DMF in acetic anhydride: A useful reagent for multiple-component syntheses of merocyanine dyes

Article abstract of DOI:10.1055/s-1999-3635

A simple and highly efficient method for the preparation of merocyanine dyes is reported from mixtures of CH-acidic heterocycles and electron-rich dialkylaminothiazoles or methylene bases and various formylating reagents without isolation of the formylated intermediates. With the particularly useful formylation-condensation system of DMF in acetic anhydride and highly acidic 1,2,5,6-tetrahydro-2,6-dioxo-3-pyridinecarbonitriles 8, the transformations could be carried out as multicomponent reactions to give pure dyes 3-6 in 50-90% yield directly from the reaction mixtures.

Full text of DOI:10.1055/s-1999-3635

PAPER
2103
DMF in Acetic Anhydride: A Useful Reagent for Multiple-Component
Syntheses of Merocyanine Dyes
Frank Würthner*
Abteilung Organische Chemie II, Universität Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
Fax +49(731)5022840; E-mail: frank.wuerthner@chemie.uni-ulm.de
Received 12 July 1999
colors on polyester were achieved which hold promise for
textile coloration. Moreover, the balanced electronic sys-
tem of these chromophores with a bond-order of one and
Abstract: A simple and highly efficient method for the preparation
of merocyanine dyes is reported from mixtures of CH-acidic hetero-
cycles and electron-rich dialkylaminothiazoles or methylene bases
7
and various formylating reagents without isolation of the formylat- a half along the conjugated chain affords pretty high light
ed intermediates. With the particularly useful formylation-conden- fastness and thermal stabilities (onset of decomposition
sation system of DMF in acetic anhydride and highly acidic 1,2,5,6- >250°C according to calorimetry).
tetrahydro-2,6-dioxo-3-pyridinecarbonitriles 8, the transformations
Whereas the electronic system is an inherent property of
could be carried out as multicomponent reactions to give pure dyes
the chromophore, each area of application has its own spe-
cific demands on the chemical and thermal stabilities, the
wet and the light fastness as well as the solubility and the
compatibility to polymeric binders. Due to a lack of ratio-
nal guidelines these properties have to be optimized
through extensive substituent variations and an applica-
tion-directed screening protocol. The optimization pro-
cess may be carried out in a traditional, i.e. sequential
manner or by means of automated parallel synthesis as in
3
–6 in 50–90% yield directly from the reaction mixtures.
Key words: condensation, dyes, formylation, multicomponent re-
actions, nucleophiles, heterocycles, merocyanines
Polymethine dyes and their aza analogues have received
considerable interest especially in the field of color pho-
tography because of their brilliant shades which are diffi-
1
cult to achieve with any other class of dyes. However,
8
the case of combinatorial chemistry. Irrespective of the
their use in other fields like textile dyeing or many speci-
ality applications is often prevented because of an inferior
thermal, chemical, and photochemical stability compared
to azo- or anthraquinone dyes. Also azo dye chemistry is
based on efficient syntheses (in water!) and cheap starting
materials whereas methine dye chemistry involves more
expensive reactions like Vilsmeier formylations or ortho-
strategy, highly efficient reactions and screening methods
are of primary importance if a promising chromophore
has to be developed to a functional material which fulfills
all requirements of the desired application. In this paper
we describe such an easy and highly efficient synthesis of
merocyanine dyes based on a multiple-component reac-
tion involving a formylating reagent generated in situ
from DMF in acetic anhydride.
2
formate chemistry under anhydrous conditions.
Scheme 1 shows the retrosynthetic analysis of the dye
synthesis based on the easily accessible hydroxypyri-
9
10
11,12
dones 8, thiazoles 11, and methylene bases 12–14.
Whereas only two steps - a formylation and a condensa-
tion reaction - are required, the corresponding procedures
are not convenient at all with respect to our goal of exten-
sive variations of the substituents for the given applica-
1
5
tions. Lipophilic substituents R –R as demanded for
highly soluble dyes give high-boiling and viscous formy-
lated intermediates which are difficult to isolate. If used as
crude materials, however, lower yields and incomplete
Recently, merocyanine dyes 1–6 were shown to exhibit a dye precipitation is often observed for the condensation
particularly promising chromogenic system for several reaction. Therefore we were looking for a more straight-
3
,4
high-technology applications. First, only one electronic forward reaction sequence suited for a highly efficient
transition in the visible range with a cyanine-like narrow synthesis of dyes 3–6 that exhibits a wide scope with re-
absorption band leads to very brilliant magenta hues suit- gard to substituent variations for dyes of very different
ed for applications in digital photography and color copy- solubility properties. More specifically the reaction
5
ing. Second, high dipole moments and polarizabilities in should be based on extremely simple procedures and lab-
the direction of the conjugated chain enabled unprece- oratory equipment thus being applicable to automated
dented refractive index modulations in photorefractive parallel synthesis in simple test tubes (no dropping fun-
6
materials. Third, based on their brilliancy and the recent nels, reflux condensors, etc.). This includes also the de-
4
observation of solid-state luminescence especially bright
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2
104
F. Würthner
PAPER
This prompted us to study other common formic acid
derivatives1
4-16
in different solvents. Several of these re-
agents like N,N-dimethylchloromethylenminium chloride
Vilsmeier reagent) and dichloromethylmethylether gave
(
fairly clean conversions to dyes 3a, 4a, but the isolation
from DMF was not satisfactory giving microcrystalline
precipitates of moderate purity which required time-con-
suming filtration and washing procedures (Table 1, En-
tries 4,5). Even more impure dyes were isolated from the
reaction mixture of the common formylating reagent
N,N’-diphenylformamidine in various solvents including
DMF and acetic anhydride and almost no conversion to
dyes 3a,4a was observed for the more reactive formylat-
ing reagents dimethylformamide diethylacetal and
bis(dimethylamino)-tert-butoxymethane ("Bredereck’s
reagent").15 Finally, the ideal reagent was discovered in
the little known formylating reagent DMF in acetic
anhydride17 which afforded yields and purities compara-
ble to trialkyl orthoformates but was very tolerant towards
crude starting materials (probably because nucleophilic
impurities may react with an excess of the solvent) and al-
lowed fast reactions at 90°C clearly below the boiling
point of the mixture. For highly concentrated solutions of
equimolar amounts of 8a and 11a,12a, and 1.5-fold
amounts of a dialkylformamide derivative, almost quanti-
tative conversions to merocyanine dyes 3a,4a took place
after about half an hour at 90°C. After 2 hours the mix-
tures were allowed to cool down to room temperature and
pure crystalline solids could be isolated in a very simple
Scheme 1
mand for an easy product isolation which disfavors any
additional steps like chromatography or recrystallization.
A promising starting point was found in two papers of manner by filtration and washing of the dyes with alcohol
Hünig and Reidlinger et al. who prepared a number of (Table 1, Entries 6–10).
merocyanine dyes directly from methylene bases and CH-
Because morphological properties like compatibility to
polymeric binders or the crystallization tendency depend
acidic heterocyclic acceptors in the presence of
4
1
3a
13b
formamide or triethyl orthoformate. Whereas both
procedures are simple (however involving reflux condi-
tions), the scope seems to be somewhat limited giving
only high yields for special examples. Nevertheless we
succeeded in preparing the indoline-based merocyanine
dye 4a under both reaction conditions (Table 1). With the
orthoester method not only methylene bases like Fischer
base 12a could be used but also electron-rich dialkylami-
nothiazole 11a (Table 1, Entries 2,3). For both examples,
yields and purities were excellent. However, we encoun-
tered some problems when crude starting materials were
used. In particular only one percent of water in the solvent
on the hardly predictable packing of the dyes in the solid
state, an important aspect of our synthetic work was to
find a method that offers a broad scope with respect to
substituent variations. More specifically introduction of
substituents having a high solubilizing power like long-
and branched-chain alkyl groups and substituents with a
high influence on packing properties like sterically de-
manding groups was desired.
