A. J. F. N. Sobral et al. / Tetrahedron Letters 44 (2003) 3971–3973
3973
3. Conclusions
Cambridge CB2 1EZ, UK (Fax: +44(0)-1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk).
The synthesis of unsubstituted dipyrromethanes in water
is an efficient process giving good yields of pure com-
pounds. When pyrrole and an aldehyde or a ketone are
made to react in a aqueous medium in the presence of
an acid catalyst, the reaction proceeds with attack in a
very selective way to the a-positions of the pyrrole and
with direct isolation of the product dipyrromethane from
the reaction medium, providing for its stabilization.
Acknowledgements
We thank Chymiotechnon and FCT Sapiens POCTI/
QUI/42536/2001 for financialsupport. Wewould also like
to thank Professor Hugh D. Burrows, for interesting
discussions on the two-phase reactions and MSc. S o´ nia
Ribeiro and Dr Alexandra Gonsalves, for assistance on
the GC–MS analysis.
Besides being a cheap, non-toxic and environment
friendly solvent, water joins the physico-chemical char-
acteristics required to reach the goal of finding the way
to make simple dipyrromethanes. The synthesis of
dipyrromethanes in water involves little or no subsequent
purification procedures and needs no excess of pyrrole,
as previously known methods. Our approach is of value
for meso mono and di-substituted or free meso-
dipyrromethanes and has the advantage of avoiding the
environmental disturbing solvents.
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4. Experimental
In a typical experiment, to a solution of 15 ml (0.14 mol)
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3
0 to 45 min the suspension is left to cool to 40–50°C
and then the upper layer is transferred and allowed to
cool to room temperature. The product crystallizes in
large pale white crystals. meso-Phenyl-2,2%-dipyrro-
methane 3, dipyrromethane 4 and meso-(4-nitrophenyl)-
2
,2%-dipyrromethane 5 gave physical data in full concor-
7c
dance with the literature. Dipyrromethanes 1 and 2 are
new compounds and have the following physical data: (1)
meso-diethyl-2,2%-pyrromethane: mp: 108.5–110°C. Ele-
mental analysis for C H N : calcd% (C, 77.1; H, 8.9;
1
3
18
2
1
N, 13.3). Found%: (C, 76; H, 8.9; N, 13.4). H NMR
solvent: CDCl ; internal standard: TMS): l=0.60 (6H,
(
3
t, J=7.4 Hz, CH -CH -C), 1.80 (4H, q, J=7.4 Hz,
3
2
CH -CH -C), 6.0 (4H, m, pyrrole-H), 6.40 (2H, m,
3
2
−
1
pyrrole-H), 7.2 (2H, ls, NH). FT-IR (cm ; group): (2933,
CꢀC), (3361, wN-H). GC–MS: C H N needs 202, found
13
18
2
by EI+: M+ at m/z=202. (2) meso-Methyl-meso-phenyl-
2
,2%-pyrromethane: mp: 102–104°C. Elemental analysis
for C H N : calcd% (C, 81.3; H, 6.8; N, 11.8). Found%:
1
6
16
2
1
(
C, 81.4; H, 6.8; N, 11.3). H NMR (solvent: CDCl ;
3
internal standard: TMS): l=2.0(3H, s, CH -C), 5.97(2H,
m, pyrrole-H), 6.17 (2H, m, pyrrole-H), 6.60 (2H, m,
pyrrole-H), 7.1 (2H, PhH , m), 7.2 (3H, PhH , m), 7.3,
3
9. (a) Geier, G. R., III; Lindsey, J. S. J. Chem. Soc., Perkin
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m
o,p
−
1
(
2H, ls, NH). FT-IR (cm ; group): (2974, CꢀC), (3385,
N-H). GC–MS: C H N needs 236, found by EI+: M+
at m/z=236.
1
6
16
2
1
1. (a) Jiuh, K.; Wu, J.-Y.; Chen, C.-T. Acta Crystallogr.
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Acta Crystallogr. 1999, C55, 1079–1082.
Crystallographic data (excluding structure factors) for
the structures 1 and 2 in this paper have been deposited
with the Cambridge Crystallographic Data Centre as
supplementary publication numbers CCDC 205932 and
CCDC 205933. Copies of the data can be obtained, free
of charge, on application to CCDC, 12 Union Road,
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