Protonation and alkylation of cross-conjugated ω,ω'- bis(dimethylamino) ketones (ketocyanines) containing the piperidine ring and the synthesis of the corresponding thiapentacarbocyanine dyes

Article abstract of DOI:10.1007/s11172-010-0166-4

Protonation or alkylation of 3,5-bis(3-dimethylaminoprop-2-enylidene)-1- methylpiperi-din-4-one with Et₂O HBF₄, Et ₃O+BF₄-, Me₂SO₄, or Et ₂SO₄ (1 equiv.) involves the

Full text of DOI:10.1007/s11172-010-0166-4

Russian Chemical Bulletin, International Edition, Vol. 59, No. 4, pp. 812—819, April, 2010
812
Protonation and alkylation of crossꢀconjugated
ω,ω´ꢀbis(dimethylamino) ketones (ketocyanines) containing the piperidine ring
and the synthesis of the corresponding thiapentacarbocyanine dyes
Zh. A. Krasnaya, E. O. Tret´yakova, V. V. Kachala, and S. G. Zlotin
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: kra@ioc.ac.ru
Protonation or alkylation of 3,5ꢀbis(3ꢀdimethylaminopropꢀ2ꢀenylidene)ꢀ1ꢀmethylpiperiꢀ
dinꢀ4ꢀone with Et2O•HBF4, Et3O+BF4–, Me2SO4, or Et2SO4 (1 equiv.) involves the endocyꢀ
clic N atom, yielding the corresponding piperidinium salts. With 2 equivalents of the above
reagents, the reactions occur at two reactive sites (the N and O atoms) to give doubly charged
4ꢀhydroxy or 4ꢀalkoxy polymethine salts. Protonation and alkylation of ethyl 3,5ꢀbis(3ꢀdimethylꢀ
aminopropꢀ2ꢀenylidene)ꢀ4ꢀoxopiperidineꢀ1ꢀcarboxylate involve only the O atom, affording
the corresponding singly charged 4ꢀhydroxy and 4ꢀalkoxy polymethine salts. The latter were
used to obtain previously unknown mesoꢀalkoxythiapentacarbocyanine dyes containing the
1ꢀethoxycarbonylꢀ1,2,3,6ꢀtetrahydropyridine fragment in the polymethine chain.
Key words: ketocyanines, protonation, alkylation, polymethine salts, cyanine dyes, elecꢀ
tronic absorption spectra.
Earlier, we have obtained crossꢀconjugated ω,ω´ꢀbisꢀ
(dimethylamino polyenyl) ketones (ketocyanines, BDAK)
and examined their specific luminescent spectroscopic and
chemical properties.1—4
According to this property, BDAK are very sensitive
indicators for acid traces in organic solvents and reagents.
The content of an acid in a solvent can be estimated from
the color of the solution. More precisely, the concentraꢀ
tion of free acid can be determined using spectrophotomeꢀ
try (threshold detectable concentration 10–7 mol L–1) suitꢀ
able for use in aprotic solvents with low dielectric conꢀ
stants (<10), for which direct and highly sensitive methꢀ
ods are absent.5—7
Like protonation, alkylation of BDAK occurs at the O
atom to give stable crystalline alkoxy polymethine salts in
high yields3,8,9 (see Scheme 1).
Polymethine salts are major intermediate products in
the synthesis of cyanine dyes, which are used as sensitizers
of silverꢀhalide photographic emulsions, passive Qꢀswitchꢀ
es and active media of lasers in quantum electronics, fluoꢀ
BDAK
n = 1, 2; m = 1—3
For instance, easy Oꢀprotonation of BDAK results in
lengthening of the conjugation chain and, accordingly, in
considerable deepening of their color (the bathochromic
shift of the absorption peak is Δλmax = 100—105 nm)
(Scheme 1).
Scheme 1
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 796—803, April, 2010.
1066ꢀ5285/10/5904ꢀ0812 © 2010 Springer Science+Business Media, Inc.

Protonation and alkylation of ketocyanines
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
813
rescent probes, photoresistors, and materials for nonlinear
optics and recording systems.10—14
Recently,15 we have obtained new ketocyanines 1 and
2, which are crossꢀconjugated ω,ω´ꢀbis(dimethylamino)
ketones containing the piperidine ring.
sites suitable for attacks of electrophiles: the carbonyl group
and the endocyclic N atom. The complex Et2O•HBF4
was employed as a proton source (Scheme 2). First of all,
we studied for comparison the reaction of this complex
with the known2 ketocyanine 3 and obtained crystalline
salt 4 in 76% yield. It turned out that the longꢀwavelength
peak λmax in the electronic absorption spectrum of salt 4
experiences a hypsochromic shift by 30 nm compared to
the λmax value for the previously3 described ethoxy polyꢀ
methine salt 5.
Salt 4 is unstable in the crystalline state and especially
in CHCl3 and EtOH solutions. In a highly dilute ethanolꢀ
ic solution, salt 4 undergoes rapid (5—10 min) transformaꢀ
tion into ketocyanine 3: the blue solution (λmax = 620 nm)
turned yellow (λmax = 490 nm).
