mixture was refluxed for 30 h. Progress of the isomerization was
monitored by 1H NMR (DMSO-d6; olefinic protons). The ratio
of 3a and 4a (not determined in this case) reached ca. 20 : 1 and
a rough estimation of the purity of 3a was 90%. After removal of
the solvent, the viscous oil was dissolved in chloroform (300 ml).
The solution was washed with water (2 × 200 ml), dried over
sodium sulfate and concentrated in vacuo to give tetraethyl
all-trans-bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylate (3a) in
quantitative yield (purity ca. 90%) as a viscous oil. This material
was used without further purification.
(1H, dd, J = 3.9 and 2.5 Hz); dC (CDCl3) 138.70, 137.21, 136.03,
135.48, 134.16, 132.64, 132.63, 132.53, 132.04, 129.13, 127.73,
127.71, 127.70, 127.58, 127.50, 126.03, 125.88, 125.87, 125.83,
125.16, 124.69, 123.14, 122.08, 63.68, 57.90, 52.54, 49.23 and one
carbon could not be found due to peak overlapping; MS (EI)
m/z 448 (M+), 412, 303, 278 and 247; IR (KBr) 3050, 3016, 2950
and 2865 cm−1 (Found: C, 80.33; H, 4.98. C30H21ClS requires C,
80.25; H, 4.71%).
trans-15-Chloro-16-phenylsulfonyl-6,13-dihydro-6,13-
ethanopentacene (10)
Tetramethyl all-endo-bicyclo[2.2.2]oct-7-ene-2,3,5,6-
To a solution of 9 (0.197 g, 0.439 mmol) in dry dichloromethane
(30 ml) was added mCPBA (0.219 g, 1.27 mmol) at 0 ◦C and
the mixture was stirred for 2 h. After precipitates were removed
by filtration, the filtrate was washed with sat. NaHCO3, water
and brine, dried over Na2SO4 and concentrated. The residual
solid was recrystallized from ethanol to give 0.173 g (82%)
of the title compound as colourless crystals: mp 164 ◦C; dH
(CDCl3) 7.90 (1H, s), 7.90–7.70 (9H, m), 7.59 (1H, m), 7.55–
7.40 (6H, m), 5.23 (1H, m), 4.70 (2H, m) and 3.67 (1H, m); dC
(CDCl3) 138.78, 137.38, 136.54, 135.43, 134.23, 134.00, 132.85,
132.59, 132.56, 132.52, 129.21, 128.50, 127.96, 127.68, 126.17,
126.15, 126.09, 126.03, 125.42, 124.60, 123.08, 122.17, 73.57,
56.62, 52.47 and 43.84 and two carbons could not be found
due to peak overlapping; MS (EI) m/z 480 (M+), 444, 339, 303
and 278; IR (KBr) 3058, 2946 and 2873 cm−1 (HRMS Found:
480.0951. C30H21ClO2S requires 480.0950).
tetracarboxylate (2b)
A
suspension of all-endo-bicyclo[2.2.2]oct-7-ene-2,3,5,6-
tetracarboxylic anhydride (1; 50.0 g, 0.20 mol), dry methanol
(80 ml), trimethyl orthoacetate (76 ml) and TsOH·H2O (0.10 g)
was refluxed for 5 days under a dry atmosphere (protected by
silica gel). The white suspension gradually became a pale brown
solution. After checking by GC (absence of intermediate diester
monoanhydride), the mixture was cooled and concentrated in
vacuo to give a white solid, which was triturated with ether to
give ◦57.8 g (85%) of the title compound as a white solid: mp
120 C; dH (CDCl3) 6.42 (2H, m), 3.42 (12H, s), 3.34 (2H, m)
and 3.06 (4H, m); dC (CDCl3) 171.92, 130.65, 51.92, 46.38 and
35.44; MS (EI) m/z 340 (M+), 309, 249, 248 and 189; IR (KBr)
1739, 1439, 1215, 1195 and 1176 cm−1 (Found: C, 56.19; H,
5.92. C16H20O8 requires C, 56.47; H, 5.92%).
Tetramethyl all-trans-bicyclo[2.2.2]oct-7-ene-2,3,5,6-
tetracarboxylate (3b)
Ethyl 2,3-(6,13-dihydro-6,13-pentaceno)pyrrole-1-carboxylate
(11)
To a solution of 2b (59.5 g, 0.17 mol) in dry methanol (500 ml)
was added a 28% methanol solution of sodium methoxide
(1.0 ml) and the mixture was refluxed for 55 h. After checking
completion of the isomerization by 1H NMR (DMSO-d6;
olefinic protons), the mixture was cooled and acetic acid (1.0 ml)
was added. The mixture was concentrated in vacuo to leave a
viscous slurry. The slurry was triturated with ether (100 ml)
and the white precipitates were filtered off. Concentration of
the filtrate gave the title compound as a pale brown viscous
oil: dH (CDCl3) 6.31 (2H, m), 3.75 (6H, s), 3.68 (6H, s), 3.49
(2H, m), 3.18 (2H, m) and 2.96 (2H, m); dC (CDCl3) 173.80,
172.85, 133.09, 52.45, 52.31, 45.14, 40.89 and 35.11; MS (EI)
m/z 340 (M+), 308, 248 and 137; IR (neat) 2954, 1732, 1437 and
1201 cm−1 (Found: C, 56.47; H, 5.99. C16H20O8 requires C, 56.47;
H, 5.92%).
