Substituent effects in tetrapyrrole subunit reactivity and pinacol-pinacolone rearrangements: Vic-dihydroxychlorins and vic-dihydroxybacteriochlorins

✍ Scribed by Ravindra K. Pandey; Fuu-Yau Shiau; Meden Isaac; S. Ramaprasad; Thomas J. Dougherty; Kevin M. Smith

• Book ID: 104214763
• Publisher: Elsevier Science
• Year: 1992
• Tongue: French
• Weight: 281 KB
• Volume: 33
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)74751-4

✦ Synopsis

Regiospeciflcity of pyrrole subunit 0~04 oxidation in porphyrins is affected significantly by the presence of electron-withdrawing groups on the macrocycle. the oxidation taking place at the subunit in the quadrant opposite to the electronegative group. Migratory aptitudes in subsequent pinacol-pinacolone rearrangements of porphyrin and pheophorbide vie-dihydroxy systems are likewise dependent upon the presence of electron-withdrawing functionalities. Almost 55 years ago Fisher et al. were the first to investigate the oxidation of octaalkylporphyrins with hydrogen peroxide in acidic media to give gem-dialkyl-P-oxoporphyrins. 1.2 This reaction was interpreted as involving an acidcatalyzed pinacol-pinacolone rearrangement of an initially formed vicinal B$'-dihydmxychlorin.3~4 a view confirmed by the sulfuric acid-catalyzed rearrangements to the identical material from porphyrins oxidized by 0~04. This chemistry