Table 2 shows our results for reactions of several thiazoles
1
1a–c and indolines 12a–d with hydroxypyridones 8a–e.
The selected combinations provided dyes 3a–f and 4a–h
that cover a solubility range of more than four orders of
(
or in any of the other starting materials) resulted in sig-
nificantly lower yields. For highly soluble dyes like 4e
see below), no product could be precipitated out of the
oily reaction mixture when only 99% ethanol was used.
magnitude and melting points ranging from 100 to
4
>
330°C. It is noteworthy that all yields given in Table 2
(
refer to the overall process of turnover, precipitation, and
washing until analytically pure dyes could be isolated.
Even with starting materials of a purity of only 70–90%,
crystallization took place in fairly good yields from the re-
action mixtures to afford pure dyes which exhibit only the
single narrow and intense UV/Vis-absorption band that is
characteristic for this chromophore.3 Most important to
our work, starting materials with sterically demanding
substituents close to the reaction center could also be re-
acted (3d–f, 4d,f,h). Here, the isolated yields are some-
what lower, which might be a consequence of an
,4
Synthesis 1999, No. 12, 2103–2113 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
DMF in Acetic Anhydride: A Useful Reagent for Multiple-Component Syntheses of Merocyanine Dyes
2105
a
Table 1 Isolated Yields of Merocyanine Dyes 3a and 4a with Different Formylating Reagents (General Procedure A)
Entry
Dye
4a
3a
4a
3a
3a
4a
3a
4a
3a
3a
3a
Formylating Reagent
Solvent
(equiv)c
Temp/Time (h)
130°C/8
90°C/1
Yield
(%)
b
(
equiv)
1
2
3
4
5
6
7
8
9
HCONH2
–
20
85
80
40d
45d
40
85
85
85
60
72
(
25)
HC(OMe)3
EtOH
(10)
(
1.5)
HC(OEt)3
EtOH
(10)
90°C/2
(
1.5)
Cl CHOMe
DMF
(5)
90°C/5
2
(
1.5)
Cl CHNMe
DMF
(5)
100°C/2
40°C/10
90°C/2
2
2
(
1.5)
DMF
Ac O
2
(
1.5)
(4.5)
DMF
Ac O
2
(
1.5)
(4.5)
DMF
Ac O
90°C/2
2
(
1.5)
(4.5)
N-FP
Ac O
90°C/2
2
(
1.5)
(4.5)
1
1
0
1
N-MFA
Ac O
90°C/2
2
(
1.5)
(4.5)
DMF
AcCl
(2)
100°C/3
(
4)
a
Yields of >90% pure dyes as isolated from the reaction mixture after washing with i-PrOH.
Molar amounts of the formylating reagent; N-FP = N-formylpiperidine, N-MFA = N-methylformanilide, Cl CHNMe = [ClCHNMe ] Cl
b
+
-
2
2
2
(
Vilsmeier reagent).
Molar amount of the solvent.
Dye precipitation after addition of water.
c
d
Table 2 Merocyanine Dyes 3b–f and 4b–h Prepared
General Procedure B)
(
incomplete precipitation caused by the increased solublity
of these dyes.
Start-
Dye
Yielda
(%)
ing Ma-
terials
R1
R2
R3
8b,11a
8d,11a
8b,11b
8a,11b
8b,11c
3b
3c
3d
3e
3f
Me
Hex
Me
Bu
Bu
Bu
Bu
Bu
Et
Ph
Ph
t-Bu
t-Bu
85
75
60
50
60
Me
Neo-
pentyl
8b,12a
8a,12b
8a,12c
8a,12d
8d,12c
8c,12d
8e,12c
4b
4c
4d
4e
4f
Me
Bu
Bu
Bu
Me
Pr
i-Pr
Bu
i-Pr
Bu
i-Pr
–
–
–
–
–
–
–
85
70
60
70
50
70
Hex
Pentyl
2-
4g
4h
b
80
Ethexc
a
For a mechanistic understanding we investigated the reac-
tion of the single components 8a, 11a and 12a with DMF
in acetic anhydride at 80–100°C (Scheme 2). No reaction
was observed for thiazole 11a under these conditions
Yields of pure dyes as isolated from the reaction mixture after
washing with i-PrOH and/or EtOH/H O.
2
b
Isolated by chromatography.
c
2
-Ethylhexyl.
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2
106
F. Würthner
PAPER
also supported by the possibility to use acetyl chloride in-
stead of acetic anhydride for the activation of DMF (Table
1
, Entry 11).
To elucidate the scope of this one-pot procedure we per-
formed reactions with a number of electron–rich aromat-
ics and methylene bases as well as CH-acidic acceptor
heterocycles. The variations of the electron-donating unit
in the dyes included dimethylaniline, julolidine,
thiophene 10a and several methylene bases (13, 14, 17,
1
9). The less nucleophilic aromatics failed to give the de-
sired merocyanines and thiophene 10a afforded only a
low yield of dye 2a, however, benzoxazole and benzothi-
azole dyes 5a,6a could be prepared in remarkable yields
from the in situ generated methylene bases. This variation
of the reaction conditions was advantagous because of the
high reactivity of these more nucleophilic methylene
bases towards acetylation and the easy availability of the
iodide salts 13a and 14a. No attempts were made with re-
spect to an optimization of the base.
Scheme 2
while the other two nucleophiles reacted completely with-
in 2 hours. However, after addition of the second reactant
to the mixtures, dye formation was only observed from the
intermediate obtained from hydroxypyridone 8a. Here
both dyes 3a and 4a could be obtained in rather exother-
mic reactions and the yields were comparable to those
given in Table 1 for the multicomponent reactions. It was
also possible to isolate the intermediate enamine 16a in
good yields under strictly anhydrous conditions. Other-
wise, in the presence of water immediate hydrolysis of the
highly reactive enamine 16a takes place to give the
formylated pyridone 7a (as already observed in NMR ex-
periments in CDCl or DMSO-d at very low water con-
3
6
tents). Under more severe conditions even deformylation
to the starting material 8a was observed. On the other
hand, the unreactive intermediate which could be isolated
in high yield from the reaction mixture of the methylene
base 12a, DMF and acetic anhydride, was shown to be the
acetylated derivative 1518a,b instead of the expected
formylation product. DMF is not crucial for this acetyla-
tion which also takes place in pure acetic anhydride at
temperatures above 60°C and requires about 5 hours at
Unlike the compounds described above, the even more
nucleophilic methylene bases of 1,4-dimethylpyridinium
7
0°C or 1.5 hours at 90°C for >95% conversion. We
therefore conclude that the reaction sequence leading to
dyes 3 and 4 involves an O-acylation of the dialkylforma-
mide by acetic anhydride to a Vilsmeier-type reagent as
(
17) and 1-ethyl-4-methylquinolinium (19) iodide could
not be reacted in a multicomponent fashion. Therefore
stepwise reactions were carried out, first converting the
pyridone to the enamine and then adding the heterocyclic
iodide salts and one equivalent of a base. With potassium
acetate the yield of 18 was only 20%, but with triethyl-
amine 54% of pure pyridine dye 18 and 90% of quinoline
dye 20 could be isolated directly from the reaction mix-
1
7
proposed by Eiden, which is sufficiently reactive to
formylate the highly nucleophilic hydroxypyridones 8 to
yield enamines 16. In the presence of electron-rich
methylene bases 11 or heterocycles 12, subsequent acetic
anhydride promoted condensations take place instant-
aneously to give merocyanine dyes 3 and 4 in almost
quantitative yields. This mechanistic understanding is
Synthesis 1999, No. 12, 2103–2113 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
DMF in Acetic Anhydride: A Useful Reagent for Multiple-Component Syntheses of Merocyanine Dyes
2107
ture. The stronger base 1,8-diazabicyclo[5.4.0]undec-7-
ene (DBU) afforded comparable yields.