R = Me (1), COOEt (2)
In the present work, we studied protonation and alkylꢀ
ation of ketocyanines 1 and 2. Unlike the previously exꢀ
amined ketocyanines, these compounds have two reactive
The action of an equimolar amount of the complex
Et2O•HBF4 gives tetrafluoroborate 6 in 90% yield as
Scheme 2

814
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
Krasnaya et al.
a result of protonation at the endocyclic N atom. The
reaction of ketocyanine 1 with two equivalents of
Et2O•HBF4 yields, through protonation at the endocyꢀ
clic N atom and the O atom, salt 7 in 93% yield. The same
salt can also be obtained from tetrafluoroborate 6 under
the action of one equivalent of Et2O•HBF4.
yield. Salts 6—8 are even less stable than salt 4, especially
in ethanolic solutions.
Alkylation of ketocyanines 1 and 2 was studied in reacꢀ
tions with such alkylating agents as triethyloxonium tetraꢀ
fluoroborate Et3O+BF4– and dialkyl sulfates (Scheme 3).
Ketocyanine 1 is readily alkylated at the endocyclic N
atom under the action of an alkylating agent (1 equiv.) in
dry CH2Cl2. The resulting salts 9a and 9b can be protonatꢀ
Protonation of ketocyanine 2, in which the N atom is
less basic than that in compound 1, produces salt 8 in 80%
Scheme 3

Protonation and alkylation of ketocyanines
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
815
1
ed with the complex Et2O•HBF4 in CH2Cl2 to give salts
10a and 10b in high yields.
for salts 11a,b (Table 1) and 1D H NMR spectroscopy
for salts 12a,b (Table 2). The signals in the 1H NMR
spectrum of salt 12b were assigned with the aid of selective
NOESY experiment. It follows from the coupling conꢀ
stants of the methine protons (3Jβ,γ = 13.3—13.7 Hz,
Reactions of salts 9a,b with dialkyl sulfates in the abꢀ
sence of CH2Cl2 produced Oꢀalkylated salts 11a,b. Howꢀ
ever, the action of the alkylating reagents (Et3O+BF4
,
–
Me2SO4, or Et2SO4) on salts 9a,b in the presence of
CH2Cl2 resulted in not only Oꢀalkylation but also (in part)
Oꢀprotonation leading to salts 10a,b as byꢀproducts. Comꢀ
pounds 10a,b were also obtained when ketocyanine 1 was
treated with an excess of the alkylating reagents in CH2Cl2.
Apparently, the proton source is an acid generated in trace
amounts from CH2Cl2 under the action of salts 9a,b. Keꢀ
tocyanine 2, which contains no quaternized N atom, reꢀ
3Jγ δ = 11.2—11.3 Hz) that the protons at the double bonds
β—γ and γ—δ are trans to each other and that the diene
fragments in the polymethine chains mainly exist in the
Sꢀtransꢀconformation.
Salts 12a,b were used for the synthesis of earlier unꢀ
known mesoꢀalkoxythiapentacarbocyanine dyes 13a,b conꢀ
taining the 1ꢀethoxycarbonylꢀ1,2,3,6ꢀtetrahydropyridine
fragment in the polymethine chain (Scheme 4).
Dyes 13a,b were obtained in high yields by condensaꢀ
tion of salts 12a,b with tosylate 14 in acetic anhydride in
the presence of triethylamine (see Scheme 4). Dyes 13a
and 13b are stable black crystalline solids with absorption
peaks at λmax = 1006 and 1005 nm (ε = 219 650 and
174 500, respectively) in CH2Cl2.
,
acts with Et3O+BF4 or Me2SO4 in CH2Cl2 to give salts
–
12a,b as sole products.
The structures of salts 4, 6, 7, 8, 9a,b, and 10a,b were
1
confirmed by H NMR spectroscopy in DMSOꢀd6 and
electronic absorption spectroscopy.
The electronic absorption spectra of Nꢀprotonated salt
1
6 and tetraalkylammonium salts 9a,b in CHCl3 (λmax
=
Structure 13a was identified using 1D and 2D H and
= 476—482 nm, yellow solution) are much the same as
the spectrum of the starting ketocyanine 1 (λmax = 470 nm).
The previously described (see Schemes 2, 3) Oꢀprotonatꢀ
ed salts 4, 7, 8, and 10a,b absorb at λmax = 600 nm (bright
blue solution).
13C NMR spectroscopy (13CꢀAPT, COSY, NOESY,
HSQC, and HMBC), which allowed complete assignment
of all signals (Table 3). The coupling constants of the
methine protons (3Jα β = 13.5 Hz, Jβ γ = 12.2 Hz, and
3
,
,
3Jγ,δ = 12.8 Hz) suggested the transꢀarrangement of the
protons at the double bonds in the polymethine chain and
the Sꢀtransꢀconformation of the diene fragments.
