Structure and condensation reactions of 2,3-dihydrofuro[3,2-c]coumarin-3- one

Article abstract of DOI:10.1007/s11172-011-0287-4

2,3-Dihydrofuro[3,2-c]coumarin-3-one was synthesized in quantitative yield from 3-(ffl-bromoacetyl)-4-hydroxycoumarin in the presence of nucleophiles (including solvents). This compound undergoes keto-enol tautomerization and easily reacts with aromatic and hetero-aromatic aldehydes to form crotonization products having a Z configuration and exhibiting strong fluorescence.

Full text of DOI:10.1007/s11172-011-0287-4

Russian Chemical Bulletin, International Edition, Vol. 60, No. 9, pp. 1906—1916, September, 2011
1906
Structure and condensation reactions
of 2,3ꢀdihydrofuro[3,2ꢀc]coumarinꢀ3ꢀone
N. A. Kondratova,a O. N. Kazheva,b G. G. Aleksandrov,c A. N. Chekhlov,b O. A. D´yachenko,b and V. F. Travena
aD. I. Mendeleev University of Chemical Technology of Russia,
9 pl. Miusskaya, 125047 Moscow, Russian Federation.
Eꢀmail: traven@muctr.ru; cumarin@mail.ru
bInstitute of Problems of Chemical Physics, Russian Academy of Sciences,
1 prosp. Akad. Semenova, 142432 Chernogolovka, Moscow Region, Russian Federation
cA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation
2,3ꢀDihydrofuro[3,2ꢀc]coumarinꢀ3ꢀone was synthesized in quantitative yield from
3ꢀ(ωꢀbromoacetyl)ꢀ4ꢀhydroxycoumarin in the presence of nucleophiles (including solvents).
This compound undergoes ketoꢀenol tautomerization and easily reacts with aromatic and heteroꢀ
aromatic aldehydes to form crotonization products having a Z configuration and exhibiting
strong fluorescence.
Key words: furocoumarinones, ketoꢀenol tautomerism, dimerization, crotonization, Xꢀray
diffraction study, fluorescence.
Many coumarin derivatives are characterized by strong
CDCl3, acetoneꢀd6, and DMSOꢀd6. However, the ketoꢀ
enol tautomerization of compound 2 was observed by elecꢀ
tronic absorption spectroscopy (Scheme 2).7
It was shown that the transformations of the keto and
enol forms of compound 2 provide a convenient route
to the functionalization of furocoumarin 4 at the furan
ring.8,9
In the present study, we report a convenient procedure
for the synthesis of the isomer of
compound 2, viz., 2,3ꢀdihydroꢀ
furo[3,2ꢀc]coumarinꢀ3(2H)ꢀone (5),
its tautomeric transformations, and
some reactions at the furan ring.
Another field of our research on
the reactions of βꢀdiꢀ and β,βꢀtriꢀ
carbonyl compounds in the series of coumarin and its anꢀ
alogs10,11 concerns the synthesis and transformations of
ketone 5.
photochemical activity and exhibit intense fluorescence.
Due to such properties, these compounds are widely used
as optical bleaching agents, luminescent labels, and laser
dyes.1,2 Furocoumarins are important coumarin derivaꢀ
tives, many of which not only exhibit photochemical acꢀ
tivity but also have therapeutical properties and are used
as efficient pharmaceuticals.3,4
Earlier, we have examined several new approaches to
the synthesis of furocoumarins and their analogs. One of
these approaches is based on the unusual Fries rearrangeꢀ
ment of 7ꢀhydroxyꢀ4ꢀmethylcoumarin chloroacetate (1)
giving 4ꢀmethylꢀ8Hꢀfuro[2,3ꢀh]chromeneꢀ2,9ꢀdione (2)
followed by the reduction of 2 to alcohol 3 and the aromaꢀ
tization of the latter to form furo[2,3ꢀh]coumarin derivaꢀ
tive (4) (angelicin) (Scheme 1).5,6
1
The H NMR spectroscopic study showed that comꢀ
pound 2 exists exclusively in the keto form in solutions in
Scheme 1
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1873—1883, September, 2011.
1066ꢀ5285/11/6009ꢀ1906 © 2011 Springer Science+Business Media, Inc.

Reactions of dihydrofuro[3,2ꢀc]coumarinꢀ3ꢀone
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 9, September, 2011
1907
Scheme 2
pounds 7a—c also undergo cyclization to form ketone 5 in
quantitative yield on heating in ethanol even in the abꢀ
sence of bases.
As can be seen from Scheme 3, ketone 5 can theoretiꢀ
cally exist both in the keto and enol forms. Although the
difference in the enthalpies of formation of two tautomers
is very large (35.8 kcal mol–1, see Table 1), we observed
tautomeric transformations of ketone 5 when studying the
solvatochromism by gradually changing the composition
of the solvent from 100% CCl4 to 100% MeOH. Thus, the
corresponding spectral curves display an isosbestic point.
The electronic absorption spectra of ketone 5 in
CCl4—MeOH mixtures of variable composition are shown
in Fig. 1.
To assign the observed spectral changes to the keto and
enol forms, the electronic absorption spectra of both forms
were calculated by the ZINDO/S method. Table 2 gives
the calculated wavelengths and oscillator strengths.
Based on a comparison of the experimental data (see
Fig. 1) with the results of the calculations (see Table 2), it
can be concluded that the bathochromic shift of the longꢀ
wavelength absorption maximum of ketone 5 in methanol
with respect to this maximum in carbon tetrachloride is,
most likely, attributed to an increase in the contribution of
the enol form to its structure. In a nonpolar solvent, the
enol form can be stabilized by a hydrogen bond between
the hydroxy group of the enol and the carbonyl oxygen
atom of the lactone moiety. As shown earlier,10 compound
6 undergoes similar tautomeric transformations.
Results and Discussion
Earlier,12 ketone 5 has been synthesized by the reacꢀ
tion of 3ꢀ(ω−bromoacetyl)ꢀ4ꢀhydroxycoumarins with triꢀ
ethylamine or a 1% sodium hydroxide solution in acetone.
We found that ketone 5 can be easily synthesized by the
bromination of 3ꢀacetylꢀ4ꢀhydroxycoumarin (6) followed
by the treatment of bromo ketone 7 at room temperature
for several minutes in DMSO in the presence of various
nucleophilic and basic reagents, for example, of nitrite,
nitrate, cyanide, or carbonate ions, amines (Scheme 3).
