissolution in chloroform.
4
5
6
7
8
9
4a
8a
181.60
125.70
124.70
134.60
117.30
154.60
120.30
154.20
137.60
118.30
130.60
135.20
20.30
178.50
126.40
124.30
134.50
117.40
153.20
120.60
154.90
134.50
118.40
130.60
135.20
20.90
The isomerization is clearly detected by NMR specꢀ
troscopy. The 1Н NMR spectrum of compound 2b immeꢀ
diately after dissolution in chloroformꢀd exhibits a signal
for the NHꢀproton at δ 11.9 corresponding to one major
isomer whose content in solution is 95%. After 24 h, the
isomer characterized by the signal for the NH proton at
δ 13.6 becomes dominant. The content of this isomer
increases from 5 to 70% (Fig. 1).
10
11, 15
12, 14
13
The 13С NMR spectrum of the equilibrium solution of
compound 2b in CDCl3 also exhibits signals of two isoꢀ
СН3

Z/E(C=C)ꢀIsomerization of coumarin enamines
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 8, August, 2010
1607
mation of Eꢀketo enamine is lower than that of the Zꢀketo
enamine form. The energy difference ΔЕ = 0.65 kcal mol–1
corresponds to a thermodynamic equilibrium between two
isomers in a 75 : 25 ratio, being in good agreement with
the experimental E : Z ratio of nearly 70 : 30. The calculꢀ
ated energies of formation of the hydroxy imine form are
6.35 and 12.72 kcal mol–1 (for the 4ꢀ and 2ꢀhydroxy forms,
respectively) higher than that of the Еꢀketo enamine. As a
consequence, the amount of the hydroxy imine form can
be at most 10–3 and 10–8%, respectively.
The hydrogen bond NH...O=C(4) in the Eꢀisomer
(1.81 Å) is much shorter and, therefore, stronger than the
corresponding bond NH...O=C(2) in the Zꢀisomer (1.87 Å).
The relative strengths of the two hydrogen bonds can be
estimated from the partial charges on the donor and
acceptor atoms. Our DFT calculations showed that the
partial charges on the imine proton and carbonyl oxygen
atoms bound to the C(2) and C(4) atoms in the Eꢀisomer
are +0.440, –0.297, and –0.269, respectively. The correꢀ
sponding values for the Zꢀisomer are +0.417, –0.292, and
–0.267. As can be seen, the positive charge of the imino
proton involved in the formation of the hydrogen bond is
higher in the Eꢀisomer.
We calculated the chemical shifts of protons and
carbon atoms for both isomers of compound 2b by the
B3LYP GIAO/6ꢀ311++G(2d,p) method. The calculated
values are in good agreement with the experimental data
(Table 2). The relative chemical shifts of NНꢀprotons
excellently correlate with the strengths of the hydrogen
bonds in the Eꢀ and Zꢀisomers. The largest changes in the
13С chemical shift on going from one isomer to the other
were found for the С(2) and С(4) atoms. The calculated
differences in the chemical shifts are different for the
С(2) and С(4) atoms of two isomers (–1.6 and +3.1,
respectively) and agree with the corresponding experiꢀ
mental values (–1.5 and +4.0). The results of the GIAO
calculations also enable reliable assignment of the signals
for the Н(9) proton in the Eꢀ and Zꢀisomers, viz., the
signal for H(9) in the Еꢀketo enamine is shifted upfield
(δ 8.9) relative to the proton signal in the spectrum of the
Zꢀisomer (δ 9.0).
Examples of E/Zꢀisomerization around the С=С bond
were reported earlier.13—17 In particular, we have estabꢀ
lished14,15 that the merocyanine derivatives of 3ꢀformylꢀ
4ꢀhydroxycoumarin exist as mixtures of Еꢀ and Zꢀisoꢀ
mers. An unprecedented coexistence of spirooxazine and
photomerocyanine in four transꢀconformations is docuꢀ
mented.16 Transꢀtransꢀcis/transꢀtransꢀtransꢀisomerism in
photochromic spiropyranꢀmerocyanines was studied exꢀ
perimentally and using DFT calculations.17 At the same
time, only one isomer of the keto enamine form was
1
detected in a study of the Н NMR spectra of imines of
3ꢀformylꢀ4ꢀhydroxycoumarin.18
We also determined the kinetic parameters of
Z/Eꢀisomerization of imine 2b. To this end, we measured
changes in the intensities of the signals of the Еꢀ and
Zꢀisomers of imine 2b with time in the temperature range
from 30 to 50 °С and calculated the rate constants. It was
found that the decrease in the intensities of the signals of
the Zꢀisomer and an increase in the intensities of the
signals of the Еꢀisomer in the initial stage of the reaction
is correctly described by a firstꢀorder kinetic equation.
