Donor-acceptor substituted benzo-, naphtho- and phenanthro-fused norbornadienes

Article abstract of DOI:10.3390/molecules25020322

The photochromic norbornadiene/quadricyclane (NBD/QC) couple has found interest as a molecular solar thermal energy (MOST) system for storage of solar energy. To increase the energy difference between the two isomers, we present here the synthesis of a selection of benzo-fused NBD derivatives that contain an aromatic unit, benzene, naphthalene or phenanthrene, fused to one of the NBD double bonds, while the carbon atoms of the other double bond are functionalized with donor and acceptor groups. The synthesis protocols involve functionalization of benzo-fused NBDs with bromo/chloro substituents followed by a subjection of these intermediates to a cyanation reaction (introducing a cyano acceptor group) followed by a Sonogashira coupling (introducing an arylethynyl donor group, -C≡CC₆H₄NMe₂ or -C≡CC₆H₄OMe). While the derivatives have good absorption properties in the visible region (redshifted relative to parent system) in the context of MOST applications, they lack the ability to undergo NBD-to-QC photoisomerization, even in the presence of a photosensitizer. It seems that loss of aromaticity of the fused aromatics is too significant to allow photoisomerization to occur. The concept of destroying aromaticity of a neighboring moiety as a way to enhance the energy density of the NBD/QC couple thus needs further structural modifications, in the quest for optimum MOST systems.

Full text of DOI:10.3390/molecules25020322

molecules
Article
Donor-Acceptor Substituted Benzo-, Naphtho- and
Phenanthro-Fused Norbornadienes
Mads Mansø 1,2, Lorette Fernandez , Zhihang Wang , Kasper Moth-Poulsen and
Mogens Brøndsted Nielsen *
2
2
2
1
,
1
Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø,
Denmark; madsmansoe@gmail.com
Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Kemivägen 10,
2
4
1296 Gothenburg, Sweden; fernandez.lorette11@gmail.com (L.F.); zhihang@chalmers.se (Z.W.);
kasper.moth-poulsen@chalmers.se (K.M.-P.)
*
Correspondence: mbn@chem.ku.dk; Tel.: +45-51700144
ꢀ
ꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀ
ꢁꢂꢃꢄꢅꢆ
Received: 17 December 2019; Accepted: 9 January 2020; Published: 13 January 2020
Abstract: The photochromic norbornadiene/quadricyclane (NBD/QC) couple has found interest as a
molecular solar thermal energy (MOST) system for storage of solar energy. To increase the energy
difference between the two isomers, we present here the synthesis of a selection of benzo-fused
NBD derivatives that contain an aromatic unit, benzene, naphthalene or phenanthrene, fused to
one of the NBD double bonds, while the carbon atoms of the other double bond are functionalized
with donor and acceptor groups. The synthesis protocols involve functionalization of benzo-fused
NBDs with bromo/chloro substituents followed by a subjection of these intermediates to a cyanation
reaction (introducing a cyano acceptor group) followed by a Sonogashira coupling (introducing an
arylethynyl donor group, -C
≡
CC H NMe or -C CC H OMe). While the derivatives have good
≡
6
4
2
6 4
absorption properties in the visible region (redshifted relative to parent system) in the context of MOST
applications, they lack the ability to undergo NBD-to-QC photoisomerization, even in the presence of
a photosensitizer. It seems that loss of aromaticity of the fused aromatics is too significant to allow
photoisomerization to occur. The concept of destroying aromaticity of a neighboring moiety as a way
to enhance the energy density of the NBD/QC couple thus needs further structural modifications,
in the quest for optimum MOST systems.
Keywords: aromaticity; chromophore; cycloaddition; norbornadiene; photoswitch; polycyclic
aromatic hydrocarbon; ring strain; solar energy storage; Sonogashira coupling; quadricyclane
1
. Introduction
Functionalized norbornadiene/quadricyclane (NBD/QC) couples have been identified as promising
candidates for molecular solar thermal energy storage (MOST) systems that can undergo a closed
energy cycle of light absorption, energy storage and energy release [ ]. NBD undergoes a [2 + 2]
1–3
cycloaddition upon irradiation, forming a strained high-energy QC isomer (Scheme 1). By introduction
of donor-acceptor substituents on one or both double bonds of NBD, its absorption maximum can
conveniently be redshifted from the UV to the visible region [
spectrum. This functionalization, however, decreases the energy density (from the optimum 1 MJ kg
4–6], thereby better matching the solar
-
1
of the parent system) on account of the increased molecular weight of the molecule. Yet, by using the
same aryl group as a bridging substituent between two NBD units, this decrease in energy density can
to some extent be counter-balanced [7].
Molecules 2020, 25, 322; doi:10.3390/molecules25020322
www.mdpi.com/journal/molecules

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Scheme 1. Norbornadiene/quadricyclane (NBD/QC) interconversions and benzo-fused derivatives.
We became interested to investigate the possibility for other structural approaches of increasing
the energy density. One approach could be to couple the isomerization reaction with loss of aromaticity
of a fused benzene ring as shown for the benzo-fused couple 1NBD
derivatives of 1NBD with various substituents at the benzene ring did not result in QC formation but
instead in rearrangement reactions [ 10]. Along this line, some of us recently investigated benzo-fused
dihydroazulene/vinylheptafulvene (DHA/VHF) derivatives [11 12]. For this photo-thermoswitch
/1QC in Scheme 1. Yet, irradiation of
8–
,
couple, benzannulation was also, in most cases, accompanied by the loss of the desired photoactivity
of the DHA photochrome. A theoretical study showed that loss of aromaticity in the excited state
reaction profile inhibits the DHA-to-VHF photoswitching [13]. In consequence, it seems that we need
to seek a compromise by designing systems with less significant loss of aromatic character during
photoswitching. One solution could potentially be to fuse a polycyclic aromatic hydrocarbon to the
photochrome instead of just a single benzene ring.
Here we explore further the influence of benzannulation by fusing a benzene, naphthalene
and phenanthrene unit to the one double bond of NBD, while at the same time maintaining an
absorption in the visible region by donor-acceptor substitution at the other double bond, providing
target molecules of general structures shown in Figure 1. As acceptor unit, we chose a cyano group,
while N,N-dimethylanilino and anisyl groups connected via different bridges were chosen as donor
groups. We present synthetic protocols for achieving such new derivatives and their properties.
Figure 1. Norbornadiene target molecules with fused aromatic units at one double bond and
donor-acceptor substituent groups at the other double bond.
2
. Results
2
.1. Synthesis
A one-pot procedure for introducing a bromo and chloro substituent at the one double bond of
NBD has previously been described [14] and the resulting 2-bromo-3-chloronorbornadiene was used as
a convenient precursor for incorporating donor and acceptor functionalities [ ]. Subjecting in a similar
manner the known [15] starting material to the conditions shown in Scheme 2, we obtained the new
chloro/bromo-substituted building block . A cyanation reaction of this compound using CuCN in
6
1
2

