Triarylcorroles by oxidative coupling of triaryltetrapyrranes

Article abstract of DOI:10.1055/s-2001-11409

A general two-step, one-pot synthesis of meso-triphenylcorrole from 5-phenyldipyrrane is presented. A number of p-phenyl-substituted 5-phenyldipyrranes were condensed with substituted benzaldehydes under acid catalyzed conditions to produce a mixture high

Full text of DOI:10.1055/s-2001-11409

4
42
LETTER
Triarylcorroles by Oxidative Coupling of Triaryltetrapyrranes
Raymond P. Briñas, Christian Brückner*
Department of Chemistry, University of Connecticut, Storrs, CT 06269, USA
Fax +1 (860) 486-2981; E-mail: bruckner@nucleus.chem.uconn.edu
Received 20 December 2000
Abstract: A general two-step, one-pot synthesis of meso-triphenyl-
corrole from 5-phenyldipyrrane is presented. A number of p-phe-
nyl-substituted 5-phenyldipyrranes were condensed with
substituted benzaldehydes under acid catalyzed conditions to pro-
duce a mixture highly enriched in the corresponding tetrapyrranes.
The crude mixtures were oxidized with DDQ or chloranil to pro-
duce the corresponding meso-triarylcorroles in good to excellent
yield. The method is applicable to the synthesis of meso-triarylcor-
Figure
roles containing two differently substituted phenyl groups in the
5
-,15- and 10-positions, respectively.
Key words: corrole synthesis, tetrapyrrane, oxidative coupling,
2+2” condensation
meso-triphenylcorrole did not become known until 1999,
“
although synthetic corroles have also had a long histo-
2,6-9
ry.
Iron complexes of meso-tri(pentafluorophenyl)cor-
role have been pioneered by Gross as catalysts for
epoxidation, hydroxylation and cyclopropanation reac-
Corroles, the parent compound of the hydrocorrole (cor-
rin) macrocycle found in coenzyme B , are tetrapyrrolic
10
1
2
tions. His group also described chiral N-substituted cor-
fully conjugated macrocycles containing three methine
11
roles. However, the convenient and simple one-step
1
bridges and one direct pyrrole-pyrrole linkage. Thus,
syntheses described by Gross and Goldberg for meso-
tri(pentafluorophenyl)corrole are not general since they
their macrocycle skeleton is contracted by one carbon
atom as compared to that of porphyrins. This difference
results inter alia in altered metal coordination properties
of the smaller trianionic tetradentate corrole ligand when
compared to those of the tetradentate dianionic porphyrin
are restricted to the use of highly reactive pentafluoro-
7,12
benzaldehyde as reactant.
The parent unsubstituted
meso-triphenylcorrole was isolated in (unoptimized) 6%
yield as one of several macrocyclic products from a mod-
2
ligand. Corroles are particularly able to stabilize high
8
ified Rothemund reaction. Clearly, this method is limited
3
,4
metal oxidation states.
with respect to the amounts of corrole accessible.
One of the most studied porphyrins is meso-tetraphe-
The aforementioned syntheses of triarylcorrole hint at the
mechanism operating in its formation. Particularly,
Gross’s and Goldberg’s paper, describing linear oligo-
nylporphyrin (TPP) for which optimized syntheses have
5
been available for some time. Surprisingly, the analogous
Scheme Reagents and conditions: (a)17 TFA, 25 °C (b) solvent (see Table), 1 equiv TFA; no isolation of 4a-e (c) neutralization with Et N; 5
3
equiv oxidant (see Table) in toluene, 12 h, 25 °C; chromatography CH Cl :pet ether 1:1.
2
2
Synlett 2001, No. 3, 442–444 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Triarylcorroles by Oxidative Coupling of Triaryltetrapyrranes
443
Table Triarylcorrole derivatives 5a-e produced as shown in the Scheme
a
b
c
d
13
CH CN, 1 equiv TFA, 25 °C (ref. 23) oxidant DDQ oxidant chloranil 5a-e were characterised by C NMR, UV-VIS and MS;
3
e
f
analytical purity of 5a was proven by elemental analysis in DMSO-d additional signal at -2.7 (br s, 3H) CH Cl distilled over
CaH ; 1 equiv TFA, 0 °C (ref. 23) 9 mmol scale, yield of 1.9g 2a.
6
2
2
g
2
pyrrolic pigments isolated as side products of their corrole excess dipyrranes were oxidized to form the basic and po-
1
2
synthesis, indicated to us that it was likely that a tetra- lar meso-aryldipyrrins, visible as bright yellow spot on
1
3
pyrrane was formed as a primary condensation product TLC plates developed with polar solvents, and do not in-
22
and that, upon oxidation, the pyrrole-pyrrole linkage was terfere with the isolation of the corroles. The table pro-
established. The macrocycle subsequently formed oxidiz- vides detailed information about the reactions.
es to the final corrole oxidation state. Similar oxidatively
The above described syntheses of corroles have the ad-
induced formations of direct pyrrole-pyrrole linkages are
vantage that the isolation of the intermediate triaryltet-
known reactions in pyrrole and pyrrolic macrocycle
chemistry, including the formation of heterocorroles.1
Some ß-alkylcorrole syntheses also rely on the formation
of the pyrrole-pyrrole linkage as the penultimate step (be-
fore oxidation), although their mechanisms are di-
19
rapyrranes, while possible, is not required. In fact,
4,15
isolation of the triaryltetrapyrranes and subsequent oxid-
ation lowered the overall yield as the chromatographic
isolation of the tetrapyrranes is difficult and the products
obtained are only moderately stable. Secondly, the condi-
tions for preparing the tetrapyrranes 4 were selected by
2
,6,16
verse.
Hence, the task became the directed synthesis of 5,10,15- Lindsey to be sufficiently mild to prevent acid-catalyzed
23
triphenyltetrapyrrane and its oxidative ring closure. The scrambling of the aryl groups. This presented us with the
chemistry of 5-phenyldipyrranes, 5,10-diphenyltripyr- option of choosing a substituted benzaldehyde with sub-
ranes and their higher homologues has seen rapid devel- stituents differing from those of the 5-aryldipyrro-
1
7,18
opment in past years.
One- and multi-step syntheses of methane. The resulting tetrapyrrane and the derived
5
,10,15-triaryltetrapyrranes were recently described by triarylcorrole (5d-e) contain, regiospecifically, two differ-
1
8
18,19
Lindsey and co-workers, Lee and co-workers
and ently substituted phenyl groups. Our synthesis parallels
2
0
Liebeskind and Nickel, respectively. We opted for an al- the strengths of 2+2 syntheses of TPP. Recent work by
ternative two-step one-pot route towards the required tet- Lee and co-workers describing the oxidative ring closure
rapyrranes, illustrated in the Scheme. Pyrrole (1) and of tetrapyrranes and oxidative fusion of tri- with dipyr-
benzaldehydes 2a-c were reacted in known fashion to pro- ranes to form corroles and expanded corroles corroborates
duce 5-aryldipyrranes 3a-3c. They were condensed with our conclusions with complementary findings. However,
benzaldehydes 2a-c under mild acid catalysis (molar ratio their method is not applicable to the synthesis of triaryl-
of 2:3 1:6). Upon the disappearance of benzaldehyde, as corroles containing regiospecifically two types of phenyl
monitored by TLC, the crude reaction mixture containing substituents in the 5-, 15-, and 10-positions, respective-
1
6
1
9
the tetrapyrranes 4a-c was treated with a 5-fold molar ex- ly. After the submission of our manuscript, a paper by
cess (based on the amount of benzaldehyde used) of DDQ Gryko describing the synthesis of A B-corroles using a
2
2
1
or chloranil. Flash column chromatography, followed by number of (sterically encumbered) 2,6- and 2,4,6-phenyl-
recrystallization, was used to isolate and purify the dark substituted phenyldipyrromethanes and benzaldehydes
green non-polar corroles 5a-c in moderate to high yields. was published.24 While the exclusive use of benzalde-
Importantly, only traces of other pyrrolic macrocycles and hydes with electron-withdrawing substituents, the dipyr-
no TPP could be detected in these corrole syntheses. The rane:benzaldehyde ratio, the details of the procedure and
Synlett 2001, No. 3, 442–444 ISSN 0936-5214 © Thieme Stuttgart · New York

