3-Phenothiazinyl propiolates – Fluorescent electrophores by Sonogashira coupling of ethyl propiolate

Article abstract of DOI:10.1016/j.dyepig.2017.04.049

Fluorescent ethyl 3-phenothiazinyl propiolates with reversible Nernstian oxidation potentials were efficiently synthesized by an improved Sonogashira coupling of aryl iodides and ethyl propiolate. The versatility of this modified alkynylation was illustrated by 13 ethyl 3-arylpropiolates in mostly excellent yields with a broad substrate scope. In addition to reversible one-electron oxidations, the title compounds reveal large Stokes shifts, high fluorescence quantum yields, and solvatochromic emission. The photophysical characteristics were corroborated and rationalized by DFT and TD-DFT calculations.

Full text of DOI:10.1016/j.dyepig.2017.04.049

Dyes and Pigments 143 (2017) 308e316
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3-Phenothiazinyl propiolates e Fluorescent electrophores by
Sonogashira coupling of ethyl propiolate
*
€
Alissa C. Gotzinger, Carina S. Michaelis, Thomas J.J. Müller
€
€
Institut für Organische Chemie und Makromolekulare Chemie, Heinrich-Heine-Universitat Düsseldorf, Universitatsstraße 1, D-40225, Düsseldorf, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Fluorescent ethyl 3-phenothiazinyl propiolates with reversible Nernstian oxidation potentials were
efficiently synthesized by an improved Sonogashira coupling of aryl iodides and ethyl propiolate. The
versatility of this modified alkynylation was illustrated by 13 ethyl 3-arylpropiolates in mostly excellent
yields with a broad substrate scope. In addition to reversible one-electron oxidations, the title com-
pounds reveal large Stokes shifts, high fluorescence quantum yields, and solvatochromic emission. The
photophysical characteristics were corroborated and rationalized by DFT and TD-DFT calculations.
© 2017 Published by Elsevier Ltd.
Received 17 March 2017
Received in revised form
22 April 2017
Accepted 23 April 2017
Available online 27 April 2017
Keywords:
Alkynoates
Cross-coupling
Cyclic voltammetry
DFT calculations
Fluorescence
Phenothiazines
Redox systems
Solvatochromism
1. Introduction
In principle, Sonogashira coupling of aryl halides with alkyl pro-
piolates as alkynyl partner circumvents these problems, thus
Phenothiazines bearing conjugated
p
-substituents in 3- and/or
considerably broadening functional group tolerance and substrate
scope. However, electron-poor alkynes such as alkyl propiolates are
often less reactive and tend to decompose or undergo self-
condensation [8]. In the past years, several approaches have been
published that address these issues e. g. by in situ generation of
alkynylzinc [9] or lithium-indium [10] reagents or by replacement
of the aryl halide component by diaryliodonium salts [11] or aryl-
boronic esters [12] To the best of our knowledge, and to our sur-
prise, no direct and general approach to aryl propiolates from aryl
halides and alkyl propiolates has been reported to date [13]. We
therefore set out to develop a straightforward Sonogashira coupling
with ethyl propiolate, compensating its reduced reactivity and
diminished stability by carefully adjusting the reaction conditions.
In addition, we report the application of this improved methodol-
ogy to the synthesis of 3-phenothiazinyl ethyl propiolates, inter-
esting novel functional chromophores.
7-position present interesting classes of functional chromophores
[1] that are both luminescent and redox active [2]. In particular,
alkynylated phenothiazines [3] have been employed to decorate
gold [4] or zinc and iron surfaces [5] with functional reversible
redox systems. These systems were readily accessible by Pd-
catalyzed alkynylation reactions. However, for synthetic trans-
formations and extended functionalizations, electrophilic three-
carbon building blocks such as 3-aryl propiolates, which contain
an ester moiety and a conjugated triple bond, are particularly
desirable. In heterocycle syntheses, aryl propiolates are for instance
particularly valuable as Michael systems [6] or as dienophiles. Most
commonly, 3-aryl propiolates are synthesized by the reaction of
alkynyl metal species with chloroformates [7]. This methodology,
however, only has a limited substrate scope as many functional
groups are incompatible with the strongly basic reaction conditions
required for the metalation of terminal alkynes. Further limitations
arise from the limited availability of the alkyne starting materials.
2. Results and discussion
2.1. Synthesis of ethyl aryl propiolates by Sonogashira coupling
For the coupling of aryl iodides 1 a quick screening of the
* Corresponding author.
E-mail address: thomasjj.mueller@uni-duesseldorf.de (T.J.J. Müller).
http://dx.doi.org/10.1016/j.dyepig.2017.04.049
0143-7208/© 2017 Published by Elsevier Ltd.

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A.C. Gotzinger et al. / Dyes and Pigments 143 (2017) 308e316
309
Table 1
could also be employed on a 10 mmol scale without any significant
loss in isolated yield of compound 3a (Table 1, entry 4). For com-
parison, the reaction was repeated under the optimized condition
without the use of a syringe pump and upon adding the entire
amount of ethyl propiolate (2) at the beginning of the reaction. This
resulted in almost no conversion of 1a with a drastically reduced
yield of 3a of only 3% (Table 1, entry 5).
Selected optimization reactions for the synthesis of ethyl p-tolylpropiolate 3a.
With these optimized conditions in hand, we examined the
scope of the reaction (Table 2).
entry
T [ꢀC]
t [h]
remark
yield of 3a (%)a
To our delight, the functional group tolerance of the reaction
proved to be excellent, giving high to nearly quantitative isolated
yields for electron-rich (Table 2, entries 1, 4, and 6), electron-poor
(Table 2, entries 3, 5, and 10) and sterically hindered substrates
(Table 2, entries 6 and 8). The use of 4-iodopyridine (1g) resulted in
full conversion of the substrate but the desired product 3g was only
isolated in moderate yield, presumably due to the propensity of 3g
for polymerization.
The reaction was additionally employed for the synthesis of
phenothiazinyl propiolates, furnishing the desired products 3k and
3l in moderate to high yields. In the case of 3l, the carbon-iodine
bond of the bromo-iodo substrate (1l) could be selectively
addressed, leaving the bromo functionality intact for possible
further transformations. Using 3,7-diiodophenothiazine 1m, phe-
nothiazinyl bis(ethyl propiolate) 3m was also accessible by double
Sonogashira coupling (Scheme 1).
1
2
3
4
5
90
40
40
40
40
1
traces
88
96
94
3
16
20
20
20
10 mmol scale
without syringe pump
a
Isolated yields after chromatography on silica gel.
stoichiometry, catalyst system, base, and solvent gave the use of 2
equivs of ethyl propiolate (2), catalytic amounts of PdCl2(PPh3)2 and
copper(I) iodide as well as 2 equivs of potassium carbonate in DME
as most promising for further optimization studies. As we observed
a rapid consumption of ethyl propiolate (2) during the course of the
reaction, we reasoned that a low stationary concentration by a slow
addition of 2 via a syringe pump should be beneficial for the
coupling product formation. We chose the Sonogashira coupling of
4-iodotoluene (1a) with ethyl propiolate (2) to give ethyl p-tolyl
propiolate (3a) as a model reaction (Table 1).