Alternatively highly reactive nucleophiles 21,23,25 which
1
9
are prone to acetylation in acetic anhydride could be re-
acted with enamine 16a in inert solvents to give another
series of dyes 22,24,26 in moderate to high yields. In con-
trast to the former dyes, which exhibit magenta and violet
hues, these chromophores are characterized by yellow and
orange colors and very interesting solid-state lumines-
cence properties.
3
7 took place in a high yield, the yellow dye 38 proved to
be stable and rather unreactive in contrast to the highly
electrophilic lower homologue 16a.
After studying methine bond formation between enamine
1
6a and donor bases of different nucleophilicity, varia-
tions of the CH-acidic acceptor heterocycles were investi-
gated. The reactions were carried out with the following
substrates: 1,3-indanedione, dioxopyrazole 34, Mel-
drum’s acid 32 and barbituric acid (27). In all cases the re-
spective enamines were formed at 90°C, but their
reactivity was significantly reduced compared to 16a (de-
creasing in the order 8 > 27 > 32 > 34 > indandione).20
Only the reaction between barbituric acid, DMF and the
less nucleophilic thiazole base 11a gave a satisfactory
yield of 40% of pure dye 29 in the multicomponent syn-
thesis, whereas the more reactive indoline 12a reacted Finally it is noteworthy that all of the chromophores de-
partly to 15 giving an isolated yield of only 3% of dye 30. scribed in this work are very brilliant dyestuffs as desired
However, from the in situ generated enamines of the six- for printing applications. This brilliancy is related to an
membered heterocycles 32 and 27, thiazole as well as in- electronic structure with almost identical contributions of
doline dyes are obtained in satisfactory yields. Attempts the unpolar and the zwitterionic resonance structures for
to react the even less electrophilic enamines of the five- both the ground and the excited states.3 For this special
membered heterocycles were not successful because of electron distribution there is no dipole change and almost
the predominant acetylation of the methylene base. Thus no change in the nuclear coordinates of the dyes and no re-
the product isolated by precipitation from the reaction orientation of the surrounding solvent molecules upon op-
mixture of 34 and 12a was a mixture of enamine 35 (60 tical excitation. As a result the dye exhibits only one
,21
mol%) and dye 36 (40 mol%), whereas the acetylated me- strongly allowed electronic transition from the S to the S1
0
thylene base 15 remained in solution.
electronic state with a most intense vibrational 0,0-transi-
tion affording very intense and narrow absorption bands
For the same reason our attempts to synthesize tri- and tet-
ramethine dyes according to the vinylogic principle have
not been successful. Although the reaction with acrolein
-
1
(
half width Dn = 900–1500 cm ) and brillant hues
1/2
which are otherwise only observed for the symmetric cat-
ionic cyanine or anionic oxonole dyes. As an example the
Synthesis 1999, No. 12, 2103–2113 ISSN 0039-7881 © Thieme Stuttgart · New York

2
108
F. Würthner
PAPER
absorption spectra of three selected dyestuffs of our series Starting materials were prepared according to the literature and
were typically used in crude form (at a purity of 70–95% according
which form a nice trichromatic system of the primary col-
1
to GC or H NMR analysis): 1-alkyl-4-methyl-2,6-dioxo-1,2,3,6-
ors yellow (30, l = 466 nm), magenta (3f, lmax = 526
max
9
tetrahydro-pyridine-3-carbonitriles 8a–e, 2-dialkylamino-4-substi-
nm) and cyan (20, l = 617 nm) are displayed in the fig-
max
10
tuted thiazoles 11a–c, 1-alkyl-3,3-dimethyl-2-methylene-indo-
ure.
11a
12a
lines 12a–d, , 2-piperidinothiophene (10a). DMF, EtOH and
2
2
MeOH were dried according to known procedures. All other sol-
vents were used without further purification and reactions were car-
ried out without protection from moisture or oxygen unless specific
details are given in the text. The dyes were dried in vacuo at 50–
6
0°C for 1 d. Spectral and physical data of all the compounds pre-
pared are given in Table 3.
Multicomponent Reactions Using Various Formylating Re-
agents; General Procedure A (Table 1)
Equimolar amounts of indoline 12a (or thiazole 11a) and pyridone
8
a were mixed in the solvent given in Table 1 by stirring. The
formylating reagent was added and the mixture was heated accord-
ing to the conditions given in Table 1. After the reaction was com-
plete (TLC control) the mixtures were allowed to cool to r.t., stirred
for 2–18 h and the precipitated dyes were collected and washed with
i-PrOH until the color of the filtrate changed from violet to pink (3a)
or pale orange (4a). The dyes were dried at 60°C in vacuo and the
purity was controlled by HPLC to be at least 90% for all reactions
given in Table 1.
Figure UV/VIS absorption spectra of a trichromatic system based
on the yellow indoline dye 30 (left), the magenta thiazole dye 3f
(
middle) and the blue quinoline dye 20 (right) in dichloromethane.
Multicomponent Reactions Using DMF in Acetic Anhydride;
General Procedure B, for Dyes 3a–f, 4a–h (Table 2) and 2a
To a mixture of equimolar amounts of a thiazole 11a–c or an indo-
line 12a–d and a pyridone 8a–e, a 1.5-fold molar amount of DMF
In conclusion we have described very efficient one-pot
procedures for the preparation of merocyanine dyes based and a 4–5-fold molar amount of Ac O were added and the mixture
2
on a simple formylating reagent derived from DMF in was heated at a bath temperature of 90°C for 2–3 h. The mixture was
allowed to cool to r.t. and stirring was continued for 2–18 h. The
precipitated dye was collected on a Büchner funnel, washed thor-
acetic anhydride. The reactions proceed through reactive
enamines of the CH-acidic heterocycles 8, 32, 27 and a
subsequent condensation with the electron-rich heterocy-
cles 10, 11 or methylene bases 12–14,17,19. For the most
oughly with i-PrOH (or EtOH/H O for more soluble derivatives)
2
until the color of the filtrate changed from violet to pink (3) or or-
ange (4). After drying at 60°C in vacuo dyes of a purity of 96–100%
are obtained based on spectroscopy (NMR, UV/VIS) and elemental
valuable magenta dyes 3–6 the reactions could be carried
out in high yields and purities in a multicomponent fash- analyses.
ion by simply mixing all reactants together for 2 hours at
0°C and washing the precipitated dye with alcohol/wa- methyl-2,6-dioxo-1,2,5,6-tetrahydropyridine-3-carbonitrile
ter. It is interesting that this convenient one-step proce- (3a)
1
-Butyl-5-(2-dibutylamino-4-phenylthiazol-5-ylmethylene)-4-
9
From 11a (14.4 g, 0.05 mol), 8a (10.3 g, 0.05 mol) and DMF (5.5 g,
.075 mol) in Ac O (25 mL, 0.25 mol). After cooling to r.t., the pre-
cipitated dye was filtered, washed with i-PrOH (3 × 20 mL) and
dried to give 19–20 g (80–85%) of green needles.
dure was applicable exactly to those dyes which are
characterized by equal contributions of the nonpolar and
the zwitterionic resonance structures (merocyanines in the
0
2
3
,21a
"
cyanine limit")
which are highly desired for elec-
1
-Butyl-5-[2-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-
trooptic materials, digital printing technologies and poly-
ylidene)ethylidene]- 4-methyl-2,6-dioxo-1,2,5,6-tetrahydropyri-
dine-3-carbonitrile (4a)
3
,4,7
ester dyeing.