We also found that the intramolecular cyclization giving
ketone 5 competes with the bimolecular nucleophilic subꢀ
stitution of bromine. The substitution readily occurred with
ammonium thiocyanate and sodium iodide in acetone at
~20 °C, whereas the reaction performed with heating gave
ketone 5 as the only product. It should be noted that comꢀ
Scheme 3
7: Nu = I (b), SCN (c)

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Russ.Chem.Bull., Int.Ed., Vol. 60, No. 9, September, 2011
Kondratova et al.
Table 1. Enthalpies of formation and the relative energies (in
parentheses) of two tautomeric forms of ketone 5 based on the
results of quantum chemical calculations by the AM1, PM3, and
Table 2. Parameters of the electronic absortpion spectra of the
keto and enol forms of ketone 5 calculated by the ZINDO/S
method
MNDO methods (kcal mol–1
)
Compound
λmax*/nm
Oscillator strength f
Compound
АМ1
РМ3
MNDO
5 (keto form)
315
0.532
0.251
0.384
0.254
0.498
0.08
276.5
224.3
221.7
349
249.9
243.7
230
5 (keto form)
–84.438
(0.00)
–48.985
(–35.45)
–101.051
(0.00)
–64.728
(–36.32)
–108.49
(0.00)
–70.55
(–37.94)
5 (enol form)
5 (enol form)
0.146
0.542
Being a β,βꢀtricarbonyl compound, ketone 6 easily acts
as a CHꢀacid in the condensation reaction at the methyl
group of the acetyl moiety only when it is involved in the
complex with BF3.10,11 According to the Xꢀray diffraction
data,10 the acetyl group of 3ꢀacetylꢀ4ꢀhydroxycoumarin
in the aboveꢀmentioned complex undergoes structural
changes corresponding to its enolization, which apparently
facilitates subsequent condensation reactions with aldeꢀ
hydes. When considering ketone 5 as a cyclic analog of
compound 6, we found that it can be subjected to condenꢀ
sation with aldehydes in the absence of complexation with
boron compounds (Scheme 4).
The resulting α,βꢀunsaturated dicarbonyl compounds 8
and 9 were characterized by 1H NMR spectroscopy, mass
spectrometry, and elemental analysis. In the 1H NMR
spectra, the signal for the protons of the methylene group
of the dihydrofuran ring is absent, but the spectra show
a singlet at δ 7.0—7.5 characteristic of the methine proton.
According to the Xꢀray diffraction data for monoꢀ
hydrate of compound 8j, there is oneꢀhalf of the C20H15NO
* The position of the longꢀwavelength absorption maximum.
molecule lying in a special position (on a plane of symmeꢀ
try) and oneꢀhalf of the disordered water molecule in the
general position per asymmetric unit. The molecular strucꢀ
ture of 8j and the atomic numbering scheme are shown in
Fig. 2. As can be seen from this figure, molecule 8j has a Z
configuration.
Ketone 5 is not involved in the crotonization with aliꢀ
phatic aldehydes and ketones, as well as with aromatic
ketones; however, it can react with heteroaromatic aldeꢀ
hydes. Some condensation reactions of ketone 5 afforded
not the expected reaction products but dimer 10 (Scheme 5)
as a result of the selfꢀcondensation of ketone 5.
We examined in detail the reaction conditions, in which
dimeric products are formed from 5. Thus, the heating
under reflux of compound 5 in acetic acid in the presence
of catalytic amounts of concentrated hydrochloric (or sulꢀ
A
1.8
1.6
1.4
1.2
1
3
1.0
0.8
0.6
0.4
0.2
2
4
1
2
3
4
305
325
345
365
385
λ/nm
Fig. 1. Electronic absorption spectra of ketone 5 recorded at different CCl4 to MeOH ratios: 100% CCl4 (1), 60% CCl4—30% MeOH (2),
30% CCl4—60% MeOH (3), and 100% MeOH (4).

Reactions of dihydrofuro[3,2ꢀc]coumarinꢀ3ꢀone
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 9, September, 2011
1909
Scheme 4
8
a
b
c
d
e
f
R1
H
Cl
H
H
H
R2
H
H
H
H
R3
H
H
NO2
OMe
OMe
OMe
R4
H
H
H
H
R5
H
H
H
H
H
H
8
g
h
i
j
k
l
R1
OH
OMe
OMe
H
R2
OMe
H
H
H
R3
H
OMe
H
NMe2
H
OMe
R4
H
H
Br
H
H
R5
H
Cl
H
H
H
Br
OMe
H
OMe
H
OMe
Cl
H
H
H
H
9: R = H (a), Br (b)
furic) acid led to the formation of 2,3´ꢀbi(furo[3,2ꢀc]ꢀ
chromene)ꢀ3,4,4´ꢀtrione 10 in 45% yield.
dergoes aromatization through dehydration to form
the furan ring. Final dimer 10 appeared to be more staꢀ
ble than crotonization product 12. As reported earlier,13
the condensation of compound 2 proceeds in a simiꢀ
lar way.aa
Apparently, ketone 5 can react with compounds 8 as
well. The reaction of 5ꢀbromoꢀ2ꢀhydroxybenzaldehyde
with ketone 5 produced (2E,2´Z)ꢀ2´ꢀ(5ꢀbromoꢀ2ꢀhydroxꢀ
ybenzylidene)ꢀ2´H,3H,4H,4´Hꢀ2,3´ꢀbifuro[3,2ꢀ
c]chromeneꢀ3,4,4´ꢀtrione 13 in 27% yield (Scheme 6). It
should be noted that we did not detect the crotonization
product, viz., 2ꢀ(5´ꢀbromoꢀ2´ꢀhydroxybenzylidene)ꢀ2Hꢀ
furo[3,2ꢀc]chromeneꢀ3,4ꢀdione (8m), in the reaction mixꢀ
ture. It appeared that in the synthesis of compound 13, the
precipitation of the latter begins immediately after the
addition of the mineral acid.
1
The H NMR spectrum is consistent with the strucꢀ
ture of dimer 10. Thus, the spectrum shows an intense
doublet at δ 6.50 assigned to one proton at the C(2) atom
of the dihydrofuranone ring and a singlet at δ 8.59 belongꢀ
ing to the proton at the C(2´) atom of the furan ring. In
addition, there are peaks between the aboveꢀmentioned
signals at δ 7.40—8.00 belonging to eight protons of the
coumarin rings.
The mass spectrum of compound 10 has the most inꢀ
tense peak at m/z = 387 corresponding to the molecular
ion [M + 1].
