A new synthesis of [2,3]naphthoporphyrins

Article abstract of DOI:10.1039/b002213f

A new synthesis of [2,3]naphthoporphyrins using 4,9-ethano-2H- benz[f]isoindole as a synthon of 2H-benz[f]isoindole is described; soluble precursors of [2,3]naphthoporphyrins are converted into insoluble [2,3]naphthoporphyrins by simply heating at 290 °C.

Full text of DOI:10.1039/b002213f

A new synthesis of [2,3]naphthoporphyrins
Satoshi Ito,a Naoyuki Ochi,a Hidemitsu Uno,b Takashi Murashimaa and Noboru Ono*a
a Department of Chemistry, Faculty of Science, Ehime University, Matsuyama 790-8577, Japan.
E-mail: ononbr@dpc.ehime-u.ac.jp
b Advanced Instrumentation Center for Chemical Analysis, Ehime University, Matsuyama 790-8577, Japan
Received (in Cambridge, UK) 20th March 2000, Accepted 14th April 2000
A
new synthesis of [2,3]naphthoporphyrins using
glycol at 165 °C gave 4,9-dihydro-4,9-ethano-2H-benz[f]-
isoindole 6 in 83% yield.
4,9-ethano-2H-benz[f]isoindole as a synthon of 2H-benz[f]-
isoindole is described; soluble precursors of [2,3]naph-
thoporphyrins are converted into insoluble [2,3]naphthopor-
phyrins by simply heating at 290 °C.
Porphyrin 7a was prepared from pyrrole 5 by reduction with
LiAlH4 at 0 °C followed by subsequent tetramerization and
oxidation. Various metals can be introduced into 7a by the usual
method using metal acetates. Porphyrins 7a,b were purified by
column chromatography (alumina, CHCl3) followed by wash-
ing the resulting powder with MeOH–H2O (ca. 1+1). Porphyr-
ins 7a,b were converted into pure tetranaphtho[2,3-b;2A,3A-g;
2B,3B-l;2BA,3BA-q]porphyrins 8a,b in 100% yield by heating at
290 °C under vacuum (10 mm Hg) for 10 min. Thus, porphyrins
7a,b can be regarded as soluble equivalents of the correspond-
ing tetra[2,3]naphthoporphyrins 8a,b. The reaction of 6 with
benzaldehydes in the presence of BF3·OEt2 followed by
oxidation and metallation gave meso-tetraarylated porphyrin
zinc complexes 9a,b. They were also converted into the
Highly conjugated porphyrins have attracted attention as
conducting materials, near-IR dyes, nonlinear optical materi-
als,1 or photosensitizers for photodynamic therapy (PDT) of
cancer tissues on in vivo studies.2 We and Lash et al. have
reported syntheses of various highly conjugated porphyrins
using pyrroles fused with polycyclic aromatic rings.3 The
requisite pyrroles are prepared by the reaction of polycyclic
aromatic nitro compounds with ethyl isocyanoacetate. How-
ever, this method has a severe limitation. The reaction of
nitrobenzene and nitronaphthalene with ethyl isocyanoacetate
does not give the desired isoindole4 and benz[f]isoindole.5 In
general, such isoindole derivatives are very difficult to prepare
owing to their instability. In addition, highly conjugated
porphyrins and their metal complexes are very difficult to
purify, since they are insoluble in most organic solvents.6 We
have reported a simple solution of these problems using
4,7-dihydro-4,7-ethano-2H-isoindole as a synthon of isoindole
for benzoporphyrin synthesis.7,8 Thus, heating porphyrins fused
with bicyclo[2.2.2]octadiene rings at 200–230 °C results in
clean formation of benzoporphyrins via retro Diels–Alder
reaction; the products are pure and do not require further
purification. Here, we report a new synthesis of [2,3]naph-
thoporphyrins using a similar strategy, in which 4,9-ethano-2H-
benz[f]isoindole is used as a synthon of 2H-benz[f]isoindole.
The synthesis of 4,9-dihydro-4,9-ethano-2H-benz[f]isoin-
dole 6 is summarized in Scheme 1.† 1,4-Dihydro-1,4-ethano-
naphthalene 1 was converted into sulfide 2 by reaction with
PhSCl. Oxidation of 2 with m-CPBA followed by treatment
with DBU gave a,b-unsaturated sulfone 4. The pyrrole 5 was
prepared in good yield by treatment of 4 with ethyl iso-
cyanoacetate in the presence of 2.0 equivalents of ButOK.9 De-
ethoxycarbonylation upon heating 5 with KOH in ethylene
corresponding
meso-tetraarylnaphtho[2,3-b;2A,3A-g;2B,3B-l;
2BA,3BA-q]porphyrin zinc complexes 10a,b in 100% yield by
heating at 290 °C in vacuo for 10 min (Scheme 2).
Mono[2,3-b]naphthoporphyrin 13 was also prepared in 100%
yield by heating porphyrin 12 at 290 °C (Scheme 3).† Porphyrin
12 was prepared by the well established 3 + 1 approach
consisting of the reaction of tripyrrane 11 with 3,4-di-
ethylpyrrole-2,5-dicarbaldehyde followed by oxidation.10 The
requisite 11 was prepared by the reaction of 6 with 2.0
equivalents of tert-butyl 5-acetoxymethyl-4-butyl-3-methyl-
1H-pyrrole-2-carboxylate in PriOH–AcOH.
Scheme 2 Reagents and conditions: i, LiAlH4, THF, 0 °C, 1 h; ii, p-TsOH,
CHCl3, room temp., 15 h; iii, p-chloranil, room temp., 24 h, 20% (three
steps from 5); iv, Zn(OAc), CHCl3–MeOH (9+1), room temp., 30 min, 95%;
v, ArCHO, BF3·OEt2, CHCl3, room temp., 4 h; vi, p-chloranil, room temp.,
4 h; vii, Zn(OAc)2, CHCl3–MeOH (9+1), room temp., 30 min (9a = 39%;
9b = 16%, for three steps from 6); viii, 290 °C, 10 min, 100%.
Scheme 1 Reagents and conditions: i, PhSCl, CH2Cl2, 278 °C, 1 h, 99%;
ii, m-CPBA, CHCl3, room temp., 2 h, 99%; iii, DBU, THF, 0 °C, 30 min,
99%; iv, ethyl isocyanoacetate, ButOK, THF, 0 °C, 3 h, 91%; v, KOH,
HO(CH2)2OH, 165 °C, 1.5 h, 83%.
DOI: 10.1039/b002213f
Chem. Commun., 2000, 893–894
This journal is © The Royal Society of Chemistry 2000
893