From 12a (8.65 g, 0.05 mol), 8a (10.3 g, 0.05 mol) and DMF (5.5 g,
0
.075 mol) in Ac O (25 mL, 0.25 mol). After cooling to r.t., the pre-
1H NMR spectra were recorded at r.t. on Bruker instruments at 200
2
cipitate was filtered, washed with i-PrOH (3 × 20 mL) and dried to
give 16.5 g (85%) of a pink solid. Recrystallization from toluene
gave red leaflets.
and 500 MHz. Chemical shifts (d) are given in ppm downfield from
TMS as internal standard. All dialkylamino substituents of the thia-
zole dyes 3a–f show characteristic broad signals (br s) due to hin-
dered rotation around the N–Cthiazole bond. EI mass spectra (70 eV)
were recorded using a Finnigan MAT SSQ 7000 spectrometer. UV/
VIS absorption spectra were measured on a Perkin Elmer Lambda
1-Butyl-5-[2-(1,3-dihydro-3,3-dimethyl-1-propyl-2H-indol-2-
ylidene)ethylidene]-2,6-dioxo-1,2,5,6-tetrahydropyridine-3-
carbonitrile (4c)
4
0P instrument from 230–800 nm in CH Cl (Merck Uvasol). Ab-
Reaction was carried out as described for 4a starting from 12b (2.0
g, 0.01 mol), 8a (2.06 g, 0.01 mol) and DMF (1.1 ml, 0.015 mol) in
2
2
sorption maxima l and extinction coefficients emax are given in
max
-1
-
1
nm and Lmol cm . All melting points were determined with a Bü-
chi SMP 20 instrument with a heating rate of 2°C/min and are un-
corrected. For HPLC measurements a Merck-Hitachi system (pump
L-6200A, UV detector L-4000) and a Merck LiChroCart 250-4 col-
umn packed with LiChrospher Si 60 (5 mm) was used.
Ac
completed in an ice–bath and Et
for the washing procedure, giving 2.9 g (70%) of a red solid.
2
O (5 mL). Because of the good solubility, precipitation was
O and EtOH/H O (7:3) were used
2
2
Synthesis 1999, No. 12, 2103–2113 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
DMF in Acetic Anhydride: A Useful Reagent for Multiple-Component Syntheses of Merocyanine Dyes
2109
Table 3 Spectroscopic and Physical Data of Dyes Prepareda,b
1
Dye
mp (°C)
UV/VIS
CH Cl )
H NMR (200 MHz, CDCl /TMS)
3
c
(
d, J (Hz)
2
2
lmax (e) [nm
-
1
(
Lmol cm-1)]
3
3
4
a
175
242
250
536
7.77 (s, 1 H, met-H), 7.45–7.7 (m, 5 H, Ph-H), 3.98 (t, 2 H, J = 7, NCH ), 3.8 (br s, 2 H, NCH ),
2
2
(
89000)
3.5 (br s, 2 H, NCH ), 2.20 (s, 3 H, CH ), 1.2–1.8 (m, 12 H, CH ), 0.9–1.1 (m, 9 H, CH )
2
3
2
3
f
526
7.86 (s, 1 H, met-H), 3.7 (br s, 4 H, NCH ), 3.34 (s, 3 H, NCH ), 2.84 (s, 2 H, CH ), 2.55 (s,
2
3
2
(
118000)
3 H, CH ), 1.35 (br s, 6 H, CH ), 1.04 (s, 9 H, t-C H )
3
3
4
9
a
522
7.99 (AB, 2 H, J = 14, met-H), 7.1–7.5 (m, 4 H, ar-H), 3.99 (t, 2 H, J = 8, NCH ), 3.64 (s, 3
2
(
135000)
H, NCH ), 2.53 (s, 3 H, CH ), 1.73 (s, 6 H, CH ), 1.62 (m , 2 H, CH ), 1.41 (m , 2 H, CH ),
3
3
3
c
2
c
2
0
.94 (t, 3 H, J = 7, CH3)
4c
193
527
130000)
8.02 (AB, 2 H, J = 14, met-H), 7.35–7.45 (m, 2 H, ar-H), 7.20–7.30 (m, 1 H, ar-H), 7.08 (mc,
1 H, ar-H), 4.04 (t, 2 H, J = 7, NCH ), 3.99 (t, 2 H, J = 7, NCH ), 2.51 (s, 3 H, CH ), 1.93 (m ,
(
2
2
3
c
2
H, J = 7, CH ), 1.72 (s, 6 H, CH ), 1.62 (m , 2 H, CH ), 1.41 (m , 2 H, CH ), 1.06 (t, 3 H, J
2 3 c 2 c 2
=
7, CH ), 0.94 (t, 3 H, J = 7, CH )
3 3
4
f
185–186
185–187
8.09 (AB, 2 H, J = 14, met-H), 7.15–7.45 (m, 4 H, ar-H), 4.87 (m , 1 H, NCH), 3.98 (t, 2 H, J
c
=
8, NCH ), 2.52 (s, 3 H, CH ), 1.71 (s, 6 H, CH ), 1.69 (d, 6 H, CH ), 1.64 (m , 2 H, CH ),
2 3 3 3 c 2
1
.33 (m , 6 H, CH ), 0.88 (t, 3 H, J = 7, CH )
c
2
3
4
g
8.03 (AB, 2 H, met-H), 7.10 – 7.45 (m, 4 H, ar-H), 4.07 (t, 2 H, J = 7, NCH ), 3.97 (t, 2 H, J
2
=
7, NCH ), 2.52 (s, 3 H, CH ), 1.2 – 2.0 (m, 10 H, CH ), 1.72 (s, 6 H, CH ), 1.01 (t, 3 H, J =
2 3 2 3
7
, CH ), 0.89 (t, 3 H,
3
J = 7, CH3)
4h
2a
5a
158
235
312
8.08 (AB, 2 H, met-H), 7.2–7.4 (m, 4 H, ar-H), 4.86 (m , 1 H, NCH), 3.92 (m , 2 H, NCH ),
c
c
2
2
.52 (s, 3 H, CH ), 1.90 (m , 1 H, CH), 1.71 (s, 6 H, CH ), 1.68 (d, 6 H, J = 6, CH ), 1.31 (m ,
3 c 3 3 c
8
H, CH ), 0.90 (m , 6 H, CH )
2
c
3
538
157000)
7.50 (m , 2 H, thio-H4, met-H), 6.44 (d, 1 H, J = 5, thio–H3), 3.97 (t, 2 H, J = 7, NCH ), 3.67