The structures of salts 11a,b and 12a,b were deterꢀ
mined using electronic absorption spectroscopy (λmax
=
= 640 nm) and 1D and 2D 1H and 13C NMR spectroscopy
(COSY, NOESY, 1H—13C HSQC, and 1H—13C HMBC)
Comparison of the integral intensities of the signals of
the protons in the tosylate anion and in the cationic part
Table 1. 1H and 13C NMR spectra of salts 11a,b in DMSOꢀd6
Atom
11а
1H
δ (J/Hz)
11b
13C
1H
13C
α
—
105.1
147.0
102.2
162.5
73.1
15.4
57.6
7.8
61.2
15.0
47.6
39.20
46.1
57.6
164.5
—
—
104.77
146.87
102.28
162.43
—
—
—
—
—
β
7.55 (d, 3Jγ,β = 13.5)
7.58 (d, 3Jγ,β = 13.7)
γ
δ
5.90 (t, 3Jγ β = 13.5, 3Jγ δ = 11.2)
5.84 (t, 3Jγ β = 13.7, 3Jγ δ = 11.2)
,
,
,
,
8.05 (d, 3Jγ,δ = 11.2)
8.02 (d, 3Jγ,δ = 11.2)
CH2 (OEt)
CH3 (OEt)
CH2 (EtN+)
CH3 (EtN+)
CH2 (EtSO4–
CH3 (EtSO4
(MeN+)*
4.0 (q)
1.45 (t)
3.40 (q)
1.30 (t)
3.70 (q)
1.10 (t)
3.05 (s)
3.15 (s, 6 Н)
3.35 (s, 6 Н)
4.30—4.40 (m, 4 H)
—
—
—
—
—
—
—
–
)
)
—
3.15 (6 H)
3.20 (s, 6 Н)
3.34 (s, 6 Н)
4.38 (s, 4 H)
—
51.10
39.50
46.05
59.67
—
64.52
165.17
52.73
(=NMe2)*
CH2
COEt
OMe
COMe
—
—
—
3.86
—
3.4**
—
—
–
MeSO4
* For compound 11b, δ15N (δCH NO = 0.0): –246.6 (=NMe2); –333.2 (MeN+).
3
** Overlap with the signal of HDO 2in DMSOꢀd6.

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Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
Krasnaya et al.
Table 2. 1H NMR spectra of salts 12a,b in DMSOꢀd6
Atom
δ (J/Hz)
12а
12b
β*
7.40 (d, 2 H, 3Jβ γ = 13.3)
7.44 (d, 2 H, 3Jβ γ = 13.3)
,
,
γ
5.72 (t, 2 H, 3Jβ γ = 13.3, 3Jδ γ = 11.5)
5.75 (t, 2 H, 3Jβ γ = 13.3, 3Jδ γ = 11.3)
,
,
δ
7.85 (d, 2,H, 3Jδ γ = 11.5)
7.87 (d, 2,H, 3Jδ γ = 11.3)
,
,
OMe
—
3.79 (s)
3.27 (br.s, 12 H)
4.29 (s, 4 H)
4.10 (q, 2 H)
1.21 (t, 3 H)
—
=NMe2
CH2
CH2 (COOEt)
CH3 (COOEt)
CH2 (OEt)
CH3 (OEt)
3.20 (br.s, 12 H)
4.28 (s, 4 H)
4.10 (q, 2 H)
1.18 (t, 3 H)
3.90 (q, 2 H)
1.38 (t, 3 H)
—
—
3.4**
–
MeSO4
* The SelNOESY experiment for compound 12b revealed that only the βꢀH proton (δ 7.44) remains close to
OMe upon its irradiation.
** Overlap with the signal of HDO in DMSOꢀd6.
Scheme 4
R = Et, X– = BF4– (12a)
R = Me, X– = MeSO4– (12b)
R = Et, X– = BF4–/Tos– (1 : 1) (13a)
R = Me, X– = Tos– (13b)
trometer (600.13 and 150.90 MHz, respectively) according to
the Bruker standard procedures. The mixing time in NOESY
and selective NOESY experiments was 0.7 s.
of the dye shows that the anions in compound 13a are
Tos– and BF4– in a ratio of 1 : 1.
Structure 13b was confirmed by 1D (1H, selective
NOESY for OMe) and 2D 1H NMR spectroscopy (COSY).
For assignment of the signals, we used the NMR data
obtained for dye 13a.
Electronic absorption spectra were recorded on a Specord
UVꢀVis spectrophotometer for salts 4, 6—8, 9a,b, 10a,b, 11a,b,
and 12a,b and on an Agilent 8453 spectrophotometer for dyes
13a,b. The molar absorption coefficients ε were not determined
for sparingly soluble salts. The course of the reactions was monꢀ
itored by electronic absorption spectroscopy. Since many of the
resulting salts are sparingly soluble in CH2Cl2 and CHCl3, a
sample of a reaction mixture was dissolved in a minimum amount
of dry DMSO and then diluted with CHCl3 for recording elecꢀ
tronic absorption spectra. All reactions with the complexes
Et2O•HBF4 and Et3O+BF4– were carried out under argon. Dry
CH2Cl2 free from acid traces was used.
