Synthesis and Molecular Properties of Partially Fluorinated DNTTs**

Article abstract of DOI:10.1002/ejoc.202001635

1,2,3,4-Tetrafluoro-dinaphthothienothiophene (F₄DNTT) and 1,2,3,4,8,9,10,11-octafluoro-dinaphthothienothiophene (F₈DNTT) were synthesized via bisthiomethyl alkene intermediates which were accessible by McMurry coupling or Wittig olefination of partially fluorinated naphthalene precursors. DFT-based electronic structure calculations, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and UV/Vis measurements were used for HOMO/LUMO gap determination and to analyze the electronic structures of the partially fluorinated DNTTs. Reduced exciton binding was observed in thin films.

Full text of DOI:10.1002/ejoc.202001635

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Very Important Paper
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Synthesis and Molecular Properties of Partially Fluorinated
DNTTs**
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Matthias W. Tripp,[a] Daniel Bischof,[b] Maximilian Dreher,[b] Gregor Witte,*[b] and
Ulrich Koert*[a]
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1,2,3,4-Tetrafluoro-dinaphthothienothiophene (F4DNTT) and
1,2,3,4,8,9,10,11-octafluoro-dinaphthothienothiophene (F8DNTT)
were synthesized via bisthiomethyl alkene intermediates which
were accessible by McMurry coupling or Wittig olefination of
partially fluorinated naphthalene precursors. DFT-based elec-
tronic structure calculations, near-edge X-ray absorption fine
structure (NEXAFS) spectroscopy, and UV/Vis measurements
were used for HOMO/LUMO gap determination and to analyze
the electronic structures of the partially fluorinated DNTTs.
Reduced exciton binding was observed in thin films.
Introduction
The promising potential of using π-conjugated molecules or
polymers as active semiconducting material for flexible organic
electronics applications such as e.g. rollable displays, cost-
effective sensors, or electronic skin has triggered the synthesis
of new organic materials suited for such applications.[1] Among
the organic semiconductors, pentacene 1 (Figure 1) has long
been considered a model system, as it forms well-ordered
crystalline films with reasonably high charge carrier mobility
that were commonly used to benchmark other organic
semiconductors.[2] In addition, the electronic structure of this
highly symmetric alternant hydrocarbon can be well-under-
stood by Hückel theory,[3] while also the intermolecular coupling
in molecular solids was analyzed theoretically in detail.[4] On the
other hand, there are the disadvantages of the larger acenes
such as their sensitivity to oxidation and light-induced dimeriza-
tion of the central ring as well as their low solubility in organic
solvents,[5] which complicates their processing in organic
electronics. To address these problems, synthetic strategies
such as the addition of functional side groups or heterosub-
stitutions have been developed to enhance chemical stability
and processability.[6,7]
Figure 1. Examples for functionalized pentacenes, benzobisbenzothio-
phenes, and DNTTs.
A different approach is the substitution of the central ring
by chemically more robust moieties such as thienothiophenes,[8]
which has led to the synthesis of a new class of diacene-fused
thienothiophenes (DAcTT).[9]
[a] M. W. Tripp, Prof. Dr. U. Koert
Department of Chemistry
Philipps-Universität Marburg
Hans-Meerwein-Straße 4, 35032 Marburg, Germany
E-mail: koert@chemie.uni-marburg.de
https://www.uni-marburg.de/en/fb15/researchgroups/ag-koert
[b] D. Bischof, M. Dreher, Prof. Dr. G. Witte
Department of Physics
Among this new material class, the dinaphthothienothio-
phene (DNTT) 2 stands out because it combines superior charge
carrier mobility with excellent stability against oxidation and
chemical decomposition, making it one of the most stable
organic semiconductors.[10–13] Increased solubility has also been
realized for DNTTs by addition of peripheral side chains.[14]
Adjustments of the electronic structure of such π-conjugated
systems are possible either through modification of their
length[15–17] or incorporation of further thiophene moieties.[9,18–20]
A different, for polycyclic aromatic hydrocarbons well-
established, strategy is heteroatom substitution, which allows
precise tailoring of the molecular properties.[5,21–23] In particular
fluorination has become a common strategy to alter the
electronic properties of organic semiconductors,[24] as the polar
Philipps-Universität Marburg
Renthof 7, 35032 Marburg, Germany
E-mail: gregor.witte@physik.uni-marburg.de
https://www.uni-marburg.de/de/fb13/molekulare-festkoerperphysik
[**] A previous version of this manuscript has been deposited on a preprint
server (DOI: doi.org/10.26434/chemrxiv.13385351.v1)
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejoc.202001635
© 2021 The Authors. European Journal of Organic Chemistry published by
Wiley-VCH GmbH. This is an open access article under the terms of the
Creative Commons Attribution License, which permits use, distribution and
reproduction in any medium, provided the original work is properly cited.
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CÀ F bonds directly lower the energy levels of the π-system and
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simultaneously change the charge density distribution leading
to electron accumulation at the fluorine atoms.[25–30] Partially
fluorinated pentacenes 3 and azapentacenes 4 have been
studied.[29,30] So far, however, fluorination has rarely been used
to functionalize the vast class of thienoacene-based organic
semiconductors with 5 as rare example.[31] Here, we introduce
partially fluorinated DNTTs 7 and 8.
We present new synthetic strategies to chemically alter the
electronic properties of the more promising semiconductor
DNTT by partial fluorination. For the symmetrically fluorinated
F8DNTT (7) we utilized a McMurry approach, while for the one-
sidedly fluorinated F4DNTT (8) we had to apply a Wittig
approach. Using DFT-based electronic structure calculations,
NEXAFS, and UV/Vis measurements we observe a similar
reduction of the HOMO and LUMO levels, leaving the optical
gap virtually unchanged. We also observe a reduced exciton
binding energy in thin films. Last, we have analyzed the
electronic structure of the DNTTs more in detail, revealing that
the carbon K-edge NEXAFS signatures of the DNTTs exhibit
characteristic naphthalene-, perfluoro-naphthalene- and
thiophene-like features, which may serve as “fingerprints”.[32]
Retrosynthetic pathways towards functionalized DNTTs of
type 9 are shown in Scheme 1. The group of Takimiya
developed different synthetic methods for symmetric as well as
non-symmetric DNTTs.[10,14,33–36] For symmetric compounds, an
olefinic precursor 10 is used, which can undergo an iodine-
promoted double-ring-closing reaction to the corresponding
DNTT 9. In previous studies of Takimiya, the olefinic precursor
10 is built up in an ortho-thiomethylation/McMurry-sequence
starting from aldehyde 11.[10] While the McMurry-reaction of
these compounds usually works smoothly, the ortho-thiometh-
ylation of aldehyde 11 is very tedious, due to the formation of a
regioisomer and difficult chromatographic isolation. In 2011,
they reported a different strategy for the synthesis of the
olefinic precursor 10, utilizing a double Stille-reaction of triflate
12 with the bis-stannane 13.[33] While the Stille-reaction gave
good to excellent yield, this route also has the advantage, that
the introduction of the thiomethyl moiety works with high
selectivity in the desired 3-position.
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Scheme 1. Retrosynthesis of functionalized DNTTs.
ylation-sequence of ester 18, based on a work by Hosoya.[37] For
the synthesis of the non-symmetric F4DNTT (8), a new route was
developed, including the synthesis of the olefinic precursor 10
in a Wittig-reaction. The advantage of this route is, that the
phosphoniumbromide 19 can also be synthesized utilizing the
same strategy, starting from an ester of type 18.
A different strategy had to be developed for the selective
synthesis of non-symmetric functionalized DNTT-derivatives. A
possible pathway for this problem was shown by Takimiya
when the final step of the synthesis is a thio-Friedel-Crafts-type
ring-closure of the sulfoxide-precursor 14.[34] This precursor can
be synthesized via a Stille-coupling of the functionalized
naphthothiophene 15 with triflate 16, allowing the introduction
of a non-symmetric substitution pattern. Takimiya showed the Results and Discussion
applicability of this route by the selective synthesis of 2-bromo-
DNTT, which was derivatized in a late-stage functionalization
into different non-symmetric DNTTs, including the TMS-
acetylene-compound 6.[34]
In this contribution, we demonstrate the synthesis of
partially fluorinated DNTTs 7 and 8. In the case of the symmetric
F8DNTT (7), we applied the McMurry-approach to build up the
olefinic precursor 10. The aldehyde 17 is, however, synthesized
in a highly regioselective ortho-borylation/deborothiometh-
The starting point of the syntheses was the known tetrafluor-
onaphthyltriflate 20,[38] that was converted to aldehyde 23 in
five steps, which served as a common precursor for both
partially fluorinated DNTTs (Scheme 2). The first step was a
carbonylative cross coupling[39] of 20 to methyl ester 21,
followed by an iridium catalyzed directed ortho-borylation.[40]
The crude pinacolboronate was subjected to a deborothiometh-
ylation-procedure[37] to provide thioether 22 in excellent yield
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be built up in
a
Wittig-reaction. The corresponding
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phosphonium bromide 29 should be accessible in five steps,
starting from ester 27, using the same strategy to introduce the
thiomethyl group. For this substrate the ortho-borylation/
deborothiomethylation sequence to obtain 28 worked in 67%
yield over two steps, indicating that the ortho-borylation works
better for electron-deficient compounds. The ester moiety of 28
was then reduced to the corresponding alcohol and subjected
to an Appel-reaction. The benzylic bromide was then refluxed
in toluene with PPh3 to obtain phosphonium bromide 29 in
70% yield over three steps. The following Wittig-reaction with
aldehyde 23 worked smoothly, to give alkene 30 in 96% yield.
