Design of crystal packings of styrylheterocycles and [2+2] photocycloaddition reactions in their single crystals 6. Synthesis and crystal packings of neutral crown-containing and model styrylheterocycles

Article abstract of DOI:10.1007/s11172-009-0155-7

Neutral crown-containing and model styrylheterocycles of the 4-pyridine, 4-quinoline, and 9-acridine series were synthesized under acidic catalysis. The influence of the molecular geometry of these compounds, as well as of related styrylheterocycles of th

Full text of DOI:10.1007/s11172-009-0155-7

Russian Chemical Bulletin, International Edition, Vol. 58, No. 6, pp. 1192—1210, June, 2009
1192
Design of crystal packings of styrylheterocycles and
[2+2] photocycloaddition reactions in their single crystals
6.* Synthesis and crystal packings of neutral crownꢀcontaining
and model styrylheterocycles**
L. G. Kuz´mina,a A. I. Vedernikov,b N. A. Lobova,b S. K. Sazonov,b
S. S. Basok,c J. A. K. Howard,d and S. P. Gromovb
aN. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
31 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (495) 954 1279. Eꢀmail: kuzmina@igic.ras.ru
bPhotochemistry Center, Russian Academy of Sciences,
7A ul. Novatorov, 119421 Moscow, Russian Federation.
Fax: +7 (495) 936 1255. Eꢀmail: gromov@photonics.ru
cA. V. Bogatsky PhysicoꢀChemical Institute, National Academy of Sciences of Ukraine,
86 Lustdorfskaya doroga, 65080 Odessa, Ukraine
dDepartment of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Neutral crownꢀcontaining and model styrylheterocycles of the 4ꢀpyridine, 4ꢀquinoline,
and 9ꢀacridine series were synthesized under acidic catalysis. The influence of the molecular
geometry of these compounds, as well as of related styrylheterocycles of the 2ꢀbenzothiazole
and benzobisthiazole series, on the formation of a particular crystal packing was investigated
based on Xꢀray diffraction data. An extension of the conjugation system in the molecules can
result in the sandwichꢀherringbone packing motif as the only one of the three packing motifs
most typical of this class of compounds. This packing provides the preorganization of the
structural units for the [2+2] photocycloaddition reaction. The styrylheterocycle containing
the bulky 9ꢀacridine moiety is nonplanar due to strong intramolecular steric interactions. The
packing motifs formed by nonplanar molecules do not provide the preorganization of the
molecules for the [2+2] photocycloaddition. The introduction of the crown ether moiety into
the benzene ring of the styrylheterocycle can decrease the predictability of the packing motif as
a result of the inclusion of solvent molecules capable of hydrogen bonding with the heteroatꢀ
oms of the macrocycle in the crystal structure.
Key words: styrylheterocycles, synthesis, Xꢀray diffraction study, crystal packing, design of
crystal packings.
Unsaturated organic compounds, such as cinnamic
acid derivatives, stilbenes, their aza analogs and vinilogs
containing one or several ethylene bonds within the
πꢀconjugated fragment, can be involved in the [2+2]
photocycloaddition (PCA) reaction to form cyclobutane
derivatives (Scheme 1).2—15 This method of the construcꢀ
tion of carbon—carbon bonds holds promise because of
the relative ease of the synthesis (irradiation at a specified
wavelength), the reversibility and, in some cases, high
stereoselectivity of the photoreaction yielding only some
of the theoretically possible cyclobutane isomers. The PCA
reaction can occur in concentrated solutions and in the
solid state, including the single crystals. Single crystalꢀtoꢀ
single crystal transformations (i.e., the transformations
that occur without the degradation of the single crystal)
are of particular interest. Due to the topochemical
control of the crystal lattice, these transformations virꢀ
tually always occur stereospecifically and are accompaꢀ
nied by substantial changes in the physical properties
of the crystals.16—21
We found that cationic styryl dyes, which are heteroꢀ
analogs of stilbene, are involved in the PCA reaction in
solution22—25 and in the solid state1,25—29 under visibleꢀ
light irradiation. An extended conjugation chain of the
molecular cations of the dyes consists of the quaternized
nitrogenꢀcontaining heterocycle and the substituted
benzene ring bridged by an ethylene group. In these comꢀ
* For Part 5, see Ref. 1.
** Dedicated to Academician O. N. Chupakhin on the occasion
of his 75th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1161—1178, June, 2009.
1066ꢀ5285/09/5806ꢀ1192 © 2009 Springer Science+Business Media, Inc.

Crystal packings of neutral styrylheterocycles
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 6, June, 2009
1193
Scheme 1
Neutral styrylheterocycles, which are synthetic preꢀ
cursors of styryl dyes, are also of considerable interest
for the PCA reaction. Previously,30 we have shown that
15ꢀcrownꢀ5ꢀcontaining 2ꢀstyrylbenzothiazole forms headꢀ
toꢀheadꢀtype sandwich complexes (B) in the presence of
Ba2+ ions in solution, and these complexes undergo
stereoselective PCA. In the crystals, the dimethoxy
derivative of 4ꢀstyrylquinoline forms dimer pairs. We have
found27 that this compound undergoes the single crystalꢀ
toꢀsingle crystal photoreaction giving the only rctt isomer
of the cyclobutane derivative. Since the styrylheterocycle
of the benzoxazole series containing the dimethylamino
group in the benzene moiety is involved in the efficient
reversible solidꢀstate PCA reaction accompanied by a
sharp change in the spectroscopic characteristics, it was
suggested to use this compound in rewritable optical data
storage systems.31 However, the possibility of performing
the PCA reaction in styrylheterocycles without the assistꢀ
ance of additional factors, such as the complexation with
metal cations or the protonation of the heterocycle at the
nitrogen atom, remains poorly known. Based on the data
on the crystal structures of neutral styrylheterocycles (priꢀ
marily, of derivatives of benzannulated fiveꢀmembered
nitrogenꢀcontaining heterocycles, such as benzothiazole,
benzoselenazole, and benzimidazole; see, for example,
Refs 32—36), no definite conclusions can be drawn as
to the tendency of unsaturated compounds of this class to
form a particular packing motif, which could be favorable
for the solidꢀstate PCA reaction.
pounds, the PCA reaction can occur stereoselectively in
the case of a particular preorganization of a pair of the
starting structural units. It is known3,14,18 that for the PCA
reaction to occur in a pair of unsaturated molecules
(a dimer pair), their ethylene fragments should be
arranged approximately in the parallel planes one above
another with a distance d between these fragments in a
range of 3.3—4.2 Å (see Scheme 1). The preorganization
of the dye molecules in solution is achieved due to the
presence of the crown ether moiety facilitating the formaꢀ
tion of dimeric headꢀtoꢀtail complexes with ammonium
ions (A) or headꢀtoꢀhead sandwich complexes with metal
cations (B). In the solid state, styryl dyes are prone
to form stacking motifs in the molecular packings due to
stacking interactions between the conjugated fragꢀ
ments and the efficient intramolecular charge transfer in
the organic cations from the donor benzene moiety to
the acceptor heterocyclic fragment. Previously, the possiꢀ
bility of the solidꢀstate PCA reaction in styryl dyes has
been analyzed27,28 and attempts have been made1,29 to
design crystal structures, i.e., to predict and design such
crystal packings, in which the PCA reaction can occur
(including the single crystalꢀtoꢀsingle crystal photoreacꢀ
tion) to give various isomers of cyclobutane.
In the present study, we investigated the crystal
packings of styrylheterocycles 1—6 containing heteroꢀ
cyclic moieties of different size along with the flexible
bulky crown ether moiety in the benzene ring or small
methoxy/dimethylamino groups, which mimic the elecꢀ
tronic effect of (aza)crown ethers on the styryl chromogen.
It was found that the successive extension of the conꢀ
R1 = R2 = OMe (1a, 2a, 3, 4a);
R
R
R
1 + R2 = OCH2(CH2OCH2)nCH2O, n = 3 (1b, 4b, 5), 4 (2b);
1 = NMe2, R2 = H (6a);
1 = N[CH2(CH2OCH2)2CH2]2O, R2 = H (6b)