While an addition over the course of 1 h at 90 ꢀC gave only traces
of the desired product 3a (Table 1, entry 1), we were delighted to
find that decreasing the temperature to 40 ꢀC with a prolonged
addition over 16 h already resulted in a yield of 88% of 3a (Table 1,
entry 2). Extending the ethyl propiolate addition to 20 h finally
resulted in complete conversion and nearly quantitative isolation of
compound 3a (Table 1, entry 3). The optimized reaction conditions
2.2. Photophysical properties of ethyl 3-phenothiazinyl propiolates
The synthesized ethyl phenothiazinyl propiolates 3kem are
yellow in solution and show pronounced fluorescence upon irra-
diation with UV light (Fig. 1).
The photophysical properties of all three compounds were
studied by absorption and emission spectroscopy in
Table 2
Synthesized ethyl aryl popiolates 3.
entry
(hetero)aryl iodide 1
yield of propiolate 3 (%)
1
2
3
4
5
6
7
8
(hetero)aryl ¼ 4-Tol (1a)
3a (97, 94a)
3b (86)
3c (88)
3d (97)
3e (83)
3f (83)
3g (50)
3h (92)
3i (96)
(hetero)aryl ¼ Ph (1b)
(hetero)aryl ¼ 4-AcC6H4 (1c)
(hetero)aryl ¼ 4-MeOC6H4 (1d)
(hetero)aryl ¼ 4-F3CC6H4 (1e)
(hetero)aryl ¼ 2-MeOC6H4 (1f)
(hetero)aryl ¼ 4-pyridyl (1g)
(hetero)aryl ¼ 9-phenanthryl (1h)
(hetero)aryl ¼ 2-naphthyl (1i)
(hetero)aryl ¼ 3-ClC6H4 (1j)
9
10
11
12
3j (93)
3k (82)
3l (68)
(hetero)aryl ¼ 10-hexyl-10H-phenothiazin-3-yl (1k)
(hetero)aryl ¼ 7-brom-10-hexyl-10H-phenothiazin-3-yl (1l)
a
Prepared on a 10.0 mmol scale.
Scheme 1. Synthesis of diethyl-3,3'-(10-hexyl-10H-phenothiazin-3,7-diyl)dipropiolate (3m).

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310
and 372 nm, only the absorption in dichloromethane is shown
exemplarily. The emission band, however, shows a pronounced
dependency on the solvent polarity, spanning a range from 465 nm
in cyclohexane to 542 nm in N,N-dimethyl formamide (Table 4).
A Lippert plot [14] of the respective Stokes shifts Dneagainst the
orientation polarizabilities
Df of the solvent gives an excellent
linear correlation with a fit of r2 ¼ 0.95 (Fig. 5).
Orientation polarizabilities were calculated according to equa-
tion (1) from the relative permittivity εr and the optical refractive
Fig. 1. Fluorescence of phenothiazinyl propiolates 3kel (left to right, lexc ¼ 365 nm,
hand-held UV lamp).
dichloromethane solutions (Table 3).
All compounds show several absorption maxima (Fig. 2), two in
the UV at 235e244 and 274e291 nm, respectively. The longest
wavelength absorption band can be found between 366 nm (3l)
and 391 nm (3m). For compound 3l, an additional absorption
maximum appears at 337 nm. The highest molar decadic extinction
coefficient is found for compound 3m at 291 nm (48500 M
ꢁ1cmꢁ1).
The emission maxima lie between 514 nm for dipropiolate 3m
and 526 nm for 7-unsubstituted compound 3k (Fig. 2). This results
in remarkably large Stokes shifts of 6100e7900 cmꢁ1, which can be
explained to some extent by the push-pull-character of the
acceptor-substituted phenothiazine chromophore. The introduc-
tion of a weakly electron-withdrawing bromo substituent (com-
pound 3l) or a second propiolic ester moiety (compound 3m) in
position 7 of the phenothiazine core mitigates this effect, causing a
reduction of the Stokes shifts in comparison to compound 3k.
Relative fluorescence quantum yields were determined with
coumarin 153 as a standard (Ff ¼ 0.53 in ethanol) and show an
inverse trend as quantum yields increase from 0.50 for parent
compound 3k over 0.61 for bromo compound 3l to 0.66 for
dipropiolate 3m.
Fig. 2. UV/Vis absorption (solid lines) and emission (dashed lines) spectra of pheno-
thiazinyl propiolates 3kel. Recorded in dichloromethane, T ¼ 293 K.
It is evident upon eyesight that the emission properties of the
synthesized phenothiazinyl propiolates 3kem depend on the sol-
vent system. We therefore performed a solvatochromism study,
using ethyl 3-(10-hexyl-10H-phenothiazin-3-yl)-propiolate (3k) as
a model system. With increasing solvent polarity, the emission is
shifted bathochromically, ranging from blue fluorescence in
cyclohexane to yellow-green fluorescence in N,N-dimethyl form-
amide (Fig. 3).
This positive emission solvochromicity was further studied by
recording the absorption and emission spectra in the respective
solvents (Fig. 4).
Fig. 3. Fluorescence of 3k with variable solvent polarity (left to right: cyclohexane,
toluene, ethyl acetate, dichloromethane, acetone, N,N-dimethyl formamide, acetoni-
trile; lexc ¼ 365 nm, hand-held UV lamp).
As the absorption band remains almost unchanged between 358
Table 3
Photophysical properties of ethyl phenothiazinyl propiolates 3kem.
b,c
entry
compound
lmax,abs [nm] (ε [
M
ꢁ1cmꢁ1])a
lmax,em [nm] (FF
)
Dne[cmꢁ1
]
1
2
3
3k
3l
3m
240 (20400), 274 (28100), 371 (9000)
244 (18000), 275 (30300), 337 (7800), 366 (7900)
235 (23500), 291 (48500), 391 (12900)
526 (0.50)
515 (0.61)
514 (0.66)
7900
7500
6100
a
Recorded in dichloromethane, T ¼ 293 K, c(3) ¼ 10ꢁ5 M.
b
c
Recorded in dichloromethane, T ¼ 293 K, c(3) ¼ 10ꢁ7 M.
Fluorescence quantum yields were determined relative to coumarin 153 (FF ¼ 0.53) as a standard in ethanol.

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A.C. Gotzinger et al. / Dyes and Pigments 143 (2017) 308e316
311
Table 4
UV/Vis absorption and emission data for compound 3k in seven solvents of different
polarity.
entry solvent
lmax,abs [nm]a lmax,em [nm]b Dne[cmꢁ1
]
1
2
3
4
5
6
7
cyclohexane
toluene
358
368
363
371
369
465
488
502
526
527
539
542
6400
6700
7600
7900
8200
8300
8900
ethyl acetate
dichloromethane
acetone
N,N-dimethyl formamide 372
acetonitrile 366
a
Recorded at T ¼ 293 K, c(3k) ¼ 10ꢁ5 M.
b
Recorded at T ¼ 293 K, c(3k) ¼ 10ꢁ7 M.
