1,3,2-(2H)-dioxaborine polymethine dyes on the base of dehydroacetic acid - Effective fluorescent amine probes

Article abstract of DOI:10.1002/jhet.5570450617

(Chemical Equation Presented) A number of new polymethine dyes based on the boron difluoride complexes of dehydroacetic acid and 3-acetyl-4-hydroxypyridone has been synthesized. Their spectral-luminescent properties have been investigated. The reaction of obtained merocyanines with primary and secondary amines has been studied. These low fluorescent dyes gave highly fluorescent open chain products, which on further heating cyclized to weakly fluorescent pyridone dyes.

Full text of DOI:10.1002/jhet.5570450617

Nov-Dec 2008
1665
1,3,2-(2H)-Dioxaborine Polymethine Dyes on the Base of
Dehydroacetic Acid – Effective Fluorescent Amine Probes
Andriy O. Gerasova, Mykola P. Shanduraa, Yuriy P. Kovtuna*, Yuriy G. Vlasenkoa,
Vasyliy F. Gorchevb
aInstitute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanska str., 02660 Kyiv, Ukraine
bPalladin Institute of Biochemistry, National Academy of Sciences of Ukraine, 9 Leontovicha Str., 01030 Kyiv, Ukraine
yu_kovtun@svitonline.com
Received May 6, 2008
F
F
F
F
F
F
B
B
B
O
O
NHR
O
O
O
O
N
N
N
+
RNH3
O
O
N
R
O
O
O
strong fluorescence
weak fluorescence
weak fluorescence
A number of new polymethine dyes based on the boron difluoride complexes of dehydroacetic acid and
3-acetyl-4-hydroxypyridone has been synthesized. Their spectral-luminescent properties have been
investigated. The reaction of obtained merocyanines with primary and secondary amines has been studied.
These low fluorescent dyes gave highly fluorescent open chain products, which on further heating cyclized
to weakly fluorescent pyridone dyes.
J. Heterocyclic Chem., 45, 1665 (2008).
INTRODUCTION
Scheme 1
OH
O
O
O
The reaction of 4-hydroxypyran-2-ones with amines is
well known as the method for the preparation of pyridone
system. In 1885 Heitinger first obtained 2,6-dimethyl-
pyridine-4-one B (R = H) via reaction of dehydroacetic
acid A with ammonia [1]. A large amount of works
related to the reactions of dehydroacetic acid [2-7] and its
derivatives of type C [8-10] with the amines have been
published since then. The latter form open-chain
decarboxylated products by the reaction with amines.
Depending on the nature of substituents, amines and the
reaction conditions the monosubstituted enamine
derivatives of 1,3,5-triketones of type D [8,9] or disubsti-
tuted derivatives of type E could be obtained [10]. In all
cases amine attacks the C-6 position of the pyranone
system which leads to its further opening and decarboxyl-
ation of the obtained acid (Scheme 1).
It is well-known, that structural analogs of dehydro-
acetic acid – 4-hydroxy-3-acetylcumarines easily form
boron difluoride complexes which can provide intense
and deep colored polymethine dyes with high ability to
fluorescence [11,12]. Moreover, the interest to none-linear
optical properties (NLO) of 2,2-difluoro-1,3,2-(2H)-
dioxaborine dyes, recently tends to increase [13-18].
Consequently, it was decided to synthesize and
investigate chemical and structural properties of the dyes
based on the derivatives of dehydroacetic acid.
R`NH2
-CO2
O
N
R`=H, Alk
R`
B
A
R`
1eq. R`NH2
-CO2
R`= Alk
NH
O
OH
OH
O
O
R
D
R
O
N
N
O
2 eq.
-CO2
N
C
R
E
the reaction of boron trifluoride etherate and
dehydroacetic acid in the presence of acetic anhydride.
The melting point of the prepared compound is 48 ºC
higher than reported in literature, but the NMR spectra are
coincident.
This complex easily reacts with 2-(1,3,3-trimethyl-
indolin-2-ylidene)acetaldehyde to form dye 3a. The
reaction of the complex 2a with ethyl isoformanilide leads
to hemicyanine 4a, which forms merocyanines 5a and 6a
with quaternary salts of the heterocycles. The reaction of
the compound 2a with triethylorthoformate and
triethylamine in acetic anhydride media leads to
symmetrical anionic dye 7a (Scheme 2). Compound 2a,
as well as other boron difluoride complexes of 1,3-
diketones are stable in aprotic solvents, but easily
hydrolyzes in alcohol/water media. The dyes 3 – 7 are
stable in protic solvents.
RESULTS AND DISCUSSION
The starting boron difluoride complex 2a was described
earlier, however, it was prepared not as a desired product
[19]. For our purposes this compound was obtained with

1666
A. Gerasov, M. Shandura, Yu. Kovtun, Yu. Vlasenko and V. Gorchev
Vol 45
Scheme 2
OH
O
X
O
1a,b
F
F
F
F
F
F
F
F
B
B
-
B
B
O
O
O
O
O
O
O
O
N
+
HNEt3
X
O
O
X
X
2a,b
O
X
O
3a,b
7a,b
F
F
F
F
F
F
B
B
B
O
O
O
O
O
O
N
S
N
NHPh
X
O
X
O
X
O
5a,b
4a,b
6a,b
a X=O, b X=NCH2CH2OCH3
The prepared dyes are relatively weak luminophors.
