Iron(III)Picolinate-Catalyzed Oxygenation of Cholesteryl Acetate with Hydrogen Peroxide or Peracetic Acid

The reaction of cholesteryl acetate 1 with a FeIII(PA; picolinate)3/H2O2/MeCN system (reagent system A), a simple model system for mono-oxygenases, gave mainly the 7α-hydroxylation product 2a, along with 7-ketonization product 3 and the 5, 6-epoxidation product 4. On the other hand, reaction of 1 using a Fe(PA)3/peracetic acid (AcOOH)/MeCN system (reagent system C) or a FeIII(ClO4)3·9H2O-picolinic acid(PAH)-pyridine(Py)/AcOOH/MeCN system (reagent system F), provided 4 predominantly without formation of 2a. The former reaction may proceed via the dimeric FeIII-FeV manifold complex, (PAH)(PA)2FeIII-O-O-FeV=O(PA)2 (VII) as a hypothetically active species and a nonradical pathway, and the latter may proceed through monomeric iron complexes, [(PAH)(PA)2FeV=O]+ (IX) and [(PAH)(PA)2FeV(OH)(OOH)]+ (X).