2.3. Computations of the electronic structure of ethyl 3-
phenothiazinyl propiolates
The geometries of the electronic ground-state structures were
optimized using Gaussian09 [15] with the hybrid exchange corre-
lation functional CAM-B3LYP [16] and the Pople-311Gþ(d,p) basis
set [17]. As the experimental investigation of the absorption and
emission properties was carried out in dichloromethane solutions,
we employed the polarizable continuum model (PCM) for
dichloromethane as a solvent [18]. All minimum structures were
unambiguously confirmed by analytical frequency analysis.
For determining and rationalizing the absorption characteris-
tics, TD-DFT calculations were then performed, again using PCM for
dichloromethane as solvent. The results reasonably reproduce the
experimentally obtained values. Table 5 summarizes the calculated
and measured absorption maxima. In several cases, more than one
excited state significantly contributes to the absorption band. For
these, all wavelengths are stated.
For all three ethyl 3-phenothiazinyl propiolates 3kem, the
longest wavelength absorption band originates predominatly from
the HOMO-LUMO transition. Fig. 6 exemplarily shows the respec-
tive KohneSham molecular frontier orbitals for parent compound
3k.
A shift in coefficient density from the phenothiazine core
donor to the ester acceptor is apparent, supporting a pronounced
charge-transfer character of the transition. Sufficient overlap is
ensured by coefficient density on the ester-substituted phenyl
ring of the phenothiazine moiety. This interpretation is in good
agreement with the observed large Stokes shift and sol-
vatochromic behavior.
Fig. 4. UV/Vis absorption in dichloromethane (solid line) and emission (dashed lines)
spectra in seven solvents of different polarity (recorded at T ¼ 293 K).
index n of the respective solvent.
εr ꢁ 1
n2 ꢁ 1
Df ¼
ꢁ
(1)
2n2 þ 1
2εr þ 1
The change in dipole moment from the ground to the vibra-
tionally relaxed excited state can be calculated using SI units in the
Lippert-Mataga equation (Equation (2))
2Df
mGÞ2 þ const
(2)
~
na
~
nf
ꢁ
¼
ð
4p
ε0hca3
mE
ꢁ
where nea and nef represent the absorption and emission maxima (in
m
ꢁ1), mE and mG are the dipole moments in the excited and ground
state (in Cm), ε0 (8.8542$10ꢁ12 AsVꢁ1mꢁ1) is the vacuum permit-
tivity constant,
h c
(6.6256$10ꢁ34 Js) is Planck's constant,
(2.9979$108 msꢁ1) is the speed of light and a is the radius of the
solvent cavity occupied by the molecule (in m).
To estimate the radius of the solvent cavity, the Onsager radius
was calculated by a DFT-level optimization of the ground-state
structure of 3k (vide infra), followed by a gas phase calculation of
the molecular volume. Using a value of 5.6 Å (5.6$10ꢁ10 m), the
change in dipole moment was calculated to Dm ¼ 11 D (3.74$10ꢁ29
Cm), clearly indicating a charge transfer character of the involved
electronic transition.
2.4. Electrochemical properties of ethyl 3-phenothiazinyl
propiolates
The electrochemical properties of phenothiazinyl propiolates
3kem were examined using cyclic voltammetry. Fig. 7 exemplarily
shows the cyclic voltammogram for parent compound 3k. All three
compounds exhibit Nernstian reversible one-electron oxidations,
with no second oxidations appearing in the measuring window.
The results are summarized in Table 6. Parent compound 3k ex-
hibits an oxidation potential at 0.88 V, which is higher than that of
literature-known arylethynyl phenothiazines [19]. This is caused by
the electron-withdrawing effect of the ester acceptor functionality.
The introduction of a second propiolate moiety (compound 3l) has
little effect on the oxidation potential while a bromo substituent in
position 7 causes a slight shift to 0.82 V.
3. Conclusions
We have established a straightforward general synthesis of 3-
aryl propiolic esters 3 in nearly quantitative yields with excellent
Fig. 5. Lippert plot for compound 3k (n ¼ 7, r2 ¼ 0.95).

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312
Table 5
TD-DFT calculations (CAM-B3LYP 6-311Gþ(d,p)) of the absorption maxima for phenothiazinyl propiolates 3kem.
structure
experimental lmax,abs [nm]a
calculated lmax,abs [nm]
most dominant contributions
3k
240
274
246
269
275
353
247
270
284
291
353
242
272
276
298
370
HOMO / LUMO þ 3 (49%), HOMO ꢁ 1 / LUMO (21%)
HOMO ꢁ 1 / LUMO (43%), HOMO / LUMO þ 3 (20%)
HOMO / LUMO þ 2 (71%)
371
244
275
HOMO / LUMO (82%)
3l
HOMO / LUMO þ 3 (56%), HOMO ꢁ 1 / LUMO (19%)
HOMO ꢁ 1 / LUMO (40%), HOMO / LUMO þ 3 (20%)
HOMO / LUMO þ 2 (60%), HOMO / LUMO þ 1 (23%)
HOMO / LUMO þ 1 (59%), HOMO / LUMO þ 2 (16%)
HOMO / LUMO (80%)
HOMO ꢁ 2 / LUMO (38%), HOMO-1 / LUMOþ1 (25%), HOMO / LUMOþ2 (11%)
HOMO ꢁ 1 / LUMO (55%), HOMO / LUMO þ 3 (11%)
HOMO / LUMO þ 2 (58%), HOMO / LUMO þ 1 (17%)
HOMO / LUMO þ 1 (70%), HOMO / LUMO þ 2 (18%)
HOMO / LUMO (88%)
337
366
235
291
3m
391
a
Recorded in dichloromethane, T ¼ 293 K, c(3) ¼ 10ꢁ7 M.
Table 6
Oxidation potentials of ethyl phenothiazinyl propiolates 3kem.
entry
compound
E00/þ1 [V]a
1
2
3
3k
3l
3m
0.88
0.82
0.86
a
Recorded in dichloromethane, T ¼ 293 K, 0.1 M electrolyte [B
U
4N][PF6], Pt
working electrode, Pt counter electrode, Ag/AgCl reference electrode (the potentials
were corrected to the internal standard of Fc/Fcþ in CH2Cl2 (E00/þ1 ¼ 450 mV [20])).
consumption of this substrate. The optimized conditions were then
employed for the synthesis of three 3-phenothiazinyl propiolates.
Due to conjugation of the ester acceptor substituent to the
phenothiazine core via the ethynyl bridge, interesting electronic
properties such as large Stokes shifts, emission solvatochromy and
Nernstian reversible one-electron oxidations are found for these
Fig. 6. Selected Kohn-Sham molecular frontier orbitals for 3k.
extended
p-systems. The experimentally obtained results were
corroborated and rationalized by calculations on the DFT and TD-
DFT level of theory. Expansion of the synthetic methodology to-
wards novel one-pot syntheses and application of the functional-
ized phenothiazines for obtaining novel luminescent electrophores
are currently underway.