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Kuz´mina et al.
jugation system in styrylheterocycles and the nature of
the substituents in the benzene ring have an effect on the
ability of the molecules to form dimer pairs preorganized
for PCA.
nucleophilic addition of 9ꢀmethylacridine to veratralꢀ
dehyde, affords both geometric isomers of 3 and/or subꢀ
stantially hinders the thermal Z→E isomerization.
The synthesis of styrylheterocycles by the condensaꢀ
tion under acidic catalysis is more convenient than the
corresponding synthesis under basic catalysis because it
does not require the use of unstable alkali metal alkoxides
and anhydrous solvents.37 We synthesized the dimethoxy
derivative of 4ꢀstyrylpyridine (E)ꢀ1a in 23% yield by the
condensation of 4ꢀpicoline with veratraldehyde in acetic
anhydride by analogy with the synthesis of styrylpyridines
substituted at the benzene ring.43 The dimethylaminoꢀ
derivative (E)ꢀ6a was synthesized in 21% yield according
to a known procedure44 by the condensation of 4ꢀpicoline
with 4ꢀdimethylaminobenzaldehyde in the presence
of benzoyl chloride and pyridine. Azacrownꢀcontaining
4ꢀstyrylpyridine (E)ꢀ6b was synthesized by the conꢀ
densation of 4ꢀpicoline with Nꢀ(4ꢀformylphenyl)azaꢀ
18ꢀcrownꢀ6 ether in the presence of Lewis acids (see
Scheme 2). The reaction was activated by the protonation
of picoline with hydrogen chloride or anhydrous SnCl2.
In both cases, the target compound was prepared in
moderate yield (22 and 27%, respectively).
The condensation of lepidine with veratraldehyde in
acetic anhydride gave the compound (E)ꢀ2a in 7% yield
and led to the recovery of the starting aldehyde (84%).
Unlike the synthesis of styrylacridine 3, the use of ZnCl2
in acetic acid resulted in an increase in the yield of the
target styrylquinoline (E)ꢀ2a to 36% without the formaꢀ
tion of (Z)ꢀ2a or the side product of the Michael addition
(TLC monitoring). Hence, this method can be recomꢀ
mended as the more convenient approach alternative to
the condensation under strongly basic conditions,27,37
which afforded (E)ꢀ2a in 38—46% yields.
For this purpose, we developed a procedure for the
synthesis of new compounds 3 and 6b, studied for the first
time compounds 1a,b, 3, and 6a,b by Xꢀray diffraction,
and analyzed the changes in certain molecular geometric
parameters and the crystal packings of these compounds,
as well as of neutral styrylheterocycles 2a,b,27,37 4a,b,36,38
and 5,39 which we have investigated previously. The strucꢀ
ture of bisheterocyclic compound 7, which is a product
of the Michael addition of the methylheterocycle at the
ethylene bond of the styrylheterocycle, was established
by Xꢀray diffraction.
Synthesis of compounds 1—6. The synthesis of deriꢀ
vatives of 4ꢀpyridine (E)ꢀ1a,b, 4ꢀquinoline (E)ꢀ2a,b,
2ꢀbenzothiazole (E)ꢀ4a,b, and benzobisthiazole (E)ꢀ5 by
the condensation of the corresponding methylꢀsubstituted
heterocyclic bases with benzaldehydes in the presence of
alkali metal alkoxides in aprotic solvents has been docuꢀ
mented previously.27,37—39 We found that under these
conditions 9ꢀmethylacridine does not react with veratrꢀ
aldehyde. The synthesis of 9ꢀstyrylacridines containing
various substituents in the benzene moiety by the conꢀ
densation of 9ꢀmethylacridine with the corresponding
benzaldehydes with heating in a mixture of acetic anhyꢀ
dride and acetic acid was described.40 The condensation
of 9ꢀmethylacridine with veratraldehyde under these conꢀ
ditions afforded an inseparable mixture of the E and Z
isomers (1 : 4.3) of compound 3 in a total yield of 3% and
gave bisacridine 7 as a result of the Michael addition of
the second 9ꢀmethylacridine molecule at the activated
C=C bond of compound 3 (Scheme 2) in 26% yield. The
use of anhydrous ZnCl2 in acetic acid as the catalyst
resulted in an increase in the yield of compound 7 (to
36%), which was formed as the only product under these
conditions.
Previously, we have obtained27,37,41,42 the correspondꢀ
ing bisheterocycles as a result of the Michael addition of
methylheterocycles to 4ꢀstyrylpyridines, 4ꢀstyrylpyrimiꢀ
dines, 4ꢀstyrylquinolines, and 2ꢀstyrylbenzothiazoles,
when performing the condensation under basic conditions.
It should be noted that the structure of the bisheterocyclic
products was established for the first time by the Xꢀray
diffraction study of compound 7 (see below). The unusuꢀ
ally high reactivity of the ethylene bond in compound 3
with respect to nucleophilic agents is apparently attribꢀ
uted to a substantial disturbance of the πꢀconjugation in
(E)ꢀ9ꢀstyrylacridine caused by the steric effects. This leads
to a strong twisting of the chromogen (E)ꢀ3, as was
confirmed by Xꢀray diffraction. Evidently, as a result of
this twisting, the E isomer becomes thermodynamically
less favorable than the Z isomer. Hence, the dehydration
of the intermediate alcohol, which is formed through the
Xꢀray diffraction study. To perform the design of moꢀ
lecular crystals, it is necessary to construct the unsaturꢀ
ated molecules, which are selfꢀorganized in the solid state
and form dimer pairs with short distances between the
ethylene fragments, resulting in the preorganization of
these molecules for the PCA reaction. Our studies1,26—29
on the crystal packings of a large series of crownꢀcontainꢀ
ing and model styryl dyes showed that, in most cases, the
planar cations of these dyes are packed to form stacks
with either a parallel (Fig. 1, a) or a herringbone (Fig. 1, b)
mutual arrangement. Evidently, in the case of a stacked
Fig. 1. Parallel (a) and herringbone (b) packing motifs of the
cations of styryl dyes in the crystals; the lateral projections of
the planar cations are indicated by lines.

Crystal packings of neutral styrylheterocycles
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 6, June, 2009
1195
Scheme 2
structure, the crystal lattice can retain structural units as
dimer pairs. In such single crystals, the solidꢀstate PCA
reaction can occur. In most cases, this reaction is accomꢀ
panied by the degradation of the single crystal. However,
in some cases, the single crystalꢀtoꢀsingle crystal PCA
reaction is observed.1,26—29
The possibility of the single crystalꢀtoꢀsingle crystal
PCA reaction depends on many factors, including the
symmetry of the stacks. The most often occurring stacks
are those in which the cations of the dyes are arranged in a
headꢀtoꢀtail fashion; the headꢀtoꢀhead arrangement of
the molecules in stacks is observed more rarely (Fig. 2).
Any two adjacent cations in the stacks of the first type are
related by a center of symmetry, resulting in that the
stacks are composed of dimer pairs of the cations with
the shorter distance d1 between the ethylene fragments
in the dimer pair compared to the distance d2 between the
ethylene fragments of adjacent dimer pairs.27—29 This

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Kuz´mina et al.
parallel planes in the stacks arranged in a headꢀtoꢀhead
fashion. In the latter case, the ethylene fragments of
adjacent cations are generally so distant from each other
(>5 Å) that the PCA reaction in single crystals becomes
impossible.
In continuation of our research on the solidꢀstate PCA
reactions, we investigated these reactions with neutral
styrylheterocycles related to styryl dyes, because the catꢀ
ions of the dyes are structurally similar to the correspondꢀ
ing styrylheterocycles. The main difference is that the
quaternized fragment of the heterocyclic moiety in
the dye is replaced by the nonꢀquaternized fragment
in the styrylheterocycle. This leads to substantial changes
in the spectroscopic properties of the compounds, such as
large hypsochromic shifts of the longꢀwavelength absorpꢀ
tion maximum for the styrylheterocycles compared to that
observed for the related dyes. This is associated with the
fact that the intramolecular electron density transfer from
the benzene ring to the uncharged heterocyclic moiety is
less favorable. Therefore, for the PCA reaction to occur
in styrylheterocycles, the irradiation should be performed
at a shorter wavelength. Substantial changes associated
with the destruction of the conjugation chain of the chroꢀ
mophore as a result of the formation of cyclobutane are
observed in the nearꢀUV region.30,31 It should be noted
that styrylheterocycles have a great scope for the crystal
design, because the presence of the neutral nitrogen atom
in the heterocyclic moiety allows their use as photosensiꢀ
tive ligands in coordination structures stabilized by hydroꢀ
gen bonds or based on metal complexes.19—21 Later, we
will investigate this area of the crystal design of styrylꢀ
heterocycles and examine the possibility of the solidꢀstate
PCA reactions in such structures.
Molecular structures. The molecular structures of neuꢀ
tral styrylheterocycles 1—6 and bisacridine 7 are shown in
Figs 3 and 4. In a series of compounds 1—3 and 4, 5, the
πꢀconjugation system gradually increases due to the
annulation of the heterocyclic moiety to the benzene or
thiazole rings. In compounds 1 and 6, the heterocyclic
moiety (4ꢀpyridine) remains unchanged, but the subꢀ
stituents in the benzene ring are varied. Compounds 1a,
2a, 4a, and 6a contain electronꢀdonating methoxy or
dimethylamino groups, whereas the related compounds
1b, 2b, 4b, and 6b contain the crown ether moiety with
the same type of annulation of the heteroatoms to the
chromogen.
Fig. 2. Modes of the mutual arrangement of the cations of styryl
dyes in the stacks formed in a headꢀtoꢀtail fashion (a) and in a
headꢀtoꢀhead fashion (b) presented in two ways; the conjugated
fragments of the cations are indicated by lines; the substituents
in the benzene ring are outlined by ovals, the centers of symmetry
are indicated as
.
•
symmetry of the stacks is favorable for the single crystalꢀ
toꢀsingle crystal PCA reaction.
The stacks with a headꢀtoꢀhead arrangement of the
molecules are formed by translationally related structural
units. Hence, even one event of the PCA reaction in this
stack necessarily leads to the violation of the local symꢀ
metry, i.e., to the formation of defects. In addition, the
pairs of adjacent cations in the stack of translationally
related structural units are identical (d1 = d2 = d); hence,
the PCA reaction occurs statistically. Thus, the reaction
of the selected molecular cation can occur with equal
probability with adjacent cations in the stack located above
or below this cation. The progression of the PCA reaction
throughout the bulk of the crystal will give rise to “extra”
structural units in the stacks (i.e., the structural units,
which have no pairs for the PCA reaction), which results
in an enlargement of defect regions. Hence, the PCA
reaction in the crystals of styryl dyes packed in a headꢀtoꢀ
head fashion cannot occur without the degradation of the
single crystal.
In the crystals, compounds 1b and 4b exhibit the
soꢀcalled “bicycleꢀpedal” isomerization,46 which is often
observed in the crystal structures of styryl dyes1,28,29 as a
consequence of the temperatureꢀdependent dynamic proꢀ
cess in the crystals, resulting in that the ethylene fragment
is twisted about the single bonds. This isomerization leads
to the disorder of the central azastilbene moiety over two
positions related by the rotation of the structural unit
about its long axis by 180°. In the structure of 1b, all atoms
It should also be noted that the positive charge in the
cations of styryl dyes is located primarily on the heteroꢀ
cyclic moiety.45 In stacks, Coulomb repulsions are miniꢀ
mized as a results of either a headꢀtoꢀtail arrangement of
the molecular cations or a substantial mutual shift in the

