Liu and Lash
3-Meth ylp yr r ole (10a ). Ethyl 3-methylpyrrole-2-carboxy-
late38 (20.01 g) and sodium hydroxide (7.85 g) were stirred
under nitrogen with ethylene glycol (80 mL) and heated under
reflux for 2 h. The solution was cooled to room temperature,
diluted with dichloromethane (100 mL), washed with water
(200 mL), and back-extracted with dichloromethane. Following
evaporation of the solvent under reduced pressure, the residue
was steam distilled. The resulting distillate was extracted with
dichloromethane (3 × 50 mL), and the organic phases were
combined, dried over magnesium sulfate, and evaporated on
a rotary evaporator to give 3-methylpyrrole (4.67 g, 44%) as a
colorless oil. 1H NMR (CDCl3): δ 2.02 (3H, s), 6.14 (1H, br m),
6.61 (1H, br m), 6.75 (1H, br m), 7.97 (1H, br s). 13C NMR
(CDCl3): δ 12.0, 109.9, 115.8, 118.0, 119.0.
Calcd for C36H39N3O4‚1/4H2O: C, 74.27; H, 6.84; N, 7.22.
Found: C, 74.29; H, 6.78; N, 7.24.
8,17-Diet h yl-7,12,18-t r im et h yl-21-ca r b a b en zo[b]p or -
p h yr in (8). Triethylamine (10 drops) was added to a solution
of tripyrrole dibenzyl ester 12a (1.00 g) in THF (150 mL) and
methanol (50 mL). The air was displaced with nitrogen, 10%
Pd/C (200 mg) was added, and the resulting mixture was
shaken under a hydrogen atmosphere at room temperature
and 40 psi for 16 h. The catalyst was removed by suction
filtration, the solvent evaporated under reduced pressure, and
the residue taken up in 3% aqueous ammonia. The solution
was neutralized with acetic acid, the temperature being
maintained between 0 and 5 °C throughout. After 1 h, the
resulting precipitate was suction filtered, washed well with
water, and dried under vacuum overnight to give the tripyr-
roledicarboxylic acid 13a (702 mg, 94%) as a pink powder that
was used without further purification. Tripyrrole 13a (100 mg)
was stirred with TFA (1 mL) under nitrogen for 10 min. The
solution was diluted with dichloromethane (19 mL) and 1,3-
diformylindene42 (42 mg) added immediately. The resulting
mixture was stirred under nitrogen for 2 h. The solution was
neutralized with triethylamine, DDQ (56 mg) was added, and
the resulting mixture was stirred at room temperature for 1
h. The solution was diluted with chloroform, washed with
water, and evaporated to dryness on a rotary evaporator. The
residue was chromatographed on grade 3 alumina eluting with
dichloromethane. The product fraction was evaporated and the
residue recrystallized from chloroform-methanol to give the
benzocarbaporphyrin (55 mg, 50%) as brown crystals. Mp:
>300 °C. UV-vis (CHCl3): λmax (log ꢀ) 381 (4.56), 424 (5.08),
512 (4.21), 545 (4.15), 601 (3.83), 661 (3.50). UV-vis (0.01%
TFA-CHCl3, monocation): λmax (log ꢀ) 392 (sh, 4.67), 436
(4.87), 475 (4.39), 548 (4.07), 587 (3.92), 610 (3.87), 669 (3.40).