Taking into account the linear dependence of lnk on
1/T (Fig. 2), the calculated activation energy of isomerꢀ
ization of imine 2b from Zꢀketo enamine to the correꢀ
sponding Еꢀisomer is 84 6 kJ mol–1
.
The activation energy of rotation about the С(3)—С(9)
bond in compound 2b was also calculated by the
B3LYP/6ꢀ311++G(d,p) method, which gave a value of
148 kJ mol–1. This is much higher (by 64 kJ mol–1) than
the experimental value. Probably, the real mechanism of
E/Zꢀisomerization is more complex than a simple rotaꢀ
tion about the С(3)—С(9) bond assumed in the quantum
chemical calculations. For instance, isomerization may
involve ketoꢀenol tautomeric transformations accompaꢀ
nied by intramolecular proton migration, which may cause
lnC
–4.7
Table 2. 1Н and 13С chemical shifts (δ) for Eꢀ and
Zꢀisomers of compound 2b obtained from GIAO
calculations and experimental data (in parentheses)
298 K
303 K
–4.8
lnk
–4.9
–4.5
–5.0
–5.5
–6.0
308 K
–5.0
–5.1
–5.2
–5.3
313 K
Atom,
group
ЕꢀIsomer
ZꢀIsomer
NH
012.60 (13.60)
009.07 (8.90)
011.40 (12.00)
009.46 (9.00)
3.20 3.30
0.34 1/T•103
H(9)
С(2)
С(3)
С(4)
C(9)
C(10)
167.80 (163.60)
105.10 (98.37)
188.30 (181.60)
161.62 (154.60)
124.32 (137.62)
169.30 (165.20)
107.10 (98.39)
184.30 (178.50)
160.67 (153.20)
124.24 (134.48)
500 1000 1500 2000 2500 3000 3500 4000
t/s
Fig. 2. Changes in the signal for the Н(9) proton in the
Zꢀisomer in chloroformꢀd at different temperatures. Inset: the
plot of ln k vs. 1/T calculated using the expression ln k =
= –9566.4 (1/T) + 25.985.

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Traven et al.
a decrease in the activation energy. At the same time,
the much higher energies of formation of the 4ꢀ and
2ꢀhydroxy forms compared to that of the keto enamine
form suggest that their involvement in isomerization is
unlikely. Probably, there is also a contribution of the solꢀ
vent effect because calculations were carried out for a
molecule in the gas phase while the experimental value
was obtained for the compound dissolved in chloroform.
In addition, the difference between the calculated and
experimental activation energies (46 kJ mol–1) obtained
in the present work is close to the activation energy
difference between the gas phase and C2H2Cl2 solution
(55 kJ mol–1) for Е/Zꢀisomerization of spiropyranꢀ
merocyanine obtained analogously.19
2
1
13.0
12.0
11.0
10.0
9.0 δ
Fig. 3. 1Н NMR spectra recorded immediately (1) and 4 h after
dissolution of imine 2b in DMSOꢀd6 (2).
the solvent should be about 2 Hz. Moreover, the signal for
the H(9) proton should appear as a triplet due to the
interaction with the quadrupole deuterium atom (S = 1).
The joint effect of these factors leads to broadening of this
signal (the width at halfꢀheight is 5.4 Hz).
Other imines 2—4 exhibit similar spectral and isomerꢀ
ization properties. The 1Н NMR spectra of all compounds
show signals of Zꢀ and Eꢀisomers. The chemical shifts for
the NHꢀprotons and H(9) atom are listed in Table 3.
In addition, all imines are characterized by a similar
isomeric composition (Z : E ratio), as shown below.