Only symmetrical dye 7a has a fluorescent quantum yield
12 % (Table 1). However, some interesting spectral
effects were observed on addition of primary and
secondary aliphatic amines to their solutions. For
instance, after short time treatment of merocyanine 3a
with 2-methoxyethylamine (this amine was chosen for the
convenience due to its low volatility and easy
identification with 1H NMR spectroscopy), intense
fluorescence appeared, TLC analysis showed the
formation of a new dye. Though, the absorption maxima
of the prepared dye is a little different from that of starting
compound, which points on the retaining of the
dioxaborine cycle. When equimolecular quantities of dye
3a and amine were mixed, the TLC analysis of the
reaction mixture always showed the presence of the
significant quantity of starting dye. The reaction of 3a
with an excess of amine in acetonitrile at room
temperature was carried out and the dye which can not be
purified to the analytical purity grade was isolated.
1
However, according to the H NMR data that dye has the
1
structure 8a. The H NMR spectrum (CDCl3) of prepared
Scheme 3
F
F
F
F
B
R1
R2
B
O
O
NH2
N
O
O
O
N
N
or
O
O
N
H
-
R1
+
O
O
NH2
R2
3a
8a,b
a R1=CH2CH2OCH3, R2=H
b R1=R2=-(CH2)4-
O
ꢀ
ꢀ
for 8a
NH2
F
F
B
O
O
F
F
O
B
N
N
O
O
+
N
O
N
9
3b
O

Nov-Dec 2008
Dyes on the Base of Dehydroacetic Acid – Effective Fluorescent Amine Probes
1667
compound showed two none-equivalent amine residues,
one proton of NH group (9.43 ppm), the protons of
polymethine chain (8.03; 6.40; 5.68 ppm), one proton of
enamine fragment (5.47 ppm), and match to the structure
8a (Scheme 3). The mass-spectrum of this dye gave
molecular ion with mass number [475] which corresponds
to the anionic part of the molecule (474+H+).
Therefore, in the case of boron difluoride complexes of
chalcones of dehydroacetic acid, which per se are dyes
3a, 5a, and 6a (the dyes 5a and 6a react with amines
similar to dye 3a), the similar mechanism for the opening
the pyran cycle possibly realizes, that was previously
observed for free chalcones of the type C [8-10]. Due to
the higher electron accepting properties of annelated 2,2-
difluoro-1,3,2-(2H)-dioxaborine fragment in comparison
with free ꢀ-diketonate group, the carboxylic acid formed
by opening of the pyran cycle is stronger, than formed
from C. That’s why probable formation of more stable
salt is more evident. This fact partly prevents
decarboxylation and allows to provide cyclization to
pyridone cycle by heating of open cycle product.
The reaction of dye 3a with amine in boiling ethanol
forms intermediate compound 8a, which transforms to the
mixture of two other dyes. The less soluble product of
structure 3b was isolated (Scheme 3). The analogous
result was obtained on heating of the isolated dye 8a in
acetonitrile: the mixture of two different dyes in
1
proportion 1:1 (according to H NMR data) was formed.
One of them was isolated and identified as pyridone dye
3b, other possibly has the structure of decarboxylated
product 9 (due to the appearance of the singlet at 4.72
ppm, which could correspond to the proton of dioxaborine
cycle).
Thus, these dyes are effective fluorescent indicators with
high speed of response on the amino group. To investigate
this phenomenon in details on several examples, some
pyridone dyes were prepared for comparison (Scheme 2).
As it was already mentioned, they can be synthesized
from enamines 8. Although, using direct synthesis is
much more convenient. The nessessary 3-acetyl-4-
hydroxypyrid-2-one 1b was obtained analogously to [20]
(Scheme 4). Pyridone dyes 3b – 7b were synthesized
similarly to their oxygen analogs. According to analytical
and spectral data merocyanine 3b, prepared from
pyridone complex 2b, and the compound prepared earlier
by alternative method have completely identical
constants.
C23
O2
O1
C17
C2
N2
C16
C12
C1
C24
C8
C10
C18
C3
C6
C13
C14
N1
C5
C9
O4
C11
C15
C22
C19
C7
C4
C20
C21
O3
B1
C25
F1
F2
Scheme 4
Figure 1. Molecular structure of 8b. Selected bond lengths and
angles for 8b: N(1)-C(1) 1.482(4), N(1)-C(4) 1.474(4), N(1)-
C(5) 1.335(3), O(3)-C(7) 1.321(3), O(4)-C(9) 1.338(4), O(4)-
B(1) 1.447(4), O(3)-B(1) 1.471(4), N(2)-C(16) 1.400(4), N(2)-
C(13) 1.384(4), C(5)-C(6) 1.389(4), C(6)-C(7) 1.407(4), C(9)-
C(10) 1.436(4), C(10)-C(11) 1.342(4), C(11)-C(12) 1.437(5),
C(12)-C(13) 1.345(4); C(1)N(1)C(4) 111.6(2), C(7)O(3)B(1)
123.8(2), O(3)B(1)O(4) 113.7(3), C(9)O(4)B(1) 121.9(2),
C(13)N(2)C(16) 111.9(3)
O
OH
N
OH
O
O
N
OH
N
O
O
OH
O
O
O
1b
11
10
O
O
O
To ensure the legitimization of our assumptions for the
structure of the compound 8a, its structural analog –
enamine 8b was prepared by the reaction of the dye 3a
with pyrrolidine. It appears more stable than 8a, which
allows the establishment of its exact structure. The NMR
spectra and X-ray structural analysis (Figure 1) uniquely
determined the structure 8b. In the 1H NMR spectra
(DMSO-d6) the mixture of E- and Z- isomers (enamine
fragment) was observed, which is evidenced by doublet
splitting of the enamine proton. However, in the solid
state, according to X-ray data, the molecule exists only as
E- isomer and has almost planar structure. Interestingly,
the alternation of the bonds through the chromophore
could be found even in dioxaborine cycle (the bond
lengths values for C7-C8 and C8-C9 are 1.367 and 1.428
Å correspondingly).