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DMF (in analogy to conditions used for cyanation of the parent 2-bromo-3-chloronorbornadiene [
subsequently gave the product where one cyano acceptor group has been introduced (Scheme 2).
A small amount of the product 4 resulting from twofold cyanation was also isolated in this reaction.
6])
3
◦
◦
◦
Scheme 2. Reagents and conditions: (
1
) i. t-BuOK, THF; ii. BuLi,
−
84 C to
−
41 C; iii. TsCl, 84 C; iv.
−
◦
◦
◦
◦
BuLi, −84 C to −41 C; v. TsBr, −84 C to rt; (2) CuCN, DMF, 105 C.
Next, we introduced anilino and anisyl donor groups by Sonogashira coupling reactions between
3
and the terminal alkynes and , furnishing the products and , respectively (Scheme 3). By employing
5
6
7
8
more than two equivalents of the terminal alkynes, we obtained instead the products and 10. The two
9
products 9 and 10 bear a resemblance to previously reported compounds obtained from Sonogashira
coupling with 3-iodoflavones and 3-iodothioflavones, and it is believed that this is due to a second
palladium catalyzed coupling step [16].
Scheme 3. Reagents and conditions: (1) Pd(PPh ) Cl , CuI, THF/Et N; i. alkyne: 1 equiv.; ii.
3 2 2 3
alkyne: excess.
Our next objective was to expand the aromatic unit to a naphthalene moiety. First, compound 11
,
prepared according to literature procedure [17], was subjected to a similar reaction sequence as above,
providing the bromo/chloro derivative 12 (Scheme 4) (as an inseparable mixture with starting material
1
1
). A subsequent cyanation reaction gave the product 13. Sonogashira couplings between 13 and
alkynes 5 and 6 gave the donor-acceptor substituted products 14 and 15, respectively (Scheme 5).

Molecules 2020, 25, 322
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◦
◦
◦
Scheme 4. Reagents and conditions: (
1
) i. t-BuOK, THF; ii. BuLi,
−
84 C to
−
41 C; iii. TsCl, 84 C; iv.
−
◦
◦
◦
◦
BuLi, −84 C to −41 C; v. TsBr, −84 C to rt; (2) CuCN, DMF, 100 C.
Scheme 5. Reagents and conditions:(1) Pd(PPh ) Cl , CuI, THF/Et N.
3
2
2
3
For introducing a phenanthrene unit, we first had to develop a protocol for fusing this polycyclic
0
0
aromatic hydrocarbon to NBD as shown in Scheme 6. First, 2,2 -dimethyl-1,1 -biphenyl (16) was
converted into the tetrabromide 17 by radical bromination and, upon subsequent treatment with
strong base, the dibromo-substituted phenanthrene 18 resulted. This compound was turned into the
corresponding benzyne derivative that was reacted in a cycloaddition reaction with cyclopentadiene to
give the NBD derivative 19. This compound was then converted into the bromo/chloro derivative 20
(
2
isolated as an inseparable mixture with 19) that was subsequently converted into the cyano compound
. Sonogashira couplings finally gave the donor-acceptor derivatives 22 and 23 as shown in Scheme 7.
1
Scheme 6. Reagents and conditions: (
1
) 1-bromopyrrolidine-2,5-dione, benzoyl peroxide, PhH, reflux;
◦
◦
◦
◦
(2
) t-BuOK, DMF, 0 C; (
3
) BuLi, PhMe; (
4) i. t-BuOK, THF; ii. BuLi,
−84 C to
−
41 C; iii. TsCl, 84 C;
−
◦
◦
◦
iv. BuLi, −84 C to −41 C; v. TsBr, −84 C to rt; 5) CuCN, DMF.

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Scheme 7. Reagents and conditions: (1) Pd(PPh ) Cl , CuI, THF/Et N.
3
2
2
3
2
.2. Optical and Switching Properties
The UV-Vis absorption spectra of the new NBD derivatives are shown in Figure 2; Figure 3 and
longest-wavelength absorption maxima are listed in Table 1. Comparison of compounds and 15 as
well as compounds and 14 shows that it has little influence on the absorption spectra whether the
NBD is benzo- or naphtho-fused. Instead, compounds and 10 with expanded donor units exhibit
significantly redshifted absorptions, owing to their significantly larger -conjugated system. It is seen
8
7
9
π
that the spectra are changed significantly when the fused aromatic group is changed for a phenanthrene
unit in the case of 22 and 23.
Figure 2. UV-Vis absorption spectra of benzo-fused NBDs 7–10 recorded in toluene.
Figure 3. UV-Vis absorption spectra of naphtho- and phenanthro-fused NBDs 14, 15, 22 and 23 recorded
in toluene.
3
−1
−1
Table 1. Longest-wavelength absorption maxima (λmax/nm) and molar absorptivities (
ε
/10 M cm )
in brackets.
3
−1
−1
Compound
λmax/nm (ε/10 M cm )
7
8
9
399 (32.4)
355 (20.4)
440 (32.8)
378 (25.9)
400 (33.4)
356 (22.6)
410 (24.3)
336 (20.8)
1
1
1
2
2
0
4
5
2
3

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The structures of compounds
9
and 10 were confirmed by HSQC, HMBC and NOE NMR
spectroscopic analyses (see Supplementary Materials). The Z-configuration was assigned based on an
NOE correlation between the vinylic proton and the closest ortho-proton on the phenyl group directly
attached to the vinyl unit. By subjecting
9 and 10 to irradiation at their absorption maxima using a 450-W
Xe lamp, the spectra changed as revealed in Figure 4; the intensity of the longest-wavelength absorption
(
slightly blueshifted) was found to decrease, while the intensity of the higher-energy absorption
1
around 300 nm was found to increase. Conversions occurred with isosbestic points and by H-NMR
spectroscopic analysis of compound 9 it was found that rather than NBD-to-QC photoisomerization,
Z-to-E isomerization occurred. After 22 h of irradiation at 440 nm, a 1:1 ratio of E and Z isomers was
obtained for compound 9 (Figure 5).
Figure 4. UV-Vis absorption spectra of (a) 9 in toluene during irradiation with 440-nm light, (b) 10 in
toluene during irradiation with 378 nm light.
Figure 5. 1H-NMR Spectra (toluene-d , 500 MHz) of
9 recorded after various times of irradiation
8
(440 nm).
To investigate the switching properties of the benzo-fused systems
7
and 8, they were irradiated at
the longest-wavelength absorption maxima with a 450 W Xe-lamp. After irradiation for up to 60 min
no sign of isomerization was observed in both cases. Switching the light source to a broad-spectrum