UV-vis (50% TFA-CHCl3, dication): λmax (log ꢀ) 346 (4.55),
Ben zyl 5-Acetoxym eth yl-3-m eth ylp yr r ole-2-ca r boxy-
la te (11b). Benzyl 3,5-dimethylpyrrole-2-carboxylate39 (15b;
2.29 g) was dissolved in chloroform (100 mL), lead tetraacetate
(95%; 4.63 g) was added immediately, and the mixture was
stirred vigorously under reflux for 5 h. The mixture was cooled,
filtered through Celite, and evaporated under reduced pres-
sure. The residue was chromatographed on grade 3 alumina
eluting with dichloromethane. Recrystallization from ether/
hexanes gave the acetoxymethylpyrrole (0.892 g, 31%) as white
1
crystals. Mp: 119-120 °C. H NMR (CDCl3): δ 2.07 (3H, s),
2.33 (3H, s), 4.99 (2H, s), 5.31 (2H, s), 6.08 (1H, d, J ) 2.8
Hz), 7.38 (5H, m), 9.09 (1H, br s). 13C NMR (CDCl3): δ 13.0,
21.1, 58.8, 66.0, 113.9, 120.0, 128.3, 128.4, 128.7, 128.8, 130.4,
136.5, 161.4, 171.8. Anal. Calcd for C16H17NO4‚1/4H2O: C,
65.85; H, 6.04; N, 4.80. Found: C, 65.88; H, 5.79; N, 4.88.
2,5-Bis(5-ben zyloxyca r bon yl-3-eth yl-4-m eth yl-2-p yr r o-
lylm eth yl)-3-m eth ylp yr r ole (12a ). 3-Methylpyrrole (0.36 g)
and benzyl 5-acetoxymethyl-4-ethyl-3-methylpyrrole-2-carbox-
ylate40 (11a ; 2.79 g) were dissolved in ethanol (30 mL) and
acetic acid (2 mL), and the was mixture stirred and heated
under reflux under a nitrogen atmosphere for 16 h. The
mixture was cooled in an ice bath and the resulting precipitate
suction filtered, washed with cold ethanolc and dried in vacuo
overnight to give the title tripyrrole (1.761 g, 68%) as a pale
yellow powder. Mp: 198 °C. 1H NMR (CDCl3): δ 0.94-0.99
(6H, 2 overlapping triplets), 2.07 (3H, s), 2.24 (6H, s), 2.32-
2.36 (4H, 2 overlapping quartets), 3.51 (2H, s), 3.58 (2H, s),
4.41 (4H, br s), 5.75 (1H, s), 7.04 (4H, m), 7.25 (6H, m), 8.88
(1H, br s), 10.98 (2H, br s). 13C NMR (CDCl3): δ 11.1, 11.2,
15.8, 15.9, 17.3, 17.4, 22.3, 24.5, 65.5, 107.1, 113.2, 117.3, 117.5,
123.5, 124.0, 126.9, 127.0, 127.5, 128.4, 132.8, 137.2, 162.8.
EI MS: m/z (rel intens) 591 (100, M+), 483 (73). HRMS (EI):
m/z calcd for C37H41N3O4 591.3097, found 591.3087. Anal.
Calcd for C37H41N3O4‚1/4H2O: C, 74.53; H, 7.07; N, 7.05.
Found: C, 74.47; H, 6.96; N, 7.08.
1
424 (5.00), 607 (3.88), 660 (4.21). H NMR (CDCl3): δ -7.04
(1H, s), -4.24 (2H, br s), 1.81-1.85 (6H, 2 overlapping triplets),
3.60 (6H, s), 3.62 (3H, s), 3.99-4.06 (4H, 2 overlapping
quartets), 7.73-7.75 (2H, m), 8.80-8.82 (2H, m), 8.85 (1H, s),
9.65 (1H, s), 9.77 (1H, s), 10.04 (2H, s). 1H NMR (1 drop TFA-
CDCl3): δ -6.90 (1H, s), -4.60 (1H, br s), -3.32 (1H, s), -3.25
(1H, s), 1.69-1.74 (6H, 2 overlapping triplets), 3.57 (3H, s),
3.58 (3H, s), 3.74 (3H, s), 4.02-4.09 (4H, 2 overlapping
quartets), 7.71-7.72 (2H, m), 8.67-8.69 (2H, m), 9.18 (1H, s),
10.04 (1H, s), 10.08 (1H, s), 10.31 (1H, s), 10.34 (1H, s). 1H
NMR (50% TFA-CDCl3): δ -5.02 (2H, s), -1.43 (2H, br s),
1.75-1.79 (6H, 2 overlapping triplets), 3.57 (3H, s), 3.58 (3H,
s), 3.59 (3H, s), 3.99-4.04 (4H, 2 overlapping quartets), 8.93-
8.95 (2H, m), 9.16 (1H, s), 10.12-10.14 (2H, m), 10.43 (1H, s),
10.46 (1H, s), 11.02 (1H, s), 11.03 (1H, s). 13C NMR (TFA-
CDCl3): δ 11.7, 13.9, 16.7, 16.8, 19.9, 20.0, 94.8, 96.5, 104.2,
104.5, 118.4, 121.7, 127.7, 128.4, 135.4, 135.7, 137.1, 137.7,
138.1, 139.6, 141.6. EI MS: m/z (rel intens) 457 (100, M+), 442
(18), 427 (3), 229 (20, M2+). HRMS (EI): m/z calcd for C32H31N3
457.2518, found 457.2522.