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R. P. Briñas, C. Brückner
LETTER
the resulting products differ from those described here,
Gryko’s paper further highlights the synthetic utility of
the triarylcorrole synthesis by oxidative coupling of tet-
rapyrranes.
(9) Paolesse, R.; Licoccia, S.; Bandoli, G.; Dolmella, A.; Boschi,
T. Inorg. Chem. 1994, 33, 1171-1176.
10) Gross, Z.; Simkhovich, L.; Galili, N. Chem. Commun. 1999,
(
(
(
599-600.
11) Gross, Z.; Galili, N. Angew. Chem., Int. Ed. 1999, 38, 2366-
2369.
12) Gross, Z.; Galili, N.; Simkhovich, L.; Saltsman, I.;
Botoshansky, M.; Bläser, D.; Boese, R.; Goldberg, I. Org.
Lett. 1999, 1, 599-602.
13) The naming of tetrapyrranes follows suggestions of H. Falk
In The Chemistry of Oligopyrroles and Bile Pigments,
Springer: Wien, 1989, and is preferred over the more common
but misleading names tetrapyrromethane or bilane.
14) (a) Sessler, J. L.; Seidel, D.; Lynch, V. J. Am. Chem. Soc.
In summary, we present herein a general method for the
synthesis of triarylcorroles, and a method of making tri-
arylcorroles containing regiospecifically two types of aryl
substituents. We present further evidence for the stepwise
mechanism of the corrole formation in Rothemund-type
(
8
condensations.
(
Acknowledgement
1999, 121, 11257-11258. (b) Narayanan, S. J.; Sridevi, B.;
Chandrashekar, T. K.; Englich, U.; Ruhland-Senge, K. Org.
Lett. 1999, 1, 587-590.
15) Cho, W.-S.; Lee, C.-H. Tetrahedron Lett. 2000, 41, 697-701.
16) Licoccia, S.; Di Vona, M. L.; Paolesse, R. J. Org. Chem. 1998,
This work was supported by a grant from the University of Connec-
ticut Research Foundation. We thank Professor Chan-Hee Lee,
Kangwon National University, South Korea, for providing us with
a pre-print of his article (reference 19).
(
(
63, 3190-3195.
(
17) (a) Lee, C.-H.; Lindsey, J. S. Tetrahedron 1994, 50, 11427-
11440. (b) Brückner, C.; Sternberg, E. D.; Boyle, R. W.;
Dolphin, D. Chem. Commun. 1997, 1689-1690. (c) Brückner,
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J.-W.; Lee, C.-H. Tetrahedron Lett. 2000, 41, 4609-4613.
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Article Identifier:
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Synlett 2001, No. 3, 442–444 ISSN 0936-5214 © Thieme Stuttgart · New York