One-pot three-component synthesis and photophysical characteristics of novel triene merocyanines

Article abstract of DOI:10.3762/bjoc.10.51

Novel triene merocyanines, i.e. 1-styryleth-2-enylidene and 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones are obtained in good to excellent yields in a consecutive three-component insertion Sonogashira coupling-addition sequence. The selectivity of either series is remarkable and has its origin in the stepwise character of the terminal addition step as shown by extensive computations on the DFT level. All merocyanines display intense absorption bands in solution and the film spectra indicate J-aggregation. While 1-styryleth-2-enylideneindolones show an intense deep red emission in films, 4-(1,3,3-trimethylindolin-2- ylidene)but-2-en-1-ylideneindolones are essentially nonemissive in films or in the solid state. TD-DFT computations rationalize the charge-transfer nature of the characteristic broad long-wavelength absorptions bands.

Full text of DOI:10.3762/bjoc.10.51

One-pot three-component synthesis and photo-
physical characteristics of novel triene merocyanines
Christian Muschelknautz, Robin Visse, Jan Nordmann
and Thomas J. J. Müller*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2014, 10, 599–612.
Institut für Organische Chemie und Makromolekulare Chemie,
Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, D-40225
Düsseldorf, Germany
doi:10.3762/bjoc.10.51
Received: 06 December 2013
Accepted: 28 January 2014
Published: 05 March 2014
Email:
Thomas J. J. Müller* - ThomasJJ.Mueller@uni-duesseldorf.de
This article is part of the Thematic Series "Multicomponent reactions II"
and is dedicated to Dr. Hans-Ulrich Wagner on the occasion of his 75th
birthday.
* Corresponding author
Keywords:
alkynes; cross coupling; enamines; fluorescence; heterocycles;
multicomponent reactions
Associate Editor: J. A. Porco Jr.
© 2014 Muschelknautz et al; licensee Beilstein-Institut.
License and terms: see end of document.
Abstract
Novel triene merocyanines, i.e. 1-styryleth-2-enylidene and 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones are
obtained in good to excellent yields in a consecutive three-component insertion Sonogashira coupling–addition sequence. The
selectivity of either series is remarkable and has its origin in the stepwise character of the terminal addition step as shown by exten-
sive computations on the DFT level. All merocyanines display intense absorption bands in solution and the film spectra indicate
J-aggregation. While 1-styryleth-2-enylideneindolones show an intense deep red emission in films, 4-(1,3,3-trimethylindolin-2-
ylidene)but-2-en-1-ylideneindolones are essentially nonemissive in films or in the solid state. TD-DFT computations rationalize the
charge-transfer nature of the characteristic broad long-wavelength absorptions bands.
Introduction
Functional organic materials [1], such as chromophores, fluo- push–pull chromophores always have been accessed by
rophores, and electrophores, constitute the active components in Knoevenagel condensations [12-14] or substitution reactions
molecular electronics [2], photonics [3], and bioanalytics [4-6]. [15-18]. Still the quest for new synthetic strategies, novel
Among many chromophores the class of merocyanines [7-9], substitution patterns, and eventually unusual properties and
i.e. α-donor-ω-acceptor-substituted polyenes, has become effects has become an ongoing challenge for organic synthesis,
increasingly interesting due to their fine-tunable electronic physical organic chemistry, and photophysics.
distribution [10]. For instance, merocyanines are perfectly
suited for developing molecule-based non-linear optical ma- Inspired by the concept of a diversity-oriented synthetic ap-
terials and photovoltaic chromophores [11]. Classically, these proach to chromophores [19-26] we have launched a program to
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Beilstein J. Org. Chem. 2014, 10, 599–612.
apply transition metal-catalyzed processes as an entry to electronic properties. Here we report our findings on the diver-
consecutive multicomponent [27,28] and domino reactions [29]. sity-oriented and highly selective three-component synthesis of
These highly convergent strategies paved the way to lumines- a new class of deeply colored triene merocyanines in a one-pot
cent push–pull dienes 1–4 with conformationally flexible and fashion. Furthermore, their absorption and emission characteris-
fixed acceptor units (Figure 1) [30-32], pyrazoles [33,34], tics are investigated.
benzodiazepines [35], furans and pyrroles [36,37] by consecu-
tive multicomponent reactions and to highly emissive spiro- Results and Discussion
cycles [38-40] and pyranoindoles [41] via domino sequences. After the coupling of the N-methyl-substituted alkynoyl
Interestingly, our versatile three-component enaminone syn- o-iodoanilides 5a and terminal arylalkynes 6 at room tempera-
thesis [42,43] could be readily extended in a vinylogous fashion ture under Sonogashira conditions forming ynylideneindolones
with enamines furnishing orange or deep red diene chro- as intermediates (the reaction was monitored by TLC to ensure
mophores 2 and 3 that display aggregation induced emission complete conversion) [30-32], which were not isolated, an
[31].
ethanolic solution of Fischer’s base (7) was added and reacted
at reflux temperature to give 1-styryleth-2-enylideneindolones 8
In particular, the electrophilic enyne intermediate [32,40], in good to excellent yields as violet solids with a metallic luster
which is trespassed in the three-component synthesis of solid- (Scheme 1, Table 1). In contrary to the reaction with secondary
state luminescent push–pull indolones 4, intrigued our interest amines, where the E,E-configured butadiene chromophores are
for accessing even triene push–pull systems and to study their formed with excellent stereoselectivity [30-32], Fischer’s base
Figure 1: Linear push–pull solid-state diene lumophores with conformationally flexible and fixed acceptor moieties.
