1.7.6.3 Nickel and Iron Catalyzed Epoxidation
Nickel and iron based catalysts have been used for the epoxidation of alkenes using molecular oxygen as terminal oxidant in the presence of aliphatic aldehyde as a reducing agent. For example, Ni(dmp)2 and Fe(dmp)3 complexes have been shown to catalyze the epoxidation of substituted alkenes in the presence of t -butanal and molecular oxygen (Scheme 16). The aldehyde is oxidized in situ to peracid that transfers oxygen atom to alkenes to give the epoxides.
Scheme 17
1.7.7 Photooxidation
1.7.7.1 Excitation
The ground state triplet dioxygen (3 O 2 ) could be excited to give singlet state dioxygen ( 1 O 2 ) by photolytic energy transfer.
1.7.7.2 Cycloaddition
The excited singlet oxygen can undergo [4+2]-cycloaddition reaction with 1,3-diene to give cyclic peroxides (Scheme 18).
Scheme 18
Cholestodiene does not give the similar expected peroxide but gives cholestidienone as the product (Scheme 19).
Scheme 19