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 & DEG;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 were synthesized for the first time using Vilsmeier-Haack conditions. These porphyrins were then used as building blocks to construct diverse β-pyrimidine-fused 5,10,15,20-tetraarylporphyrins in good yields through a cascade ammonia-mediated condensation and intramolecular aza-6 π-annulation/aromatization in 1,2-dichloroethane at 80°C. Additionally, copper-(II) β-pyrimidine-fused porphyrins underwent demetallation in the presence of conc. H2SO4 to afford free-base porphyrins, which were further inserted with zinc to obtain zinc-(II) β-pyrimidine-fused porphyrins.