Scheme 1: Three-component synthesis of 1-styryleth-2-enylideneindolones 8.
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Table 1: Three-component synthesis of 1-styryleth-2-enylidene indolones 8.
Entry
Alkyne 6
1-Styryleth-2-enylideneindolones 8
Yield [%]a
1
R3 = H (6a)
93 (d.r. = 56:44)b
8a
2
3
4
5
R3 = OMe (6b)
81 (d.r. = 62:38)b
82 (d.r. = 56:44)b
87 (d.r. = 52:48)b
91 (d.r. = 52:48)b
8b
8c
8d
8e
R3 = Cl (6c)
R3 = CN (6d)
R3 = NO2 (6e)
aThe yields were determined after chromatography on silica gel. bThe diastereomeric ratios were determined by 1H NMR spectroscopy after chroma-
tography on silica gel.
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Beilstein J. Org. Chem. 2014, 10, 599–612.
gives rise to the formation of a mixture of E,E- and E,Z-config-
ured push–pull dienes with 3-styryl substituents in narrow
diastereomeric ratios ranging from 52:48 to 62:38 (Table 1,
entries 1–5) as indicated by the appearance of a second set of
many signals in the proton and carbon NMR spectra.
The structures of the 1-styryleth-2-enylideneindolones 8 were
assigned by NMR, mass spectrometry and by combustion
analysis. The diastereomeric ratios of the E,E- and E,Z-config-
ured push–pull dienes 8 were determined by integration of the
distinct signals of the corresponding pairs of geminal olefinic
protons appearing at δ 4.8–5.2 and δ 5.5–5.8 for the major dia-
stereomer and at δ 4.5–4.8 and δ 5.3–5.5 for the minor dia-
Figure 2: DFT-computed energy differences of the stereoisomers of
2Z,4Z-8a and 2Z,4E-8a.
stereomer in the 1H NMR spectra. The signals of the corres- an ethanolic solution of Fischer’s base (7), the 4-(1,3,3-
ponding carbon nuclei are accordingly identified in the trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones 10a–g
13C NMR spectra as methylene signals at δ 114.7–117.5 for the (X = CMe2) were isolated in good to excellent yields as bluish-
major diastereomer and at δ 118.1–123.5 for the minor dia- black solids with a metallic luster (Scheme 2, Table 2, entries
stereomer.
1–7). The sequence starting from the N-methyl-substituted
alkynoyl o-iodoanilide 5a surprisingly furnishes after coupling
Based upon computations (B3LYP functional, 6-31G* basis set) and reaction with an ethanolic solution of benzothiazolium
[44] on geometry-optimized diastereomers 2Z,4Z-8a and 2Z,4E- iodide 9 in the presence of diisopropylethylamine (DIPEA) the
8a the former is energetically favored by 1.5 kcal mol−1 over 4-(3-methylbenzo[d]thiazol-2(3H)-ylidene)but-2-en-1-
the latter (Figure 2), nicely reproducing the experimentally ylideneindolone 10h (X = S) as a greenish-black solid and not
determined very similar diastereomeric distribution of the the corresponding 1-styryleth-2-enylideneindolones 8 (Table 2,
1-styryleth-2-enylideneindolones 8.
entry 8).
Interestingly, upon coupling of the N-tosyl-substituted alkynoyl The structures of the 4-(1,3,3-trimethylindolin-2-ylidene)but-2-
o-iodoanilides 5b and 5c with terminal arylalkynes 6 at room en-1-ylideneindolones 10 were unambiguously assigned by
temperature under Sonogashira conditions and reacting the NMR, mass spectrometry and by combustion analysis. The
ynylideneindolone intermediates (complete conversion moni- appearance of only a single set of signals in the NMR spectra
tored by TLC) [30-32] under the same conditions as above with indicates that the process is highly stereoselective. The occur-
Scheme 2: Three-component synthesis of 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones 10.
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Beilstein J. Org. Chem. 2014, 10, 599–612.
rence of deep-colored products indicates the presence of a chro- 4-aminoprop-3-enylideneindolones [30-32] and computations
mophore with extended π-electron conjugation where the (B3LYP functional, 6-31G* basis set) [44] on geometry-opti-
terminal acceptor and donor functionalities are connected via an mized 2E,4Z,6Z- and 2E,4Z,6E-diastereomers of 10a and 10h
essentially coplanar methine bridge. Based upon analogy to the the stereochemistry of the most stable isomers of these novel
Table 2: Three-component synthesis of of 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones 10.
Entry
Alkynoyl
o-iodoanilides 5
Alkyne 6
Enamine 7 or
benzothiazolium
salt 9
4-(1,3,3-trimethylindolin-2-ylidene)but-2-
Yield [%]a
en-1-ylideneindolones 10
R1 = pTos, R2 = H
(5b)
1
6a
7
7
7
7
98
10a
10b
10c
10d
2
3
4
5b
5b
5b
6e
6c
6d
90b
78
82
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Beilstein J. Org. Chem. 2014, 10, 599–612.