c 2
(
(br s, 4 H, pip–NCH ), 2.46 (s, 3 H, CH ), 1.79 (br s, 6 H, pip–CH ), 1.66 (m , 2 H, CH ), 1.41
2 3 2 c 2
(
m , 2 H, CH ), 0.94 (t, 3 H, J = 7, CH )
c 2 3
533
137000)
500 MHz: 8.07 (d, 1 H, J = 13, met-H), 7.77 (d, 1 H, J = 13, met-H), 7.69 (d, 1 H, J = 8, ar-
(
H), 7.54 (t, 1 H, J = 8, ar-H), 7.40 (m, 2 H, ar-H), 4.37 (q, 2 H, J = 7, NCH ), 3.99 (t, 2 H, J =
2
8
, NCH ), 2.52 (s, 3 H, CH ), 1.63 (m , 2 H, CH ), 1.55 (m , 3 H, CH ), 1.40 (m , 2 H, CH ),
2
3
c
2
c
3
c
2
0
.95 (t, 3 H, J = 7, CH3)
6a
284–288
495
145000)
500 MHz: 8.14 (d, 1 H, J = 14, met-H), 7.62 (d, 1 H, J = 14, met-H), 7.55 (m, 1 H, ar-H), 7.42
(m, 2 H, ar-H), 7.30 (m, 1 H,ar-H), 4.22 (q, 2 H, J = 7, NCH ), 3.99 (t, 2 H, J = 7, NCH ),
(
2
2
2
.55 (s, 3 H, CH ), 1.62 (m , 2 H, CH ), 1.55 (t, 3 H, J = 7, CH ), 1.40 (m , 2 H, CH ), 0.95 (t,
3 c 2 3 c 2
3
H, J = 7, CH3)
1
8
0
290–294
285–287
550
110000)
DMSO-d : 8.40 (d, 2 H, J = 7, pyr-H), 7.70–7.90 (m, 4 H, pyr-H, met-H), 4.07 (s, 3 H, NCH ),
6 3
(
3.82 (t, 2 H, J = 7, NCH ), 2.42 (s, 3 H, CH ), 1.46 (m , 2 H, CH ), 1.30 (m , 2 H, CH ), 0.90
2 3 c 2 c 2
(t, 3 H, J = 7, CH3)
2
617
116000)
500 MHz in DMSO-d : 8.73 (d, 1 H, J = 14, met-H), 8.70 (d, 1 H, J = 7, quin-H), 8.45 (d, 1
6
(
H, J = 9, quin-H), 8.23 (d, 1 H, J = 9, quin-H), 8.07 (d, 1 H, J = 7, quin-H), 8.05 (m , 1 H,
c
quin-H), 8.03 (d, 1 H, J = 14, met-H), 7.85 (t, 1 H, J = 8, quin-H), 4.73 (q, 2 H, J = 7, NCH2),
3
.86 (t, 2 H, J = 7, NCH ), 2.50 (s, 3 H, CH ), 1.48 (m , 5 H, CH ,CH ), 1.28 (m , 2 H, CH ),
2 3 c 2 3 c 2
0
.90 (t, 3 H, J = 7, CH3)
22
24
26
282–283
203–204
330–335
471
69000)
7.93 (d, 1 H, J = 15, met-H), 7.55 (s, 4 H, ar-H), 7.48 (d, 1 H, J = 14, met-H), 4.46 (q, 4 H, J
= 7, NCH ), 4.01 (t, 2 H, J = 7, NCH ), 2.42 (s, 3 H, CH ), 1.65 (t, 6 H, J = 7, CH ), 1.5–1.7
(
2
2
3
3
(
m, 2 H, CH ), 1.3–1.5 (m, 2 H, CH ), 0.92 (t, 3 H, J = 7, CH )
2
2
3
13.1 (br d, 1 H, J = 13, NH), 8.25 (d, 1 H, J = 13, met-H), 7.49 (m , 2 H, ar-H), 7.33 (m , 3 H,
c
c
ar-H), 3.98 (t, 2 H, J = 7, NCH ), 2.54 (s, 3 H, CH ), 1.61 (m , 2 H, CH ), 1.39 (m , 2 H, CH ),
2
3
c
2
c
2
0
.95 (t, 3 H, J = 7, CH3)
500 MHz in DMSO-d at 120°C: 12.9 (br s, 2 H, NH), 8.52 (s, 2 H, met-H), 7.69 (s, 4 H,
6
(
dec)
ar-H), 3.92 (t, 4 H, J = 7, NCH ), 2.55 (s, 6 H, CH ), 1.58 (m , 4 H, CH ), 1.33 (m , 4 H, CH ),
2 3 c 2 c 2
0
.92 (t, 6 H, J = 7, CH3)
Synthesis 1999, No. 12, 2103–2113 ISSN 0039-7881 © Thieme Stuttgart · New York

2
110
F. Würthner
PAPER
Table 3 (continued)
1
Dye
mp (°C)
UV/VIS
CH Cl )
H NMR (200 MHz, CDCl /TMS)
3
c
(
d, J (Hz)
2
2
lmax (e) [nm
-
1
(
Lmol cm-1)]
2
9
0
180–181
315
8.55 (s, 1 H, met-H), 7.63 (m , 2 H, ar-H), 7.52 (m , 3 H, ar-H), 3.7 (br s, 4 H, NCH ), 3.38 (s,
c c 2
3
7
H, NCH ), 3.33 (s, 3 H, NCH ), 1.70 (m , 4 H, CH ), 1.40 (m , 4 H, CH ), 0.99 (t, 6 H, J =
, CH3)
3 3 c 2 c 2
3
466
93000)
DMSO-d : 8.53 (d, 1 H, J = 15, met-H), 7.57 (m , 1 H, ar-H), 7.48 (d, 1 H, J = 15, ar-H), 7.38
6 c
(
(m , 2 H, ar-H), 7.25 (m , 1 H, ar-H), 3.54 (s, 3 H, NCH ), 3.19 (s, 3 H, NCH ), 3.17 (s, 3 H,
c
c
3
3
NCH ), 1.63 (s, 6 H, CH )
3
3
31
33
38
>310
505
104000)
DMSO-d : 8.06–8.12 (m, 3 H, pyr-H, met-H), 7.42 (d, 2 H, J = 6, pyr-H), 7.38 (d, 1 H, J = 15,
6
(
met-H), 3.93 (s, 3 H, NCH ), 3.14 (s, 6 H, NCH )
3
3
235–
450
(68000)
8.63 (d, 1 H, J = 14, met-H), 7.15–7.45 (m, 4 H, ar-H, met-H),
7.00–7.08 (m, 1 H, ar-H), 3.53 (s, 3 H, NCH ), 1.73 (s, 6 H, CH )
d
238
3
3
265–270
dec)
462
(106000)
7.25–7.60 (m, 3 H, met-H), 3.96 (t, 2 H, J = 7, NCH ), 3.37 (s, 3 H, NCH ), 3.23 (s, 3 H,
2 3
(
NCH ), 2.39 (s, 3 H, CH ), 1.58 (m , 2 H, CH ), 1.39 (m , 2 H, CH ), 0.93 (t, 3 H, J = 7, CH )
3 3 c 2 c 2 3
a
b
c
d
Spectroscopic data for thiazole dyes 3b-e and indoline dyes 4b, 4d-f are given in Lit.4
Satisfactory elemental analyses were obtained for all dyes: C ± 0.28, H ± 0.17, N ± 0.17, S ± 0.20.
br s = broad signal, met = methine, thio = thiophene, pip = piperidyl, pyr = pyridine, quin = quinoline.
25
Lit. mp 232–235°C.
