Straightforward Syntheses That Avoid Scrambling of meso-Substituted [28]Hexaphyrins

Article abstract of DOI:10.1002/ejoc.201601342

A two-step synthesis of meso-substituted [28]hexaphyrins in an aqueous medium was developed and optimized, and scrambling processes are avoided despite the use of a high acid concentration. The efficiency of this procedure relies on the nature of the star

Full text of DOI:10.1002/ejoc.201601342

A Journal of
Accepted Article
Title: Straightforward Syntheses That Avoid Scrambling of meso-
Substituted [28]Hexaphyrins
Authors: Rémi Plamont, Teodor Silviu Balaban, and Gabriel Canard
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201601342
Link to VoR: http://dx.doi.org/10.1002/ejoc.201601342
Supported by

10.1002/ejoc.201601342
European Journal of Organic Chemistry
COMMUNICATION
Straightforward Syntheses that Avoid Scrambling of meso-
Substituted [28]Hexaphyrins
Rémi Plamont,[a] Teodor Silviu Balaban,[a] and Gabriel Canard*[b]
Dedication ((optional))
Abstract: A two-step synthesis of meso-substituted [28]hexaphyrins
using an aqueous medium was developed, optimized and was
shown to avoid the scrambling process despite the use of high
concentration of acid. The efficiency of this procedure relies on the
nature of the starting material and it can be extended to the
unit 1 (R ≠ H).[7] Nevertheless, this one-pot procedure produces
a complex mixture of expanded porphyrins which are difficult to
separate and purify. This problem can be overcome through ring
size selective syntheses of hexaphyrins using oligopyrranes. For
example, the acidic condensation of meso-substituted
dipyrromethanes 3 with aldehydes 2 can produce, after oxidation,
A3B3-hexaphyrin derivatives bearing up to two different kinds of
meso groups (route b).[8] The first example of a meso-substituted
hexaphyrin bearing six phenyl groups was prepared starting
from the condensation of a tripyrrane 4 with benzaldehyde in
acidic media (Scheme 1, route c).[9] This approach was later
used to synthesize from simple to very sophisticated hexaphyrin
derivatives such as A2B4 type compounds bearing an internal
strap or dyes incorporating Bodipy units.[3a, 10] Less symmetric
compounds were prepared using the acidic condensation of
tetrapyrranes 5 with dipyrromethane dicarbinols 6 (route d). This
elegant strategy, that could allow an access to derivatives
bearing up to six different meso groups, was used to prepare
unsymmetrical compounds bearing a meso free position or
straightforward
preparation
of
unprecedented
AB2C2D-
[28]hexaphyrins bearing up to four different kinds of meso appended
aryl groups.
Introduction
Expanded porphyrins and their core-modified analogues have
been the subject of a growing interest because of their versatile
chemical, optical, electrochemical properties as well as their
unique coordination chemistry.[1] Among the numerous
described
expanded
porphyrinoids
structures,
hexaphyrin(1.1.1.1.1.1) derivatives (Scheme 1) that can be
viewed as the first expanded porphyrin homologues (alternating
pyrrolic units and bridging carbon atoms) were the subject of a
particularly intense research activity because of their fascinating
physico-chemical properties. For example, their cavities are
suitable for the concomitant coordination of two identical or
different metallic centers.[2] Moreover, if most of the
hexaphyrin dimers.[11] Reactive compounds
6 were also
condensend with β-substituted pyrrolic units 1 to prepare
partially β-substituted hexaphyrins (route e).[12]
[26]hexaphyrins are planar macrocycles exhibiting Hückel
3]
aromaticity,[1g,
their reduced forms namely [28]hexaphyrins
(Scheme 1) and their metal complexes may have twisted Möbius
structures in solution.[1g, 4] Consequently, the oxidation form of
hexaphyrins has a crucial impact on their light-absorption and
emission properties.[5]
The main synthetic procedures giving access to meso-
substituted hexaphyrins are summarized on Scheme 1. The first
stable derivative bearing six meso pentafluorophenyl groups
was prepared through a simple and straightforward synthesis
starting from commercially available pyrrole 1 (R = H) and
pentafluorobenzaldehyde (route a).[6] This strategy can be used
to introduce various kind of meso substituents together with
various β groups when these are born by the starting pyrrolic
[a]
[b]
Dr. R. Plamont, Prof. Dr. T. S. Balaban
Chirosciences
Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Chirosciences,
France.
Dr. G. Canard
Aix Marseille Univ, CNRS, CINAM, France.
Campus de Luminy, Case 913, 13288 Marseille Cedex 09, France.
E-mail: gabriel.canard@univ-amu.fr
http://www.cinam.univ-mrs.fr/
http://orcid.org/0000-0002-3572-9091
Scheme 1. Synthetic preparations of meso-substituted hexaphyrins.