Bathochromic shift of the absorption maxima of 14 nm
is observed upon the transition from symmetrical
pyranone dye 7a to pyridone 7b, the absorption intensity
hardly changed (Table 1). The similar tendency is
observed in the fluorescence spectra of this part of the
symmetrical dyes. In case of merocyanines 3b, 5b and 6b
insignificant bathochromic shift of the absorption and
fluorescence maxima takes place in comparison with their
oxygen analogs. The fluorescent quantum yields of the
merocyanines remain low, but molar absorptivity,
contrarily to the symmetrical dyes, increases by almost
1.5 times.
The reaction of the dehydroacetic acid derivatives with
amines was investigated in detail rely on spectral
properties of the dioxaborine dyes based on pyranone and

1668
A. Gerasov, M. Shandura, Yu. Kovtun, Yu. Vlasenko and V. Gorchev
Vol 45
finished for the first minutes, but when reaction was
carried out in dichloromethane changes lasted about 15
min.
3b
5b
1,2
1,0
0,8
0,6
0,4
0,2
0,0
3a
The absorption maxima of the merocyanine 3a hardly
changes after addition of 2-methoxyethylamine, only the
absorption band becomes slightly broader and less
intense. Although, addition of the amines to the solutions
of the dyes 5a and 6a leads to bathochromic shift of the
absorption maxima of 20 and 44 nm correspondingly
(Figure 3). It means that the enamine derivatives in this
case are colored deeper in comparison with the pyridone
analogs 5b and 6b. The absorption intensity
insignificantly increases.
6b
5a
6a
400
500
600
700
Wavelength, nm
The fluorescence spectra recorded after reaction of the
dyes 3 and 5 with alkylamines showed the most
significant changes (Figure 4). Decreasing of electron-
accepting properties of the dioxaborine cycle, (because
Figure 2. The absorption spectra of merocyanines 3a,b, 5a,b and 6a,b in
acetonitrile (C=1ꢀ10-5 molꢀl-1).
pyridone moiety. In the case of symmetrical dye 7a,
reaction with amines in acetonitrile occurs immediately,
but all attempts to isolate any individual product from the
reaction mixture failed. The absorption and fluorescence
bands become broad and the fluorescent intensity
decreases greatly.
3,0
2,5
5a+H NCH CH OCH
2
2
2
3
2,0
1,5
1,0
0,5
0,0
In the case of merocyanine dyes 3a, 5a and 6a spectral
changes occur slower (from several minutes for dye 3a to
5a
3b
5b
1,2
1,0
0,8
0,6
0,4
0,2
0,0
550
600
650
700
Wavelength, nm
3a
6b
5a
Figure 4. The changes occurring in the fluorescence spectra of the
solutions of dye 5 in acetonitrile after the addition of 10 eq. of 2-
methoxyethylamine (excitation at 500 nm).
6a
of presence of the electron-donating enamine fragment in
the open chain products) leads to increase of the
fluorescent quantum yield (up to 19 % for the compound
3 and to 13 % for 5) in comparison with the analogous
pyranone or pyridone dyes. The fluorescence maxima
batochromically shift on 33 and 48 nm for the compounds
3 and 5 correspondingly. The similar spectral effect was
observed for the dioxaborine dyes based on coumarine
nuclei. For instance, in the acetonitrile solution of the dye
12 with unsubstituted coumarine nuclei ꢁ = 0.2% whereas
the quantum yield increases to 11% with the introduction
of the electron donating diethylamino group (dye 13) [12].
400
500
600
700
Wavelength, nm
Figure 3. The changes occurring in the absorption spectra of the
solutions of merocyanines 3a, 5a and 6a in acetonitrile (C=1ꢀ10-5 molꢀl-1)
after the addition of 10 eq. of 2-methoxyethylamine
several hours for 6a). It means that pyranone nuclei
opening rate decreases as well as electron-donating ability
of other end nuclei get stronger. It is obvious because
more electron-donating end groups strongly deliver
electron density to the pyranone fragment, and decrease
its sensitivity to the nucleopfilic attack.
F
F
B
O
O
The investigated reaction is sensitive to polarity of the
solvent. For instance, after addition of the excess of amine
to acetonitrile solution of the dye 3a, spectral changes
12 R=H
13 R=NEt2
N
R
O
O

Nov-Dec 2008
Dyes on the Base of Dehydroacetic Acid – Effective Fluorescent Amine Probes
1669
Table 1
Spectral-luminescent properties of the dyes
Absorption
ꢁmax(MeCN), nm (ꢂ*10-5)
Emission (excitation 500 nm)
ꢀ
ꢁmax(MeCN), nm (ꢀ)
3a
554 (0.88)
551 (0.71)
558 (0.77)
578 (0.78)
601 (0.59)
645 (0.69)
554 (1.55)
558 (1.29)
567 (1.20)
625 (1.00)
568 (1.47)
554 (0,44)
566 (0.013)
599 (0.19)
570 (0.012)
618 (0.13)
630 (0.008)
-
560 (0.12)
575 (0.021)
576 (0.019)
641 (<0.005)
575 (0.20)
598 (0.085)
3a+H2NCH2CH2OCH3 [a]
5a
5a+H2NCH2CH2OCH3 [b]
6a
6a+H2NCH2CH2OCH3 [c]
7a
3b
5b
6b
7b
8b
[a] After 5 min of the reaction. [b]After 20 min of the reaction. [c] After 5 h of the reaction.
