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The photooxygenation of imperatorin (1a) afforded the corresponding allylic hydroperoxides 2a and 3a in very good yields. Similarly, the photooxygenation of alloimperatorin derivatives 1c, d gave the allylic hydroperoxides 2c, d and 3c, d in quantitative yields. On the other hand, on photooxygenation of alloimperatorin (1b) exclusively the dienone hydroperoxide 4b was obtained. When the reaction time was prolonged, the bis(hydroperoxide) 5b was also formed by successive photooxygenation of 4b.

The epoxidation of allylic hydroperoxides 2a–h by dimethyldioxirane afforded the epoxy hydroperoxides 3a–h in very good yields. On the other hand, only the substrates 2a, b and 2d–f can be converted into the corresponding epoxy hydroperoxides by peroxy acids in reasonable to good yields. The peroxy acid and dimethyldioxirane epoxidations of allylic hydroperoxides proceed, in contrast to those of the allylic alcohols, in low but opposite diastereoselectivity. The configuration of diastereomeric epoxy hydroperoxides were determined by NMR-NOE experiments and chemical correlation.

Epoxidation of imperatorin (1a) by dimethyldioxirane (DMD) affords the natural product prangenin (2a) in excellent yield. Similarly, alloimperatorin (1b) and its methyl and acetate derivatives 1b–d are epoxidized with DMD to give the corresponding epoxides 2b–d in quantitative yields. Furthermore, the reaction of the imperatorin allylic hydroperoxide 1e with DMD, and for comparison with m-chloroperbenzoic acid (CPBA), yields the diastereomeric epoxy hydroperoxides (R*,S*)- and (R*,R*)-2e in low but of opposite diastereoselectivity. Thus, for DMD the (R*,S*)/(R*,R*-2e ratio is 56:44 and for CPBA 40:60.