4. Experimental
4.1. General considerations
All reactions were performed in flame-dried Schlenk tubes un-
der a nitrogen atmosphere. Reaction progress was qualitatively
monitored by thin layer chromatography using silica gel layered
aluminium foil (60 F254 Merck, Darmstadt). For detection, UV light
of wavelengths 254 and 366 was employed. Column chromatog-
raphy was performed using silica gel 60 (Macherey Nagel), mesh
230e400. The commercially available chemicals 1a-j were pur-
chased from Sigma Aldrich, Alfa Aesar, Fluorochem, and ACROS and
were used as received without any further purification. The iodo
phenothiazines 3k-m were prepared according to the literature
[21]. Ethyl propiolate (2) was purchased from Sigma Aldrich. 1H and
13C NMR spectra were measured on a Bruker Avance III-300 or
Fig. 7. Cyclic voltammogram of 3k (recorded in dichloromethane, T ¼ 293 K, 0.1 M
electrolyte [BU N][PF6], Pt working electrode, Pt counter electrode, Ag/AgCl reference
4
electrode).
functional group tolerance by a modified Sonogashira coupling of
aryl iodides 1 and ethyl propiolate (2). The slow addition of pro-
piolate
2 via a syringe pump prevents the unproductive

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313
Bruker Avance III-600 spectrometer. Chemical shifts are given in
ppm ( ) and were referenced to the internal solvent signal: CDCl3
(1H 7.26, 13 77.2) or acetone-d6 (1H 2.50, 13
39.5). Multi-
plicities are stated as: s (singlet), d (doublet), t (triplet), q (quartet),
dd (doublet of doublet), ddd (doublet of doublet of doublet), m
(multiplet). Coupling constants (J) are given in Hz. The assignment
of primary (CH3), secondary (CH2), tertiary (CH) and quaternary
carbon nuclei (Cquat) was made using DEPT-135 spectra. Mass-
spectrometric investigations were carried out in the Department
of Mass Spectrometry of the Institute of Inorganic and Structural
4.2.2. Ethyl 3-phenylpropiolate (3b)
d
According to the GP using iodobenzene (1b), 150 mg
(0.861 mmol, 86%) of 3b were obtained as a colorless oil. Purifica-
tion was performed using manual flash technique (n-hexane/EtOAc
d
C
d
d
C d
50:1). 1H NMR (CDCl3, 300 MHz):
d
1.36 (t, 3 H, CH3, 3JH ¼ 7.1 Hz),
4.30 (q, 2 H, OCH2, 3JH ¼ 7.1 Hz), 7.34e7.40 (m, 2 H, CHAr), 7.42e7.48
(m, 1 H, CHAr), 7.57e7.61 (m, 2 H, CHAr). 13C NMR (CDCl3, 75 MHz):
d
14.2 (CH3), 62.2 (OCH2), 80.8 (Cquat), 86.2 (Cquat), 119.8 (Cquat),
128.7 (CH), 130.7 (CH), 133.1 (CH), 154.3 (Cquat). EI þ MS (m/z (%)):
174 (12) [Mþ], 129 (100) [C9H5Oþ$], 102 (66) [C8H6þ$], 75 (14). FT-IR:
Chemistry, Heinrich-Heine-Universitat Düsseldorf. IR spectra were
n
e[cmꢁ1] ¼ 606 (w), 756 (w), 860 (w), 922 (w), 947 (w), 1020 (m),
€
recorded using a Shimadzu IRAffinity-1. The intensities of the IR
bands are abbreviated as w (weak), m (medium), s (strong). Cyclic
voltammetry experiments were performed under argon in dry and
degassed CH2Cl2 at rt and at scan rates of 100, 250, 500, and
1000 mVsꢁ1 using an electrochemical workstation with [Bu4N]
1070 (w), 1096 (w), 1115 (w) 1175 (s), 1188 (s), 1242 (w), 1285 (s),
1368 (w), 1391 (w), 1445 (w), 1491 (w), 1705 (s), 2210 (w), 2236 (w),
2904 (w), 2940 (w), 2984 (w). HRMS (ESI) (m/z) calcd for
[C11H11O2]þ: 175.0754; Found: 175.0753.
[PF6] (0.1
M
) as electrolyte, a 1 mm platinum disk as working
4.2.3. Ethyl 3-(4-acetylphenyl)propiolate (3c)
electrode, a platinum wire as counter electrode, and a an Ag/AgCl
reference electrode. The potentials were corrected to the internal
standard of Fc/Fcþ in CH2Cl2 (E00/þ1 ¼ 450 mV [20]) Melting points
(uncorrected) were measured using a Büchi Melting Point B-540.
Combustion analyses were measured on a Perkin Elmer Series II
Analyser 2400 in the Institute of Pharmaceutical and Medicinal
Chemistry, Heinrich-Heine University, Düsseldorf.
According to the general procedure using 4-iodoacetophenone
(1c), 191 mg (0.883 mmol, 88%) of 3c were obtained as a colorless
solid. Purification was performed using manual flash technique (n-
hexane/EtOAc 20:1 / 6:1). Mp 84 ꢀC (lit. 82e83.5 ꢀC [10]). 1H NMR
(CDCl3, 300 MHz):
d
1.36 (t, 3 H, CH3, 3JH ¼ 7.1 Hz), 2.61 (s, 3 H, CH3),
4.31 (q, 2 H, OCH2, 3JH ¼ 7.1 Hz), 7.64e7.68 (m, 2 H, CHAr), 7.93e7.96
(m, 2 H, CHAr). 13C NMR (CDCl3, 75 MHz):
d 14.2 (CH3), 26.8 (CH3),
62.5 (OCH2), 83.0 (Cquat), 84.6 (Cquat), 124.4 (Cquat), 128.4 (CH), 133.2
(CH), 138.1 (Cquat), 153.8 (Cquat), 197.2 (Cquat). EI þ MS (m/z (%)): 216
(38) [Mþ], 171 (100) [C11H7O2þ$], 144 (73) [C10H7Oþ$], 129 (74)
4.2. General procedure for the synthesis of ethyl arylpropiolates 3
[C9H5Oþ$], 101 (12) [C8H5þ$], 100 (12) [C8Hþ4 $]. FT-IR:
n
e[cmꢁ1] ¼ 689
Bis(triphenylphosphane)palladium(II)dichloride
(14.2
mg,
(s), 746 (s), 816 (m), 837 (s), 849 (m), 866 (m), 949 (m), 959 (m),
1009 (m), 1024 (s), 1078 (m), 1173 (s), 1196 (s), 1256 (s), 1259 (s),
1287 (s),1266 (m),1400 (m),1431 (w),1445 (w),1458 (m),1558 (w),
1599 (m), 1682 (s), 1726 (w), 2210 (m), 2247 (w), 2872 (w), 2901
(w), 2926 (w), 2959 (w), 2995 (w). Anal. calcd. for C13H12O3 (216.2):
C 72.21, H 5.59; found: C 72.09, H 5.86.
20.0 mol, 2.00 mol%) and copper(I) iodide (7.62 mg, 40.0
m
mmol,
4.00 mol%) were placed in a flame-dried 10 mL Schlenk tube with a
magnetic stir bar under a nitrogen atmosphere and the Schlenk
tube was evacuated and flushed with nitrogen two more times.