We did not found products of aldol condensation (11)
and crotonization (12) from the dimerization of comꢀ
pound 5. Apparently, intermediate aldol 11 rapidly unꢀ
Scheme 5

1910
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 9, September, 2011
Kondratova et al.
Scheme 6
Most likely, the initially formed crotonization product
rapidly reacts with the second molecule 5 that acts as
a CHꢀacid. In this case, the initial formation of comꢀ
pound 10 is excluded, because this compound has a very
low solubility and, if it were formed, it will immediately
precipitate. This is why we failed to perform the correꢀ
sponding condensation reactions with the use of comꢀ
pound 10, including the use of 5ꢀbromoꢀ2ꢀhydroxybenzꢀ
aldehyde.
All condensation products of ketone 5 with aldehydes
show intense absorption in the electronic absorption specꢀ
tra (Table 3) and exhibit strong fluorescence (Table 4).
We estimated the solvent effect on the electronic abꢀ
sorption spectra of the resulting compounds. In particuꢀ
lar, the absorption spectra of compound 8j are solventꢀ
dependent (Fig. 3). The solvent and the position of the
longꢀwavelength absorption maximum (λ/nm) of this
compound in the electronic absorption spectrum are as
C(21)
N(1)
C(22)
C(19)
C(20)
C(18)
Table 3. Experimental parameters of the electronic absorpꢀ
tion spectra of compounds 8 and 9 and the corresponding
parameters calculated by the ZINDO/S method
C(17)
C(16)
C(15)
C(14)
Comꢀ
pound
Calculation,
max/nm (logε)
Experiment,
max/nm (f )
λ
λ
MeOH
CCl4
O(1)
C(13)
8а
8b
8с
8d
8e
8f
8g
8h
8i
308.73 (0.705)
352 (4.35)
351 (4.20)
354 (3.83)
394 (4.34)
384 (4.37)
396 (4.70)
355 (4.50)
411 (4.42)
392 (4.22)
494 (4.87)
348 (4.04)
422 (4.49)
381 (4.54)
358 (4.25)
350 (4.23)
356 (3.88)
392 (4.35)
383 (4.35)
392 (4.74)
358 (4.51)
413 (4.41)
389 (4.19)
454 (4.82)
349 (4.56)
411 (4.47)
370 (4.55)
C(12)
C(2)
C(3)
340.69 (1.022)
340.90 (0.875)
C(4)
O(2)
C(11)
C(10)
C(5)
C(6)
340.48 (0.841)
340.51 (0.872)
C(8)
O(3)
C(7)
O(9)
8j
8k
8l
354.61 (0.864)
346.98 (0.874)
Fig. 2. Molecular structure of 8j. Thermal ellipsoids are drawn at
9b
the 50% probability level.

Reactions of dihydrofuro[3,2ꢀc]coumarinꢀ3ꢀone
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 9, September, 2011
1911
Table 4. Fluorescence data for compounds 8 and 9*
Comꢀ
pound
Solvent
Absorption band,
Absorption,
Fluorescence,
Stokes shift,
Δλ/nm
abs
fl
λ/nm
λ
max/nm
λ /nm (Irel
)
8a
8b
8c
8d
8e
8f
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
389—399
352—362
356—366
391—401
381—391
363—373
400—410
360—370
363—373
417—427
367—377
386—396
462—472
454—464
484—494
353—363
414—424
377—387
389
352
356
391
381
363
400
360
363
417
367
386
462
454
484
353
414
377
410 (29.6)
—
21
—
—
76
—
152
128
112
130
76
—
—
84
56
152
—
78
—
467 (9.2)
—
515 (299.93)
528 (476)
472 (9.26)
493 (173)
493 (185)
—
8g
8h
Toluene
Toluene
8i
8j
Toluene
—
Toluene
CCl4
DMF
Toluene
Toluene
Toluene
546 (364)
510 (873)
636 (16)
—
492 (169.5)
—
8k
8l
9b
—
* The spectra were recorded at concentrations of 1•10–5 mol L–1
.
follows: CCl4 (454), toluene (462), DMF (484), acetone
(472), methanol (494), and aqueous acetone (499). It can
be seen that the longꢀwavelength absorption maximum of
compound 8j undergoes a bathochromic shift in going
from a nonpolar to polar solvent. This result is apparently
associated with a substantial contribution of the bipolar
resonance structure B (Scheme 7) to the electronic strucꢀ
ture of compound 8j.
Polar solvents provide better solvation of polarized
molecules, thus increasing the contribution of the charge
transfer to the longꢀwavelength absorption of compound
8j in the electronic absorption spectrum.
This effect was particularly pronounced when we used
aqueous acetone as the solvent. Thus, the absorption maxꢀ
imum of compound 8j is bathochromically shifted almost
to 500 nm, which is accompanied by an increase in the
intensity of the absorption.
When analyzing the electronic absorption spectra of
compound 8j, the molecular parameters determined by
Xꢀray diffraction should be considered in more detail. It is
noteworthy that the N(1)—C(18), C(16)—C(17), and
C(19)—C(20) bonds are substantially shortened, which is
indicative of the electronꢀwithdrawing properties of the
dihydrofurocoumarinone moiety in accordance with the
A
3.0
1
2.5
2.0
2
3
4
1.5
5
1.0
0.5
6
360
390
420
450
480
510
540
570
600
λ/nm
Fig. 3. Electronic absorption spectra of compound 8j in different solvents: DMF (1), methanol (2), water—acetone, 2 : 3 (3),
toluene (4), acetone (5), and CCl4 (6).

1912
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 9, September, 2011
Kondratova et al.
Scheme 7
(Fig. 5). The disordered water molecules located between
the stacks form intermolecular O(W)—H(1W)...O(2),
O(W´)—H(1W)...O(2), O(W)—H(2W)...O(2),* and
O(W´)—H(2W)—O(2)* hydrogen bonds with molecules 8j
(O...O, 2.824(2)—3.032(2) Å; O...H, 2.06—2.15 Å).
The resulting compounds exhibit fluorescence, which
is particularly substantial in the case of compounds 8f,h,j,l
containing strong electronꢀreleasing substituents. As can
be seen from Table 4, the compounds containing halogen
atoms or the nitro group at the phenyl ring do not
have fluorescence. The exception is compound 8h. Alꢀ
though the latter contains two strong electronꢀreleasing
groups in the ortho and para positions, it does not exhibit
fluorescence.
