Linearly -π- extended porphyrins: Synthesis of novel tetrabenzoylporphyrins

Article abstract of DOI:10.1002/jhet.5570420405

The π-extended porphyrins 11a - c with a λ_max = 644, 643 and 639 nm were synthesized by an acid catalysed reaction of the dipyrrolylmethane 10 with different aldehydes followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-quinone (DDQ). In a

Full text of DOI:10.1002/jhet.5570420405

Linearly -π- Extended Porphyrins: Synthesis of Novel
Tetrabenzoylporphyrins
May-Jun 2005
503
Ibrahim Elghamry [a]* and Lutz F. Tietze [a]
[a] Institut für Organische und Biomolekulare Chemie der Georg-August-Universität Göttingen,
Tammannstraße 2, D-37077 Göttingen, Germany. E-mail: elghamry@hotmail.com
Received June 3, 2004
The π-extended porphyrins 11a – c with a λ
= 644, 643 and 639 nm were synthesized by an acid catal-
max
ysed reaction of the dipyrrolylmethane 10 with different aldehydes followed by oxidation with 2,3-dichloro-
5,6-dicyano-1,4-quinone (DDQ). In a second approach, 10 was decarboxylated to yield 12, which was
treated with DMF and benzoylchloride to give the diformyl compound 13. Acid catalysed reaction of 12 and
13 led to the porphyrin 11a after oxidation.
J. Heterocyclic Chem., 42, 503 (2005).
Introduction.
Highly conjugated porphyrins with a strong absorption
in the far-visible/near-IR region have attracted a great level
of interest in recent years due to their intrinsic value as
photosensitiser for the photodynamic therapy of cancer
(PDT) [1], multibit molecular-based information storage
arrays [2-7], or near-IR dyes and nonlinear optical materi-
als [8,9].
The π–electron system of the porphyrin macrocycles
have been reported to be extended by peripheral sub-
stituents at the meso-/β-positions [10-13], or fused poly-
cyclic ring systems [14-16]. Although extension of the
chromophore by introducing fused aromatic rings or single
chromophoric groups (e.g., C=O, CN, or ester) was
expected to produce a major bathochromic shift, in many
cases the effects are actually rather small [9,10,17].
Tetraphenylporphyrin (TPP) [10] and tetraformylpor-
phyrin (TFP) [11] give Soret bands at 409 nm and 405 nm
and longest wavelength Q-bands at 624 and 623 nm,
respectively; values that are only slightly higher than those
reported for polyalkylporphyrins (PAP) [18,19] such as
octaethylporphyrin (OEP) [19,20] (400 and 622 nm,
respectively). With this in mind, we targeted the synthesis
of porphyrins containing benzoyl groups as substituents;
the element of both carbonyl and phenyl moieties repre-
sents a structural unit that could potentially produce a
strong effect on the UV-vis absorption.
Results and Discussion.
ization [26,27] followed by oxidation with DDQ [28-30].
For this purpose we prepared the dipyrrolylmethanes 5a-d;
but heating of the pyrroles 4a-d for 15 minutes in
dimethoxymethane and trifluoroacetic acid (TFA) gave
Enaminones are versatile synthetic intermediates in the
synthesis of many heterocycles and natural products [21].
In a recent communication we reported a regioselective
synthesis of 4-oxoaryl pyrrole-2-carboxylate 4 from enam-
inone 1 and 2-oximinacetoacetate 2 under Knorr-conditions
in moderate yield [22]. A slight improvement for the yield
was achieved by using 2-aminoacetoacetate [3] 3 instead of
producing it in situ from the oxime 2 (Scheme 1).
only low yields (25-30%) [31]. However, when BF ·OEt
3
2
[32] was used as a Lewis acid catalyst, the conversion was
complete in 3 hours without heating and the dipyrrolyl-
methanes 5a-d were obtained in high yields (75-80%)
(Scheme 1).
