Synthesis of a naphthalocyanine-like dye: The first report on Zn(II)-1,6-methano[10]annulenecyanine

Article abstract of DOI:10.3390/molecules25092164

The synthesis of the new dye 1,6-methano[10]annulenecyanine is described. For this purpose, the 3,4-dicyano-1,6-methano[10]annulene and 3,4-carboxyimide-1,6-methano[10]annulene buildings blocks were synthesized in six to eight steps. In both cases, these

Full text of DOI:10.3390/molecules25092164

molecules
Communication
Synthesis of a Naphthalocyanine-Like Dye: The First
Report on Zn(II)-1,6-methano[10]annulenecyanine
Nicholas Roberto da Silva Gobo 1,2, Timothy John Brocksom 1 and
1
,
Kleber Thiago de Oliveira *
1
Departamento de Química, Universidade Federal de São Carlos, São Carlos CEP 13.565-905,
São Paulo 01000-000, Brazil; nicholas.gobo@accert.com (N.R.d.S.G.); brocksom@terra.com.br (T.J.B.)
ACCERT Chemistry and Biotechnology, São Carlos CEP 13.574-033, São Paulo 01000-000, Brazil
2
*
Correspondence: kleber.oliveira@ufscar.br
ꢀ
ꢁꢂꢀꢃꢄꢅꢆꢇ
Academic Editor: José A. S. Cavaleiro
Received: 1 April 2020; Accepted: 30 April 2020; Published: 5 May 2020
ꢀ
ꢁꢂꢃꢄꢅꢆ
Abstract: The synthesis of the new dye 1,6-methano[10]annulenecyanine is described. For this
purpose, the 3,4-dicyano-1,6-methano[10]annulene and 3,4-carboxyimide-1,6-methano[10]annulene
buildings blocks were synthesized in six to eight steps. In both cases, these building blocks were then
cyclotetramerized to furnish a new Zn(II)-1,6-methano[10]annulenecyanine which presents a strong
red-shifted absorption band at 800 nm and high solubility in common organic solvents.
Keywords: annulene; naphthalocyanine; phthalocyanine; NIR chromophores and dyes
1
. Introduction
Near-infrared (NIR) dyes have received increasing attention due to their versatile applications
in materials science [1–5], medical applications [6–14], catalysis and other advanced technology
devices [12 15 17]. In this context, phthalocyanines and naphthalocyanines are very robust dyes with
,
–
relevant photophysical properties and must be highlighted [18–23].
These classes of compounds are not naturally occurring, unlike their analogues porphyrins,
chlorins and bacteriochlorins [24,25]. Phthalocyanines were accidentally discovered at the beginning
of the last century and only systematically studied in the 1930s by Linstead and Robertson, who finally
established their structure and a general synthetic methodology [26–31]. Since then their thermal
stability, low solubility and intense color took up attention. Over the past few decades many improved
synthetic approaches for phthalocyanine and also naphthalocyanine derivatives have been established,
with a relevant molecular diversity which allows the modulation of both chemical and photochemical
properties of these dyes [26]. In general, the classic synthetic approach to obtain phthalocyanines
and naphthalocyanines is the cyclotetramerization of their building blocks phthalonitriles and
naphthalonitriles, respectively [26–31]. Depending on the building block substitution pattern, it
is possible to modulate the photophysical properties of the phthalocyanine/naphthalocyanine of
interest, fine-tuning the dye for the desired application. The literature furnishes a vast number of
interesting and creative molecules using this approach [26–31].
Seeking for new NIR building blocks our group decided to explore a class of molecules called
1
,x-methano[10]annulenes, especially the 1,6-methano[10]annulene (Figure 1) [32]. These compounds
have fascinated a number of scientists since Emanuel Vogel’s discovery in 1964 [33]. Vogel and
coworkers achieved the required planarity of fully conjugated 10-membered carbon rings by inserting a
carbon bridge between C-1 and C-6 (Figure 1), thus furnishing 1,6-methano[10]annulene as an example
of an aromatic cyclodecapentaene ring. Up to now, this class of compounds was extensively studied in
synthetic, theoretical and biological areas [34]. However, to our knowledge, suitable derivatives of
Molecules 2020, 25, 2164; doi:10.3390/molecules25092164
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Molecules 2020, 25, 2164
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these compounds have not been described in the literature as building blocks for phthalocyanine and
naphthalocyanine-like compounds.
Figure 1. Vogel’s bridged annulenes.
Herein, we describe two approaches for the synthesis of a new naphthalocyanine-like compound
which we name as Zn(II)-1,6-methano[10]annulenecyanine (10), using annulenenitrile
annulenemaleimide 13 as building blocks (Schemes 1–5).