This time, the iodine-promoted cyclization to F4DNTT (8)
worked fine in one step with 73% yield (see Scheme 4).
In addition to the chemical synthesis also the optoelectronic
properties of the new compounds were analyzed and compared
to the unsubstituted DNTT (2). At first, we studied the influence
of partial fluorination on the electronic structure by means of
DFT calculations. The results are visualized in Figure 2. As
expected, the fluorine atoms prove to be strongly electron-
withdrawing, which affects the charge density distribution
within the molecule. In the case of DNTT (2) a high electrostatic
potential (indicated by blue color) is present at the molecular
rim and a low electrostatic potential (indicated by red color)
and thus a high electron density appears in the center, while
for the fluorinated species also the outer fluorine atoms exhibit
a high electron density, yielding a nearly inverted electrostatic
potential at the fluorinated aromatic subunits. For F4DNTT (8)
the asymmetric functionalization even leads to a permanent
molecular dipole moment of jpj =4.26 D, which is slightly
smaller than the dipole moment of related fluoroazaacenes
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Scheme 2. Synthesis of aldehyde 23. Reagents and conditions: a) CO (1 atm),
°
Pd(OAc)2 (5 mol%), dppf (10 mol%), Et3N (2.0 eq), DMF/MeOH, 65 C, 6 h; b)
°
[Ir(OMe)(cod)]2 (2.5 mol%), L1 (5 mol%), B2pin2 (1.0 eq), THF, 55 C, 2 h; c)
°
TsSMe (1.2 eq), CsF (2.0 eq), CuSO4 (0.1 eq), TMEDA (0.12 eq), MeOH, 50 C,
°
26 h; d) DIBAH (3.0 eq), THF, 0 C to rt, 20 min; e) (COCl)2 (1.5 eq), DMSO
(3.0 eq), CH2Cl2, À 78 C, 30 min; Et3N (5.0 eq), À 78 C, 30 min; rt, 15 min.
°
°
and regioselectivity over two steps. Reduction of the ester to
the alcohol using DIBAH and reoxidation under Swern-
conditions gave aldehyde 23.
Since the F8DNTT (7) is a symmetric compound, the carbon-
backbone can be built up in a McMurry-reaction of aldehyde 23
(Scheme 3). The reaction worked smoothly in 93% yield to
obtain the olefinic precursor 24. Unfortunately, the final
double-ring-closing reaction, using an excess of iodine in
boiling dichloroethane or acetic acid, did not give the desired
DNTT. The main product of the reaction was compound 25,
where only one of the thiophene rings was closed, with the
other thiomethyl-group still intact. The thiomethyl-group was
then oxidized to the corresponding sulfoxide 26 using mCPBA
and cyclized in a thio-Friedel-Crafts type reaction[34] to obtain
F8DNTT (7).
(tetrafluorodiazatetracene:
jpj =4.31 D,
hexafluorodiaza-
A different strategy had to be developed for the synthesis
of F4DNTT (8). The non-symmetric olefinic precursor 30 could
Scheme 4. Synthesis of F4DNTT 8. Reagents and conditions: j) [Ir(OMe)(cod)]2
(2.5 mol%), L1 (5 mol%), B2pin2 (1.0 eq), THF, 55 C, 22 h; k) TsSMe (1.2 eq),
CsF (2.0 eq), CuSO4 (0.1 eq), TMEDA (0.12 eq), MeOH, 50 C, 22 h; l) DIBAH
°
°
Scheme 3. Synthesis of F8DNTT 7. Reagents and conditions: f) TiCl4 (3.0 eq),
°
°
°
°
°
Zn (3.0 eq), THF, 0 C to 66 C, 3 h; 23 (1.0 eq), rt to 66 C, 14 h; g) I2 (29.0 eq),
(3.0 eq), THF, 0 C to rt, 2 h; m) NBS (2.0 eq), PPh3 (2.0 eq), CH2Cl2, 0 C, 1 h; n)
PPh3 (1.2 eq), toluene, 110 C, 17 h; o) 29 (1.1 eq), n-BuLi (1.09 eq), THF, 0 C,
°
°
°
°
(CH2Cl)2, 84 C, 22 h; h) mCPBA (1.0 eq), CH2Cl2, 0 C to rt, 26 h; i) P2O5 (1.0 eq),
°
°
°
TfOH, rt, 3 d; pyridine, 115 C, 23 h.
30 min; 23 (1.0 eq), 0 C to rt, 15 min; p) I2 (29.0 eq), AcOH, 118 C, 21 h.
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Figure 3. UV/Vis spectra of DNTT (2), F4DNTT (8), and F8DNTT (7) in solution
(saturated solution in CH2Cl2) and as solid films evaporated onto quartz glass
substrates. The dashed lines indicate the energy of the lowest absorption
band (optical gap). Arrows visualize the exciton binding energies (ΔE).
Figure 2. Comparison of calculated energy levels, frontier orbitals HOMO
and LUMO, and molecular electrostatic potentials (MEPs) of DNTT (2),
F4DNTT (8), and F8DNTT (7) obtained by DFT at the B3LYP/6-311G(d,p) level.
which can be assigned to excitonic excitations in the solid. The
exciton binding energies, which can be approximated by the
difference between the lowest energy excitation in solution and
in the solid (indicated as ΔE in Figure 3), are notably smaller for
the partially fluorinated molecules when compared to the non-
fluorinated pendent DNTT (2) (DNTT: 330 meV F4DNTT (8):
180 meV, F8DNTT (7): 160 meV). Hence the optical solid-state
properties are modified notably upon fluorination, as also
observed for partially fluorinated acenes, which could be
attributed to a changed packing motif in the respective
molecular solids.[30,41] Unfortunately, a crystal structure analysis
that would rationalize this effect has not yet been possible,
because the crystallites obtained so far are too small. This is in
line with our observation that fluorinated aromatic molecules
generally tend to crystallize in smaller crystallites than their
non-fluorinated pendants.[30]
To obtain deeper insights into the nature of unoccupied
electronic states, we have utilized NEXAFS spectroscopy. The
carbon K- edge NEXAFS spectrum of F4DNTT (8) (cf. Figure 4a)
exhibits sharp π*-resonances, which can be assigned to
excitations from C1s core levels into unoccupied molecular π-
orbitals, and broad resonances corresponding to excitations in
unoccupied σ-orbitals. The comparison of the magnified π*
region of the differently fluorinated DNTTs (cf. Figure 4b) shows
that some resonances appear at unchanged positions, while
others occur only for the fluorinated species. This is particularly
pronounced for F4DNTT (8), which exhibits final states with
mixed character, as it has also been observed also for
unilaterally fluorinated acenes.[30] As DNTT topologically consists
of naphthalene and thiophene units, a comparison of the
corresponding signatures is useful. Indeed, the NEXAFS spec-
trum of DNTT can be well-described by the NEXAFS signatures
of these units,[42,43] as indicated by the dashed lines (blue:
naphthalene-like resonance, orange: thiophene-like resonance,
pentacene 4: jpj =5.27 D).[29] The electron withdrawing effect
of the fluorine atoms leads to a reduction of the electron
density at the carbon atoms that not only affects the electro-
static potential through the frontier orbitals but also increases
the C1s binding energy upon fluorination, which transfers in
the sense of Hückel theory to a larger Coulomb integral.[3] This
leads to a lowering of the energy levels of the π-system,
including the frontier orbitals HOMO and LUMO. Interestingly,
in the case of the partially fluorinated DNTTs, the energy levels
of both frontier orbitals are lowered almost equally, so that the
optical gap changes only marginally. According to Hückel
theory, this effect is expected for alternant hydrocarbons[25] and
has been verified experimentally for other fluorinated organic
semiconductors such as e.g. acenes, rubrene, and hexabenzo-
coronene.[26–30] The presently observed effect of an (approx-
imately) equal energetically reduction of both frontier orbitals
due to fluorination, even in the case of non-alternant hydro-
carbons such as DNTT, suggests that partial fluorination
generally leads to a reduction in both frontier orbitals for π-
conjugated molecules.
The molecular HOMO-LUMO gap was experimentally ob-
tained by optical spectroscopy. UV/Vis solution spectra (cf.
Figure 3) yield HOMO-LUMO gaps of 3.09 eV (DNTT (2)), 3.04 eV
(F4DNTT (8)) and 3.03 eV (F8DNTT (7)), respectively. Hence the
experimental data show only a slight reduction of the HOMO-
LUMO gap and are qualitatively consistent with the DFT
calculations. Since for device applications the optical solid-state
properties are more relevant, we also carried out UV/Vis
absorption measurements on solid molecular thin films of
about 50 nm evaporated under vacuum conditions onto quartz
slides. As depicted in Figure 3, the transmission absorption
spectra exhibit new bands below the HOMO-LUMO transition,
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ining that the analysis of characteristic subunits can be used to
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shed a light on the electronic structure of such extended π-
conjugated systems. The high chemical stability of the (partially
fluorinated) DNTTs can be attributed to the low-lying HOMO
originating from the topological structure of these molecules.