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thin-layer chromatography (TLC) lamp (365 nm), only decomposition of the compounds was observed,
verified by no backreaction occurring posterior to light irradiation. A more concentrated sample (6 mM)
of
7 in toluene was argon-flushed and irradiated with a 405 nm light emitting diode (LED). Following
the reaction on TLC showed a complex mixture of decomposition products. For the two naphtho-fused
NBDs 14 and 15, an absorbance decrease was observed after irradiation at the longest-wavelength
absorption maxima with a 450-W Xe-lamp but no backreaction was seen posterior to irradiation.
An NMR sample of the methoxy-substituted NBD 15 in d -toluene was irradiated at 356 nm but after
8
1
9 h this also resulted in a complex mixture according to TLC inspection and no QC characteristic
signals were seen in the complex NMR spectrum of the mixture (See ESI). For the phenanthro-fused
NBDs 22 and 23 once again no signs of isomerization were observed. For all the systems 14 15 22
7,
8,
,
,
and 23 low temperature UV-Vis experiments using a cryostat were performed to investigate whether
the lack of observed NBD-to-QC photoconversion was caused by a rapid QC-to-NBD backreaction.
◦
Unfortunately, no signs of isomerization were observed even at temperatures down to −60 C.
2
.3. Sensitized Switching Studies
Previously, it has been found that unsubstituted norbornadiene can be converted to quadricyclane
in presence of sensitizer [18]. We note that the compounds, 7, 8, 14 and 15 did not lead to the
corresponding quadricyclanes during direct excitation at their maximum absorption wavelength.
This could in principle be due to too low-lying S1 states of these compounds. One possible alternative
could be to try to convert the compounds via their triplet excited states. Michler’s ketone is a known
triplet sensitizer that has been used for the conversion of other NBD compounds and therefore,
the conversion of 22 and 23 with this photosensitizer was attempted. Compounds 22 and 23 were
individually mixed in toluene with excess of sensitizer. Since the maximum absorption of Michler’s
ketone extends from 290 nm to 381 nm, a 300 nm LED light source was used to irradiate the
1
prepared samples. Unfortunately, no conversion was observed in both cases according to H NMR
spectroscopic analysis.
3
. Discussion
We have in this work shown that the previously one-pot procedure for functionalization
of norbornadiene at one double bond can conveniently be expanded to benzo-, naphtho- and
phenanthro-fused norbornadienes. This expansion has allowed the synthesis of a selection of
derivatives with donor-acceptor substituent groups. The identity of the fused aromatic has little
influence on the longest-wavelength absorption maximum of the compounds; this absorption maximum
is rather determined by the donor and acceptor groups at the other double bond. None of the new
derivatives were able to undergo norbornadiene-to-quadricyclane photoisomerization, not even by
the use of a photosensitizer; instead, photodegradations of the compounds occurred. Due to the
experimental conditions, we cannot rule out that a short-lived QC form of the molecules exists but due
to the time resolution of our experiments, we cannot assess this. For allowing the photoswitching event,
it seems that the loss of aromaticity should be further decreased from that of the phenanthrene unit.
4
. Materials and Methods
4
.1. General Methods
THF used for coupling reactions was distilled over a Na/benzophenone couple or retrieved from
TM
an Innovative Technology PURESOLV solvent purification system of the model PS-MD-05. UV-Vis
spectra were acquired using a Varian Cary 50 Bio spectrophotometer. UV-Vis spectroscopy experiments
were performed using a quartz cuvette with a 1 cm path length coupled to a Peltier element for
temperature control. Irradiation studies were performed using an ozone-free 450-W Xe lamp equipped
with a monochromator, a broad spectrum TLC lamp (365 nm) or a Thorlabs 405 nm LED lamp of the
model M405LP1. Thin-layer chromatography (TLC) was carried out using aluminum sheets precoated