9 and
2
. Results and Discussion
Synthesis
The synthesis of the building block 3,4-dicyano-1,6-methano[10]annulene (
as shown in Scheme 1 [35]. First, cycloheptatriene ( ) was mono-acetylated at low temperature by
a Friedel–Crafts reaction furnishing compound in 60% yield. Then, the resulting ketone
acetylated again, yielding the 1,3-diketone in 55% yield. The diacid
by submitting compound to the haloform reaction. Subsequently, the bis-Weinreb amide
9
) was carried out
1
2
2
was
was
3
4
was obtained in 62% yield
3
5
prepared using N-O-dimethylhydroxylamine hydrochloride (72% yield), and the dialdehyde
6
obtained
◦
after reduction with LiAlH at
−
78 C (69% yield). The next steps required selective olefinations of
4
dialdehyde
yield by a chemoselective Horner–Wadsworth–Emmons olefination of dialdehyde
describes an olefination under phase-transfer catalysis conditions that could give compound
our hands only HBr elimination was observed [36]. Therefore, a modified procedure to reach
tested and furnished the desired compound in 30% yield. Attempts to optimize this yield were tested,
but unsuccessfully. The annulenenitrile was obtained by a one-pot electrocyclization followed by
HBr elimination/aromatization (52% yield) (Scheme 1). The overall yield for the eight steps is 0.90%.
6
with two different olefination agents (Scheme 1). First, compound
7
was obtained in 57%
. The literature
, but, in
was
6
8
8
9
Scheme 1. Synthetic approach to the annulenenitrile 9 building block.

Molecules 2020, 25, 2164
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As the synthesis of annulenenitrile
9
involves eight steps we decided to scale-up some reactions
in order to obtain gram-scale amounts of intermediates like
we considered the linear synthesis of (Scheme 2) starting from 3.00 g of
intermediate by column chromatography, thus obtaining in a 0.95 g-scale (20.5% overall yield after
three steps). Attempts to synthesize from with no intermediate purification by chromatography
were performed starting from 50.0 g of cycloheptatriene ( ) and, to our delight, the diacid was
4
(Scheme 2) and
6
(Scheme 3). First,
4
1 and isolating each
4
4
1
1
4
obtained in 16.4% overall yield in a very short time. Additionally, only a simple final crystallization
yielded 16.0 g of 4.
Scheme 2. Scale-up of the intermediate 4.
Next, we tested two additional optimizations. First, the synthesis of the bis-Weinreb amide
was carried out starting from 12.0 g of , thus obtaining in 76% (13.4 g - Scheme 3). Furthermore,
the scaled-up reduction of 3.0 g of was successfully achieved, obtaining the di-aldehyde in
.16 g (69% yield). It is important to mention that the reduction of Weinreb amides requires a finely
5
4
5
5
6
1
temperature-controlled reaction, with difficult scalabilities in batch conditions.
Scheme 3. Scale-up of the intermediate 6.
After achieving improved conditions for obtaining annulenonitrile
9 in practical
amounts, we tested the first cyclotetramerization condition for obtaining the desired
Zn(II)-1,6-methano[10]annulenecyanine (10) (Scheme 4) using N,N-dimethylethanolamine (DMAE)
and zinc acetate dihydrate under thermal conditions. However, the new dye 10 was obtained in
only trace amounts as determined by UV–Vis spectroscopy [5,12]. Fortunately, using zinc triflate in

Molecules 2020, 25, 2164
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◦
hexamethyldisilazane (HMDS) and N,N-dimethylformamide (DMF) at 100 C for 24 h yielded 10 in
6
3% yield after purification by chromatography [37].
N
Zn(OTf)2
CN
N
N
N
Zn
N
CN
o
N
N
HMDS/DMF, 100 C,
N
9
24 h, 63%
1
0
diastereoisomeric mixture
Scheme 4. Synthesis of annulenecyanine 10.
The compound 10 (diastereoisomeric mixture) was initially characterized by UV–Vis
spectroscopy showing characteristic naphthalocyanine-like absorption bands at 362 and 800 nm
Figure 2). Additionally, solutions of 10 in DMF indicated good solubility up to 10 M and
(
µ
apparent non-aggregation in solution, which are very important properties of highly conjugated
naphthalocyanine-like dyes. This preliminary observation on non-aggregation was obtained only
considering UV–Vis analysis at concentrations up to 10.6 mM in DMF, since linear increases of
absorbance are achieved with increased concentrations (see Figures S56–S58 in the supporting
information). However, since a mixture of diastereoisomers is present in solution, further studies are
necessary to conclude about the aggregation of 10.
Figure 2. UV–Vis spectra of annulenocyanine 10 in DMF.

Molecules 2020, 25, 2164
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The HRMS-MALDI-TOF analysis of 10 was also consistent with a characteristic isotopic pattern
+
for metallated naphthalocyanine-like compounds and the experimental m/z for [M] correspond to the
+
+
expected for this dye (Figure 3 - Calc. for [M] , C H N Zn , 832.2041, found: 832.2053).
52
32
8
Figure 3. HRMS-MALDI-TOF of 10.