thermal parameters (only H(1) and H(2) atoms which take part
in the hydrogen bonds were refined isotropically). The SADABS
[23] absorption correction (the ratio of minimum to maximum
apparent transmission is 0.416803) was applied. In the
refinement 6676 reflections (2308 reflections with I ꢇ 3ꢈ(I))
were used. Convergence was obtained at R1 = 0.042 and wR2 =
0.046, GOF = 1.113 (360 parameters; observed/variable ratio
6.41; the largest and minimal peaks in the final difference map
0.17 and –0.18 e/Å3, Chebychev weighting scheme [24] with 3
parameters (24.2, -17.6, 19.5) was used.
Therefore, the boron difluoride complexes of the
merocyanines based on dehydroacetic acid were found to
be sensitive fluorescence indicators for primary and
secondary aliphatic amines. The speed of response can be
regulated by nature of the second end nuclei and media
polarity. This allows them to be utilized for the detection
of the nature based amines, which is going to be reported
later
The full crystaltallographic data sets (excluding structure
factors) for the structure in this paper have been deposited with
the Cambridge Crystallographic Data Centre as supplementary
publication number CCDC 681809. Copies of data can be
obtained, free of charge, on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK [fax: +44(0)-1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk].
EXPERIMENTAL
Electronic absorption spectra were recorded on a Shimadzu
UV-3100 spectrophotometer in acetonitrile. NMR spectra were
obtained with a Varian VXR-300 instrument (300 MHz) at 25°C
using tetramethylsilane as an internal standard. LC/MS spectra
were recorded using
a
liquid chromatography/mass
spectrometric system consisting of an Agilent 1100 Series high-
performance liquid chromatograph equipped with a diode-matrix
and an Agilent LC/MSD SL mass-selective detector.
Fluorescence spectra were recorded on a Signe-4M fluorescence
spectrophotometer and are not corrected. Relative fluorescence
quantum yields (ꢃ) were determined relative to Rhodamine 6G
(ꢃ=0.95, EtOH) [21].
F
F
B
1
O
O
ꢁ
R`
8
ꢀ
ꢂ
X
6
O
X-ray Structure determination for 8b: Crystal data:
C29H38B1F2N3O4, M 541.45, monoclinic, space group P 21/c (N
14), ꢀ = 16.9422(8), b = 7.5994(4), c = 24.671(1) Å, ꢁ =
94.620(2)°, V = 3166.1(3) Å3, Z = 4, dc = 1.14 g·cm-3, μ = 0.083
mm-1, F(000) = 1152, crystal size ca. 0.08 ꢂ 0.21 ꢂ 0.48 mm. All
crystallographic measurements were performed at 173 K on a
Bruker Smart Apex II diffractometer operating in the and ꢀ
scans mode. The intensity data were collected within the range
of 1.2 ꢃ ꢄ ꢃ 26.9° using Mo-Kꢅ radiation (ꢆ = 0.71078 Å). The
intensities of 22378 reflections were collected (6676 unique
reflections). Data were corrected for Lorentz and polarization
effects. The structure was solved by direct methods and refined
by the full-matrix least-squares technique in the anisotropic
approximation for non-hydrogen atoms using the CRYSTALS
program package [22]. Hydrogen atoms were located in the
difference Fourier maps and refined with fixed positional and
2,2-Difluoro-4,7-dimethyl-5-oxo-(5H)-pyrano[4.3-d][1,3,2]-
(2H)-dioxaborine (2a). The mixture of dehydroacetic acid (1a)
(8.4 g, 0.05 mol), acetic anhydride (3 mL) and boron trifluoride
etherate (8 mL, 0.063 mol) in toluene (25 mL) was refluxed for
1-2 min. The solution was cooled; the product was filtered off
1
and washed with toluene. Yield 8.4 g (78%). M.p. 135º. H
NMR (CDCl3): 2.40 (s, 3 H, CH3), 2.87 (s, 3 H, CH3), 6.14 (s, 1
H, 8-H). Anal. calcd. for C8H7BF2O4: C, 44.50; H, 3.27. Found:
C, 44.59; H, 3.36.
2,2-Difluoro-7-methyl-5-oxo-(5H)-4-[3-(1,3,3-trimethyl-
indolin-2-ylidene)-1-propenyl]-pyrano[4,3-d][1,3,2]-(2H)-
dioxaborine (3ꢀ).The mixture of complex 2a (0.43 g, 2
mmol) and 2-(1,3,3-trimethylindolin-2-ylidene)acetaldehyde
(0.42 g, 2 mmol) was refluxed for 2 min in acetic anhydride
(3 mL). The mixture was cooled and allowed to stand for 12 h
to crystallize. The product was collected by filtration, washed

1670
A. Gerasov, M. Shandura, Yu. Kovtun, Yu. Vlasenko and V. Gorchev
Vol 45
with acetic acid, and diethyl ether. Yield: 0.72 g (90 %). M.p.