Molecules 2020, 25, 322
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with silica gel. NMR spectra were acquired using a Bruker 500 MHz instrument with a non-inverse
cryo-probe or a Varian 400 MHz instrument using the residual solvent peak as the reference (CDCl :
3
1
13
1
H 7.26 ppm (CHCl3), C 77.16 ppm. d8-Toluene: H 2.090 ppm (d7-toluene)). Mass spectra (HRMS)
were acquired on an ESP-MALDI-FT-ICR spectrometer equipped with a 7 T magnet (calibration of the
instrument was done with NaTFA cluster ions). Elemental analyses were performed at Department of
Chemistry, University of Copenhagen. Purification by flash column chromatography was carried out
on silica gel (SiO , 60 Å, 40–63
µ
m). When referring to petroleum spirit a technical grade with boiling
2
◦
point 40–65 C was used.
1
3
General assignments of H-NMR resonances: NBD bridgehead C(sp )-H signals are observed
in the region 2.3–3.0 ppm when the NBD positions are differently substituted as a pair of signals
(
each integrating as 1H) with apparent dt multiplicities (in principle, ddd with two similar coupling
constants). NBD-CH protons are observed in the region 3.8–4.9 ppm as two multiplets (each 1H).
2
N(CH ) and OCH protons are observed as singlets at 3.0 ppm (6H) and 3.8–3.9 ppm (3H), respectively;
3
2
3
for compounds
9 and 10, two singlets are observed (corresponding to two different N(CH ) and OCH
3 2 3
units, respectively). Aromatic protons are seen at or above 6.6 ppm.
4
.2. Synthesis Protocols
2
-Bromo-3-chloro-1,4-dihydro-1,4-methanonaphthalene (2). To a solution of t-BuOK (4.88 g,
◦
4
3.5 mmol) in anhydrous THF (100 mL) at
n-BuLi (2.5 M in hexanes, 16.8 mL, 42.0 mmol) over the course of 30 min. The mixture was stirred
for 1 h at
was added and the mixture was stirred at
6.8 mL, 42.0 mmol) was added over the course of 30 min, before the mixture was stirred at
for 1 h. The mixture was cooled to
added. The mixture was stirred for 20 min at
−
84 C were added
1
(7.09 g, 49.9 mmol) followed by
◦
◦
−
41 C, before it was cooled to
−
84 C and p-toluenesulfonyl chloride (8.03 g, 42.1 mmol)
◦
−
84 C for 30 min. Once again n-BuLi (2.5 M in hexanes,
◦
1
−
41 C
◦
−
84 C and p-toluenesulfonyl bromide (9.95 g, 42.3 mmol) was
◦
−
84 C, before it was allowed to reach rt. The reaction
mixture was quenched with H O (400 mL), the phases were separated and the aqueous phase was
2
extracted with Et O (3
×
200 mL). The combined organic phases were dried over Na SO , filtered
2 4
2
and concentrated in vacuo. The crude mixture was redissolved in hexane, poured through a plug of
silica (43–60
affording
CDCl3):
µ
m) and concentrated in vacuo. The mixture was concentrated by a stream of nitrogen
1
2
as a white solid of sufficient purity for further reaction (6.78 g, 54%). H NMR (400 MHz,
δ
= 7.34 (dd, J = 5.2, 3.0 Hz, 2H), 7.05 (dd, J = 5.2, 3.0 Hz, 2H), 3.92 (m, 1H), 3.86 (m, 1H), 2.74
dd, J = 7.4, 1.8 Hz, 1H), 2.40 (dd, J = 7.4, 1.8 Hz, 1H) ppm. 1 C NMR (100 MHz, CDCl3):
3
δ
+
= 148.31,
(
147.86, 144.49, 143.13, 129.32, 125.67, 125.64, 122.19, 66.90, 58.14, 57.14 ppm. HR-MS (APCI FT-ICR):
+
79
+
m/z = 254.95769 [M+H ], calcd. for [C H BrCl ]: m/z = 254.95707.
11
9
3
-Chloro-1,4-dihydro-1,4-methanonaphthalene-2-carbonitrile (3). To an argon flushed solution
of
2
(6.00 g, 23.5 mmol) in DMF (80 mL) was added CuCN (1.88 g, 21.0 mmol) and the mixture was
◦
heated to 105 C for 15 h. The mixture was allowed to reach rt, before it was poured into saturated
aqueous Na CO (200 mL) and extracted with Et O (3
×
300 mL). The combined organic phases were
2
3
2
washed with water (2
×
400 mL) and brine (2
×
400 mL), dried over Na SO , filtered and concentrated
2
4
in vacuo. The crude mixture was purified by flash column chromatography (30% CH Cl /heptane to
2
2
1
3
00% CH Cl ) affording
3
as an off-white solid (2.20 g, 46%) along with
4 (326 mg, 7%). Compound
2
2
-
1
: R (50% CH Cl /petroleum spirit) = 0.47. IR: 3070, 3051, 3022, 2990, 2950, 2874, 2215, 1589 cm .
f
2
2
1
H NMR (400 MHz, CDCl3):
δ = 7.42–7.33 (m, 2H), 7.15–7.03 (m, 2H), 4.18 (m, 1H), 3.96 (m, 1H), 2.72
13
(dt, J = 7.9, 1.7 Hz, 1H), 2.45 (dt, J = 7.9, 1.7 Hz, 1H) ppm. C NMR (100 MHz, CDCl3):
δ = 164.18,
+
1
47.36, 145.79, 126.54, 126.13, 123.15, 122.75, 121.09, 114.12, 68.22, 58.13, 53.63 ppm. HR-MS (ESI
FT-ICR): m/z = 202.04186 [M+H+], calcd. for [C H ClN ]: m/z = 202.04180. Compound 4: 1H NMR
+
12
9
(
2
1
400 MHz, CDCl3):
δ = 7.42 (dd, J = 5.3, 3.1 Hz, 2H), 7.13 (dd, J = 5.3, 3.1 Hz, 2H), 4.32 (t, J = 1.6 Hz,
13
H), 2.70 (dd, J = 8.4, 1.6 Hz, 1H), 2.53 (dd, J = 8.4, 1.6 Hz, 1H) ppm. C NMR (126 MHz, CDCl3):
44.87, 140.47, 126.85, 123.74, 112.84, 70.06, 54.86 ppm. HR-MS (ESI FT-ICR): m/z = 193.07619 [M+H ],
δ =
+
+