Table 2: Three-component synthesis of of 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones 10. (continued)
R1 = pTos, R2 = Cl
(5c)
5
6
7
8
R3 = t-Bu (6e)
7
82
92
90
84
10e
5c
5c
5a
6c
6d
6c
7
10f
7
10g
9c
10h
aThe yields were determined after chromatography on silica gel. bThe nitro group was reduced to an amino group under the reaction conditions.
cDiisopropylethylamine was added for in situ generation of the S,N-ketene acetal.
triene merocyanines was assigned to be 2E,4Z,6Z for both the step) it can be assumed that the assigned structures represent the
Fischer’s base derivatives 10a–g (X = CMe2) and the benzo- thermodynamically and kinetically controlled products in this
thiazole derivative 10h (X = S) (Figure 3). Since the stereocon- series.
vergent-product formation (only single sets of signals are
obtained in the NMR spectra for all representatives of 10) Mechanistically the observed unusual selectivity for the forma-
occurs at elevated temperatures (boiling ethanol in the terminal tion of 1-styryleth-2-enylideneindolones 8 vs 4-(1,3,3-
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Beilstein J. Org. Chem. 2014, 10, 599–612.
Figure 3: DFT-computed energy differences of the stereoisomers of 10a and 10h.
trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones 10 sigmatropic H-shift, giving directly rise to the formation of the
obviously originates from minute electronic differences in the conjugated push–pull triene 10.
ynylideneindolone intermediate 11. This species was previ-
ously isolated and unambiguously structurally identified [40]. In This mechanistic rationale suggests that the observed remark-
the case of amine additions to ynylideneindolone intermediates able chemoselectivity in the formation of two different triene
11 we recently could show by experimental and computational merocyanines could originate from minute electronic distribu-
studies that the terminal Michael addition proceeds in a step- tions in the zwitterionic key intermediate, which is controlled in
wise fashion with the intermediacy of an allenyl enol that the allenyl enolate moiety by the indolyl nitrogen substituent R1
undergoes a rapid, irreversible 1,5-sigmatropic hydride shift and by the fragment X on the iminium part, which participates
triggering the allenyl enol–dienone tautomerism [30]. There- in the stabilization on that side of the zwitterion. The former
fore, we propose a similar mechanism for the formation of the hypothesis is supported by the fact that only methyl-substituted
merocyanines 8 and 10 (Scheme 3). The sequences commence ynylideneindolone intermediates 11 enable the cyclobutene
after oxidative addition of the Pd species in the carbon–iodine pathway, whereas all N-tosyl derivatives exclusively give the
bond of 5 with a 5-exo-dig insertion of the appended alkynoyl merocyanines 10 via the allenyl enol pathway. All other remote
moiety, which is coupled by transmetallation with the alkyne 6 substituents on the ynylideneindolone intermediates 11 do not
and reductive elimination to give the ynylideneindolone inter- influence the outcome of the sequence. The latter hypothesis of
mediate 11. The ynylideneindolone 11 is a vinylogous Michael the iminium-ion stabilization obviously influences the lifetime
system, and therefore, it is reasonable to assume a 1,4-addition of the zwitterion 13. Furthermore the enamine formed by depro-
of the nucleophilic enamine 12, which is employed directly (as tonation of 9 is a S,N-ketene acetal, which is significantly more
in the case of Fischer’s base (7)) or generated in situ by depro- nucleophilic than Fischer’s base (7). The higher reactivity of the
tonation of the benzothiazolium salt 9. Hence, in both cases a latter enamine and the higher thermodynamic stability of the
resonance-stabilized iminium–allenyl enolate 13 is formed. iminium intermediate both account for a stepwise pathway that
Here, the bifurcation of the sequences takes over. Based upon proceeds via the intermediacy of zwitterion 13. Therefore, if
product analysis the pathway to the formation of the merocya- intermediate 13 is long lived enough to undergo the prototropy
nines 8 begins with a 1,4-dipolar cyclization of 13 furnishing the merocyanines 10 will be the obvious product. Therefore, the
the highly substituted cyclobutene intermediate 14. Finally, the local charge density in 13 is most crucial for the bifurcation
conrotatory electrocyclic ring opening of the cyclobutene and, hence, for the product formation.
occurs under thermodynamic control, which is obviously only
governed by steric effects as reflected by very similar levels of For scrutinizing this rationale we computed the electrostatic
diastereoselectivity of the double-bond formation. In contrast charges on the atoms 1–7 of the allenyl enolate moiety of model
the formation of the merocyanines 10 starts with a proton zwitterions 16, which only differ by the N-substituent, on the
transfer from the CH-acidic α-position of the iminium moiety of density functional level of theory (B3LYP functional, 6-31G*
13 to the amide enolate part. The resulting enol 15 is part of an basis set) [40]. For a stepwise cyclobutene formation via 1,4-
allenyl enol, which is just perfectly suited for undergoing a 1,5- dipolar cyclization the negative partial charge on the central
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Beilstein J. Org. Chem. 2014, 10, 599–612.
Scheme 3: Mechanistic rationale of the three-component sequence furnishing the 1-styryleth-2-enylideneindolones 8 and 4-(1,3,3-trimethylindolin-2-
ylidene)but-2-en-1-ylideneindolones 10.
allenyl carbon atom 6 should be relatively high. The computa- All merocyanines 8 and 10 are expectedly deeply colored both
tions of the electrostatic charges for an N-methyl (16a) and an in the solid state and in solution. For further investigation of the
N-tosyl intermediate (16b) clearly shows charge density differ- photophysical properties the absorption spectra were recorded
ences at five distinct atoms (Table 3).
in dichloromethane solution and of thin films prepared by drop-
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Beilstein J. Org. Chem. 2014, 10, 599–612.
Table 3: Selected computed electrostatic charges of zwitterion inter-
mediates 16 (DFT computations with B3LYP functional and the 6-31G*
basis set).