1
7a was precipitated by the addition of 2-propanol. The product
was recrystallized from EtOH. Yield: 230 mg (43%). M.p. 233-
288-289º. H NMR (DMSO-d6): 1.65 (s, 6 H, CH3), 2.28 (s, 3
H, CH3), 3.73 (s, 3 H, NCH3), 6.26 (s, 1 H, 8-H), 6.61 (d, 3JH,H
234º. 1H NMR (DMSO-d6): 1.17 (m, 9 H, CH3), 2.28 (s, 6 H,
= 14.7 Hz, 1 H, ꢀ-H), 7.27 (d, 3JH,H = 12.3 Hz, 1 H, ꢁ-H), 7.36
CH3), 3.10 (m, 6 H, NCH2), 6.29 (s, 2 H, 8-H), 7.23 (d, JH,H
=
3
3
3
(m, 1 H, 5`-H), 7.48 (m, 1 H, 6`-H), 7.53 (d, JH,H = 7.5 Hz, 1
13.5 Hz, 2 H, ꢁ-H, ꢁ`-H), 8.70 (t, JH,H = 13.5 Hz, 1 H, ꢂ-H),
8.85 (br s, 1 H, N+H). Anal. calcd. for C23H27B2F4NO8: C, 50.83;
H, 4.97; N, 2.58. Found: C, 50.86; H, 5.08; N, 2.49.
3
3
H, 7`-H), 7.67 (d, JH,H = 7.5 Hz, 1 H, 4`-H), 8.59 (t, JH,H
=
13.5 Hz, 1 H, ꢂ-H). APSI MS: M++1 = 400. Anal. calcd. for
C21H20BF2NO4: C, 63.18; H, 5.05; N, 3.51. Found: C, 63.21;
H, 5.01; N, 3.53.
8a: A mixture of dye 3a (105 mg, 0.26 mmol) and 2-
methoxyethylamine (100 mg, 1.3 mmol) in dichloromethane was
stirred at room temperature for 1.5 h. The solvent was
evaporated in vacuo without heat, the residue treated with 2-
propanol and collected by filtration. Yield: 120 mg (86%).1H
NMR (CDCl3): 1.54 (s, 6 H, CH3), 2.06 (s, 3 H, CH), 3.03 (m, 2
H, NCH2), 3.16-3.53 (m, 15 H, NCH3, NCH2, 2-OCH2, 2-
2,2-Difluoro-7-methyl-5-oxo-4-(2-(phenylamino)vinyl)-(5H)-
pyrano[4,3-d][1,3,2]-(2H)-dioxaborine (4ꢀ). Complex 2a
(1.08 g, 5 mmol) was dissolved in warm acetic anhydride (3
mL), cooled down, treated with ethyl isoformanilide (1 g, 6.7
mmol), and kept for 1 h at room temperature. The reaction
mixture was diluted with ethylacetate (10 mL), and the
precipitate was collected by filtration. Yield: 1.25 g (78 %). M.p.
3
OCH3), 5.47 (s, 1 H, NCH2), 5.68 (d, JH,H = 13.2 Hz, 1 H, CH),
3
5.94 (br s, 3 H, H3N+CH2), 6.40 (d, JH,H = 14.1 Hz, 1 H, CH),
1
280- 282º (dec). H NMR (DMSO-d6): 2.30 (s, 3 H, CH3), 6.32
6.70 (m, 1 H, 7`-H), 6.90 (m, 1 H, 5`-H), 7.15 (m, 2 H, 4`-H, 6`-
H), 8.03 (m, 1 H, CH), 9.73 (s, 1 H, NH).
(s, 1 H, 8-H), 7.27 (m, 2 H, Ph-H), 7.49 (m, 4 H, ꢁ-H, Ph-H),
8.86 (t, 3JH,H = 13.0 Hz, 1 H, ꢂ-H), 12.31 (d, 3JH,H = 15.0 Hz, 1 H,
NH). ꢃmax 416 nm(MeCN). Anal. calcd. for C15H12BF2NO4: C,
56.47; H, 3.79; N, 4.39. Found: C, 56.61; H, 3.86; N, 4.45.
4-[3-(3-butylbenzothiazol-2(3H)-ylidene)-1-propenyl]-2,2-
difluoro-7-methyl-5-oxo-(5H)-pyrano[4.3-d][1,3,2]-(2H)-
dioxaborine (5ꢀ). A mixture of hemicyanine 4a (160 mg, 0.5
mmol), 3-butyl-2-methylbenzothiazolium iodide (170 mg, 0.51
mmol) and diisopropylethylamine (100 mg, 0.78 mmol) in dry
acetonitrile was refluxed for 10 min. The mixture was cooled
and allowed to stand for 12 h to crystallize. The product was
collected by filtration, washed with acetic acid, and diethyl
Pyrrolidinium 2,2-difluoro-4-[2-(pyrrolidin-1-yl)-1-
propenyl]-6-[3-(1,3,3-trimethylindolin-2-ylidene)-1-propenyl]-
1,3,2-(2H)-dioxaborine-5-carboxylate (8b). Pyrollydine
(178 mg, 2.5 mmol) was added to the solution of dye 3a (200
mg, 0.5 mmol) in dichloromethane. The reaction mixture was
stirred at room temperature for 30 min, and the precipitate
collected by filtration. The product was recrystallized from
1
acetonitrile. Yield: 170 mg (63%). M.p. 170-1º (dec). H NMR
(DMSO-d6): 1.53 (s, 6 H, CH3), 1.80 (m, 4 H, CH2), 1.92 (m, 4
H, CH2), 2.52 (s, 3 H, CH3), 3.04 (m, 4 H, NCH2), 3.20 (s, 3 H,
NCH3), 3.32 (m, 2 H, NCH2), 3.60 (m, 2 H, NCH2), 5.56 (m, 1.5
H, ꢀ-H+5-H), 5.75 (s, 0.5 H, 5-H), 6.29 (d, 3JH,H = 14.7 Hz, 1 H,
ꢁ-H), 6.88 (m, 2 H, 5`-H, 7`-H), 7.19 (t, 3JH,H = 7.5 Hz, 1 H, 6`-
H), 7.30 (d, 3JH,H = 7.5 Hz, 1 H, 4`-H), 7.66 (t, 3JH,H = 13.2 Hz, 1
H, ꢂ-H). Anal. calcd. for C29H36BF2N3O3: C, 64,33; H, 7,02; N,
7,76. Found: C, 64,45; H, 7,11; N, 7,68.
