Limonene reaction with singlet oxygen

Olefins containing at least one allylic hydrogen are suitable substrates and are of special importance and interest with regard to the intrinsic mechanism involved in their reactions with singlet oxygen. Allylic hydroperoxides are formed, but the mechanism of their formation is clearly distinct from that by which allylic hydroperoxides are produced in thermal or photochemically initiated (see example above for a Type I process) autoxidation reactions. This has unequivocally been shown with optically active limonene as a substrate, which gives rise to different products in free radical and Type II photo-oxygenation reactions (22, 57, 61). 

Scheme 6.6. A possible pathway for the reaction of S-(-)-limonene with singlet oxygen ( 02) yielding a chiral hydroperoxide.

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