Crystal packings of neutral styrylheterocycles
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 6, June, 2009
1197
C(14)
C(9)
C(8)
C(10)
C(11)
C(1)
C(2)
O(1)
C(6)
C(3)
C(4)
N(1)
C(5)
C(12)
C(7)
C(13)
O(2)
C(15)
C(14´)
C(15)
C(9´)
C(10´)
C(14)
1a
C(15´)
C(9)
C(7´)
C(2)
O(2)
O(1´)
O(2´)
C(11´)
C(6)
C(2´)
C(10)
C(8´)
C(12´)
C(16)
C(1)
N(1´)
O(1)
C(11)
C(1´)
C(3)
C(4)
C(17)
C(8)
C(7)
C(13´)
C(16´)
O(3)
N(1)
O(5´)
C(6´)
C(3´)
C(12)
C(13)
C(21´)
O(5)
C(17´)
C(5)
C(3)
C(4)
C(5)
C(4´)
C(5´)
C(18)
O(4)
O(3´)
C(2)
C(20´)
C(19)
C(23)
C(21)
1b
C(6)
C(7)
O(2)
C(18´)
C(19´)
C(16)
C(1)
C(21)
C(20)
O(4´)
C(20)
O(1)
C(19)
C(14)
N(1)
C(18)
C(22)
C(8)
C(13)
C(15)
C(17)
C(35)
C(36)
N(2)
C(25)
C(12)
C(24)
C(29)
C(34)
C(9)
C(10)
C(26)
C(11)
C(28)
C(33)
C(11)
C(32)
C(27)
3
C(31)
C(30)
C(12)
C(37)
C(15)
C(10)
C(13)
C(17)
O(2)
C(9)
C(16)
N(1)
C(18)
C(19)
C(1) C(8)
C(6)
C(22)
C(7)
C(21)
C(14)
C(2)
O(1)
C(5)
C(23)
C(3)
C(4)
7
C(9)
C(8)
C(5)
C(14)
C(10)
C(11)
C(7)
C(4)
C(3)
N(2)
N(1)
C(1)
C(12)
C(6)
C(15)
C(16)
O(2)
C(14)
C(10)
C(2)
C(9)
C(13)
O(1)
N(2)
C(15)
C(17)
C(18)
C(8)
C(6)
C(11)
6a
C(25)
C(12)
C(24)
C(7)
C(4)
C(5)
C(3)
C(19)
O(5)
C(13)
O(3)
N(1)
C(23)
O(4)
C(20)
C(21)
C(1)
C(2)
C(22)
6b
Fig. 3. Molecular structures of styrylheterocycles 1a,b, 3, and 6a,b (two s conformers for 1b) and bisacridine 7. The nonhydrogen
atoms are shown as displacement ellipsoids at the 50% probability level.

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Kuz´mina et al.
O(2)
O(1)
O(6)
N(1)
Cl(2)
O(2)
O(1)
N(1)
O(3)
O(1W)
Cl(1)
O(4)
O(5)
2a
2b•CH2Cl2•H2O
S(2)
S(1´)
N(1)
O(2)
O(3)
O(4)
N(2)
S(1)
O(1)
O(3)
O(5)
S(1)
N(1´)
O(1)
O(4)
O(2)
N(1)
4 b
4a
O(4)
S(1)
O(5)
O(3)
N(2)
N(1)
O(1)
S(2)
O(2)
5
Fig. 4. Molecular structures of styrylheterocycles 2a,b, 4a,b, and 5 (two s conformers for 4b; two independent molecules for 4a; the
solvate with CH2Cl2 and water for 2b). The hydrogen bonds in the structure of 2b•CH2Cl2•H2O are indicated by dashed lines.
of the same type of two “bicycleꢀpedal” s conformers are
nonequivalent to each other. In the structure of 4b, only
atoms of the ethylene and thiazole fragments are nonꢀ
equivalent.
The geometric characteristics of styrylheterocycles
1—6, which are of most importance for our discussion,
are as follows: the bond lengths in the ethylene fragment
CHet—C=C—CAr (l1, l2, and l3, respectively) and the
dihedral angles between the planes of the heterocycle and
the ethylene bridge (τ1), the ethylene bridge and the
benzene ring (τ2), and the heterocyclic and benzene rings
(τ3). These parameters for compounds 1—6 are given in
Table 1.
C=C double bonds and is indicative of a high degree
of localization of the πꢀelectron density on this bond and,
consequently, of a weak influence of the conjugation on
the stabilization of a particular molecular conformation
of the styrylheterocycle. This conclusion is consistent
with the existence of two 4ꢀstyrylquinolines, 2a and 2b,
having planar and nonplanar conformations, respectively,
whereas the corresponding bond lengths in the ethylene
fragments of the molecules are virtually equal. It should
be noted that the substantial twisting of the planar heteroꢀ
cyclic moiety in crown ether 2b with respect to the ethylꢀ
ene fragment (τ1 = 41.8°) is not a consequence of the
steric repulsion, because the same fragments in dimethoxy
derivative 2a are only weakly twisted (τ1 = 16.0°). In all
the molecules under consideration, the lengths of the
The ethylene bond length l2 in these compounds
varies in the range of 1.31—1.35 Å, which is typical of

Crystal packings of neutral styrylheterocycles
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 6, June, 2009
1199
Table 1. Bond lengths in the ethylene fragment CHet—C=C—CAr
(l1, l2, and l3, respectively) and the dihedral angles between the
a
b
c
planes of the heterocycle and the ethylene bridge (τ ), the ethylꢀ
1
ene bridge and the benzene ring (τ ), and the heterocyclic and
2
benzene rings (τ ) in molecules 1—6
3
Comꢀ
pound
Bond/Å
Angle/deg
l1
l2
l3
τ
τ
τ
3
1
2
Fig. 5. Typical crystal packing motifs (ladder (a), ladderꢀherꢀ
ringbone (b), and sandwichꢀherringbone (c)) of neutral styrylꢀ
heterocycles; the lateral projections of the conjugated fragments
of the molecules are indicated by solid lines; the projections of
the conjugated fragments onto each other are indicated by dashed
lines.
1a
1b*
1.469(2) 1.341(2) 1.470(2)
1.463(5), 1.331(5), 1.469(6), 6.2, 11.1, 17.2,
1.447(8) 1.313(7) 1.471(7) 4.8 10.0 14.8
1.471(1) 1.341(2) 1.469(2) 16.0 16.6 2.3
1.471(8) 1.342(4) 1.466(8) 41.8 13.3 55.0
1.478(2) 1.332(2) 1.469(2) 51.5 21.7 73.2
5.7 10.2 15.7
2a
2b
3
4a*
1.455(2), 1.341(2), 1.463(2), 5.4,
1.451(2) 1.342(2) 1.467(2) 8.7
1.453(7), 1.327(10), 1.530(9), 5.9,
1.458(8) 1.349(9) 1.444(11) 8.2
9.6, 14.9,
3.9 11.9
7.5, 13.2,
6.2 14.2
ladder (Fig. 5, a), ladderꢀherringbone (Fig. 5, b), and
sandwichꢀherringbone (Fig. 5, c) packings. Undoubtedly,
there is a genetic relationship between these types
of the arrangement of the structural units. The packing
motifs presented in Fig. 5, a and b are derived from
the motifs presented in Fig. 1, a and b, respectively, by
the shift of each subsequent molecule in the stack with
respect to the previous molecule in the same direction
until the mutual projection disappears. The packing shown
in Fig. 5, c is formed in the case of the analogous destrucꢀ
tion of the stacking architecture (see Fig. 1, b) but with
respect not only to one structural unit but also with
respect to the dimer pair of the molecules.
4b*
5b
6a
6b
1.438(6) 1.322(6) 1.485(6)
1.474(4) 1.336(4) 1.469(4)
1.459(6) 1.353(6) 1.471(6)
2.1
3.8
2.4
4.6
0.9
2.5
4.2
4.4
4.9
* For two orientations corresponding to the disordered ethylene
fragment or for two independent molecules.
formally single bonds l1 and l3 vary in the range of
1.44—1.53 Å, which is typical of an essentially localized
ethylene bonds.
The presence of stacked or ladderꢀherringbone packings
in the crystal structures depends on the different contriꢀ
butions of two weak directed interactions most typical of
aromatic compounds, which are responsible for the selfꢀ
organization of the molecules in solution followed by
the nucleation and the crystal growth. These are the
π...π interactions (stacking interactions) and the weak
C—H...πꢀsystem hydrogen bonds.47 These two types of
interactions require a different geometry of the mutual
arrangement of the pair of molecules, from which the
selfꢀassembly of a supramolecular structure begins. For
benzene and aromatic compounds devoid of heteroatoms,
the perpendicular (Tꢀshaped) mutual arrangement of two
molecules corresponds to the global minimum, whereas
the parallel arrangement of the molecules with a shift is
energetically less favorable.48 In the packings shown in
Fig. 5, a and b, the C—H...πꢀsystem hydrogen bonds play
the major role in the stabilization of the crystal structure.
In heteroaromatic compounds or aromatic compounds
containing an electronꢀwithdrawing substituent, the
contribution of stacking interactions increases due to
an increase in the donorꢀacceptor contribution.48 Hence,
at least regions with stacking interactions (for example, of
relatively isolated dimer pairs of molecules), if not the
stacking arrangement of the molecules most favorable for
the PCA reaction, would be expected to appear. It is this
situation that is observed in the sandwichꢀherringbone
packing (see Fig. 5, c), where both the C—H...πꢀsystem
Most of the molecules under study are almost planar
(except for 2b and 3). The molecule of 9ꢀstyrylacridine 3
cannot be planar due to considerable steric interactions
between the hydrogen atoms at the C(15) and C(5) (or
C(15) and C(9)) atoms. The simple geometric considerꢀ
ation shows that if this molecule is planar, the distances
between the aboveꢀmentioned hydrogen atoms would
be shorter than 0.7 Å. In the planar conformation of 5,
which (like compound 3) contains the bulky heterocyclic
moiety, the ethylene fragment directly interacts only with
the heteroatoms S and N devoid of hydrogen atoms.
Hence, there is no substantial steric hindrance in
molecule 5, and the latter is almost planar (see Table 1).
Crystal packings. To perform the rational crystal
design of neutral styrylheterocycles, it is important to
analyze the crystal packings of a large number of structurꢀ
ally related compounds. Compounds 1—6 serve this purꢀ
pose. For these compounds, it is interesting to reveal the
relationship between the gradual extensions of the conjuꢀ
gation system and the bulkiness of the substituents in the
benzene ring, on the one hand, and the packing motif of
these compounds, on the other hand, and consequently,
to reveal the structural parameters favorable for the
preorganization of styrylheterocycles to the PCA reaction.
Previously,27,36—39 we have shown with several
examples that the stacking motifs typical of styryl dyes
(see Fig. 1, a and b) are not characteristic of neutral
styrylheterocycles. The latter compounds tend to form