4-Hydroxy-1-(2-methoxyethyl)-6-methylpyridin-2(1H)-one
(10). A mixture of 4-hydroxy-6-methylpyran-2-one (25.2 g, 0.2
mol) and 2-methoxyethylamine (15 g, 0.2 mol) in water (50 mL)
was refluxed for 6 h. The mixture was cooled and the product
was collected by filtration. Yield: 27.5 g (75%). M.p. 203-205º.
1H NMR (DMSO-d6): 2.30 (s, 3 H, CH3), 3.20 (s, 3 H, OCH3),
3.47 (m, 2 H, OCH2), 3,98 (m, 2 H, NCH2), 5.47 (s, 1 H, 3-H),
5.72 (s, 1 H, 5-H), 10,39 (s, 1 H, OH). Anal. calcd. for
C9H13NO3: C, 59.02; H, 7.10; N, 7.65. Found: C, 58.86; H, 7,20;
N, 7,69.
1
ether. Yield: 130 mg (60%). M.p. 257-258º. H NMR (DMSO-
d6): 0.95 (m, 3 H, CH3), 1.45 (m, 2 H, CH2), 1.76 (m, 2 H, CH2),
2.26 (s, 3 H, CH3), 4.52 (m, 2 H, NCH2), 6.16 (s, 1 H, 8-H), 6.97
3
3
(d, JH,H = 13.2 Hz, 1 H, ꢀ-H), 7.17 (d, JH,H = 11.7 Hz, 1 H, ꢁ-
H), 7.54 (m, 1 H, 6`-H), 7.66 (m, 1 H, 5`-H), 7.91 (d, 3JH,H = 7.8
Hz, 1 H, 4`-H), 8.09 (d, 3JH,H = 7.5 Hz, 1 H, 7`-H), 8.29 (t, 3JH,H
= 13.4 Hz, 1 H, ꢂ-H). Anal. calcd. for C21H20BF2NO4S: C, 58.49;
H, 4.67; N, 3.25. Found: C, 58.37; H, 4.61; N, 3.30.
4-[3-(1-Butylquinolin-4(1H)-ylidene)-1-propenyl]-2,2-
difluoro-7-methyl-5-oxo-(5H)-pyrano[4,3-d][1,3,2]-(2H)-
dioxaborine (6ꢀ). A mixture of hemicyanine 4a (160 mg, 0.5
mmol), 1-butyl-4-methylquinolinium iodide (165 mg, 0.505
mmol) and diisopropylethylamine (100 mg, 0.78 mmol) in acetic
anhydride (1 mL) was stirred at room temperature for 1 h. The
dye was precipitated by 2-propanol and recrystallized from
DMF/2-propanol mixture. Yield: 75 mg (35%). M.p. 284-285º.
1H NMR (DMSO-d6): 0.92 (m, 3 H, CH3), 1.38 (m, 2 H, CH2),
1.84 (m, 2 H, CH2), 2.23 (s, 3 H, CH3), 4.73 (m, 2 H, NCH2),
3-Acetyl-4-hydroxy-1-(2-methoxyethyl)-6-methylpyridin-
2(1H)-one (1b). A mixture of hydroxypyridone 10 (18.3 g, 0.1
mol) and diethylmalonate (18.3 g, 0.11 mol) in diphenyl ether
was slowly heated to 215 ºC and kept at this temperature for 2 h.
The reaction mixture was cooled, 2-propanol (50 mL) was
added, the precipitate collected by filtration and recrystallized
from 2-propanol. Yield: 16 g (64%). M.p. 171-172º.