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
1
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COMMUNICATION
The use of cyclic or linear oligopyrranes suffers often from
a major drawback called “scrambling”. These compounds are
usually condensed or prepared using an acidic medium which
can also causes their acidolysis into fragments that then
recombine into other different oligopyrranes.[13] This scrambling
process was for example put into evidence during the
condensation of a tripyrrane 4 with an aldehyde or an N-sulfonyl
aldimine that leads to the formation of unexpected N-fused
pentaphyrins, heptaphyrins or octaphyrins.[8c, 10f] If the acidolysis
of oligopyrranes can be avoided by sterically hindered or
Soret-like band maximum (max= 610 nm). For each subsequent
experiment, the solvent volume was kept constant (25 mL)
during the acidic condensation and the oxidation steps. On the
contrary, variations were applied to the concentrations of the
reactants, the nature of the organic solvent, the amount and the
nature of the oxidant. After the oxidation step, multiple colored
species are present in the reaction mixture and can be detected
by TLC or UV-Visible spectroscopy. Consequently, an aliquot of
1 mL was collected from this mixture and was passed over a
short chromatography on silica gel and using dichloromethane
as solvent (See scheme 3). The first red fractions containing the
trans-A2B2 porphyrin and traces of p-chloranil were removed
before the elution of 7a (Scheme 3) All the following blue
fractions containing 7a were gathered in a volumetric flask
completed with dichloromethane. The UV-Visible spectrum of
the resulting solution was then recorded and used to attribute
the corresponding UV-yield value. Considering the different prior
strongly electron-withdrawing meso aryl substituents,[14]
a
spectacular breakthrough, reported by Koszarna and Gryko in
2006, showed that it can also be suppressed when the solvent is
an alcohol-water mixture despite the use of very high
concentrations of aqueous HCl.[15] This efficient preparation of
trans A2B corroles was later extended to the synthesis of
porphyrins bearing up to three different kinds of meso
substituents.[16] We report herein how this strategy can be
extended to the straightforward preparation of simple to complex
meso-substituted [28]hexaphyrins bearing up to four different
kinds of meso groups.
steps (extraction, washing, purification etc.),
a probable
overestimation of the UV-yields cannot be excluded and can be
partly responsible of the discrepancies between the values of
the UV and isolated yields. Since these uncertainties cannot be
the principal source of the trends affecting the UV-yields values,
we kept this short and quick procedure to optimize the synthetic
preparation of 7a.
Results and Discussion
The highest UV-yield was reached when
a DPM
concentration of 33.3 mM was used as observed previously in
the synthesis of [26]hexaphyrins (20%, Table 1 entry 4)).[8b] The
replacement of ethanol by other organic solvents as well as the
modification of the acidic condensation time did not increase the
yield of 7a (Table 1, entries 7-12). Interestingly, no expanded
porphyrin was detected when a higher quantity of p-chloranil (3
equivalents) was introduced during the oxidation step or when
air was the oxidizing agent (Table 1, entries 13-14).
The optimized preparation of a trans-A2B2 porphyrin starting
from dipyrromethane 3 (DPM) and an aldehyde 2 in an aqueous
medium were chosen as the starting point to develop a new
synthetic access to meso-substituted expanded porphyrin
derivatives (Scheme 2). Equal amounts of DPM and aldehyde
were dissolved in 4 mM concentrations in an ethanol/water
mixture in a 4 to 1 ratio in the presence of an HCl concentration
of 38 mM. The porphyrinogen is then oxidized by p-chloranil
during one hour in boiling chloroform. Within these conditions
and using DPM 3a, aldehyde 2a and 2 equivalents of p-chloranil
(Table 1, entry 1), no expanded porphyrin was observed in the
final mixture. The concentration of the starting materials was
then raised to 100 mM because this value was optimal to
produce A4B4-octaphyrins starting from DPM (Table 1, entry
2).[8e] The chromatographic purification of the oxidized reaction
mixture revealed that only one supplementary colored
Consequently,
meso
substituted
[28]hexaphyrins
or
[26]hexaphyrins are probably unstable within strong oxidative
conditions which have to be avoided when considering their
interconversion. This transformation was effective when 7a was
dissolved in a suspension of MnO2 in dichloromethane affording
quantitatively its oxidized form [26]hexaphyrins 8a (Scheme 2).
The optimized conditions were used on a preparative scale
to produce [28]hexaphyrins 7a and 7b with respective yields of 8
and 11%. The nature of the starting compounds is crucial. For
example, only 2% of 7a was formed when DPM 3a and
aldehyde 2a were replaced by 3b and 2b respectively (Scheme
2). Even if the meso-pentaflurophenyl group is known to slightly
stabilize dipyrromethane 3a towards acidolysis,[14] no scrambling
occurred during the utilization of 3b as illustrated by the
concomitant formation of only the corresponding trans-A2B2
porphyrin. Moreover, a single and pure hexaphyrin (7a) was
formed as proved by its exact mass spectrum. The difference
compound was eluted after the trans A2B2 porphyrin.
A
combination of 1H NMR, UV-vis spectroscopy and mass
spectrometry analyses proved that this compound was the
[28]hexaphyrin 7a (Scheme 2) and not the expected A4B4-
octaphyrin. This result was quite surprising since previous
syntheses of [26]hexaphyrins starting from DPM 3a and
aldehydes were requiring ortho substituted benzaldehyde
derivatives.[8b] Moreover, despite the strong acidic conditions, no
scrambling occurred as demonstrated by the single isotopic
cluster in the corresponding HRMS spectrum (see the
Supporting Information). Consequently, we chose to improve the
first isolated synthetic yield (2%) of 7a by varying the different
reactions parameters such as the concentration of the reactants
or the time of the acidic condensation (Table 1).
between the two yields could be due to
a different pre-
organisation of the intermediate olygopyrranes towards the
cylisation. In the same way, we did not succeed to prepare meso
free or meso alkyl derivatives from the condensation of DPMs
3c-e with aldehyde 2b or using DPM 3a with aldehyde 2d
(Scheme 2).