Atom
16a (R1 = Me)
16b (R1 = pTos)
O1
N2
C3
C4
C5
C6
C7
−0.564
−0.107
0.480
−0.520
−0.299
0.416
−0.296
0.035
−0.209
−0.060
−0.119
−0.089
−0.162
−0.070
Figure 4: DFT-computed (B3LYP functional, 6-31G* basis set) HOMO
(left) and LUMO (right) of merocyanine 8a.
casting of concentrated dichloromethane solutions on glass-
probe cuvettes (Table 4). For the powders and films of the and 665 nm (Figure 5), the emission in solution is completely
merocyanines 8 intense deep-red luminescence was detected quenched. As already witnessed for the film absorption maxima
upon eyesight. The emission spectra of the films of 8 were of the 4-amino-prop-3-enylideneindolones 4 [30,32] the
recorded, whereas the films of the merocyanines 10 did not J-aggregation results in an induced emission [46,47] by
display emission upon eyesight.
Davydov splitting of the vibrationally relaxed lowest excited-
state energy level [48,49] and causes a significant red shift of
The 1-styryleth-2-enylideneindolones 8 are deep red in solution the sharp emission bands.
and in the films with intense, broad unstructured absorption
bands between 510 and 522 nm in dichloromethane solutions,
whereas the maxima of the films are slightly red-shifted and
appear between 519 and 532 nm as a result of a J-aggregation
[45]. Apparently, the aryl substitution on the triene moiety only
affects the absorption bands to a minor extent. The merocya-
nine character of the 1-styryleth-2-enylideneindolones 8 is addi-
tionally supported by quantum chemical calculations on the
DFT level (B3LYP functional, 6-31G* basis set) [40]. The
computed Kohn–Sham frontier molecular orbitals of compound
8a clearly indicate a charge transfer from the aminovinyl
dominated donor fragment in the HOMO to the indolone-
centered LUMO, which is generally responsible for the intense
longest-wavelength absorption band upon optical excitation
(Figure 4).
Figure 5: Absorption and emission spectrum of the dropcasted film of
compound 8a (recorded at room temperature, normalized spectra,
λmax,exc = 490 nm).
In contrast to the deep-red luminescence of both amorphous
films and dyes in the solid state with sharp bands between 644
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Beilstein J. Org. Chem. 2014, 10, 599–612.
Table 4: Selected absorption and emission data of the 1-styryleth-2-enylidene indolones 8 and the 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-
ylidene indolones 10.
Absorption
Emission
Entry
Compound
Stokes shift
λmax,abs [nm]
(ε, L·mol−1·cm−1)a
λmax,abs [nm] (film)b λmax,em [nm] (film)b
Δ
[cm−1]c (film)
1
2
8a
8b
510 (23600)
330 (20100)
290 (33200)
519
523
655
662
4000
4000
513 (24200)
327 (25800)
267 (56300)
3
4
8c
8d
513 (17900)
259 (40200)
525
527
665
665
4000
3900
517 (21500)
298 (39700)
265 (51300)
5
6
7
8
9
8e
522 (14900)
317 (29300)
532
601
623
599
604
665
–
3800
10a
10b
10c
10d
587 (33600)
290 (20400)
–
–
–
–
592 (57500)
276 (51400)
–
577 (30200)
257 (66400)
–
592 (34000)
375 (15200)
269 (36100)
–
10
10e
597 (50900)
373 (40300)
266 (37300)
609
–
–
11
12
10f
591 (28700)
604
607
–
–
–
–
10g
597 (39400)
376 (20400)
276 (40700)
13
10h
563 (68900)
345 (24500)
617
572 (sh)
–
–
aRecorded in dichloromethane. bPrepared by dropcasting. cΔ = λmax,abs−1 − λmax,em−1 [cm−1].
The 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylidene-
indolones 10a–g are dark-blue to black solids and display in di-
chloromethane solutions broad unstructured longest wave-
length absorption bands in a range from 577 to 597 nm with
high molar extinction coefficients. As a consequence of
J-aggregation the absorption bands of the films are red-shifted
and appear between 599 and 623 nm (Table 4, Figure 6). The
benzothiazol-terminated merocyanine 10h displays in dichloro-
methane solution a hypsochromically shifted absorption band at
563 nm with the highest molar extinction coefficient (Table 4,
entry 13), yet for the amorphous film the most pronounced
bathochromic shift in the series of the merocyanines 10
(Figure 7). In the solid state a merocyanine characteristic
metallic green luster can be seen. Again, the aryl substitution on
Figure 6: Absorption spectrum of the dropcasted film of compound
10d (recorded at room temperature, normalized spectrum).
the triene moiety only affects the absorption bands to a minor
extent.
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Beilstein J. Org. Chem. 2014, 10, 599–612.
along the triene axis in the molecule, which generates the
intense longest wavelength absorption band upon optical excita-
tion (Figure 8). While the phenyl substituents on the triene
chromophore largely contribute to shorter wavelength absorp-
tion bands, the tosyl moiety does not display any coefficient
density in the FMOs and, therefore, qualifies as a favorable
electronic innocent bridge for ligating other chromophores to
this novel class of merocyanines.
Figure 7: Absorption spectra of compound 10h in dichloromethane
(right trace) and of the dropcasted film (left trace) (recorded at room
temperature, normalized spectrum).
For elucidation of the absorption characteristics of the 4-(1,3,3-
trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones 10, a
thorough geometry optimization of the ground-state structure of
compound 10a was performed using Gaussian09 [50] with the
B3LYP functional [51-55] and the Pople 6-311G(d,p) basis set
[56]. For a better comparison with the experimentally deter-
mined solution spectrum the calculation was carried out using
the Polarizable Continuum Model (PCM) applying dichloro-
methane as a solvent [57]. The minimum structure of 10a was
unambiguously confirmed by an analytical frequency analysis.