The fluorescence spectra of compound 8j were recordꢀ
ed in three solvents. An anomalously large Stokes shift
was observed in DMF, the fluorescence intensity being
decreased.
The reactions under study comprise one of the areas of
our research on the transformations of βꢀdiꢀ and β,βꢀtriꢀ
carbonyl compounds in the coumarin series.10,11 Ketone 5
is a readily available compound and can be easily transꢀ
formed at the furan ring to give new derivatives, which can
be considered as promising fluorophores and biologically
active compounds.
contribution of the resonance structure B to the electronic
structure of molecule 8j.
It was of interest to compare our results with the correꢀ
sponding data for N,Nꢀdimethylꢀ4ꢀnitroaniline. Studies
by Xꢀray diffraction and computational methods showed14
that there is a substantial direct polar conjugation between
the dimethylamino group and the nitro group in N,Nꢀdiꢀ
methylꢀ4ꢀnitroaniline, which is consistent with the quinoid
resonance structure of this compound (Scheme 8).
A comparison of the structures displayed in Scheme 8
shows that the dihydrofurocoumarinone moiety in comꢀ
pound 8j causes the rearrangement of the electronic strucꢀ
ture of the benzene ring toward the resonance structure
with quinoid character by analogy with the nitro group in
N,Nꢀdimethylꢀ4ꢀnitroaniline. Earlier, similar effects have
been found in other N,Nꢀdimethylaniline derivatives conꢀ
taining the electronꢀwithdrawing substituent in the para
position.15
Experimental
The 1H NMR spectra were recorded on a Bruker WPꢀ200ꢀSY
spectrometer operating at 200 MHz in deuterated solvents
(DMSOꢀd6, CDCl3, CF3COOD) with Me4Si as the internal
standard.
The mass spectra were obtained on a Finnigan MAT SSQꢀ710
mass spectrometer with 70 eV ionization energy.
The electronic absorption spectra were measured on an
APEL PDꢀ303UV spectrometer. The fluorescence spectra were
recorded on a Shimadzu RFꢀ50 spectrofluorometer with the use
of a cell containing the solvent as the reference.
According to the Xꢀray diffraction data, molecules 8j
in the crystals are arranged in a headꢀtoꢀtail fashion to form
regular stacks running along the b axis (Fig. 4). The interꢀ
planar distance between the molecules in the stacks is 3.30 Å
* The symmetry code: 2 – x, –y, 1 – z.
Scheme 8

Reactions of dihydrofuro[3,2ꢀc]coumarinꢀ3ꢀone
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 9, September, 2011
1913
C(6A)
C(5A)
O(2B)
C(22A)
C(4A)
O(3B)
C(7A)
C(12B)
C(17A)
C(14B)
O(1A)
C(3A)
N(1A)
C(13B)
C(10B)
C(8A)
C(15B)
C(16B)
C(20B)
C(19B)
C(11B)
C(2B)
C(18A)
O(9A)
C(21A)
C(2A)
O(1B)
C(10B)
C(21B)
O(9B)
C(13A)
C(18B)
C(19A)
C(15A)
C(20A)
C(11A)
C(17B)
C(16B)
C(8B)
N(1B)
C(14A)
C(12A)
C(3B)
O(3A)
C(7B)
C(4B)
O(2A)
C(22B)
C(5B)
C(6B)
Fig. 4. Stacking of molecules 8j in the crystal structure.
The course of the reactions was monitored and the purity of
the reaction products was checked by TLC on Sillufol UVꢀ254
plates using chloroform—acetone (16 : 1) (A), chloroform—acetꢀ
one (5 : 1) (B), and hexane—acetone (2 : 1) (C) as solvent systems.
C(7)
O(9)
C(6)
C(5)
C(8)
O(3)
c
C(10)
C(11)
C(4)
C(3)
C(2)
b
0
O(2)
C(12)
O(W´A)
O(1)
C(13)
O(WA)
C(14)
C(16)
a
C(15)
C(20)
O(W)
O(W´)
C(17)
C(18)
C(19)
C(22)
N(1)
C(21)
Fig. 5. Crystal structure of 8j and hydrogen bonds.

1914
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 9, September, 2011
Kondratova et al.
Quantum chemical calculations by the ZINDO/S method
were carried out using the Hyper Chem 6.0 program. The preꢀ
liminary geometry optimization was performed by the MM+
molecular mechanics method.
a solution of compound 7a (1 g, 3.5 mmol) in acetone (20 mL) at
~20 °C. The precipitate of sodium bromide that formed was
filtered off. The reaction mixture was poured onto ice. The preciꢀ
pitate that formed was filtered off and dissolved in acetone. The
product was reprecipitated with water and washed with acetone.
The yield was 0.52 g (45%), m.p. 134—136 °C. 1H NMR
(CDCl3), δ: 4.72 (s, 2 H, CH2); 7.30—7.39 (m, 2 H, H(6), H(8));
Single crystals of compound 8j were obtained by crystallizaꢀ
tion from acetic anhydride. The Xꢀray diffraction study was perꢀ
formed at 173(2) K on a Bruker SMART APEX2 CCD diffractoꢀ
meter (MoꢀKα radiation, 2θmax = 60.98°). The crystal structure
was solved by direct methods followed by calculations of Fourier
maps with the use of the SHELXSꢀ97 program package.16 The
structure was solved by the fullꢀmatrix leastꢀsquares method with
anisotropic displacement parameters for all nonhydrogen atoms
using the SHELXLꢀ97 program package.16 The hydrogen atoms
(except for the H atoms of the water molecule) were located in
the difference Fourier map and then positioned geometrically
and refined isotropically by the leastꢀsquares method. In the
crystal structure, the water molecule is disordered over two closely
spaced positions, O(W) and O(W´), which are also disordered
about the crystallographic plane, resulting in four positions with
occupancies 0.25. One of the H atoms of the water molecule was
found in difference Fourier map, and the second H atom was
positioned geometrically on the direction of the only possible
intermolecular hydrogen bond with molecule 8j.
2
7.70—7.73 (m, 1 H, H(7)); 8.08 (dd, 1 H, H(5), J5,6 = 8 Hz,
2J5,7 = 2 Hz); 16.87 (s, 1 H, OH). MS, m/z (Irel (%)): 331
[M + 1]+ (100), 330 [M]+ (80). Found (%): C, 40.23; H, 2.18;
I, 38.29. C11H7IO4. Calculated (%): C, 40.03; H, 2.14; I, 38.45.