Attempts to perform the separation of the diastereoisomers of 10 were tested by HPLC, but
unsuccessfully, making the NMR characterizations even more difficult. We tested different deuterated
solvents (THF-d , DMF-d , acetone-d and CDCl ) but in all cases aggregation and complex mixtures
8
7
6
3
of signals were observed making it difficult to complete assignments. Despite this, it was possible to
1
identify in the H-NMR signals at the aromatic region 7.50–8.30 ppm corresponding to the hydrogens
of the macrocycle periphery, and multiplets at 0.82–0.92 ppm which are consistent with the expected
for CH -bridged [10]annulenes (signals at upfield region—see examples of the precursors
9 and 13
2
in the supporting information). It is important to comment that difficulties for characterizations by
NMR of naphthalocyanine and phthalocyanine derivatives are well-known in the literature, and the
evidence presented here is consistent with the expected for the new dye 10.
We then decided to find improvements for our original linear synthetic approach (Schemes 1–4,
0
.57% overall yield, nine steps).
Our alternative approach for the synthesis of 10 uses the precursor annulenemaleimide 13
(
Scheme 5). For the synthesis of 13 we decided to use the same di-aldehyde intermediate
6, which in a
one-pot Witting olefination with the ylide 12 and a 10π electrocyclization and dehydration yielded
13 in 56% yield [38,39]. Subsequently, compound 13 was submitted to the same cyclotetramerization
conditions and furnished 10 in 16% yield. Attempts to optimize this last step were carried out, but no
better results were achieved. Overall, the diastereomeric mixture of dye 10 is now obtained in seven
steps and 0.91% overall yield.

Molecules 2020, 25, 2164
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The fluorescence quantum yield (ΦF) of 10 was determined using as standard the corresponding
zinc naphthalocyanine by exiting both at 350 nm (Figure 4). We found the ΦF for 10 as being 0.01 with
an emission band at 820 nm, a common value for organic compounds which present aggregation and
dissipate energy in solution by non-radiant processes [40,41]. Therefore, the fluorescence technique
reinforces that comprehensive studies on aggregation should be conducted in the future, in order
to understand better the self-association properties of 10 (being a mixture of diastereoisomers) in
solutions. These additional studies will be essential for using this new dye as a photosensitizer and for
NIR applications.
Figure 4. Emission spectra of compound 10 in comparison with standard Zn(II)-naphthalocyanine
(
ZnNc), both excited at 350 nm and analyzed in DMF.
Overall, this first report on the dye 10 opens up many possibilities for the synthesis of hybrid
systems with modulated chemical, photochemical and photophysical properties.
O
NH
AcOH, P(Ph)3
O
145 °C, 3.5 h
'
'annuleneimide''
11
90%
alternative building block
O
O
H
N
O
O
O
AcOH
CHO
H
H
+
NH
O
NH
o
r.t.
145 C
6 h
56%
Ph3P
O
O
8
6
12
13
N
HMDS, DMF, Zn(OTf)2
N
N
N
N
N
Zn
N
160 °C, 24 h
N
16%
10
diastereoisomeric mixture
Scheme 5. Alternative approach to the synthesis of 10.

Molecules 2020, 25, 2164
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3
. Materials and Methods
All reagents and starting materials and solvents were purchased from commercial sources and used
as received or purified when necessary. Some reactions were carried out under an argon atmosphere as
specified in the experimental procedures (see the supporting information). For NMR spectra (performed
1
in CDCl or in DMSO-d solutions) tetramethylsilane was used as internal reference for H (0 ppm), and
3
6
13
C-D coupling signal as internal reference for C (CDCl —77.0 ppm and DMSO—39.5 ppm).
3
Flash chromatography was carried out using silica gel (230–400 mesh). Infrared spectra were
registered using KBr cells for liquid (films) and KBr pellets for solids. Fluorescence emission spectra
◦
were recorded using 1 cm optical length cuvettes at 25 C and N,N-dimethylformamide as solvent.
Analytical TLC was carried out on precoated aluminum sheets with silica gel (0.2 mm thick). UV–Vis
analyses were performed using a double beam spectrometer with 0.1 nm of resolution. High resolution
mass spectrometry was carried out on a MALDI-TOF for compound 10, and ESI-TOF for compounds
, 4, 5, 6, 7, 8, 9 and 13.
Experimental details, spectroscopic and spectrometric data of all key compounds are available
online in the supporting information.