The benzoyl pyrrole 4 as asymmetrically substituted
pyrrole could be employed for the synthesis of porphyrins
using a variety of routes [10,24,25] however, one of the
most successful method is the '2+2' MacDonald tetramer-
The cleavage of an ester moiety to furnish the corre-
sponding carboxylic acids is a common organic transfor-
mation that is usually carried out in a routine way by basic
or acidic hydrolysis. However, pyrrole derivatives are very

504
I. Elghamry and L. F. Tietze
Vol. 42
sensitive to acidic conditions and saponification of pyr-
role-2-carboxylic acid esters under basic conditions usu-
ally furnishes the corresponding α-unsubstituted pyrrole
derivative by subsequent thermal decarboxylation. But
saponification of the dipyrrolylmethanes 5a,b with NaOH
and KOH gave the corresponding dicarboxylic acid but in
a very low yield and the main product was the pyrrolo[3,2-
f]indolizine 6 a product of intramolecular cyclization of
dipyrrolylmethane (Scheme 2). When LiOH was used
only the starting material 5 was recovered even after 8
hours of reflux.
diketone 7 with oxime 2d to yield pyrrole 8 which on oxi-
dation with lead tetraacetate in acetic acid furnished the
acetoxy pyrrole-2-carboxylate 9. Reaction of 9 with the
pyrrole 4d in the presence of BF ·Et O afforded the
3
2
dipyrrolylmethane 5d in almost quantitative yield (Scheme
3). Catalytic hydrogenolysis of 5d in the presence of 10%
Pd/C gave the free diacid 10 in an excellent yield (Scheme
3). Over time, compound 10 changes from colourless to
black upon exposure to air, however it is stable under
argon in the refrigerator for at least 5 months.
Synthesis of Porphyrins 11a-c.
The conversion of the dipyrrylmethane 10 into the corre-
sponding porphyrins 11a-c with four benzoyl groups was
accomplished by two routes. First, we used a one-pot-
three-step approach, which starts with decarboxylation fol-
lowed by formation of the corresponding porphyrinogen
with subsequent oxidation. Thus, a solution of dipyrrolyl-
methane 10 in dichloromethane/methanol (DCM /MeOH)
(4:1) was heated under argon atmosphere at 50 °C for 1
hour in the presence of hydrobromic acid and formalde-
hyde and afterwards kept at room temperature for 24
hours. Subsequent addition of 3 equivalents of DDQ
afforded the desired porphyrin 11a as a violet powder in
25% yield. In a similar manner, porphyrins 11b and 11c
were synthesized in 26% and 24% yield, respectively by
reaction of 10 with benzaldehyde and p-phenylbenzalde-
hyde, respectively (Scheme 4).
In order to avoid the intramolecular cyclization of the
dipyrrolylmethane 5 under the saponification conditions,
the benzyl ester 5d was prepared and subsequently cleaved
by catalytic hydrogenolysis to furnish the dicarboxylic
acid.
In a first attempt to synthesize 5d, the pyrrole 4d was
synthesized by transesterification of the methyl ester 4b in
the presence of LiN(Si(CH ) ) /BzOH in a moderate yield
In a second approach, the α,α'−dicarboxylic acid 10 was
transformed into 12 by decarboxylation, which on treat-
ment with dimethylformamide (DMF) and benzoylchlo-
ride gave the diformyl derivative 13. Reaction of 12 and 13
according to the MacDonald procedure in the presence of
an acid catalyst led, after oxidation, to the porphyrin 11a.
The decarboxylation of 10 to furnish the dipyrrylmethane
12 in a good yield was achieved by heating the compound
3 3 2
of 50% [21]. A much better overall yield of 60 % of 4d
was obtained by Knorr-pyrrole synthesis employing enam-
inone 1 and the oxime 2d (Scheme 1). Electrophilic substi-
tution of the pyrrole 4d with dimethoxymethane in the
presence of BF ·OEt gave the dipyrrylmethane 5d in 75%
3
2
yield. In an another approach the latter compound was
obtained in 85% yield by reductive condensation of 1,3-

May-Jun 2005
Linearly -π- Extended Porphyrins: Synthesis of Novel Tetrabenzoylporphyrins
505
in DMF or DEF at 170 °C [33]. Interestingly, when the
diacid 10 was heated in ethanolamine [34] the pyrolo[3,2-
f]indololizine 6 was obtained in almost quantitative yield
and no bis-α-free dipyrrylmethane was detected in the
reaction mixture. Reaction of 12 with benzoyl chloride
[35] in DMF and subsequent hydrolysis of the isolable
iminium salt afforded the diformyl derivative 13 in a mod-
erate yield. The condensation of 12 with 13 was accom-
plished at room temperature in the presence of p-TsOH to
give the corresponding porphyrinogen, which on oxidation
with DDQ afforded the porphyrin 11a in 28% yield.