The optimized structure of 10a was submitted to a TD-DFT
calculation for assigning the experimentally determined
absorption characteristics (Table 5). Therefore, the hybrid
exchange–correlation functional CAM-B3LYP [58] was imple-
mented and a non-equilibrium solvation [59-63] for the state-
specific solvation of the vertical excitation was included.
The computations reveal that the longest wavelength absorp-
tion maximum appears at 541 nm, i.e., at a comparable energy
as in the experimental spectrum. This transition is exclusively
dominated by the HOMO–LUMO transition. The computed
Kohn–Sham frontier molecular orbitals of structure 10a clearly
indicate the charge-transfer character from HOMO to LUMO
Figure 8: DFT-computed (B3LYP functional, 6-311G(d,p) basis set)
FMOs (HOMO, bottom; LUMO (center), and LUMO+2 (top)) of mero-
cyanine 2E,4Z,6Z-10a.
Table 5: Experimental and TD-DFT computed (CAM-B3LYP 6-311G(d,p)) absorption maxima of the 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-
ylideneindolone 2E,4Z,6Z-10a.
Structure
Experimental λmax,abs [nm]a
Computed λmax,abs [nm]
Dominant contributions
290
–
286
345
541
HOMO → LUMO+2 (56%)
HOMO−1 → LUMO (89%)
HOMO → LUMO (96%)
2E,4Z,6Z-10a
587
aRecorded in dichloromethane.
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Beilstein J. Org. Chem. 2014, 10, 599–612.
Conclusion
(CH), 121.3 (CH), 122.2 (CH), 124.3 (Cquat), 124.8 (Cquat),
In conclusion, we enabled the diversity-oriented synthesis of 126.4 (CH), 127.4 (CH), 127.8 (CH), 128.0 (CH), 128.9 (CH),
novel triene merocyanines with intense bathochromic absorp- 129.5 (CH), 130.0 (CH), 131.2 (CH), 132.9 (Cquat), 133.2
tion by a consecutive three-component insertion–coupling–ad- (Cquat), 140.2 (Cquat), 140.4 (Cquat), 140.5 (Cquat), 141.4
dition sequence in good to excellent yields. While the (Cquat), 144.4 (Cquat), 145.5 (Cquat), 153.9 (Cquat), 165.4
N-substituent on the indolone moiety exerts minute electronic (Cquat); additional signals for the minor diastereomer: δ 26.3
differences in the dipolar intermediate, which is responsible for (CH3), 37.4 (CH3), 50.1 (Cquat), 107.2 (Cquat), 107.2 (CH),
the bifurcation as supported by computational studies, enamine 120.1 (CH2), 120.8 (CH), 121.6 (CH), 122.5 (CH), 126.5 (CH),
nucleophiles favorably lead to 1-styryleth-2-enylidenein- 127.5 (CH), 128.2 (CH), 128.3 (CH), 128.4 (CH), 128.6 (CH),
dolones diastereomers for N-methyl-substituted anilides. The 129.0 (CH), 129.5 (CH), 132.5 (CH), 154.4 (Cquat), 167.5
S,N-ketene acetal derived from dimethyl benzothiazolium (Cquat); EIMS (70 eV) m/z (% relative intensity): 544
favors the formation of the corresponding 4-(3- ([37Cl–M]+, 23), 542 ([35Cl–M]+, 100), 382 ([C25H1835ClNO]+,
methylbenzo[d]thiazol-2(3H)-ylidene)but-2-en-1-ylidenein- 22), 158 ([C11H12N]+, 38); IR (KBr) : 3080, 3053, 2968,
dolone. 4-(1,3,3-Trimethylindolin-2-ylidene)but-2-en-1- 2924, 2862, 1654, 1598, 1541, 1471, 1456, 1438, 1413, 1373,
ylideneindolones are also the exclusive products for N-tosyl- 1352, 1336, 1288, 1263, 1236, 1203, 1138, 1122, 1085, 1074,
anilides as starting materials. As a result of aggregation-induced 1024, 1009, 958, 925, 893, 846, 825, 799, 732, 711, 693, 650,
luminescence, 1-styryleth-2-enylideneindolones display in films 619 cm−1; UV–vis (CH2Cl2) λmax, nm (ε): 259 (40200), 513
and in the solid state distinct and intensive deep-red emission (17900); HRMS (m/z) calcd for C36H3135ClN2O: 542.2125;
upon excitation of the longest wavelength absorption band. found: 542.2119; Anal. calcd for C36H31ClN2O (543.1): C,
4-(1,3,3-Trimethylindolin-2-ylidene)but-2-en-1-ylidene- 79.61; H, 5.75; N, 5.16; found: C, 79.80; H, 6.02; N, 5.16.
indolones neither luminesce in solution nor in the solid state
upon electronic excitation, yet, they display broad absorption 10a: In a flame-dried and argon-flushed Schlenk tube
bands and computations suggest, that novel types of panchro- iodophenylanilide 5b (501 mg, 1.00 mmol), alkyne 6a (112 mg,
matic absorbing bichromophores should be readily available by 1.10 mmol), and dry, degassed THF (5 mL) were placed. After
ligating the second chromophore via the electronically nonper- the addition of PdCl2(PPh3)2 (35 mg, 0.05 mmol), and CuI
turbing N-sulfonyl moiety. Synthetic, photophysical, and (10 mg, 0.05 mmol), diisopropylethylamine (1.7 mL, 10 mmol)
computational studies addressing aggregating broad-band was added and the reaction mixture was stirred at rt for 16 h.
absorbing bichromophores are currently underway.