2,
3
4
. Experimental Procedures
1
-(cyclohepta-1,3,5-trien-1-yl)ethan-1-one (
2
): To a suspension of zinc (II) chloride (36.0 g, 264 mmol)
◦
in 23 mL of dichloromethane at
acetyl chloride and 5.60 mL (5.87 g; 97.8 mmol) of acetic acid were added. Then, 3.40 mL (3.00 g;
−
30 C, under an argon atmosphere, 7.00 mL (7.73 g; 98.4 mmol) of
3
2.4 mmol) of cycloheptatriene (
1
) were added dropwise (during ca 10 min). The reaction mixture was
◦
stirred for 3 h at
−
30 C. The reaction mixture was quenched with 50 g of ice and neutralized with
sodium bicarbonate. The organic layer was washed with brine (50 mL) and dried over anhydrous
sodium sulphate. The solvent was removed under vacuum and the organic residue was purified by
chromatography on silica gel using CH Cl :hexano (5:5)
→
(6:4) as eluent, furnishing a yellow oil as
product. Yield: 60% (2.63 g; 19.6 mmol). H-NMR (CDCl , 400.15 MHz), ppm): 2.38 (s, 3H); 2.65 (d,
H, J = 7,0 Hz); 5.57 (dt, 1H, J = 9.0 Hz, J = 7.0 Hz); 6.27 (dd, 1H, J = 9.3 Hz, J = 5.7 Hz); 6.70 (ddt,
2
2
1
δ
3
2
1
1
2
1
2
1
H, J = 11.2 Hz, J = 6.0 Hz, J = 0.8 Hz); 6.86 (dd, 1H, J = 11.2 Hz, J = 5.7 Hz); 7.09 (d, 1H, J = 6.0
1
1
2
3
1
2
3
Hz). C-NMR (CDCl , 100.0 MHz)
νmax: (KBr): 3308 cm ; 3024 cm ; 2928 cm ; 2886 cm ; 2839 cm ; 1732 cm ; 1666 cm ; 1605 cm
1
7
δ
(ppm): 25.4; 26.3; 125.9; 127.2; 129.3; 131.8; 133.1; 136.1; 197.6. IR:
3
−
1
−1
−1
−1
−1
−1
−1
−1
−1
−1
;
−
1
−1
−1
−1
−1
−1
−1
528 cm ; 1431 cm ; 1385 cm ; 1364 cm ; 1209 cm ; 1211 cm ; 1182 cm ; 976 cm ; 789 cm ;
−
1
−1
+
+
58 cm ; 708 cm . HRMS (ESI-TOF): calc. for [M+H] , C H O , 135.0804; found: 135.0806.
9
11
1
,1’-(cyclohepta-3,5,7-triene-1,3-diyl)diethanone (
3
): In a suspension containing 1.49 g(11.2 mmol) of
◦
aluminium chloride and 6.00 mL of dry dichloromethane at 0 C, 0.79 mL (870 mg; 11.2 mmol) of acetyl
chloride was added under an argon atmosphere. After 5 min, 500 mg (3.73 mmol) of
2 was added.
◦
Then, the cooling bath was removed and the reaction mixture heated to 55 C for 3 h. After this period,
◦
◦
the reaction mixture was cooled to 0 C and 5 mL of water at 5 C was added. The reaction mixture was
neutralized with sodium bicarbonate solution and filtered in a sintered funnel. The filtrate was washed
with ethyl acetate (5
×
50 mL). The solvent was removed under vacuum and the organic residue (a
brown oil) was purified by column chromatography on silica gel using toluene: ethyl acetate (95:5) as
eluent, furnishing a yellow oil as product. Yield: 50% (333 mg; 1.89 mmol). 1H-NMR (CDCl , 400.15
3
MHz),
δ (ppm): 2.24(s, 6H); 2.99(s, 2H); 6.98 (dd, 2H, J = 4.0 Hz, J = 3.0 Hz); 7.17 (dd, 2H, J = 3.9
1 2 1
13
Hz, J = 3.0 Hz). C-NMR (CDCl , 100.0 MHz)
δ
(ppm): 24.0; 26.7; 132.6; 134.1; 134.4; 197.1. HRMS
2
3
+
+
(ESI-TOF): calc for [M+H] , C H O , 177.0910; found: 177.0912. Note: Compound is unstable
3
11
13
2
under light and room temperature exposure. It must be stored at low temperature and protected
from light.
cyclohepta-3,5,7-triene-1,3-dicarboxylic acid (
mol/L), 14 mL of 1,4-dioxane was added. Then this mixture was cooled to
4
): To 150 mL aqueous sodium hydroxide solution (1.2
◦
−
5 C and 2.60 mL of bromine
(
8.06 g; 50.7 mmol) was added. After 5 min, a solution containing 1.5 g (8.5 mmol) of compound 3 in 14

Molecules 2020, 25, 2164
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◦
mL 1,4-dioxane was added dropwise (ca 10 min). Then, the reaction mixture was allowed to reach 5 C
and stirred for 15 h. After that, 100 mL of a solution 0.3 mol/L of sodium metabisulfite was added
and stirred for 1h. The pH of the medium was adjusted to 3–4 with 10% solution of hydrochloric
acid. The product was obtained as a precipitate which was filtered and washed with water (100 mL),
ethanol (50 mL) and ethyl ether (50 mL) and dried. Yield: 62% (949 mg; 5.26 mmol). 1H-NMR (DMSO,
4
00.15 MHz),
δ
(ppm): 2.88 (s, 2H); 6.91 (t, 2H, J = 2.8 Hz); 7.19 (t, 2H, J = 2.8 Hz); 12.60 (s, 2H).