(Scheme 5)
strengths, relative to those of 11a, of δ = –1.95 and δ =
–1.89, respectively. These can be attributed to a distortion
of the planar macrocyclic structure and therefore a
decrease of the ring current effect [36]. Also, the effect of
the benzoyl groups on the meso-protons at positions 10
and 20 of porphyrins 11a-c is noticeable. Thus, the signal
for 5-H and 15-H in porphyrin 11a is observed at δ = 10.28
as found also for the porphyrins OEP [19,20] and TPP [10]
(Table 1), whereas the other two meso-hydrogens at posi-
tions 10 and 20 in 11a - c resonate at δ = 9.91, 9.61 and
9.69, respectively due to shielding caused by the benzoyl
groups.
Structure elucidation of the new porphyrins was per-
1
formed by EI-MS, H-NMR, and UV-visible spectroscopy
and the data were compared with those of OEP [19,20,32],
TPP [10] and TFP [11] (Table 1).
1
In the H NMR spectra porphyrins the internal NH pro-
tons are shielded due to a ring current effect of the aro-
matic macrocycle [13-16]. Thus, the NH of porphyrin 11a
containing no phenyl groups at the meso-position res-
onates at δ = –3.25. On the other hand, porphyrins 11b and
11c contain a phenyl and a p-diphenyl group at the meso-
position, signals for the NH-group are found at lower field
The UV-visible spectra of the new porphyrins 11a – c
show a bathochromic shift in both the Soret and the Q-
bands compared to those of TPP and TFP (Table 1). Thus,
the Soret bands of 11a-c are red shifted and observed at
λ
= 424 nm, 427 nm and 428 nm, respectively while
max
Table 1
1
Selected UV-visible and H-NMR spectroscopic data of the new porphyrins 11a-c, as well
as of OEP [19,20], TPP [10] and TFP [11].
1
Porphyrin UV-visible [a],
Soret
λmax/nm
(logε)
Q-bands
H NMR [b]
δ/ppm
Meso-H
NH
OEP
TPP
TFP
11a
396
409
405
424
(5.13)
427
(5.19)
428
497
504
456
516
(4.15)
518
530
540
581
551
(3.85)
550
564
570
-
590
(3.85)
590
620
624
623
10.08 (s,4H)
10.17 (s,4H)
10.56 (s, 4H)
10.28 (s,2H)
9.91 (s,2H)
9.61 (s,2H)
-3.80
-3.39
-3.30
-3.25
644
(3.77)
643.5
(3.92)
639
11b
11c
-1.95
-1.89
(4.30)
518
(4.22)
551
(3.92)
589
9.69 (s,2H)
(4.89)
(3.95)
(3.62)
(3.62)
(2.88)
[a] in chloroform:
[b] in CDCl .
3

506
I. Elghamry and L. F. Tietze
Vol. 42
128.9, 129.0, 130.6, 131.7, 135.7, 140.0 ppm; ms: m/z (%) 320
TPP and TFP gave Sort bands at λ
nm, respectively. Also, the longest wavelength of the Q-
bands of 11a-c are red shifted and observed at λ = 644,
643 and 639 nm, respectively. These values are higher than
those reported for TPP and TFP (Table 1).
= 409 nm and 405
max
+
+
(M +1), (10), 319 (M ) (65), 210 (20), 91 (100), 77 (15).
Anal. Calcd for C H NO : C, 75.22: H, 5.37. Found: C,
20 17
3
max
75.02: H, 5.24.
Ethyl 4-(p-Methylbenzoyl)-3-methyl-2-carboxylate (4e).
In conclusion, new porphyrins 11a-c were synthesized
and their spectral data were measured and compared to
previously reported related porphyrins. More photochemi-
cal and photophysical studies on the new synthesized por-
phyrins including emission spectra, the mechanism of the
deactivation of the excited molecules e.g. electron transfer
and energy transfer process are under way.
This compound was obtained as colourless crystals (ethanol),
mp 129.4 °C; ir: NH 3318, CO 1691, CO 1620 cm ; H nmr
-1
1
(CDCl ): δ 1.38 (t, J = 7.13, 3H, CH ), 2.42 (s, 3H, CH ), 2.63 (s,
3
3
3
3H, CH ), 4.38 (q, 2H, J = 7.13, CH ), 7.21 (s, 3H, Ar-H and 5-
3
2
13
H
), 7.66 (m, 2H, Ar-H), 9.66 (s, 1H, NH); C nmr: 11.7,
pyrr
14.4, 21.6, 60.6, 121.4,124.6, 124.7, 128.9, 129.3, 130.0, 137.4,
+
142.4, 161.8, 191.7 ppm; ms: m/z (%) 272 (M +1) (10), 271
+
(M ) (58), 256 (100), 224 (57), 210 (95), 134 (50), 91 (20).
Anal. Calcd. for C H NO : C, 70.83; H, 6.32. Found: C,
70.63; H, 6.23.