DME (3.0 mL) was added and the resulting yellow solution was
stirred for several minutes at rt. Aryl iodide 1 (1.00 mmol, 1.00
equiv) and potassium carbonate (276 mg, 2.00 mmol, 2.00 equiv)
were added and the vessel was closed and heated to 40 ꢀC. Ethyl
propiolate (2) (198 mg, 2.00 mmol, 2.00 equiv) was dissolved in
DME (0.95 mL) and added slowly over 21 h (1.0 mL syringe,
0.50 mm/min feed rate). After complete addition, the syringe was
rinsed in the reaction mixture and stirring was continued for 1 h at
40 ꢀC. Celite® was added to the dark brown mixture and the solvent
was removed under reduced pressure. For purification, chroma-
tography on silica gel was performed using manual flash technique
or a Biotage SP4 flash purification system with eluents consisting of
n-hexane and EtOAc or acetone.
4.2.4. Ethyl 3-(4-methoxyphenyl)propiolate (3d)
According to the general procedure using 4-iodoanisole (1d)
198 mg (0.969 mmol, 97%) of 3d were obtained as a colorless oil.
Purification was performed using manual flash technique (n-hex-
ane/EtOAc 10:1). 1H NMR (CDCl3, 600 MHz):
d 1.35 (t, 3 H, CH3,
3JH ¼ 7.1 Hz), 3.83 (s, 3 H, OCH3), 4.28 (q, 2 H, OCH2, 3JH ¼ 7.1 Hz),
6.87e6.89 (m, 2 H, CHAr), 7.52e7.54 (m, 2 H, CHAr). 13C NMR (CDCl3,
150 MHz):
d 14.3 (CH3), 55.5 (OCH3), 62.1 (OCH2), 80.3 (Cquat), 87.0
(Cquat),111.6 (Cquat),114.4 (CH),135.1 (CH),154.5 (Cquat),161.6 (Cquat).
EI þ MS (m/z (%)): 204 (30) [Mþ], 159 (61) [C10H7Oþ2 $], 142 (100)
[C9H8Oþ$]. FT-IR:
n
e[cmꢁ1] ¼ 644 (w), 746 (m), 789 (w), 810 (m), 831
(s), 860 (w), 947 (w), 1022 (s), 1096 (m), 1109 (m), 1159 (s), 1192 (s),
1250 (s), 1285 (s), 1368 (w), 1389 (w), 1443 (w), 1460 (w), 1508 (s),
1603 (m), 1701 (s), 2203 (m), 2236 (w), 2841 (w), 2907 (w), 2938
(w), 2980 (w). HRMS (ESI) (m/z) calcd. for [C12H13O3]þ: 205.0859;
Found: 208.0865.
4.2.1. Ethyl 3-(p-tolyl)propiolate (3a)
According to the GP using 4-iodotoluene (1a), 181 mg
(0.961 mmol, 96%) of 3a were obtained as a colorless oil. Purifica-
tion was performed using manual flash technique (n-hexane/EtOAc
30:1). The reaction was repeated on a 10 mmol scale using a 70 mL
Schlenk tube and a 10 mL syringe for the addition of ethyl pro-
piolate to give 1.76 g (9.35 mmol, 94%) of 3a. 1H NMR (CDCl3,
4.2.5. Ethyl 3-(4-(trifluoromethyl)phenyl)propiolate (3e)
According
to
the
general
procedure
using
4-
300 MHz):
d
1.35 (t, 3 H, CH3, 3JH ¼ 7.1 Hz), 2.37 (s, 3 H, CH3), 4.29 (t,
iodobenzotrifluoride (1e), 202 mg (0.834 mmol, 83%) of 3e were
obtained as a colorless oil. Purification was performed using
manual flash technique (n-hexane/EtOAc 50:1). 1H NMR (CDCl3,
2 H, OCH2, 3JH ¼ 7.1 Hz), 7.15e7.19 (m, 2 H, CHAr), 7.45e7.49 (m, 2 H,
CHAr). 13C NMR (CDCl3, 75 MHz):
d 14.2 (CH3), 21.8 (CH3), 62.1
(OCH2), 80.5 (Cquat), 86.7 (Cquat), 116.6 (Cquat), 129.5 (CH), 133.1 (CH),
300 MHz):
d
1.36 (t, 3 H, CH3, 3JH ¼ 7.1 Hz), 4.29 (q, 2 H, OCH2,
141.4 (Cquat), 154.3 (Cquat). EI þ MS (m/z (%)): 188 (28) [Mþ], 143
3JH ¼ 7.1 Hz), 7.62e7.65 (m, 2 H, CHAr), 7.67e7.71 (m, 2 H, CHAr). 13
C
(100) [C10H7Oþ$], 116 (98) [C9Hþ8 $]. IR:
n
e[cmꢁ1] ¼ 708 (w), 725 (w),
NMR (CDCl3, 75 MHz): d 14.2 (CH3), 62.1 (OCH2), 82.4 (Cquat), 83.9
746 (m), 816 (m), 860 (w), 947 (w), 1018 (w), 1094 (w), 1113 (m),
1165 (s), 1190 (s), 1242 (w), 1287 (s), 1366 (m), 1389 (w), 1447 (w),
1464 (w), 1508 (m), 1607 (w), 1701 (s), 2207 (m), 2236 (w), 2872
(w), 2907 (w), 2926 (w), 2938 (w), 2984 (w), 3032 (w). Anal. calcd.
for C12H12O2 (188.2): C 76.57, H 6.43; Found: C 76.65, H 6.73.
(Cquat), 123.6 (q, Cquat, 5JF ¼ 1 Hz), 123.7 (q, Cquat, 1JF ¼ 273 Hz), 125.7
(q, CH, 3JF ¼ 4 Hz), 132.3 (q, Cquat
,
2JF ¼ 33 Hz), 133.3 (CH), 153.7
(Cquat). EI þ MS (m/z (%)): 242 (4) [Mþ], 197 (100) [C10H4F3Oþ$], 170
(69) [C9H5Fþ3 $]. FT-IR:
n
e[cmꢁ1] ¼ 741 (m), 749 (m), 843 (s), 947 (w),
1016 (s), 1065 (s), 1107 (s), 1126 (s), 1167 (s), 1198 (s), 1283 (s), 1321

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314
(s), 1368 (m), 1406 (m), 1449 (w), 1516 (w), 1616 (w), 1709 (s), 2214
(w), 2239 (m), 2878 (w), 2909 (w), 2941 (w), 2988 (w). Anal. calcd.
for C12H9F3O2 (242.2): C 59.51, H 3.75; found: C 59.46, H 3.97.
(1i), 215 mg (0.959 mmol, 96%) of 3i were obtained as a colorless
solid. Purification was performed using manual flash technique (n-
hexane/EtOAc 30:1). Mp 56 ꢀC. 1H NMR (CDCl3, 300 MHz):
d 1.38 (t,
3 H, CH3, 3JH ¼ 7.1 Hz), 4.33 (q, 2 H, OCH2, 3JH ¼ 7.1 Hz), 7.50e7.59
(m, 3 H, CHAr), 7.81e7.85 (m, 3 H, CHAr), 8.15e8.16 (m, 1 H, CHAr). 13
C
4.2.6. Ethyl 3-(2-methoxyphenyl)propiolate (3f)
NMR (CDCl3, 75 MHz):
d 14.3 (CH3), 62.3 (OCH2), 81.0 (Cquat), 86.7
According to the general procedure using 2-iodoanisole (1f),
170 mg (0.832 mmol, 83%) of 3f were obtained as a colorless oil.