The first short sample of 7a was used to record its UV-
Visible spectrum and to measure the molar absorptivity at the
2
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COMMUNICATION
Scheme 2. Syntheses of meso-substituted [28]Hexaphyrins 7a, 7b and [26]Hexaphyrins 8a.
1 mL
7a
Oxidized
reaction
mixture
Short
chromatography
Fractions
gathering
Scheme 3. Schematic presentation of the procedure used to measure the UV yields of 7a-during the optimization of the synthetic parameters.
3
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10.1002/ejoc.201601342
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COMMUNICATION
of the starting materials and is decreasing with the electron-
withdrawing strength of the substituents. Several combinations
were tested (3a/2a/5b; 3a/2a/5d; 3c/2b/5c and 3b/2e/5e) and
failed to give any expanded porphyrins. However, when the
procedure was applied to the two sets 3b/2a/5a and 3a/2e/5f,
the purification of the final reaction mixture afforded the novel
compounds 7d and 7e with a yield of 1%. 7d is the cis isomer of
7a where the identical substituents are born by three successive
meso carbon atoms. Even if the synthetic yield of 7e is low (1%),
it puts into evidence how this simple procedure can conduct to
sophisticated compounds bearing up to four different kinds of
meso aryl groups. However, we have noticed that
[28]hexaphyrins display a moderate stability emphasized by
electron-donating substituents. After one year, the solid
compounds 7a-e were slowly converted into a mixture of colored
compounds containing their [26] isomer, albeit being stored at -
20 °C under argon.
Table 1. Optimization of the synthesis of [28]hexaphyrin 7a.
Entry
[3a]
(mmol/L)
Solvent
t (h)
Oxidation
step[a]
UV yield (%)
1
4
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
MeOH
iPrOH
THF
16
16
16
16
16
16
16
16
16
2
a
a
a
a
a
a
a
a
a
a
a
a
b
c
0
2
100
10
33.3
50
75
33
33
33
33
33
33
33
33
14 (2 %)[b]
3
1
4[c]
5
20 (8 %)[b]
17
16
7
6
1
The complete H NMR characterization of [28]hexaphyrins
7
is difficult because of the equilibrium existing between the
different interconverting twisted Möbius isomers.[4b] The
complexity of this task is here increased by the presence of
different tautomeric forms resulting from the substitution.
8
8
9
0
1
Consequently, the complete assignment of the H NMR signals
10
11
12
13
14
EtOH
EtOH
EtOH
EtOH
EtOH
1
of 7a-e and 8a is far beyond the scope of the present work
which focuses on their synthetic preparation. We chose to report
in the experimental part their 1H NMR spectra recorded in
deuterated tetrahydrofuran because this solvent gave the best
resolved spectra at room temperature (see the supporting
information). On the other hand, the UV-Visible spectra of
[28]hexaphyrin 7a-e give first insights of the relationship
between the nature of the meso aryl groups and the physico-
chemical properties of these derivatives (see the supporting
information). The Soret-like band maxima of 7a-e are reported in
Table 2 and are compared with the one of 7f bearing six meso
pentaflurophenyl groups.[6a] Peripheral electron-donating groups
produce a red-shift of the absorption maxima. For example,
when the three 5,15,25 meso groups of 7f are replaced by p-
fluorophenyl groups in 7b and by p-tolyl ones in 7a, the Soret
like band is red-shifted by 44 nm and 49 nm respectively. A
higher red-shift is observed for 7e bearing several electron-
donating groups. Even if the bulkiness of the meso-substituents
cannot be excluded from the sources of these shifts, the light
absorption properties of [28]hexaphyrin are also controlled by
their symmetry as illustrated by the different absorption maxima
of the two isomeric compounds 7a and 7d (610 and 602 nm
respectively).
6
3
48
16
16
12
0
0
[a] Oxidation step: a) p-Chloranil (2 equiv.) in CHCl3 at reflux (1 hour). B) p-
Chloranil (3 equiv.) in CHCl3 at reflux (1 hour). c) Air in CHCl3 at reflux (1
hour). [b] Isolated yield. [c] The optimal conditions of entry 4 highlighted in
bold.
The lack of scrambling observed when the optimized
conditions are applied, prompted to introduce bilanes 5 in the
reaction mixture (Scheme 4). Triaryl bilanes (5a-f) were then
prepared using the conditions of Gryko’s group and purified on
silica (see the experimental section).[15] Assuming that during the
first step of the [28]hexaphyrins synthesis, bilanes are formed in
situ by the condensation of two DPM on an aldehyde, we
studied the condensation of bilanes with aldehyde and DPM in a
1/2/1 ratio and using a three times lower DPM concentration of
11.1 mM (Scheme 4). 7c was then produced with a mixture of
different porphyrins and was isolated with an encouraging yield
of 6% starting from the condensation of 3a, 2a and 5a (Scheme
3). The yield of this synthesis is again depending on the nature
4
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10.1002/ejoc.201601342
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COMMUNICATION
Scheme 4. Synthesis of meso-substituted [28]hexaphyrins starting from tetrapyrranes.
Pure pyrrole was freshly purified by passing over a short chromatography
column filled with neutral alumina. All others reagents were purchased
from commercial suppliers and were used without further purifications.
Column chromatographies were performed on GEDURAN silica gel 40 –
63 μm from VWR. Reactions were controlled by thin layer
Table 2. Selected UV-vis maxima of [28]hexaphyrins in dichloromethane
(Numbering scheme of Scheme 3) .