3
6.13 (s, 1 H, 8-H), 7.15 (d, JH,H = 11.4 Hz, 1 H, ꢀ-H), 7.34 (d,
3JH,H = 14.4 Hz, 1 H, ꢁ-H), 7.80 (m, 1 H, 6`-H), 8.00 (d, JH,H
3
=
7.5 Hz, 1 H, 8`-H), 8.07 (m, 1 H, 7`-H), 8.26 (d, 3JH,H = 8.4 Hz, 1
3
3
H, 5`-H), 8.41 (dd, JH,H = 14.4 Hz, JH,H = 11.4 Hz, 1 H, ꢂ-H),
3
3
8.73 (d, JH,H = 7.2 Hz, 1 H, 5`-H), 8.77 (d, JH,H = 8.4 Hz, 1 H,
2`-H). Anal. calcd. for C23H22BF2NO4: C, 64.96; H, 5.21; N,
3.29. Found: C, 65.12; H, 5.34; N, 3.36.
A mixture of compounds 11 (15 g, 0.06 mol), ethylene glycol
(260 mL), sodium hydroxide (30 g, 0.75 mol) and water (38 mL)
was heated to 175 – 180 ºC (bath temperature) and refluxed with
stirring for 2 h. The solution was poured into water (1000 mL),
and neutralized with hydrochloric acid. The warm solution was
filtered, and after cooling down the precipitate was collected by
Triethylammonium 2,2-difluoro-4-[3-(2,2-difluoro-7-methyl-
5-oxo-(5H)-pyrano[4,3-d][1,3,2]-(2H)-dioxaborin-4-ylidene)-
1-propenyl]-7-methyl-5-oxo-(5H)-pyrano[4,3-d][1,3,2]-(2H)-
dioxaborinate (7ꢀ). A mixture of complex 2a (432 mg, 2 mmol)
and triethylorthoformiate (150 mg, 1 mmol) in acetic anhydride
(2 mL) was refluxed for 1 min. The reaction mixture was cooled
down to room temperature; triethylamine (121 mg, 1.2 mmol)
was added, and stirred at room temperature for 30 min. The dye
1
filtration. Yield: 8.4 g (62%). M.p. 108-110º. H NMR (CDCl3):
2.45 (s, 3 H, CH3), 2.73 (s, 3 H, CH3), 3.32 (s, 3 H, OCH3), 3.67
(m, 2 H, OCH2), 4.15 (m, 2 H, NCH2), 5.83 (s, 1 H, 8-H), 15.51
(s, 1 H, OH). Anal. calcd. for C11H15NO4: C, 58.66; H, 6.71; N,
6.22. Found: C, 58.61; H, 6.73; N, 6.19.

Nov-Dec 2008
Dyes on the Base of Dehydroacetic Acid – Effective Fluorescent Amine Probes
1671
3
2,2-Difluoro-4,7-dimethyl-6-(2-methoxyethyl)-5-oxo-(5H)-
pyrido[4,3-d][1,3,2]-(2H)-dioxaborine (2b). mixture of
= 7.8 Hz, 1 H, 7`-H), 8.29 (t, JH,H = 12.8 Hz, 1 H, ꢂ-H). Anal.
calcd. for C24H27BF2N2O4S: C, 59.03; H, 5.57; N, 5.74. Found:
C, 59.14; H, 5.66; N, 5.79.
A
acetylpyridone 1b (4.5 g, 0.02 mol), boron trifluoride etherate
(4.5 g, 0.032 mol) and acetic anhydride (3.5 g) in diethyl ether
(15 mL) was stirred at room temperature for 7 h. The precipitate
was collected by filtration, and washed with ether. Yield: 5.06 g
4-[3-(1-Butylquinolin-4(1H)-ylidene)-1-propenyl]-2,2-
difluoro-6-(2-methoxyethyl)-7-methyl-5-oxo-(5H)-pyrido
[4,3-d][1,3,2]-(2H)-dioxaborine (6b). Triethylamine (101 mg, 1
mmol) was added to the mixture of hemicyanine 4b (174 mg,
0.46 mmol) and 1-butyl-4-methylquinolinium iodide (150 mg,
0.46 mmol) in acetic anhydride (4 mL). The reaction mixture
was stirred for 3 h at room temperature, and the precipitate was
collected by filtration. The product was recrystallized from
1
(93 %). M.p. 135-136º. 1H H NMR (CDCl3): 2.53 (s, 3 H,
CH3), 2.85 (s, 3 H, CH3), 3.30 (s, 3 H, OCH3), 3.63 (m, 2 H,
OCH2), 4.16 (m, 2 H, NCH2), 5.96 (s, 1 H, 8-H). Anal. calcd. for
C11H14BF2NO4: C, 48.39; H, 5.17; N, 5.13. Found: C, 48.55; H,
5.28; N, 5.19.
1
acetonitrile. Yield: 135 mg (61 %). M.p. 236-238º. H NMR
2,2-Difluoro-6-(2-methoxyethyl)-7-methyl-5-oxo-(5H)-4-[3-(1,
3,3-trimethylindolin-2-ylidene)-1-propenyl]-pyrido[4,3-d]-
[1,3,2]-(2H)-dioxaborine (3b).
(DMSO-d6): 0.92 (m, 3 H, CH3), 1.38 (m, 2 H, CH2), 1.82 (m, 2
H, CH2), 2.40 (s, 3 H, CH3), 3.25 (s, 3 H, OCH3), 3.57 (m, 2 H,
OCH2), 4.11 (m, 2 H, NCH2), 4.65 (m, 2 H, NCH2), 5.88 (s, 1 H,
8-H), 7.21 (d, JH,H = 14.1 Hz, 1 H, ꢀ-H), 7.64 (d, JH,H = 12.3
Hz, 1 H, ꢁ-H), 7.74 (t, 3JH,H = 8.1 Hz, 1 H, 6`-H), 7.85 (d, 3JH,H
7.2 Hz, 1 H, 8`-H), 8.01 (t, JH,H = 8.0 Hz, 1 H, 7`-H), 8.18 (d,
3JH,H = 9.0 Hz, 1 H, 3`-H), 8.50 (t, JH,H = 13.8 Hz, 1 H, ꢂ-H),
8.56 (d, JH,H = 6.9 Hz, 1 H, 5`-H), 8.69 (d, JH,H = 9.0 Hz, 1 H,
2`-H). Anal. calcd. for C26H29BF2N2O4: C, 64.74; H, 6.06; N,
5.81. Found: C, 64.89; H, 6.18; N, 5.90.
3
3
From compound 3a: A mixture of dye 3a (0.2 g, 0.5 mmol)
and 2-methoxyethylamine (0.18 g, 2.4 mmol) was refluxed in
ethanol for 2 h. The hot reaction mixture was filtered off, the
precipitate collected. Yield: 70 mg (31 %).