13
−1
C-NMR (DMSO, 100.0 MHz)
δ
(ppm): 25.1; 125.7; 132.4; 133.6; 166.5. IR: νmax: (KBr pellet): 744 cm
;
−
1
−1
−1
−1
−1
−1
−1
−1
−1
9
2
2
05 cm ; 935 cm ; 1227 cm ; 1421 cm ; 1440 cm ; 1609 cm ; 1678 cm ; 2619 cm ; 2928 cm ;
974 cm ; 3004 cm ; 3474 cm
03.0317.
−
1
−1
−1
. HRMS (ESI-TOF): calc for [M+Na] , C H O Na , 203.0315; found:
9 8 4
+
+
1
3
1
3
N ,N -dimethoxy-N ,N -dimethylcyclohepta-3,5,7-triene-1,3-dicarboxamide (
5
): To a suspension containing
◦
9
00 mg (5.00 mmol) of diacid
4
in 60 mL of dichloromethane at 0 C and under an argon atmosphere
was added 1.65 g (16.9 mmol) of N-O-dimethylhydroxylamine hydrochloride, 390.0 mg (3.18 mmol) of
N,N-Dimethyl-4-aminopyridine, 2.70 g (13.1 mmol) of N, N’-Dicyclohexylcarbodiimide and 3.60 mL
◦
(
2.61 g; 25.6 mmol) of triethylamine. The reaction mixture was stirred for 1 h at 0 C, then 48 h at
room temperature. After this period, the solvent was removed under vacuum and the residue partially
dissolved with 150 mL of ethyl acetate/pentane mixture (1:1) and filtered off. The organic phase was
concentrated under vacuum and the residue was purified by column chromatography on silica gel
using dichloromethane/ethyl acetate (8:2)
→
(6:4) as eluent furnishing a yellow oil as product. Yield:
(ppm): 2.84 (s, 2H); 3.18 (s, 6H); 3.53 (s,
1
7
6
2% (960 mg; 3.60 mmol). H-NMR (CDCl , 400.15 MHz),
δ
3
H); 6.62–6.63 (m, 4H). 13C-NMR (CDCl , 100.0 MHz)
δ
(ppm): 30.7; 33.4; 61.2; 129.4; 130.2; 132.0; 169.5.
3
+
+
−1
HRMS (ESI-TOF): calc. for [M+H] , C H O , 267.1339; found: 267.1341. IR: νmax: (KBr): 750 cm
;
9
9
−1
2
−
1
−1
−1
−1
−1
−1
−1
7
63 cm ; 973 cm ; 1275 cm ; 1380 cm ; 1610 cm ; 1634 cm ; 2934 cm ; 2963 cm .
Cyclohepta-3,5,7-triene-1,3-dicarbaldehyde (
6
): To a suspension containing 2.73 g (71.9 mmol) of lithium
◦
aluminum hydride and 180 mL of anhydrous tetrahydrofuran at −78 C under an argon atmosphere,
amide
5 (3.00 g; 11.3 mmol) previously dissolved in 80 mL of anhydrous tetrahydrofuran was
added dropwise (ca 80 min). The reaction was stirred for 20 min, 100 mL of 0.50 mM aqueous
◦
solution of potassium bisulphate was added and the reaction allowed to reach 0 C. Then 200 mL
of 5% aqueous solution (wt/v) of citric acid was added and the reaction mixture was extracted with
dichloromethane (3
×
100 mL). The organic layer was dried over anhydrous sodium sulphate, filtered
◦
and the solvent removed under vacuum (thermal bath at 20 C). The aldehyde
6
was crystalized in
an ethyl acetate/pentane mixture, furnishing a yellow-pale solid (999 mg; 6.73 mmol). The mother
liquor was purified by chromatography on silica gel using CH Cl CH Cl :AcOEt (9:1) furnishing
→
2
2
2
2
1
3
55.7 mg (1.05 mmol). Total Yield: 69% (1.15 g, 7.78 mmol). 1H-NMR (CDCl , 400.15 MHz),
δ (ppm):
3
13
.08 (s, 2H); 7.00 (d, J = 2.7 Hz); 7.04 (dd, 2H, J = 3.8 Hz, J = 2.7 Hz); 9.54 (s, 2H). C-NMR (CDCl ,
(ppm): 19.0; 134.2; 136.2; 141.3; 191.0. IR: νmax: (KBr pellet): 1059 cm ; 1233 cm ;
431 cm 1; 1609 cm ; 1682 cm ; 2777 cm , 2849 cm , 2920 cm , 3020 cm , 3308 cm , 3449 cm
1
2
3
−1
−
1
1
1
00.0 MHz)
δ
−
−1
−1
−1
−1
−1
−1
−1
−1
.
+
+
◦
HRMS (ESI-TOF): calc for [M+H] , C H O , 149.0597; found: 149.0599. mp: 121–123 C.