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Experimental Section
General Information. All anhydrous reactions were carried out
using flame-dried glassware under argon atmosphere. All solvents
were distilled by rotary evaporation. THF for anhydrous reactions
was dried with KOH and subsequently distilled from sodium/
benzophenone and from Solvona® respectively. All other solvents
employed under anhydrous and/or anaerobic conditions were
bought in anhydrous form. All commercially available reagents and
reactants were used without further purification unless otherwise
noted. Reactions were monitored by thin-layer chromatography
(TLC) using MERCK Silica Gel 60 F254 and visualized by fluorescence
quenching under UV-light. In addition, TLC-plates were stained
using a cerium sulfate/phosphomolybdic acid stain or a potassium
permanganate stain. Chromatographic purification of products was
performed on MACHEREY-NAGEL Silica Gel 60 (230–400 mesh)
using a forced flow of eluents. All crude products were adsorbed
onto silica by dissolving in an appropriate solvent and removing
the solvent under reduced pressure. Concentration under reduced
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Figure 4. Summary of carbon K-edge NEXAFS data of the differently
fluorinated DNTTs obtained for their solid films grown on SiO2 substrates
°
and recorded at an incident angle of 55 . a) NEXAFS spectrum of a thin film
of F4DNTT (8) prepared on SiO2. b) Comparison of the leading NEXAFS
resonances of DNTT (2), F4DNTT (8), F8DNTT (7), and perfluoronaphthalene
(PFN, which is shown in c) and taken from ref. [44]). The gray line represents
an energetically shifted PFN spectrum, which resembles the features of
F8DNTT at energies larger than 286 eV surprisingly well.
°
pressure was performed by rotary evaporation at 40 C and
appropriate pressure and by exposing to high vacuum at room
temperature if necessary.
more details are given in Supp. Inf.). In addition, the carbon K-
edge NEXAFS spectrum of F8DNTT (7) can be well described by
the spectra of DNTT and perfluoronaphthalene, since F8DNTT
(7) consists of thiophene units and semifluorinated naphthalene
units, which impressively shows that more complex NEXAFS
spectra can be understood by the analysis of characteristic
NEXAFS signatures of subunits, which serve as “fingerprints”.
We note that the comparison of F8DNTT (7) with perfluoroben-
zene would not be sufficient, as the resonance at 286.4 eV
results from carbon atoms not directly bond to fluorine atoms
(indicated by purple arrow in panel (c)).[44] More details on the
comparison of DNTT NEXAFS spectra with naphthalene and
thiophene NEXAFS spectra as well as a topological justification
of the high chemical stability and low lying HOMO of DNTT-
derivatives based on Hückel theory are presented in the
supporting information.
NMR-Spectroscopy. NMR-spectra were recorded on a BRUKER AVIII
HD250, AVII 300, AVIII HD300, AVIII 500, or AVIII HD500 spectrom-
eter at room temperature unless otherwise mentioned. Chemical
shifts are reported in ppm with the solvent resonance as internal
standard. All reported 19F-NMR spectra are proton decoupled 19F
{1H}-measurements and referenced to external CFCl3. Data are
reported as follows: s=singlet, d=doublet, t=triplet, q=quartet,
quin=quintet, m=multiplet and combination thereof. All correla-
tions of atoms from NMR spectra of new compounds could be
achieved via additional 2D-NMR data (HSQC- and HMBC-spectra)
which is not shown within these SI. All 13C{19F} spectra were
recorded on AVIII 500 equipped with a 5 mm BBO (broadband
observation) Cryo probe Prodigy. Due to the very low solubility in
most routine solvents, some 13C{1H} and 13C{19F} spectra were taken
in deuterated 1,1,2,2-tetrachloroethane at elevated temperatures,
whereby 1H and 13C chemical shifts of 5.98 ppm and 73.8 ppm
relative to TMS were used for internal calibration.
High Resolution Mass Spectrometry. HR-ESI and APCI mass spectra
were acquired with a Finnigan LTQ-FT Ultra mass spectrometer
(THERMO FISCHER SCIENTIFIC). EI mass spectra were acquired with
an AccuTOF GCv (JEOL) mass spectrometer.
Conclusion
In conclusion, the syntheses of two partially fluorinated DNTTs
1,2,3,4-tetrafluoro-dinaphthothienothiophene (F4DNTT (8) and
1,2,3,4,8,9,10,11-octafluoro-dinaphthothienothiophene (F8DNTT
(7)) were accomplished via McMurry coupling or Wittig
olefination of partially fluorinated naphthalene precursors and
subsequent formation of the thienothiophene core. The elec-
tron-withdrawing character of the fluorine atoms strongly
modifies the charge distribution and leads to a likewise
reduction of both frontier orbital energy levels, thus only
slightly reducing the optical bandgap. As DNTTs are non-
alternant π-conjugated molecules, this appears to be a general
effect of fluorination. Furthermore, the carbon K-edge NEXAFS
spectra of these compounds can roughly be built up from the
units naphthalene, thiophene, and perfluoronaphthalene, exam-
Infrared Spectroscopy. FT-IR spectra were recorded on a BRUKER
IFS 200 spectrometer. Intensities are reported as follows: s=strong,
m=medium, w=weak.
Melting Points. Melting points were determined on an MP70
(METTLER TOLEDO) using one end closed capillary tubes.
UV-Vis-Spectroscopy. The optical UV/Vis absorption spectra in
solution have been acquired using an Agilent 8453 spectrometer.
The absorption spectra of the thin films have been obtained using
an OceanOptics HDX-HR spectrometer.
Ligands and Reagents. For the synthesis of TsSMe and ligand L1,
see SI.
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Thin film preparation. The organic thin films (DNTT, Sigma-Aldrich,
with Et2O (30 mL). The combined organic layers were washed with
brine (30 mL) and dried over MgSO4. The crude product was
adsorbed onto silica and purified via column chromatography (n-
pentane/EtOAc 5:1) to give 5,6,7,8-tetrafluoronaphthalen-2-ol
(174 mg, 806 μmol, 75%) as brownish solid. The analytical data
were in agreement with the literature.[38] Rf =0.52 (n-pentane/EtOAc
5:1). 1H-NMR (250 MHz, CDCl3): δ=7.96 (d, J=9.1 Hz, 1H, H4), 7.32–
7.31 (m, 1H, H1), 7.20 (dd, J=9.1, 2.2 Hz, 1H, H3), 5.23 (s, 1H, OH)
ppm. 19F-NMR (235 MHz, CDCl3): δ=À 150.3 (dd, J=18.6, 15.8 Hz,
1F), À 151.8 (dd, J=17.3, 15.5 Hz, 1F), À 158.4 (t, J=18.6 Hz, 1F),
À 163.1 (t, J=18.8 Hz, 1F) ppm.
1
2
3
4
5
6
7
8
9
purity 99%, and the synthesized fluorinated DNTTs) were grown
under high vacuum conditions by organic molecular beam
deposition (OMBD) from aluminium crucibles of resistively heated
Knudsen cells. Transparent quartz substrates (MicroChemicals) were
used for optical measurements, whereas natively oxidized Si(100)
wafers (Siegert Wafers, referred to as SiO2) were used as substrates
for NEXAFS measurements. The substrates were cleaned by rinsing
in ethanol and acetone and heated in vacuum before film
deposition. The film growth rates were monitored by a quartz
crystal microbalance (QCM) and processed at rates of about
4 ÅminÀ 1
.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Tf2O (1.60 mL, 9.50 mmol, 1.30 eq) was added dropwise to a
solution of 5,6,7,8-tetrafluoronaphthalen-2-ol (1.58 g, 7.31 mmol,
1.00 eq) and pyridine (0.89 mL, 11.0 mmol, 1.50 eq) in CH2Cl2
NEXAFS-Spectroscopy. The NEXAFS measurements were carried
out at the HE-SGM dipole beamline of the synchrotron storage ring
BESSY II in Berlin (Germany), which provides linearly-polarized light
(polarization factor =0.91 and an energy resolution at the carbon
K-edge of about 300 meV). All NEXAFS-spectra were recorded in
°
°
(28 mL) at 0 C. The solution was stirred for 45 min at 0 C before
sat. aq. NaHCO3 (50 mL) was added. The layers were separated and
the aqueous layer was extracted with CH2Cl2 (3×50 mL). The
combined organic layers were washed with 2 m aq. HCl (50 mL)
and dried over MgSO4. The crude product was adsorbed onto silica
and purified via column chromatography (n-pentane) to obtain
triflate 20 (2.39 g, 6.86 mmol, 94%) as a colorless solid. The
analytical data were in agreement with the literature.[38] Rf =0.61 (n-
pentane/EtOAc 50:1). 1H-NMR (250 MHz, CDCl3): δ=8.19 (d, J=
9.3 Hz, 1H, H4), 7.97 (s, 1H, H1), 7.52 (dd, J=9.3, 2.2 Hz, 1H, H3)
ppm. 19F-NMR (235 MHz, CDCl3): δ=À 72.6 (s, 3F, CF3), À 147.9–
À 148.1 (m, 2F), À 154.6–À 154.8 (m, 1F), À 155.6–À 155.8 (m, 1F)
°
partial electron-yield (PEY) mode at a sample orientation of 55
(magic angle) using a channel-plate detector with a retarding field
of À 150 V. The acquired spectra were normalized by considering
the transmission of the beamline and energy-calibrated via a
reference signal. All samples for the NEXAFS measurements were
prepared without contact to air in order to prevent effects from
contaminations. Details on the experimental setup and data
evaluation of NEXAFS measurements are provided in literature.[45]
Quantum Chemical Calculations. The electronic structures of
compounds DNTT, F4DNTT (8) and F8DNTT (7) have been analyzed
theoretically in the frame of DFT-calculations carried out with an 6-
311G(d,p) basis set, using the B3LYP functional as implemented in
the US GAMESS-code.[46–47] In each case the structure of the
individual molecules (i.e. gas phase) was optimized using the
highest available symmetry. Based on these data precise energy
levels and dipole moments, as well as frontier orbitals and
molecular electrostatic potentials (MEPs) are derived. The orbital
visualizations were performed with the MacMolPlt package,[48]
whereas the MEPs are generated by Molekel.[49]
°
ppm. m.p.: 74 C (EtOAc).
