A new synthesis of pyrroles and porphyrins fused with aromatic rings

Abstract

Pyrroles fused with aromatic rings (isoindole derivatives) have been readily prepared by the reaction of aromatic nitro compounds with ethyl isocyanoacetate in the presence of DBU. The ease of this reaction depends on the aromaticity of the starting nitro aromatics. Polycyclic aromatic nitro compounds such as 1-nitroacenaphthylene or 9-nitrophenanthrene are more reactive than simple nitro aromatics such as nitrobenzene or nitronaphthalenes and give the corresponding pyrroles in good yields. Pyrroles prepared by this method have been converted into porphyrins fused with various aromatic rings by the reduction with LiAlH, followed by treatment with an acid catalyst and oxidation with chloranil or oxygen. Tetra-lY2-naphthoporphyrin has been prepared by the reaction of 2-nitro-3,4dihydronaphthalene or 1-nitronaphthalene with ethyl isocyanoacetate followed by reduction, tetramerization and oxidation. Thus, highly conjugated porphyrins are readily prepared starting from aromatic nitro compounds, and their electronic and optical properties can be controlled by choice of the starting aromatic nitro compound.

Five‐Membered Heterocycles: Pyrrole and Related Systems

“…Synthesis of the fused pyrrole derivatives 114 and 115 from 9-nitrophenanthrene (116) constitutes an interesting application of the Barton-Zard approach (Scheme 4.33) [160,161]. Other condensed nitroaromatics, such as 3-nitrobenzothiophene, also give fused pyrrole derivatives under these conditions [162]. In cases where relatively unreactive nitroaromatics are involved, the use of a strong phosphazene base may give improved yields [163].…”

Linearly -π- extended porphyrins: Synthesis of novel tetrabenzoylporphyrins

“…In the 1 H NMR spectra porphyrins the internal NH protons are shielded due to a ring current effect of the aromatic macrocycle [13][14][15][16]. Thus, the NH of porphyrin 11a containing no phenyl groups at the meso-position resonates at δ = -3.25.…”

“…The π-electron system of the porphyrin macrocycles have been reported to be extended by peripheral substituents at the meso-/β-positions [10][11][12][13], or fused polycyclic ring systems [14][15][16]. Although extension of the chromophore by introducing fused aromatic rings or single chromophoric groups (e.g., C=O, CN, or ester) was expected to produce a major bathochromic shift, in many cases the effects are actually rather small [9,10,17].…”

Synthesis and evaluation of the antiproliferative activity of novel isoindolo[2,1-a]quinoxaline and indolo[1,2-a]quinoxaline derivatives

“…Condensation of nitrocyclohexenes with ethyl isocyanoacetate in the presence of 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU) afforded the corresponding fused pyrroles 2a-b using a Barton-Zard reaction [14][15][16] . The not commercially available, starting material 2-nitro-3,4-dihydronaphthalene was readily prepared by the nitration of the corresponding alkene 17 .…”