Photochemical and photophysical data for dyes 13a,b
will be published elsewhere.
Experimental
The 1H NMR spectra of salts 4, 6, 7, 8, 9a,b, 10a,b, and 12a
were recorded on a Bruker Avance 300 instrument (300.13 MHz)
1
in DMSOꢀd6. The H and 13C NMR spectra of salts 11a,b and
Elemental analysis of the protonated salts and the dyes conꢀ
taining more than one anion was not carried out.
12b and dyes 13a,b were recorded on a Bruker Avance 600 specꢀ

Protonation and alkylation of ketocyanines
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
817
Table 3. NMR spectra of dyes 13a,b in DMSOꢀd6
Atom
13a
1H
δ (J/Hz)
13b,
1H
13C
α
7.20 (d, 3Jα,β = 13.5)
135.5
120.8
145.2
103.1
122.9
124.6
128.0
112.7
125.6
141.2
159.3
42.1
119.71
159.7
41.3
12.6
71.3
7.24 (d, 3Jα,β = 13.5)
β
6.46 (t, 3Jα β = 13.5, 3Jβ γ = 12.2)
6.50 (t, 3Jα β = 13.5, 3Jβ γ = 12.2)
,
,
,
,
γ
δ
7.41 (t, 3Jγ,δ = 12.8, 3Jγ,β = 12.2)
7.45 (t, 3Jγ,δ = 13.0, 3Jγ,β = 12.2)
6.70 (d, 3Jγ,δ = 12.8)
6.73 (d, 3Jγ,δ = 13.0)
C(4´)
C(5´)
C(6´)
C(7´)
C(3a´)
C(7a´)
C(2´)
CH2 (ring)
C(3) (ring)
C(4) (ring)
CH2 (NEt)
CH3 (NEt)
CH2 (OEt)
CH3 (OEt)
OMe
7.93 (d, 3J4´,5´ = 7.2)
7.96 (d, 3J4´,5´ = 7.8)
7.34 (t, 3J4´,5´ = 7.2, 3J6´,5´ = 7.2)
7.38 (t, 3J4´,5´ = 7.8, 3J6´,5´ = 7.2)
7.52 (t, 3J6´,5´ = 7.2, 3J6´,7´ = 8.11)
7.51 (t, 3J6´,5´ = 7.2, 3J6´,7´ = 8.1)
7.66 (d, 3J6´,7´ = 8.11)
7.65 (t, 3J6´,7´ = 8.1)
—
—
—
4.35 (s)
—
—
4.35 (q)
1.32 (t)
—
—
—
4.37 (s)
—
—
4.37 (q)
1.32 (t)
3.92 (q)
1.44 (t)
—
—
3.80 (s)
15.4
—
CH2 (COOEt)
CH3 (COOEt)
C=O (COOEt)
C(1″)
4.14 (q)
1.24 (t)
—
2.28 (s)
61.2
14.6
154.6
20.7
137.4
125.4
128.0
145.8
4.11 (q)
1.25 (t)
—
2.25 (s)
C(2″)
—
—
C(3″)
7.48 (d, 3J3″,4″ = 7.5)
7.10 (d, 3J3″,4″ = 7.5)
—
7.46 (d, 3J3″,4″ = 7.5)
7.08 (d, 3J3″,4″ = 7.5)
—
C(4″)
C(5″)
Nꢀ(9ꢀDimethylaminoꢀ5ꢀhydroxyꢀ4,6ꢀtrimethylenenonaꢀ
2,4,6,8ꢀtetraenylidene)ꢀN,Nꢀdimethylammonium tetrafluoroꢀ
borate (4). A solution of the complex Et2O•HBF4 (0.073 g,
0.45 mmol) in dry CH2Cl2 (2 mL) was added dropwise at –7 to
0 °C to a stirred solution of ketocyanine 3 (0.0765 g, 0.3 mmol)
in dry CH2Cl2 (3 mL). The blue reaction mixture was stirred at
this temperature for 20 min. Then the mixture characterized by
an absorption peak at λmax = 610 nm (salt 4) instead of the peak
N+Me); 2.95 (s, 12 H, NMe2); 4.10 (s, 4 H, CH2); 5.08 (t, 2 H,
γꢀH, J = 12.5 Hz); 7.18 (d, 2 H, δꢀH, J = 12.5 Hz); 7.40 (d, 2 H,
βꢀH, J = 12.5 Hz).
3ꢀ(3ꢀDimethylaminopropꢀ2ꢀenylidene)ꢀ5ꢀ(3ꢀdimethyliminioꢀ
propꢀ1ꢀenyl)ꢀ4ꢀhydroxyꢀ1ꢀmethylꢀ1,2,3,6ꢀtetrahydropyridinium
bis(tetrafluoroborate) (7). A. A solution of the complex
Et2O•HBF4 (0.03 g, 0.18 mmol) in CH2Cl2 (1 mL) was added
dropwise at –7 °C to a solution of tetrafluoroborate 6 (0.4 g,
0.11 mmol) in CH2Cl2 (3 mL). The reaction mixture was kept
cooled for 1 h and concentrated in vacuo. The residue was washed
with dry ether and the precipitate was separated. The yield of
bis(tetrafluoroborate) 7 was 0.034 g (70%), black crystals, m.p.