4ꢀHydroxyꢀ3ꢀ(αꢀthiocyanatoacetyl)coumarin (7c). A solution
of ammonium thiocyanate (0.27 g, 3.5 mmol) in acetone (5 mL)
was added to a solution of compound 7a (1 g, 3.5 mmol) in
acetone (30 mL) at ~20 °C. The precipitate that formed was
filtered off, and the filtrate was poured into water. The resulting
precipitate was filtered off and washed with acetone. The yield
was 0.97 g (80.8%), m.p. 145—147 °C. 1H NMR (CDCl3), δ:
4.59 (s, 2 H, CH2); 7.30—7.45 (m, 2 H, H(6), H(8)); 7.75—7.83
(m, 1 H, H(7)); 8.11 (dd, 1 H, H(5), 2J5,6 = 8 Hz, 2J5,7 = 2 Hz);
15.91 (s, 1 H, OH). MS, m/z (Irel (%)): 261 [M + 1]+ (100).
Found (%): C, 55.37; H, 2.72; N, 5.30; S, 12.40. C12H7NO4S.
Calculated (%): C, 55.17; H, 2.70; N, 5.36; S, 12.27.
Principal crystallographic parameters and the Xꢀray data colꢀ
lection and refinement statistics for compound 8j•H2O at
173 K:* C20H15NO4•H2O, M = 351.35, orthorhombic system,
space group Pnma, a = 9.238(1) Å, b = 6.597(1) Å, c = 28.037(3) Å,
2,3ꢀDihydrofuro[3,2ꢀc]coumarinꢀ3ꢀone (5). An equimolar
amount of sodium cyanide (potassium carbonate, sodium carbꢀ
onate, aniline, or diethylamine; see Scheme 2) was added with
stirring to a solution of compound 7a (14 g, 0.05 mol) in DMSO
(100 mL). After 10 min, the reaction mixture was poured onto
ice. The precipitate that formed was filtered off and recrystalꢀ
lized from ethanol. The yield was 9 g (80%), m.p. 227—228 °C
(cf. lit. data:12 m.p. 227.5—228.5 °C). 1H NMR (CDCl3), δ: 4.86
(s, 2 H, —CH2—); 7.25—7.40 (m, 2 H, H(6), H(8)); 7.77—7.87
(m, 1 H, H(7)); 7.95 (dd, 1 H, H(5), J5,6 = 8 Hz, J5,7 = 1 Hz).
MS, m/z (Irel (%)): 203 [M + 1]+• (100).
Condensation of ketone 5 with aromatic aldehydes (general
procedure). Ketone 5 (0.3 g, 1.5 mmol) was dissolved with heatꢀ
ing in glacial acetic acid. A solution of the corresponding aldeꢀ
hyde (0.002 mol) in acetic acid (3 mL) and concentrated sulfuric
acid (0.1 mL) were added dropwise. The mixture was refluxed
for 1 h and then cooled. The precipitate that formed was filtered
off, washed with acetic acid, and recrystallized from acetic acid.
(2Z)ꢀ2ꢀBenzylideneꢀ4Hꢀfuro[3,2ꢀc]chromeneꢀ3,4(2H)ꢀdione
(8a). The yield was 0.3 g (69%), m.p. 226—228 °C. 1H NMR
(CDCl3), δ: 7.09 (s, 1 H); 7.40—7.60 (m, 5 H, H(8), H(6),
H(3´), H(5´), H(4´)); 7.75—7.95 (m, 3 H, H(7), H(2´), H(6´));
8.07 (d, 1 H, H(9), J9,8 = 8 Hz). MS, m/z (Irel (%)): 291 [M + 1]+
(100). Found (%): C, 74.97; H, 3.41. C18H10O4. Calculated (%):
C, 74.48; H, 3.47.
V = 1708.7(4) Å3, Z = 4, dcalc = 1.37 g cm–3, μ = 0.099 mm–1
,
the total number of reflections is 10028, 2749 independent reflecꢀ
tions, 189 refined parameters, R = 0.055 based on 1813 reflecꢀ
tions with F0 > 4σ(F0), wR(F2) = 0.144, GOOF = 1.015,
hkl ranges: –11 < h < 13, –8 < k < 9, –40 < l < 34; Δρ
=
max
= 0.417 e Å–3, Δρmin = –0.232 e Å–3
.
3ꢀ(αꢀBromoacetyl)ꢀ4ꢀhydroxycoumarin (7a). Bromine (18.9 g,
6.1 mL, 0.115 mol), which was dissolved in acetic acid (5 mL),
was added dropwise with stirring (as the solution turned colorꢀ
less) to a solution of 3ꢀacetylꢀ4ꢀhydroxycoumarin 2 (see Ref. 17)
(20 g, 0.098 mol) in warm glacial acetic acid (70 mL). The reacꢀ
tion mixture was heated to 100 °C. After 10 min, the bromine
color completely disappeared. The reaction mixture was allowed
to cool. The precipitate that formed was filtered off and recrysꢀ
tallized from acetic acid. The yield was 22.9 g (82.6%), m.p.
145—146 °C (cf. lit. data:12 m.p. 145—146 °C). 1H NMR
(CDCl3), δ: 4.83 (s, 2 H, CH2); 7.26—7.43 (m, 2 H, H(6), H(8));
2
7.70—7.80 (m, 1 H, H(7)); 8.08 (dd, 1 H, H(5), J5,6 = 8 Hz,
2J5,7 = 2 Hz); 16.45 (s, 1 H, OH).
4ꢀHydroxyꢀ3ꢀ(αꢀiodoacetyl)coumarin (7b). A solution of soꢀ
dium iodide (0.53 g, 3.5 mmol) in acetone (5 mL) was added to
(2Z)ꢀ2ꢀ(2´ꢀChlorobenzylidene)ꢀ4Hꢀfuro[3,2ꢀc]chromeneꢀ
3,4(2H)ꢀdione (8b). The yield was 0.31 g (63%), m.p. 231—233 °C.
1H NMR (CDCl3), δ: 7.26—7.56 (m, 6 H, H(8), H(6), H(4´),
H(5´), H(6´), CH); 7.79—7.84 (m, 1 H, H(7)); 8.05 (d, 1 H,
H(9), J9,8 = 8 Hz); 8.20 (m, 1 H, H(3´)). MS, m/z (Irel (%)): 325
[M + 1]+ (100), 326 [M + 2]+ (90), 324 [M] (10), 327 [M + 3]+
(13). Found (%): C, 66.59; H, 2.89; Cl, 11.04. C18H9ClO4. Calcuꢀ
lated (%): C, 66.58; H, 2.79; Cl, 10.92.