Purification was performed using manual flash technique (n-hex-
(Cquat), 116.9 (Cquat),127.1 (CH),128.00 (CH), 128.04 (CH), 128.3 (CH),
128.4 (CH), 128.5 (CH), 132.7 (Cquat), 134.0 (Cquat), 134.4 (CH), 154.2
(Cquat). EI þ MS (m/z (%)): 224 (33) [Mþ], 179 (47) [C13H7Oþ$], 152
ane/EtOAc 30:1). 1H NMR (CDCl3, 300 MHz):
d 1.35 (t, 3 H, CH3,
(100) [C12Hþ8 $]. FT-IR:
n
e[cmꢁ1] ¼ 644 (m), 711 (m), 745 (s), 824 (s),
3JH ¼ 7.1 Hz), 3.90 (s, 3 H, OCH3) 4.30 (q, 2 H, OCH2, 3JH ¼ 7.1 Hz),
6.88e6.96 (m, 2 H, CHAr), 7.40 (ddd, 1 H, CHAr, 3JH ¼ 8.4 Hz, 7.5 Hz,
4JH ¼ 1.8 Hz), 7.51e7.54 (m, 1 H, CHAr). 13C NMR (CDCl3, 75 MHz):
862 (m), 905 (m), 955 (w), 970 (m), 1028 (s), 1115 (m), 1126 (m),
1167 (s), 1200 (s), 1234 (s), 1252 (m), 1269 (s), 1285 (s), 1346 (w),
1366 (m), 1393 (w), 1497 (w), 1593 (w), 1624 (w), 1692 (s), 1701 (s),
2212 (m), 2266 (w), 2907 (w), 2986 (w), 3059 (w), 3372 (w). HRMS
(ESI) (m/z) calcd. for [C15H13O2]þ: 225.0910; Found: 225.0912.
d
14.2 (CH3), 55.9 (OCH3), 62.1 (OCH2), 83.2 (Cquat), 84.7 (Cquat),
108.9 (Cquat), 110.9 (CH), 120.6 (CH), 132.4 (CH), 135.0 (CH), 154.3
(Cquat), 161.6 (Cquat). EI þ MS (m/z (%)): 204 (42) [Mþ], 159 (31)
[C10H7Oþ2 $], 132 (100) [C9H8Oþ$], 115 (21) [C8H3Oþ$], 103 (11), 77
(16) [C6Hþ5 $]. FT-IR:
n
e[cmꢁ1] ¼ 608 (m), 746 (s), 789 (w), 810 (w),
4.2.10. Ethyl 3-(3-chlorophenyl)propiolate (3j)
858 (w), 945 (w), 1018 (s), 1045 (m), 1074 (w), 1094 (w), 1113 (m),
1161 (s), 1184 (s), 1223 (m), 1244 (s), 1277 (s), 1298 (s), 1366 (w),
1466 (w), 1435 (m), 1464 (m), 1491 (m), 1576 (w), 1597 (m), 1701 (s),
2210 (m), 2839 (w), 2872 (w), 2938 (w), 2861 (w), 2980 (w), 3076
(w). Anal. calcd. for C12H12O3 (204.2): C 70.58, H 5.92; Found: C
70.31, H 6.19.
According to the general procedure using 1-chloro-4-
iodobenzene (1j), 194 mg (0.930 mmol, 93%) of 3j were obtained
as a light yellow oil. Purification was performed using manual flash
technique (n-hexane/EtOAc 49:1). 1H NMR (CDCl3, 600 MHz):
d 1.36
(t, 3 H, CH3, 3JH ¼ 7.1 Hz), 4.30 (q, 2 H, OCH2, 3JH ¼ 7.1 Hz), 7.29e7.34
(m, 1 H, CHAr), 7.41e7.48 (m, 2 H, CHAr), 7.56e7.58 (m, 1 H, CHAr). 13
C
NMR (CDCl3, 150 MHz):
d 14.1 (CH3), 62.3 (OCH2), 81.5 (Cquat), 84.1
(Cquat), 121.4 (Cquat), 129.9 (CH), 130.9 (CH), 131.0 (CH), 132.6 (CH),
134.5 (Cquat), 153.7 (Cquat). EI þ MS (m/z (%)): 210 (6) [Mþ, 37Cl], 208
(17) [Mþ, 35Cl], 165 (33) [C9H4O37ClOþ$], 163 (100) [C9H4O35ClOþ$],
4.2.7. Ethyl 3-(pyridin-4-yl)propiolate (3g)
According to the general procedure using 4-iodopyridine (1g),
88.0 mg (0.502 mmol, 50%) of 3g were obtained as a light brown oil
which turned black within a few hours upon exposure to laboratory
atmosphere. Purification was performed using manual flash tech-
nique (n-hexane/EtOAc 9:1 / 4:1). 1H NMR (CDCl3, 300 MHz):
138 (22) [C8H537Clþ$], 136 (67) [C8H535Clþ$], 99 (15) [C8Hþ3 $]. FT-IR:
n
e
[cmꢁ1] ¼ 608 (w), 679 (s), 746 (m), 785 (m), 833 (w), 860 (w), 881
(w), 943 (w), 961 (w), 1022 (m), 1080 (m), 1094 (m), 1113 (w), 1184
(s), 1258 (m), 1368 (m), 1558 (m), 1589 (w), 1705 (s), 2214 (w), 2239
d
1.34 (t, 3 H, CH3, 3JH ¼ 7.1 Hz), 4.30 (q, 2 H, OCH2, 3JH ¼ 7.1 Hz),
7.39e7.41 (m, 2 H, CHAr), 8.64e8.66 (m, 2 H, CHAr). 13C NMR (CDCl3,
(w), 2907 (w), 2983 (2), 2984 (w), 3069 (w). HRMS (ESI) (m/z) calcd.
35
for [C
H
ClO2]þ: 209.0364; Found: 209.0363.
75 MHz):
d 14.1 (CH3), 62.7 (OCH2), 82.2 (Cquat), 83.9 (Cquat), 126.2
11 10
(CH), 128.0 (Cquat), 150.2 (CH), 153.3 (Cquat). EI þ MS (m/z (%)): 175
(16) [Mþ], 130 (100) [C8H4NOþ$], 103 (29) [C7H5Nþ$], 75 (11). FT-IR:
4.2.11. Ethyl 3-(10-hexyl-10H-phenothiazin-3-yl)propiolate (3k)
According to the general procedure using 10-hexyl-3-iodo-10H-
phenothiazine (1k) [19], 313 mg (0.825 mmol, 82%) of 3k were
obtained as an orange resin. Purification was performed using
manual flash technique (n-hexane/acetone 10:1), followed by a
second purification step using the flash purification system (n-
n
e[cmꢁ1] ¼ 669 (w), 748 (m), 818 (m), 858 (w), 953 (w), 989 (w),
1020 (m), 1065 (w), 1096 (w), 1113 (w), 1190 (s), 1217 (m), 1285 (s),
1368 (m), 1406 (m), 1447 (w), 1466 (w), 1474 (w), 1489 (w), 1537
(w), 1589 (m), 1709 (s), 2218 (w), 2245 (w), 2940 (w), 2984 (w),
3042 (w). HRMS (ESI) (m/z) calcd. for [C10H10NO2]þ: 176.0708;
Found: 176. 0706.
