Synthesis and spectroscopic properties of cross-conjugated ketones and meso-substituted tridecamethine salts containing the pyran or pyridone fragment

Article abstract of DOI:10.1023/B:RUCB.0000009648.77315.15

The reactions of substituted 4H-pyrones and N-methyl-2,6-dimethylpyridone with dimethylformamide acetal and aminal acetals of conjugated ω-dimethylaminoaldehydes were studied. Cross-conjugated ketones and meso-ethoxy(dialkylamino)tridecamethine salts cont

Full text of DOI:10.1023/B:RUCB.0000009648.77315.15

Russian Chemical Bulletin, International Edition, Vol. 52, No. 9, pp. 2029—2037, September, 2003
2029
Synthesis and spectroscopic properties of crossꢀconjugated ketones
and mesoꢀsubstituted tridecamethine salts
containing the pyran or pyridone fragment
a
b
b
b
Zh. A. Krasnaya,a Yu. V. Smirnova, L. A. Shvedova, A. S. Tatikolov, and V. A. Kuz´min
ꢀ
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 938 2156. Eꢀmail: kra@ioc.ac.ru
bN. M. Emanuel´ Institute of Biochemical Physics, Russian Academy of Sciences,
4 ul. Kosygina, 119991 Moscow, Russian Federation.
Fax: +7 (095) 137 4101. Eꢀmail: shvedova@sky.chph.ras.ru
The reactions of substituted 4Hꢀpyrones and Nꢀmethylꢀ2,6ꢀdimethylpyridone with
dimethylformamide acetal and aminal acetals of conjugated ωꢀdimethylaminoaldehydes were
studied. Crossꢀconjugated ketones and mesoꢀethoxy(dialkylamino)tridecamethine salts conꢀ
taining the pyran or pyridone fragment were synthesized and their spectroscopic properties
were investigated. The replacement of the bridging O atom by the NMe group precludes an
interaction between chromophores in crossꢀconjugated ketone and the related tridecamethine
salt. In addition, the insertion of a mesoꢀamino substituent into the polymethine chain of the
salts containing the central pyrylium fragment leads to a sharp weakening of the chromophore
interaction. In spite of the dramatic differences in the UV spectra of ketocyanines containing
the bridging O or NMe fragments, these dyes have similar 13C NMR spectra.
Key words: polyenic bisꢀaminoketone, pyran and pyridone fragments, aminal acetals,
tridecamethine salts, protonation, prototropic equilibrium, chromophore interaction.
Ketocyanine dyes, ω,ω´ꢀbis(aminopolyenyl) ketones,
belong to bichromophoric crossꢀconjugated polyenes conꢀ
taining two polymethine chains. Due to simple strucꢀ
tures, these compounds appeared to be convenient for
modeling various photophysical and photochemical proꢀ
cesses. Recently, we have developed a procedure for the
synthesis of a new type of ketocyanine dyes (Scheme 1),
viz., 2,6ꢀbis(4ꢀdimethylaminoalkaꢀ1,3ꢀdienyl)ꢀ4Hꢀpyꢀ
ranꢀ4ꢀones 3a—d* and related ethoxytridecamethine
salts 4a—c**.1
tigating the effect of their structures on the spectral lumiꢀ
nescence properties. Another goal of our investigation is
to examine the possibility of using these compounds for
the preparation of new cyanine dyes containing the pyran
fragment in the polymethine chain.
It was of interest to prepare symmetrical ketones, which
differ from ketones 3 by the length of polyenic chains,
unsymmetrical ketones containing different chromophores
at positions 2 and 6, and ketones containing only one
chromophore.
Studies of the photonics of these dyes revealed that
they exhibit unusual absorption features. Thus, the specꢀ
tra of these compounds have a longꢀwavelength absorpꢀ
tion band in the visible region along with a much more
intense shortꢀwavelength band in the nearꢀUV region. We
explained such absorption spectrum patterns based on a
model of the chromophore interaction assuming an acute
angle between these chromophores.1,2 The aim of the
present study was to synthesize compounds structurally
similar to bisꢀpolyenic ketones 3 for the purpose of invesꢀ
We studied condensation of 2,6ꢀdimethylꢀγꢀpyrone
(1) with aminal acetal 5 3 and dimethylformamide acetal
(Scheme 2) with the aim of synthesizing bisꢀdimethylꢀ
aminopyranones 6 and 8. We failed to prepare polyenic
ketones 6 and 8 by varying the reaction conditions (temꢀ
perature, solvent, reagent ratio). The reaction with aminal
acetal 5 afforded only resinous products, whereas the reꢀ
action with dimethylformamide acetal gave rise only to
2ꢀdimethylaminoethenylꢀ6ꢀmethylꢀ4Hꢀpyranꢀ4ꢀone (7)
in low yield (5%).
An attempt to prepare compound 9 containing
one polyenic chromophore also failed. The reaction of
equimolar amounts of 2,6ꢀdimethylꢀγꢀpyrone (1) and
βꢀdimethylaminoacrolein aminal acetal 2a afforded only
bisꢀaminoketone 3a in low yield (see Scheme 2).
* Compound 3d was prepared in the present study.
** Compounds 4 can be represented by limit structures A
(ethoxytridecamethine salts) and B (pyrylium salts).1 For conꢀ
venience of discussion, we use mesomeric structure 4B.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1920—1928, September, 2003.