1
2
-Hexyl-5-[2-(1,3-dihydro-3,3-dimethyl-1-isopropyl-2H-indol-
-ylidene)ethylidene]-2,6-dioxo-1,2,5,6-tetrahydropyridine-3-
had disappered according to TLC control (silica gel; toluene/
EtOAc, 9:1). After cooling to r.t., EtOAc (20 mL) was added and
the organic phase was washed with brine and aq 2 N NaOH until a
pH of 9 was reached. The organic layer was washed once more with
brine, dried (Na SO ), filtered and concentrated to give 4.0 g of a
carbonitrile (4f)
Reaction was carried out as described for 4c starting from from 8d
(2.34 g, 0.01 mol), 12c (2.0 g, 0.01 mol) and DMF (1.1 mL, 0.015
2
4
mol) to give a pink solid in 50% yield. Recrystallization from tolu-
ene/hexane gave red crystals.
red oil. Column chromatography on silica gel with toluene/EtOAc
(9:1) as eluent afforded a yellowish solid which was recrystallized
from cyclohexane to give 3.83 g (89%) of pale yellow crystals; mp
5
-[2-(1-Butyl-1,3-dihydro-3,3-dimethyl-2H-indol-2-
2
b
9
8°C (Lit. mp 98–99°C).
ylidene)ethylidene]-2,6-dioxo-1-pentyl-1,2,5,6-tetrahydropyri-
dine-3-carbonitrile (4g)
1
H NMR (200 MHz, CDCl ): two isomers in a 9:1 ratio: d = 7.10–
3
Reaction was carried out as described for 4c from 12d (2.68 g, 0.01
mol of 80% purity), 8c (2.20 g, 0.01 mol) and DMF (1.1 g, 0.015
7.25 (m, 2 H, ar-H), 6.80–7.00 (m, 1 H, ar-H), 6.72 (d, 1 H, J = 8
Hz, ar-H), 5.30 (s, 0.9 H, met-H), 5.17 (s, 0.1 H, met-H), 3.58 (s, 0.3
H, NCH ), 3.16 (s, 2.7 H, NCH ), 2.20 (s, 0.3 H, acetyl-H), 2.18 (s,
mol) in Ac O (5 mL) to give 3.1 g (70%) of a pink solid which was
2
3
3
recrystallized from toluene to yield 2.3 g of violet needles.
2.7 H, acetyl-H), 1.78 (s, 0.6 H, CH ), 1.72 (s, 5.4 H, CH ).
3
3
1
2
-(2-Ethylhexyl)-5-[2-(1,3-dihydro-1-isopropyl-3,3-dimethyl-
H-indol-2-ylidene)ethylidene]-4-methyl-2,6-dioxo-1,2,5,6-tet-
MS (EI): m/z (%) = 215 (100), 199 (97).
rahydropyridine-3-carbonitrile (4h)
1-Butyl-4-methyl-5-dimethylaminomethylene-2,6-dioxo-
1,2,5,6-tetrahydropyridine-3-carbonitrile (16a)
A mixture of 8a (10.3 g, 0.05 mol), DMF (5.5 g, 0.075 mol) and
Reaction was carried out as described for 4a starting from 8e (2.62
g, 0.01 mol), 12c (2.0 g, 0.01 mol) and DMF (1.1 mL, 0.015 mol).
After cooling, a dark red solution was obtained. This mixture was
concentrated to give an oily residue which was purified by column
chromatography on silica gel using CH Cl /MeOH (97:3) as eluent.
Ac O (25 mL) was heated at 80–90°C for 1 h. Upon cooling to r.t.
2
1
6a precipitated. Filtration and washing with cold Ac O and abso-
2
2
2
lute Et O afforded a cream-white solid which was dried to yield
2
After evaporation of the solvent an oil was obtained which crystal-
lized in the refrigerator after several days to give a pink solid in 80%
yield which could be recrystallized from EtOH.
1
0.2 g (78%) of 8a; mp 185–190°C (dec).
1
H NMR (200 MHz, CDCl ): d = 7.76 (s, 1 H, met-H), 3.93 (t, 2 H,
3
J = 7 Hz, NCH ), 3.53 (s, 3 H, NCH ), 3.27 (s, 3 H, NCH ), 2.39 (s,
2
3
3
1
-Butyl-4-methyl-2,6-dioxo-5-(2-piperidinothiophen-5-ylmeth-
3 H, CH ), 1.56 (m , 2 H, CH ), 1.36 (m , 2 H, CH ), 0.92 (t, 3 H,
J = 7 Hz, CH3).
3
c
2
c
2
ylene)-1,2,5,6-tetrahydropyridine-3-carbonitrile (2a)
From 10a (1.7 g, 0.01 mol), 8a (2.1 g, 0.01 mol) and DMF (1.1 g,
MS (EI): m/z (%) = 261 (45), 244 (79), 190 (100).
0
.0015 mol) in Ac O (3.7 mL, 0.035 mol). After cooling to r.t., the
2
precipitate was filtered, washed with i-PrOH (3 × 4 mL), recrystal-
Anal. calcd for C14 (261.3): C, 64.35; H, 7.33; N, 16.08.
H N O
19 3 2
lized from toluene and dried to give 0.6 g (15%) of green needles.
Found C, 64.11; H, 7.30; N, 15.85.
1
-(1,3-Dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)propan-2-
1-Butyl-5-formyl-6-hydroxy-4-methyl-2-oxo-1,2-dihydropyri-
dine-3-carbonitrile (7a)
one (15)
A mixture of 12a (3.46 g, 0.02 mol), DMF (2.20 g, 0.03 mol) and
Compound 16a (1.30 g, 0.005 mol) was suspended in 96% EtOH
Ac O (8 mL) was heated at 100°C for 2 h till all the starting material
(40 mL) and stirred at r.t. After addition of H O (10 mL), the solid
2
2
Synthesis 1999, No. 12, 2103–2113 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
DMF in Acetic Anhydride: A Useful Reagent for Multiple-Component Syntheses of Merocyanine Dyes
2111
dissolved and the solution turned red. After 30 min additional
mL). The bright yellow solid was recrystallized from EtOH (50 mL)
amount of H O (30 mL) was added and the solution was concentrat-
and dried to yield 0.40 g (49%) of 22.
2
ed. 1 N HCl (ca 4 mL) was added until a pH of 1 was reached and a
cream-white solid precipitated, which turned a little brownish dur-
ing drying at 40°C in vacuo to give 1.1 g (94%) of 7a, which was
1-Butyl-2,6-dioxo-5-phenylaminomethylene-1,2,5,6-tetrahy-
dropyridine-3-carbonitrile (24)
>95% pure according to NMR. Sublimation afforded a white solid;
To a suspension of 16a (1.30 g, 5 mmol) in anhyd EtOH (8 mL) was
added dropwise 23 (0.60 g, 6.5 mmol). A yellow precipitate formed
immediately and the mixture solidified. The mixture was refluxed
for 2 min and allowed to cool to r.t. The yellow product was collect-
ed on a Büchner funnel, washed thoroughly with EtOH and dried in
vacuo at 60°C to give 1.38 g (89%) of a bright yellow solid which
exhibits intense luminescence under UV irradiation.
mp 98°C.
1
H NMR (200 MHz, CDCl ): d = 8.83 (s, 1 H, CHO), 4.01 (t, 2 H,
3
J = 7 Hz, NCH ), 2.53 (s, 3 H, CH ), 1.63 (m , 2 H, CH ), 1.39 (m ,
2
3
c
2
c
2
H, CH ), 0.95 (t, 3 H, J = 7 Hz, CH ).
2
3
MS (EI, 70eV): m/z (%) = 234 (28), 217 (100), 192 (49), 179 (88),
50 (48).
1
Anal. calcd C H N O (234.3): C, 61.53; H, 6.02; N, 11.96. Found
C, 61.70; H, 5.99; N, 11.82.