(2Z)ꢀ2ꢀ(4´ꢀNitrobenzylidene)ꢀ4Hꢀfuro[3,2ꢀc]chromeneꢀ3,4ꢀ
(2H)ꢀdione (8c). The yield was 0.23 g (45.5), m.p. >320 °C.
1H NMR (DMSOꢀd6), δ: 7.24 (s, 1 H, CH); 7.60 (m, 2 H, H(8),
H(6)); 7.97 (m, 1 H, H(7)); 8.33 (m, 5 H, H(9), H(2´), H(3´),
H(5´), H(6´)). MS, m/z (Irel (%)): 336 [M + 1]+ (100), 337
* The singleꢀcrystal Xꢀray diffraction study of 8j•H2O was perꢀ
formed also at room temperature. It was found that the crystal
system and molecular geometry of compound 8j remained unꢀ
changed. The lowꢀtemperature experiment allowed us to more
precisely determine the disorder of the water molecule, the posꢀ
sible positions of its H atoms, and the intermolecular hydrogen
bonds with the participation of these atoms. Principal crystalloꢀ
graphic data for compound 8j•H2O at 293 K: C20H15NO4•H2O,
M = 351.35, orthorhombic system, space group Pnma, a =
= 9.262(2) Å, b = 6.666(1) Å, c = 28.045(6) Å, V = 1731.5(6) Å3,
Z = 4.

Reactions of dihydrofuro[3,2ꢀc]coumarinꢀ3ꢀone
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 9, September, 2011
1915
[M + 2]+ (17), 335 [M] (10). Found (%): C, 64.40; H, 2.51;
N, 4.10. C18H9NO6. Calculated (%): C, 64.48; H, 2.71; N, 4.18.
(2Z)ꢀ2ꢀ(4´ꢀMethoxybenzylidene)ꢀ4Hꢀfuro[3,2ꢀc]chromeneꢀ
3,4(2H)ꢀdione (8d). The yield was 0.32 g (66%), m.p. 227—228
°C. 1H NMR (CDCl3), δ: 3.90 (s, 3 H, OMe); 7.00 (s, 1 H, CH);
7.04 (d, 2 H, H(2´), H(4´), J4´,5´ = 1.5 Hz); 7.44—7.52 (m, 2 H,
H(8), H(6)); 7.81—7.87 (m, 3 H, H(7), H(1´), H(5´)); 8.07
(d, 1 H, H(9), J9,8 = 8 Hz). MS, m/z (Irel (%)): 321 [M + 1]+
(100). Found (%): C, 71.10; H, 3.55. C19H12O5. Calculated (%):
C, 71.25; H, 3.78.
(2Z)ꢀ2ꢀ(3´ꢀBromoꢀ4´ꢀmethoxybenzylidene)ꢀ4Hꢀfuro[3,2ꢀc]ꢀ
chromeneꢀ3,4(2H)ꢀdione (8e). The yield was 0.2 g (34.2%), m.p.
307—308 °C. 1H NMR (DMSOꢀd6), δ: 3.97 (s, 3 H, OMe); 7.13
(s, 1 H, CH); 7.30 (d, 1 H, H(5´), J5´,6´ = 8.79 Hz); 7.61 (m, 2 H,
H(8), H(6)); 7.96 (m, 1 H, H(7)); 8.16—8.24 (m, 3 H, H(9),
H(2´), H(6´)). MS, m/z (Irel (%)): 399 [M + 1]+ (100), 401
[M + 2] (80), 400 [M + 3]+ (25), 398 [M] (5). Found (%):
C, 57.01; H, 2.69; Br, 19.42. C19H11BrO5. Calculated (%):
C, 57.17; H, 2.78; Br, 20.02.
(2Z)ꢀ2ꢀ(3´,4´,5´ꢀTrimethoxybenzylidene)ꢀ4Hꢀfuro[3,2ꢀc]ꢀ
chromeneꢀ3,4(2H)ꢀdione (8f). The yield was 0.23 g (41%), m.p.
>328 °C. 1H NMR (CDCl3), δ: 3.95 (s, 3 H, OMe); 3.98 (s, 6 H,
2 OMe); 7.03 (s, 1 H, CH); 7.18 (s, 2 H, H(2´), H(6´));
7.47—7.51 (m, 2 H, H(8), H(6)); 7.82 (m, 1 H, H(7)); 7.92
(d, 1 H, H(9), J9,8 = 8 Hz). MS, m/z (Irel (%)): 381 [M + 1]+
(100), 382 [M + 2]+ (10), 380 [M] (7). Found (%): C, 66.23;
H, 4.37. C21H16O7. Calculated (%): C, 66.32; H, 4.24.
(2Z)ꢀ2ꢀ(2´ꢀHydroxyꢀ3´ꢀmethoxybenzylidene)ꢀ4Hꢀfuro[3,2ꢀc]ꢀ
chromeneꢀ3,4(2H)ꢀdione (8g). The yield was 0.1 g (20.5%), m.p.
262—263 °C. 1H NMR (DMSOꢀd6), δ: 3.85 (s, 3 H, OMe); 6.97
(m, 1 H, H(5´)); 7.11 (d, 1 H, H(3), J4´,5´ = 8.33 Hz); 7.37
(s, 1 H, CH); 7.52—7.59 (m, 2 H, H(8), H(6)); 7.8 (d, 1 H,
H(6´), J6´,5´ = 7.86 Hz); 7.93 (m, 1 H, H(7)); 8.21 (d, 1 H, H(9),
J9,8 = 8 Hz); 9.76 (s, 1 H, OH). MS, m/z (Irel (%)): 337 [M + 1]+
(100). Found (%): C, 67.39; H, 3.80. C19H12O6. Calculated (%):
C, 67.86; H, 3.60.
(2Z)ꢀ2ꢀ(6´ꢀChloroꢀ2´,4´ꢀdimethoxybenzylidene)ꢀ4Hꢀfuroꢀ
[3,2ꢀc]chromeneꢀ3,4(2H)ꢀdione (8h). The yield was 0.32 g
(55.4%), m.p. 293—295 °C. 1H NMR (DMSOꢀd6), δ: 3.89 (s, 3 H,
OMe); 3.98 (s, 3 H, OMe); 7.17 (s, 1 H, CH); 7.25 (s, 1 H,
H(3´)); 7.55—7.62 (m, 2 H, H(8), H(6)); 7.84 (s, 1 H, H(5´));
7.80—8.20 (m, 2 H, H(9), H(7´)). MS, m/z (Irel (%)): 385
[M + 1]+ (100), 386 [M + 2]+ (20). Found (%): C, 61.85; H, 3.39.