152—153 °C. UV (CHCl3), λmax/nm: 600. 1H NMR, δ: 2.95 (s, 3 H,
N+Me); 3.20 (s, 12 H, NMe2); 4.30 (m, 4 H, CH2); 5.62 (t, 2 H,
γꢀH, J = 12.5 Hz); 7.65 (d, 2 H, βꢀH, J = 12.5 Hz); 7.70 (d, 2 H,
δꢀH, J = 12.5 Hz); 9.95 (br.s, 1 H, OH).
at λ
= 460 nm corresponding to ketocyanine 3 was concenꢀ
max
trated in vacuo. Dry ether was added to the residue and the
precipitate was separated and repeatedly washed with ether. The
yield of tetrafluoroborate 4 was 0.08 g (76%), black crystals, m.p.
107—108 °C. UV, λmax/nm (ε): (EtOH) 620 (27 235); (CHCl3)
610 (90 729). 1H NMR, δ: 1.70 (br.s, 2 H, CH2); 2.30 (br.s, 4 H,
CH2); 3.10 (s, 12 H, NMe2); 5.60 (t, 2 H, γꢀH, J = 12.5 Hz);
7.50—7.70 (m, 4 H, βꢀH, δꢀH).
3,5ꢀBis(3ꢀdimethylaminopropꢀ2ꢀenylidene)ꢀ1ꢀmethylꢀ4ꢀoxꢀ
opiperidinium tetrafluoroborate (6). Dichloromethane (1.4 mL)
containing Et2O•HBF4 (0.07 g, 0.43 mmol) was added dropwise
to a solution of ketocyanine 1 (0.1 g, 0.36 mmol) in CH2Cl2
(3 mL). The reaction mixture was stirred at –8 to 0 °C for 1 h and
the precipitate that formed was separated. The mother liquor
was concentrated in vacuo, the residue was treated with dry ether,
and the resulting precipitate was separated. Both precipitates
were combined and washed with dry ether. The yield of tetrafluꢀ
oroborate 6 was 0.12 g (90%), black crystals, m.p. > 250 °C.
UV (CHCl3), λmax/nm (ε): 476 (28 750). 1H NMR, δ: 2.90 (s, 3 H,
B. A solution of the complex Et2O•HBF4 (0.15 g, 1 mmol)
in dry CH2Cl2 (0.8 mL) was added dropwise at –7 °C to a soluꢀ
tion of ketocyanine 1 (0.1 g, 0.36 mmol) in dry CH2Cl2 (3 mL).
The reaction mixture was kept at –7 °C for 1 h and concentratꢀ
ed. The residue was washed with dry ether. The yield of bisꢀ
(tetrafluoroborate) 7 was 0.15 g (93%), crystals, m.p. 152—153 °C.
The UV and H NMR spectra of the product are identical with
those of salt 7 obtained according to procedure A.
Nꢀ{3ꢀ[3ꢀ(3ꢀDimethylaminopropꢀ2ꢀenylidene)ꢀ1ꢀethoxycarꢀ
bonylꢀ4ꢀhydroxyꢀ1,2,3,6ꢀtetrahydropyridinꢀ5ꢀyl]propꢀ2ꢀenylꢀ
idene}ꢀN,Nꢀdimethylammonium tetrafluoroborate (8). A solution
1

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Krasnaya et al.
of the complex Et2O•HBF4 (0.05 g, 0.3 mmol) in dry CH2Cl2
(1 mL) was added dropwise at –5 °C to a solution of ketocyanine
2 (0.1 g, 0.3 mmol) in CH2Cl2 (3 mL). The reaction mixture was
kept at –5 °C for 1 h and concentrated in vacuo. Dry ether was
added and the precipitate that formed was separated and washed
with dry ether. The yield of tetrafluoroborate 8 was 0.1 g (80%),
m.p. 143—145 °C. UV (CHCl3), λmax/nm: 600. 1H NMR, δ:
1.20 (t, 3 H, OCH2CH3, J = 7 Hz); 3.00 (s, 12 H, NMe2); 4.05
(q, 2 H, CH3CH2O); 4.20 (br.s, 4 H, CH2); 5.10 (t, 2 H, γꢀH,
J = 12.5 Hz); 7.20 (d, 2 H, βꢀH, J = 12.5 Hz); 7.30 (d, 2 H, δꢀH,
J = 12.5 Hz).
oil. UV (CHCl3), λmax/nm: 580. 1H NMR, δ: 3.15 (s, 6 H,
N+Me2); 3.20 (br.s, 12 H, NMe2); 3.40 (s, 2 H, MeSO4–); 4.25
(s, 4 H, CH2); 5.60 (t, 2 H, γꢀH, J = 12.5 Hz); 7.70 (m, 4 H, βꢀH,
δꢀH); 5.00 (br.s, OH (10b), HOD (DMSOꢀd6)).