1
chromatography (Merck 60 F254). H-NMR spectra were recorded either
R1
R2
R3
R4
max (nm)
at 500 MHz on a BRUKER Avance DPX-500, at 400 MHz on a BRUKER
Avance DPX-400, at 300 MHz on
a BRUKER Avance DPX-300
7a
C6F5
C6F5
C6F5
pMeC6H4
C6F5
C6F5
pMeC6H4
pFC6H4
p-MeC6H4
pMeC6H4
pMeOC6H4
C6F5
C6F5
C6F5
C6F5
C6F5
pFC6H4
C6F5
pMeC6H4
pFC6H4
C6F5
610
605
605
602
615
561
instrument and at 200 MHz on a BRUKER Avance DPX-200 instrument.
1H NMR Chemical shifts are given in ppm relative to the residual solvent
peaks of CDCl3 (δ = 7.26) or THF-d8 (δ= 1.72 and 3.58 ppm). UV/Vis
spectra were measured with a Shimadzu UV-2401 (PC) instrument or
with a Varian Cary 1E spectrophotometer. HRMS-ESI mass spectra were
recorded on a QStar Elite (Applied Biosystems SCIEX) spectrometer
which is equipped with an ion source at atmospheric pressure (API).
Dipyrromethanes 3a-f[17] and bilanes 5a-b[16, 18] were prepared according
to literature procedures.
7b
7c
7d
7e
C6F5
2,4,6-F3C6H2
C6F5
7f[a]
General procedure for the investigation of the reaction conditions
forming A3B3-[28]hexaphyrins. 5-(Pentafluorophenyl)dipyrromethane
3a (1 equiv.) and p-tolualdehyde 2a (1 equiv.) were dissolved in an
organic solvent (20 mL) before an aqueous solution of HCl (37% 0.1 mL)
in water (5 mL) was added. The reaction mixture was stirred during a
certain time and then extracted with CHCl3 (150 mL). The organic phase
was washed three times with water (100 mL), washed once with a
saturated aqueous solution of NaHCO3 (100 mL), dried on MgSO4 and
filtered before the oxidation step using p-chloranil or air. The resulting
mixture was heated to reflux during 1 hour and then cooled to room
temperature. A 1 mL aliquot of the resulting mixture was then subjected
to a very short chromatography on silica gel using a Pasteur pipette and
CH2Cl2 as solvent. The first eluting fractions containing porphyrin
derivatives together with un-reacted oxidant were removed. The second
eluting blue fraction was entirely collected in a 25 mL volumetric flask
which was completed with CH2Cl2. The UV-visible spectra of these
solutions were recorded and used to determine the corresponding
amount of [28]hexaphyrin 7a in the crude mixture.
[a] From ref [6].
Conclusions
We have described herein a new strategy to produce meso-
substituted [28]hexaphyrin using a mixture of ethanol and water
as a solvent and high concentrations of HCl. The yields are
modest but these syntheses afford a single expanded porphyrin
without any scrambling and which is easily separated from the
other porphyrin products. Starting from bilanes, this new
procedure can afford unprecedented [28]hexaphyrins bearing up
to four different kinds of meso-substituents thereby extending
the variety of these compounds enabling the study of their
physico-chemical properties.
5,15,25-Tris(pentafluorophenyl)-10,20,30-tris(4-
methylphenyl)hexaphyrin[28] 7a:
(pentaflurophenyl)dipyrromethane 3a (0.26 g, 0.83 mmol, 1 equiv.) and
p-tolualdehyde 2a (98 µl, 0.83 mmol, 1 equiv.) in ethanol (20 mL) was
A
solution
of
5-
Experimental Section
5
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10.1002/ejoc.201601342
European Journal of Organic Chemistry
COMMUNICATION
stirred before an aqueous solution of HCl (37% 0.1 mL) in water (5 mL)
was added. The reaction mixture was stirred for 16 hours and then
extracted with CHCl3 (150 mL). The organic phase was washed three
times with water (100 mL), one time with a saturated aqueous solution of
NaHCO3 (100 mL), dried on MgSO4 and filtered before p-chloranil (410
mg, 1.67 mmol, 2 equiv.) was added. The resulting mixture was heated
to reflux during 1 hour, cooled to room temperature and concentrated
under reduced pressure. The residue was purified by chromatography on
silica gel (CH2Cl2) to afford pure 7a a dark blue powder (27 mg, 22 µmol,
10-(pentafluorophenyl)tetrapyrrane 5c: Dipyrromethane 3c (585 mg, 4
mmol) and pentafluorobenzaldehyde 2b (247 µL, 2 mmol) were dissolved
in MeOH (200 mL). Subsequently, a solution of HCl (36%, 10 mL) in
water (200 mL) was added, and the reaction was stirred at room
temperature for 2 hours. The resulting precipitate was filtered, washed
with a mixture of MeOH/water (1:1, 200 mL) and then with water (100
mL). The subsequent chromatography on silica gel (n-hexane/ethyl
acetate/CH2Cl2, 7:1:2) afforded the pure bilane 5c as a mixture of
stereoisomers (380 mg, 0,81 mmol, 40%). 1H-NMR (300 MHz, CDCl3): =
7.80-7.88 (m, 4H, NH), 6.66 (m, 2Hi, H-α), 6.14 (m, 2H, H-β), 5.96 (m, 2H,
1
8%). H-NMR (400 MHz, THF-d8, 25 °C): = 9.22 (brs, NHouter), 8.03 (d,
3J(H, H)= 7.8 Hz, 2H, Ar-H), 7.92 (m, 6H, β-Houter), 7.68 (d, 3J(H, H)= 7.8
H-β), 5.91 (m, 2H, H-β), 5.86 (m, 4H, H-β), 5.73 (s, 1H, Hmeso), 3.91 ppm
3
3
+
Hz, 2H, β-Houter), 7.54 (d, J(H, H)= 7.8 Hz, 2H, Ar-H), 7.49 (d, J(H, H)=
7.7 Hz, 4H, Ar-H), 7.26 (d, 3J(H, H)= 7.9 Hz, 4H, Ar-H), 4.72 (s, 2H,
NHinner), 2.38 (brs, 4H, β-Hinner), 2.58 (s, 3H, CH3), 2.38 ppm (s, 6H, CH3);
UV-VIS (CH2Cl2): λmax (log εmax)= 397 (4.59), 441 (4.47), 610 (5.19), 640
(4.93), 778 (4.16), 869 (3.99), 925 (3.92), 1051 nm (3.83); HRMS-ESI
([M+H]+): 1235.2919; calcd. for C69H38N6F15+: 1235.2913.