C20H13ClO6. Calculated (%): C, 62.43; H, 3.41.
(2Z)ꢀ2ꢀ(3´ꢀChlorobenzylidene)ꢀ4Hꢀfuro[3,2ꢀc]chromeneꢀ
3,4(2H)ꢀdione (8k). The yield was 0.09 g (19%), m.p. 242—244 °C.
1H NMR (CDCl3), δ: 7.02 (s, 1 H, CH); 7.48—7.58 (m, 4 H,
H(8), H(6), H(4´), H(6´)); 7.80—7.70 (m, 1 H, H(5´)); 7.86
4
(m, 1 H, H(7)); 7.94 (d, 1 H, H(2´), J2´,4´ = 2.13 Hz); 8.07
(d, 1 H, H(9), J9,8 = 8 Hz). MS, m/z (Irel (%)): 325 [M + 1]+
(100), 327 [M + 3]+ (25), 326 [M + 2]+ (20). Found (%):
C, 66.09; H, 2.58; Cl, 11.32. C18H9ClO4. Calculated (%):
C, 66.58; H, 2.79; Cl, 10.92.
(2Z)ꢀ2ꢀ(2´,4´ꢀDimethoxybenzylidene)ꢀ4Hꢀfuro[3,2ꢀc]ꢀ
chromeneꢀ3,4(2H)ꢀdione (8l). The yield was 0.28 g (53%), m.p.
294—296 °C. 1H NMR (CDCl3), δ: 3.88 (s, 3 H, OMe); 3.89
4
(s, 3 H, OMe); 6.48 (d, 1 H, H(3´), J3´,5´ = 2.13 Hz); 6.66
(dd, 1 H, H(5´), 4J5´,3´ = 2.13 Hz, 3J5´,6´ = 8.86 Hz); 7.37—7.52
(m, 2 H, H(6), H(8)); 7.56 (s, 1 H, CH); 7.80 (m, 1 H, H(7));
8.16 (d, 1 H, H(6´), J6´,5´ = 8.85 Hz); 8.50 (d, 1 H, H(9), J9,8
=
= 7.94 Hz). MS, m/z (Irel (%)): 351 [M + 1]+ (100). Found (%):
C, 68.79; H, 3.96. C20H14O6. Calculated (%): C, 68.57; H, 4.03.
(2Z)ꢀ2ꢀ(2´ꢀThienylmethylidene)ꢀ4Hꢀfuro[3,2ꢀc]chromeneꢀ
3,4(2H)ꢀdione (9a). The yield was 0.16 g (36.6%), m.p. 254—256 °C.
1H NMR (CDCl3), δ: 7.23 (t, 1 H, H(4´)); 7.38 (s, 1 H, CH);
7.46—7.56 (m, 2 H, H(6), H(8)); 7.65 (d, 1 H, H(5´), J5,4 = 4.61
Hz); 7.78 (d, 1 H, H(3´), J3,4 = 5.57 Hz); 7.86 (m, 1 H, H(7));
8.12 (d, 1 H, H(9), J9,8 = 7.7 Hz). MS, m/z (Irel (%)): 297 [M + 1]+
(100), 298 [M + 2]+ (18). Found (%): C, 64.86; H, 2.72;
S, 10.82. C16H8O4S. Calculated (%): C, 64.69; H, 2.78; S, 10.97.
(2Z)ꢀ2ꢀ[(4´ꢀBromoꢀ2´ꢀthienyl)methylidene]ꢀ4Hꢀfuro[3,2ꢀc]ꢀ
chromeneꢀ3,4(2H)ꢀdione (9b). The yield was 0.26 g (46.7%), m.p.
276—278 °C. 1H NMR (DMSOꢀd6), δ: 7.49 (s, 1 H, CH);
7.55—7.61 (m, 2 H, H(8), H(6)); 7.81 (d, 1 H, H(3´), J3´,5´
=
= 1.4 Hz); 7.96 (m, 1 H, H(7)); 8.06—8.16 (m, 2 H, H(5´),
H(9´)). MS, m/z (Irel (%)): 377 [M + 1]+ (100), 375 [M – 1]+
(98), 376 [M] (23), 378 [M + 2]+ (22). Found (%): C, 51.41;
H, 1.89; Br, 21.32; S, 8.59. C16H7BrO4S. Calculated (%):
C, 51.22; H, 1.88; Br, 21.30; S, 8.55.
(2E,2´Z)ꢀ2´ꢀ(5´ꢀBromoꢀ2´ꢀhydroxybenzylidene)ꢀ4H,4´Hꢀ
2,3´ꢀbifuro[3,2ꢀc]chromenylideneꢀ3,4,4´ꢀtrione (13). Ketone 5
(0.3 g, 1.5 mmol) was dissolved with heating in glacial acetic
acid, and a solution of the corresponding aldehyde (2 mmol) in
acetic acid (3 mL) was added dropwise followed by the addition
of concentrated sulfuric acid (0.1 mL), after which a precipitate
immediately formed. The reaction mixture was refluxed for 1 h
and then cooled. The precipitate that formed was filtered off,
washed with acetic acid, and recrystallized from acetic acid. The
yield was 0.16 g (27%), m.p. >315 °C. 1H NMR (CF3COOD), δ:
7.66—7.85 (m, 5 H, H(8), H(8´), H(6´), H(6), H(3″)); 8.11—8.79
(m, 3 H, H(7´), H(7), H(4″)); 8.20—8.50 (m, 3 H, H(9), H(9´),
H(6″)); 9.53 (s, 1 H, CH) (the absence of the signal of the OH
group is associated with the effect of the solvent CF3COOD).
MS, m/z (Irel (%)): 567 [M – 2]+ (100), 569 [M] (99), 568
[M – 1]– (25), 570 [M + 1]+ (23). Found (%): C, 60.60; H, 2.10.
C29H13BrO8. Calculated (%): C, 61.18; H, 2.30.