3ꢀ(3ꢀDimethylaminopropꢀ2ꢀenylidene)ꢀ5ꢀ(3ꢀdimethyliminioꢀ
propꢀ1ꢀenyl)ꢀ4ꢀethoxyꢀ1ꢀethylꢀ1ꢀmethylꢀ1,2,3,6ꢀtetrahydropyriꢀ
dinium bis(ethyl sulfate) (11a). Diethyl sulfate (0.1 g, 0.7 mmol)
was added to a stirred solution of ketocyanine 1 (0.2 g, 0.7 mmol)
in CH2Cl2 (1 mL). After 10 min, the reaction mixture was conꢀ
centrated in vacuo. Diethyl sulfate (0.53 g, 3.5 mmol) was added
to the dry residue of salt 9a (0.29 g, λmax(CHCl3) = 480 nm). The
reaction mixture was stirred at 60—65 °C for 1 h and then treated
with dry ether. The resulting precipitate was separated and reꢀ
peatedly washed with ether. The yield of salt 11a was 0.28 g
(68%), dark gray crystals, m.p. 151—154 °C. Found (%):
C, 49.15; H, 7.52; N, 7.05. C20H35N3O•2EtSO4. Calculated (%):
C, 49.40; H, 7.72; N, 7.20. UV (CHCl3), λmax/nm: 640.
3ꢀ(3ꢀDimethylaminopropꢀ2ꢀenylidene)ꢀ5ꢀ(3ꢀdimethyliminioꢀ
propꢀ1ꢀenyl)ꢀ4ꢀmethoxyꢀ1,1ꢀdimethylꢀ1,2,3,6ꢀtetrahydropyriꢀ
dinium bis(methyl sulfate) (11b). Dimethyl sulfate (0.8 g, 6 mmol)
was added with stirring to methyl sulfate 9b (0.26 g, 0.66 mmol).
The reaction mixture was heated at 55—60 °C for 30 min, cooled,
and treated with dry ether. The resulting precipitate was separatꢀ
ed and washed with CH2Cl2 and ether. The yield of bis(methyl
sulfate) 11b was 0.32 g (94%), dark violet crystals, m.p. > 260 °C.
Found (%): C, 45.15; H, 6.85; N, 7.62. C18H31N3O•2MeSO4.
Calculated (%): C, 45.24; H, 7.02; N, 7.97. UV (CHCl3),
3,5ꢀBis(3ꢀdimethylaminopropꢀ2ꢀenylidene)ꢀ1ꢀethylꢀ1ꢀmethꢀ
ylꢀ4ꢀoxopiperidinium tetrafluoroborate (9a). A solution of the
–
complex Et3O+BF4 (0.021 g, 0.11 mmol) in dry CH2Cl2
(0.5 mL) was added dropwise at –10 °C to a solution of ketoꢀ
cyanine 1 (0.03 g, 0.109 mmol) in CH2Cl2 (1 mL). The reaction
mixture was kept at this temperature for 1 h and concentrated
in vacuo. The resulting precipitate was washed with dry ether. The
yield of tetrafluoroborate 9a was 0.033 g (78%), m.p. 133—135 °C.
Found (%): C, 55.45; H, 7.50; N, 11.12. C18H30N3O•BF4. Calꢀ
culated (%): C, 55.24; H, 7.67; N, 10.74. UV (CHCl3), λmax/nm:
482. 1H NMR, δ: 1.25 (t, 3 H, NCH2CH3, J = 7 Hz); 2.95 (s, 12 H,
NMe2); 3.05 (s, 3 H, NMe); 3.30 (q, 2 H, NCH2CH3);
4.20—4.40 (m, 4 H, CH2); 5.12 (t, 2 H, γꢀH, J = 12.5 Hz); 7.22
(d, 2 H, δꢀH, J = 12.5 Hz); 7.45 (d, 2 H, βꢀH, J = 12.5 Hz).
3,5ꢀBis(3ꢀdimethylaminopropꢀ2ꢀenylidene)ꢀ1,1ꢀdimethylꢀ4ꢀ
oxopiperidinium methyl sulfate (9b). Dimethyl sulfate (0.14 g,
1.1 mmol) was added to a solution of ketocyanine 1 (0.3 g,
1.1 mmol) in CH2Cl2 (1 mL). This immediately resulted in the
formation of a precipitate. The reaction mixture was concentratꢀ
ed in vacuo. The residue was treated with dry ether and the
precipitate that formed was separated and washed with ether.
The yield of methyl sulfate 9b was 0.4 g (91%), brown crystals,
m.p. 189—192 °C. Found (%): C, 53.62; H, 7.51; N, 10.32.
C17H28N3O•MeSO4. Calculated (%): C, 53.86; H, 7.73; N, 10.47.
