5136 J . Org. Chem., Vol. 62, No. 15, 1997
Paolesse et al.
dihydrobromide 7 (0.5 g, 0.83 mmol),16a and TsOH hydrate
(0.25 g) were dissolved in 100 mL of absolute ethanol, and the
mixture was heated at reflux in the dark (aluminum foil).
Progress of the reaction was monitored spectrophotometrically;
when absorbances attributable to 714 disappeared, the solvent
was evaporated under vacuum, the resulting solid was redis-
solved in CH2Cl2, washed with water (three times), and dried
over anhyd Na2SO4. The solvent was evaporated under
vacuum, and the crude mixture was chromatographed on silica
gel; the column was first eluted with CH2Cl2 to yield two
bands. The first (red-brown) fraction to be eluted contained
10 (65 mg) together with traces of 11, while the second (red-
violet) fraction contained 12 (48 mg). These compounds were
identified on the basis of comparison of their spectral proper-
ties with those in the literature1,2,14 and by comparison with
authentic samples. The column was then eluted with CH2Cl2
containing increasing amounts of methanol (2-10%). A green
fraction was collected, the solvent was evaporated under
vacuum, and the residue was crystallized from CH2Cl2/hexane
to give 9 as its p-toluensulfonate salt (158 mg, 20%), mp >
300 °C. UV-vis: λmax 434 nm (ꢀ 112 000), 456 (360 000), 579
F igu r e 2. Changes in the 1H NMR spectrum of [2H‚9]2+[F-
PF6-] in CDCl3 by dilution: trace A, 10-3 M solution; trace B,
10-5 M solution.
1
(6500), 627 (16 000), 680 (18 500); H NMR: δ 11.50, 11.48,
11.46, 11.45, 11.43, 11.40, 11.38, 11.34 (s, 4 H), 5.33 (d, J 8.0
Hz, 4 H), 4.64/4.45 (m, 12 H), 4.20/4.05 (s, 18 H), 2.30 (t, J 8.0
Hz, 12 H), 1.85 (s, 6 H), -5.22/-5.81 (br s, 5 H). FAB-MS: 573
(M+); 287 (M2+). Anal. Calcd for C52H61N5O6S2: C, 68.17; H,
6.71; N, 7.64. Found: C, 68.05; H, 6.94; N, 7.21. The
dihydrochloride derivative was obtained by washing a CH2-
Cl2 solution of [2H‚92+](pTSA)2 with saturated Na2CO3 until
spectrophotometry showed the formation of the corresponding
free base; subsequent treatment with dilute HCl quantitatively
afforded [2H‚92+]Cl2. UV-vis: λmax 456 nm (ꢀ 551 000), 577
(5 200), 627 (15 500), 681 (19 100). 1H NMR: δ 11.69, 11.66,
11.63, 11.60 (s, 4 H), 4.71 (m, 8 H), 4.24/4.05 (s, 18 H), 2.28 (t,
J 7.5 Hz, 12 H), -4.22, -4.24, -4.47, 4.88, 4.92 (br s, 5 H).
Anal. Calcd for C38H47Cl2N5: C, 70.79; H, 7.35; N, 10.86.
Found: C, 70.56; H, 7.11; N, 10.31. [2H‚92+](F)(PF6) can be
obtained following the procedure previously reported by
Sessler.8a
even in CDCl3, in the spectra of the [2H‚9 ]
2+ 2+[X-Y-]
species, where X and Y represent the counterions. When
X ) Y ) Cl-, four resonances are observed, as expected
on the basis of symmetry considerations, while eight
peaks are present in the spectrum when X ) Y ) pTSA-
or X ) F- and Y ) PF6-. The effect of dilution upon the
spectral pattern is shown in Figure 2 for [2H‚9]2+[F-
PF6-]; trace A shows the low field region of the spectrum
of a 10-3 M solution, with eight resonances meso-proton
between 11.25 and 10.80 ppm. At 10-5 M the spectrum
shown in trace B is observed, with only four resonances
shifted to lower field (11.83-11.75 ppm). Such spectral
changes are consistent with the unsymmetrical sapphy-
rin molecules existing as stacked aggregates, even in
CHCl3. The NMR data interpretation is confirmed by
the observation that Beer's law is not observed by
[2H‚9]2+(pTSA)2 even in CHCl3.