(s, 4H, Hmeso); HRMS-ESI ([M+H]+): 471.1603; calcd. for C25H20F5N4
:
471.1603.
10-(4-Methoxyphenyl)-5,15-bis(4-fluorophenyl)tetrapyrrane 5d: 5-(4-
Fluorophenyl)dipyrromethane 3f (480 mg, mmol) and 4-
2
methoxybenzaldehyde 2e (121 µL, 1 mmol) were dissolved in MeOH
(100 mL). Subsequently, a solution of HCl (36%, 5 mL) in water (100 mL)
was added, and the reaction was stirred at room temperature for 2 hours.
5,15,25-Tris(pentafluorophenyl)-10,20,30-tris(4-
fluorophenyl)hexaphyrin[28]
7b:
A
solution
of
5-
The resulting precipitate was filtered, washed with
MeOH/water (1:1, 100 mL) and then with water (100 mL). The
subsequent chromatography on silica gel (n-hexane/ethyl
acetate/CH2Cl2, 7:1:2) afforded the pure bilane 5d as a mixture of
stereoisomers (205 mg, 0.34 mmol, 34%). 1H-NMR (300 MHz, CDCl3): =
7.91 (s, 2H, NH), 7.69 (s, 2H, NH), 7.12-7.05 (m, 6H, Ar-H), 6.97 (m, 4H,
Ar-H), 6.82 (d, 3J(H,H) = 8.64 Hz, 2H, Ar-H), ), 6.69 (m, 2H, H-α), 6.12 (m,
2H, H-β), 5.82 (m, 2H, H-β), 5.69 (m, 4H, H-β), 5.34 (m, 2H, Hmeso), 5.24
(s, 1H, Hmeso), 3.79 ppm (s, 3H, O-CH3); HRMS-ESI ([M+H]+): 599.2618;
calcd. for C38H33N4OF2+: 599.2617.
a mixture of
(pentafluorophenyl)dipyrromethane 3a (0.26 g, 0.83 mmol, 1 equiv.) and
of p-fluorobenzaldehyde 2c (89 µl, 0.83 mmol, 1 equiv.) in ethanol
(20 mL) was stirred before a solution of HCl (37% 0.1 mL) in water
(5 mL) was added. The reaction mixture was stirred for 16 hours and
then extracted with CHCl3 (150 mL). The organic phase was washed
three times with water (100 mL), one time with a saturated aqueous
solution of NaHCO3 (100 mL), dried on MgSO4 and filtered before p-
chloranil (410 mg, 1.67 mmol, 2 equiv.) was added. The resulting mixture
was heated to reflux during 1 hour, cooled to room temperature and
concentrated under reduced pressure. The crude residue was purified by
chromatography on silica gel (CH2Cl2) to afford pure 7b a dark blue
powder (38 mg, 30 µmol, 11%). 1H-NMR (400 MHz, THF-d8, 25 °C): =
8.16 (m, 2H, Ar-H), 7.97 (m, 2H, β-Houter), 7.92 (m, 4H, β-Houter), 7.74 (m,
2H, β-Houter), 7.64 (m, 4H, Ar-H), 7.49 (m, 2H, Ar-H), 7.22 (m, 4H, Ar-H),
4.75 (brs, 1H, NHinner), 4.10 (brs, 1H, NHinner), 2.18 (s, 2H, β-Hinner), 1.93
ppm (s, 2H, β-Hinner); UV-VIS (CH2Cl2), λmax (log εmax)= 398 (4.69), 605
(5.17), 776 (4.16), 864 (4.03), 918 (3.97), 1041 nm (3.81); HRMS-ESI
([M+H]+): 1247.2161; calcd. for C66H29N6F18+: 1247.2161.
10-(4-Fluorophenyl)-5,15-bis(pentafluorophenyl)tetrapyrrane 5e: 5-
(Pentafluorophenyl)dipyrromethane 3a (624 mg,
2 mmol) and 4-
fluorobenzaldehyde 2c (107 µL, 1 mmol) were dissolved in MeOH (100
mL). Subsequently, a solution of HCl (36%, 5 mL) in water (100 mL) was
added, and the reaction was stirred at room temperature for 2 hours. The
resulting precipitate was filtered, washed with a mixture of MeOH/water
(1:1, 100 mL) and then with water (100 mL). The subsequent
chromatography on silica gel (n-hexane/ethyl acetate/CH2Cl2, 7:1:2)
afforded the pure bilane 5e as a mixture of stereoisomers (400 mg, 0.55
mmol, 55%). 1H-NMR (300 MHz, CDCl3): = 8.13 (s, 2H, NH), 7.85 (s, 2H,
NH), 7.10 (m, 2H, Ar-H), 6.98 (m, 2H, Ar-H), 6.72 (m, 2H, H-α), 6.14 (m,
2H, H-β), 5.96 (m, 2H, H-β), 5.88 (m, 2H, H-β), 5.81 (m, 2H, H-β), 5.70
(m, 2H, Hmeso), 5.30 ppm (s, 1H, Hmeso); HRMS-ESI ([M+H]+): 731.1662;
calcd. for C37H22F11N4+: 731.1663.