=
3
3
3
3
From boron difluoride complex 2b: A mixture of compound
2b (273 mg, 1 mmol) and 2-(1,3,3-trimethylindolin-2-ylidene)-
acetaldehyde (212 mg, 1.05 mmol) in acetic anhydride (0.5 mL)
was refluxed for 2 min. The mixture was cooled and allowed to
stand for 12 h to crystallize. The product was collected by
filtration and washed with acetic anhydride and ether. Yield: 275
Triethylammonium
2,2-difluoro-4-[3-(2,2-difluoro-6-(2-
methoxyethyl)-7-methyl-5-oxo-(5H)-pyrido[4,3-d][1,3,2]-
(2H)-dioxaborin-4-ylidene)-1-propenyl]-6-(2-methoxyethyl)-
7-methyl-5-oxo-(5H)-pyrido[4,3-d][1,3,2]-(2H)-dioxaborinate
(7b). A mixture of complex 2b (273 mg, 1 mmol) and
diphenylformamidine (100 mg, 0.51 mmol) in acetic anhydride
(0.5 mL) was refluxed for 1 min. The solution was cooled down
to room temperature, triethylamine (150 mg, 1.49 mmol) was
added, and the reaction mixture was stirred at room temperature
for 2 h. 2-Propanol was added, the precipitate collected by
filtration, and finally recrystallized from 2-propanol. Yield: 120
1
mg (60 %). M.p. 264-265º. H NMR (DMSO-d6): 1.63 (s, 6 H,
CH3), 2.44 (s, 3 H, CH3), 3.25 (s, 3 H, OCH3), 3.57 (m, 2 H,
OCH2), 3.64 (s, 3 H, NCH3), 4.11 (m, 2 H, NCH2), 5.98 (s, 1 H,
3
8-H), 6.40 (d, JH,H = 14.4 Hz, 1 H, ꢀ-H), 7.27 (m, 1 H, 5`-H),
3
7.42 (m, 2 H, 6`-H, 7`-H), 7.60 (d, JH,H = 7.2 Hz, 1 H, 4`-H),
7.71 (d, 3JH,H = 13.2 Hz, 1 H, ꢁ-H), 8.59 (t, 3JH,H = 13.5 Hz, 1 H,
ꢂ-H). APSI MS: M++1 = 457.Anal. calcd. for C24H27BF2N2O4:
C, 63.17; H, 5.96; N, 6.14. Found: C, 63.15; H, 5.92; N, 6.16.
2,2-Difluoro-6-(2-methoxyethyl)-7-methyl-5-oxo-4-(2-(phenyl-
amino)vinyl)-(5H)-pyrido[4,3-d][1,3,2]-(2H)-dioxaborine
(4b). A mixture of complex 2b (550 mg, 2 mmol) and
ethylisoformanilide (600 mg, 4 mmol) was fused at 120 ºC
during for 1 h. The melt was cooled and triturated with
chloroform. The resulting solid was collected by filtration and
washed with chloroform. Yield: 515 mg (69 %). M.p. 208-210º.
1H NMR (DMSO-d6): 2.46 (s, 3 H, CH3), 3.26 (s, 3 H, OCH3),
3.58 (m, 2 H, OCH2), 4.13 (m, 2 H, NCH2), 6.02 (s, 1 H, 8-H),
1
mg (40 %). M.p. 194-195º. H NMR (DMSO-d6): 1.17 (m, 9 H,
CH3), 2.44 (s, 6 H, CH3), 3.10 (m, 6 H, NCH2), 3.24 (s, 6 H,
OCH3), 3.56 (m, 4 H, OCH2), 4.11 (m, 4 H, NCH2), 5.98 (s, 2 H,
3
3
8-H), 7.60 (d, JH,H = 13.5 Hz, 2 H, ꢁ-H, ꢁ`-H), 8.73 (t, JH,H
=
13.5 Hz, 1 H, ꢂ-H), 8.81 (br s, 1 H, N+H). Anal. calcd. for
C29H41B2F4N3O8: C, 52.97; H, 6.24; N, 6.39. Found: C, 52.83; H,
6.34; N, 6.37.
3
REFERENCES
7.25 (m, 1 H, Ph-H), 7.44 (m, 4 H, Ph-H), 7.68 (d, JH,H = 12.0
Hz, 1 H, ꢁ-H), 8.81 (t, 3JH,H = 12.0 Hz, 1 H, ꢂ-H), 11.97 (d, 3JH,H
= 13.5 Hz, 1 H, NH). ꢃmax 431 nm (MeCN). Anal. calcd. for
C18H19BF2N2O4: C, 57.47; H, 5.09; N, 7.45. Found: C, 57.58; H,
5.17; N, 7.51.
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1
Yield: 200 mg (82 %). M.p. 267-268º. H NMR (DMSO-d6):
0.93 (m, 3 H, CH3), 1.44 (m, 2 H, CH2), 1.72 (m, 2 H, CH2),
2.42 (s, 3 H, CH3), 3.25 (s, 3 H, OCH3), 3.56 (m, 2 H, OCH2),
4.10 (m, 2 H, NCH2), 4.46 (m, 2 H, NCH2), 5.94 (s, 1 H, 8-H),
6.86 (d, 3JH,H = 13.8 Hz, 1 H, ꢀ-H), 7.49 (m, 1 H, 6`-H), 7.62 (m,
2 H, ꢁ-H, 5`-H), 7.86 (d, 3JH,H = 7.8 Hz, 1 H, 4`-H), 8.04 (d, 3JH,H
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