9
9
2
2-bromo-3-(6-formylcyclohepta-1,3,5-trien-1-yl)acrylonitrile (7): To a previously flamed round-bottom
flask, under an argon atmosphere, 205 mg sodium hydride (60% wt.) and 10 mL of anhydrous
◦
tetrahydrofuran were added, then cooled to 0 C. A solution containing 1.33 g (5.19 mmol) of
diethyl(bromo(cyano)methyl)phosphonate previously dissolved in 20 mL of anhydrous tetrahydrofuran
was added dropwise (ca 5 min) and stirred for 30 min (the solution acquired an intense red color).
This solution was transferred via cannula (25 min) to a solution containing aldehyde 6 (500.0 mg, 3.37
◦
mmol) in 30 mL of anhydrous tetrahydrofuran at
−
−
30 C. The reaction mixture was stirred for 2 h at
◦
◦
30 C and 12 h at 0 C. After that, the reaction was quenched with 60 mL of saturated ammonium
acetate solution and washed with dichloromethane (3 70 mL). The organic phases were united
and dried over anhydrous sodium sulphate, filtered and the solvent removed under vacuum. The
organic residue was purified by column chromatography on silica gel using the gradient hexane
×
→

Molecules 2020, 25, 2164
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hexane:ethyl acetate (9.5:0.5) as eluent, furnishing a yellow solid as product. Yield: 58% (486 mg; 1.94
1
mmol). H-NMR (CDCl , 400.15 MHz),
δ
(ppm): 2.96 (2H, s); 6.87–7.04 (5H, m); 7.15 (1H, s); 9.57 (1H,
3
s). 13C-NMR (CDCl , 100.0 MHz)
δ (ppm): 26.1; 87.7; 115.4; 129.6; 130.9; 132.0; 133.5; 135.3; 141.2;
3
− −1 −1 −1 −1 −1
1
1
1
(
48.3; 191.1. IR: νmax: (KBr pellet): 738 cm ; 752 cm ; 875 cm ; 1149 cm ; 1193 cm ; 1232 cm ;
−
1
−1
−1
−1
−1
−1
−1
−1
429 cm ; 1516 cm ; 1566 cm ; 1585 cm ; 1674 cm ; 2205 cm ; 2725 cm ; 2821 cm . HRMS
+
◦
ESI-TOF): calc for [M+Na] , C H BrNNaO, 271.9681; found: 271.9690. mp: 92–94 C.
11 8
2-bromo-3-(6-((E)-2-cyanovinyl)cyclohepta-1,3,5-trien-1-yl)acrylonitrile (8): To a previously flamed
round-bottom flask, under an argon atmosphere, 970 mg (3.88 mmol) of compound
7
was dissolved
◦
in 50 mL of anhydrous tetrahydrofuran. This solution was cooled to
−78 C. In another flamed
◦
round-bottom flask with a suspension at 0 C of 194 mg NaH (60% wt.) and 15 mL of anhydrous
tetrahydrofuran, 810
µL (887 mg; 5.00 mmol) of diethylcyanomethylphosphonate was added dropwise
(
5 min). The mixture was left to react for 30 min, and then transferred via cannula to the solution
◦
containing compound 7 at −78 C. The reaction mixture was left to react for 36 h, and then quenched
with 50 mL of a saturated solution of NH Cl and the reaction mixture was allowed to reach room
4
temperature. The reaction mixture was extracted with dichloromethane (3
layer washed with 50 mL of water. The organic layer was dried over anhydrous Na SO , filtered and
×
100 mL) and the organic
2
4
the solvent removed under vacuum. The organic residue was purified by column chromatography on
silica gel using the gradient hexane to hexane: AcOEt (9.5: 0.5) as eluent, furnishing a yellow solid as
product. Yield: 30% (315 mg; 1.15 mmol). 1H-NMR (CDCl , 400.15 MHz),
δ (ppm): 3.05 (2H, s); 5.34
3
13
(
1H, d, J = 12.1 Hz); 6.27–6.91 (4H, m); 6.88 (1H, d, J = 12.1 Hz); 7.40 (1H, s).
C-NMR (CDCl , 100
3
MHz)
δ (ppm): 31.4; 86.3; 96.1; 116.0; 117.5; 127.4; 128.9; 132.6; 132.9; 133.1; 133.5; 148.2; 148.9. IR: νmax:
− −1 −1 −1 −1 −1 −1 −1
1
(KBr pellet): 754 cm ; 864 cm ; 923 cm ; 1088 cm ; 1177 cm ; 1246 cm ; 1381 cm ; 1445 cm ;
− −1 −1 −1 −1 −1 −1
1
1574 cm ; 1589 cm ; 2203 cm ; 2849 cm ; 2913 cm ; 3059 cm ; 3447 cm . HRMS (ESI-TOF):
+
◦
calcd for [M+H] , C H BrN , 273.0022, found: 273.0034. mp: 47–50 C.