16 17
3
EXPERIMENTAL
General.
Dipyrrolylmethanes 5a-d.
Method 1.
Melting points are uncorrected. NMR spectra were recorded
on Bruker WM 300 and DRX 500 spectrometers (300 MHz and
A mixture of pyrrole-2-carboxylate (4) (1 mmol) and
dimethoxymethane (0.6 mmol) was purged with Argon, 0.5 ml
TFA was added. The mixture was stirred at 70-80 °C for 30 min
during which the reaction mixture turned to pale green. The mix-
ture was then poured into 100 ml ice-water and the solid so
obtained was collected by filtration and washed several times
with water-ethanol mixture (1:1) and recrystallized from acetone.
1
500 MHz, respectively for H, 75 and 125 MHz, respectively, for
13
C) using TMS as internal standard and the deuterated solvent as
lock. IR spectra were obtained by using a Perkin-Elmer 983 spec-
trophotometer. Electron impact ionisation mass spectrometry
(EIMS) and electrospray ionization (ESI) were performed on a
Varian AMD 604 instrument using 70 eV ionization energy. All
chromatographic separations were performed using Grade 3 neu-
tral alumina 70-230 mesh silica gel. Pyrrole-2-carboxylates 4a-d
were prepared by reacting enaminone 1 with 2-oximinoacetoac-
etate 2 under knorr-conditions [22] or 2-aminoacetoacetate [23]
under standard conditions in acetic acid.
Method 2.
In an atmosphere of Argon, boron trifluoride diethyl etherate
was added to a solution of pyrrole-2-carboxylate 4 (1 mmol) and
dimethoxymethane (0.6 mmol) in dichloromethane (50 ml) and
the mixture was stirred for 3 hours at room temperature. The
mixture was poured into ice-water and extracted with
dichloromethane. The dichloromethane layer was washed with
Methyl 4-Benzoyl-3-methyl-2-carboxylate (4b).
This compound was obtained as colourless crystals
-
water and dried over anhydrous MgSO . After evaporation of the
(methanol), mp 192.6 °C; ir: NH 3400, CO17167, (CO) 1670 cm
4
1
1
solvent under vacuum, the residue was recrystallized from ace-
tone.
; H nmr (dimethyl sulfoxide-d ): δ 2.51 (s, 3H, CH ), 3.81
6
3
(s,3H, OCH ), 7.22 (s,1H, 5-H ), 7.45 (m, 3H, Ar-H), 7.71 (m,
3
pyrr.
13
2H, Ph-H), 12.21 (s,1H, NH); C nmr: δ 11.4, 51.1, 120.6,
Diethyl 3,3'-Dimethyl-4,4'-dibenzoylpyrroylmethane-2,2'-dicar-
boxylate (5a).
122.8, 128.3, 128.9, 129.8, 131.5,139.8,161.1,190.6 ppm; ms:
+
m/z (%) 243 (M ) (100), 210 (80), 134 (60), 77 (20).
This compound was obtained as colourless crystals, mp 276.7
Anal. Calcd. for C
H NO C: 69.12; H, 5.39. Found: C,
14 13 3
-1
1
°C; ir: NH 3359, CO 1710, CO 1630 cm ; H nmr (CDCl ): δ
3
68.81; H, 5.16.
1.41 (t, J = 7.20, 6H, 2CH ), 2.12 (s, 6H, 2CH ), 4.15 (s, 2H, -
3
3
Methyl 4-(p-Methoxybenzoyl)-3-methyl-2-carboxylate (4c).
CH -) 4.58 (q, 2H, J = 7.20, 2CH ), 7.51 (m, 4H, Ar-H), 7.61 (m,
2
2
13
2H, Ar-H), 7.81 (m,4H, Ar-H), 11.10 (s, 2H, 2NH); C nmr:
12.9, 14.4, 24.1, 60.25, 119.0, 122.8, 127.6, 128.4, 129.7, 132.7,
137.8, 139.5, 161.0, 104.6 ppm; ms: esi (methanol) 526.7 (M ).
This compound was obtained as colourless crystals (methanol),
-1
1
mp 186.3 °C; ir: NH 3469, CO1716, CO 1624 cm ; H nmr
(CDCl ): δ 2.61 (s, 3H, CH ), 3.84 (s,3H, OCH ), 3.90 (s, 3H,
+
3
3
3
Anal. Calcd. for C H N O C: 70.71; H, 5.74. Found: C,
OCH ),6.93 (s,1H, 5-H ), 6.95 (m, 2H, Ar-H), 7.19(m, 1H, 5-
31 30
2 6 :
3
pyrr.