1066ꢀ5285/03/5209ꢀ2029 $25.00 © 2003 Plenum Publishing Corporation

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Russ.Chem.Bull., Int.Ed., Vol. 52, No. 9, September, 2003
Krasnaya et al.
Scheme 1
R = H (a), Me (b), Ph (c), OEt (d)
Scheme 2
taining different chromophores at positions 2 and 6, beꢀ
cause we expected that the synthesis of this compound
would present no problems. However, the use of a simple
procedure proposed for the preparation of this vinyl keꢀ
tone4 gave rise to 2,6ꢀdistyrylꢀ4Hꢀpyranꢀ4ꢀone (10)
(Scheme 3).
Scheme 3
The twoꢀstep synthesis of 6ꢀmethylꢀ2ꢀstyrylꢀ4Hꢀ
5—7
pyranꢀ4ꢀone (13) from dehydroacetic acid 11
(Scheme 4) proved to be more successful.
Condensation of ketone 13 with βꢀdimethylaminoꢀ
acrolein aminal acetal 2a under mild conditions (25 min,
70—75 °C) afforded unsymmetrical polyenic ketone 14
(Scheme 5) in good yield (63%).
It was of interest to compare the physicochemical
properties of polyenic compounds containing the γꢀpyrone
fragment with the properties of compounds containing
the pyridone fragment. For this purpose, we prepared
polyenic pyridone 16 in 33% yield by condensation of
Nꢀmethylꢀ2,6ꢀdimethylpyridinꢀ4ꢀone8,9 (15) with aminal
acetal 2a (Scheme 6).
The structures of the resulting ketones were confirmed
by 1H and 13C NMR, electronic, and mass spectra.
1
We chose 6ꢀmethylꢀ2ꢀstyrylꢀ4Hꢀpyranꢀ4ꢀone as the
According to the H NMR spectroscopic data, the
starting compound for the synthesis of compounds conꢀ
methine protons in ketones 7, 14, and 16 have a trans

Crossꢀconjugated ketones and tridecamethine salts
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 9, September, 2003
2031
Scheme 4
configuration and these ketones exist predominantly as
the sꢀtrans conformers (J = 11.1—15.1 Hz).
1
A comparison of the H NMR spectra of compounds
3a and 16 shows that the signals for the corresponding
protons are located virtually in the same regions. In going
from pyrone 3a to pyridone 16, a substantial change is
observed only for the signals of the H(3) and H(5) proꢀ
tons. The spectrum of compound 3a has a signal for the
H(3) and H(5) protons at δ 5.87, whereas the correspondꢀ
ing signal in the spectrum of compound 16 is observed at
δ 6.52. The 13C NMR spectrum of ketone 3a is also very
similar to that of ketone 16. The only essential difference
is that the signals for the C(2) and C(3) atoms in the
spectrum of pyridone 16 are shifted upfield (δ 151.9) comꢀ
pared to those in the spectrum of pyrone 3a (δ 167.0).
Alkylation of ketone 16 with triethyloxonium tetraꢀ
fluoroborate under mild conditions (0 °C, 1 h) afforded
1
salt 17 (Scheme 7). According to the H NMR spectroꢀ
scopic data, salt 17 contained up to 10% of unidentified
impurities. Attempts to purify product 17 were unsucꢀ
cessful.
Scheme 7
Scheme 5
According to the data published in the literature,
pyrylium and alkoxypyrylium salts are readily subjected to
recyclization in reactions with ammonia and primary
amines to form pyridine derivatives. Recyclization of
alkoxypyrylium salts is accompanied by the replacement
of the alkoxy group by the amino group.10—12 In this
connection, it was of interest to examine the possibility of
preparing polyenic pyridinium salts from alkoxypolyꢀ
methine salts 4 and to study the influence of long
aminopolyenic substituents at positions 2 and 6 on the
properties of pyrylium salts.
Scheme 6
We investigated the behavior of alkoxypolymethine
salt 4a in the reactions with ammonia and primary amines
(methylamine and benzylamine). It appeared that neither
the reaction of salt 4a with ammonia nor the reactions
with primary amines led to recyclization giving rise to a
new heterocyclic system. For example, the reaction of
salt 4a with aqueous ammonia produced aminopyrylium
salt 18 in good yield (72%) (Scheme 8).
The reactions of salt 4a with methylamine and benzylꢀ
amine afforded complex mixtures of products. In these
reactions, individual compounds were not isolated. Howꢀ

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Russ.Chem.Bull., Int.Ed., Vol. 52, No. 9, September, 2003
Krasnaya et al.
Scheme 8
methine salts derived from bisꢀdimethylaminopolyenic
ketones, which we have studied earlier.16,17
We attempted to prepare cyanine dyes containing the
γꢀpyrone fragment based on salt 4a. However, in spite of
the use of different conditions of condensation, pyrylium
salt 4a did not react with Nꢀethylbenzooxazolium tosylate
(20) and 5ꢀmethylꢀNꢀphenylpyrazolone (21).
The photophysical study of the newly synthesized
bichromophoric compounds revealed a series of interestꢀ
ing features, whose investigation will serve to the further
development of the theory of chromophore interactions.