Methyl 5,6,7,8-tetrafluoro-2-naphthoate (21)
Triflate 20 (1.05 g, 3.02 mmol, 1.00 eq), dppf (166 mg, 0.30 mmol,
0.10 eq) and Pd(OAc)2 (33.7 mg, 0.15 mmol, 0.05 eq) were dissolved
in DMF (5.0 mL) in a 100 mL Schlenk flask and Et3N (0.84 mL,
6.04 mmol, 2.00 eq) and MeOH (2.8 mL) were added. The mixture
°
was degassed and purged with CO (3×) and then stirred at 65 C
for 6 h. H2O (50 mL) and brine (10 mL) were added and the mixture
was extracted with Et2O (3×60 mL). The combined organic layers
were washed with 2 m aq. HCl (40 mL) and brine (30 mL) and dried
over MgSO4. The crude product was adsorbed onto silica and
purified via column chromatography (n-pentane/EtOAc 29:1) to
obtain ester 21 (706 mg, 2.73 mmol, 91%) as colorless solid. Rf =
Synthesis of F8DNTT (7)
5,6,7,8-Tetrafluoronaphthalen-2-yl trifluoromethanesulfonate
(20)
1
0.46 (n-pentane/EtOAc 20:1). H-NMR (500 MHz, CDCl3): δ=8.79 (s,
1H, H1), 8.18 (d, J=8.9 Hz, 1H, H3), 8.11 (d, J=8.9 Hz, 1H, H4), 4.01
(s, 3H, CO2Me) ppm. 13C-NMR (126 MHz, CDCl3): δ=166.1 (s, 1 C,
CO2Me), 142.2 (dddd, J=252.4, 10.4, 5.0, 2.6 Hz, 1 C, CF), 143.0
(dddd, J=253.8, 10.3, 5.0, 2.8 Hz, 1 C, CF), 139.5 (dtd, J=256.1, 15.0,
3.0 Hz, 1 C, CF), 138.4 (dtd, J=254.3, 15.6, 2.7 Hz, 1 C, CF), 129.3 (s,
1 C, C2), 127.1 (s, 1 C, C3), 123.2–123.1 (m, 1 C, C1), 121.7–121.5 (m,
1 C, Cq.), 120.8–120.7 (m, 1 C, C4), 119.1 (dd, J=14.6, 3.9 Hz, 1 C, Cq.),
52.8 (s, 1 C, CO2Me) ppm. 19F-NMR (283 MHz, CDCl3): δ=À 147.4–
À 147.5 (m, 1F), À 148.8–À 149.0 (m, 1F), 154.3 (dt, J=18.5, 2.0 Hz,
n-BuLi (2.5 m in hexane, 1.60 mL, 4.00 mmol, 2.00 eq) was added
dropwise to
a
solution of 3-methoxythiophene (0.20 mL,
2.00 mmol, 1.00 eq) and bromopentafluorobenzene (0.62 mL,
°
5.00 mmol, 2.50 eq) in n-pentane (10 mL) at À 20 C. The suspension
was allowed to warm up to rt over 3 h and Et2O (50 mL) was added.
The mixture was washed successively with 2 m aq. HCl (20 mL), 13w
% aq. NaOCl (20 mL), 1 m aq. NaOH (20 mL) and brine (15 mL). The
organic layer was dried over MgSO4 and the crude product was
adsorbed onto silica and purified via column chromatography (n-
pentane) to obtain 1,2,3,4-tetrafluoro-6-methoxy-naphthalene
(255 mg, 1.11 mmol, 56%) as light yellow solid. The analytical data
1F), À 156.8–À 156.9 (m, 1F) ppm. HRMS (EI+): m/z calc. for C12H6F4O2
+
~
[M] : 258.03039, found: 258.02913. FT-IR: film; v=3098 (w), 3058
(w), 3022 (w), 2961 (w), 1723 (s), 1667 (w), 1617 (w), 1518 (w), 1492
(s), 1459 (m), 1422 (w), 1367 (s), 1299 (m), 1278 (w), 1249 (m), 1193
(w), 1132 (w), 1106 (m), 1037 (m), 995 (w), 954 (m), 910 (w), 853 (w),
816 (w), 772 (w), 753 (w), 715 (w), 672 (w), 637 (w), 536 (w), 448 (w)
1
were in agreement with the literature.[38] Rf =0.32 (n-pentane). H-
NMR (250 MHz, CD2Cl2): δ=7.95 (d, J=8.8 Hz, 1H, H4), 7.29–7.24 (m,
2H, H1 & H3), 3.94 (s, 3H, OMe) ppm. 19F-NMR (235 MHz, CD2Cl2): δ=
À 151.3 (dd, J=19.1, 15.5 Hz, 1F), À 152.5 (t, J=16.7 Hz, 1F), À 160.0
(t, J=18.6 Hz, 1F), À 164.6 (t, J=18.9 Hz, 1F) ppm.
BBr3 (1 m in CH2Cl2, 4.31 mL, 4.31 mmol, 4.00 eq) was added to a
solution of 1,2,3,4-tetrafluoro-6-methoxy-naphthalene (248 mg,
cmÀ 1. m.p.: 74 C (EtOAc).
°
Methyl 5,6,7,8-tetrafluoro-3-(methylthio)-2-naphthoate (22)
°
A solution of ester 21 (323 mg, 1.25 mmol, 1.00 eq), B2pin2 (317 mg,
1.25 mmol, 1.00 eq), [Ir(OMe)(COD)]2 (20.5 mg, 0.03 mmol, 0.025 eq)
and ligand L1 (23.3 mg, 0.06 mmol, 0.05 eq) in THF (1.6 mL) was
1.08 mmol, 1.00 eq) in CH2Cl2 (15 mL) at 0 C. The solution was
allowed to warm to rt and was stirred for 22 h. The mixture was
°
cooled to 0 C before H2O (50 mL) and Et2O (100 mL) were added.
°
degassed and purged with argon (3×) and stirred at 55 C. After 2 h
The layers were separated and the aqueous layer was extracted
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Full Papers
doi.org/10.1002/ejoc.202001635
sat. aq. NH4Cl (30 mL) and H2O (10 mL) were added and the mixture
(m), 1508 (s), 1464 (m), 1418 (m), 1387 (w), 1363 (w), 1337 (m), 1252
(w), 1170 (w), 1122 (w), 1075 (w), 1052 (s), 993 (m), 959 (m), 886 (w),
855 (w), 785 (w), 737 (w), 709 (w), 672 (w), 641 (w), 530 (w), 438 (w)
1
2
3
4
5
6
7
8
9
was extracted with EtOAc (3×30 mL). The combined organic layers
were washed with brine (20 mL), dried over MgSO4, and filtered
over a short plug of celite and silica. The solvent was removed
under reduced pressure and the crude methyl-5,6,7,8-tetrafluoro-3-
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2-naphthoate was used
in the next step without further purification. 1H-NMR (250 MHz,
CDCl3): δ=8.68 (s, 1H, H1), 8.18 (s, 1H, H4), 4.00 (s, 3H, CO2Me), 1.47
(s, 12H, 4×CH3) ppm. 19F-NMR (235 MHz, CDCl3): δ=À 148.3 (t, J=
17.3 Hz, 1F), À 149.3 (t, J=17.3 Hz, 1F), À 154.8 (t, J=18.5 Hz, 1F),
À 156.7 (t, J=18.4 Hz, 1F) ppm. 11B-NMR (160 MHz, CDCl3): δ=22.31
(s, 1B) ppm. HRMS (EI+): m/z calc. for C18H17BF4O4 [M]+: 384.11560,
found: 384.11594.
cmÀ 1. m.p.: 150 C (EtOAc).
°
Oxalyl chloride (36.0 μL, 0.42 mmol, 1.50 eq) was added to a
solution of DMSO (60.0 μL, 0.84 mmol, 3.00 eq) in CH2Cl2 (5.0 mL) at
°
À 78 C. The solution was stirred for 10 min before it was added to a
suspension of (5,6,7,8-tetrafluoro-3-(methylthio)naphthalen-2-yl)
°
methanol (77 mg, 0.28 mmol, 1.00 eq) in CH2Cl2 (5.0 mL) at À 78 C.