13
70.51; H, 5.44.
H
),7.81 (m, 2H, Ar-H), 9.51 (s,1H, NH); C nmr: δ 11.6, 51.6,
pyrr
55.4, 113.5, 121.1, 124.8, 127.8, 129.9, 131.4, 132.6, 162.1,
162.7, 190.6 ppm; ms: m/z (%) 274 (M +1) (20), 273 (M ) (100),
256 (15), 240 (90),210 (50), 134(58), 92 (10), 77 (15).
Dimethyl 3,3'-Dimethyl-4,4'-dibenzoylpyrroylmethane-2,2'-
dicarboxylate (5b).
+
+
This compound was obtained as colourless crystals, mp > 300
Anal. Calcd for C
H NO (273.10): C, 65.92; H, 5.53.
15 15 4
-1
1
°C; ir: NH 3363, CO 1719, CO 1631 cm ; H nmr (dimethyl sul-
foxide-d ): δ 1.91 (s, 6H, 2CH ), 3.73 (s, 6H, 2CH ), 3.95 (s, 2H,
Found: C, 65.82; H, 5.33.
6
3
3
Benzyl 4-Benzoyl-3-methyl-2-carboxylate (4d).
-CH -), 7.51 (m, 8H, Ar-H), 7.64 (m, 2H, Ar-H), 11.75 (s, 2H,
2
13
2NH); C nmr: 11.8, 24.08, 50.9, 81.9, 117.98, 122.2, 126.9, 128.2,
This compound was obtained as colourless crystals (ethylac-
-1
1
128.7, 132.1, 136.2, 139.2, 160.8, 192.42 ppm; ms: m/z (%): 498
etate), mp 149.4 °C; ir: NH 3377, CO 1675, CO1633 cm ; H
nmr (CDCl ): δ 2.63(s, 3H, CH ), 5.38 (s, 2H, -CH -), 7.19 (s,
+
(M ) (40), 393 (100), 361 (38), 329 (10), 105 (45), 77 (10).
3
3
2
Anal. Calcd. for C H N O : C, 69.87; H, 5.26. Found: C,
69.67; H, 5.17.
1H, 5-H ) 7.41 (m, 8H, Ar-H), 7.68 (m, 2H, Ar-H), 9.60 (s,
1H, NH); C nmr 11.7, 66.4, 121.1, 124.2, 128.1, 128.3, 128.6,
29 26
2 6
pyrr.
13

May-Jun 2005
Linearly -π- Extended Porphyrins: Synthesis of Novel Tetrabenzoylporphyrins
507
Dimethyl 3,3'-Dimethyl-4,4'-(p-methoxybenzoyl)pyrroyl-
methane-2,2'-dicarboxylate (5c).
give 9 (300 mg, 85%) as white crystals from ethanol mp 123.3
-1
1
°C; ir: NH 3272, CO 1733, CO 1666, CO 1645 cm ; H nmr
(CDCl ): δ 2.12 (s, 3H, CH ), 2.23 (s, 3H, CH ), 5.11 (s, 2H, -
3
3
3
This compound was obtained as colourless crystals, mp > 250
CH -), 5.38 (s, 2H, -CH -), 7.45 (m, 8H, Ar-H), 7.77 (m, 2H, Ar-
-1
1
2
2
°C; ir: NH 3360, CO 1720, CO 1640 cm ; H nmr (CDCl ): δ
3
13
H), 9.62 (s, 1H, NH). C nmr: 12.3, 20.8, 57.4, 66.3, 119.8,
124.7, 128.2, 128.3, 128.4, 128.6, 129.3, 132.7, 133.5, 135.8,
139.5, 160.9, 171.5, 193.1 ppm; ms: ei, m/z (%): 391 (M ) (25),
2.11 (s, 6H, 2CH ), 3.85 (s, 6H, 2CH ), 3.91 (s, 6H, 2-OCH ),
3
3
3
4.05 (s, 2H, -CH -), 6.98 (d, J = 14 Hz, 4H), 7.85 (d, J = 14 Hz,
2
+
13
2H), 11.10 (s, 2H, 2NH); C nmr: 12.8, 24.0, 51.4, 55.4, 113.5,
331 (45), 240 (58), 91(100).
113.8, 118.7, 123.1, 127.6, 132.1, 132.2, 132.3, 137.5, 161.4,
Anal. Calcd. for C H NO : C, 70.58; H, 5.41. Found: C,
+
23 21
5
163.5, 193.3 ppm; ms: EI, m/z (%): 558 (M ) (25), 423 (48), 406
70.45; H, 5.38.