As mentioned above, the S—S absorption spectra of dyes
3a—d consist of two bands, viz., an intense shortꢀwaveꢀ
length band and a much less intense longꢀwavelength
band. The positions of these bands, their intensity ratio,
and the energy splitting (∆ν) between the S1 and S2 levels
were explained based on this theory. The chromophores
composing the dye (halves of dye 3a from the NMe2
fragment to the carbonyl group) are oriented at an acute
angle with respect to each other.1,2 We found that the
replacement of the O atom in the pyran ring of ketocyanine
3a by the NMe group (dye 16) led to a radical change in
the absorption spectrum of the dye (Fig. 1). Unlike comꢀ
pound 3a, the absorption spectrum of ketocyanine 16 has
only one band (λmax = 395 nm) located between two
ever, it can be said with assurance that recyclization givꢀ
ing rise to Nꢀsubstituted pyridinium salts did not occur,
because the 1H NMR spectra of the mixtures prepared by
both reactions have no signals at δ 3.90—4.15 characterisꢀ
tic of Nꢀsubstituted pyridinium salts.13,14 Therefore, salt
4a reacted with primary amines with retention of the
pyrylium ring. This can be associated with the lower elecꢀ
trophilicity of salt 4a with respect to nitrogenꢀcontaining
nucleophiles compared to structurally simple pyrylium
salts. Presumably, a decrease in the electrophilicity of salt
4a is favored by a higher degree of delocalization of the
positive charge of the mesomeric cation compared to that
observed in pyrylium salts devoid of long aminopolyenic
substituents.
The retention of the pyrylium structure is typical of
the reactions of structurally simple 2ꢀ and 4ꢀalkoxyꢀ
pyrylium salts with secondary amines.10,15 The reactions
of salt 4a with dimethylamine and piperidine afforded
aminopyrylium salts 19a,b (Scheme 9). In the reaction of
salt 4a with piperidine, the replacement of the alkoxy
group by the amino group was accompanied by transamiꢀ
nation of the terminal amino groups. Complete transamiꢀ
nation of the NMe2 groups to form salt 19b was achieved
only with the use of a tenfold molar excess of piperidine
and the reaction time of 3 days.
A
1
2
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Scheme 9
R1 = R2 = Me (a), R1 + R2 = (CH2)5 (b)
28000
24000
20000 ν/cm–1
It should be noted that the replacement of the ethoxy
group by the amino group is not typical of alkoxypolyꢀ
Fig. 1. Absorption spectra of compounds 3a (1) and 16 (2)
in PriOH.

Crossꢀconjugated ketones and tridecamethine salts
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 9, September, 2003
2033
A
absorption bands of dye 3a, i.e., the chromophore interꢀ
action is not manifested (the fluorescence excitation specꢀ
trum of ketone 16 also consists of one band, like the
absorption spectrum). Therefore, the presence of the NMe
group in the pyridone fragment, apparently, precludes the
chromophore interaction in compound 16. Since the abꢀ
sorption band of dye 16 is bathochromically shifted on
1
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
2
3
going from toluene to chloroform and PriOH (λmax
=
385, 389, and 395 nm, respectively), it is, apparently, a
chargeꢀtransfer band. The carbonyl group acts as an elecꢀ
tron acceptor and the amino groups serve as electron
donors (the longꢀwavelength absorption band of ketoꢀ
cyanine 3a 1 is analogous in character). The addition of
trace amounts of acid (CHCl ≈ 10–6 mol L–1) to a solution
of dye 16 led to a sharp change in its absorption spectrum.
Thus, the intensity of the initial band (λmax = 395 nm in
PriOH) decreased and a new band at λmax = 468 nm with
a shoulder at λmax = 390 nm appeared. Apparently, the
latter band corresponds to the protonated form (PF) of
dye 16 (PFꢀ16). An isosbestic point, which was observed
in the absorption spectra in the course of titration of
ketocyanine 16 with acid, indicates that there is a simple
equilibrium between the starting and protonated forms
(Fig. 2). The addition of small amounts of diethylꢀ
amine restored the initial spectral pattern, which is eviꢀ
4
5
6
7
28000
24000
20000 ν/cm–1
Fig. 3. Changes in the absorption spectrum of PFꢀ16 in
the course of titration with diethylamine (DEA) in PriOH
(CHCl = 2.3•10–5 mol L–1): CDEA = 0 (1), 2.23•10–5 (2),
3.01•10–5 (3), 3.74•10–5 (4), 4.47•10–5 (5), 5.24•10–5 (6),
6.70•10–5 mol L–1 (7).
dence for the reversibility of the prototropic equilibrium
A
Dye + H+
DyeH+(Fig. 3).
9
8
0.8
The absorption spectrum of PFꢀ16 is similar to that of
polymethine salt 17 (Fig. 4). A slight bathochromic shift
in the spectrum of salt 17 compared to the spectrum of
PFꢀ16 is, apparently, associated with the electronꢀreleasꢀ
ing effect of the Et group at the O atom. This indicates
7
6
0.7
0.6
5
A
0.5
0.8
2
1
4
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.4
0.3
3
0.2
2
0.1
1
28000
24000
20000 ν/cm–1
Fig. 2. Changes in the absorption spectrum of ketocyanine 16
in the course of titration with hydrochloric acid in PriOH:
CHCl = 0 (1), 3.84•10–6 (2), 7.70•10–6 (3), 1.15•10–5 (4),
1.54•10–5 (5), 1.92•10–5 (6), 2.31•10–5 (7), 2.69•10–5 (8),
4.69•10–5 mol L–1 (9).
28000
24000
20000
ν/cm–1
Fig. 4. Absorption spectra of salts PFꢀ16 (1) and 17 (2) in PriOH.

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Krasnaya et al.
A
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
3
∆ν
∆ν
2
1
2
1
28000
26000
24000
22000
20000
18000
16000
ν/cm–1
Fig. 5. Absorption spectra of salts 4a (1), PFꢀ3a (2), and 19a (3) in PriOH (for ∆ν and ∆ν , see comments in the text).