13
10
2
(
annulenonitrile) - bicyclo[4.4.1]undeca-1(10),2,4,6,8-pentaene-3,4-dicarbonitrile (9): A solution of 233 mg
(
0.44 mmol) of compound
8
in 25 mL of freshly distilled DMF was degassed for 10 min under an argon
◦
atmosphere. Then, this solution was heated to 160 C and stirred for 13 h. After this period, 50 mL of
water was added and the reaction extracted with toluene (3
×
50 mL) The organic layer was washed
with 50 mL of water, dried over anhydrous Na SO , filtered and the solvent removed under vacuum.
2
4
The organic residue was purified by chromatography on neutral alumina utilizing gradient hexane to
hexane: AcOEt (8:2) as eluent, furnishing a yellow solid as product. Yield: 52% (85.0 mg; 0.44 mmol).
1
2
4
2
H-NMR (CDCl , 400,15 MHz),
δ
(ppm): –0.23 (1H, dt, J = 9.6 Hz, J = 1.2 Hz);
−
0.01 (1H, dt, J =
3
4
13
9
.6 Hz, J = 1.2 Hz); 7.30–7.36 (2H, m); 7.53–7.60 (2H, m); 8.02(2H, s). C-NMR (CDCl , 100 MHz)
δ
3
−1
−1
−1
−1
(
ppm): 34.1; 110.1; 115.8; 118.5; 129.9; 130.1; 137.3. IR: νmax: (KBr pellet): 718 cm ; 870 cm ; 908 cm
;
;
−
1
−1
−1
−1
−1
−1
−1
−1
1
022 cm ; 1261 cm ; 1437 cm ; 1458 cm ; 2218 cm ; 2851 cm ; 2918 cm ; 2962 cm ; 3031 cm
445 cm . HRMS (ESI-TOF): calc for [M+H] , C H N2+, 193.0760; found: 193.0759. mp: 185–187
−
1
+
3
13
9
◦
C.
Zn(II)-1,6-methano[10]annulenecyanine (10) via annulenonitrile (
an argon atmosphere were added 50.0 mg (260 mol) annulenonitrile
triflate – Zn(OTf) , 114 L (87.8 mg; 540 mol) of hexamethyldisilazane (HMDS) and 266
9
): To a high pressure glass tube under
µ
9
, 24.2 mg (60.0 mol) of zinc (II)
µ
µ
µ
µ
◦
L (253 mg;
2
3.46 mmol) of N,N-dimethylformamide (DMF). The reaction mixture was stirred at 120 C for 24 h.
After this period, the solvent was removed and the organic residue was purified by chromatography
on silica gel utilizing CH Cl : MeOH (9.5:0.5) as eluent furnishing a green solid as product. For
2
2
additional purification, it was necessary to utilize preparative TLC utilizing CH Cl :MeOH (9:1) as
2
2
eluent. Yield: 63% (34.8 mg; 40.0
HRMS (MALDI-TOF): calc for [M] , C H N Zn , 832.2041, found: 832.2053.
µ
+
mol). UV-Vis (DMF), νmax, (log
ε
): 362(4.89), 720(4.62), 800(5.07).
+
52
32
8
3-(triphenylphosphoranylidene)pyrrolidine-2,5-dione (12): To a round-bottom flask containing 10 mL of
acetic acid, 485.0 mg (5.00 mmol) of maleimide 11 and 1.38 g (5.25 mmol) of triphenylphosphine

Molecules 2020, 25, 2164
10 of 13
◦
were added. The reaction mixture was stirred and refluxed at 125 C for 3.5 h. After this period,
the acetic acid was removed under vacuum and the organic residue dissolved in acetone (10 mL),
and then diethyl ether was slowly added resulting in the precipitation of an off-white solid. This
solid was filtered, washed with diethyl ether (3
×
20 mL) and dried under vacuum. Yield: 90% (1.61
(ppm): 1.65 (1H, bs); 3.03 (2H, s); 7.51–7.65 (15H,
1
g; 4.49 mmol). H-NMR (CDCl , 400.15 MHz),
δ
3
13
m). C-NMR (CDCl , 100.0 MHz) δ (ppm): 38.5; 125.1; 126.0; 128.6; 128.7; 128.8; 129.3; 129.4; 132.9;
3
− −1 −1
1
1
2
33.0; 133.5; 133.6; 133.8; 134.0; 171.0; 178.0. IR: νmax: (KBr pellet): 3453 cm ; 3111 cm ; 3087 cm ;
−
1
−1
−1
−1
−1
−1
−1
−1
−1
−1
−1
961 cm ; 2818 cm ; 2743 cm ; 1715 cm ; 1616 cm , 1483 cm ; 1435 cm , 1373 cm ; 1312 cm ,
−
1
−1
−1
−1
−1
◦
1
287 cm ; 1213 cm ; 1167 cm ; 1109 cm ; 997 cm ; 899 cm ; 837 cm . mp: 218–220 C.