N,N‘-Bis-(1-butyl-3-cyano-2,6-dioxo-1,2,5,6-tetrahydropyri-
din-5-ylidenemethylene)-p-phenylenediamine (26)
1
2
14
2
3
A mixture of 16a (0.52 g, 2 mmol) and 25 (0.11 g, 1 mmol) was sus-
pended in of anhyd chlorobenzene (20 mL). During shaking, the co-
lour of the precipitate changed from white to orange. To complete
the reaction, the mixture was first stirred at r.t. for 2 h and then heat-
ed under reflux for another hour. After cooling the orange solid was
filtered and thoroughly washed with EtOH to give 0.46 g (85%) of
26. Recrystallization from DMF (30 mL), washing with EtOH and
drying in vacuo at 80°C afforded 0.30 g of an intensively lumines-
cent orange powder.
1
-Butyl-5-[2-(3-ethyl-3H-benzothiazol-2-ylidene)ethylidene]-4-
methyl-2,6-dioxo-1,2,5,6-tetrahydropyridine-3-carbonitrile
5a); Typical Procedure
(
A mixture of 13a (0.92 g, 3 mmol), 8a (0.62 g, 3 mmol), DMF (0.33
g, 4.5 mmol), KOAc (0.30 g, 3 mmol) and Ac O (2 mL) was stirred
at 90°C for 2.5 h. After cooling, the precipitate was collected on a
Büchner funnel and washed with H O/EtOH and H O. After drying
0
2
2
2
.72 g (61%) of a violet solid was obtained which could be recrys-
tallized from Ac O (100 mL) to give 0.50 g (42%) of red needles.
2
5
-Dimethylaminomethylene-1,3-dimethylpyrimidine-2,4,6-tri-
1
-Butyl-5-[2-(3-ethyl-3H-benzoxazol-2-ylidene)ethylidene]-4-
methyl-2,6-dioxo-1,2,5,6-tetrahydropyridine-3-carbonitrile
6a)
one (28)
A mixture of 27 (1.56 g, 0.01 mol), DMF (1.1 g, 0.015 mol) and
Ac O (5 mL) was heated at 90°C for 2 h. After cooling to r.t., the
liquid was triturated with Et O (5 mL) to give almost colorless crys-
tals during standing for 2 h. The crystals were filtered and washed
(
Following the procedure given above for the preparation of 5a, re-
action of 14a (2.7 mmol) with 8a (0.56 g, 2.7 mmol), DMF (0.30 g,
4
g (45%) of an orange powder. Recrystallization from Ac O yielded
0
2
2
mmol), KOAc (0.27 g, 2.7 mmol), and Ac O (2 mL)afforded 0.46
2
with Et O (3 × 4 mL) and dried in vacuo at 40°C to yield 1.60 g
2
2
2
2
(
76%) of 28; mp 107–108°C (Lit. mp 109°C).
.40 g (39%) of orange crystals.
1
H NMR (200MHz, CDCl /TMS, 25°C): d = 8.14 (s, 1 H, met-H),
3
1
-Butyl-4-methyl-5-[2-(1-methyl-1H-pyridin-4-ylidene)eth-
3.42 (s, 3 H, NCH ), 3.38 (s, 3 H, NCH ), 3.31 (s, 6 H, barb–NCH ).
3
3
3
ylidene]- 2,6-dioxo-1,2,5,6-tetrahydropyridine-3-carbonitrile
18)
A mixture of 8a (2.06 g, 0.01 mol), DMF (1.1 g, 0.015 mol) and
(
5-(2-Dibutylamino-4-phenylthiazol-5-ylmethylene)- 1,3-dime-
thylpyrimidine-2,4,6-trione (29)
A mixture of 27 (1.56 g, 0.01 mol), DMF (1.1 g, 0.015 mol) and
Ac O (4 mL) was heated at 90°C for 40 min when the mixture so-
2
lidified due to the formation of 16a. After cooling iodide 17 (1.88 g,
Ac O (4 mL) was heated at 90°C for 1 h. Compound 11a (3.6 g, 0.01
2
8
mmol) and Et N (1.0 g, 0.01 mol) were added and the mixture was
mol of 80% purity) was added to the pale-yellow solution and the
mixture was stirred at 90°C for another 2 h. The solid which precip-
itated on cooling, was collected, washed with i-PrOH and EtOH/
3
heated at 90°C for another hour. After cooling the red precipitate
was collected, washed with Et O and EtOH/H O (1:1) and dried to
2
2
yield 1.4 g (54%) of a violet solid which was pure according to
H O (8:2), and dried to give 3.0 g (66%) of an orange dye which was
2
NMR. Recrystallization from Ac O gave dark-green crystals.
pure according to NMR. Recrystallization from toluene yielded 2.7
g (59%) of orange crystals. If the reaction was carried out with all
components mixed together (General Procedure B, see above) a
yield of only 40% was obtained.
2
1
-Butyl-5-[2-(1-ethyl-1H-quinolin-4-ylidene)ethylidene]- 4-
methyl-2,6-dioxo-1,2,5,6-tetrahydropyridine-3-carbonitrile
20)
(
5
-[2-(1,3-Dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-eth-
A mixture of 8a (1.03 g, 5 mmol), DMF (0.55 g, 7.5 mmol) and
ylidene]-1,3-dimethylpyrimidine-2,4,6-trione (30)
Reaction was carried out as described for 29 staring from 27 (1.56
Ac O (4 mL) was heated at 90°C for 1 h. The mixture was cooled to
2
5
0°C and iodide 19 (1.20 g, 4 mmol) and Et N (0.5 g, 5 mmol) were
3
g, 0.01 mol), DMF (1.1 g, 0.015 mol) Ac O (4 mL) and 12a (1.73
2
added. After another hour at 90°C the mixture was cooled to r.t. and
g, 0.01 mol) to give 3.20 g (94%) of a luminescent orange solid. If
the reaction was carried out with all components mixed together
the precipitate was collected and washed with Et O and EtOH/H O
2
2
(
7:3) until the colour of the filtrate changed from violet to almost
(General Procedure B, see above) a yield of only 3% was obtained.
colorless. The dye was dried to yield 1.36 g (90%) of a green solid
which was pure according to NMR. Recrystallization from Ac O
gave 0.90 g (60%) of green crystals.
2
1
,3-Dimethyl-5-[2-(1-methyl-1H-pyridin-4-ylidene)ethylidene]-
pyrimidine-2,4,6-trione (31)
A mixture of 27 (1.56 g, 0.01 mol), DMF (1.1 g, 0.015 mol) and
1
-Butyl-5-[2-(1,3-diethyl-1,3-dihydro-2H-benzimidazol-2-
Ac O (4 mL) was heated at 90°C for 1 h to give a pale yellow solu-
2
yliden)ethylidene]- 2,6-dioxo-1,2,5,6-tetrahydropyridine-3-car-
bonitrile (22)
A suspension of 16a (0.52 g, 2 mmol) in anhyd EtOH (5 mL) was
stirred under argon and 21 (0.38 g, 2 mmol) was added dropwise.
The mixture was stirred at 80°C for 4 h. The yellow precipitate
formed was cooled to r.t., filtered and washed with EtOH (3 × 3
tion. To this solution were added 17 (1.88 g, 0.008 mol) and Et N
3
(
0.8 g, 0.008 mol) added and the mixture was stirred at 90°C for an-
other 2 h. The solid which precipitated on cooling was collected,
washed with Et O and EtOH/H O (7:3) and dried to give 0.20 g
2
3
2
2
(
9%) of an orange dye which was pure according to NMR. Recrys-
tallization from AcOH gave orange crystals.