The work was partly supported by Grants-in Aid for
Scientific Research from the Ministry of Education, Science,
Sports and Culture of Japan. We are also grateful to Dr Y.
Takahashi (JEOL) for recording the FAB mass spectra of
porphyrins (8a and 10a).
Notes and references
† New compounds gave satisfactory elementary analyses. Selected data: for
1
5: white plates, mp 144–145 °C, H NMR (CDCl3, J/Hz) d 1.39 (3H, t, J
7.08), 1.58–1.80 (4H, m), 4.28 (1H, m), 4.33 (2H, q, J 7.33, 14.16), 4.79
(1H, m), 6.66 (1H, d, J 2.44), 7.04–7.13 (2H, m), 7.16–7.32 (2H, m), 8.41
(1H, br s); m/z 267 (M+, 9), 239 (95), 193 (100). For 6: white needles, mp
182–183 °C, 1H NMR (CDCl3) d 1.65–1.83 (4H, m), 4.26 (2H, m), 6.53
(2H, d, J 2.44), 7.03–7.07 (2H, m), 7.18–7.22 (2H, m), 7.53 (1H, br s); m/z
(EI) 195 (M+, 14), 167 (100). For 7a (a mixture of four isomers): 1H NMR
(CDCl3) d 24.66 (2H, br s), 2.15–2.52 (16H, m), 6.18 (8H, m), 7.25 (8H,
m), 7.80 (8H, m), 10.52 (4H, m); m/z (FAB) 823 (M+ + 1). Calc. for
C
60H46N4·0.5H2O: C, 86.61; H, 5.69; N, 6.73. Found: C, 86.49; H, 5.71; N,
Scheme 3 Reagents and conditions: i, AcOH–PriOH (1+1), reflux, 17 h; ii,
3,4-diethylpyrrole-2,5-carbaldehyde, TFA, room temp., 2 h; iii, Et3N, DDQ,
CHCl3, room temp., 1 h, 18% for three steps; iv, 290 °C, 100%.
6.53%. For 8a: m/z (FAB) not assigned. Calc. for C52H30N4·H2O: C, 85.69;
H, 4.43; N, 7.69. Found: C, 85.92; H, 4.31; N, 7.62%. For 9a (a mixture of
four isomers): 1H NMR (CDCl3) d 1.0–2.2 (16H, m), 3.77 (8H, m), 6.9–7.2
(16H, m), 7.9–8.6 (20H, m); m/z (FAB) 1189 (M+). Calc. for
C84H60N4·3.5H2O: C, 80.47; H, 5.39; N, 4.47. Found: C, 80.44; H, 5.35; N,
4.21%. For 10a: 1H NMR (CDCl3) d 7.48 (8H, m), 7.67 (8H, s), 7.69 (8H,
m), 7.98 (8H, m), 8.11 (4H, m), 8.39 (8H, m); m/z (FAB) 1076 (M+). Calc.
for C76H44N4·2.5H2O: C, 81.24; H, 4.40; N, 4.99. Found: C, 81.53; H, 4.58;
N, 4.84%. For 12: 1H NMR (CDCl3) d 23.95 (2H, br s), 1.15 (6H, t, J 7.33),
1.81 (4H, m), 1.92 (6H, t, J 7.33), 2.21 (2H, m), 2.28–2.39 (4H, m), 2.31
(2H, m), 3.63 (6H, s), 4.09–4.14 (8H, m), 6.07 (2H, m), 7.25 (2H, m), 7.78
(2H, m), 10.11 (2H, s), 10.23 (2H, s); m/z (FAB) 635 (M+ + 1). Calc. for
Table 1 Selected UV–VIS data for [2,3]naphthoporphyrins and their
precursors
Porphyrin
lmax (CHCl3)/nm (log10 e)
7a
8aa
9a