Rou te b. Pyrrole 8 (0.5 g, 3.31 mmol) and biladiene 7 (0.5
g, 0.83 mmol) were dissolved in 100 mL of acetic acid and
refluxed under dark (aluminum foil) for 1 h. The solvent was
evaporated under vacuum, and the resulting solid was redis-
solved in CH2Cl2, washed with saturated Na2CO3 and then
with dilute HCl, and dried over anhyd Na2SO4. The solvent
was evaporated under vacuum and the crude mixture was
chromatographed on silica gel as reported in route a. The
appropriate green fraction was collected, the solvent was
vacuum evaporated to give [2H‚92+]Cl2 (98 mg, 18%).
13,17-Diet h yl-2,3,7,8,12,18,22,23-oct a m et h ylsa p p h y-
r in (13). This sapphyrin was obtained following the procedure
described above for 9, starting from 3 (0.5 g, 4.06 mmol)16a
and 7 (0.5 g, 0.83 mmol). In this case 5 (42 mg) and 12 (54
mg) were obtained as byproducts; [2H‚132+](pTSA)2 was
obtained in 24% yield (184 mg). Mp > 300 °C. UV-vis: λmax
432 nm (ꢀ 69 000), 457 (415 000), 577 (4 600), 628 (15 000),
683 (18 000). 1H NMR: δ 11.51, 11.49, 11.43, 11.39 (s, 4 H),
5.34 (d, J 8.0 Hz, 4 H), 4.65 (m, 8 H), 4.20/4.05 (s, 24 H), 2.31
(t, J 8.0 Hz, 6 H), 1.88 (s, 6 H), -5.20, -5.35, -5.75, -5.80 (br
s, 5 H). FAB-MS: 545 (M+); 273 (M2+). Anal. Calcd for
Con clu sion s
Fully 30 years since their original disclosure, sapphy-
rins are increasing in interest due notably to their
unusual chemical, physical, and spectroscopic character-
istics. A novel synthetic approach is reported which
allows the preparation of sapphyrins by an acidic con-
densation reaction between 1,19-diunsubstituted a,c-
biladienes and 3,4-dialkylpyrrole-2-carbaldehydes. This
methodology avoids the preparation of bipyrrolic inter-
mediates and enables the preparation of sapphyrins with
an unsymmetrical distribution of the peripheral substit-
uents; such substances were previously impossible to
obtain using the classical MacDonald-type approach.
Exp er im en ta l Section
C
50H57N5O6S2: C, 67.62; H, 6.47; N, 7.89. Found: C, 67.32;
General conditions are as previously reported,19 with the
exception that 1H NMR spectra were measured in CDCl3
solution at 400 MHz using a Bruker AM 400 spectrometer,
mass spectra were obtained using a VG Quattro spectrometer
(FAB mode), elemental analyses were obtained from the
Microanalytical Laboratory at University of Padova, Italy, and
electronic absorption spectra were measured in CH2Cl2 or
CHCl3 using a Philips PU8700 spectrophotometer.
H, 6.71; N, 7.91. [2H‚132+]Cl2 was obtained as reported for 9.
UV-Vis: λmax 456 nm (ꢀ 524 000), 576 (5 500), 624 (16 000),
686 (19 000). 1H NMR: δ 11.60, 11.56, 11.51, 11.45 (s, 4 H),
4.60 (m, 4 H), 4.22, 4.04 (s, 24 H), 2.20 (t, J 7.0 Hz, 6 H), 1.88
(s, 6 H), -4.34, -4.40, -4.74, -5.06, -5.10 (br s, 5 H). Anal.
Calcd for C36H43Cl2N5: C, 70.12; H, 7.03; N, 11.36. Found:
C, 69.99; H, 7.11; N, 11.11.
2,3,13,17-Tetr aeth yl-7,8,12,18,22,23-h exam eth ylsapph y-
2,3,7,8,12,13,17,18,22,23-Decam eth ylsapph yr in (4). This
compound was obtained in 21% yield from 214 and 3, as
reported above. Spectral properties were in accord with data
previously reported7 and with an authentic sample prepared
according to the literature.7
r in (9). Rou te a . Pyrrole 8 (0.5 g, 3.31 mmol),16a a,c-biladiene
(19) Wallace, D. M.; Leung, S. H.; Senge, M. O.; Smith, K. M. J .
Org. Chem. 1993, 58, 7245.