hexane). 1H NMR (acetone-d6, 300 MHz):
d 0.82e0.87 (m, 3 H; CH3),
1.25e1.34 (m, 7 H; CH2, CH3), 1.41e1.51 (m, 2 H; CH2), 1.74e1.84 (m,
2 H; CH2), 3.96e4.00 (m, 2 H, NCH2), 4.25 (q, 2 H, OCH2,
3JH ¼ 7.1 Hz), 6.96e7.01 (m, 1 H, CHAr), 7.04e7.08 (m, 2 H, CHAr),
4.2.8. Ethyl 3-(phenanthren-9-yl)propiolate (3h)
According to the general procedure using 9-iodophenanthrene
(1h), 252 mg (0.919 mmol, 92%) of 3h were obtained as a light
yellow solid. Purification was performed using manual flash tech-
nique (n-hexane/EtOAc 30:1). Mp 85 ꢀC. 1H NMR (CDCl3, 300 MHz):
7.12e7.16 (m, 1 H, CHAr), 7.22 (ddd, 1 H, CHAr
,
3JH ¼ 8.2 Hz, 7.2 Hz,
4JH ¼ 1.6 Hz), 7.34 (d, 1 H, CHAr
,
4JH ¼ 1.9 Hz, 7.45 (dd, 1 H, CHAr
,
3JH ¼ 8.5 Hz, 4JH ¼ 2.0 Hz). 13C NMR (acetone-d6, 75 MHz):
d 14.2
d
1.42 (t, 3 H, CH3, 3JH ¼ 7.2 Hz), 4.38 (q, 2 H, OCH2, 3JH ¼ 7.1 Hz), 7.62
(CH3), 14.4 (CH3), 23.3 (CH2), 27.0 (CH2), 27.4 (CH2), 32.1 (CH2), 48.1
(NCH2), 62.4 (OCH2), 81.8 (Cquat), 86.2 (Cquat), 113.4 (Cquat), 116.6
(CH), 117.2 (CH), 124.2 (CH), 124.3 (Cquat), 125.8 (Cquat), 128.1 (CH),
128.7 (CH), 131.8 (CH), 133.6 (CH), 144.9 (Cquat), 148.7 (Cquat), 154.3
(Cquat). EI þ MS (m/z (%)): 379 (100) [Mþ], 334 (8) [C18H14NOSþ$],
308 (60) [C18H14NO2Sþ$], 294 (57) [C17H12NO2Sþ$], 266 (11), 222
(ddd, 1 H, CHAr, 3JH ¼ 8.0 Hz, 7.1 Hz, 4JH ¼ 1.2 Hz), 7.68e7.75 (m, 3 H,
CHAr), 7.86e7.89 (m, 1 H, CHAr), 8.19 (s, 1 H, CHAr), 8.39e8.45 (m,
1 H, CHAr), 8.64e8.71 (m, 2 H, CHAr). 13C NMR (CDCl3, 75 MHz):
d
14.3 (CH3), 62.3 (OCH2), 84.7 (Cquat), 85.0 (Cquat), 116.3 (Cquat),
122.8 (CH), 126.7 (CH), 127.3 (CH), 127.6 (CH), 127.7 (CH), 128.9 (CH),
129.2 (CH), 130.1 (Cquat), 130.7 (Cquat), 130.8 (Cquat), 131.3 (Cquat),
135.6 (CH), 154.3 (Cquat). EI þ MS (m/z (%)): 274 (38) [Mþ], 229 (21)
(35) [C14H8NSþ$]. FT-IR:
(s), 814 (m), 858 (m), 883 (m), 964 (w), 1026 (m), 1103 (m), 1165 (s),
1238 (s), 1250 (m), 1271 (m). Anal. calcd. for C23H25NO2S (379.5): C
72.79, H 6.64, N 3.69, S 8.45; Found: C 72.58, H 6.51, N 3.47, S 8.48.
n
e[cmꢁ1] ¼ 629 (w), 669 (w), 694 (w), 745
[C17H19
O
þ$], 202 (100) [C16H1þ0$]. FT-IR:
n
e[cmꢁ1] ¼ 667 (w), 723 (s),
746 (s), 766 (s), 804 (w), 854 (m), 889 (m), 920 (w), 1016 (m), 1074
(m), 1109 (m), 1148 (w), 1192 (s), 1211 (s), 1233 (m), 1260 (s), 1319
(m), 1368 (w), 1379 (w), 1452 (w), 1474 (w), 1692 (s), 2210 (m), 2857
(w), 2905 (w), 2863 (w), 2978 (w), 3366 (w). HRMS (ESI) (m/z)
calcd. for [C19H15O2]þ: 275.1067; Found: 275.1067.
4.2.12. Ethyl-3-(7-bromo-10-hexyl-10H-phenothiazin-3-yl)
propiolate (3l)
Departing from the GP, the reaction was performed on a
4.00 mmol scale. Using 10-hexyl-7-bromo-3-iodo-10H-phenothia-
zine (1l) [19], 1.24 g (2.71 mmol, 68%) of 3l were obtained as an
orange resin that crystallized slowly. Purification was performed
4.2.9. Ethyl 3-(naphthalen-2-yl)propiolate (3i)
According to the general procedure using 2-iodonaphthalene

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315
using manual flash technique (n-hexane / n-hexane/acetone
50:1 / 25:1 / 10:1). Mp 60e65 ꢀC. 1H NMR (acetone-d6,
300 MHz): 0.81e0.87 (m, 3 H; CH3), 1.25e1.30 (m, 7 H, CH2, CH3),
References
[1] (a) Levi L, Müller TJJ. Multicomponent syntheses of functional chromophores.
Chem Soc Rev 2016;45:2825e46.
d
1.40e1.50 (m, 2 H; CH2), 1.73e1.83 (m, 2 H; CH2), 3.95e4.00 (m, 2 H,
(b) Müller TJJ. Diversity-oriented synthesis of chromophores by combinatorial
strategies and multi-component reactions. In: Müller TJJ, Bunz UH, editors.
Functional organic materials. Syntheses, strategies, and applications. Wein-
heim: Wiley-VCH Verlag GmbH & Co. KGaA; 2007. p. 179e223.
NCH2), 4.25 (q, 2 H, OCH2, 3JH ¼ 7.1 Hz), 7.01 (d, 1 H, CHAr
,
3JH ¼ 8.7 Hz), 7.09 (d, 1 H, CHAr
,
3JH ¼ 8.5 Hz), 7.30 (d, 1 H, CHAr
,
,
4JH ¼ 2.3 Hz), 7.33e7.37 (m, 3 H, CHAr), 7.47 (dd, 1 H, CHAr
€
[2] (a) Hauck M, Stolte M, Schonhaber J, Kuball HG, Müller TJJ. Synthesis, elec-
3JH ¼ 8.5 Hz, 4JH ¼ 2.0 Hz). 13C NMR (acetone-d6, 75 MHz):
d 14.2
tronic and electrooptical properties of emissive solvatochromic phenothia-
zinyl merocyanine dyes. Chem Eur J 2011;17:9984e98.