392 (5.20), 495 (4.14), 527 (3.66), 563 (3.69), 615 (3.12)
359 (0.34), 419 (0.50), 464 (1.00), 697 (0.13), 773 (0.87)
349 (3.29), 426 (5.43), 549 (4.17)
10a
12
13
487 (4.96), 662 (3.73), 723 (4.87)
399 (5.17), 497 (4.12), 531 (3.86), 566 (3.73), 619 (3.49)
419 (5.34), 519 (3.92), 551 (4.53), 587 (3.75), 643 (4.34)
C
44H50N4·CH3OH: C, 81.04; H, 8.16; N, 8.40. Found: C, 81.38; H, 8.18; N,
8.11%. For 13: 1H NMR (CDCl3) d 23.52 (2H, br s), 1.14 (6H, t, J 7.32),
1.78 (4H, m), 1.89 (6H, t, J 7.32), 2.29 (4H, m), 3.63 (6H, m), 3.93–4.12
(8H, m), 7.80 (2H, m), 8.51 (2H, m), 9.56 (2H, s), 9.96 (2H, s), 10.18 (2H,
s); m/z (FAB) 607 (M+ + 1). Calc. for C42H46N4·0.5H2O: C, 81.91; H, 7.69;
N, 9.10. Found: C, 81.78; H, 7.64; N, 8.78%.
a In 5% TFA–CHCl3; here relative intensities are given in parentheses.
Absorption spectrum data of [2,3]naphthoporphyrins and
their precursors are summarized in Table 1. As porphyrin 8a
was insoluble in most solvents, its absorption spectrum was
measured in 5% TFA-CHCl3. The Soret and Q bands of the
dication 8a were observed at 464, 697 and 773 nm, respectively.
The absorbance at 773 nm is unusually intense (0.87 3 that of
Soret band), showing behaviour reminiscent of phthalocya-
nines. meso-Tetraphenyltetra[2,3]napthoporphyrin 10a was
moderately soluble in organic solvents such as CH2Cl2 or
CHCl3. The Soret band of 10a was rather weak compared to that
of other porphyrins, owing to steric hindrance between meso-Ph
and fused [2,3]naphthalene rings. By contrast, the intensity of
the absorption at 723 nm is very strong (log10 e = 4.87), this
value is considerably larger than that of known p-extended
meso-tetraphenylporphyrins.3 The UV–VIS spectrum of 13 is
rhodo-type (Q band: III > I > IV > II) which is typical for
monobenzoporphyrins.7
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In conclusion, we have succeeded in developing a new
strategy for the preparation of [2,3]naphthoporphyrins using
4,9-ethano-2H-benz[f]isoindole as a synthetic equivalent of 2H-
benz[f]isoindole. This strategy may extend to the synthesis of
other p-extended molecules such as polypyrroles or pyrrole
oligomers, which are fused with naphthalene rings.
10 T. D. Lash, Chem. Eur. J., 1996, 2, 1197 and references therein.
894
Chem. Commun., 2000, 893–894