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The porphyrin handbook - Kadish K.M.

Kadish K.M. The porphyrin handbook - Academic press, 2000. - 368 p.
Download (direct link): kadishsmishgulilard2000.djvu
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asymmetric unit displays a dramatically different conformation. In this
case, the dihedral angles between the rings and the plane through
Figure 25. The X-ray crystal structure of the calix[2]pyridino[2]-pyrrole
22 showing hydrogen bonds between adjacent pyrrole and pyridine rings.
Crystal structure originally published in Krai, V.; Gale, P. A.;
Anzenbacher Jr., P.; Jursikova, K.; Lynch, V.; Sessler, J. L. Chem.
Commun. 1998, 9. Diagram produced using data from the Cambridge
Crystallographic Database.
the bridging mew-like carbon atoms arc 51.2(2), 89.3(2), 55.5(2) and
21.5(2) for rings I to 4, respectively.
The single crystal X-ray structure of the calix(4Ipyridine
20 was also solved.It revealed that the molecule adopts a flattened
partial cone conformation in the solid state (the dihedral angles between
pyridine rings and plane through the calixpyridine mew-carbon atoms are
10.4(2), 82.5 (2), 80.8(2) and -79.0(2) . respectively) (Figure 27). In
this
274
Sessler and Gale
Figure 26. The X-ray crystal structure of the two crystallographically
distinct molecules (a and b) of calix[3]pyridino[1 ]pyrrole 23 in the
unit cell. Crystal structure originally published in Krai, V.; Gale, P.
A.; Anzenbacher Jr., P.; Jursfkova, K.; Lynch, V.; Sessler, J. L. Chem.
Commun. 1998, 9. Diagram produced using data from the Cambridge
Crystallographic Database.
Scheme 3. Synthesis of calix[3]indole.
MeO'
Figure 27. The X-ray crystal structure of the tetrachloro-meso-
octamethylcalix[4]pyridine 20. Crystal structure originally published in
Krai, V.; Gale, P. A.; Anzenbacher Jr., P.; Jursfkova, K.; Lynch, V.;
Sessler, J. L. Chem. Commun. 1998, 9. Diagram produced using data from
the Cambridge Crystallographic Database.
case there is only one crystallographically distinct calix[4]-pyridine
molecule in the unit cell.
X. Related Heterocalixarene Analogues
A. CALIXINDOLES
Calixarene analogues containing indole rings have been synthesized
recently by Black and coworkers.82 In initial studies, 4,6-dimethoxy-3-
methylindole 24 was condensed with a range of aryl aldehydes in the
presence of phosphoryl chloride to produce the calix[3]indoles 25 in
moderate to high yields (Scheme 3).82 The same calix[3]indoles were also
produced from the intermediate hydroxymethyl compounds.
a, R = Ph 12%
b: H = p-ClC6H4 83%
c. H = o-CIC6H4 10%
d, R = p-BrCeH4 81%
The crystal structure of compound 25d revealed that the
calix[3Jindole adopts a flattened partial cone conformation in the solid
state, that is, one indole NH points up, one down, and one is almost flat
in the plane of the macrocycle (Figure 28).83
Similarly, the reaction could be repeated substituting 3-aryl-4,6-
dimethylindoles for 3-methyl-4,6-dimethoxyin-dole.84-85 However, when 3-
arylindoles were condensed with formaldehyde in the presence of
phosphoryl chloride, an intractable mixture of products was produced.
Hydro-xymethylated 3-arylindoles were therefore prepared by reduction of
the corresponding aldehydes,86 and the acid-catalyzed reactions of these
materials were studied.87 Vilsmeier formylation (using one equivalent of
the reagent) of a 3-arylindole followed by a purification step yielded
the 7-carbaldehyde as the major product but also yielded some 2-
carbaldehyde. Use of two equivalents of the Vilsmeier reagent readily
yielded the 2,7-dicarbaldehyde. Reduction of all these compounds with
sodium borohydride gave the hydroxymethylated indoles. Both the 2- and 7-
hydroxy-methylated compounds could be individually condensed to form a
calix[3]indole, and interestingly, the 2,7-dihydrox-
45 / Calixpyrroles: Novel Anion and Neutral Substrate Receptors
275
Figure 28. The X-ray crystal structure of calix[3]indole 25d. Crystal
structure originally published in Black, D. S.; Craig, D. C.; Kumar,
N. Aust j. Chem. 1996, 49, 311. Diagram produced using data from
R
a 4-BrC6H^ b 4-ClC6H4 4-FC6H4
3.4-Cl2C6H3
26
ymethylated compound could be condensed either with a 3-aryl indole or a
diindolylmethane to produce a calix[3]-indole.
By tuning the reaction conditions, calix[4Jindoles have been
isolated.ss For instance, when the 7-hydroxymethy-lindole is condensed in
THF in the presence of hydrochloric acid, the calix|4|indole 26a was
found to precipitate in a yield of 25%.
The crystal structure of the calix[4Jindole 26a was elucidated and it
was found that the molecule adopts a 1,3-alternate conformation in the
solid state forming a "square" channel (Figure 29) that is analogous to
what is seen in the
1,3-alternate conformation of calixarenes.s4
In a recent paper, Black and coworkers have reported the preparation
of calix|3|indoles that are locked into a rigid cone conformation.411 As
a predicate to this work, these researchers found that the 'H NMR spectra
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