5,10,15-Tris(pentafluorophenyl)tetrapyrrane
5a:
Pentafluorobenzalldehyde (0.62 mL, 5 mmol) and pyrrole (694 μL,
10 mmol) were dissolved in a mixture of MeOH (200 mL) and water (200
mL). Subsequently, HCl (36%, 4.25 mL) was added and the reaction
mixture was stirred at room temperature for 3 hours. The resulting
precipitate was filtered, washed with a mixture of MeOH/water (1:1,
100 mL) and with water (100 mL). The resulting paste was purified by
chromatography on silica gel (n-hexane/ethyl acetate/CH2Cl2, 7:1:2) to
yield the pure bilane 5a as a mixture of stereoisomers (0.46 g,
0.57 mmol, 34%). 1H-NMR (300 MHz, CDCl3, 25 °C): = 8.10 (s, 2H,
NH), 7.99 (s, 2H, NH), 6.73 (m, 2H, H-α), 6.15 (m, 2H, β-H), 5.99 (m, 2H,
10-(2,4,6-Trifluorophenyl)-5,15-bis(4-fluorophenyl)tetrapyrrane 5f: 5-
(4-Fluorophenyl)dipyrromethane 3f (480 mg,
2 mmol) and 2,4,6-
trifluorobenzaldehyde (160 mg, 1 mmol) were dissolved in MeOH (100
mL). Subsequently, a solution of HCl (36%, 5 mL) in water (100 mL) was
added, and the reaction was stirred at room temperature for 2 hours. The
resulting precipitate was filtered, washed with a mixture of MeOH/water
(1:1, 100 mL) and then with water (100 mL). The subsequent
chromatography on silica gel (n-hexane/ethyl acetate/CH2Cl2, 7:1:2)
afforded the pure bilane 5f as a mixture of stereoisomers (306 mg, 49%).
1H-NMR (300 MHz, CDCl3, 25 °C): = 7.88 (s, 2H, NH), 7.69 (s, 2H, NH),
7.12 (m, 4H, Ar-H), 6.97 (m, 4H, Ar-H), 6.70 (m, 2H, H-α), 6.65 (m, 2H,
Ar-H), 6.14 (m, 2H, β-H), 5.80 (m, 4H, β-H), 5.68 (m, 3H, β-H + Hmeso),
5.34 ppm (s, 2H, Hmeso); HRMS-ESI ([M+H]+): 623.2231; calcd. for
C37H28F5N4O+: 623.2229.
H-β), 5.73-7.99 ppm (m, 7H, H-β/ Hmeso); HRMS-ESI ([M+H]+): 803.1285;
+
calcd. for C37H18F15N4
: 803.1286. These analytical data are in
accordance with literature values.[16, 18]
5,10,15-Tris(p-methylphenyl)tetrapyrrane 5b: p-Tolualdehyde (0.59
mL, 5 mmol) and pyrrole (694 μL, 10 mmol) were dissolved in a mixture
of MeOH (200 mL) and water (200 mL). Subsequently, HCl (36%, 4.25
mL) was added and the reaction mixture was stirred at room temperature
for 3 hours. The resulting precipitate was filtered, washed with a mixture
of MeOH/water (1:1, 100 mL) and with water (100 mL). The resulting
paste was purified by chromatography on silica gel (n-hexane/ethyl
acetate/CH2Cl2, 7:1:2) to yield the pure bilane 5b as a mixture of
stereoisomers (0.55 g, 0.96 mmol, 57%). 1H-NMR (300 MHz, CDCl3) =
7.86 (s, 2H, NH), 7.66 (s, 2H, NH), 7.00-7.1 (m, 12H, Ar-H), 6.66 (m, 2H,
H-α), 6.12 (m, 2H, β-H), 5.86 (m, 2H, β-H), 5.65-5.76 (m, 4H, β-H), 5.32
(m, 2H, Hmeso), 5.21 (m, 1H, Hmeso), 2.33 ppm (s, 9H, CH3); HRMS-ESI
([M+H]+): 575.3168; calcd. for C40H40N4+: 575.3169.
