Syntheses of symmetrically substituted 5-alkyl- and 5-aryl-dihydrodipyrrins and of porphyrins and bisporphyrins therefrom
1997
Acid-catalysed treatment of 2-unsubstituted pyrroles with alkyl or
aryl acetals affords good yields of the corresponding symmetrical
5-substituted dihydrodipyrrins (e.g. 7, 19, 38, 51,
52). Using MacDonald ‘2 + 2’ methodology, such
dihydrodipyrrins are transformed in several steps into
5,15-disubstituted porphyrins (e.g. 5, 23, 24, 26,
36), wherein the 5- and 15-substituents can be identical or different.
Further functionalization of 5 affords
nickel(II) 5-vinyl-15-substituted porphyrin 4
which, after Vilsmeier formylation (POCl3–DMF) of the
nickel(II) complex, yields the corresponding
nickel(II) 5-(formylvinyl)porphyrin 3;
cyclization under acidic conditions then gives the nickel
15-phenylbenzochlorin 1. Nickel(0)-catalysed reductive dimerization of
the nickel(II)
15-(p-chloromethylphenyl)porphyrin 48 yields the
dihydrostilbene dimer 53, which can also be obtained in lower yield by
reductive dimerization of
5-(p-chloromethylphenyl)dihydrodipyrrin 57, followed
by MacDonald-type cyclization and metallation of the free-base dimer
54.
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