2,5-Bis(5-b en zyloxyca r b on yl-4-m et h yl-2-p yr r olylm e-
th yl)-3,4-d ieth ylp yr r ole (12b). 3,4-Diethylpyrrole41 (0.22 g)
and benzyl 5-acetoxymethyl-3-methylpyrrole-2-carboxylate (1.00
g) were dissolved in ethanol (20 mL) and acetic acid (1 mL),
and the mixture was refluxed under a nitrogen atmosphere
for 16 h. The mixture was cooled in an ice bath and the
resulting precipitate filtered, washed with cold ethanol, and
dried under vacuum overnight. The tripyrrole diester (402 mg,
40%) was obtained as a light brown powder. Mp: 175-176
12,13-Dieth yl-7,18-d im eth yl-21-ca r ba ben zo[b]p or p h y-
r in (9). Tripyrrole dibenzyl ester 12b (400 mg) was placed in
a hydrogenation vessel and dissolved in THF (67 mL) and
methanol (27 mL). Triethylamine (10 drops) was added, the
air flushed out with nitrogen, and 10% Pd/C added (67 mg).
The resulting mixture was shaken under an atmosphere of
hydrogen at room temperature and 40 psi for 16 h. The catalyst
was removed by suction filtration and the solvent evaporated
under reduced pressure. The residue was taken up in 3%
aqueous ammonia and then neutralized with glacial acetic
acid, the temperature being maintained between 0 and 5 °C
throughout. The mixture was allowed to stand at 0 °C for 1 h
and the precipitate filtered and washed well with water to
remove all traces of acetic acid. After being dried overnight in
vacuo, the tripyrroledicarboxylic acid 13b (270 mg; 98%) was
obtained as a light purple powder that was used without
1
°C. H NMR (CDCl3): δ 1.05 (6H, t, J ) 7.6 Hz), 2.21 (6H, s),
2.40 (4H, q, J ) 7.6 Hz), 3.74 (4H, s), 4.42 (4H, br s), 5.85 (2H,
d, J ) 2 Hz), 7.14 (4H, m), 7.29 (6H, m), 8.91 (1H, br s), 11.11
(2H, br s). 13C NMR (CDCl3): δ 13.7, 16.8, 17.8, 24.6, 66.0,
111.4, 118.5, 119.3, 122.6, 127.7, 128.3, 129.2, 136.0, 136.7,
163.0. EI MS: m/z (rel intens) 577 (100, M+), 469 (58). HRMS
(EI): m/z calcd for C36H39N3O4 577.2940, found 577.2936. Anal.
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B. J . Chem. Soc. 1959, 3416.
(41) Sessler, J . L.; Mozaffari, A.; J ohnson, M. R. Org. Synth. 1991,
70, 68.
(42) Arnold, Z. Collect. Czech. Chem. Commun. 1965, 30, 2783.
1760 J . Org. Chem., Vol. 68, No. 5, 2003