1
2
that ketocyanine 16 is protonated at the carbonyl group of
the dye to form the corresponding polymethine salt (proꢀ
tonation of simple pyrones proceeds analogously18).
chromophore interaction is sharply weakened by the cenꢀ
tral NMe group, like in the case of ketocyanine 16.
The addition of larger amounts of acid to ketocyanine
16 led to a decrease in the intensity and a small hypsochꢀ
romic shift of the absorption band (the shortꢀwavelength
shoulder disappeared). In this case, the spectral changes
were irreversible (Fig. 6). An analogous situation was obꢀ
A
2
0.8
3
4
0.7
Alkylation of ketocyanines 3a—c proceeded in a simiꢀ
lar way to produce polymethine salts 4a—c (see above).
The absorption spectra of PFꢀ16 and salt 17 differ
sharply from the spectrum of analogous polymethine salt
4a containing the central pyrylium fragment, which has
been described earlier.1,2 Two bands in the spectrum of
salt 4a were attributed to the interaction between the chroꢀ
mophores (halves of the molecule) oriented at an acute
angle. The absorption bands of PFꢀ16 and salt 17 are
substantially shifted toward the shortꢀwavelength region
with respect to the longꢀwavelength band of salt 4a. Beꢀ
sides, the second (more intense) shortꢀwavelength band
observed in the spectrum of salt 4a is weakly manifested
in the spectra of PFꢀ16 and salt 17 (Fig. 5). The latter
5
6
0.6
0.5
0.4
0.3
0.2
0.1
1
spectra have only a shortꢀwavelength shoulder at λmax
=
28000
24000
20000 ν/cm–1
380 nm and an intense band at 480 nm. Since the shift of
the bands (spectrumꢀline splitting ∆ν) caused by the chroꢀ
mophore interaction depends on the energy of this interꢀ
action, it can be concluded that this interaction in PFꢀ16
and salt 17 is much weaker than that in salt 4a, i.e., the
Fig. 6. Absorption spectra of ketocyanine 16 in PriOH upon
the addition of acid in high concentrations: CHCl = 0 (1),
2.30•10–4 (2), 4.30•10–3 (3), 6.20•10–3 (4), 1.06•10–2 (5),
1.70•10–2 mol L–1 (6).

Crossꢀconjugated ketones and tridecamethine salts
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 9, September, 2003
2035
served upon the addition of acid to salt 17. Apparently,
this is associated with further protonation of these comꢀ
pounds accompanied by secondary irreversible reactions.
In spite of the fact that the absorption spectrum of
ketocyanine 3a differs substantially from that of 16 (see
Fig. 1), their 13C NMR spectra are similar (see the Exꢀ
perimental section). The absorption spectra of bichromoꢀ
phoric ketocyanines are determined by the chromophore
interaction (which influences the positions of the S1 and
S2 levels), whereas the 13C NMR spectra reflect the elecꢀ
tron density distribution within the polymethine chains of
both chromophores. Therefore, one would hardly expect
that a change in this interaction upon the replacement of
the bridging O atom outside the chromophores by the
NMe group would radically change the electron density
distribution on the C atoms of the polymethine chains
inside the chromophores, because the chromophore inꢀ
teraction via conjugation through the carbonyl group is
much weaker than the πꢀelectron conjugation within each
chromophore. This is reflected in similar values of the
chemical shifts in the 13C NMR spectra of dyes 3a and 16.
It was of interest to compare the absorption spectra of
salt 4a, the salt prepared by protonation of ketocyanine 3a
(PFꢀ3a), and newly synthesized salt 19a (see Fig. 5).
with an additional band at ∼430 nm, which is observed as
a small plateau in the spectra of salts 4a and PFꢀ3a and is
much more pronounced in the spectrum of salt 19a. This
band is, apparently, attributed to excitation localized on
the central pyrylium fragment, because the longꢀwaveꢀ
length absorption band of the triphenylpyrylium cation is
located in this region. The presence of the amino group in
salt 19a increases the intensity of this band.
The absorption spectra of ketones 7 and 14 containing
the terminal amino group are characterized by a longꢀ
wavelength chargeꢀtransfer band, which is shifted bathoꢀ
chromically in alcohols compared to that in toluene. Tiꢀ
tration of these compounds with hydrochloric acid afꢀ
forded protonated forms, which are characterized by abꢀ
sorption in the longerꢀwavelength region compared to the
spectrum of the starting compound. The absorption specꢀ
tra show isosbestic points. The initial absorption specꢀ
trum was restored upon the addition of diethylamine to
the reaction solution, which indicates that protonation is
reversible.
Experimental
The 1H NMR spectra were recorded on Bruker WMꢀ250
(250 MHz) and Bruker AMꢀ300 (300.13 MHz) instruments with
respect to Me4Si. The 13C NMR spectra were measured on a
Bruker ACꢀ200 spectrometer (50.32 MHz). The mass spectra
(EI, 70 eV, direct inlet of the sample) were obtained on an
MSꢀ30 instrument. The absorption spectra of the dyes were
measured on a Specord UV—VIS spectrophotometer. The fluoꢀ
rescence and fluorescence excitation spectra of the dyes were
studied on an Aminco—Bowman spectrofluorometer equipped
with an R136 photomultiplier.