UV (CHCl3), λmax/nm (ε): 480 (46 000). 1H NMR, δ: 2.95 (br.s,
12 H, NMe2); 3.10 (s, 6 H, N+Me2); 3.35 (s, 3 H, MeSO4); 4.30
(s, 4 H, CH2); 5.05 (t, 2 H, γꢀH, J = 12.5 Hz); 7.22 (d, 2 H, δꢀH,
J = 12.5 Hz); 7.45 (d, 2 H, βꢀH, J = 12.5 Hz).
3ꢀ(3ꢀDimethylaminopropꢀ2ꢀenylidene)ꢀ5ꢀ(3ꢀdimethyliminioꢀ
propꢀ1ꢀenyl)ꢀ1ꢀethylꢀ4ꢀhydroxyꢀ1ꢀmethylꢀ1,2,3,6ꢀtetrahydroꢀ
pyridinium bis(tetrafluoroborate) (10a). A solution of the comꢀ
plex Et2O•HBF4 (0.05 g, 0.28 mmol) in CH2Cl2 (1.5 mL) was
added dropwise at –5 °C to a solution of tetrafluoroborate 9a
(0.1 g, 0.25 mmol) in CH2Cl2 (2 mL). After 40 min, the resulting
precipitate was separated and washed with dry ether. The yield of
bis(tetrafluoroborate) 10a was 0.08 g (70%), m.p. 132—135 °C.
UV (CHCl3 + 5% DMSO), λmax/nm: 600. 1H NMR, δ: 1.10
(t, 3 H, NCH2CH3); 3.10 (s, 3 H, N+Me); 3.20, 3.35 (both s,
6 H each, NMe2); 4.20—4.40 (m, 6 H, CH2, NCH2CH3); 5.75
(t, 2 H, γꢀH, J = 12.5 Hz); 7.75 (m, 4 H, βꢀH, δꢀH); 10.00 (br.s,
1 H, OH).
λ
max/nm: 640.
Nꢀ{3ꢀ[3ꢀ(3ꢀDimethylaminopropꢀ2ꢀenylidene)ꢀ4ꢀethoxyꢀ1ꢀ
ethoxycarbonylꢀ1,2,3,6ꢀtetrahydropyridinꢀ5ꢀyl]propꢀ2ꢀenylꢀ
idene}ꢀN,Nꢀdimethylammonium tetrafluoroborate (12a). A soluꢀ
–
tion of Et3O+BF4 (0.07 g, 0.37 mmol) in CH2Cl2 (1 mL) was
added dropwise at –7 °C to a solution of ketocyanine 2 (0.1 g,
0.3 mmol) in CH2Cl2 (3 mL). After 1 h, the reaction mixture was
concentrated in vacuo and the residue was treated with dry ether.
The resulting precipitate was separated and washed with dry
ether. The yield of tetrafluoroborate 12a was 0.11 g (82%),
m.p. 168—170 °C. Found (%): C, 53.15; H, 6.85, N, 9.12.
C20H32N3O3•BF4. Calculated (%): C, 53.45; H, 7.13; N, 9.35.
UV, λmax/nm (ε): (CHCl3) 640 (143 360); (EtOH) 640 (204 800).
Nꢀ{3ꢀ[3ꢀ(3ꢀDimethylaminopropꢀ2ꢀenylidene)ꢀ1ꢀethoxycarꢀ
bonylꢀ4ꢀmethoxyꢀ1,2,3,6ꢀtetrahydropyridinꢀ5ꢀyl]propꢀ2ꢀenylꢀ
idene}ꢀN,Nꢀdimethylammonium methyl sulfate (12b). A solution
of Me2SO4 (0.24 g, 1.9 mmol) in CH2Cl2 (2 mL) was added
dropwise to a solution of ketocyanine 2 (0.2 g, 0.6 mmol) in
CH2Cl2 (3 mL). The reaction mixture was refluxed with stirring
for 7 h until ketocyanine 2 was completely consumed (disapꢀ
pearance of the absorption band with λ
= 485 nm from the
max
UV spectrum (CHCl3)) and then concentrated in vacuo. The
residual viscous oil was triturated six times with dry ether
in portions of 5—6 mL. The precipitate that formed as a dark
brown powder was separated and washed with dry ether.
The yield of methyl sulfate 12b was 0.26 g (94%), black crystals,
m.p. 132—134 °C. Found (%): C, 51.95; H, 7.32; N, 8.86.
C19H30N3O3•MeSO4. Calculated (%): C, 52.28; H, 7.19; N, 9.15.
UV (CHCl3), λmax/nm (ε): 640 (72 000).