(25), 359 (20), 135 (100).
Anal. Calcd for C H N O : C, 66.66; H, 5.41. Found: C,
66.45; H, 5.11.
31 30
2
8
3,3'-Dibenzoyl-4,4'-dimethyl-2,2'-dipyrrolylmethane-5,5'-dicar-
boxylic Acid (10).
Dibenzyl 3,3'-Dimethyl-4,4'-dibenzoylpyrroylmethane-2,2'-
Dicarboxylate (5d).
A solution of 5d (100 mg, 0.18 mmol), in tetrahydrofurane (10
ml) was shaken in an atmosphere of hydrogen in the presence of
10% Pd-C (50 mg) until absorption of hydrogen was no longer
observed. After removal of the catalyst by filtration and evapora-
tion of the solvent, the residue was crystallised from
dichloromethane to give 10 (72 mg, 99%) as colourless crystals
This compound was obtained as colourless crystals, mp 198.4
-1
1
°C; ir: NH 3362, CO 1719, CO 1628 cm ; H nmr (CDCl ): δ
3
2.05 (s, 6H, 2CH ), 4.11 (s, 2H, -CH ), 5.93 (s, 4H, 2 -CH -Ph),
3
2
2
7.44 (m, 16H, Ar-H), 7.81(m, 4H, Ar-H), 11.15 (s, 2H, 2NH);
1
13
mp (decomp.) >200 °C; H nmr (dimethyl sulfoxide-d ): δ 1.06
C nmr: 12.9, 24.19, 65.9, 118.7, 122.9, 127.9, 128.1, 128.2,
6
(s, 6H, 2CH ), 3.94 (s, 2H, -CH ), 7.39 (m, 4H, Ar-H), 7.51 (m,
128.4, 128.5, 129.7, 132.7, 136.1, 138.2, 139.5, 160.7,
3
2
+
6H, Ar-H), 11.67 (s, 2H, 2NH), 12.30 (s, 2H, carboxylic acid);
194.6ppm; ms: esi 650.5 (M ) for C H N O .
41 34
2 6
13
C nmr: 11.8, 59.6, 119.0, 122.2, 122.3, 126.3, 128.2, 128.7,
Anal. Calcd for C H N O : C, 75.68; H, 5.27. Found: C,
41 34
2 6
128.8, 132.1, 135.8, 139.4, 162.1, 192.6 ppm.
2,8,12,18-Tetrabenzoyl-3,7,13,17-tetramethylporhyrin (11a).
Method A.
75.55; H, 5.22.
8-Benzoyl-3,7-dimethyl-4-phenyl-1H-pyrrolo[3,2-f]indolizine
(6).
This compound was obtained as pale yellow crystals, mp > 300
A solution of dipyrrolylmethanedicarboxylic acid 10 (125 mg,
0.26 mmol) and formaldehyde (37%) (3.5 ml) in
dichloromethane/methanol mixture (120 ml) (4:1) was refluxed
for 5 min under an atmosphere of Argon. After the addition of
hydrobromic acid (48%) (1 ml) as one portion the solution turned
immediately to deep pink then was allowed to reflux for 1 h. The
reaction mixture was then allowed to stirr at room temperature
for 20 h. DDQ was added (180 mg, 0.8 mmol) and the cloudy
mixture was stirred at room temperature for additional 20 h. The
mixture was concentrated under vacuum and the residue was dis-
solved in 500 ml dichloromethane and washed with water. The
-1 1
°C; ir: NH 3364, CO 1680 cm ; H nmr (dimethyl sulfoxide-d ):
6
δ 1.59 (s, 3H, -CH ), 1.81 (s, 3H, -CH ), 6.61 (s, 1H), 7.21 (s,
3
3
13
1H), 7.45 (m, 10H, Ar-H), 8.10 (s, 1H), 10.85 (s, 1H); C nmr:
11.23, 13.47, 96.1, 107.1, 108.1, 109.6, 119.6, 127.1, 127.4,
128.0, 128.2, 128.7, 128.9, 129.7, 130.1, 132.2, 137.7, 138.5,
+
144.0, 188.0 ppm; ms: EI, m/z (%): 364 (M ) (100), 287 (20),
259 (10), 232 (10), 182 (5).
Anal. Calcd. for C H N O: C, 82.39; H, 5.53. Found: C,
25 20
2
82.31; H, 5.43.