The spectrum of salt 4a is similar to that of PFꢀ3a
(a small bathochromic shift of the bands in the spectrum
of 4a is, apparently, attributed to the electronꢀreleasing
effect of the central Et group), whereas the spectrum of
salt 19a much more substantially differs from the spectra
of 4a and PFꢀ3a. First, the line splitting ∆ν2 in the specꢀ
trum of salt 19a is much smaller than that observed in the
spectra of 4a (∆ν1) and PFꢀ3a, which is indicative of
weakening of the chromophore interaction in 19a. Apꢀ
parently, this is a consequence of the perturbing elecꢀ
tronic effect of the mesoꢀamino group on the polymethine
chromophore of the salt. An analogous phenomenon was
also observed for mesoꢀaminoꢀsubstituted thiacarboꢀ
cyanines. Thus, the insertion of the mesoꢀamino group
leads to broadening and a hypsochromic shift in the abꢀ
sorption spectrum of the dye.19 An analogous perturbing
effect of the amino group resposible for a sharp weakening
of the chromophore interaction, was also observed in salts
17 and PFꢀ16. The elimination of the chromophore inꢀ
teraction in ketocyanine 16 is, apparently, explained
analogously.
2,6ꢀBis(4ꢀdimethylaminoꢀ3ꢀethoxybutaꢀ1,3ꢀdienyl)ꢀ4Hꢀpyꢀ
ranꢀ4ꢀone (3d) was prepared from 2,6ꢀdimethylꢀγꢀpyrone (1)
and βꢀdimethylaminoꢀαꢀethoxyacrolein aminal acetal 2d 20 in
38% yield analogously to ketones 3a—c 1, m.p. 163—165 °C.
1
UV (EtOH), λmax/nm (ε): 370 (44900), 480 (20500). H NMR
(CD3OD), δ: 1.32 (t, 6 H, Me, J = 7.5 Hz); 3.07 (s, 12 H,
NMe2); 3.76 (q, 4 H, CH2, J = 7.5 Hz); 5.77 (d, 2 H, αꢀH,
J = 14.5 Hz); 5.88 (s, 2 H, CH); 6.19 (s, 2 H, δꢀH); 6.90 (d,
2 H, βꢀH, J = 14.5 Hz). MS, m/z (Irel (%)): 374 [M]+ (7),
329 [M – OEt]+ (43), 300 [M – OH – NMe2]+ (96), 284
[M – 2 OEt]+ (85), 272 [M – OEt – Me2NCH2]+ (8), 255
[M – OH – Me2NCH2 – Me2NH]+ (46), 243 [M – OH –
2 Me2NCH2]+ (21), 228 [M – OEt – Me2NCH2 – Me2N]+
(100), 200 [M – OEt – Me2NCH2 – CO]+ (16).
(13ꢀDimethylaminoꢀ5,9ꢀepoxyꢀ7ꢀethoxytridecaꢀ
2,4,6,8,10,12ꢀhexaenylidene)dimethylammonium tetrafluoroꢀ
borate (4a). The synthesis of compound 4a has been described in
our earlier study.1 13C NMR (DMSOꢀd6), δ: 14.0 (OCH2Me);
65.5 (OCH2Me); 96.6 (γꢀC); 99.7 (C(3), C(5)); 104.1 (αꢀC);
146.3 (βꢀC); 156.3 (δꢀC); 167.0 (C(2), C(6)); 169.4 (C(4)). The
signals of the dimethylamino groups overlap with the residual
signal of DMSOꢀd6.
2ꢀDimethylaminoethenylꢀ6ꢀmethylꢀ4Hꢀpyranꢀ4ꢀone (7).
A mixture of 2,6ꢀdimethylꢀγꢀpyrone (1) (0.2 g, 1.6 mmol) and
dimethylformamide acetal (0.58 g, 4.8 mmol) was heated at
The absorption spectra of polymethine salts 4a, 19a,
and PFꢀ3a have bands at ∼380 and 500—600 nm along

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Krasnaya et al.
110—120 °C for 2 h. Then the reaction mixture was cooled,
anhydrous diethyl ether was added, and the precipitate that
formed was separated. After recrystallization from anhydrous
ether, compound 7 was obtained in a yield of 15 mg (5%) as paleꢀ
yellow crystals, m.p. 106—108 °C. UV (EtOH), λmax/nm (ε):
Anhydrous acetone was added to the semicrystalline residue.
The precipitate that formed was filtered off and washed first
with anhydrous acetone and then with anhydrous diethyl ether.
Product 16 was obtained in a yield of 90 mg (33%) as redꢀorange
crystals, m.p. 187—190 °C. UV (EtOH), λmax/nm (ε): 412
(37700). 1H NMR (CDCl3), δ: 2.84 (s, 12 H, NMe2); 3.51 (s,
3 H, Me); 5.13 (dd, 2 H, γꢀH, J = 11.1 Hz, J = 13.1 Hz); 5.84 (d,
2 H, αꢀH, J = 14.4 Hz); 6.30 (d, 2 H, δꢀH, J = 13.1 Hz); 6.52 (s,
2 H, CH); 6.78 (dd, 2 H, βꢀH, J = 14.4 Hz, J = 11.1 Hz).
13C NMR (CDCl3), δ: 36.6 (NMe); 40.3 (NMe2); 97.6 (γꢀC);
110.0 (C(3), C(5)); 111.4 (αꢀC); 139.0 (βꢀC); 147.7 (δꢀC); 151.9
(C(2), C(6)); 177.4 (C=O). MS, m/z (Irel (%)): 299 [M]+ (11),
258 [M – MeCN]+ (4), 254 [M – Me2NH]+ (72), 239 [M –
Me2NH – Me]+ (13), 237 [M – Me2NH – OH]+ (44), 210
[M – Me2NH – Me2N]+ (100), 196 [M – Me2NH – OH –
MeCN]+ (18), 181 [M – 2 Me2NH – CO]+ (35), 168 [M –
2 Me2NH – MeCN]+ (20), 166 [M – 2 Me2NH – CO –
Me]+ (16).