annulenoimide) - 1H-5,10-methanocyclodeca[c]pyrrole-1,3(2H)-dione (13): To a round-bottom flask
containing 8 mL of acetic acid, 100 mg (0.68 mmol) of dialdehyde and 364 mg (1.00 mmol) of
(
6
◦
phosphorane 12 were added. The reaction mixture was heated to 145 C and stirred for 86 h. After
this period, the acetic acid was removed under vacuum and the organic residue was purified by
chromatography on silica gel utilizing hexane:AcOEt (6:4) as eluent, furnishing a yellow solid as
product. Yield: 56% (80.7 mg; 0.38 mmol). 1H-NMR (CDCl , 400.15 MHz),
δ
(ppm):
9.9 Hz, J = 1.1 Hz); 0.10 (1H, dt, J = 9.9 Hz, J = 1.1 Hz); 7.32–7.38 (2H, m); 7.58–7.65 (2H, m); 7.96
1H, bs); 8.27(2H, s). 13C-NMR (CDCl , 100.0 MHz)
(ppm): 35.4; 119.5; 129.1; 129.4; 130.3; 130.8;
−
0.20 (1H, dt, J
3
=
(
δ
3
− −1 −1 −1 −1 −1
1
1
1
69.9. IR: νmax: (KBr pellet): 3184 cm ; 3046 cm ; 2955 cm ; 2916 cm ; 2848 cm ; 1800 cm ;
−1
−1
−1
−1
−1
−1
−1
−1
−1
757 cm ; 1688 cm
,
1520 cm ; 1422 cm , 1368 cm ; 1163 cm
,
1020 cm ; 872 cm
,
◦
745 cm .
+
+
HRMS (ESI-TOF): calc for [M+H] , C H NO , 212.0706; found: 212.0706. mp 230–232 C.
13
10
2
Zn(II)-1,6-methano[10]annulenecyanine (10) via annulenoimide (13): To a high pressure glass tube were
added under an argon atmosphere 119.0 mg (560.0 mol) of annulenoimide 13, 51.2 mg (140 mol)
of Zn(OTf) , 470 L (360.0 mg; 2.23 mmol) of HMDS and 43 L (41.8 mg; 573 mol) of DMF. The
reaction mixture was stirred at 160 C for 24 h. After this period, the solvent was removed and the
organic residue was purified by chromatography on silica gel utilizing CH Cl :MeOH (9.8:0.2) as
µ
µ
µ
µ
µ
2
◦
2
2
eluent, furnishing a green solid as product. For additional purification, it was necessary to utilize
preparative TLC utilizing CH Cl :MeOH (9.4:0.6) as eluent. Yield: 16% (22.5 mg; 27.0 µmol).
2
2
5
. Conclusions
We have developed two different approaches for the first total synthesis of
Zn(II)-1,6-methano[10]annulenecyanine (10). Multistep synthetic approaches for naphthalocyanine and
phthalocyanine derivatives always presents low overall yields but are very necessary for dye-discovery
with improved photochemical properties, particularly compounds with NIR absorption bands. This
synthesis is the first part of the dye-discovery process and many additional photochemical and
photophysical studies are necessary to achieve all the potential of 10 and related compounds. It is
important to highlight that only preliminary studies on aggregation are reported in this communication.
However, as mentioned before, this phenomenon should be evaluated in different solvents, with
different techniques and, if possible, using the separated diastereoisomers, before presenting conclusions
on self-association properties of 10 in solutions.
Herein, we have also demonstrated for the first time the potential of bridged-annulene derivatives
as precursors for phthalocyanine and naphthalocyanine-like dyes, thus opening up many possibilities
for the synthesis of hybrid structures with common precursors like phthalimides and phthalonitriles.
Supplementary Materials: The following are available online. It contains details and characterization data along
1
13
with copies of the H-NMR and C-NMR spectra and high-resolution mass spectra for compounds.
Author Contributions: Chemical synthesis and photophysical studies, N.R.d.S.G.; writing and editing, N.R.d.S.G.,
K.T.d.O. and T.J.B.; supervisor: K.T.d.O. All authors have read and agreed to the published version of
the manuscript.
Funding: The authors would like to thank the S
ão Paulo Research Foundation (FAPESP) for financial support
and a fellowship (Grants 2018/00106–7, 2013/07276-1 and N.R.S G. fellowship 2012/24092-9). We also thank

Molecules 2020, 25, 2164
11 of 13
CAPES (CODE 001) and CNPq (Grant 407990/2018-6 and K.T.O. research fellowship 303890/2019-3) for additional
financial support.
Acknowledgments: The authors special thanks go to E. Rodrigues-Filho, T. M. C. Pereira, Q. B. Cass, B. Rebelo
for HRMS-TOF analyses, and R. M. Carlos and M. Cali for fluorescence analyses.
Conflicts of Interest: The authors declare no conflict of interest.
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2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).