Autoxidation and solvolysis products of octaethylverdohaemochrome

Abstract

Aerobic degradations of (i) octaethylverdohaemochrome (1) bis(pyridine) iron (II) 2,3,7,8,12,13,17,18-octaethyl-5-oxaporphyrinate in 5% pyridine–methanol, (ii) octaethylbilindione (2) in the presence of thallium(III) acetate in methanol, and (iii)(2) upon t.l.c. have been investigated. These degradations were caused by solvolysis and autoxidation. Eight degradation products obtained from reaction (i) were isolated, and their structures were elucidated by electronic absorption spectrophotometry and mass and n.m.r. spectroscopy as follows: octaethylbilindione (2), 2,3,7,8,12,13,17,18-octaethyl-19-methoxy-21H-bilin-1-one (3), 2,3,7,8,12,13-hexaethyl-14-methoxy-15H,16H-tripyrrin-1-one (4), methyl 2,3,7,8,12,13-hexaethyl-1-oxo-15H,16H-tripyrrin-14-carboxylate (5), 2,3,7,8,12,13-hexaethyl-1-oxo-15H,16H-tripyrrin-14-carbaldehyde (6), (4RS,5RS)-(7) and (4RS,5SR)- 2,3,7,8,12,13,17,18-octaethyl-4,5-dimethoxy-4,5-dihydro-21H,24H-bilin-1,19-dione (8), and 2,3,7,8,12,13-hexaethyl-14-pyridinio-15H,16H-tripyrrin-4-yl tetrafluoroborate (9). The products (6), (7), and (8) obtained from reaction (ii), and (6) obtained from reaction (iii) were identical with those obtained from reaction (i). Both (4RS,5RS)-(7) and (4RS,5SR)-dimethoxy adduct (8) were obtained from reactions (i) and (ii). Only the (4RS,5RS)-ethylenedioxy adduct (10) was obtained when ethylene glycol instead of methanol was used as solvent.