The mixture was stirred for 30 min and Et3N (193 μL, 1.39 mmol,
5.00 eq) was added. After stirring for 30 min at À 78 C the cooling
°
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
bath was removed and the solution was stirred for additional
15 min at rt. H2O (20 mL) and brine (5 mL) were added and the
mixture was extracted with CH2Cl2 (3×20 mL). The combined
organic layers were dried over MgSO4 and the crude product was
adsorbed onto silica and purified via column chromatography (n-
pentane/EtOAc 29:1) to obtain aldehyde 23 (70 mg, 255 μmol,
91%) as fluffy yellow solid. Rf =0.55 (n-pentane/EtOAc 10:1). 1H-
NMR (500 MHz, CDCl3): δ=10.35 (s, 1H, CHO), 8.51 (d, J=1.3 Hz, 1H,
H1), 7.73 (s, 1H, H4), 2.61 (s, 3H, SMe) ppm. 13C-NMR (126 MHz,
CDCl3): δ=190.6 (s, 1 C, CHO), 143.1 (dddd, J=254.9, 10.6, 4.5,
3.0 Hz, 1 C, CF), 141.3 (dddd, J=252.0, 10.0, 5.0, 2.0 Hz, 1 C, CF),
141.1 (s, 1 C, C3), 140.5 (dtd, J=257.1, 15.1, 3.1 Hz, 1 C, CF), 137.6
(dtd, J=254.4, 15.3, 2.9 Hz, 1 C, CF), 132.5 (s, 1 C, C2), 128.5–128.4
(m, 1 C, C1), 122.1–122.0 (m, 1 C, Cq.), 116.1 (dd, J=15.2, 4.1 Hz, 1 C,
Cq.), 114.8–114.7 (m, 1 C, C4), 15.5 (s, 1 C, SMe) ppm. 19F-NMR
(283 MHz, CDCl3): δ=À 147.1–À 147.3 (m, 1F), À 150.1 (dd, J=17.9,
16.5 Hz, 1F), À 152.2–À 152.3 (m, 1F), À 158.6 (t, J=18.5 Hz, 1F) ppm.
HRMS (EI+): m/z calc. for C12H6F4OS [M]+: 274.00755, found:
TMEDA (22.6 μL, 0.15 mmol, 0.12 eq) was added to a suspension of
methyl-5,6,7,8-tetrafluoro-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
2-yl)-2-naphthoate (crude, ~1.25 mmol, 1.00 eq), TsSMe (303 mg,
1.50 mmol, 1.20 eq), CuSO4 (21 mg, 0.13 mmol, 0.10 eq) and CsF
(380 mg, 2.50 mmol, 2.00 eq) in MeOH (12.7 mL). The mixture was
°
stirred at 50 C for 26 h and was then filtered over a short plug of
celite and rinsed with EtOAc (150 mL). The crude product was
adsorbed onto silica and purified via column chromatography (n-
pentane/EtOAc 49:1) to give thioether 22 (346 mg, 1.14 mmol,
91% over two steps) as light yellow solid. Rf =0.58 (n-pentane/
1
EtOAc 10:1). H-NMR (500 MHz, CDCl3): δ=8.69 (d, J=1.4 Hz, 1H,
H1), 7.69 (s, 1H, H4), 4.00 (s, 3H, CO2Me), 2.57 (s, 3H, SMe) ppm. 13C-
NMR (126 MHz, CDCl3): δ=166.0 (s, 1 C, CO2Me), 142.8 (dddd, J=
254.3, 10.2, 5.2, 2.7 Hz, 1 C, CF), 141.8 (s, 1 C, C3), 141.2 (dddd, J=
251.5, 10.7, 4.7, 2.2 Hz, 1 C, CF), 140.0 (dtd, J=256.3, 15.5, 3.4 Hz,
1 C, CF), 137.5 (dtd, J=252.9, 15.4, 2.9 Hz, 1 C, CF), 127.6 (s, 1 C, C2),
124.8–124.7 (m, 1 C, C1), 121.5–121.4 (m, 1 C, Cq.), 115.8 (dd, J=
14.7, 4.1 Hz, 1 C, Cq.), 114.3–114.2 (m, 1 C, C4), 52.8 (s, 1 C, CO2Me),
16.1 (s, 1 C, SMe) ppm. 19F-NMR (283 MHz, CDCl3): δ=À 147.7–
À 147.8 (m, 1F), À 150.4 (t, J=16.9 Hz, 1F), À 153.5 (td, J=18.3,
~
274.00669. FT-IR: film; v=2927 (w), 2848 (w), 2734 (w), 1694 (s),
1668 (w), 1603 (m), 1507 (s), 1458 (s), 1420 (w), 1381 (w), 1343 (m),
1262 (w), 1184 (w), 1131 (w), 1077 (m), 1051 (w), 995 (m), 967 (w),
898 (w), 863 (w), 812 (w), 716 (w), 680 (w), 651 (w), 625 (w), 553 (w),
2.9 Hz, 1F), À 158.9 (t, J=18.3 Hz, 1F) ppm. HRMS (EI+): m/z calc. for
446 (w) cmÀ 1. m.p.: 151 C (EtOAc).
°
+
~
C13H8F4O2S [M] : 304.01811, found: 304.01533. FT-IR: film; v=3001
(w), 2960 (w), 2929 (w), 2848 (w), 1720 (s), 1665 (w), 1600 (m), 1505
(m), 1455 (m), 1437 (w), 1413 (w), 1384 (w), 1341 (m), 1290 (w),
1264 (w), 1232 (s), 1192 (w), 1130 (m), 1108 (w), 1068 (s), 1000 (w),
969 (w), 932 (w), 862 (w), 815 (w), 785 (w), 742 (w), 655 (w), 614 (w),
1,2-Bis(5,6,7,8-tetrafluoro-3-(methylthio)naphthalen-2-yl)ethene
(24)
TiCl4 (0.12 mL, 1.09 mmol, 3.00 eq) was added dropwise to a
suspension of zinc-powder (71 mg, 1.09 mmol, 3.00 eq) in THF
447 (w) cmÀ 1. m.p.: 149 C (EtOAc).
°
°
°
(1.8 mL) at 0 C. The mixture was stirred at 66 C for 3 h and then
cooled to rt. A solution of aldehyde 23 (100 mg, 365 μmol, 1.00 eq)
in THF (1.2 mL) was added and the resulting mixture was stirred at
5,6,7,8-Tetrafluoro-3-(methylthio)-2-naphthaldehyde (23)
°
DIBAH (1.0 m in CH2Cl2, 0.82 mL, 818 μmol, 3.00 eq) was added
dropwise to a suspension of ester 22 (83 mg, 273 μmol, 1.00 eq) in
66 C for 14 h. The reaction was carefully quenched by adding sat.
aq. NaHCO3 (2 mL) and the suspension was stirred vigorously for
1.5 h at rt. The mixture was filtered over a short plug of celite and
rinsed with CH2Cl2 (200 mL). The solution was washed with brine
(30 mL) and dried over MgSO4. The crude product was adsorbed
onto silica and purified via column chromatography (CH2Cl2) to
obtain olefin 24 (88 mg, 170 μmol, 93%) as yellow solid with very
low solubility. 1H-NMR-spectroscopy showed an E/Z-ratio of 1:0.9.
Rf =0.69 (n-pentane/EtOAc 10:1). 1H-NMR (300 MHz, CD2Cl2): E-
isomer: δ=8.21 (s, 2H, 2×Har.), 7.74 (s, 2H, 2×Har.), 7.61 (s, 2H, 2×
°
THF (2.2 mL) at 0 C. The solution was stirred for 20 min at rt before
H2O (5 mL) and 2 m aq. HCl (10 mL) were added. The mixture was
extracted with CH2Cl2 (3×25 mL) and the combined organic layers
were dried over MgSO4. The crude product was adsorbed onto
silica and purified via column chromatography (n-pentane/EtOAc
5:1) to obtain (5,6,7,8-tetrafluoro-3-(methylthio)naphthalen-2-yl)
methanol (70 mg, 255 μmol, 93%) as colorless solid. Rf =0.36 (n-
1
pentane/EtOAc 5:1). H-NMR (500 MHz, CDCl3): δ=8.06 (s, 1H, H1),
7.65 (s, 1H, H4), 4.88 (s, 2H, CH2OH), 2.63 (s, 3H, SMe), 2.20 (s, 1H,
OH) ppm. 13C-NMR (126 MHz, CDCl3): δ=142.4 (dddd, J=250.9,
10.1, 4.5, 3.0 Hz, 1 C, CF), 141.3 (dddd, J=250.1, 10.5, 4.9, 2.2 Hz,
1 C, CF), 138.5 (s, 1 C, C3), 138.3 (s, 1 C, C2), 138.3 (dtd, J=252.0,
15.4, 2.8 Hz, 1 C, CF), 137.4 (dtd, J=251.2, 15.2, 2.8 Hz, 1 C, CF),
119.5 (dd, J=14.4, 4.1 Hz, 1 C, Cq.), 118.0–117.9 (m, 1 C, C1), 117.0
(dd, J=14.0, 4.1 Hz, 1 C, Cq.), 114.1–113.9 (m, 1 C, C4), 62.9 (s, 1 C,
CH2OH), 15.2 (s, 1 C, SMe) ppm. 19F-NMR (283 MHz, CDCl3): δ=
À 150.2 (dd, J=18.3, 15.5 Hz, 1F), À 151.6 (dd, J=18.2, 15.6 Hz, 1F),
À 158.6 (t, J=18.5 Hz, 1F), À 160.4 (t, J=18.6 Hz, 1F) ppm. HRMS
(EI+): m/z calc. for C12H8F4OS [M]+: 276.02320, found: 276.02215. FT-
Holef.), 2.65 (s, 6H, 2×SMe) ppm. Z-isomer: δ=7.68 (s, 2H, 2×Har.),
7.54 (s, 2H, 2×Har.), 7.04 (s, 2H, 2×Holef.), 2.66 (s, 6H, 2×SMe) ppm.