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a
Kuz´mina et al.
b
a
C
c
0
B
A
b
Fig. 6. Projection of the crystal packing of 1b along the a axis (a) and the projection of adjacent molecules located in the parallel planes
onto the mean plane of the conjugated fragment of the molecule labeled A (b). Only the major conformers of 1b are shown for clarity.
hydrogen bonds and the stacking interactions are present.
Among the known packing motifs, only the latter motif
provides the preorganization of the structural units for the
PCA reaction to occur in crystals of neutral styrylheteroꢀ
cycles.
in the benzene fragment of styrylheterocycles with the
retention of their electronꢀdonating character, because,
as has been found previously26,28 for styryl dyes, flexible
crown ether moieties are favorable for single crystalꢀtoꢀ
single crystal PCA reactions.
We made an attempt to design the packing of styrylꢀ
heterocycles 1—6 favorable for the PCA reaction by
extending the conjugation system of the heterocyclic
moiety, which should increase the contribution of stackꢀ
ing interactions to the total stabilization of the crystal
structure. We also varied the bulkiness of the substituents
The crystal packing of crownꢀcontaining styrylpyridine
1b is shown in Fig. 6, a. This packing can be described
as a ladder, in which the planar conjugated fragments of
the molecules that form the ladders are separated from
each other by vast hydrophilic layers composed of the
crown ether moieties. In the ladders, the adjacent molꢀ
A
b
B
E
a
F
0
C
D
G
H
c
Fig. 7. Fragment of one herringbone layer of the packing of 1a projected onto the mean plane of the molecules labeled A, B, C, and D.

Crystal packings of neutral styrylheterocycles
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1201
herringbone layer in the packing of 1a projected onto the
mean plane of four molecules labeled A, B, C, and D is
shown in Fig. 7. Molecules labeled E, F, G, and H are
located between the aboveꢀdescribed layers; the planes of
the latter molecules are inclined at an angle of 85.5° to the
planes of the molecules of the first group. The subsequent
layers in the packing are shifter with respect to the previous
layers so that the nearest molecules from the other layers
are located above any molecule of the layer under considꢀ
eration at the same angle (85.5°). Within one herringbone
layer, any two adjacent molecules 1a are arranged in a
headꢀtoꢀtail fashion.
The similar crystal packing is observed for compound
6a containing the dimethylamino group in the benzene
ring. In the projection of the crystal packing shown in
Fig. 8 (cf. Fig. 5, b), the ladderꢀherringbone packing of
the planar molecules of this styrylpyridine is clearly seen.
The mean planes of the molecules labeled A, B, and C
are inclined at an angle of 65.5° to the mean planes of the
molecules D and E.
b
A
a
D
c
B
E
C
In the crystal structure of azacrownꢀcontaining styrylꢀ
pyridine 6b, the molecules also form a ladderꢀherringꢀ
bone packing motif. However, unlike the packings of comꢀ
pounds 1a and 6a, molecules 6b within a herringbone
layer are arranged in a headꢀtoꢀhead fashion. This packꢀ
ing leads to an alternation of the closeꢀpacked layers
formed by the conjugated fragments and the loose layers
composed of the crown ether moieties (Fig. 9, a). The
mean planes of the conjugated fragments of the molecules
labeled A and C and the molecules labeled B and D,
which are located in one herringbone layer, are inclined
with respect to each other at an angle of 69.2° (Fig. 9, b).
Two independent molecules of 2ꢀstyrylbenzothiazole
4a, like molecules 6b, form a ladderꢀherringbone packꢀ
ing. In the herringbone layers, the molecules are arranged
Fig. 8. Ladderꢀherringbone packing of the molecules in the
crystal structure of 6a.
ecules labeled A, B, and C are related by the translation
along the a axis and are arranged in a headꢀtoꢀhead
fashion, without the mutual projection of their conjuꢀ
gated fragments (see Fig. 6, b). The ethylene fragments of
adjacent molecules are substantially shifted with respect
to each other in the parallel planes; the distance between
their carbon atoms is 5.22 Å. Evidently, there are no
geometric conditions for the PCA reaction to occur in
this crystal packing.
In the crystal structure, molecules 1a form a ladderꢀ
herringbone packing (see Fig. 5, b). The fragment of one
a
b
A
b
B
a
0
c
C
D
Fig. 9. Projection of the crystal packing of 6b along the c axis (a) and the herringbone packing motif of the molecules projected onto the
mean plane of the conjugated fragments of the molecules labeled A and C (b).

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a
Kuz´mina et al.
b
A
B
a
0
c
C
b
D
Fig. 10. Projection of the crystal packing of 4a along the a axis (a) and the herringbone packing motif of the molecules projected onto
the mean plane of the molecules labeled A and C (b).
a
c
0
a
b
b
A
B
C
Fig. 11. Projection of the crystal packing of 4b along the a axis (a) and the mutual projection of three adjacent molecules in the stack
onto the mean plane of the conjugated fragment of the molecule labeled A (b). Only the major conformers of 4b are shown for clarity.

Crystal packings of neutral styrylheterocycles
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 6, June, 2009
1203
in a headꢀtoꢀhead fashion. In this crystal structure, the
herringbone layers are parallel to the ac plane (Fig. 10, a).
The pairs of the molecules labeled A and C and alterꢀ
nating molecules labeled B and D, which are located in
one herringbone layer, are related by the translation along
the a axis. The mean planes of the independent molecules
A and B are inclined at an angle of 38.4° to each other
(Fig. 10, b). The distances between the carbon atoms of
the ethylene bonds of adjacent molecules labeled A and
B, B and C are in the range of 4.57—5.71 Å. Therefore, it
is evident that the ladderꢀherringbone packing in the crysꢀ
tal structures of 1a, 4a, and 6a,b excludes the possibility
of the PCA reaction.
Basically, an increase in the contribution of stacking
interactions could be expected in going to styrylheteroꢀ
cycles of the benzothiazole and quinoline series due
to their more extended conjugation systems compared to
styrylpyridines and, consequently, to the formation of a
different packing motif. This is actually observed in the
crystal structures of compounds 4b and 2a, but it is accomꢀ
plished in different ways. The crystal packing of 4b, which
is similar to the ladder packing of crownꢀcontaining
styrylpyridine 1b (see Fig. 6, a), is shown in Fig. 11, a.
However, the mutual projection of adjacent molecules in
the ladder presented in Fig. 11, b is more similar to the
packing of the stacks in a headꢀtoꢀhead fashion typical of
styryl dyes (see Fig. 2, b). In the crystal structure of 4b,
the projection of the conjugated fragments is observed
only at the periphery. Hence, the latter packing motif can
be considered as the incomplete transition between the
stacking packing (see Fig. 1, a) and the ladder packing
(see Fig. 5, a). In the stack formed by translationally
related structural units, the distances between the correꢀ
sponding atoms of the ethylene fragments are 5.06 Å,
and, consequently, the PCA reaction in this case is hardly
probable.
In the crystals of 4ꢀstyrylquinoline 2a, the molecules
are packed in a sandwichꢀherringbone fashion (Fig. 12, a)
(cf. Fig. 5, c). The structure of the dimer pair of molecules
2a is presented in two projections in Fig. 12, b. In the
upper projection, it is clearly seen that the mutual projecꢀ
tion of the molecules includes virtually the whole πꢀconꢀ
jugation system. The ethylene fragments in the dimer pair
are strictly antiparallel due to its centrosymmetric strucꢀ
ture, and the distance between the carbon atoms of these
fragments is 3.63 Å. Therefore, there are all geometric
conditions necessary for the efficient PCA reaction to
occur in this crystal. Actually, the visibleꢀlight irradiation
of a single crystal of 2a afforded the only rctt isomer of the
corresponding cyclobutane derivative without the degraꢀ
dation of the single crystal, which was established27 by
Xꢀray diffraction and NMR spectroscopy. It should be
noted that a comparison of the molecular structure of
cyclobutane prepared by the irradiation of a crystal of 2a
and the molecular structure of the same cyclobutane
recrystallized from solution showed27 that the former
a
b
N(1)
O(2)
O(1A)
a
O(1)
O(2A)
N(1A)
O(1)
O(2)
N(1A)
b
0
N(1)
O(2A)
O(1A)
c
Fig. 12. Sandwichꢀherringbone packing motif in the crystal structure of 2a (a) and two projections of the centrosymmetric pair of the
molecules (b) (the upper part of the panel represents the projection onto the mean plane of the molecule with continuous bonds).