Molecules 2020, 25, 322
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+
calcd. for [C H N ]: m/z = 193.07602. EA (C H N ): calcd. C 81.23, H 4.20, N 14.57; found C 80.86,
13
9
2
13
8
2
H 4.51, N 15.00.
-((4-(Dimethylamino)phenyl)ethynyl)-1,4-dihydro-1,4-methanonaphthalene-2-carbonitrile
7). To an argon flushed solution of (200 mg, 0.992 mmol) and 4-ethynyl-N,N-dimethylaniline (
156 mg, 1.07 mmol) in THF (20 mL) and Et N (12 mL) were added CuI (18 mg, 0.095 mmol) and
3
(
3
5)
(
3
Pd(PPh ) Cl (71 mg, 0.10 mmol) and the mixture was stirred overnight. The reaction mixture was
3
2
2
poured through a plug of silica (43–60
µm, CH Cl ) and concentrated in vacuo. The residue was
2 2
subjected to flash column chromatography (60% CH Cl /hexane) affording
7
as a yellow solid (238 mg,
= 7.41–7.33 (m, 2H), 7.38 (d, J =
.1 Hz, 2H), 7.11–7.00 (m, 2H), 6.62 (d, J = 9.1 Hz, 2H), 4.16 (m, 1H), 4.11 (m, 1H), 3.01 (s, 6H), 2.59
2
2
1
77%). R (60% CH Cl /hexane) = 0.38. H NMR (400 MHz, CDCl ): δ
f 2 2 3
9
13
(dt, J = 7.9, 1.7 Hz, 1H), 2.41 (dt, J = 7.9, 1.7 Hz, 1H) ppm. C NMR (100 MHz, CDCl3):
δ
= 153.61,
1
6
51.06, 147.86, 147.02, 133.67, 126.03, 125.83, 124.45, 123.00, 122.49, 116.73, 111.69, 111.04, 108.22, 82.26,
+
+
+
7.96, 57.02, 53.49, 40.20 ppm. HR-MS (ESI FT-ICR): m/z = 311.1552 [M+H ], calcd. for [C H N ]:
22 19 2
m/z = 311.1543.
Compound 8. To a solution of ((4-methoxyphenyl)ethynyl)trimethylsilane (230 mg, 1.13 mmol)
in THF and MeOH (20 mL, 1:1, v/v) was added K CO (594 mg, 4.30 mmol) and the mixture was
2
3
stirred at rt for 1 h. The mixture containing
almost concentrated in vacuo zand then THF (50 mL) was added and the mixture was concentrated
to approx. 10 mL. Then (207 mg, 1.03 mmol) and Et N (10 mL) were added and the mixture was
flushed with argon. Pd(PPh ) Cl (85 mg, 0.12 mmol) and CuI (17 mg, 89
6 was poured through a plug of silica (40–63 µm, CH Cl ),
2 2
3
3
µ
mol) were added and the
mixture was stirred for 19 h at rt. The reaction mixture was poured through a plug of silica (40–63 m,
CH Cl ) and concentrated in vacuo. The residue was subjected to flash column chromatography (50%
3
2
2
µ
2
2
CH Cl /heptane to 70% CH Cl /heptane) affording
8
as a slightly brown semicrystalline oil (222 mg,
3%). R (70% CH Cl /heptane) = 0.45. H NMR (500 MHz, CDCl3): = 7.45 (d, J = 8.9 Hz, 2H),
.41–7.37 (m, 1H), 7.37–7.34 (m, 1H), 7.09–7.04 (m, 2H), 6.87 (d, J = 8.9 Hz, 2H), 4.17 (m, 1H), 4.12 (m,
2
2
2
2
1
7
7
1
δ
f
2
2
H), 3.83 (s, 3H), 2.61 (dt, J = 8.0, 1.8 Hz, 1H), 2.42 (dt, J = 8.0, 1.8 Hz, 1H) ppm. 13C NMR (126 MHz,
= 160.91, 153.27, 147.60, 146.87, 133.85, 126.80, 126.14, 125.97, 123.07, 122.67, 116.26, 114.33,
CDCl3):
δ
+
+
1
14.01, 108.70, 82.10, 68.26, 56.93, 55.51, 53.65 ppm. HR-MS (ESI FT-ICR): m/z = 298.12310 [M+H ],
+
calcd. for [C H NO ]: m/z = 298.12264. EA (C H NO): calcd. C 84.82, H 5.08, N 4.71; found C
21
16
21 15
8
4.29, H 5.20, N 4.85.
Compound 9.
To an argon flushed solution of 3 (221 mg, 1.10 mmol) and
4-ethynyl-N,N-dimethylaniline (5) (246 mg, 1.69 mmol) in THF (20 mL) and Et N (12 mL) were
3
added CuI (20 mg, 0.11 mmol) and Pd(PPh ) Cl (77 mg, 0.11 mmol) and the mixture was stirred
3
2
2
for 2 h. More 4-ethynyl-N,N-dimethylaniline (181 mg, 1.25 mmol) was added and the mixture was
stirred overnight. The reaction mixture was poured through a plug of silica (43–60 m, CH Cl ) and
concentrated in vacuo. The residue was subjected to flash column chromatography (80% CH Cl /hexane
µ
2
2
2
2
to 100% CH Cl ) affording
9 as a red solid (363 mg, 73%). R (80% CH Cl /heptane) = 0.28. IR = 3047,
f 2 2
2
2
−1 1
2
986, 2941, 2896, 2862, 2804, 2192, 2208sh, 2177sh, 1606, 1553, 1557sh, 1517 cm . H NMR (400 MHz,
CDCl3): = 8.04 (d, J = 9.1 Hz, 2H), 7.55 (d, J = 9.0 Hz, 2H), 7.42–7.33 (m, 2H), 7.15 (s, 1H), 7.09–6.98
m, 2H), 6.70 (d, J = 9.1 Hz, 2H), 6.69 (d, J = 9.0 Hz, 2H), 4.50 (m, 1H), 4.18 (m, 1H), 3.04 (s, 6H), 2.99
δ
(
(
s, 6H), 2.54 (dt, J = 7.8, 1.7 Hz, 1H), 2.35 (dd, J = 7.8, 1.7 Hz, 1H) ppm. 1 C NMR (100 MHz, CDCl3):
3
δ = 168.37, 151.12, 150.35, 149.32, 147.32, 136.99, 132.67, 131.80, 125.60, 125.49, 124.03, 122.45, 122.07,
18.19, 115.18, 112.04, 111.59, 111.34, 110.32, 99.08, 84.78, 65.77, 55.04, 53.25, 40.34, 40.24 ppm. HR-MS
1
+
+
+
(ESI FT-ICR): m/z = 456.2438 [M+H ], calcd. for [C H N ]: m/z = 456.2434.
32 30 3
Compound 10. To a solution of ((4-methoxyphenyl)ethynyl)trimethylsilane (649 mg, 3.18 mmol)
in THF/MeOH (20 mL, 1:1, v/v) was added K CO (1.56 g, 11.3 mmol) and the mixture was stirred at
2
3
rt for 2 h. The mixture was poured through a plug of silica (43–60
in vacuo to provide . THF (20 mL), Et N (12 mL) and (180 mg, 0.893
mixture was flushed with argon. CuI (17 mg, 0.089 mmol) and Pd(PPh ) Cl (69 mg, 0.098 mmol) were
µm, CH Cl ) and concentrated
2 2
6
3
µmol) were added and the
3
3
2
2
added and the mixture was stirred at rt for 23 h. The reaction mixture was poured through a plug