Benzyl 4-benzoyl-3,5-dimethyl pyrrole 2-carboxylate (8).
dichloromethane layer was dried over MgSO and chro-
matographed on a Grade 3 alumina column. A deep violet frac-
tion was collected and evaporation under vacuum gave 11a as a
4
Was prepared from benzoylacetone (7) and benzyl 2-oximinace-
toacetate (2d) as mentioned [22]. This compound was obtained as
colourless crystals (petroleum ether/ethylacetate, 4:1), mp 120-121
violet powder (26 mg, 25%) from CHCl /methanol mp > 300 °C;
1
3
°C; ir: NH 3277, CO 1669, CO 1644; H nmr (CDCl ): 2.20 (s, 3H,
3
1
H nmr (CDCl ): δ -3.25 (s, 2H), 1.58 (s, 12H), 7.95 (m, 8H),
3
CH ), 2.25 (s, 3H, CH ), 5.28 (s,2H, -CH -), 7.41 (m, 8H), 7.75
3
3
2
7.42 (m, 4H), 7.62 (m, 4H) 8.15 (m, 4H), 9.91 (s, 2H), 10.28 (s,
13
(m, 2H), 9.21 (s,1H, NH). C nmr: 12.4, 13.5, 66.1, 118.1, 123.3,
128.1, 128.3, 128.4, 128.6, 129.15, 129.8, 132.2, 135.9, 137.0,
140.18, 161.3, 193.8; ms, esi: 333.3 (M ).
+
2H); ms: ei, m/z (%): 782 (M ) (55), 105 (50), 77 (25), 44 (100).
Anal. Calcd. for C H N O : C, 79.78; H, 4.89. Found: C,
+
52 38
4 4
79.56; H, 4.65.
Anal. Calcd. for C H NO : C, 75.66; H, 5.74. Found: C,
21 19
3
75.55; H, 5.48.
2,8,12,18-Tetrabenzoyl-3,7,13,17-tetramethyl-5,10,15,20-tetra-
phenylporhyrin (11b).
Benzyl 5-Acetoxymethyl-4-benzoyl-3-methylpyrrole-2-car-
boxylate (9).
This compound was prepared using 10 and benzaldehyde by
the previous procedure. Following chromatography as described
for 11a, the product was recrystallised from chloroform-
methanol to give the title porphyrin (32 mg, 26%) as dark violet
In a stream of Ar, lead(IV) acetate (1.00 g, 2.26 mmol) was
added to a solution of benzylpyrrole 2-carboxylate (8) (300 mg,
0.77 mmol) in acetic acid (10 ml), and the mixture was stirred for
7 h at 90 °C. After the excess lead(IV) acetate was decomposed
by ethylene glycol, the mixture was poured into ice-water and
extracted with dichloromethane. The dichloromethane layer was
1
crystals mp > 300 °C; H nmr (CDCl ): δ -1.95 (s, 2H), 2.41 (s,
3
12H), 7.38 (m, 8H), 7.51 (m, 4H), 7.71 (m, 6H), 7.81 (m, 8H),
+
8.15 (m, 4H), 9.61 (s, 2H); ms: ei, m/z (%): 936 (M +2) (40),
+
+
935 (M +1) (8), 934 (M ) (100), 105 (95).
washed with H O and dried over anhydrous MgSO . After evap-
2
4
Anal. Calcd. for C H N O : C, 82.21; H, 4.96. Found: C,
82.01; H, 4.78.
oration of the solvent under vacuum, the residue was purified by
column chromatography (petroleum ether/ethylacetate, 4:1) to
64 46
4 4

508
I. Elghamry and L. F. Tietze
Vol. 42
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(1998).
[6] T. Ogawa, Y. Nishimoto, N. Yoshida, N. Ono and A. Osuka,
Chem. Commun., 337 (1998)
[7] T. Ogawa, Y. Nishimoto, N. Yoshida, N. Ono and A. Osuka,
Angew. Chem., Int. Ed. Engl., 38, 176 (1999).
2,8,12,18-Tetrabenzoyl-3,7,13,17-tetramethyl-5,10,15,20-
tetra(p-diphenyl)porhyrin (11c).
This compound was prepared using 10 and p-phenylbenzalde-
hyde by the procedure given above and by using the chromatog-
raphy conditions described for 11a. The product was recrys-
[8] S. A. Vinogradov and D. F. Wilson, J. Chem. Soc. Perkin
Trans. 2, 103, (1995).
tallised from chloroform-methanol to give the title porphyrin (34
1
mg, 24%) as dark violet crystals mp> 300 °C; H nmr (CDCl ): δ
3
[9] P. Chen, A. S. Dvornikov, M. Nakashima, J. F. Roach, D. M.