2ꢀ(4ꢀ{4ꢀEthoxyꢀ1ꢀethoxycarbonylꢀ3ꢀ[4ꢀ(3ꢀethylbenzothiazoꢀ
linꢀ2ꢀylidene)butꢀ2ꢀenꢀ1ꢀylidene]ꢀ1,2,3,6ꢀtetrahydropyridinꢀ5ꢀ
yl}butaꢀ1,3ꢀdienꢀ1ꢀyl)ꢀ3ꢀethylbenzothiazolium tosylate and tetꢀ
rafluoroborate (1 : 1 mixture) (13a). A 1 M solution of Et3N
(1 mL) in Ac2O was added dropwise at 20 °C to a mixture of
3ꢀ(3ꢀDimethylaminopropꢀ2ꢀenylidene)ꢀ5ꢀ(3ꢀdimethyliminioꢀ
propꢀ1ꢀenyl)ꢀ4ꢀhydroxyꢀ1,1ꢀdimethylꢀ1,2,3,6ꢀtetrahydropyridinꢀ
ium methyl sulfate and tetrafluoroborate (10b). A solution of the
complex Et2O•HBF4 (0.065 g, 0.4 mmol) in CH2Cl2 (0.35 mL)
was added dropwise at –7 °C to a solution of methyl sulfate 9b
(0.11 g, 0.27 mmol) in CH2Cl2 (3 mL). The reaction mixture was
stirred under cooling for 1 h and concentrated in vacuo. The
precipitate that formed was separated and washed with dry ether.
The yield of a mixture of salts 10b was 0.11 g (85%), very viscous

Protonation and alkylation of ketocyanines
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
819
3ꢀethylꢀ2ꢀmethylbenzothiazolium tosylate 14 (0.25 g, 0.7 mmol)
and tetrafluoroborate 12a (0.08 g, 0.18 mmol) in Ac2O (4 mL).
The reaction mixture was kept for 1.5 h and diluted with ether.
After 30 min, the resulting precipitate was separated and washed
with ether, a small amount of water, and again ether. The yield
of dye 13a was 0.105 g (83%), black crystals, m.p. 187—189 °C.
UV, λmax/nm (ε): (CH2Cl2) 1006 (219 650); (EtOH) 989.
2ꢀ(4ꢀ{1ꢀEthoxycarbonylꢀ3ꢀ[4ꢀ(3ꢀethylbenzothiazolinꢀ2ꢀylꢀ
idene)butꢀ2ꢀenꢀ1ꢀylidene]ꢀ4ꢀmethoxyꢀ1,2,3,6ꢀtetrahydropyridinꢀ
5ꢀyl}butaꢀ1,3ꢀdienꢀ1ꢀyl)ꢀ3ꢀethylbenzothiazolium tosylate (13b).
A 1 M solution of Et3N (1.1 mL) in Ac2O was added dropwise at
20 °C to a mixture of 3ꢀethylꢀ2ꢀmethylbenzothiazolium tosylate
14 (0.3 g, 0.8 mmol) and methyl sulfate 12b (0.1 g, 0.2 mmol) in
Ac2O (4 mL). The reaction mixture was kept for 1.5 h. After the
workup described above, the yield of dye 13b was 0.09 g (63%),
black crystals, m.p. 170—171 °C. UV (CH2Cl2), λmax/nm (ε):
1005 (174 500).
5. USSR Inventor´s Certificate 1 492 272; Byull. Izobret. [Bulꢀ
letin of Inventions], 1989, 25 (in Russian).
6. Yu. A. Fanov, Zh. A. Krasnaya, T. S. Stytsenko, V. I. Slovꢀ
etskii, E. I. Isaev, Izv. Akad. Nauk SSSR, Ser. Khim., 1989,
493 [Bull. Acad. Sci. USSR, Div. Chem. Sci. (Engl. Transl.),
1989, 38, 436].
7. N. M.ꢀG. Shvechgeimer, Zh. A. Krasnaya, T. S. Stytsenko,
V. I. Slovetskii, Neftekhimiya, 1990, 29, 567 [Petroleum Chemꢀ
istry (Engl. Transl.), 1990, 29].
8. USSR Inventor´s Certificate 536 165; Byull. Izobret. [Bulleꢀ
tin of Inventions], 1976, 43 (in Russian).
9. Zh. A. Krasnaya, T. S. Stytsenko, V. S. Bogdanov, N. V.
Monich, M. M. Kul´chitskii, S. V. Pazenok, L. M. Yaguꢀ
pol´skii, Izv. Akad. Nauk SSSR, Ser. Khim., 1989, 636 [Bull.
Acad. Sci. USSR, Div. Chem. Sci. (Engl. Transl.), 1989,
38, 562].
10. T. H. James, The Theory of the Photographic Process, Macꢀ
millan, New York, 4th ed., 1977.
11. A. A. Ishchenko, Stroenie i spektral´noꢀlyuminestsentnye
svoistva polimetinovykh krasitelei [The Structures and Lumiꢀ
nescent Spectroscopic Properties of Polymethine Dyes], Naukꢀ
ova dumka, Kiev, 1994, 231 pp. (in Russian).
12. I. I. Levkoev, Organicheskie veshchestva v fotograficheskikh
protsessakh [Organic Compounds in Photographic Processes],
Nauka, Moscow, 1982, 368 pp. (in Russian).
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Received May 26, 2009;
in revised form October 2, 2009