Molecules 2020, 25, 322
10 of 14
of silica (43–60
µm, CH Cl ) and concentrated in vacuo. The residue was subjected to flash column
2 2
chromatography (70% CH Cl /hexane to 90% CH Cl /hexane) affording 10 as a yellow solid (303 mg,
2
2
2
2
1
7
(
8
=
9%). R (80% CH Cl /heptane) = 0.41. H NMR (400 MHz, CDCl ):
δ
= 8.03 (d, J = 8.9 Hz, 2H), 7.59
d, J = 8.9 Hz, 2H), 7.43–7.35 (m, 2H), 7.19 (s, 1H), 7.11–7.00 (m, 2H), 6.94 (d, J = 8.9 Hz, 2H), 6.90 (d, J =
.9 Hz, 2H), 4.48 (m, 1H), 4.21 (m, 1H), 3.86 (s, 3H), 3.83 (s, 3H), 2.56 (dt, J = 7.9, 1.7 Hz, 1H), 2.38 (dt, J
7.9, 1.7 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3):
= 167.72, 160.87, 160.14, 148.98, 147.04, 136.88,
33.20, 131.74, 128.52, 125.79, 125.68, 122.48, 122.31, 117.79, 117.62, 115.13, 114.29, 114.06, 113.84, 98.10,
f
2
2
3
δ
1
8
[
+
+
4.59, 66.14, 55.53, 55.46, 55.20, 53.21 ppm. HR-MS (ESI FT-ICR): m/z = 430.1811 [M+H ], calcd. for
C H NO ]: m/z = 430.1802. EA (C H NO ): calcd. C 83.89, H 5.40, N 3.26; found C 83.34, H 5.40,
30 24 2 30 23 2
+
N 3.35.
-Bromo-3-chloro-1,4-dihydro-1,4-methanoanthracene (12).
tert-butoxide (4.53 g, 40.4 mmol) in anhydrous THF (180 mL) was cooled to
2
A
solution of potassium
◦
−78 C, before
11 (9.32 g, 48.5 mmol) was added followed by n-BuLi (16.16 mL, 2.5 M, 40.41 mmol). The temperature
◦
was elevated to
−
41 C and the mixture was stirred for 1 h. The reaction mixture was cooled to
◦
−
78 C before p-toluenesulfonyl chloride (7.71 g, 40.4 mmol) was added. The mixture was stirred
◦
for 30 min at
elevated to
before p-toluenesulfonyl bromide (9.63 g, 41.0 mmol) was added and the mixture was stirred for
5 min. The reaction mixture was heated to rt using a water bath, poured into water (300 mL) and
extracted with diethyl ether (3 200 mL). The combined organic phases were washed with water (2
00 mL) and brine (400 mL), dried over Na SO , filtered and concentrated in vacuo. Flash column
−
78 C; then n-BuLi (16.16 mL, 2.5 M, 40.41 mmol) was added, the temperature was
◦
◦
−
41 C and the mixture was stirred for 1 h. The mixture was once again cooled to
−
78 C
1
×
×
4
2
4
chromatography (petroleum spirit) furnished 12 (estimated yield of ca. 15%) and 11 as a 41:59 mixture
based on NMR integration) (3.40 g). The mixture of 12 and 11 was used in the next step without
further purification.
(
3
-Chloro-1,4-dihydro-1,4-methanoanthracene-2-carbonitrile (13). To an argon-flushed solution
of the mixture of 11 and 12 (3.14 g) in DMF (40 mL) was added CuCN (435 mg, 4.86 mmol) and the
◦
mixture was heated to 100 C and stirred for 10h. The mixture was allowed to cool to rt before it was
poured into saturated aqueous sodium carbonate (200 mL) and extracted with diethyl ether (3
mL). The combined organic phases were washed with water (3 200 mL) and brine (200 mL), dried
over Na SO , filtered and concentrated in vacuo. Flash column chromatography (30% CH Cl /heptane
×
150
×
2
4
2
2
to 50% CH Cl /heptane) afforded 13 as a white solid (415 mg, 31%). IR = 3076, 3063, 3048, 2998, 2953,
2
2
−1 1
2
4
(
1
217, 1591, 1509sh, 1506 cm . H NMR (400 MHz, CDCl ):
δ
= 7.80–7.73 (m, 4H), 7.53–7.43 (m, 2H),
.27 (m, 1H), 4.07 (m, 1H), 2.76 (dt, J = 8.3, 1.7 Hz, 1H), 2.45 (dt, J = 8.3, 1.7 Hz, 1H) ppm. 13C NMR
= 162.47, 143.13, 141.78, 132.56, 132.30, 128.18, 128.11, 126.59, 126.47, 121.97,
3
100 MHz, CDCl3):
δ
+
+
21.32, 120.40, 113.96, 64.72, 57.33, 52.83 ppm. HR-MS (ESI FT-ICR): m/z = 252.05767 [M+H ], calcd.
+
for [C H ClN ]: m/z = 252.05745. EA (C H ClN): calcd. C 76.35, H 4.00, N 5.56; found C 76.21, H
16
11
16 10
4
.12, N 5.71.
-((4-(Dimethylamino)phenyl)ethynyl)-1,4-dihydro-1,4-methanoanthracene-2-carbonitrile
14). To an argon flushed solution of 13 (151 mg, 0.600 mmol) and 4-ethynyl-N,N-dimethylaniline (
95 mg, 0.65 mmol) in THF/Et N (20 mL, 1:1, v/v) were added CuI (12 mg, 63 mol) and Pd(PPh ) Cl
2
3
(
(
(
5)
µ
3
3 2
44 mg, 63
µmol) and the mixture was stirred at rt for 4 h. The reaction mixture was poured through a
plug of silica (43–60
µ
m, CH Cl ) and concentrated in vacuo. The crude mixture was purified by flash
2
2
column chromatography (50% CH Cl /heptane) affording 14 as a yellow solid (186 mg, 86%). R (50%
2
2
f
1
CH Cl /heptane) = 0.13. H NMR (400 MHz, CDCl ):
δ
= 7.80–7.69 (m, 4H), 7.49–7.39 (m, 2H), 7.38 (d,
2
2
3
J = 9.1 Hz, 2H), 6.61 (d, J = 9.1 Hz, 2H), 4.25 (m, 1H), 4.21 (m, 1H), 3.00 (s, 6H), 2.64 (dt, J = 8.3, 1.7
Hz, 1H), 2.40 (dd, J = 8.3, 1.7 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3):
= 152.19, 151.09, 143.97,
43.25, 133.74, 132.53, 132.40, 128.08, 128.01, 126.16, 126.08, 123.45, 121.55, 120.86, 116.54, 111.68, 110.66,
δ
1
1
+
+
08.13, 82.18, 64.52, 56.17, 52.65, 40.19 ppm. HR-MS (ESI FT-ICR): m/z = 361.17004 [M+H ], calcd. for
+
[C H N ]: m/z = 361.16993.
26
21
2