We found that the higher the solvent polarity the stronꢀ
ger the effect of solvent on E/Zꢀisomerization. For inꢀ
stance, the isomerization of imine 2b in DMSOꢀd6 proꢀ
ceeds at a much higher rate. Immediately after dissoluꢀ
tion, the signal for the Н(9) atom is observed as a broadꢀ
ened singlet. It splits into two doublets at δ 8.66
(Еꢀisomer, J9,10а = 13.5 Hz, 73%) and 8.72 (Zꢀisomer,
J9,10a = 14.8Hz, 27%) after 4 h and then the signal intensiꢀ
ties remain unchanged. The same can be observed in a
lower field (δ 11—14) for the signals for the NH protons.
Two broad NH proton signals at δ 13.4 (Еꢀisomer) and
1
11.7 (Zꢀisomer) are observed in the H NMR spectrum
Compound 2a
2b
2d
3
2c
2e
4
Z/E (%) 31/69 34/66 24/76 30/70 27/73 30/70 30/70
However, compounds 2—4 differ in equilibration rates
for the Zꢀ and Eꢀforms in chloroform. For compounds
2а,d and 3, equilibration takes a few hours to complete as
for compound 2b. However, for compounds 2с,е and 4,
the equilibrium is attained immediately after dissolution,
as indicated by the lack of changes in their 1Н NMR
spectra which show two groups of doublet signals of the
Eꢀ and Zꢀisomers near δ 9 for Н(9) proton and at δ 11—14
immediately after dissolution of imine 2b in DMSOꢀd6
(Fig. 3).
When dissolved in methanolꢀd4, the thermodynamic
equilibrium between two isomers of imine 2b is attained
1
immediately as well. The Н NMR spectrum recorded
immediately after dissolution exhibits two broadened sinꢀ
glet signals for Н(9) of different intensity. The stronger
signal at δ 8.94 was assigned to the Еꢀisomer while the
weaker signal at δ 9.06 was assigned to the Zꢀisomer. The
intensity ratio of these signals remains unchanged with
time. Low resolution of both signals is most likely due to
fast H/Dꢀexchange of NHꢀprotons of the keto enamine
form in methanol. The JH,D coupling constant is 6.5 times
smaller than the corresponding JH,H constant; therefore,
1
for NНꢀprotons. Like the Н NMR spectra of the soluꢀ
tions in chloroform, those recorded in DMSOꢀd6 also
remain unchanged and immediately after dissolution they
show wellꢀdefined doublets of Н(9) proton and NHꢀproꢀ
tons. The properties of compound 2с deserve particular
attention. In its 1Н NMR spectrum in DMSOꢀd6, the
signal for the Н(9) proton appears as a singlet at δ 8.78
3
1
the JH,D constant in the Н NMR spectra of imine 2b
after exchange of NHꢀproton by a deuterium atom from
Table 3. Chemical shifts (δ) of protons in compounds 2—4 in chloroform
Comꢀ N—H H(9)
H(5)
pound
EꢀIsomer
ZꢀIsomer
EꢀIsomer
ZꢀIsomer
EꢀIsomer
ZꢀIsomer
2a
2b
2c
2d
2e
3
13.72
13.68
13.75
13.70
13.79
13.82
12.12
11.98
11.94
11.94
11.90
12.00
12.04
10.49
8.90
8.86
8.79
8.84
8.92
8.93
8.49
9.04
9.01
8.93
8.98
9.04
9.07
8.67
8.08
8.07
8.07
8.07
8.08
8.08
7.96
8.14
8.14
8.14
8.14
8.14
8.15
8.06
4

Z/E(C=C)ꢀIsomerization of coumarin enamines
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 8, August, 2010
1609
and a strongly broadened singlet at δ 13.0 is observed in
the region δ 11—14. The spectrum remains unchanged
with time. One would assume that compound 2с exists in
DMSOꢀd6 in the hydroxy imine form. To refine the strucꢀ
ture of compound 2с, we studied the multiplicity of the
signal for the С(9) atom. In the 13С NMR spectrum of
the hydroxy imine form, one would expect for this atom
the appearance of a doublet with a direct heteronuclear
spinꢀspin coupling constant С(9)—Н of 140—160 Hz. In
the case of the keto enamine form, one would expect the
appearance of a doublet of doublets with the direct spinꢀ
spin coupling constant С(9)—Н and the spinꢀspin couꢀ
pling constant through two bonds C(9)—H(N). A DEPT90
experiment revealed that the signal for the atom С(9) is a
doublet of doublets with a direct spinꢀspin coupling conꢀ
stant of 153.6 Hz and a spinꢀspin coupling constant
through two bonds of 8.5 Hz. An increase in the concenꢀ
tration of compound 2с in solution led to splitting of the
singlet signal for the Н(9) proton into two doublets and
the appearance of corresponding doublet signals for the
NHꢀproton at δ 11.8 and 13.5. Therefore, the appearance
of a singlet signal for the Н(9) proton at a lower concenꢀ
tration may be a consequence of intense proton exchange
of NH groups with water containing in DMSOꢀd6.