5,10,15,25-Tetrakis(pentafluorophenyl)-20,30-bis(4-
methylphenyl)hexaphyrin[28] 7c:
To
a
solution
of
5-
(pentafluorophenyl)dipyrromethane 3a (87 mg, 0.28 mmol, 1 equiv.),
bilane 5a (225 mg, 0.28 mmol, 1 equiv.) and p-tolualdehyde 2a (66 µl,
0.56 mmol, 2 equiv.) in EtOH (20 mL) was added a solution of HCl (36%
0.1 mL) in water (5 mL). This mixture was stirred at room temperature
during 16 hours before it was extracted with CHCl3 (150 mL). The organic
phase was washed three times with water (100 mL) and one time with a
6
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201601342
European Journal of Organic Chemistry
COMMUNICATION
saturated aqueous solution of NaHCO3 (100 mL). The organic layer was
dried on MgSO4 before p-chloranil (410 mg, 1.67 mmol, 2 equiv.) was
added. The resulting mixture was heated to reflux during 1 hour, cooled
to room temperature and concentrated under reduced pressure. The
reaction mixture was purified by chromatography on silica gel (CH2Cl2) to
afford 7c as a dark blue powder (22 mg, 17 µmol, 6%). 1H-NMR (300
MHz, THF-d8, 25 °C): = 9.41 (brs, 2H, NHouter), 7.82 (d, 3J(H,H)= 4.7 Hz,
1H, β-Houter), 7.78 (d, 3J(H,H)= 4.7 Hz, 2H, β-Houter), 7.70 (m, 4H, β-
Houter), 7.61 (d, 3J(H,H)= 4.6 Hz, 2H, β-Houter), 7.43 (d, 3J(H,H)= 7.8 Hz,
4H, Ar-H), 7.24 (d, 3J(H,H)= 7.8 Hz, 4H, Ar-H), 5.02 (s, 1H, NHinner), 4.74
(s, 1H, NHinner), 2.37 (s, 4H, β-Hinner), 1.28 ppm (s, 6H, CH3); UV-VIS
(CH2Cl2), λmax (log εmax)= 398 (4.78), 421 (4.81), 605 (5.01), 776 (4.18),
882 (4.14), 1082 nm (3.60); HRMS-ESI ([M+H]+): 1311.2277; calcd. for
C68H31N6F20+: 1311.2285.
Hz, 2H, β-Houter), 9.07 (d, 3J(H, H)= 4.7 Hz, 2H, β-Houter), 9.05 (d, 3J(H,
H)= 4.7 Hz, 2H, β-Houter), 8.52 (d, 3J(H, H)= 7.6 Hz, 4H, Ar-H), 8.27 (d,
3J(H, H)= 7.7 Hz, 2H, Ar-H), 7.73 (d, 3J(H, H)= 7.7 Hz, 2H, Ar-H), 7.69 (d,
3J(H, H)= 7.7 Hz, 4H, Ar-H), 2.74 (s, 3H, CH3), 2.70 (s, 6H, CH3), -1.53 (s,
2H, β-Hinner), -1.60 ppm (s, 2H, β-Hinner); UV-VIS (CH2Cl2), λmax (log εmax)=
434 (4.47), 577 (4.94), 734 (3.98), 804 (3.95), 912 (3.70), 1049 nm (3.82).
HRMS-ESI ([M+H]+): 1233.2764; calcd. For C69H36N6F15+: 1233.2756.
Acknowledgements
R. P. gratefully acknowledges the FP7 Future and Emerging
Technologies for Energy Efficiency Programme through the
project PEPDIODE.
5,10,15-Tris(pentafluorophenyl)-20,25,30-tris(4-
methylphenyl)hexaphyrin[28] 7d:
To
a
solution
of
5-(4-
Keywords: Hexaphyrins • Porphyrinoids • Scrambling
methylphenyl)dipyrromethane 3b (66 mg, 0.28 mmol, 1 equiv.), bilane 5a
(225 mg, 0.28 mmol, 1 equiv.) and p-tolualdehyde 2a (66 µL, 0.56 mmol,
2 equiv.) in EtOH (20 mL) was added a solution of HCl (36% 0.1 mL) in
water (5 mL). This mixture was stirred at room temperature during 16
hours before it was extracted with CHCl3 (150 mL). The organic phase
was washed three times with water (100 mL) and one time with a
saturated aqueous solution of NaHCO3 (100 mL). The organic layer was
dried on MgSO4 before p-chloranil (410 mg, 1.67 mmol, 2 equiv.) was
added. The resulting mixture was heated to reflux during 1 hour, cooled
to room temperature and concentrated under reduced pressure. The
crude mixture was purified by chromatography on silica gel (CH2Cl2) to
afford 7d as a dark blue powder (3.5 mg, 2.8 µmol, 1%). 1H-NMR (500
MHz, THF-d8): = 7.76 (d, 3J(H, H)= 4.9 Hz, 2H, β-Houter), 7.68 (m, 4H, β-
Houter), 7.59 (d, J(H, H)= 4.2 Hz, 2H, β-Houter), 7.46 (d, J(H, H)= 7.1 Hz,
2H, Ar-H), 7.43 (d, 3J(H ,H)= 7.9 Hz, 4H, Ar-H), 7.32 (d, 3J(H, H)= 7.2 Hz,
2H, Ar-H), 7.24 (d, 3J(H, H)= 7.1 Hz, 4H, Ar-H), 4.67 (s, 2H, NHinner), 4.08
(s, 1H, NHinner), 3.10 (s, 2H, β-Hinner), 2.90 (s, 2H, β-Hinner), 1.28 ppm (s,
9H, CH3); UV-VIS (CH2Cl2), λmax (rel. intensity)= 392 (0.30), 437 (0.26),
602 (1.00), 772 nm (0.12); HRMS-ESI ([M+H]+): 1235.2913; calcd. For
C69H38N6F15+: 1235.2913.
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10.1021/acs.chemrev.6b00371.
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8278.
