Cascade Amination and Aza-6π-Annulation-Aromatization Strategy for the Synthesis of β-Pyrimidine-Fused Porphyrins

Novelnickel-(II) and copper-(II) complexes of 2-(N,N-dimethylformamidine)-3-formyl-5,10,15,20-tetraarylporphyrinshave been synthesized for the first time from 2-aminoporphyrins underVilsmeier-Haack conditions. These porphyrins are utilized asnew building blocks to construct diverse beta-pyrimidine-fused5,10,15,20-tetraarylporphyrins in good yields via a cascade ammonia-mediated condensation and intramolecular aza-6 pi-annulation/aromatizationin 1,2-dichloroethane at 80 degrees C. Furthermore, copper-(II) beta-pyrimidine-fusedporphyrins underwent demetallation in the presence of conc. H2SO4 to afford free-base porphyrins, which on zincinsertion using Zn-(OAc)(2) in CHCl3-MeOHprovided zinc-(II) beta-pyrimidine-fused porphyrins in appreciableyields. Notably, these newly synthesized pi-extended porphyrinsdisplayed a modest bathochromic shift in their electronic absorptionand emission spectra as compared to the traditional meso-tetraarylporphyrins. However, the protonated porphyrins (2a) and (3g) displayed a significant red-shifted absorption.

Automated summary

Novelnickel-(II) and copper-(II) complexes of 2-(N,N-dimethylformamidine)-3-formyl-5,10,15,20-tetraarylporphyrins have been synthesized for the first time from 2-aminoporphyrins under Vilsmeier-Haack conditions. These porphyrins are utilized as new building blocks to construct diverse beta-pyrimidine-fused 5,10,15,20-tetraarylporphyrins in good yields via a cascade ammonia-mediated condensation and intramolecular aza-6 pi-annulation/aromatization in 1,2-dichloroethane at 80 degrees C. Furthermore, copper-(II) beta-pyrimidine-fused porphyrins underwent demetallation in the presence of conc. H2SO4 to afford free-base porphyrins, which on zinc insertion using Zn-(OAc)(2) in CHCl3-MeOH provided zinc-(II) beta-pyrimidine-fused porphyrins in appreciable yields. Notably, these newly synthesized pi-extended porphyrins displayed a modest bathochromic shift in their electronic absorption and emission spectra as compared to the traditional meso-tetraarylporphyrins. However, the protonated porphyrins (2a) and (3g) displayed a significant red-shifted absorption.