From analysis of the 1H NMR spectrum of compound
4 it follows that, as in the case of compound 2b, the Еꢀketo
enamine form is the major isomer, the Zꢀketo enamine
form being the minor one.
Our Xꢀray diffraction study of crystals of compound 4
showed that, as in solution, this compound exists in the
crystalline phase as a mixture of two keto enamine isoꢀ
mers (Fig. 4). In the solid state, both isomers are characꢀ
terized by wellꢀdefined intramolecular interactions
between N—H...O=C(4) and N—H...O=C(2) groups in
the Eꢀ and Zꢀketo enamine forms, viz., the lengths of the
corresponding hydrogen bonds are 2.00 and 2.16 Å.
Experimental
1Н and 13С NMR spectra were recorded on Bruker WP200ꢀSY
(200 MHz) and Unity Plus (Varian, 400 MHz) spectrometers in
CD3OD, CDCl3, and DMSOꢀd6. The chemical shifts were calꢀ
culated using Me4Si as the internal standard. Mass spectra were
obtained on a Finnigan mass spectrometer (electron ionization
energy 70 eV, T = 443 K).
The rates of Z/Eꢀisomerization were determined at imine
concentrations of 1—3 mmol L–1. Signals of the Eꢀ and Zꢀketo
enamine forms were recorded within the time interval 6—70 min.
The first spectrum was recorded 6 min after preparation of the
sample. The relative concentrations of isomers were determined
from the integrated intensities of the Н(9) proton signals. The
rate constants k were calculated from the firstꢀorder kinetic
equation lnc = kt.
Quantum chemical calculations were carried out using the
GAUSSIAN 98 program.12 Geometry optimization was perꢀ
formed within the density functional theory (DFT) using the
B3LYP functional and 6ꢀ311++G(d,p) basis set. The 1Н and
13С NMR chemical shifts were calculated by the GIAO method
in the 6ꢀ311++G(2d,p) basis set.20—22 To determine the absoꢀ
lute values of the chemical shifts, the isotopic shielding was
calculated for Me4Si with the same basis set.
The energy profile for rotation about the С(3)—С(9) bond
was obtained from the Hartree—Fock calculations in the
6ꢀ31++G(d,p) basis set. Geometry optimization was performed
for all intermediate structure with a fixed value of the torsion
angle with respect to the С(3)—С(9) bond with an increment of
5 or 30°. Geometric parameters obtained for the structure with
the maximum energy were then used as the initial approximaꢀ
tion in the search for a firstꢀorder saddle point.
Xꢀray diffraction analysis. A single crystal was grown from
isopropyl alcohol. An Xꢀray study of the crystals of 2 was carried
out on a Bruker SMART APEX2 CCD diffractometer (MoꢀKα
radiation) at 20 °C. The crystal structure was solved by the diꢀ
rect methods followed by the Fourier syntheses using the
SHELXSꢀ97 software. The structure was refined by the least
squares method in the fullꢀmatrix anisotropic approximation for
all nonꢀhydrogen atoms using the SHELXLꢀ97 software. Posiꢀ
tions of hydrogen atoms were calculated geometrically.
The atomic coordinates, bond lengths, and bond angles were
deposited at the Cambridge Structural Database (www.ccdc.cam.uk/
conts/retrieving.html, CCDC, record No. 700853).
