Pyrroles condensation with aryl aldehydes

Tietze et al. (88LA9) (Scheme 77) alkylated 2-hydroxybenzaldehyde with 5-bromo-2-methylpent-2-ene and 1 //-pyrrole-2-carbaldehyde with l-bromo-3-methyl-but-2-ene and obtained the corresponding aryl aldehydes 246 and 248. Condensation of the latter with pyrazol-3-one 262 in acetonitrile containing ethylenediamine diacetate as a catalyst provided (7 /Z)-4- 2-[(4-methylpent-3-enyl)oxy]benzylidine -pyrazol-3-one 247 and ( /Z)-4- [l-(3-methylbut-2-enyl)-177-pyrrol-2-yl]methylene -pyrazol-3-one 249, in 67 and 99% yield, respectively. 

Analogous condensations with a pyrrole aldehyde lead to mesomeric dipyrro-methene cations, which play an important part in porphyrin synthesis. Under appropriate conditions one can combine four mol equivalents of pyrrole and four of an aromatic aldehyde to produce a tetra-aryl substituted porphyrin in one pot. ... 

Similar conditions were used to prepare pyrroles from both t-butyl and benzyl isocyanoacetate. <94JHC255, 94S170> The reaction was also effective for preparing some rather hindered 3-aryl-4-methylpyrrole-2-carboxylates. Several p-methylnitrostyrenes were prepared by condensation of an aromatic aldehyde with nitroethane. These nitrostyrenes condensed with ethyl or methyl isocyanoacetate. Even o,o -disubstituted... 

In all the glycoporphyrins presented above, a carbohydrate moiety is linked directly to an aryl substituent. However, it is possible to have meso-glycosylarylporphyrins with the carbohydrate moiety separated from the aryl group by a spacer. This has been achieved by Bolbach et al. either by direct glycosylation of the ortho- or para-hydroxyalkoxyarylporphyrins (Sect. 3.2.1) or by condensation of required aldehydes with pyrrole [120]. The latter procedure gave rise to the monoglycosylporphyrins 116(o,p)-119(o,p) (Fig. 15). 

The synthetic route into p-octafluorinated corroles is somewhat different from the Lewis acid-catalyzed macrocyclization under dilute conditions used for p-octafluoroporphyrins. The most successful route employs a neat condensation of pyrrole and aryl aldehydes, which was first demonstrated with non-fluorinated corroles [3,33]. Solutions of these two reactants are combined in the presence of basic alumina, heated to evaporate the solvent, concentrate the reactants, and initiate cyclization. A DDQ oxidative quench results in several maCTOcyclic compounds, including the corrole (6-8 % yield) (Schane 12). 

The condensation of furo[3,2- ]pyrrole-type aldehydes 8g and 265-267 with hippuric acid was carried out in dry acetic anhydride catalyzed by potassium acetate as is shown in Scheme 26. The product methyl and ethyl 2-[( )-(5-oxo-2-phenyl-l,3-oxazol-5(4//)-ylidene)methyl]furo[3,2- ]pyrrol-5-carboxylates 268a-d were obtained. The course of the reaction was compared with the reaction of 5-arylated furan-2-carbaldehydes with hippuric acid. It was found that the carbonyl group attached at G-2 of the fused system 8 is less reactive than the carbonyl group in 5-arylated furan-2-carbaldehydes in this reaction <2004MOL11>. The configuration of the carbon-carbon double bond was determined using two-dimensional (2-D) NMR spectroscopic measurements and confirmed the (E) configuration of the products. 

A mixture of suitable glycosylated benzaldehyde and 4-pyridinecarbox-aldehyde was used to synthesize unsymmetrical porphyrin derivatives. For example, to prepare a porphyrin with three pyridyl and one protected mono- or disaccharide aryl group at the meso-positions, Bolbach at al. carried out the condensation of a mixture of pyrrole with glycosylacetylated benzaldehyde and 4-pyridinecarboxaldehyde in propionic acid with 10% acetic anhydride (which prevented the deacetylation of the glycosylated moiety). The yields of chromatographically pure porphyrins were about 6-7% (Scheme 35). 

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