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Kuz´mina et al.
structure is somewhat strained. These single crystals
appeared to be unstable during storage, which indicates
that the strained core of the cyclobutane derivative has a
substantial effect on the possibility of the single crystalꢀ
toꢀsingle crystal PCA reaction.
the translation along the b axis. The formation of this
hydrogenꢀbonded framework involving the molecules
labeled A and E, B and F (see Fig. 13, b) in the crystals
of 2b results in that the nearest ethylene fragments of the
molecules A and B, E and F are not projected onto each
other and are far spaced (4.95 Å). This arrangement is
unfavorable for the PCA reaction in the crystal.
Therefore, the presence of the crown ether moiety
in the neutral styrylheterocycle molecule increases the
probability of the influence of new, stronger interactions
on the formation of the crystal structure as a results of the
trapping of small molecules by this fragment. This leads
to the formation of supramolecular architectures, which
are not typical of this class of compounds, resulting in
that the crystal packing is less predictable. This is the
difference between styrylheterocycles and the correspondꢀ
ing styryl dyes, in which the presence of the crown ether
moiety only improves the situation with respect to the
formation of the packing in a headꢀtoꢀtail fashion favorꢀ
able for the PCA reaction in crystals.28,29
The nonplanarity of the 9ꢀstyrylacridine molecule 3 is
apparently a consequence of intramolecular steric interꢀ
actions between the heterocyclic moiety and the ethylene
system (see above). Hence, the expected crystal packing
of this compound can also differ from the packings preꢀ
sented in Figs 1 and 5. Actually, only large acridine fragꢀ
ments in the crystal packing of 3 are arranged in stacks
that are formed by the structural units related by a center
of symmetry, where the dimer pairs of the molecules
labeled A and B, C and D are clearly distinguished,
The structure of 2a is strongly contrast27 to the strucꢀ
ture of its crownꢀcontaining analog 2b. As mentioned
above, the conjugated fragment of molecule 2b, unlike
those in many known compounds, is essentially nonplanar
(see Table 1). The crystal packing of the nonplanar molꢀ
ecules cannot be described like those presented in Figs 1
and 5. Although the projection of the crystal packing of 2b
along the b axis shown in Fig. 13, a is similar to the
projections of the packings of styrylheterocycles 1b and 4b
(see Fig. 6, a and Fig. 11, a, respectively), these packings
are different. The interactions between the oxygen atoms
of the 18ꢀcrownꢀ6ꢀether moiety and the solvent dichloroꢀ
methane and water molecules located on the opposite
sides of the plane of the macrocycle play a key role in the
formation of the packing of 2b (see Fig. 4). The CH2Cl2
molecule forms two pairs of bifurcated hydrogen bonds with
C—H...O distances varying in the range of 2.51—2.67 Å.
The water molecule is involved in one bifurcated
hydrogen bond with the crown ether moiety with the
O(1W)—H...O(1)/O(6) distances of 2.37 and 2.53 Å.
Another hydrogen atom of the water molecule was not
located due apparently to its disorder. Thus, this hydroꢀ
gen atom can be oriented toward the O(4) atom of the
macrocycle or toward the Cl(1) atom of adjacent solvate
2b•CH2Cl2•H2O related to the reference molecule by
a
b
D
E
a
F
b
c
0
C
A
B
Fig. 13. Crystal packing of 2b•CH2Cl2•H2O along the b axis (a) and the fragment of this packing (b). The solvent molecules are not
shown for clarity.

Crystal packings of neutral styrylheterocycles
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 6, June, 2009
b
1205
a
a
A
0
b
B
C
D
c
Fig. 14. Crystal packing of 3 along the b axis (a) and the fragment of this packing projected onto the mean plane of the benzene rings (b).
whereas the styryl fragments form a ladder motif (Fig. 14).
The tendency of the acridine fragment to form dimer
pairs is manifested also in the crystal structure of bisheteroꢀ
cycle 7, in which the N(1),C(1)...C(13) fragment is
involved in the centrosymmetric dimer pair stabilized
by stacking interactions.
Crownꢀcontaining compound 5, in which the N and S
atoms of the benzobisthiazole fragment nearest to the
ethylene fragment do not contain exocyclic substituents,
represents a successful attempt to extend the πꢀconjugated
fragment, which is not accompanied by the twisting of the
chromophore system. An extension of the conjugation
system in compound 5 compared to the related 2ꢀstyrylꢀ
benzothiazole 4b leads to the formation of dimer pairs of
the molecules due to the sandwichꢀherringbone packing
motif (Fig. 15). In the centrosymmetric pairs, the ethylꢀ
ene fragments of the molecules are antiparallel and are
spaced by 3.80 Å, i.e., they are preorganized for the PCA
reaction. Since the PCA reaction in the crystals of 2a
having a similar packing motif is efficient, this reaction
a
0
b
c
Fig. 15. Fragment of one sandwichꢀherringbone layer in the crystal structure of 5.