C(10A)
Selected geometric parameters of the crystal and experiꢀ
mental data are as follows: C17H13NO3, M = 279.28, triclinic
crystal system, space group Pꢀ1, a = 10.669(2) Å, b = 11.983(2)
Å, c = 12.169(2) Å, α = 62.38(3)°, β = 89.29(3)°, γ = 81.67(3)°,
C(11A)
H(11B)
H(10A)
O(2A)
O(3B)
V = 1361.3(5) Å3, Z = 4, dcalc = 1.36 g cm–3, μ = 0.094 mm–1
,
H(11D)
the total number of reflections is 9513, the number of indepenꢀ
dent reflections is 5301, 379 parameters refined, R = 0.075 for
2608 reflections with F0 > 4σ(F0).
C(11B)
N(1B)
H(1B)
O(2B)
Synthesis of imines of 3ꢀformylꢀ4ꢀhydroxycoumarin (general
procedure). A mixture of 3ꢀformylꢀ4ꢀhydroxycoumarin (0.1 g,
0.53•10–3 mol) and pꢀtoluidine (0.05 g, 0.53•10–3 mol) in EtOH
(10 mL) was heated for 2 h and cooled. The precipitate was
filtered off, washed with water, and dried in air. Needleꢀshaped
crystals were obtained (from EtOH).
3ꢀ(Phenyliminomethyl)chromaneꢀ2,4ꢀdione (2а).15 White
powder, m.p. 208—210 °С (cf. publ. data: m.p. 209—210 °С).
1Н NMR (200 MHz, CDCl3, δ,, J/Hz): 13.72 (d, 0.7 H, NH,
O(2B´)
H(1B´)
N(1B´)
Fig. 4. Intermolecular hydrogen bonds between Eꢀ and Zꢀisoꢀ
mers in crystals of compound 4.

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Traven et al.
JNH,H(9) = 13.6); 11.96 (d, 0.3 H, NH, JNH,H(9) = 14.9); 9.04 (d,
1 H, H(9), JNH,H(9) = 14.9); 8.90 (d, 0.7 H, H(9), JNH,H(9) = 13.7);
8.14 (dd, 0.3 H, H(5), J5,6 = 7.7, J5,7 = 2.0); 8.08 (dd, 0.7 H,
H(5), J = 8.2, J = 1.5); 7.74 (m, 1 H, H(7)); 7.43—7.55 (m, 2 H,
H(6), H(8)); 7.24—7.41 (m, 5 H, H(2´), H(3´), H(4´), H(5´),
H(6´)).
10.50 (m, 0.3 Н, NH); 8.66 (d, 0.3 Н, H(9), JH(9),NH = 14.9);
8.49 (d, 0.7 Н, H(9), JH(9),NH = 13.8); 8.07 (dd, 0.3 H, Н(5),
J5,6 = 7.7, J5,7 = 1.07); 8.08 (dd, 0.9 H, Н(5), J5,6 = 7.7, J5,7 = 1.5);
7.55—7.66 (m, 1 Н, H(7)); 7.42—7.53 (m, 2 H, Н(6), Н(8));
7.20—7.40 (m, 5 H, Н(1´), Н(2´), Н(3´), Н(4´), Н(5´)).
3ꢀ(pꢀTolyliminomethyl)chromaneꢀ2,4ꢀdione (2b).15 White
powder, m.p. 192—194 °С. (cf. publ. data: m.p. 191 °С).
1Н NMR (200 MHz, CDCl3, δ,, J/Hz): 13.60 (d, 0.66 Н, NH,
JNH,H(9) = 13.7); 11.91 (d, 0.34 Н, NH, JNH,H(9) = 14.5); 9.98
(d, 0.34 Н, H(9), JH(9),NH = 14.5); 9.87 (d, 0.66 Н, H(9),
JH(9),NH = 13.7); 8.14 (dd, 1 H, Н(5), J5,6 = 7.7, J5,7 = 1.7); 8.07
(dd, 1 H, Н(5), J5,6 = 8.2, J5,7 = 1.5); 7.66—7.70 (m, 1 H,
Н(7)); 7.53—7.58 (m, 2 Н, H(6), Н(8)); 7.20—7.40 (m, 4 H,
Н(1´), Н(2´), Н(4´), Н(5´)); 2.39 (s, 3 H, Me).
The present work was financially supported by
the Russian Foundation for Basic Research (Project
No. 07ꢀ03ꢀ00936).
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3ꢀ[(4ꢀMethoxyphenylimino)methyl]chromaneꢀ2,4ꢀdione (2с).
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Received September 9, 2009;
in revised form March 15, 2010