13C{19F}-NMR (126 MHz, C2D2Cl4): Z-isomer: δ=141.7 (d, J=3.8 Hz,
2 C, 2×C8), 140.9 (d, J=3.8 Hz, 2 C, 2×C5), 140.2–140.1 (m, 2 C, 2×
C3), 137.9 (s, 2 C, 2×C6), 136.7 (s, 2 C, 2×C7), 134.7 (dd, J=12.1,
6.5 Hz, 2 C, 2×C2), 130.3 (d, J=160.7 Hz, 2 C, 2×C11), 119.4 (d, J=
165.7 Hz, 2 C, 2×C1), 119.0 (d, J=6.7 Hz, 2 C, 2×C10), 116.3 (d, J=
6.7 Hz, 2 C, 2×C9), 113.1 (d, J=165.3 Hz, 2 C, 2×C4), 15.2 (q, J=
140.4 Hz, 2 C, 2×SMe) ppm. 19F-NMR (235 MHz, CD2Cl2): E-isomer:
δ=-150.7 (t, J=17.0 Hz, 2F), -151.9 (t, J=16.9 Hz, 2F), -159.1 (t, J=
18.3 Hz, 2F), -161.3 (t, J=18.5 Hz, 2F) ppm. Z-isomer: δ=-151.4 (t,
J=17.0 Hz, 2F), -152.2 (t, J=16.9 Hz, 2F), -159.6 (t, J=18.3 Hz, 2F),
~
IR: film; v=3306 (w), 2928 (w), 2886 (w), 2855 (w), 1668 (w), 1613
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Full Papers
doi.org/10.1002/ejoc.202001635
-162.0 (t, J=18.5 Hz, 2F) ppm. HRMS (EI+): m/z calc. for C24H12F8S2
(13.000 rpm, 2 min) and washed successively with MeOH (1.0 mL),
H2O (2×1.0 mL), acetone (2×1.0 mL), n-hexane (1.0 mL), and CH2Cl2
(4×1.0 mL) to obtain F8DNTT 7 (18 mg, 37.2 μmol, 60%) as green
solid. 1H-NMR (500 MHz, 343 K, C2D2Cl4): δ=8.70 (s, 2H, 2×Har.), 8.60
(s, 2H, 2×Har.) ppm. 13C{19F}-NMR (126 MHz, 343 K, C2D2Cl4): δ=
142.2, 141.4, 137.7, 137.4, 123.5, 120.2 ppm. Due to the low solubility
of 7, not all expected 13C-signals could be observed. 19F-NMR
(471 MHz, 343 K, C2D2Cl4): δ=À 149.7 (t, J=16.4 Hz, 2F), À 150.3 (t,
J=16.4 Hz, 2F), À 157.8 (t, J=17.5 Hz, 2F), À 158.7 (t, J=17.6 Hz, 2F)
ppm. HRMS (APCI+): m/z calc. for C22H4F8S2 [M]+: 483.9627, found:
1
2
3
4
5
6
7
8
9
+
~
[M] : 516.02527, found: 516.02332. FT-IR: neat; v=2962 (w), 2924
(w), 1666 (w), 1599 (m), 1502 (s), 1456 (w), 1416 (m), 1383 (w), 1343
(m), 1314 (w), 1261 (w), 1233 (m), 1165 (w), 1148 (w), 1124 (w), 1070
(s), 1001 (s), 959 (m), 907 (w), 878 (w), 858 (w), 798 (w), 767 (w), 730
(w), 699 (w), 672 (m), 648 (w), 546 (w), 499 (w), 455 (w), 439 (w) cm-
1
°
. m.p.: 262 C (CH2Cl2).
5,6,7,8-Tetrafluoro-2-(5,6,7,8-tetrafluoro-3-(methylthio)
naphthalen-2-yl)naphtho[2,3-b]thiophene (25)
~
483.9626. FT-IR: neat; v=3085 (w), 1667 (m), 1609 (w), 1592 (w),
1501 (w), 1475 (w), 1460 (m), 1411 (w), 1353 (s), 1303 (w), 1250 (m),
1199 (w), 1177 (w), 1127 (m), 1065 (m), 1006 (s), 970 (s), 913 (w),
A
suspension of olefin 24 (44 mg, 85.2 μmol, 1.00 eq) and
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
powdered iodine (627 mg, 2.47 mmol, 29.0 eq) in dichloroethane
(2.7 mL) was stirred at 84 C for 22 h under exclusion of light. After
°
863 (m), 801 (m), 726 (w), 664 (w), 635 (m), 549 (m), 434 (m) cmÀ 1
.
°
m.p.: >350 C (CH2Cl2).
cooling to rt sat. aq. Na2SO3 (2 mL) was added and the suspension
was stirred vigorously for 15 min. Additional sat. aq. Na2SO3 (18 mL)
was added and the mixture was extracted with CH2Cl2 (3×20 mL).
The combined organic layers were dried over MgSO4 and the crude
product was adsorbed onto silica and purified via column
chromatography (n-pentane/EtOAc 19:1) to obtain naphthothio-
phene 25 (10 mg, 20.0 μmol, 23%) as light yellow solid. Rf =0.25 (n-
pentane/CH2Cl2 30:1). 1H-NMR (300 MHz, CD2Cl2): δ=8.61 (s, 1H,
Har.), 8.57 (s, 1H, Har.), 8.16 (d, J=1.3 Hz, 1H, Har.), 7.80 (s, 1H, Har.),
7.76 (s, 1H, Har.), 2.61 (s, 3H, SMe) ppm. 19F-NMR (235 MHz, CD2Cl2):
δ=-150.2 (t, J=17.1 Hz, 1F), -151.0 (t, J=16.5 Hz, 1F), -151.5 (t, J=
16.9 Hz, 1F), -151.6 (t, J=16.1 Hz, 1F), -157.6 (t, J=18.4 Hz, 1F),
-160.3 (t, J=17.4 Hz, 1F), -160.5 (t, J=18.6 Hz, 1F), À 161.2 (t, J=
17.7 Hz, 1F) ppm. HRMS (EI+): m/z calc. for C23H8F8O2S2 [M]+:
Synthesis of F4DNTT (8)
Methyl 3-(methylthio)-2-naphthoate (28)
A solution of ester 27 (248 mg, 1.33 mmol, 1.00 eq), B2pin2 (338 mg,
1.33 mmol, 1.00 eq), [Ir(OMe)(COD)]2 (22 mg, 0.03 mmol, 0.025 eq)
and ligand L1 (25 mg, 0.07 mmol, 0.05 eq) in THF (1.7 mL) was
°
degassed and purged with argon (3×) and stirred at 55 C. After 2 h
sat. aq. NH4Cl (30 mL) and H2O (10 mL) were added and the mixture
was extracted with EtOAc (3×30 mL). The combined organic layers
were washed with brine (20 mL), dried over MgSO4, and filtered
over a short plug of celite and silica. The solvent was removed
under reduced pressure and the crude methyl-3-(4,4,5,5-tetrameth-
yl-1,3,2-dioxaborolan-2-yl)-2-naphthoate was used in the next step
~
499.99397, found: 499.99125. FT-IR: neat; v=2957 (w), 2921 (w),
2851 (w), 1714 (w), 1667 (w), 1592 (m), 1499 (m), 1464 (m), 1402
(w), 1379 (w), 1347 (s), 1255 (m), 1173 (w), 1117 (w), 1071 (s), 1007
(w), 966 (m), 883 (m), 860 (w), 800 (w), 741 (w), 709 (w), 657 (w), 634
1
without further purification. H-NMR (250 MHz, CDCl3): δ=8.49 (s,
(m), 537 (w), 432 (m) cmÀ 1. m.p.: 237 C decomposition (CH2Cl2).
1H, Har.), 7.99 (s, 1H, Har.), 7.92–7.84 (m, 2H, 2×Har.), 7.60–7.50 (m, 2H,
2×Har.), 3.97 (s, 3H, CO2Me), 1.46 (s, 12H, 4×CH3) ppm. 11B-NMR
(160 MHz, CDCl3): δ=22.29 (s, 1B) ppm. HRMS (APCI+): m/z calc. for
C18H22BF4O4 [M+H]+: 313.1609, found: 313.1614.
°
5,6,7,8-Tetrafluoro-2-(5,6,7,8-tetrafluoro-3-(methylsulfinyl)
naphtha-lene-2-yl)naphtho[2,3-b]thiophene (26)
TMEDA (24.7 μL, 0.16 mmol, 0.12 eq) was added to a suspension of
methyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2-naphthoate
(crude, ~1.33 mmol, 1.00 eq), TsSMe (324 mg, 1.60 mmol, 1.20 eq),
CuSO4 (21 mg, 0.13 mmol, 0.10 eq) and CsF (404 mg, 2.66 mmol,
CH2Cl2 (2.0 mL) was added to a mixture of naphthothiophene 25
(28 mg, 56.0 μmol, 1.00 eq) and mCPBA (77%, 13 mg, 56.0 μmol,
°
°
1.00 eq) at 0 C. The suspension was stirred for 5 min at 0 C and
then additional 26 h at rt. The mixture was poured into 1 m aq.