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Kuz´mina et al.
stants were measured with an accuracy of 0.01 ppm and 0.1 Hz,
respectively. The assignment of the signals for protons and
carbon atoms was made based on the twoꢀdimensional homoꢀ
nuclear 1H—1H COSY and NOESY spectra and heteronuclear
1H—13C COSY spectra (HSQC and HMBC).
would be expected to occur in the crystals of 5 as well.
The possibility of the single crystalꢀtoꢀsingle crystal reacꢀ
tion of compound 5 will be considered elsewhere.
To conclude, the present study showed that the design
of the crystal packing of neutral styrylheterocycles can be
performed. The (herringbone)ladder packing motif, to
which weak C—H...πꢀsystem interactions make the major
contribution, is the most typical motif for these comꢀ
pounds. This packing motif is unfavorable for the solidꢀ
state [2+2] photocycloaddition reaction because of the
nonparallel arrangement of the ethylene fragments of
adjacent molecules or their strong mutual shift in the
parallel planes by more than 5 Å. Only the sandwichꢀ
herringbone arrangement in the crystals of styrylheteroꢀ
cycles facilitates the organization of the molecules as
centrosymmetric dimers with the antiparallel closely
spaced C=C bonds. In this structural motif, there are all
geometric conditions necessary for the efficient PCA
reaction, including single crystalꢀtoꢀsingle crystal reacꢀ
tions. To form the sandwichꢀherringbone packing, the
styrylheterocycle molecule should have the following
structural characteristics: first, it should have a rather large
planar heterocyclic moiety favorable for strong stacking
interactions; second, it should have a planar πꢀconjugation
system throughout the chromophore; and, third, the benꢀ
zene moiety of the molecule should not contain fragments,
which are prone to form a hydrogen bond network with
solvent molecules.
4ꢀPicoline, lepidine, 9ꢀmethylacridine, veratraldehyde,
anhydrous ZnCl2, and anhydrous SnCl2 (Aldrich) were used
without additional purification. Nꢀ(4ꢀFormylphenyl)azaꢀ
18ꢀcrownꢀ6 ether,49 4ꢀ[(E)ꢀ2ꢀ(2,3,5,6,8,9,11,12ꢀoctahydroꢀ
benzoꢀ1,4,7,10,13ꢀpentaoxacyclopentadecynꢀ15ꢀyl)ꢀ1ꢀethenyl]ꢀ
pyridine (1b),37 4ꢀ[(E)ꢀ2ꢀ(2,3,5,6,8,9,11,12,14,15ꢀdecahydroꢀ
1,4,7,10,13,16ꢀbenzohexaoxacyclooctadecynꢀ18ꢀyl)ꢀ1ꢀethenyl]ꢀ
quinoline (2b),27 2ꢀ[(E)ꢀ2ꢀ(3,4ꢀdimethoxyphenyl)ꢀ1ꢀethenyl]ꢀ
1,3ꢀbenzothiazole (4a),41 2ꢀ[(E)ꢀ2ꢀ(2,3,5,6,8,9,11,12ꢀoctaꢀ
hydroꢀ1,4,7,10,13ꢀbenzopentaoxacyclopentadecynꢀ15ꢀyl)ꢀ
1ꢀethenyl]ꢀ1,3ꢀbenzothiazole (4b),41 2ꢀmethylꢀ7ꢀ[(E)ꢀ2ꢀ(2,3,5,
6,8,9,11,12ꢀoctahydroꢀ1,4,7,10,13ꢀbenzopentaoxacyclopentaꢀ
decynꢀ15ꢀyl)ꢀ1ꢀethenyl][1,3]thiazolo[5,4ꢀe][1,3]benzothiazole
(5),39 and N,NꢀdimethylꢀNꢀ{4ꢀ[(E)ꢀ2ꢀ(4ꢀpyridyl)ꢀ1ꢀethenyl]ꢀ
phenyl}amine (6a)44 were synthesized according to known proꢀ
cedures.
4ꢀ[(E)ꢀ2ꢀ(3,4ꢀDimethoxyphenyl)ꢀ1ꢀethenyl]pyridine (1a).
A mixture of 4ꢀpicoline (4.87 mL, 0.044 mol), veratraldehyde
(8.30 g, 0.050 mol), and acetic anhydride (9 mL) was heated
at 140 °C (oil bath) for 10 h. The reaction mixture was poured
into water (130 mL). Then a 10% KOH solution was added to
pH >9, the mixture was extracted with benzene (3×60 mL), and
the combined benzene extracts were extracted with 10% hydroꢀ
chloric acid (2×70 mL). Then a 25% NH4OH solution was
added to the acidic aqueous phase to pH >9. The precipitate
that formed was filtered off, washed with water, dried in air, and
recrystallized from anhydrous EtOH (10 mL). Compound 1a
was obtained in a yield of 2.48 g (23%) as paleꢀyellow crystals,
m.p. 130—131 °C (from ethanol) (cf. lit. data37: m.p. 113—115 °C).
Found (%): C, 74.69; H, 6.24; N, 5.74. C15H15NO2. Calcuꢀ
lated (%): C, 74.67; H, 6.27; N, 5.81. 1H NMR (DMSOꢀd6), δ:
3.79 (s, 3 H, 4´ꢀOMe); 3.84 (s, 3 H, 3´ꢀOMe); 7.00 (d, 1 H,
H(5´), J = 8.6 Hz); 7.15 (d, 1 H, CH=CHPy, J = 16.3 Hz); 7.17
(dd, 1 H, H(6´), J = 8.6 Hz, J = 1.8 Hz); 7.31 (d, 1 H, H(2´),
J = 1.8 Hz); 7.48 (d, 1 H, CH=CHPy, J = 16.3 Hz); 7.52 (d,
2 H, H(3), H(5), J = 5.9 Hz); 8.52 (d, 2 H, H(2), H(6), J = 5.9 Hz).
13C NMR (DMSOꢀd6), δ: 55.42 (2 OMe); 109.45 (C(2´)); 111.60
(C(5´)); 120.46 (C(3), C(5)); 120.89 (C(6´)); 123.55 (CH=CHPy);
128.94 (C(1´)); 132.94 (CH=CHPy); 144.55 (C(4)); 148.89
(C(3´)); 149.47 (C(4´)); 149.86 (C(2), C(6)).
4ꢀ[(E)ꢀ2ꢀ(3,4ꢀDimethoxyphenyl)ꢀ1ꢀethenyl]quinoline (2a).
A mixture of lepidine (0.40 mL, 3.0 mmol), veratraldehyde
(0.42 g, 2.5 mmol), anhydrous ZnCl2 (0.41 g, 3.0 mmol), and
glacial acetic acid (2 mL) was heated in the dark at 120 °C (oil
bath) for 42 h. Water (60 mL) was added to the darkꢀbrown
reaction mixture, and the mixture was extracted with chloroꢀ
form (3×20 mL). The chloroform extracts were carefully conꢀ
centrated in vacuo, and the residue was chromatographed on
silica gel (Kieselgel 60, 0.063—0.100 mm, Merck) using the
gradient elution with a benzene—AcOEt mixture to 50% of
AcOEt. The fraction containing the reaction product was conꢀ
centrated in vacuo, and the yellowish residue was extracted with
boiling isooctane (2×20 mL). The extracts were cooled to 5 °C,
and the precipitate that formed was separated by decantation
and dried in air in the dark. Compound 2a was obtained in a
yield of 0.26 g (36%) as a paleꢀyellow powder, m.p. 132—134 °C
However, it should be noted that the crystal structures
of neutral styrylheterocycles are less predictable than the
structures of related cationic styryl dyes. The packings of
the compounds under consideration can also be designed
with the use of their protonated forms or complexes with
metal salts at the heterocyclic nitrogen atom. In this case,
the electronic structures of styrylheterocycles are more
similar to those of styryl dyes, and their crystalline archiꢀ
tectures would be expected to be more similar. The results
of the examination of this possibility will be published
elsewhere.
Experimental
The melting points (uncorrected) were measured in capilꢀ
laries on a MelꢀTemp II instrument. The mass spectra were
obtained on a Varian MAT 311A instrument using a direct
inlet system; the ionization energy was 70 eV. The elemental
analysis was carried out in the Laboratory of Microanalysis of
the A. N. Nesmeyanov Institute of Organoelement Compounds
of the Russian Academy of Sciences (Moscow). The TLC moniꢀ
toring was performed on DCꢀAlufolien Aluminiumoxid 60 F254
(Merck) plates. The 1H and 13C NMR spectra were recorded on
a Bruker DRX500 spectrometer (500.13 and 125.76 MHz,
respectively) in CDCl3, MeCNꢀd3, and DMSOꢀd6 at 25—30 °C
using the solvent as the internal standard (δ 7.27, 1.96,
H
and 2.50, respectively; δ 77.00 for CDCl3, and δ 39.43 for
DMSOꢀd6). The chemicaCl shifts and the spinꢀspin coCupling conꢀ

