Nitric acid promoted formation of an N-confused porphyrin-derived porphodimethene and a violinoid

The nitration of free-base N-confused porphyrin led to a novel 5, 10-meso-dihydroxy-N-confused porphodimethene and an open-ring N-confused violinoid. The results support nitration occurring first, followed by nucleophilic addition of a hydroxyl group and a parallel reaction of oxygenolysis to cause the ring-opening. The nitro group substituted at the inner carbon of the inverted pyrrole ring is located on both the porphodimethene and violinoid. In the case of the porphodimethene, two dihydroxyl groups with v(OH) at 3404 cm(-1) are arranged in a syn conformation at the same side with the nitro group. The violinoid exhibits v(C=O) at 1659 cm(-1). NMR and structure determination suggest that oxygenolysis occurs selectively at the C=C bond between the a-pyrrole and meso carbon closest to the amino NH of the inverted pyrrole ring. The single crystal structure of porphodimethene gave a 50% disorder between the peripheral nitrogen and carbon atom on the inverted pyrrole ring, while a dimeric structure assembled through hydrogen bonding interactions was observed in the crystal lattice of the violinoid. Copyright (c) 2006 Society of Porphyrins & Phthalocyanines.