Synthesis of thefirst superstructured chiral corrole

Article abstract of DOI:10.1039/b200188h

The synthesis of the first chiral superstructured corrole has been achieved by reacting an original bis(diaminophenyl)-corrole with two chiral binaphthyl bis(acid chloride) handles.

Full text of DOI:10.1039/b200188h

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Synthesis of the first superstructured chiral corrole
Bruno Andrioletti* and Eric Rose
Laboratoire de Synthèse Organique et Organométallique UMR 7611,
Université Pierre et Marie Curie, Tour 44, couloir 44-45, 1er étage, case 181, 4, Place Jussieu,
75252 Paris cedex 05, France. E-mail: andriole@ccr.jussieu.fr, rose@ccr.jussieu.fr;
Fax: 33(0)1 4427 5504; Tel: 33(0)1 4427 3444
1
Received (in Cambridge, UK) 8th January 2002, Accepted 5th February 2002
First published as an Advance Article on the web 14th February 2002
The synthesis of the first chiral superstructured corrole has
been achieved by reacting an original bis(diaminophenyl)-
corrole with two chiral binaphthyl bis(acid chloride)
handles.
Introduction
During the last few decades, the chemistry of porphyrins has
received considerable attention, and as a result, tremendous
strides have been made in the development of new synthetic
methods to prepare these materials. Undoubtedly, these
Fig. 1 5,10,15-Tris(2,6-dinitro-4-tert-butylphenyl)corrole 1.
ongoing efforts can be attributed to the remarkable properties
of the porphyrin core that allow its use in areas as disparate as
catalysis, biomimetic modelling, medicinal chemistry and
materials.1 Perhaps due to their relatively facile synthesis,
porphyrins (and porphyrinogens) have long remained the
only tetrapyrrolic macrocycle widely studied. However, more
recently, a number of different groups have dedicated their
efforts towards the preparation of “contracted” or “expanded”
porphyrins, their goal being to investigate and compare the
properties of these materials with the parent porphyrin.2
Amongst these systems, it could be argued that corrole has
received most attention.
For many years, the investigation of the interesting features
of the corrole core was hampered by the limited synthetic avail-
ability of this macrocycle. This situation changed in 1999 when
a number of groups independently reported the improved syn-
theses of triarylcorroles. In particular, Gross et al. first reported
an 11% yield, solvent-free synthesis of tris(pentafluorophenyl)-
corrole by mixing the highly reactive pentafluorobenzaldehyde
and pyrrole.3 In parallel, Paolesse et al. described the synthesis
of the regular triphenylcorrole in an unoptimized 6% yield
using a modified Rothemund synthesis.4,5
expected corrole. The solvent free approach3 appeared not to
be successful either, even in the presence of a catalyst. Con-
sequently, we prepared the new 5-(2,6-dinitro-4-tert-butyl-
phenyl)dipyrromethane 3 in 70% yield after chromatographic
purification, according to usual procedures.11 Unfortunately,
despite many changes in the reaction conditions, condensation
of 2 with 3 did not afford the expected corrole 1.
In order to test the influence of the nature of the aldehyde, we
decided to react 3 with pentafluorobenzaldehyde. We chose
pentafluorobenzaldehyde because firstly we needed a reactive,
electron poor aldehyde and secondly, we wished to prepare
A2B-corroles that have suitable topography for the prepar-
ation of C2-symmetrically elaborated systems. Condensation
of pentafluorobenzaldehyde with 3 in the presence of BF3ؒOEt2
followed by in situ oxidative coupling with 2,3-dichloro-4,5-
dicyanobenzoquinone (DDQ) afforded the expected bis(dinitro-
phenyl)corrole 4 in an unexpected 24% yield without any trace
of porphyrin (Scheme 1).†
Thus, the reduced reactivity of 2 with respect to pentafluoro-
benzaldehyde along with an increased steric hindrance explains
the unsuccessful preparation of 1.8
Other corrole syntheses involving stepwise reactions have
also been proposed. Of these, some require the preparation of
di- or tripyrromethanes. The latter precursors can afford the
expected corroles upon final oxidative cyclization in reasonable
yields. However, certain drawbacks inherent to the use of large
excesses of dipyrromethanes, or limitations concerning the
nature of the aldehyde narrow the convenience of the method.6–9
In particular, to the best of our knowledge, there are no reports
concerning the use of sterically crowded 2,6-dinitrobenz-
aldehydes as corrole precursors. Here, we wish to report the
synthesis of a new tetranitrocorrole in addition to the con-
densation of chiral handles with the corresponding reduced
tetraaminocorrole.
Results and discussion
For many years our group has considered that corrole
chemistry is an essential complement to porphyrin chemistry.
A number of years ago, we unexpectedly isolated the tris(2,6-
dinitro-4-tert-butylphenyl)corrole 1 as a minor by-product
in a classical porphyrin synthesis (Fig. 1).10 We have recently
re-investigated its synthesis.
A modified Rothemund synthesis4 involving 2,6-dinitro-4-
tert-butylbenzaldehyde10 2 and pyrrole did not afford the
Scheme 1 Reagents: i, excess pyrrole, BF3ؒOEt2; ii, 0.5 eq. C6F5CHO,
BF3ؒOEt2, NH4Cl, propiononitrile.
DOI: 10.1039/b200188h
J. Chem. Soc., Perkin Trans. 1, 2002, 715–716
This journal is © The Royal Society of Chemistry 2002
715