Crystal packings of neutral styrylheterocycles
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 6, June, 2009
1207
(from isooctane) (cf. lit. data27: m.p. 130—132 °C). 1H NMR
(DMSOꢀd6), δ: 3.81 (s, 3 H, 4´ꢀOMe); 3.89 (s, 3 H, 3´ꢀOMe);
7.02 (d, 1 H, H(5´), J = 8.2 Hz); 7.30 (dd, 1 H, H(6´), J = 8.2 Hz,
J = 1.8 Hz); 7.51 (d, 1 H, H(2´), J = 1.8 Hz); 7.54 (d, 1 H,
CH=CHHet, J = 16.2 Hz); 7.66 (m, 1 H, H(6)); 7.79 (m, 1 H,
H(7)); 7.82 (d, 1 H, H(3), J = 4.8 Hz); 7.97 (d, 1 H, CH=CHHet,
J = 16.2 Hz); 8.03 (d, 1 H, H(8), J = 7.7 Hz); 8.56 (d, 1 H,
H(5), J = 8.2 Hz); 8.86 (d, 1 H, H(2), J = 4.8 Hz).
9ꢀ[(E/Z)ꢀ2ꢀ(3,4ꢀDimethoxyphenyl)ꢀ1ꢀethenyl]acridine (3)
and 9ꢀ[3ꢀ(9ꢀacridyl)ꢀ2ꢀ(3,4ꢀdimethoxyphenyl)propyl]acridine (7).
A mixture of 9ꢀmethylacridine (205 mg, 1.1 mmol), veratrꢀ
aldehyde (265 mg, 1.6 mmol), acetic anhydride (0.5 mL), and
glacial acetic acid (2 mL) was heated in the dark at 120 °C (oil
bath) for 15 h. The reaction mixture was carefully concentrated
in vacuo, and the residue was chromatographed on silica gel
(Kieselgel 60, 0.063—0.100 mm, Merck) using the gradient eluꢀ
tion with a benzene—AcOEt mixture to 40% of AcOEt. Two
fractions were collected. The first fraction contained a mixture
of the E and Z isomers of 3 in a ratio of 1 : 4.3 (NMR monitorꢀ
ing) in a total yield of 3% (10.5 mg). A solution of a mixture of
the E and Z isomers of 3 in a 1 : 1 CH2Cl2—hexane mixture
(3 mL) was slowly concentrated in the dark at room temperaꢀ
ture. The yellow single crystal of (E)ꢀ3 that formed was used for
Xꢀray diffraction. 1H NMR of the isomer (Z)ꢀ3 (CDCl3), δ: 2.91
(s, 3 H, 3´ꢀOMe); 3.72 (s, 3 H, 4´ꢀOMe); 6.12 (d, 1 H, H(2´),
J = 1.8 Hz); 6.55 (d, 1 H, H(5´), J = 8.3 Hz); 6.62 (dd, 1 H,
H(6´), J = 8.3 Hz, J = 1.8 Hz); 7.07 and 7.16 (2 d, 1 H each,
CH=CHHet and CH=CHHet, J = 12.6 Hz, J = 12.6 Hz); 7.47
(m, 2 H, H(2), H(7)); 7.76 (m, 2 H, H(3), H(6)); 8.22 (d, 2 H,
H(1), H(8), J = 8.7 Hz); 8.25 (d, 2 H, H(4), H(5), J = 8.6 Hz).
1H NMR of the isomer (E)ꢀ3 (CDCl3), δ: 3.97 (s, 3 H, 4´ꢀOMe);
4.02 (s, 3 H, 3´ꢀOMe); 6.97 (d, 1 H, H(5´), J = 8.2 Hz); 7.01
and 7.78 (2 d, 1 H each, CH=CHHet and CH=CHHet,
J = 16.5 Hz, J = 16.5 Hz); 7.23 (dd, 1 H, H(6´), J = 8.2 Hz,
J = 1.7 Hz); 7.26 (d, 1 H, H(2´), J = 1.7 Hz); 7.54 (m, 2 H,
H(2), H(7)); 7.79 (m, 2 H, H(3), H(6)); 8.28 (d, 2 H, H(4),
H(5), J = 9.1 Hz); 8.36 (d, 2 H, H(1), H(8), J = 8.6 Hz).
Bisacridine 7 was isolated from the second fraction in a
yield of 76 mg (26%) as a yellowish powder, m.p. 180—182 °C
(from isooctane). Found (%): C, 82.56; H, 5.71; N, 5.14.
Table 2. Crystallographic characteristics and the Xꢀray diffraction data collection and refinement statistics for
compounds 1a,b, 3 and 7.
Parameter
1a
1b
3
7
Molecular formula
Molecular weight
Crystal system
Space group
a/Å
b/Å
c/Å
α/deg
C15H15NO2
241.28
C21H25NO5
371.42
C23H19NO2
341.39
C37H30N2O2
534.63
Monoclinic
Monoclinic
P21/c
8.7021(5)
7.8008(5)
18.9403(12)
90
P21/c
5.2229(10)
13.648(3)
25.997(5)
90
P21/c
12.0961(7)
7.5847(4)
18.3393(11)
90
P21/c
14.8238(13)
10.7294(8)
18.6919(17)
90
β/deg
95.367(3)
90
1280.09(14)
4
93.438(3)
90
1849.7(6)
4
1.334
792
91.817(2)
90
1681.70(17)
4
109.978(4)
90
2794.1(4)
4
1.271
1128
γ/deg
V/Å3
Z
dcalc/g cm–3
F(000)
1.252
512
1.348
720
μ(MoꢀKα)/mm–1
Crystal dimensions/mm
θ Scan mode/range, deg
Ranges of indices of
measured reflections
0.083
0.095
0.086
0.079
0.36×0.34×0.08
ω/2.16—28.99
–11 ≤ h ≤ 11,
–6 ≤ k ≤ 10,
–25 ≤ l ≤ 24
9280
0.60×0.10×0.04
ω/1.69—29.00
–7 ≤ h ≤ 7,
–18 ≤ k ≤ 18,
–34 ≤ l ≤ 35
19996
0.55×0.48×0.14
ω/1.68—30.01
–17 ≤ h ≤ 16,
–10 ≤ k ≤ 10,
–25 ≤ l ≤ 21
10176
0.36×0.35×0.32
ω/1.46—29.96
–20 ≤ h ≤ 18,
–14 ≤ k ≤ 14,
–16 ≤ l ≤ 26
24426
Number of measured
reflections
Number of independent
reflections
Number of reflections
with I > 2σ(I)
3343
(Rint = 0.0228)
2537
4907
(Rint = 0.0613)
2555
4862
(Rint = 0.0332)
3506
7562
(Rint = 0.0269)
5985
Number of refined
parameters
223
488
311
490
R factors based on
reflections with I > 2σ(I)
based on all reflections
R1 = 0.0466,
wR2 = 0.1091
R1 = 0.0699,
wR2 = 0.1189
1.056
R1 = 0.0508,
wR2 = 0.1013
R1 = 0.1234,
wR2 = 0.1180
0.974
R1 = 0.0537,
wR2 = 0.1365
R1 = 0.0764,
wR2 = 0.1491
1.046
R1 = 0.0493,
wR2 = 0.1194
R1 = 0.0661,
wR2 = 0.1308
1.041
Goodnessꢀofꢀfit on F2
Residual electron density
(min/max)/e Å
–0.257/0.339
–0.154/0.139
–0.259/0.366
–0.205/0.413
–3

1208
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 6, June, 2009
Kuz´mina et al.
C37H30N2O2•0.25H2O. Calculated (%): C, 82.43; H, 5.70;
N, 5.20. H NMR (DMSOꢀd6), δ: 3.51 (s, 3 H, 3´ꢀOMe); 3.52
J = 8.9 Hz); 8.48 (d, 2 H, H(2), H(6), J = 5.5 Hz). 13C NMR
(DMSOꢀd6), δ: 50.52 (N(CH2)2); 67.82 (2 CH2CH2N); 69.85
(2 CH2O); 69.91 (4 CH2O); 69.98 (2 CH2O); 111.29 (C(3´),
C(5´)); 120.08 (C(3), C(5)); 120.21 (CH=CHPy); 123.25
(C(1´)); 128.44 (C(2´), C(6´)); 133.20 (CH=CHPy); 145.05
(C(4)); 148.08 (C(4´)); 149.64 (C(2), C(6)). MS, m/z (Irel (%)):
442 [M]+ (50), 265 (24), 253 (19), 223 (34), 209 (46), 208 (37),
181 (22), 59 (49), 58 (100), 57 (24).
B. A mixture of 4ꢀpicoline (0.67 mL, 5.8 mmol), Nꢀ(4ꢀformylꢀ
phenyl)azaꢀ18ꢀcrownꢀ6 ether (0.50 g, 1.4 mmol), and anhyꢀ
drous SnCl2 (0.19 g, 1.0 mmol) was heated at 160 °C (oil bath)
for 4 h. 4ꢀPicoline was carefully removed from the reaction
mixture by heating in vacuo, and the viscous brown residue was
chromatographed on silica gel (Kieselgel 60, 0.063—0.100 mm,
Merck) using a 1 : 1 benzene—AcOEt mixture as the eluent and
then a benzene—PriOH mixture for the gradient elution to 50%
of PriOH. The fraction containing the target product was conꢀ
centrated in vacuo, and the redꢀorange residue (0.26 g) was
1
(m, 1 H, CH(CH2)2); 3.65 (s, 3 H, 4´ꢀOMe); 4.12 (dd, 2 H,
2 CHH´Het, J = 13.8 Hz, J = 6.5 Hz); 4.20 (dd, 2 H, 2 CHH´Het,
J = 13.8 Hz, J = 7.9 Hz); 6.14 (br.d, 1 H, H(6´), J = 8.1 Hz);
6.39 (d, 1 H, H(5´), J = 8.1 Hz); 7.06 (br.s, 1 H, H(2´)); 7.37
(m, 4 H, 2 H(2), 2 H(7)); 7.74 (m, 4 H, 2 H(3), 2 H(6)); 8.03 (d,
4 H, 2 H(1), 2 H(8), J = 8.6 Hz); 8.08 (d, 4 H, 2 H(4), 2 H(5),
J = 8.7 Hz). 13C NMR (CDCl3), δ: 33.64 (CH(CH2)2); 49.13
(CH(CH2)2); 55.80 (3´ꢀOMe); 55.98 (4´ꢀOMe); 111.44 (C(2´));
111.47 (C(5´)); 118.90 (C(6´)); 123.92 (2 C(1), 2 C(8)); 125.24
(2 C(8a), 2 C(9a)); 125.56 (2 C(2), 2 C(7)); 129.61 (2 C(3),
2 C(6)); 130.29 (2 C(4), 2 C(5)); 135.68 (C(1´)); 143.95 (2 C(9));
148.20 (C(4´)); 148.44 (2 C(4a), 2 C(10a)); 148.68 (C(3´)).
MS, m/z (Irel (%)): 534 [M]+ (0.6), 193 (100), 97 (53), 96 (63),
89 (54), 84 (72), 73 (57), 72 (54), 59 (90), 58 (69).
9ꢀ[3ꢀ(9ꢀAcridyl)ꢀ2ꢀ(3,4ꢀdimethoxyphenyl)propyl]acridine
(7). A mixture of 9ꢀmethylacridine (211 mg, 1.1 mmol),
veratraldehyde (218 mg, 1.3 mmol), anhydrous ZnCl2 (180 mg,
1.3 mmol), and glacial acetic acid (2 mL) was heated in the dark
at 120 °C (oil bath) for 43 h. Water (60 mL) was added to the
reaction mixture, and the resulting mixture was extracted with
chloroform (4×25 mL). The chloroform extracts were carefully
concentrated in vacuo, and the residue was chromatographed on
silica gel (Kieselgel 60, 0.063—0.100 mm, Merck) using the
gradient elution with a benzene—AcOEt mixture to 50% of
AcOEt. The fraction containing the desired product was conꢀ
centrated in vacuo, and the yellowish residue was extracted with
boiling isooctane (2×25 mL). The extracts were cooled to 5 °C,
and the precipitate that formed was separated by decantation
and dried in air. Compound 7 was obtained in a yield of 105 mg
(36%) as greishꢀyellow crystals, m.p. 180—182 °C (from isoꢀ
octane).
Table 3. Crystallographic characteristics and the Xꢀray diffracꢀ
tion data collection and refinement statistics for compounds
6a,b
Parameter
6a
6b
Molecular formula
Molecular weight
Crystal system
Cpace group
a/Å
b/Å
c/Å
α/deg
C15H16N2
224.30
C25H34N2O5
442.54
Monoclinic
P21/c
5.9823(4)
7.5827(5)
26.3656(19)
90
Pc
16.7934(15)
8.3363(7)
8.6303(8)
90
16ꢀ{4ꢀ[(E)ꢀ2ꢀ(4ꢀPyridyl)ꢀ1ꢀethenyl]phenyl}ꢀ1,4,7,10,13ꢀ
pentaoxaꢀ16ꢀazacyclooctadecane (6b). A. Concentrated hydroꢀ
chloric acid (0.32 mL, 3.7 mmol) was added to a solution of
4ꢀpicoline (0.30 mL, 3.1 mmol). The solvent was carefully conꢀ
centrated in vacuo at 60 °C (water bath). Nꢀ(4ꢀFormylphenyl)ꢀ
azaꢀ18ꢀcrownꢀ6 ether (0.44 g, 1.2 mmol) and acetic anhydride
(3 mL) were added to the resulting 4ꢀpicoline hydrochloride.
The reaction mixture was heated at 140 °C (oil bath) for 12 h
and then concentrated in vacuo. A 1% NaOH solution (100 mL)
was added to the viscous black residue, and the mixture was
extracted with chloroform (4×25 mL). The chloroform extracts
were concentrated in vacuo, and the residue was chromatoꢀ
graphed on silica gel (Kieselgel 60, 0.035—0.070 mm, Merck)
using a 1 : 1 benzene—AcOEt mixture as the eluent and then a
benzene—PriOH mixture for the gradient elution to 20% of
PriOH. The fraction containing the target product was conꢀ
centrated in vacuo, and the redꢀorange residue (0.15 g) was
extracted with boiling hexane (2×40 mL). The extracts were
cooled to room temperature, and the precipitate that formed
was separated by decantation and dried in air. Compound 6b
was obtained in a yield of 0.12 g (22%) as yellowish crystals,
m.p. 94—96 °C (from a CH2Cl2—hexane mixture). Found (%):
C, 67.72; H, 7.80; N, 6.19. C25H34N2O5. Calculated (%):
C, 67.85; H, 7.74; N, 6.33. 1H NMR (MeCNꢀd3), δ: 3.57—3.65
(m, 20 H, N(CH2)2, 8 CH2O); 3.67 (m, 4 H, 2 CH2CH2N);
6.76 (d, 2 H, H(3´), H(5´), J = 8.9 Hz); 6.91 (d, 1 H, CH=CHPy,
J = 16.3 Hz); 7.36 (d, 1 H, CH=CHPy, J = 16.3 Hz); 7.41
(d, 2 H, H(3), H(5), J = 5.5 Hz); 7.45 (d, 2 H, H(2´), H(6´),
β/deg
93.936(4)
90
1193.17(14)
4
103.886(4)
90
1172.89(18)
2
γ/deg
V/Å3
Z
dcalc/g cm–3
F(000)
1.249
480
0.074
1.253
476
0.087
μ(MoꢀKα)/mm–1
Crystal dimensions/mm
θ Scan mode/range, deg
Ranges of indices of
measured reflections
0.22×0.16×0.08
ω/1.55—29.00
–7 ≤ h ≤ 8,
–9 ≤ k ≤ 10,
–33 ≤ l ≤ 35
7214
0.38×0.30×0.06
ω/2.44—29.00
–22 ≤ h ≤ 22,
–11 ≤ k ≤ 10,
–11 ≤ l ≤ 11
8000
Number of measured
reflections
Number of independent
reflections
Number of reflections
with I > 2σ(I)
Number of refined
parameters
3049
(Rint = 0.0759)
1546
5567
(Rint = 0.1195)
2695
218
398
R factors based on
reflections with I > 2σ(I) wR2 = 0.1339
based on all reflections
R1 = 0.0866,
R1 = 0.0657,
wR2 = 0.1357
R1 = 0.1566,
wR2 = 0.1617
0.857
R1 = 0.1811,
wR2 = 0.1565
1.023
Goodnessꢀofꢀfit on F2
Residual electron density
(min/max)/e Å
–0.200/0.259
–0.236/0.261
–3