(CH3), 14.4 (CH3), 23.2 (CH2), 27.0 (CH2), 27.2 (CH2), 32.1 (CH2), 48.1
(NCH2), 62.5 (OCH2), 81.9 (Cquat), 85.9 (Cquat), 113.8 (Cquat), 115.7
(Cquat), 116.8 (CH), 118.6 (CH), 124.9 (Cquat), 126.8 (Cquat), 130.1 (CH),
131.2 (CH), 131.9 (CH), 133.8 (CH), 144.3 (Cquat), 148.2 (Cquat), 154.3
€
(b) Kramer CS, Zeitler K, Müller TJJ. Synthesis of (Hetero)Aryl bridged and
directly linked redox active phenothiazinyl dyads and triads. Tetrahedron Lett
2001;42:8619e24.
(c) Meyer T, Ogermann D, Pankrath A, Kleinermanns K, Müller TJJ. Pheno-
thiazinyl rhodanylidene merocyanines for dye-sensitized solar cells. J Org
Chem 2012;77:3704e15.
(d) Sailer M, Franz AW, Müller TJJ. Synthesis and electronic properties of
monodisperse oligophenothiazines. Chem Eur J 2008;14:2602e14.
(e) Sailer M, Nonnenmacher M, Oeser T, Müller TJJ. Synthesis and electronic
properties of 3-acceptor-substituted and 3,7-bisacceptor-substituted pheno-
thiazines. Eur J Org Chem 2006:423e35.
(Cquat). EI þ MS (m/z (%)): 459 (100) [Mþ
(
81Br)], 457 (100) [Mþ
81
79
(
[C
[C
79Br)], 414 (9) [C21 BrNOSþ$], 412 (9) [C21 BrNOSþ$], 388 (59)
H H
19 19
81
79
H
H
BrNO2Sþ$], 386 (62) [C18 BrNO2Sþ$], 374 (80)
H
18 13
13
81
79
BrNO2Sþ$], 372 (71) [C17
H
BrNO2Sþ$], 356 (10), 354 (10),
17 11
11
81
346 (17), 344 (15), 328 (10), 302 (52) [C
H
BrNSþ$], 300 (52)
7
14
79
BrNSþ$], 222 (13), 220 (19), 177 (12), 149 (15), 43 (13)
[3] Müller TJJ. First synthesis and electronic properties of ring-alkynylated phe-
nothiazines. Tetrahedron Lett 1999;40:6563e6.
[4] Barkschat CS, Stoycheva S, Himmelhaus M, Müller TJJ. Synthesis, electronic
properties, and self-assembly on Au{111} of thiolated phenylethynyl pheno-
thiazines. Chem Mater 2010;22:52e63.
[C
H
14
7
[C3Hþ7 $]. FT-IR:
n
e[cmꢁ1] ¼ 652 (w), 689 (w), 719 (w), 743 (m), 766
(m), 793 (s), 829 (m), 862 (m), 968 (w), 995 (w), 1030 (m), 1107 (m),
1159 (m), 1180 (s), 1238 (m), 1271 (m), 1304 (w), 1352 (m), 1368 (w),
1393 (m), 1456 (s), 1595 (m), 1703 (m), 2205 (m), 2270 (w), 2853
(w), 2868 (w), 2926 (w). Anal. calcd. for C23H24BrNO2S (458.4): C
60.26, H 5.28, N 3.06, S 6.99; Found: C 60.54, H 5.18, N 3.05, S 7.16.
€
[5] Rechmann J, Sarfraz A, Gotzinger AC, Dirksen E, Müller TJJ, Erbe A. Surface
functionalization of oxide-covered zinc and iron with phosphonated phenyl-
ethynyl phenothiazine. Langmuir 2015;31:7306e16.
[6] Schreiner E, Braun S, Kwasnitschka C, Frank W, Müller TJJ. Consecutive three-
component synthesis of 2,6-disubstituted pyrimid-4(3H)-ones and 1,5-
disubstituted 3-hydroxy pyrazoles initiated by copper(I)-catalyzed carboxyl-
ation of terminal alkynes. Adv Synth Catal 2014;356:3135e47.
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4.2.13. Diethyl-3,3'-(10-hexyl-10H-phenothiazin-3,7-diyl)
dipropiolate (3m)
Departing from the GP, 1.00 equiv of 10-hexyl-3,7-diiodo-10H-
phenothiazine (1m) [19] were employed and all other reactants
were doubled, giving 385 mg (0.810 mmol, 81%) of 3m as an orange
solid. Purification was performed twice using manual flash tech-
nique (n-hexane/acetone 10:1, then 20:1). An analytic sample for
photophysical characterization was recrystallized from n-hexane.
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Mp 93 ꢀC. 1H NMR (acetone-d6, 300 MHz):
d 0.83e0.88 (m, 3 H;
CH3), 1.24e1.36 (m, 10 H, CH2, CH3), 1.41e1.53 (m, 2 H; CH2),
1.76e1.85 (m, 2 H; CH2), 4.01e4.05 (m, 2 H, NCH2), 4.25 (q, 4 H,
OCH2, 3JH ¼ 7.1 Hz), 7.13 (d, 2 H, CHAr, 3JH ¼ 8.6 Hz), 7.37 (d, 2 H, CHAr
,
4JH ¼ 1.9 Hz), 7.48 (d, 2 H, CHAr, 3JH ¼ 8.5 Hz, 4JH ¼ 2.0 Hz). 13C NMR
(acetone-d6, 75 MHz):
d 14.2 (CH3), 14.3 (CH3), 23.2 (CH2), 26.9
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(CH2), 27.2 (CH2), 32.1 (CH2), 48.3 (NCH2), 62.5 (OCH2), 82.0 (Cquat),
85.7 (Cquat), 114.5 (Cquat), 117.1 (CH), 124.8 (Cquat), 131.9 (CH), 133.8
(CH), 147.3 (Cquat), 154.2 (Cquat). EI þ MS (m/z (%)): 475 (100) [Mþ],
430 (14) [C26H24NO3Sþ$], 404 (51) [C23H18NO4Sþ$], 390 (61)
[C22H16NO4Sþ$], 372 (11), 318 (28) [C19H12NO2Sþ$], 290 (17), 246
(23) [C16H18NSþ$]. FT-IR:
n
e[cmꢁ1] ¼ 692 (m), 704 (m), 745 (s), 789
(w), 822 (s), 856 (m), 874 (m), 910 (w), 949 (m), 966 (m), 1028 (m),
1061 (m), 1105 (s), 1148 (s), 1175 (s), 1242 (m), 1269 (s), 1290 (m),
1300 (m),1360 (m),1379 (m),1396 (m),1460 (m),1474 (s), 1572 (m),
1697 (s), 2199 (m), 2266 (w), 2567 (w), 2872 (w), 2922 (w), 2938
(w), 2955 (w), 3375 (w). Anal. calcd. for C28H29NO4S (475.6): C
70.71, H 6.15, N 2.95, S 6.74; Found: C 70.65, H 6.20, N 2.80, S 6.79.
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acids or aryl acetylenes depending on the employed catalyst system, see
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aryl alkynes from propiolic acid and aryl halides by site selective coupling and
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Acknowledgements
The authors cordially thank the Fonds der Chemischen Industrie
and the Deutsche Forschungsgemeinschaft (Mu 1088/9-1) for
financial support.
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Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2017.04.049.
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