Then, the enamine 7 (346 mg, 2.00 mmol) and EtOH (2 mL)
were added. The sealed reaction vessel was placed in a ther-
mostatted oil bath at 80 °C and stirred for 48 h. After cooling to
Experimental
8c: In a flame-dried and argon-flushed Schlenk tube the rt the solvents were removed in vacuo and the residue was chro-
iodophenylanilide 5a (361 mg, 1.00 mmol), alkyne 6c (150 mg, matographed on silica gel (hexane/EtOAc 4:1) to give the
1.10 mmol), and dry, degassed THF (5 mL) were placed. After 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolone
the addition of PdCl2(PPh3)2 (35 mg, 0.05 mmol), and CuI 10a (636 mg, 98%) as bluish-black solid. Mp 141 °C; 1H NMR
(10 mg, 0.05 mmol), diisopropylethylamine (1.7 mL, 10 mmol) (300 MHz, CDCl3) δ 0.85 (s, 6H), 2.30 (s, 3H), 2.31 (s, 3H),
was added and the reaction mixture was stirred at rt for 16 h. 4.68 (d, J = 1.4 Hz, 1H), 5.70 (d, J = 7.3 Hz, 1H), 6.27 (d, J =
Then, Fischer’s base (7, 346 mg, 2.00 mmol), and EtOH (2 mL) 7.8 Hz, 1H), 6.56 (t, J = 7.8 Hz, 1H), 6.74 (dt, J = 7.3, 0.7 Hz,
were added. The sealed reaction vessel was placed in a ther- 1H), 6.90–7.22 (m, 12H), 7.32 (dd, J = 7.7, 1.8 Hz, 2H), 7.66
mostatted oil bath at 80 °C and stirred for 48 h. After cooling to (d, J = 1.4 Hz, 1H), 7.80 (dd, J = 8.2, 2.2 Hz, 1H), 7.86 (d, J =
rt the solvents were removed in vacuo and the residue was chro- 7.8 Hz, 1H), 7.92 (d, J = 8.4 Hz, 2H); 13C NMR (75 MHz,
matographed on silica gel (hexane/EtOAc 9:1) to give the CDCl3) δ 21.9 (CH3), 29.4 (CH3), 34.4 (CH3), 46.7 (Cquat),
1-styryleth-2-enylideneindolone 8c (441 mg, 0.82 mmol, 82%) 94.3 (CH), 107.4 (CH), 113.0 (CH), 118.2 (Cquat), 120.8 (CH),
as violet solid, dr = 56:44. Mp 228 °C; 1H NMR (300 MHz, 121.8 (CH), 122.7 (CH), 123.4 (CH), 124.6 (CH), 125.4 (Cquat),
CDCl3) δ 1.46–1.58 (m, 6H), 2.75–3.29 (m, 6H), 4.92 (0.56H), 127.3 (CH), 127.8 (CH), 127.9 (CH), 128.1 (CH), 128.7 (CH),
5.61 (s, 0.56H), 5.78 (s, 0.56H), 6.25 (d, J = 7.8 Hz, 0.56H), 128.9 (CH), 129.1 (CH), 129.3 (CH), 129.5 (CH), 129.8 (CH),
6.40–6.56 (m, 2H), 6.60–6.67 (m, 1H), 6.80–7.29 (m, 11H), 136.4 (Cquat), 137.1 (Cquat), 138.2 (Cquat), 140.7 (Cquat), 144.4
7.32 (d, J = 7.4 Hz, 0.56H); additional signals for the minor dia- (Cquat), 145.1 (Cquat), 146.4 (Cquat), 153.9 (Cquat), 155.9
stereomer: δ 4.61 (s, 0.44H), 5.33 (s, 0.44H), 6.73 (d, J = 7.5 (Cquat), 161.8 (Cquat), 165.9 (Cquat). EIMS (70 eV) m/z (% rela-
Hz, 0.88H), 7.49 (d, J = 7.1 Hz, 0.44H); 13C NMR (75 MHz, tive intensity): 648 ([M]+, 4), 493 ([C35H29N2O]+, 6), 334 (31),
CDCl3) δ 25.2 (CH3), 26.2 (CH3), 36.2 (CH3), 49.4 (Cquat), 321 (11), 306 (11), 291 (12), 222 (11), 218 (37), 144 (33), 142
106.8 (Cquat), 107.1 (CH), 107.9 (CH), 115.0 (CH2), 120.4 (47), 132 (27), 127 (22), 117 (16), 105 (53), 91 (100); IR (KBr)
610

Beilstein J. Org. Chem. 2014, 10, 599–612.
15.Kay, A. J.; Woolhouse, A. D.; Gainsford, G. J.; Haskell, T. G.;
Barnes, T. H.; McKinnie, I. T.; Wyss, C. P. J. Mater. Chem. 2001, 11,
996–1002. doi:10.1039/B008316J
: 3051, 2964, 2924, 2862, 1691, 1577, 1504, 1485, 1465,
1454, 1442, 1400, 1367, 1334, 1315, 1290, 1246, 1217, 1176,
1161, 1130, 1161, 1130, 1116, 1085, 1076, 1060, 1018, 1001,
960, 943, 925, 873, 854, 815, 773, 742, 725, 686, 663, 651, 611
cm−1; UV–vis (CH2Cl2) λmax, nm (ε): 290 nm (20400), 587
(33600); Anal. calcd for C42H36N2O3S (648.8): C, 77.75; H,
5.59; N, 4.32; found: C, 77.58; H, 5.41; N, 4.29.