Nabran and P. M. Rentzepis, J. Phys. Chem., 100, 17507 (1996).
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M. Smith, R. Guilard, Eds.; Academic Press: San Diego, CA, vol. 1, pp
45 (2000).
-1.89 (s, 2H), 2.48 (s, 12H), 7.41 (m, 18H), 7.59 (m, 4H), 7.81
(m, 8H), 8.11 (m, 4H), 8.20 (m, 4H), 9.69 (s, 2H); ms, ei, m/z
+
+
+
(%): 1088 (M +2) (10), 1087 (M +1) (10), 1086 (M ) (5), 168
(25), 105 (38), 44 (100).
Anal. Calcd. for C H N O : C, 83.95; H, 5.15. Found: C,
76 54
4
4
83.88; H, 5.10.
2,8,12,18-Tetrabenzoyl-3,7,13,17-tetramethylporhyrin (11a).
[13a] G. S. Wilson and H. L. Anderson, Synlett, 1039 (1996); [b] O.
Finikova, A. Cheprakov, Z. Beletskaya and S. Vinogradov, Chem.
Commun., 261 (2001).
Method B.
A solution of dipyrrolylmethanedicarboxylic acid 10 (200 mg,
0.43 mmol) in dimethylformaamide (DMF) (10 ml) was refluxed
for 2 h under an atmosphere of Argon. The solution was left to
cool and divided into two equal portions. The first portion was
poured into an ice-brine mixture and extracted with ethyl acetate.
The organic layer was taken and dried over anhydrous magnesium
sulphate then evaporated under reduced pressure to give the crude
dipyrrylmethane 12. The second portion was chilled on ice-bath
and an excess of benzoyl chloride (3 ml, 24.6 mmol) was added
drop wise over a two min period, and left overnight at room tem-
perature. The iminium salt crystallised out, was collected by fil-
tration, rinsed with DMF and diethyl ether, taken in water and
basified then boiled with potassium carbonate for 10 min. An oil
separated immediately which quickly solidified. The solid
diformyl 13 was recovered and recrystallised from ethanol mp>
220 °C. A solution of p-toluene sulphonic acid (PTA) (350 mg) in
methanol (15 ml) was added to a stirred mixture of 12 (95 mg) and
diformyl 13 (100 mg) in dichloromethane (300 ml) the resulting
solution was stirred in the dark under an atmosphere of Argon for
24 h. DDQ (170 mg) was added and the mixture was stirred for an
additional 24 h. Then the chromatography conditions described in
method A were used to give 11a (35 mg, 28%).
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(1993).
[19] M. G. H. Vicente, L. Jaquinod, R. G. Khoury, A. Y. Madrona
and K. M. Smith, Tetrahedron Lett., 40, 8763 (1999).
[20] D. A. May and T. D. Lash, J. Org. Chem., 57, 4820 (1992).
[21a] L. F. Tietze, A. Bergmann and K. Brueggemann, Tetrahedron
Lett., 24, 3579 (1983); [b] L. F. Tietze and A. Bergmann, Angew. Chem.,
Int. Ed. Engl., 24, 127 (1985); [c] P. J. Michael and A. S. Parsons,
Tetrahredron, 52, 2199 (1996); [d] P. J. Michael and D. Gravestock,
Synlett, 981 (1996).
[22] I. Elghamry, Synth. Commun., 32, 897 (2002).
[23] H. Iida, K. Hayashia and M. Yamada, Heterocycles, 225
(1973).
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61, 998 (1996).
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Manlely, J. Org. Chem., 66, 3152 (2001).
Acknowledgement.
[26] G. P. Arsenault, E. Bullock and S. F. MacDonald, J. Am.
Chem. Soc., 82, 4384 (1960).
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A. M. Marguerettaz, J. Org. Chem., 52, 827 (1987).
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2864 (1999).
[30] P. D. Rao, S. Dhanalekshmi, B. J. Littler and J. S. Lindsey, J.
Org. Chem., 65, 7323 (2000).
This work was supported by the Fonds der Chemischen
Industrie. I. Elghamry thanks the Alexander-von-Humboldt foun-
dation for a research fellowship (Long-Term-Co-operation
Program) during the period from March 2002 to February 2003 at
the Georg-August-University in Göttingen, Germany.
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*
Current address, Misr International University, Faculty of
Pharmacy, Department of Pharmaceutical Organic Chemistry, P. O. Box 1
Heliopolis 11341, Cairo, Egypt.
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