[4]
5-(Pentafluorophenyl)-10,30-bis(4-methoxyphenyl)-15,25-bis(4-
fluorophenyl)-30-(2,4,6-trifluorophenyl)hexaphyrin[28] 7e: To
solution of 5-(pentafluorophenyl)dipyrromethane 3a (87 mg, 0.28 mmol, 1
equiv.), bilane 5f (174 mg, 0.28 mmol, equiv.) and p-
a
1
methoxybenzaldehyde 2e (68 µL, 0.56 mmol, 2 equiv.) in EtOH (20 mL)
was added a solution of HCl (36% 0.1 mL) in water (5 mL). This mixture
was stirred at room temperature during 16 hours before it was extracted
with CHCl3 (150 mL). The organic phase was washed three times with
water (100 mL) and one time with a saturated aqueous solution of
NaHCO3 (100 mL). The organic layer was dried on MgSO4 before p-
chloranil (410 mg, 1.67 mmol, 2 equiv.) was added. The resulting mixture
was heated to reflux during 1 hour, cooled to room temperature and
concentrated under reduced pressure. The reaction mixture was purified
by chromatography on silica gel (CH2Cl2) to afford 7e as a dark blue
powder (3.2 mg, 2.8 µmol, 1%). 1H-NMR (400 MHz, THF-d8): = 7.69 (m,
[5]
a) T. K. Ahn, J. H. Kwon, D. Y. Kim, D. W. Cho, D. H. Jeong, S. K. Kim,
M. Suzuki, S. Shimizu, A. Osuka, D. Kim, J. Am. Chem. Soc. 2005, 127,
12856-12861; b) M.-C. Yoon, S. Cho, M. Suzuki, A. Osuka, D. Kim, J.
Am. Chem. Soc. 2009, 131, 7360-7367; c) Z. S. Yoon, J. H. Kwon, M.-
C. Yoon, M. K. Koh, S. B. Noh, J. L. Sessler, J. T. Lee, D. Seidel, A.
Aguilar, S. Shimizu, M. Suzuki, A. Osuka, D. Kim, J. Am. Chem. Soc.
2006, 128, 14128-14134.
3
2H, Ar-H), 7.61 (m, 4H, 2H, β-H, Ar-H), 7.47 (m, 4H, β-H), 7.36 (d, J(H,
[6]
[7]
M. G. P. M. S. Neves, R. M. Martins, A. C. Tomé, A. J. D. Silvestre, A.
M. S. Silva, V. Félix, M. G. B. Drew, J. A. S. Cavaleiro, Chem. Commun.
1999, 385-386.
H)= 8.3 Hz, 4H, Ar-H), 7.22 (m, 2H, Ar-H), 7.12 (m, 4H, Ar-H), 6.92 (d,
3J(H, H)= 8.4 Hz, 4H, Ar-H), 5.10 (brs, 1H, NHinner), 4.80 (brs, 1H,
NHinner), 3.77 (s, 6 H, OCH3), 2.90 (s, 2H, β-Hinner), 2.86 ppm (s, 2H, β-H
inner); UV-VIS (CH2Cl2), λmax (rel. intensity)= 402 (0.587), 428 (0.55), 615
(1.00), 778 nm (0.18); HRMS-ESI ([M+H]+): 1163.3123; calcd. for
C68H41N6F10O2+: 1163.3126.
a) J. Y. Shin, H. Furuta, K. Yoza, S. Igarashi, A. Osuka, J. Am. Chem.
Soc. 2001, 123, 7190-7191; b) A. Krivokapic, A. R. Cowley, H. L.
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Shin, H. Furuta, R. Ismael, A. Osuka, Angew. Chem. 2003, 115, 82-86;
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Lemmetyinen, H. Imahori, Chem. Asian J. 2008, 3, 2065-2074.
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Taniguchi, S. Shimizu, M. Suzuki, J.-Y. Shin, H. Furuta, A. Osuka,
5,15,25-Tris(pentafluorophenyl)-10,20,30-tris(4-
methylphenyl)hexaphyrin[26] 8a : MnO2 (1 mg, 12 µmol, 1 equiv.) was
added to a solution of hexaphyrin[28] 7a (15 mg, 12 µmol, 1 equiv.) in
CH2Cl2 (20 mL). The progress of the reaction was monitored using UV-
VIS absorption spectroscopy. After 90 minutes, the reaction mixture was
purified by chromatography on silica gel (CH2Cl2) to afford the pure
[8]
1
[26]hexaphyrin 8a (15 mg, 12 µmol, 100%). H-NMR (400 MHz, THF-d8,
25 °C): = 9.43 (d, 3J(H, H)= 4.7 Hz, 2H, β-Houter), 9.21 (d, 3J(H, H)= 4.8
7
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201601342
European Journal of Organic Chemistry
COMMUNICATION
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A. Osuka, Angew. Chem. 2008, 120, 9807-9811; Angew. Chem. Int. Ed.
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8
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10.1002/ejoc.201601342
European Journal of Organic Chemistry
COMMUNICATION
Entry for the Table of Contents (Please choose one layout)
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Author(s), Corresponding Author(s)*
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Title
((Insert TOC Graphic here: max.
width: 5.5 cm; max. height: 5.0 cm;
NOTE: the final letter height should
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Expanded Porphyrinoids
Rémi Plamont, Teodor Silviu Balaban,
Gabriel Canard*
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Straightforward Syntheses that Avoid
Scrambling of meso-Substituted
[28]Hexaphyrins
[28]Hexaphyrins bearing up to four different kinds of meso-substituents were
prepared using a synthesis in a water-ethanol mixture that avoids scrambling.
*one or two words that highlight the emphasis of the paper or the field of the study
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