Ozonolyses of unsaturated hydroperoxy acetals 4a-k gave in each case the mixtures of products containing the corresponding trioxanes 8a-f and 12e,f, trioxepanes 12g-i, trioxocane 12j, and trioxonane 12k. By choosing the proper conditions of the ozonolysis, the desired cyclic peroxide was selectively obtained in moderate to good yield. Alternatively, acid-catalyzed cyclization of the methanol-derived ozonolysis products 13h and 13j provided the corresponding trioxepane 12h and trioxocane 12j, respectively.