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Short Communications
of 1 : 2 : 2 6 gave (4) after column puri cation. The
crystals that formed directly from evaporation of pure
fractions in ethyl acetate/hexane were found to be
suitable for X-ray structure determination.
identical spectral data to ours, but a di erent melting
point (176–178 ).
Attempts to form porphyrins by cyclotetramerization
of (1) by using either formaldehyde or benzaldehyde
under various acidic conditions met with very limited
success. Traces of porphyrin were detected by the
presence of a Soret band in the visible spectra of the
crude tarry products, but no pure porphyrins have so
far been isolated.
Experimental
Ethyl isocyanoacetate14 and 2,3-bis(phenylsulfonyl)buta-1,3-
diene11 were prepared as described. Tetrahydrofuran was freshly
distilled from sodium and benzophenone. All solvents were
analytical reagent grade. Silica gel for ash chromatography
was Merck 9385, 230–400 mesh.
3-(Phenylsulfonyl)-N-( p-tolylsulfonyl)-3-pyrroline (5)
To a suspension of sodium hydride (0 69 g of 60% dispersion
in oil, c. 17 mmol, prewashed with hexane) in tetrahydrofuran
(60 ml), under nitrogen, was added 2,3-bis(phenylsulfonyl)buta-
1,3-diene (1 2 g, 3 6 mmol). Solid p-toluenesulfonamide (2 66
g, 15 5 mmol) was added in c. 0 5 g portions over a few minutes,
causing evolution of hydrogen. After 20 min, t.l.c. analysis
showed the absence of starting butadiene. Ethanol (1 ml) was
added to quench excess sodium hydride, then the solvents were
removed under vacuum. Dichloromethane (100 ml) was added,
and the solution was washed successively with 2 M HCl, water,
10% NaOH, and water (2 50 ml each). The dichloromethane
solution was dried over anhydrous sodium sulfate, and the
solvent was evaporated under vacuum to yield a pale yellow oil
(1 16 g) which was used without further puri cation for the
next step. N.m.r. (CDCl3) 2 44, s, CH3; 4 23, symmetrical
m, 2 CH2; 6 61, quintet, J 1 8 Hz, =CH; 7 31, 7 85, AA0BB0,
tolyl ring H; 7 5–7 7, m, Ph ring H. Mass spectrum (e.s.i.)
386 3 (M+Na)+.
Fig. 1. Molecular conformation and atom numbering scheme
for molecule 1 in crystals of compound (4). Unless otherwise
indicated, atoms are carbon.
Compound (4) was found to crystallize with two
independent and conformationally di erent molecules
(molecules 1 and 10) in the crystallographic asymmetric
unit (Fig. 1 shows molecule 1). These molecules are
pseudo-mirror-related, one being transformed into the
other by rotation of the p-tolyl group about the N(7)–
S(1) bond vector. The similarities between the molecules
may be observed in the respective magnitudes of the
torsion angles along the ethoxycarbonyl and p-tolyl
groups for molecules 1 and 10 (although the signs are
opposite) {N(1)–C(2)–C(16)–O(4) [176 5, 171 9(2) ];
C(2)–C(16)–O(4)–C(17) [ 176 0, 178 4(2) ]; C(16)–
O(4)–C(17)–C(18) [ 178 4, 173 6(2) ]; N(7)–S(1)–
C(9)–C(10) [ 86 3, 86 4(2) ]; C(6)–N(7)–S(1)–C(9)
[73 9, 69 5(2) ]}. The ester carbonyl lies in the
syn orientation with respect to the pyrrolic N–H. The
folding of the reduced ring is greater for molecule
1 than for molecule 10, as measured by the torsion
angles C(4)–C(3)–C(6)–N(7) [8 4, 3 0(2) ] and C(3)–
C(4)–C(8)–N(7) [ 6 9, 1 4(2) ], but the deviations
of the bicyclic core from planarity are small for both
molecules.
Ethyl 5-( p-Tolylsulfonyl)-2,4,5,6-tetrahydropyrrolo[3,4-
c]pyrrole-1-carboxylate (4)
To a suspension of sodium hydride (0 27 g of 60% dispersion
in oil, c. 6 8 mmol, prewashed with hexane) in tetrahydrofuran
(20 ml) was added dropwise over 10 min, under nitrogen, a
mixture of the crude 3-pyrroline (5) (1 16 g, c. 3 2 mmol)
and ethyl isocyanoacetate (0 7 ml, 6 4 mmol) in tetrahydro-
furan (20 ml). After stirring for 2 h at room temperature,
ethanol (0 5 ml) was added, and the solvents were removed
under vacuum. Dichloromethane (100 ml) was added, and the
solution was washed with saturated brine (2 50 ml), dried
over anhydrous sodium sulfate, and the solvent was evaporated
under vacuum to yield a brownish oil. N.m.r. spectroscopy
showed the presence of the required ester and a large number of
minor components. The crude product was subjected to column
chromatography, eluting with 1 : 1 ethyl acetate/hexane. T.l.c.
and n.m.r. analysis of the fractions showed a narrow band
of very pure material, which formed colourless plates upon
slow evaporation of the combined solutions (83 mg, 8%), m.p.
187 5–189 (Found: C, 57 4; H, 5 4; N, 8 2. C16H18N2O4S
requires C, 57 5; H, 5 4; N, 8 4%). 1H n.m.r. (CDCl3) 1 33,
t, CH2CH3, J 7 0 Hz; 2 41, s, ArCH3; 4 27, q, CH2CH3, J
7 0 Hz; 4 42, 4 56, br s, 2 CH2; 6 61, d, pyrrole CH; 7 31,
7 77, AA0BB0, tolyl ring H; 8 93, br, NH. 13C n.m.r. (CDCl3)
14 4, 21 36, 48 0, 48 9, 60 4, 113 6, 114 5, 124 4, 127 3,
129 4, 127 7, 134 4, 143 3, 160 4. Mass spectrum (e.s.i.)
The ethyl ester (4) was subjected to saponi cation
and decarboxylation by heating with a 50-fold excess of
potassium hydroxide in ethylene glycol at 165 . The
-
free pyrrole (1) was isolated by column chromatography
and crystallized to give a product indicated to be pure by
elemental analysis and spectroscopy, with melting point
190–192 . This compound was previously reported
by Jendralla and Fischer, who prepared it on a large
scale by a totally di erent route from 1,4-dibromo-
2,3-bis(bromomethyl)but-2-ene.13 Their product had
357 (M+Na)+. I.r.
1328s, 1166s, 1145m, 664m cm
(KBr) 3721s, 1682s, 1432m, 1346m,
1
max
.
Arnold, Dennis P.