1
364 (38600). H NMR (CDCl3), δ: 2.20 (s, 3 H, Me); 2.90 (s,
6 H, NMe2); 4.72 (d, 1 H, αꢀH, J = 12.5 Hz); 5.76 and 5.91
(both s, 1 H each, CH); 7.10 (d, 1 H, βꢀH, J = 12.5 Hz). MS,
m/z (Irel (%)): 179 [M]+ (100), 164 [M – Me]+ (3), 151 [M –
CO]+ (10), 136 [M – Me – CO]+ (13), 121 [M – CH2NMe2]+
(5), 109 [M – C2H2NMe2]+ (24), 95 [γꢀpyrone – H]+ (81).
2,6ꢀDistyrylꢀ4Hꢀpyranꢀ4ꢀone (10). Ketone 10 was prepared
in 14% yield from compound 13 using the procedure described
earlier.4 The physicochemical data are identical with those pubꢀ
lished in the literature.6 1H NMR (CD3OD), δ: 6.41 (s, 1 H,
CH); 7.02 (d, 2 H, αꢀH, J = 12.0 Hz); 7.30—7.48 and 7.62—7.76
(both m, 12 H, 2 Ph + 2 βꢀH).
3ꢀCinnamoylꢀ4ꢀhydroxyꢀ6ꢀmethylꢀ2Hꢀpyranꢀ2ꢀone (12) was
prepared according to a procedure described earlier.5 1H NMR
(CDCl3), δ: 2.68 (s, 3 H, Me); 5.98 (s, 1 H, CH); 7.45 (br.s, 3 H,
Ph); 7.70 (t, 2 H, Ph, J = 2.0 Hz); 7.91 (d, 1 H, αꢀH, J =
14.5 Hz); 8.42 (d, 1 H, βꢀH, J = 14.5 Hz); 17.86 (s, 1 H, OH).
6ꢀMethylꢀ2ꢀstyrylꢀ4Hꢀpyranꢀ4ꢀone (13) was prepared acꢀ
cording to known procedures.6,7 1H NMR (CDCl3), δ: 2.36 (s,
3 H, Me); 6.11 and 6.21 (both s, 1 H each, CH); 6.68 (d, 1 H,
αꢀH, J = 17.5 Hz); 7.30—7.42 (m, 4 H, Ph, βꢀH); 7.59—7.47
(m, 2 H, Ph).
2,6ꢀDi(4ꢀdimethylaminobutaꢀ1,3ꢀdienyl)ꢀ4ꢀethoxyꢀ1ꢀmethylꢀ
pyridinium tetrafluoroborate (17). A solution of Et3O+BF4
–
(74 mg, 0.24 mmol) in anhydrous CH2Cl2 (1 mL) was added
dropwise with stirring to a solution of ketone 16 (50 mg,
0.17 mmol) in CH2Cl2 (2 mL) cooled to 0 °C. The reaction
mixture was stirred at 0 °C for 1 h. The solvent was removed in
vacuo (without heating). The resulting viscous mixture was trituꢀ
rated with an anhydrous ether—anhydrous MeOH mixture
(20 : 1) and the solvent was removed by decantation. The preꢀ
cipitate that formed was filtered off, washed with anhydrous
ether, suspended in refluxing anhydrous MeOH, thoroughly
triturated, and filtered off. Compound 17 was prepared in a
2ꢀ(4ꢀDimethylaminobutaꢀ1,3ꢀdienyl)ꢀ6ꢀstyrylꢀ4Hꢀpyranꢀ4ꢀ
one (14). A mixture of 6ꢀmethylꢀ2ꢀstyrylꢀ4Hꢀpyranꢀ4ꢀone (13)
(150 mg, 0.71 mmol) and βꢀdimethylaminoacrolein aminal acꢀ
etal 2a (110 mg, 0.71 mmol) was heated at 70—75 °C for 25 min.
After cooling to 20 °C, anhydrous diethyl ether was added to a
glassy mixture, the mixture was triturated, and the precipitate
that formed was separated. Compound 14 was prepared in a
yield of 130 mg (63%) as dirtyꢀorange crystals, m.p. 138—142 °C
(decomp.). UV (EtOH), λmax/nm (ε): 328 (42500), 455 (23800).