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Corrole 4 was further reduced to the corresponding tetra-
aminocorrole 5 using SnCl2ؒ2H2O in acidic medium in 80%
yield. We then decided to use 5 as a precursor to prepare new
binaphthyl-strapped chiral corroles. In our previous investi-
gations we have shown that porphyrinoid systems can be
remarkably efficient for the epoxidation of non-activated
terminal olefins12 and we therefore decided to investigate the
activity of these corrole systems in similar reactions. Previously,
we described the preparation of binaphthyl-strapped por-
phyrins12 by condensing the binaphthyl bis(acid chloride) 6a13
and the α2β2 atropisomer of tetrakis(2-aminophenyl)por-
phyrin.14 Unfortunately, a CPK model revealed that the latter
strap is too short for the optimized synthesis of a binaphthyl-
corrole. Thus, we developed a preparation of a new “homo-
logated” binaphthyl bis(acid chloride) 6b the synthesis of which
will not be described in this communication.
phenyl)corroles 4 and 5, are now possible starting from 2,6-
dinitro-4-tert-butylbenzaldehyde. Trapping the amino functions
by a binaphthyl bis(acid chloride) led to the unique superstruc-
tured chiral corrole. The structural similarity of compound 7 to
a gyroscope has led us to describe this material as Љgyroscope-
corroleЉ. This represents the first report of a double-faced
protected chiral corrole. Further studies concerning the cat-
alytic properties of this material, e.g. asymmetric epoxidation
and hydroxylation, are currently under investigation in our
laboratory.
Notes and references
† Typical experimental procedure: A 100 cm3 round bottom flask
was charged with 5-(2,6-dinitrophenyl-4-tert-butyl)dipyrromethane
(500 mg, 1.36 mmol) and 10 cm3 of reagent grade propiononitrile.
The resulting brown solution was then degassed with N2 for 15 min
before pentafluorobenzaldehyde (133 mg, 0.68 mmol) and NH4Cl
(727 mg, 13.6 mmol) were added. Finally, BF3ؒEt2O (16 mm3,
0.13 mmol) was added with a syringe and the reaction was allowed
to proceed at room temperature for 90 min. After the reaction
was complete, DDQ (1.36 mmol, 309 mg) was added and the reac-
tion mixture allowed to stir for another 15 min. The crude reaction
mixture was then poured onto a pad of 60 µm silica gel and eluted
with CH2Cl2 and CH2Cl2–MeOH 98:2 until no green solution was
eluted. The corrole containing solutions were then collected together,
evaporated to dryness and purified by chromatography on a basic
alumina column with CH2Cl2–petroleum ether 1 : 1 as eluent. Analytic-
ally pure compound (150 mg, 24%) was obtained from crystalliz-
ation (CH2Cl2–petroleum ether). 1H NMR δH (200 MHz, CDCl3)
1.63 (s, 18H, tBu), 8.40–8.43 (s ϩ broad m, 8H, Haro ϩ Hβpyr), 8.58
(d, 2H, J 4.4, Hβpyr), 8.94 (d, 2H, J 4.0, Hβpyr); HRMS (Maldi-Tof )
[Found: (M ϩ H)ϩ, 909.1984. C45H33F5N8O8 ϩ Hϩ requires M,
909.2420].
High dilution condensation of two equivalents of 6b with
5 afforded the first example of chiral strapped corrole 7 in
25% yield (Scheme 2).‡
‡ Selected data for 7: 1H NMR δH (500 MHz, CDCl3) 8.90 (d, 2H, J 4.5,
H
βpyr), 8.79 (d, 2H, J 4.5, Hβpyr), 8.57 (broad s, 4H, Hmeso-aryl), 8.43 (d, 2H,
J 4.4, Hβpyr), 8.30 (d, 2H, J 4.5, Hβpyr), 7.96 (d, J 7.8, 2H), 7.84 (broad t,
2H), 7.63 (s, 2H), 7.57 (d, J 8.3, 2H), 7.38, (s, 2H), 7.15 (t, J 7.8, 2H),
7.08 (t, J 8.0, 2H), 6.82 (t, J 7.8, 2H), 6.61 (s, 2H), 6.39 (s, 2H), 6.07
(d, J 8.7, 2H), 5.72 (d, J 8.4, 2H), 3.36 (m, CH2, 8H), 2.28 (s, 6H,
OMe), 1.61 (s, 9H, tBu), 1.53 (s, 9H, tBu), Ϫ0.83 (s, 6H, OMe); m/z
(Maldi-Tof ): 1576.87 (M)ϩ. UV-Vis absorptions. λmax (CH2Cl2)/nm 411,
563, and 598.
1 For a complete overview, see for instance, The Porphyrin Handbook,
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New York, 2000 .
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Scheme
2
Reagents and conditions: high dilution, THF, N,N-
diethylaniline.
Conclusions
In conclusion, we have shown that the preparation of highly
functionalized corroles, namely bis(dinitro-) and bis(diamino-
716
J. Chem. Soc., Perkin Trans. 1, 2002, 715–716