Synthesis 1999, No. 12, 2103–2113 ISSN 0039-7881 © Thieme Stuttgart · New York

2
112
F. Würthner
PAPER
5
-[2-(1,3-Dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-eth-
(7) Grund, C.; Reichelt, H.; Schmidt, A. J.; Würthner, F.; Sens,
R.; Beckmann, S. PCT Int. Pat. Appl. WO 98/23688; Chem.
Abstr. 1998, 129, 29100.
ylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione (33)
Reaction was carried out as described for 29 starting from 32 (1.44
g, 0.01 mol), DMF (1.1 g, 0.015 mol), Ac O (4 mL) and 12a (1.73
g, 0.01 mol) to afford 1.08 g (33%) of a red solid.
(8) (a) Balkenhohl, F.; von dem Bussche-Hünnefeld, C.; Lansky,
A.; Zechel, C. Angew. Chem. 1996, 108, 2437; Angew. Chem.
Int. Ed. Engl. 1996, 35, 2288.
2
Attempted Synthesis of Dye 36
(
(
b) Thompson, L. A.; Ellman, J. A. Chem. Rev. 1996, 96, 555.
c) Armstrong, R. W.; Combs, A. P.; Tempest, P. A.; Brown,
A mixture of 34 (1.01 g, 4 mmol), DMF (0.45 g, 6 mmol) and Ac O
2
(2 mL) was heated at 90°C for 2 h to give the enamine 35 which pre-
S. D.; Keating, T. A. Acc. Chem. Res. 1996, 29, 123.
9) (a) Guareschi, J. Ber. Dtsch. Chem. Ges. Bd. 4 (Referate,
Patente, Nekrologe) 1896, 29, 654.
cipitated on cooling as a yellow solid. Addition of 12a (0.64 g, 3.7
mmol) and heating for another 2 h at 90°C afforded after cooling,
filtration and washing 1.1 g of an orange solid which was composed
(
2
6
13b
1
(b) Bello, K. A. Dyes Pigm. 1995, 28, 83.
of 60 mol% enamine 35 and 40 mol% dye 36 according to H
(
c) Katritzky, A. R.; Rachwal, S.; Smith, T. J. Heterocyclic
NMR and MS (EI) characterization. The major product in the moth-
1
Chem. 1995, 32, 1007.
er liquor was indoline 15 according to TLC and H NMR analysis.
(
10) (a) Liebscher, J. In Houben-Weyl, Vol. E8b; Schaumann, E.,
Ed.; Thieme: Stuttgart, 1994, p 1.
1
1
-Butyl-5-(3-dimethylaminoallylidene)-4-methyl-2,6-dioxo-
,2,5,6-tetrahydropyridine-3-carbonitrile (38)
(
(
b) Keil, D.; Hartmann, H. Liebigs Ann. Chem. 1995, 979.
c) Seybold, G. DE Pat. Appl. 3227329; Chem. Abstr. 1984,
A mixture of 8a (2.06 g, 0.01 mol), 37 (0.99 g, 0.01 mol) and Ac O
2
1
00, 122768k.
d) Schmidt, A. J.; Sens, R.; Etzbach, K.-H. DE Pat. Appl. 44
0 066; Chem. Abstr. 1996, 125, P60959.
11) (a) Gruda, I.; Leblanc, R. M. Can. J. Chem. 1976, 54, 576.
b) Hirano, M.; Miyashita, A.; Nohira, H. Chem. Lett. 1991,
09.
c) Brooker, L. G. S.; White, F. L. J. Am. Chem. Soc. 1935, 57,
(5 mL) was stirred at 90°C for 2 h. The precipitate which formed
(
4
upon cooling was collected on a Büchner funnel and washed with i-
PrOH to give after drying 2.58 g (90%) of a yellow dye. Recrystal-
lization from EtOH gave luminescent yellow needles. The same
product was isolated in 85% yield in the presence of 0.01 mol thia-
zole 11a.
(
(
(
2
(
MS (EI): m/z (%) = 287 (100), 270 (85), 187 (98).
547.
12) The accessibility of 2-dialkylaminothiophenes and -furans
9
,10 is rather limited and requires severals unattractive steps
with respect to yields and substituent variations, see:
a) Hartmann, H.; Scheidhauer, S. J. Prakt. Chem. 1969, 311,
27. Therefore the more readily available starting materials
for 1 and 2 are given with 2-dialkylamino-5-formylfurane and
Acknowledgement
(
8
This work was supported by BASF AG. I am grateful to my former
group at BASF Dye Stuff Laboratory, in particular to Drs. Andreas
J. Schmidt, Rüdiger Sens, Karl-Heinz Etzbach and Günther Seybold
for helpful discussions and to Karlheinz Frieß and Andrea Weigel
for their assistance in the laboratory. The Fonds der Chemischen In-
dustrie and the BMBF are acknowledged for a Liebig grant and
Prof. Peter Bäuerle for providing excellent working conditions at
the University of Ulm.
-thiophene, see:
(b) Nazarova, Z. N.; Pustarov, V. S. Khim. Geterotsikl.
Soedin. 1969, 5, 586; Chem. Abstr. 1972, 77, 7272.
c) Shulezhko, A. A. Ukr. Khim. Zh. 1972, 38, 68; Chem.
(
Abstr. 1970, 72, 31523.
(
13) (a) Hünig, S. Liebigs Ann. Chem. 1951, 574, 113.
(
b) Reidlinger, C.; Dworczak, R.; Fabian, W. M. F.; Junek, H.
Dyes Pigm. 1994, 24, 185.
14) Meerwein, H.; Florian, W.; Schön, N.; Stopp, G. Liebigs Ann.
Chem. 1961, 641, 1.
References
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(
(
1) (a) Zollinger, H. Color Chemistry; VCH: Weinheim, 1991.
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15) (a) Bredereck, H.; Effenberger, F.; Simchen, G. Chem. Ber.
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1
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(
(
3) Würthner, F.; Wortmann, R; Matschiner, R.; Lukaszuk, K.;
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(
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19) Acetylation of aromatic amines may be carried out already
18c
below room temperature using Ac O and ice-water.
comparable reactivity is described for 2-
methylenebenzimidazole 25.
A
2
1999, 38, 1649.
18b,d
(b) Sens, R.; Etzbach, K. H.; Bach, V. DE Pat. Appl. 4344116
20) The higher reactivity of the enamines of the six-membered
heterocycles may be explained by AM1 calculations which
show a tilted conjugated system in contrast to the fully planar
enamines of the five-membered heterocycles. Because of the
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(
(
5) Gregory, P. High-Technology Applications of Organic
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Synthesis 1999, No. 12, 2103–2113 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
DMF in Acetic Anhydride: A Useful Reagent for Multiple-Component Syntheses of Merocyanine Dyes
2113
high p-bond order for the Me N–C bond a highly reactive
(24) Bredereck, H.; Richter, R. Chem. Ber. 1965, 98, 131.
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2
dimethylimmonium unit is formed by this bond rotation.
(
21) (a) Würthner, F.; Thalacker, C.; Matschiner, R.; Lukaszuk, K.;
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(b) Beckmann, S.; Etzbach, K.-H.; Krämer, P.; Lukaszuk, K.;
Matschiner, R.; Schmidt, A. J.; Schuhmacher, P.; Sens, R.;
Seybold, G.; Wortmann, R.; Würthner, F. Adv. Mater. 1999,
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Article Identifier:
(
(
22) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3. Ed.; Pergamon: Oxford, 1988.
23) Reichardt, C.; Kaufmann, N. Chem. Ber. 1985, 118, 3424.
1437-210X,E;1999,0,12,2103,2113,ftx,en;H05199SS.pdf
Synthesis 1999, No. 12, 2103–2113 ISSN 0039-7881 © Thieme Stuttgart · New York