1H NMR (CDCl3), δ: 2.91 (s, 6 H, NMe2); 5.19 (t, 1 H, γꢀH,
J = 11.2 Hz); 5.77 (d, 1 H, αꢀH, J = 15.1 Hz); 5.97 and 6.16
(both d, 1 H each, CH, J = 2.0 Hz); 6.66—6.72 (m, 2 H, α´ꢀH,
δꢀH); 7.13 (dd, 1 H, βꢀH, J = 15.1 Hz, J = 11.2 Hz); 7.30—7.60
(m, 6 H, Ph, β´ꢀH). 13C NMR (CDCl3), δ: 40.5 (NMe2); 97.4
(γꢀC); 108.6 (C(3)); 109.1 (αꢀC); 113.6 (C(5)); 120.3 (β´ꢀC);
127.3 (oꢀCPh); 128.8 (mꢀCPh); 129.3 (pꢀCPh); 134.5 (α´ꢀC); 135.1
(iꢀCPh); 139.0 (βꢀC); 149.4 (δꢀC); 160.1 (C(6)); 164.1 (C(2));
180.1 (C=O). MS, m/z (Irel (%)): 293 [M]+ (78), 265 [M –
CO]+ (22), 249 [M – Me2N]+ (68), 231 [M – Me2N – H2O]+
(11), 221 [M – Me2N – CO]+ (11), 216 [M – Ph]+ (9), 196
[M – CO – Me2NC2H2 + H]+ (23), 191 [M – PhC2H2 + H]+
1
yield of 55 mg as red crystals. According to the H NMR specꢀ
troscopic data, the product contained up to 10% of unidentified
impurities. 1H NMR (CDCl3), δ: 1.41 (t, 3 H, Me); 2.83 (s, 6 H,
NMe2); 3.82 (s, 3 H, NMe); 4.32 (q, 2 H, CH2); 5.45 (t, 2 H,
γꢀH); 6.17 (d, 2 H, αꢀH); 7.00 (s, 2 H, CH); 7.03 (d, 2 H, δꢀH);
7.45 (dd, 2 H, βꢀH). The signals at δ 3.08, 3.31, 3.23, 3.54, and
3.90 were not identified.
4ꢀAminoꢀ2,6ꢀbis(4ꢀdimethylaminobutaꢀ1,3ꢀdienyl)pyrylium
tetrafluoroborate (18). A solution of ethoxypyrylium salt 4a
(150 mg, 0.37 mmol) in DMF (5 mL) was added to a concenꢀ
trated aqueous ammonia solution (7 mL) heated to 30—35 °C.
The reaction mixture was stirred at 30—35 °C for 30 min and
then kept at ∼20 °C for one day. The solvent was evaporated in
vacuo and distilled water was added to the crystalline residue.
The precipitate that formed was separated and intensely washed
with an anhydrous ether—EtOH mixture (1 : 1). Compound 17
was obtained in a yield of 100 mg (72%) as a darkꢀclaret precipiꢀ
tate, m.p. 203—205 °C (decomp.). Found (%): C, 55.41; H, 6.46.
(27), 173 [M – Me2N – Ph + H]+ (28), 162 [M – PhC2H2
–
C
λ
17H24BF4N3O. Calculated (%): C, 54.71; H, 6.48. UV (EtOH),
CO]+ (62), 155 [M – Me2N – CO – Ph + H]+ (56), 148 [M –
C3H5O – H2O – Me2NC2H2]+ (74), 141 [M – C3H5O – H2O –
Ph] (31), 131 [M – C3H5O – CO – Ph] (75), 121 [M – Ph –
Me2NC4H3]+ (100), 115 [M – Ph – Me2NH – 2 CO]+ (55),
103 [PhC2H2]+ (57).
max/nm: 383, 429, 543. UV (PriOH), λmax/nm: 380, 430, 536.
Low solubility of aminopyrylium salt 18 did not allow us to
determine ε. 1H NMR (DMSOꢀd6), δ: 2.95 (br.s, 12 H, NMe2);
3.15 (br.s, 2 H, NH2); 5.31 (t, 2 H, γꢀH, J = 12.2 Hz); 5.78 (d,
2 H, αꢀH, J = 14.0 Hz); 6.28 (s, 2 H, CH); 7.23 (d, 2 H, δꢀH,
J = 12.2 Hz); 7.44 (dd, 2 H, βꢀH, J = 14.5 Hz, J = 12.2 Hz).
4ꢀDimethylaminoꢀ2,6ꢀbis(4ꢀdimethylaminobutaꢀ1,3ꢀ
dienyl)pyrylium tetrafluoroborate (19a). A 1 : 1 solution of
Me2NH in benzene (2 mL) was added to a solution of ethoxyꢀ
pyrylium salt 4a (150 mg, 0.37 mmol) in a mixture of anhydrous
MeOH (5 mL) and anhydrous DMF (3 mL) cooled to –5 °C.
The reaction mixture was stirred at ∼20 °C for 1 h. The solvent
2,6ꢀDi(4ꢀdimethylaminobutaꢀ1,3ꢀdienyl)ꢀ1ꢀmethylꢀ1Hꢀpyriꢀ
dinꢀ4ꢀone (16). A mixture of pyridone 15 (130 mg, 0.09 mmol)
and aminal acetal 2a (450 mg, 2.9 mmol) was heated at
105—110 °C for 1 h. After cooling to 20 °C, the reaction mixture
was dissolved in anhydrous CH2Cl2 (12 mL) and then SiO2
(L 40/100; 200 mg) was added. After one day, SiO2 was filtered
off and washed with CH2Cl2. The filtrate was concentrated.