Crystal packings of neutral styrylheterocycles
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 6, June, 2009
1209
extracted with boiling hexane (4×30 mL). The extracts were
cooled to –10 °C, and the precipitate that formed was separated
by decantation and dried in air. Compound 6b was obtained in a
yield of 0.16 g (27%) as paleꢀyellow crystals, m.p. 93—94 °C
(from hexane).
9. X. Yu, D. Scheller, O. Rademacher, T. Wolff, J. Org. Chem.,
2003, 68, 7386.
10. V. Darcos, K. Griffith, X. Sallenave, J.ꢀP. Desvergne,
C. GuyardꢀDuhayon, B. Hasenknopf, D. M. Bassani, Photoꢀ
chem. Photobiol. Sci., 2003, 2, 1152.
Xꢀray diffraction study. Single crystals of all compounds were
grown by the slow evaporation of their solutions in a 1 : 1
CH2Cl2—hexane mixture in the dark at room temperature. The
single crystals were mounted on a Bruker SMARTꢀCCD difꢀ
fractometer under a cold nitrogen stream (T = 180(2) K for 1b
and 120.0(2) K for the other compounds). The unit cell paramꢀ
eters were measured and the Xꢀray diffraction data sets were
collected using MoꢀKα radiation (λ = 0.71073 Å, graphite monoꢀ
chromator, ωꢀscan mode). The Xꢀray data were processed with
the use of the SAINT program.50 All structures were solved by
direct methods and refined by the leastꢀsquares method with
anisotropic displacement parameters for all nonhydrogen
atoms. In the crystal structure of 1b, the molecules are disorꢀ
dered over two sites; the occupancy ratio for two s conformers
was 0.55 : 0.45. The hydrogen atoms were positioned geometriꢀ
cally and refined isotropically (for the structures of 1a, 3, 6a,
and 7), using a riding model (for 1b), or using a mixed scheme
(isotropically and using a riding model; for 6b).
11. D. G. Amirsakis, A. M. Elizarov, M. A. GarciaꢀGaribay,
P. T. Glink, J. F. Stoddart, A. J. P. White, D. J. Williams,
Angew. Chem., Int. Ed., 2003, 42, 1126.
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V. Enkelmann, G. Wegner, B. M. Foxman, Cryst. Growth
Design, 2005, 5, 2210.
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S. Tobita, J. Org. Chem., 2005, 70, 9693.
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H. A. Sparkes, New J. Chem., 2005, 29, 182.
15. M. Nagarathinam, J. J. Vittal, Angew. Chem., Int. Ed., 2006,
45, 4337.
16. K. Honda, F. Nakanishi, N. Feeder, J. Am. Chem. Soc.,
1999, 121, 8246.
17. S. Ohba, Y. Ito, Acta Crystallogr., Sect. B, 2003, 59, 149.
18. I. TurowskaꢀTyrk, J. Phys. Org. Chem., 2004, 17, 837.
19. Y.ꢀF. Han, Y.ꢀJ. Lin, W.ꢀG. Jia, G.ꢀL. Wang, G.ꢀX. Jin,
Chem. Commun., 2008, 1807.
The crystallographic characteristics and the Xꢀray difꢀ
fraction data collection and refinement statistics are given
in Tables 2 and 3. All calculations were carried out with the use
of the SHELXTLꢀPlus program package.51
The atomic coordinates and other experimental data were
deposited with the Cambridge Crystallographic Data Centre;*
the CCDC numbers 714928 (1a), 714929 (1b), 714930 (3),
714931 (6a), 714932 (6b), and 714933 (7).
20. L. R. MacGillivray, G. S. Papaefstathiou, T. Friscic, T. D.
Hamilton, D.ꢀK. Busar, Q. Chu, D. B. Varshney, I. G.
Georgiev, Acc. Chem. Res., 2008, 41, 280.
21. L. R. MacGillivray, J. Org. Chem., 2008, 73, 3311.
22. S. P. Gromov, M. V. Alfimov, Izv. Akad. Nauk, Ser.
Khim., 1997, 641 [Russ. Chem. Bull. (Engl. Transl.), 1997,
46, 611].
23. A. I. Vedernikov, N. A. Lobova, E. N. Ushakov, M. V.
Alfimov, S. P. Gromov, Mendeleev Commun., 2005, 15, 173.
24. S. P. Gromov, Rossiiskie Nanotekhnologii, 2006, 1, No. 1—2,
29 [Nanotechnologies in Russia (Engl. Transl.), 2006, 1,
No. 1—2].
25. S. P. Gromov, A. I. Vedernikov, N. A. Lobova, L. G.
Kuz´mina, S. N. Dmitrieva, O. V. Tikhonova, M. V. Alfimov,
Pat. RF 2278134; Byul. izobret. [Inventor Bull.], 2006, No. 17
(in Russian).
This study was financially supported by the Russian
Foundation for Basic Research (Project Nos 06ꢀ03ꢀ32456,
06ꢀ03ꢀ33162, and 08ꢀ03ꢀ00031), the Royal Society of the
UK (Personal Grants for L. G. Kuz´mina and J. A. K.
Howard), and the Royal Society of Chemistry of the UK
(Personal Grant for L. G. Kuz´mina).
26. A. I. Vedernikov, S. P. Gromov, N. A. Lobova, L. G.
Kuz´mina, Yu. A. Strelenko, J. A. K. Howard, M. V. Alfimov,
Izv. Akad. Nauk, Ser. Khim., 2005, 1896 [Russ. Chem. Bull.,
Int. Ed., 2005, 54, 1954].
27. L. G. Kuz´mina, A. I. Vedernikov, N. A. Lobova, A. V.
Churakov, J. A. K. Howard, M. V. Alfimov, S. P. Gromov,
New J. Chem., 2007, 31, 980.
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Received August 7, 2008;
in revised form January 20, 2009