Molecules 2020, 25, 322
11 of 14
3
-((4-Methoxyphenyl)ethynyl)-1,4-dihydro-1,4-methanoanthracene-2-carbonitrile (15). To a
solution of ((4-methoxyphenyl)ethynyl)trimethylsilane (97 mg, 0.47 mmol) in THF (5 mL) and MeOH
5 mL) was added K CO (284 mg, 2.05 mmol) and the mixture was stirred at rt for 1 h. The mixture
(
2
3
was poured through a plug of silica (40–63 µm, CH Cl ), almost concentrated in vacuo and then THF
2 2
(
50 mL) was added and the mixture containing 6 was concentrated to approx. 10 mL. Then 13 (110 mg,
0
.437 mmol) and Et N (10 mL) were added and the mixture was flushed with argon. Pd(PPh ) Cl
3
3 2
2
(35 mg, 50
µmol) and CuI (10 mg, 53
µmol) were added and the mixture was stirred for 22h at rt.
The reaction mixture was poured through a plug of silica (40–63
µ
m, CH Cl ) and concentrated in
2
2
vacuo. The crude material was subjected to flash column chromatography (50% CH Cl /heptane to
2
2
7
0
4
0% CH Cl /heptane) affording 15 as an off-white solid (80 mg, 53%). R (70% CH Cl /heptane) =
2 2 f 2 2
1
.47. H NMR (500 MHz, CDCl ):
δ
= 7.79–7.72 (m, 4H), 7.48–7.42 (m, 4H), 6.87 (d, J = 8.9 Hz, 2H),
3
.27 (m, 1H), 4.23 (m, 1H), 3.83 (s, 3H), 2.66 (dt, J = 8.4, 1.6 Hz, 1H), 2.43 (dt, J = 8.4, 1.5 Hz, 1H) ppm.
1
3
C NMR (126 MHz, CDCl3):
δ = 160.94, 151.82, 143.61, 142.98, 133.90, 132.51, 132.40, 128.11, 128.02,
1
26.26, 126.20, 125.74, 121.65, 121.11, 116.06, 114.32, 113.91, 108.26, 82.00, 64.76, 56.04, 55.49, 52.79 ppm.
+
+
+
HR-MS (ESI FT-ICR): m/z = 348.13845 [M+H ], calcd. for [C H NO ]: m/z = 348.13829.
2
5
18
0
0
00
00
00
2
,2 -Bis(dibromomethyl)-1,1 -biphenyl (17). A solution of 2,22 -dimethyl-1,11 -biphenyl (16
)
®
(13.5 mL, 73.3 mmol), NBS (58.10 g, 326.4 mmol) and Luperox A75, Benzoyl peroxide (1.35 g, 1.01 g
benzoyl peroxide, 4.17 mmol) in benzene (500 mL) was heated to reflux point while irradiated with a
00 W halogen lamp for 18 h. The mixture was allowed to cool to rt, poured through a plug of silica
43–60 m) and concentrated in vacuo. The crude mixture was recrystallized from CH Cl /heptane
5
(
µ
2
2
affording 17 as an off-white solid (30.10 g, 83%). The reaction was also performed on 5.49 mmol scale
1
giving a yield of 76%. H NMR (500 MHz, CDCl ): d = 8.13 (dd, J = 7.8, 1.3 Hz, 2H), 7.58 (td, J = 7.8,
1
3
13
.4 Hz, 2H), 7.41 (td, J = 7.8, 1.3 Hz, 2H), 7.12 (dd, J = 7.8, 1.4 Hz, 2H), 6.29 (s, 2H) ppm. C NMR
(
(
126 MHz, CDCl3): δ = 140.46, 133.62, 130.56, 129.96, 129.74, 129.05, 38.55 ppm.
9
,10-Dibromophenanthrene (18). To a solution of 17 (29.59 g, 59.44 mmol) in anhydrous DMF
◦
450 mL) at 0 C was added potassium tert-butoxide (21.65 g, 192.9 mmol). The mixture was stirred
◦
at 0 C for 1h, before the mixture was quenched slowly with 6 M HCl (500 mL). The precipitate was
filtered, washed with water (1.5 L) and MeOH (200 mL) and dried in vacuo affording 18 as a yellow
1
solid (18.10 g, 91%). The reaction was also done on 3.02 mmol scale giving a yield of 79%. H NMR
(
7
1
[
500 MHz, CDCl3):
δ
= 8.63 (dd, J = 8.2, 1.4 Hz, 2H), 8.47 (dd, J = 8.1, 1.5 Hz, 2H), 7.70 (ddd, J = 8.2,
= 131.27, 130.36,
.0, 1.5 Hz, 2H), 7.66 (ddd, J = 8.1, 7.0, 1.4 Hz, 2H). 13C NMR (126 MHz, CDCl ):
δ
3
+
+
29.68, 128.18, 127.76, 126.24, 122.84 ppm. HR-MS (APCI FT-ICR): m/z = 334.90806 [M+H ], calcd. for
79
+
C H Br2 ]: m/z = 334.90655.
14
9
1
,4-Dihydro-1,4-methanotriphenylene (19). To solution of 18 (17.84 g, 53.09 mmol) and
◦
cyclopentadiene (4.8 mL, 57 mmol) in anhydrous toluene (600 mL) at 0 C was added n-BuLi
(
23.4 mL, 2.5 M in hexane, 58.5 mmol). The mixture was allowed to reach rt slowly overnight, before it
was poured into water (1 L) and extracted with Et O (3 500 mL). The combined organic phases were
dried over Na SO , filtered and concentrated in vacuo. The residue was passed through a plug of silica
×
2
2
4
(
43–60
µm, 50% CH Cl /heptane) and concentrated in vacuo. Flash column chromatography (heptane
2 2
1
to 5% CH Cl /heptane) afforded 19 as a white solid (5.80 g, 45%). H NMR (500 MHz, CDCl ):
(
6
Hz, 1H) ppm. C NMR (126 MHz, CDCl ):
1
δ
= 8.73
d, J = 8.1 Hz, 2H), 8.06 (dd, J = 8.0, 1.4 Hz, 2H), 7.64 (ddd, J = 8.0, 6.9, 1.3 Hz, 2H), 7.59 (ddd, J = 8.1,
.9, 1.4 Hz, 2H), 7.03 (d, J = 1.7 Hz, 2H), 4.64 (m, 2H), 2.56 (dt, J = 6.6, 1.7 Hz, 1H), 2.47 (dt, J = 6.6, 1.7
2
2
3
13
δ = 147.89, 143.78, 129.00, 128.73, 126.51, 125.26, 123.55,
3
+
+
+
23.54, 72.46, 49.22 ppm. HR-MS (APCI FT-ICR): m/z = 243.11693 [M+H ], calcd. for [C H ]: m/z =
14
19
2
43.11683.
2
-Bromo-3-chloro-1,4-dihydro-1,4-methanotriphenylene (20). To a solution of t-BuOK (1.93 g,
◦
1
7.2 mmol) in THF (300 mL) at
until everything was in solution, before the mixture was cooled once again to
.5 M in hexanes, 17.1 mmol) was added over the course of 45 min resulting in a dark red/brown color.
The temperature was elevated to
−
78 C was added 19 (5.13 g, 21.2 mmol). The cooling bath was removed
◦
−
78 C. n-BuLi (6.85 mL,
2
◦
−
41 C and the mixture was stirred for 1 h. The mixture was cooled to