Crossꢀconjugated ketones and tridecamethine salts
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 9, September, 2003
2037
was removed in vacuo, anhydrous diethyl ether was added to the
residue, and the precipitate that formed was separated. Comꢀ
pound 19a was obtained in a yield of 50 mg (33%) as dark
crystals, m.p. 235—237 °C. UV (EtOH), λmax/nm (ε): 380
(47200), 432 (31500), 544 (21700). 1H NMR (DMSOꢀd6), δ:
2.95 (br.s, 12 H, NMe2); 3.16 (br.s, 6 H, NMe2); 5.31 (t, 2 H,
γꢀH, J = 12.0 Hz); 5.78 (d, 2 H, αꢀH, J = 14.6 Hz); 6.28 (s, 2 H,
CH); 7.22 (d, 2 H, δꢀH, J = 12.0 Hz); 7.43 (dd, 2 H, βꢀH, J =
14.8 Hz, J = 12.0 Hz). 13C NMR (DMSOꢀd6), δ: 94.4 (C(3));
97.5 (γꢀC); 105.5 (αꢀC); 143.2 (βꢀC); 153.4 (C(4)); 156.3 (δꢀC);
163.5 (C(2)). The signals of the dimethylamino groups overlap
with the residual signal of DMSOꢀd6.
4. L. L. Woods, J. Am. Chem. Soc., 1958, 80, 1440.
5. R. H. Wiley, C. H. Jarboe, and H. G. Ellert, J. Am. Chem.
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6. N. S. Vul´fson, E. V. Savenkova, and L. B. Senyavina,
Zh. Obshch. Khim., 1964, 34, 2743 [J. Gen. Chem. USSR,
1964, 34 (Engl. Transl.)].
7. J. Birch, D. W. Cameron, and R. W. Rickards, J. Chem.
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8. M. Elkaschef and M. H. Nossier, J. Am. Chem. Soc., 1960,
82, 4344.
9. P. Bellingham, C. D. Johnson, and A. R. Katritzky, J. Chem.
Soc. B, 1968, 866.
4ꢀPiperidinoꢀ2,6ꢀbis(4ꢀpiperidinobutaꢀ1,3ꢀdienyl)pyrylium
tetrafluoroborate (19b). Freshly distilled piperidine (0.5 mL,
5.1 mmol) was added to a solution of salt 4a (65 mg, 0.16 mmol)
in dry DMF (5 mL) at ∼20 °C. The reaction mixture was kept at
∼20 °C for 3 days. Then the solvent was removed in vacuo. The
residue was successively triturated with diethyl ether and water
and then filtered off. After washing with water and diethyl ether,
product 19b was obtained in a yield of 80 mg (95%) as a darkꢀ
claret precipitate, m.p. 138—141 °C. UV (EtOH), λmax/nm (ε):
385 (72000), 435 (48000), 550 (29000). 1H NMR (CDCl3), δ:
1.65 (br.s, 18 H, CH2); 3.35 (br.s, 8 H, N—CH2); 3.54 (br.s,
4 H, N—CH2); 5.34 (t, 2 H, γꢀH, J = 11.8 Hz); 5.63 (d, 2 H,
αꢀH, J = 13.8 Hz); 5.90 (s, 2 H, CH); 7.25 (d, 2 H, δꢀH); 7.57
(dd, 2 H, βꢀH, J = 14.0 Hz, J = 11.8 Hz). The signal for H
partially overlaps with the residual signal of CDCl3.
10. E. A. Zvezdina, M. P. Zhdanova, and G. N. Dorofeenko,
Usp. Khim., 1982, 52, 817 [Russ. Chem. Rev., 1982, 52 (Engl.
Transl.)].
11. K. Dimroth, Angew. Chem., 1960, 72, 331.
12. G. N. Dorofeenko, E. I. Sadekova, and E. V. Kuznetsov,
Preparativnaya khimiya pirilievykh solei [Preparative Chemꢀ
istry of Pyrylium Salts], Izdꢀvo Rostovskogo Universiteta,
RostovꢀnaꢀDonu, 1972, 226 (in Russian).
13. V. K. Lusis, A. Z. Zapdersons, D. Kh. Mutsenietse, and
G. Ya. Dubur, Khim. Geterotsikl. Soedin., 1983, 508 [Chem.
Heterocycl. Compd., 1983, 19, 415 (Engl. Transl.)].
14. A. P. Kriven´ko, O. V. Fedotova, P. V. Reshetov, and V. G.
Kharchenko, Khim. Geterotsikl. Soedin., 1984, 1652 [Chem.
Heterocycl. Compd., 1984, 20, 1361 (Engl. Transl.)].
15. J. A. Van Allan, G. A. Reynolds, and C. C. Petropoulos,
J. Heterocycl. Chem., 1972, 9, 783.
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 02ꢀ03ꢀ32924)
and the Program of the Chemistry and Materials Science
Division of the Russian Academy of Sciences "Theoretiꢀ
cal and Experimental Studies of the Nature of Chemical
Bonds and Mechanisms of Important Chemical Reacꢀ
tions and Processes."
16. Zh. A. Krasnaya, T. S. Stytsenko, E. P. Prokof´ev, and V. F.
Kucherov, Izv. Akad. Nauk SSSR, Ser. Khim., 1978, 392
[Bull. Acad. Sci. USSR, Div. Chem. Sci., 1978, 27, 399 (Engl.
Transl.)].
17. L. A. Shvedova, A. S. Tatikolov, Zh. A. Krasnaya, A. R.
Bekker, and V. A. Kuz´min, Izv. Akad. Nauk SSSR, Ser.
Khim., 1988, 61 [Bull. Acad. Sci. USSR, Div. Chem. Sci.,
1988, 37, 52 (Engl. Transl.)].
18. A. I. Tolmachev, M. Yu. Kornilov, L. M. Shulezhko, and
A. V. Turov, Teor. Eksp. Khim., 1975, 11, No. 4, 556 [Theor.
Exp. Chem., 1975, 11 (Engl. Transl.)].
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Received May 12, 2003;
in revised form June 20, 2003