The precipitates were revealed to consist of tetramethyl trans-
cis-trans-bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylate (4b)
and 3b in a ratio of 19 : 1: mp 145 ◦C; dH (CDCl3) 6.54 (1H, t,
J = 6.8 Hz), 6.09 (1H, dd, J = 7.3 and 6.8 Hz), 3.69 (6H, s),
3.66 (6H, s), 3.55 (2H, m), 3.28 (2H, m) and 2.88 (2H, m); dC
(CDCl3) 173.43, 173.02, 136.37, 130.28, 52.30, 52.19, 44.73,
44.42, 35.14 and 34.94; MS (EI) m/z 340 (M+), 308, 248 and
221; IR (neat) 2956, 1730, 1261 and 1207 cm−1. This dried
compound is very hygroscopic and the weight increased during
measurement of the elemental analysis (Found: C, 53.73; H,
5.66. C16H20O8·H2O requires C, 53.63; H, 6.19%).
To a stirred solution of 10 (0.100 g, 0.225 mmol) and ethyl
isocyanoacetate (0.03 ml, 0.27 mmol) in dry THF (10 ml) was
added a solution of potassium tert-butoxide in THF (1.0 M,
0.60 ml) at −20 ◦C. After removal of the cooling bath, the
mixture was stirred. After 12 h, a dilute HCl solution was
added and the mixture was extracted with ethyl acetate. The
organic extract was washed with brine, dried over Na2SO4 and
concentrated. The residue was chromatographed on silica gel
(20% EtOAc–hexane) to give 36 mg of the title pyrrole as
colourless crystals: mp 170 ◦C; dH (CDCl3) 8.61 (1H, br), 8.23–
7.34 (12H, m), 6.79 (1H, d, J = 2.4 Hz), 6.05 (1H, br-s), 5.57 (1H,
br-s), 4.41 (2H, q, J = 7.3 Hz) and 1.49 (3H, t, J = 7.3 Hz); dC
(CDCl3) 170.01, 142.69, 142.03, 133.74, 131.91, 130.22, 129.80,
128.26, 127.48, 127.42, 125.70, 122.17, 121.58, 115.48, 114.48,
60.42, 47.23, 46.71 and 14.63; MS (EI) m/z 415 (M+), 341 and
156; IR (KBr) 3317, 1670, 1415, 1323, 1288, 1126 and 760 cm−1
(HRMS Found: 415.1570. C29H21NO2 requires 415.1572).
2,3;7,8;12,13;17,18-Tetrakis(6,13-dihydro-6,13-pentaceno)-
21H,23H-porphine (12)
To a stirred solution of 11 (0.416 g, 1.00 mmol) in dry THF
(15 ml) was added LiAlH4 (0.14 g, 3.70 mmol) at 0 ◦C. After
disappearance of 11 by TLC, water was added. The suspension
was filtered through a Celite pad which was thoroughly washed
with chloroform. The extract was dried over Na2SO4 and
filtered. The volume was increased to 250 ml by addition of
chloroform and p-TsOH (0.03 g) was added. After the mixture
was stirred overnight at room temperature in the dark, p-
chloranil (0.05 g) was added. The mixture was further stirred
for 1 day. The mixture was washed with sat. NaHCO3, water
and brine, dried over Na2SO4 and concentrated. The residue
was chromatographed on silica gel (40% EtOAc–hexane) and
then recrystallized from dichloromethane–hexane to give 0.106 g
(30%) of the title compound as a red powder: mp >300 ◦C; dH
(CDCl3) 10.75 (4H, s), 8.36 (16H, s), 7.81 (16H, m), 7.44, (8H, s),
7.38 (16H, m) and −4.75 (2H, br); dC (CDCl3) 143.02, 131.68,
127.40, 125.79, 122.53, 98.74, 49.55 and a- and b-carbons of
porphyrin ring could not be found due to tautomerisom of the
trans-15-Chloro-16-phenylsulfanyl-6,13-dihydro-6,13-
ethanopentacene (9)
To a solution of 8 (0.200 g, 0.657 mmol) in dry dichloromethane
(15 ml) was added freshly prepared PhSCl16 (0.093 ml,
0.788 mmol) at room temperature and the mixture was stirred
for 3 days. After removal of the solvent, the residue was
chromatographed on silica gel to give 0.291 g (99%) of the title
◦
compound as colourless crystals: mp 183 C; dH (CDCl3) 7.85
(1H, s), 7.84–7.74 (4H, m), 7.80 (1H, s), 7.78 (1H, s), 7.71 (1H, s),
7.51–7.41 (6H, m), 7.38–7.27 (3H, m), 4.68 (1H, d, J = 2.8 Hz),
4.53 (1H, d, J = 2.5 Hz), 4.26 (1H, dd, J = 3.9 and 2.8 Hz), 3.74
4 5 2
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 4 4 8 – 4 5 3