Molecules 2020, 25, 322
12 of 14
◦
−
78 C and p-toluenesulfonyl chloride (3.26 g, 17.1 mmol) was added. The reaction mixture was stirred
for 40 min, before n-BuLi (6.85 mL, 2.5 M in hexanes, 17.1 mmol) was added over the course of 40 min.
◦
The temperature was elevated to
−
41 C and the mixture was stirred for 1 h. The mixture was cooled
◦
to
−
78 C, before p-toluenesulfonyl bromide (4.04 g, 17.2 mmol) was added and the mixture was stirred
◦
78 C. The mixture was heated to ambient temperature using a room tempered water
for 15 min at
bath, before water (150 mL) was added. The remaining THF was removed in vacuo and the resulting
mixture was extracted with CH Cl (3 300 mL). The combined organic phases were washed with
brine (300 mL), dried over MgSO , filtered and concentrated in vacuo. Flash column chromatography
−
×
2
2
4
(
(
heptane to 5% CH Cl /heptane) furnished 19 and 20 (estimated yield of 32%) as a 61:39 mixture
2 2
based on NMR integration) (4.03 g). The mixture of 19 and 20 was used in the next step without
further purification.
3
-Chloro-1,4-dihydro-1,4-methanotriphenylene-2-carbonitrile (21). To an argon-flushed
solution of the mixture of 19 and 20 (3.93 g) in DMF (50 mL) was added CuCN (406 mg, 4.53 mmol)
◦
and the mixture was heated to 105 C and stirred for 7 h. The mixture was allowed to cool to rt
before it was poured into saturated aqueous sodium carbonate (300 mL) and extracted with diethyl
ether (6
×
100 mL). The combined organic phases were washed with water (4
×
250 mL) and brine
(
(
(
4
(
2 × 250 mL), dried over Na SO , filtered and concentrated in vacuo. Flash column chromatography
2
4
30% CH Cl /heptane to 70% CH Cl /heptane, loaded in 1:4 CH Cl /CS ) afforded 21 as a white solid
2
2
2
2
2
2
2
1
402 mg, 25%). H NMR (500 MHz, CDCl ):
δ
= 8.79–8.72 (m, 2H), 8.08–8.00 (m, 2H), 7.73–7.64 (m, 4H),
.89 (m, 1H), 4.72 (m, 1H), 3.00 (dt, J = 7.5, 1.8 Hz, 1H), 2.72 (dt, J = 7.5, 1.8 Hz, 1H) ppm. 13C NMR
126 MHz, CDCl3): = 165.75, 145.27, 142.82, 129.58, 129.54, 128.30, 128.12, 127.36, 127.27, 126.82,
3
δ
+
126.59, 123.81, 123.72, 123.64, 123.45, 121.67, 114.24, 70.39, 57.32, 52.80 ppm. HR-MS (ESI FT-ICR):
+
+
m/z = 302.07324 [M+H ], calcd. for [C H ClN ]: m/z = 302.07310.
20
13
3
-((4-(Dimethylamino)phenyl)ethynyl)-1,4-dihydro-1,4-methanotriphenylene-2-carbonitrile
22). To a solution of N,N-dimethyl-4-((trimethylsilyl)ethynyl)aniline (92 mg, 0.42 mmol) in THF/MeOH
20 mL, 1:1, v/v) was added K CO (202 mg, 1.46 mmol) and the mixture was stirred for 1 h. The mixture
(
(
2
3
was poured through a plug of silica (43–60
50 mL) was added and the mixture containing
51 mol) and Et N (10 mL) were added and the mixture was flushed with argon. Pd(PPh ) Cl
26 mg, 37
The mixture was poured through a plug of silica (43–60
The residue was purified by flash column chromatography (50–70% CH Cl /heptanes) affording 22 as
µm, CH Cl ), almost concentrated in vacuo; then THF
2 2
(
5 was concentrated to approx. 10 mL. The 21 (106 mg,
3
µ
3
3 2
2
(
µmol) and CuI (6 mg, 0.03 mmol) were added before the mixture was stirred for 18 h.
µ
m, CH Cl ) and concentrated in vacuo.
2
2
2
2
1
a yellow solid (99 mg, 69%). H NMR (500 MHz, CDCl ):
7
6
δ
= 8.76–8.71 (m, 2H), 8.14–8.05 (m, 2H),
.72–7.60 (m, 4H), 7.35 (d, J = 9.0 Hz, 2H), 6.61 (d, J = 9.0 Hz, 2H), 4.88 (m, 1H), 4.85 (m, 1H), 3.00 (s,
H), 2.86 (dt, J = 7.5, 1.6 Hz, 1H), 2.65 (dt, J = 7.5, 1.6 Hz, 1H) ppm. 13C NMR (126 MHz, CDCl3):
154.80, 151.08, 145.16, 143.85, 133.61, 129.44, 128.62, 128.30, 127.16, 127.05, 126.40, 126.22, 125.11,
23.73, 123.72, 123.70, 123.62, 116.85, 112.19, 108.34, 82.41, 69.91, 56.27, 52.64, 40.20 ppm. HR-MS (ESI
FT-ICR): m/z = 411.18508 [M+H ], calcd. for [C H N ]: m/z = 411.18558.
3
δ
=
+
1
+
+
30
23
2
3
-((4-Methoxyphenyl)ethynyl)-1,4-dihydro-1,4-methanotriphenylene-2-carbonitrile (23). To a
solution of ((4-methoxyphenyl)ethynyl)trimethylsilane (118 mg, 557 mol) in THF/MeOH (20 mL, 1:1,
v/v) was added K CO (213 mg, 1.54 mmol) and the mixture was stirred for 1 h. The mixture was
µ
2
3
poured through a plug of silica (43–60
50 mL) was added and the mixture containing
07 mol) and Et N (10 mL) were added and the mixture was flushed with argon. Pd(PPh ) Cl
37 mg, 52 µmol) and CuI (89 µmol) were added before the mixture was stirred for 17 h. The mixture
was poured through a plug of silica (43–60 m, CH Cl ) and concentrated in vacuo. The residue was
purified by flash column chromatography (50–60% CH Cl /heptanes) affording 23 as a slightly yellow
µm, CH Cl ), almost concentrated in vacuo and then THF
2 2
(
6 was concentrated to approx. 10 mL. Then 21 (153 mg,
5
µ
3
3 2
2
(
µ
2
2
2
1
2
solid (143 mg, 71%). R (60% CH Cl /heptanes) = 0.25. H NMR (500 MHz, CDCl ):
δ
= 8.77–8.71 (m,
f
2
2
3
2
H), 8.14–8.05 (m, 2H), 7.73–7.61 (m, 4H), 7.42 (d, J = 8.9 Hz, 2H), 6.86 (d, J = 8.9 Hz, 2H), 4.90 (m,
13
1H), 4.87 (m, 1H), 3.82 (s, 3H), 2.88 (dt, J = 7.5, 1.6 Hz, 1H), 2.68 (dt, J = 7.5, 1.6 Hz, 1H) ppm.
C

Molecules 2020, 25, 322
13 of 14
NMR (126 MHz, CDCl3):
δ
= 160.91, 154.48, 144.95, 143.80, 133.78, 129.49, 129.47, 128.57, 128.29, 127.52,
1
5
27.24, 127.11, 126.52, 126.34, 123.74, 123.70, 123.66, 123.65, 116.39, 114.32, 114.07, 109.83, 82.21, 70.22,
+
+
+
6.15, 55.51, 52.81 ppm. HR-MS (ESI FT-ICR): m/z = 398.15389 [M+H ], calcd. for [C H NO ]:
29 20
m/z = 398.15394.
Supplementary Materials: NMR Spectra of all new compounds. Details on photosensitizer experiments.
Author Contributions: Conceptualization, M.M., K.M.-P. and M.B.N.; Investigation, M.M., L.F. and Z.W.; Project
administration, K.M.-P. and M.B.N.; Supervision, K.M.-P. and M.B.N.; Writing—original draft, M.M. and M.B.N.;
Writing—review and editing, L.F., Z.W. and K.M.-P. All authors have read and agreed to the published version of
the manuscript.
Funding: This research was funded by University of Copenhagen and the Knut and Alice Wallenberg Foundation.
Conflicts of Interest: The authors declare no conflict of interest.
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Sample Availability: Samples of selected compounds are available from the authors.
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