K2CO3 (20 mL) and extracted with CH2Cl2 (3×20 mL). The combined
organic layers were washed with 1 m aq. K2CO3 (20 mL) and dried
over MgSO4. The solvent was removed under reduced pressure and
the crude sulfoxide 26 (27 mg, 52.3 μmol, 93%) was used in the
next step without further purification. 1H-NMR (300 MHz, CD2Cl2):
δ=8.86 (d, J=1.3 Hz, 1H, Har.), 8.63 (s, 1H, Har.), 8.60 (s, 1H, Har.), 8.32
(d, J=1.1 Hz, 1H, Har.), 7.74 (s, 1H, Har.), 2.55 (s, 3H, OSMe) ppm. 19F-
NMR (235 MHz, CD2Cl2): δ=À 147.5 (t, J=16.9 Hz, 1F), À 148.6 (t, J=
16.9 Hz, 1F), À 150.6 (t, J=16.4 Hz, 1F), À 151.3 (t, J=16.3 Hz, 1F),
À 155.4 (t, J=18.2 Hz, 1F), À 155.7 (t, J=18.3 Hz, 1F), À 159.4 (t, J=
17.4 Hz, 1F), À 160.5 (t, J=17.5 Hz, 1F) ppm. HRMS (EI+): m/z calc.
for C23H8F8O2S2 [M]+: 515.98888, found: 515.98944.
°
2.00 eq) in MeOH (14 mL). The mixture was stirred at 50 C for 22 h
and was then filtered over a short plug of celite and rinsed with
EtOAc (60 mL). The crude product was adsorbed onto silica and
purified via column chromatography (n-pentane/EtOAc 29:1) to
give thioether 28 (207 mg, 891 μmol, 67% over two steps) as light
yellow solid. Rf =0.23 (n-pentane/EtOAc 29:1). 1H-NMR (500 MHz,
CDCl3): δ=8.54 (s, 1H, H1), 7.85 (d, J=8.2 Hz, 1H, H8), 7.76 (d, J=
8.1 Hz, 1H, H5), 7.57–7.54 (m, 2H, H4 & H7), 7.46–7.42 (m, 1H, H6),
3.98 (s, 3H, CO2Me), 2.57 (s, 3H, SMe) ppm. 13C-NMR (126 MHz,
CDCl3): δ=167.1 (s, 1 C, CO2Me), 138.1 (s, 1 C, C3), 135.4 (s, 1 C, C9),
132.8 (s, 1 C, C1), 129.5 (s, 1 C, C10), 129.0 (s, 1 C, C8), 129.0 (s, 1 C,
C7), 126.6 (s, 1 C, C5), 125.8 (s, 2 C, C2 & C6), 122.6 (s, 1 C, C4), 52.4
(s, 1 C, CO2Me), 16.1 (s, 1 C, SMe) ppm. HRMS (EI+): m/z calc. for
+
~
C13H12O2S [M] : 232.05580, found: 232.05643. FT-IR: film; v=3054
(w), 2990 (w), 2949 (w), 2919 (w), 1716 (s), 1625 (w), 1584 (w), 1488
(w), 1435 (w), 1347 (w), 1314 (w), 1276 (s), 1226 (w), 1201 (m), 1136
(w), 1110 (m), 1018 (w), 951 (w), 902 (w), 874 (w), 842 (w), 812 (w),
1,2,3,4,8,9,10,11-Octafluoronaphtho[2,3-b]naphtha[2’,3’:4,5]
thieno-[2,3-d]thiophene (F8DNTT, 7)
782 (w), 746 (w), 608 (w), 474 (w) cmÀ 1. m.p.: 75 C (EtOAc).
°
TfOH (0.69 mL) was added to sulfoxide 26 (32 mg, 62.0 μmol,
1.00 eq) and P2O5 (8.8 mg, 62.0 μmol, 1.00 eq), and the suspension
was stirred at rt for 3 d. The mixture was cooled to 0 C and ice-
water (1.0 mL) was added. The precipitate was centrifuged
(13.000 rpm, 2 min), washed with H2O (1.0 mL), and dried under
reduced pressure. Pyridine (0.57 mL) was added and the suspension
°
((3-(Methylthio)naphthalen-2-yl)methyl)
triphenylphosphonium-bromide (29)
DIBAH (1.0 m in CH2Cl2, 2.4 mL, 2.36 mmol, 3.00 eq) was added
dropwise to a suspension of ester 28 (183 mg, 788 μmol, 1.00 eq) in
°
was stirred at 115 C for 23 h. The mixture was cooled to rt and
MeOH (2 mL) was added. The precipitate was centrifuged
°
THF (6.4 mL) at 0 C. The solution was stirred for 2 h at rt before
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1302
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°
H2O (10 mL) and 2 m aq. HCl (10 mL) were added. The mixture was
extracted with CH2Cl2 (4×20 mL) and the combined organic layers
were dried over MgSO4. The crude product was adsorbed onto
silica and purified via column chromatography (n-pentane/EtOAc
5:1) to obtain (3-(methylthio)naphthalen-2-yl)methanol (143 mg,
700 μmol, 89%) as colorless solid. Rf =0.29 (n-pentane/EtOAc 5:1).
1H-NMR (500 MHz, CDCl3): δ=δ=7.82 (s, 1H, H1), 7.79 (d, J=8.1 Hz,
1H, H8), 7.75 (d, J=8.1 Hz, 1H, H5), 7.60 (s, 1H, H4), 7.48–7.45 (m,
1H, H7), 7.44–7.41 (m, 1H, H6), 4.89 (s, 2H, CH2OH), 2.60 (s, 3H, SMe),
2.25 (s, 1H, OH) ppm. 13C-NMR (126 MHz, CDCl3): δ=136.8 (s, 1 C,
C2), 135.2 (s, 1 C, C3), 133.5 (s, 1 C, C9), 131.4 (s, 1 C, C10), 127.9 (s,
1 C, C8), 126.8 (s, 1 C, C1), 126.6 (s, 2 C, C5 & C7), 125.7 (s, 1 C, C6),
124.2 (s, 1 C, C4), 63.7 (s, 1 C, CH2OH), 16.0 (s, 1 C, SMe) ppm. HRMS
(EI+): m/z calc. for C12H12OS [M]+: 204.06089, found: 204.06125. FT-
511 (s), 481 (w), 444 (w), 425 (w) cmÀ 1. m.p.: 262 C decomposition
(toluene).
1
2
3
4
5
6
7
8
9
Methyl(5,6,7,8-tetrafluoro-3-(2-(3-(methylthio)naphthalen-2-yl)
vinyl)-naphthalen-2-yl)sulfane (30)
n-BuLi (2.5 m in n-hexane, 0.32 mL, 795 μmol, 1.09 eq) was added
dropwise to a suspension of phosphonium bromide 29 (425 mg,
802 μmol, 1.10 eq) in THF (58 mL) at 0 C. The orange solution was
°
°
stirred at 0 C for 30 min before a pre-cooled solution of aldehyde
23 (200 mg, 729 μmol, 1.00 eq) in THF (5.0 mL) was added
dropwise. The ice-bath was removed and the solution was stirred at
rt for 15 min before H2O (50 mL) and brine (10 mL) were added. The
mixture was extracted with CH2Cl2 (3×60 mL) and the combined
organic layers were washed with brine (30 mL) and dried over
MgSO4. The crude product was adsorbed onto silica and purified
via column chromatography (n-pentane/CH2Cl2 29:1) to obtain
olefin 30 (311 mg, 700 μmol, 96%) as a light yellow solid. 19F-NMR-
spectroscopy showed an E/Z-ratio of 1:0.16. Rf =0.30 (n-pentane/
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
~
IR: film; v=3348 (m), 3051 (w), 2983 (w), 2918 (w), 2873 (w), 1626
(w), 1592 (w), 1490 (w), 1431 (s), 1390 (w), 1314 (w), 1273 (w), 1205
(w), 1158 (w), 1131 (m), 1053 (w), 1029 (m), 1006 (w), 954 (w), 891
(w), 868 (s), 746 (s), 600 (w), 476 (m) cmÀ 1. m.p.: 63 C (EtOAc).