16.Würthner, F. Synthesis 1999, 2103–2113. doi:10.1055/s-1999-3635
17.Würthner, F.; Yao, S. J. Org. Chem. 2003, 68, 8943–8949.
doi:10.1021/jo0351670
18.Yao, S.; Beginn, U.; Gress, T.; Lysetska, M.; Würthner, F.
J. Am. Chem. Soc. 2004, 126, 8336–8348. doi:10.1021/ja0496367
19.Müller, T. J. J. Diversity-oriented Synthesis of Chromophores by
Combinatorial Strategies and Multi-component Reactions. In Functional
Organic Materials. Syntheses, Strategies, and Applications;
Müller, T. J. J.; Bunz, U. H. F., Eds.; Wiley-VCH: Weinheim, 2007;
pp 179–223. doi:10.1002/9783527610266.ch5
Supporting Information
Supporting Information File 1
20.Müller, T. J. J.; D'Souza, D. M. Pure Appl. Chem. 2008, 80, 609–620.
doi:10.1351/pac200880030609
Experimental procedures, spectroscopic and analytical data,
and copies of NMR spectra of compounds 8 and 10.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-10-51-S1.pdf]
21.Yi, C.; Blum, C.; Liu, S.-X.; Frei, G.; Neels, A.; Stoeckli-Evans, H.;
Leutwyler, S.; Decurtins, S. Tetrahedron 2008, 64, 9437–9441.
doi:10.1016/j.tet.2008.07.084
22.Samanta, A.; Vendrell, M.; Das, R.; Chang, Y.-T. Chem. Commun.
2010, 46, 7406–7408. doi:10.1039/C0CC02366C
23.Vendrell, M.; Lee, J.-S.; Chang, Y.-T. Curr. Opin. Chem. Biol. 2010, 14,
383–389. doi:10.1016/j.cbpa.2010.02.020
Acknowledgments
The authors cordially thank the Fonds der Chemischen Indus-
24.Main, M.; Snaith, J. S.; Meloni, M. M.; Jauregui, M.; Sykes, D.;
Faulkner, S.; Kenwright, A. M. Chem. Commun. 2008, 5212–5214.
doi:10.1039/B810083G
trie for the generous support.
References
25.Briehn, C. A.; Bäuerle, P. Chem. Commun. 2002, 1015–1023.
doi:10.1039/B108846G
1. Müller, T. J. J.; Bunz, U. H. F., Eds. Functional Organic Materials.
Syntheses, Strategies, and Applications; Wiley-VCH Verlag GmbH &
Co. KGaA: Weinheim, 2007. doi:10.1002/9783527610266
2. Müllen, K.; Wegner, G., Eds. Electronic Materials: The Oligomer
Approach; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 1998.
doi:10.1002/9783527603220
26.Briehn, C. A.; Schiedel, M.-S.; Bonsen, E. M.; Schuhmann, W.;
Bäuerle, P. Angew. Chem., Int. Ed. 2001, 40, 4680–4683.
doi:10.1002/1521-3773(20011217)40:24<4680::AID-ANIE4680>3.0.CO
;2-X
27.Willy, B.; Müller, T. J. J. Curr. Org. Chem. 2009, 13, 1777–1790.
doi:10.2174/138527209789630479
3. Müllen, K.; Scherf, U., Eds. Organic Light-Emitting Diodes – Synthesis,
Properties, and Applications; Wiley-VCH Verlag GmbH & Co. KGaA:
Weinheim, 2006. doi:10.1002/3527607986
28.Willy, B.; Müller, T. J. J. ARKIVOC 2008, No. i, 195–208.
doi:10.3998/ark.5550190.0009.107
29.Müller, T. J. J. Synthesis 2012, 159–174. doi:10.1055/s-0031-1289636
30.Muschelknautz, C.; Mayer, B.; Rominger, F.; Müller, T. J. J.
Chem. Heterocycl. Compd. 2013, 49, 860–871.
See for a recent monograph.
4. Kim, E.; Park, S. B. Chem.–Asian J. 2009, 4, 1646–1658.
doi:10.1002/asia.200900102
doi:10.1007/s10593-013-1320-3
5. Cairo, C. W.; Key, J. A.; Sadek, C. M. Curr. Opin. Chem. Biol. 2010,
14, 57–63. doi:10.1016/j.cbpa.2009.09.032
31.Muschelknautz, C.; Frank, W.; Müller, T. J. J. Org. Lett. 2011, 13,
2556–2559. doi:10.1021/ol200655s
6. Wagenknecht, H.-A. Ann. N. Y. Acad. Sci. 2008, 1130, 122–130.
doi:10.1196/annals.1430.001
32.D'Souza, D. M.; Muschelknautz, C.; Rominger, F.; Müller, T. J. J.
Org. Lett. 2010, 12, 3364–3367. doi:10.1021/ol101165m
33.Willy, B.; Müller, T. J. J. Org. Lett. 2011, 13, 2082–2085.
doi:10.1021/ol2004947
7. Hamer, F. M. The Cyanine Dyes and Related Compounds;
Interscience: New York, London, 1964.
8. Mishra, A.; Behera, R. K.; Behera, P. K.; Mishra, B. K.; Behera, G. B.
Chem. Rev. 2000, 100, 1973–2012. doi:10.1021/cr990402t
9. Kulinich, A. V.; Ishchenko, A. A. Russ. Chem. Rev. 2009, 78, 141–164.
doi:10.1070/RC2009v078n02ABEH003900
34.Willy, B.; Müller, T. J. J. Eur. J. Org. Chem. 2008, 4157–4168.
doi:10.1002/ejoc.200800444
35.Willy, B.; Dallos, T.; Rominger, F.; Schönhaber, J.; Müller, T. J. J.
