The 1,2‐hydroxy hydroperoxide 7 was obtained with high threo diastereoselectivity from the ester‐conjugated allylic alcohol 6 through a porphyrin‐sensitized singlet oxygen ene reaction. Compound 7 was used as substrate for peroxy(trans)acetalization with aldehydes, orthoesters, and acetals, catalyzed by boron and indium Lewis acids, as well as by PPTS as a Brønsted acid catalyst (for trioxane 10). The 1,2,4‐trioxane 8 was formed with high diasteroselectivity with all‐equatorially positioned substitutents at C‐3, C‐5, and C‐6. Additionally, perorthoester 9 was obtained by indium(III)‐catalyzed condensation of an orthoester with the hydroperoxide 7. The new compounds 8 and 9 exhibited moderate inhibition of human placental glutathione transferase (GST), comparable to that shown by the 5‐unsubstituted model trioxane 11.