°
NBS (787 mg, 4.42 mmol, 2.00 eq) was added in portions over 3 min
to a solution of (3-(methylthio)naphthalen-2-yl)methanol (451 mg,
2.21 mmol, 1.00 eq) and PPh3 (1.16 g, 4.42 mmol, 2.00 eq) in CH2Cl2
1
EtOAc 50:1). H-NMR (500 MHz, CD2Cl2): δ=7.70 (d, J=7.9 Hz, 1H,
Har.), 7.65 (s, 1H, Har.), 7.59–7.59 (m, 2H, 2×Har.), 7.40–7.35 (m, 3H, 3×
Har.), 7.25–7.21 (m, 1H, Har.), 7.10 (dd, J=11.8, 0.7 Hz, 1H, Holef.), 6.94
(d, J=11.8 Hz, 1H, Holef.), 2.65 (s, 3H, SMe), 2.64 (s, 3H, SMe) ppm. 19F-
NMR (283 MHz, CD2Cl2): δ=À 151.0 (dd, J=18.5, 15.3 Hz, 1F),
À 152.1 (t, J=16.9 Hz, 1F), À 159.7 (t, J=18.4 Hz, 1F), À 161.8 (t, J=
18.3 Hz, 1F) ppm. HRMS (EI+): m/z calc. for C24H16F4S2 [M]+:
°
°
(10.6 mL) at 0 C. The solution was stirred at 0 C for 1 h before H2O
(50 mL) and brine (15 mL) were added. The mixture was extracted
with CH2Cl2 (3×50 mL) and the combined organic layers were dried
over MgSO4 and filtered through a short plug of silica. The crude
product was adsorbed onto silica and purified via column
chromatography (n-pentane/EtOAc 49:1) to obtain (3-(bromometh-
yl)naphthalen-2-yl)(methyl)sulfane (486 mg, 1.82 mmol, 82%) as
~
444.06295, found: 444.06325. FT-IR: film; v=3053 (w), 2987 (w),
2921 (w), 2853 (w), 1666 (w), 1600 (m), 1504 (s), 1459 (w), 1419 (m),
1344 (m), 1317 (w), 1248 (w), 1204 (w), 1175 (w), 1128 (w), 1071 (s),
1018 (w), 993 (m), 963 (w), 898 (w), 870 (w), 841 (w), 797 (w), 745
(m), 691 (w), 666 (w), 643 (w), 599 (w), 475 (w), 440 (w) cmÀ 1. m.p.:
1
colorless solid. Rf =0.73 (n-pentane/EtOAc 10:1). H-NMR (500 MHz,
CDCl3): δ=7.85 (s, 1H, H1), 7.78–7.74 (m, 2H, H5 & H8), 7.63 (s, 1H,
H4), 7.50–7.46 (m, 1H, H7), 7.44–7.41 (m, 1H, H6), 4.80 (s, 2H, CH2Br),
2.64 (s, 3H, SMe) ppm. 13C-NMR (126 MHz, CDCl3): δ=136.3 (s, 1 C,
C3), 134.0 (s, 1 C, C2), 133.8 (s, 1 C, C9), 131.2 (s, 1 C, C10), 129.9 (s,
1 C, C1), 127.9 (s, 1 C, C8), 127.3 (s, 1 C, C7), 126.7 (s, 1 C, C5), 125.9
(s, 1 C, C6), 124.9 (s, 1 C, C4), 32.2 (s, 1 C, CH2Br), 16.4 (s, 1 C, SMe)
ppm. HRMS (EI+): m/z calc. for C12H11BrS [M]+: 265.97648, found:
°
167 C (CH2Cl2).
1,2,3,4-Tetrafluoronaphtho[2,3-b]naphtho[2’,3’:4,5]thieno
[2,3-d]thio-phene (F4DNTT, 8)
~
265.97453. FT-IR: film; v=3050 (w), 3019 (w), 2986 (w), 2965 (w),
A
suspension of olefin 30 (40 mg, 90.0 μmol, 1.00 eq) and
powdered iodine (662 mg, 2.61 mmol, 29.0 eq) in AcOH (2.8 mL)
was stirred at 118 C for 21 h. The mixture was cooled to rt and sat.
aq. Na2SO3 (1 mL) was added and the suspension was stirred
vigorously for 5 min. The precipitate was centrifuged (13.000 rpm,
2 min) and successively washed with sat. aq. Na2SO3 (1.0 mL), H2O
(1.0 mL), acetone (1.0 mL) and CH2Cl2 (2×1.0 mL) to obtain F4DNTT
2918 (w), 2855 (w), 1622 (w), 1586 (w), 1489 (w), 1432 (m), 1315 (w),
1275 (w), 1246 (w), 1208 (s), 1174 (w), 1151 (w), 1134 (w), 1115 (w),
1018 (m), 952 (w), 917 (w), 896 (w), 867 (m), 836 (w), 802 (w), 748
(s), 697 (w), 598 (w), 582 (m), 521 (w), 507 (w), 474 (m), 449 (w)
°
cmÀ 1. m.p.: 106 C (n-pentane).
°
A
solution of (3-(bromomethyl)naphthalen-2-yl)(methyl)sulfane
1
8 (27 mg, 65.5 μmol, 73%) as green solid. H-NMR (500 MHz, 343 K,
(486 mg, 1.82 mmol, 1.00 eq) and PPh3 (572 mg, 2.18 mmol,
°
C2D2Cl4): δ=8.66 (s, 1H, Har.), 8.54 (s, 1H, Har.), 8.48 (s, 1H, Har.), 8.43
(s, 1H, Har.), 8.08–8.07 (m, 1H, Har.), 7.99–7.97 (m, 1H, Har.), 7.59–7.58
(m, 2H, 2×Har.) ppm. 13C-NMR (126 MHz, 343 K, C2D2Cl4): δ=128.2,
127.2, 126.4, 125.9, 123.5, 122.6, 120.6, 120.2 ppm. Due to the low
solubility of 8, not all expected 13C-signals could be observed. 19F-NMR
(471 MHz, 343 K, C2D2Cl4): δ=À 150.0 (t, J=16.4 Hz, 1F), À 150.6 (t,
J=16.1 Hz, 1F), À 158.8 (t, J=17.9 Hz, 1F), À 159.3 (t, J=17.4 Hz, 1F)
ppm. HRMS (EI+): m/z calc. for C22H8F4S2 [M]+: 412.00035, found:
1.20 eq) in toluene (20.6 mL) was stirred at 111 C for 17 h. After
cooling to rt, the precipitate was filtered, washed with toluene (3×
10 mL), and dried under reduced pressure. Phosphonium bromide
1
29 (929 mg, 1.75 mmol, 96%) was obtained as a colorless solid. H-
NMR (500 MHz, DMSO-d6): δ=7.93–7.89 (m, 3H, 3×Har.), 7.87 (d, J=
8.2 Hz, 1H, Har.), 7.79 (s, 1H, Har.), 7.74–7.70 (m, 6H, 6×Har.), 7.65–7.61
(m, 6H, 6×Har.), 7.57–7.51 (m, 3H, 3×Har.), 7.44–7.41 (m, 1H, Har.),
5.23 (d, J=14.6 Hz, 2H, CH2PPh3), 2.26 (s, 3H, SMe) ppm. 13C-NMR
(126 MHz, DMSO-d6): δ=137.4 (d, J=5.0 Hz, 1 C, Cq.), 135.2 (d, J=
2.6 Hz, 3 C, 3×Car.), 134.1 (d, J=9.9 Hz, 6 C, 6×Car.), 133.1 (d, J=
2.0 Hz, 1 C, Cq.), 130.5 (d, J=7.0 Hz, 1 C, Car.), 130.2 (d, J=13.0 Hz,
6 C, 6×Car.), 130.2–130.1 (m, 1 C, Cq.), 127.4 (s, 1 C, Car.), 127.2 (s, 1 C,
Car.), 126.8 (s, 1 C, Car.), 126.3 (s, 1 C, Car.), 125.6 (d, J=2.0 Hz, 1 C,
Car.), 124.2 (d, J=9.0 Hz, 1 C, Cq.), 117.5 (d, J=85.4 Hz, 3 C, 3×Cq.P),
26.9 (d, J=48.2 Hz, 1 C, CH2PPh3), 16.2 (s, 1 C, SMe) ppm. 31P-NMR
(202 MHz, DMSO-d6): δ=23.1 (s, 1P, PPh3) ppm. HRMS (ESI+): m/z
~
412.00176. FT-IR: neat; v=3259 (w), 1673 (w), 1592 (w), 1499 (m),
1463 (w), 1413 (w), 1383 (w), 1345 (m), 1247 (w), 1212 (w), 1121 (s),
1066 (w), 1031 (w), 1009 (m), 971 (m), 913 (w), 862 (m), 803 (w), 745
(m), 706 (w), 619 (s), 585 (w), 567 (w), 540 (w), 496 (w), 470 (w), 426
(w) cmÀ 1. m.p.: >350 C (CH2Cl2).
°
calc. for C30H26PS [MÀ Br]+: 449.1487, found: 449.1485. FT-IR: neat; Acknowledgements
~
v=3041 (w), 3004 (w), 2988 (w), 2928 (w), 2914 (w), 2843 (w), 2775
(w), 1585 (w), 1486 (w), 1436 (m), 1404 (w), 1316 (w), 1191 (w), 1162
(w), 1108 (s), 1014 (w), 995 (w), 974 (w), 929 (w), 893 (w), 867 (w),
841 (w), 771 (w), 757 (w), 740 (s), 716 (w), 690 (s), 626 (w), 550 (m),
We acknowledge support by the German Science Foundation
(Grant SFB 1083, TP A2 and A8) and thank the Helmholtz Center
Berlin (electron storage ring BESSY II) for the provision of
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1303
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by Wiley-VCH GmbH

Full Papers
doi.org/10.1002/ejoc.202001635
[23] M. Klues, G. Witte, CrystEngComm 2018, 20, 63–74.
synchrotron radiation at the beamline HE-SGM. The authors thank
Dr. Xiulan Xie for helpful discussions for the measurement and
assignment of the NMR spectra. Open access funding enabled and
organized by Projekt DEAL.
1
2
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4
5
6
7
8
9
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Conflict of Interest
The authors declare no conflict of interest.
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Keywords: Conjugated systems
·
Electronic structure
·
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Manuscript received: December 18, 2020
Revised manuscript received: January 7, 2021
Accepted manuscript online: January 11, 2021
Eur. J. Org. Chem. 2021, 1295–1304
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