Eur. J. Org. Chem. 2008, 4796–4805. doi:10.1002/ejoc.200800619
36.Braun, R. U.; Zeitler, K.; Müller, T. J. J. Org. Lett. 2001, 3, 3297–3300.
doi:10.1021/ol0165185
10.Peng, X.-H.; Zhou, X.-F.; Carroll, S.; Geise, H. J.; Peng, B.;
Dommisse, R.; Esmans, E.; Carleer, R. J. Mater. Chem. 1996, 6,
1325–1333. doi:10.1039/JM9960601325
37.Braun, R. U.; Müller, T. J. J. Synthesis 2004, 2391–2406.
doi:10.1055/s-2004-831192
11.Shirinian, V. Z.; Shimkin, A. A. Top. Heterocycl. Chem. 2008, 14,
75–105. doi:10.1007/7081_2007_110
38.Schönhaber, J.; Müller, T. J. J. Org. Biomol. Chem. 2011, 9,
6196–6199. doi:10.1039/C1OB05703K
12.Kovtun, Yu. P.; Prostota, Ya. O.; Shandura, M. P.; Poronik, Ye. M.;
Tolmachev, A. I. Dyes Pigm. 2004, 60, 215–221.
39.D'Souza, D. M.; Kiel, A.; Herten, D. P.; Rominger, F.; Müller, T. J. J.
Chem.–Eur. J. 2008, 14, 529–547. doi:10.1002/chem.200700759
40.D'Souza, D. M.; Rominger, F.; Müller, T. J. J. Angew. Chem., Int. Ed.
2005, 44, 153–158. doi:10.1002/anie.200461489
doi:10.1016/S0143-7208(03)00152-9
13.Kovtun, Y. P.; Prostota, Y. O.; Tolmachev, A. I. Dyes Pigm. 2003, 58,
83–91. doi:10.1016/S0143-7208(03)00038-X
14.Yagi, S.; Maeda, K.; Nakazumi, H. J. Mater. Chem. 1999, 9,
2991–2997. doi:10.1039/A905098A
611

Beilstein J. Org. Chem. 2014, 10, 599–612.
41.Schönhaber, J.; Frank, W.; Müller, T. J. J. Org. Lett. 2010, 12,
4122–4125. doi:10.1021/ol101709p
License and Terms
42.Karpov, A. S.; Müller, T. J. J. Org. Lett. 2003, 5, 3451–3454.
doi:10.1021/ol035212q
This is an Open Access article under the terms of the
Creative Commons Attribution License
43.Karpov, A. S.; Müller, T. J. J. Synthesis 2003, 2815–2826.
doi:10.1055/s-2003-42480
(http://creativecommons.org/licenses/by/2.0), which
permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
44.Spartan ’08, Version 1.2.0; Wavefunction Inc.: Irvine, CA, 2008.
As implemented in the software.
45.Möbius, D. Adv. Mater. 1995, 7, 437–444.
doi:10.1002/adma.19950070503
46.Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Chem. Soc. Rev. 2011, 40,
5361–5388. doi:10.1039/C1CS15113D
The license is subject to the Beilstein Journal of Organic
Chemistry terms and conditions:
47.Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Chem. Commun. 2009,
4332–4353. doi:10.1039/B904665H
(http://www.beilstein-journals.org/bjoc)
48.Davydov, A. S. Theory of Molecular Excitons; Plenum: New York,
1971.
The definitive version of this article is the electronic one
which can be found at:
49.Pope, M.; Swenberg, C. E. Electronic Processes in Organic Crystals;
Clarendon Press: Oxford, 1982.
doi:10.3762/bjoc.10.51
50.Gaussian 09, Revision A.02; Gaussian, Inc.: Wallingford, CT, 2009.
51.Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785–789.
doi:10.1103/PhysRevB.37.785
52.Becke, A. D. J. Chem. Phys. 1993, 98, 1372–1377.
doi:10.1063/1.464304
53.Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652.
doi:10.1063/1.464913
54.Kim, K.; Jordan, K. D. J. Phys. Chem. 1994, 98, 10089–10094.
doi:10.1021/j100091a024
55.Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J.
J. Phys. Chem. 1994, 98, 11623–11627. doi:10.1021/j100096a001
56.Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys.
1980, 72, 650–654. doi:10.1063/1.438955
57.Scalmani, G.; Frisch, M. J. J. Chem. Phys. 2010, 132, 114110.
doi:10.1063/1.3359469
58.Yanai, T.; Tew, D. P.; Handy, N. C. Chem. Phys. Lett. 2004, 393,
51–57. doi:10.1016/j.cplett.2004.06.011
59.Berezhkovskii, A. M. Chem. Phys. 1992, 164, 331–339.
doi:10.1016/0301-0104(92)87072-H
60.Cammi, R.; Tomasi, J. Int. J. Quantum Chem., Quantum Chem. Symp.
1995, 56 (Suppl. 29), 465–474. doi:10.1002/qua.560560850
61.Mennucci, B.; Cammi, R.; Tomasi, J. J. Chem. Phys. 1998, 109,
2798–2807. doi:10.1063/1.476878
62.Li, X.-Y.; Fu, K.-X. J. Comput. Chem. 2004, 25, 500–509.
doi:10.1002/jcc.10377
63.Cammi, R.; Corni, S.; Mennucci, B.; Tomasi, J. J. Chem. Phys. 2005,
122, 104513. doi:10.1063/1.1867373
612