Photo-oxygenation of meso-tetraphenylporphyrin derivatives: the influence of the substitution pattern and characterization of the reaction products

The photo-oxidation reactions of several meso-tetraphenylporphyrins have been studied in order to ascertain the chemical stability of this class of compounds towards singlet oxygen. The 2,6-disubstituted ones showed an excellent stability, whilst this is not the case for other porphyrins with different substitution pattern on the phenyl rings. This parallels what has been previously found using mono-oxygenated donors. The steric effects in protecting the macrocycle seems to be predominant over the electronic ones; even with electron-donating groups in the 2,6-positions, e.g. methoxy groups, the porphyrin macrocycle was not degraded. The reaction on the beta-tetrabrominated meso-tetraphenylporphyrin also proceeded easily and yielded a bilinone derivative. The structures of the final products were all elucidated by mass,H-1 and C-13 NMR spectroscopy. (C) 1998 John Wiley & Sons, Ltd

Oxidation of unsaturated monoterpenes with hydrogen peroxide catalysed by manganese(III) porphyrin complexes

Oxidation of (+)-3-carene (1), nerol (2) and geraniol (3) by hydrogen peroxide in the presence of catalytic amounts of several manganese(III) porphyrin complexes with electron withdrawing and electron donating groups was examined. The reactions were carried out at room temperature in acetonitrile, using aqueous hydrogen peroxide as oxidant and ammonium acetate as co-catalyst. The oxidation reactions of 3-carene (1) showed high conversion of the substrate with all metalloporphyrins tested and four major products were identified and characterised, namely alpha -3,4-epoxycarane (7), beta -3,4-epoxycarane (8), 3-caren-5-one (9) and 3-carene-2,5-dione (10). Nerol (2) oxidation reactions gave rise to 2,3-epoxynerol(ll), 6,7-epoxynerol (12) and 2,3,6,7-diepoxynerol (13). In the case of geraniol (3), besides 2,3-epoxygeraniol (14), 6,7-epoxygeraniol (15) and 2,3,6, 7-diepoxygeraniol (16), the oxidation reactions afforded 6,7-epoxygeranial (17). The terminal 6,7 double bond of nerol and geraniol was preferentially epoxidised. The regioselectivity induced by different porphyrins was investigated. (C) 2001 Elsevier Science B.V. All rights reserved