2,3´ꢀBi(furo[3,2ꢀc]chromene)ꢀ3,4,4´ꢀtrione (10). A mixture
of ketone 5 (0.93 g, 4.6 mmol), glacial acetic acid (12 mL), and
concentrated hydrochloric acid (6 mL) was refluxed for 3 h. The
precipitate that formed was filtered off, washed with hot acetone,
and recrystallized from DMSO. The yield was 0.71 g (80%),
dark claret crystals, m.p. 310 °C (decomp.). 1H NMR (DMSOꢀd6),
δ: 6.50 (s, 1 H, H(2)); 7.30—7.60 (m, 4 H, H(8), H(6), H(8´),
H(6´)); 7.70—8.20 (m, 4 H, H(9), H(7), H(9´), H(7´));
8.52 (s, 1 H, H(2´)). MS, m/z (Irel (%)): 387 [M + 1]+ (100).
(2Z)ꢀ2ꢀ(5´ꢀBromoꢀ2´ꢀmethoxybenzylidene)ꢀ4Hꢀfuro[3,2ꢀc]ꢀ
chromeneꢀ3,4(2H)ꢀdione (8i). The yield was 0.22 g (37%), m.p.
>330 °C. 1H NMR (CDCl3), δ: 3.70 (s, 3 H, OMe); 6.68 (d, 1 H,
H(3´), J3´,4´ = 8 Hz); 7.35—7.25 (m, 4 H, H(6), H(8), H(4´),
CH); 7.62 (m, 1 H, H(7)); 7.81 (d, 1 H, H(9), J9,8 = 8 Hz); 8.08
(d, 1 H, H(6´), J = 2 Hz). MS, m/z (Irel (%)): 399 [M] (100), 401
[M + 2]+ (90), 402 [M + 3]+ (24), 400 [M + 1]+ (10). Found (%):
C, 57.74; H, 2.50. C19H11BrO5. Calculated (%): C, 57.17;
H, 2.78.
(2Z)ꢀ2ꢀ[4´ꢀ(Dimethylamino)benzylidene]ꢀ4Hꢀfuro[3,2ꢀc]ꢀ
chromeneꢀ3,4(2H)ꢀdione (8j). The yield was 0.2 g (40%), m.p.
214—216 °C. 1H NMR (acetoneꢀd6), δ: 3.13 (s, 6 H, NMe2);
6.80—7.00 (m, 3 H, H(2´), H(6´), CH); 7.46—7.62 (m, 2 H,
H(8), H(6)); 7.69 (m, 3 H, H(7), H(3´), H(5´)); 8.25 (d, 1 H,
H(9), J9,8 = 8.54 Hz). MS, m/z (Irel (%)): 334 [M + 1]+ (100),
335 [M + 2]+ (10). Found (%): C, 71.59; H, 4.69; N, 3.9.
C20H15NO4. Calculated (%): C, 72.06; H, 4.54; N, 4.20.

1916
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 9, September, 2011
Kondratova et al.
Found (%): C, 67.77; H, 2.60. C22H10O7. Calculated (%):
C, 68.40; H, 2.61.
8. D. V. Kravtchenko, T. A. Chibisova, V. F. Traven, Heteroꢀ
cycl. Commun., 1997, 3, 331.
9. V. F. Traven, I. I. Sakharuk, D. V. Kravchenko, A. V. Ivashꢀ
chenko, Khim. Geterotsikl. Soedin., 2001, 312 [Chem. Hethꢀ
erocycl. Compd. (Engl. Transl.), 2001].
10. A. V. Manaev, T. A. Chibisova, K. A. Lyssenko, M. Yu.
Antipin, V. F. Traven, Izv. Akad. Nauk, Ser. Khim., 2006,
2012 [Russ. Chem. Bull., Int. Ed., 2006, 55, 2091].
11. A. V. Manaev, T. A. Chibisova, V. F. Traven, Izv. Akad.
Nauk, Ser. Khim., 2006, 2144 [Russ. Chem. Bull., Int. Ed.,
2006, 55, 2226].
12. M. Trkovnik, N. Zivkovic, M. Kules, R. Djudjic, Org. Prep.
Proced. Int., 1978, 10, 215.
13. V. F. Traven, D. V. Kravtchenko, T. A. Chibisova, S. V.
Shorshnev, Mendeleev Commun., 1997, 249.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 08ꢀ03ꢀ90016ꢀ
Bel_a).
References
1. U. Brackman, Laser Dyes, Lamdachrome, Data Sheets, 2nd
ed., Göttingen, Germany, 1997, p. 268.
2. R. P. Haugland, Handbook of Fluorescent Probes and Reꢀ
search Chemical, Ed. M. T. Z. Spence, Molecular Probes,
Inc., Eugene, USA, 1996.
3. A. Guiotto, P. Rodighiero, P. Manzini, G. Pastorini, F. Borꢀ
din, F. Baccichetti, F. Carlassare, D. Vedaldi, F. Dall´Acqua,
M. Tamaro, G. Recchia, M. Cristofolini, J. Med. Chem.,
1984, 27, 959.
4. D. Vedaldi, F. Dall´Acqua, F. Baccichetti, F. Carlassare,
F. Bordin, P. Rodighiero, P. Manzini, A. Guiotto, Farmaco,
1991, 46, 1381.
5. V. F. Traven, D. V. Kravtchenko, T. A. Chibisova, S. V.
Shorshnev, Heterocycl. Commun., 1996, 2, 345.
6. V. F. Traven, R. V. Rozhkov, A. Yu. Tolmachev, N. A. Kuznꢀ
ezova, N. Ya. Podhaluzina, E. A. Carberry, Heterocycl. Comꢀ
mun., 1997, 3, 339.
14. O. Y. Borbulevych, R. D. Clarc, A. Romero, L. Tan, M. Y.
Antipin, V. N. Nesterov, B. H. Cardelino, C. E. Moore,
M. Sanghadasa, T. V. Timofeeva, J. Mol. Struct., 2002, 604, 73.
15. A. S. Batsanov, J. C. Collings, R. M. Ward, A. E. Goeta,
L. Porre´s, A. Beeby, J. A. K. Howard, J. W. Steed, T. B.
Marder, Cryst. Eng. Commun., 2006, 8, 622.
16. G. M. Sheldrick, SHELXS 97, SHELXL 97, University of
Göttingen, Göttingen, Germany, 1997.
17. E. R. Eisenhauer, K. P. Link, J. Am. Chem. Soc., 1953,
75, 2044.
7. O. B. Safronova, D. V. Kravchenko, I. N. Senchenya, V. F.
Traven, Zh. Obshch. Khim., 2001, 71, 588 [Russ. J. Gen. Chem.
(Engl. Transl.), 2001, 71].
Received June 30, 2008;
in revised form December 20, 2010