The capture by aldehydes of transient zwitterionic peroxides derived from the reaction of singlet oxygen and various electron-rich olefins leads to 1,2,4-trioxanes. Ketones do not react with these transient species. However, it is shown that 1,2-dioxetanes, endo-peroxides, and hydroperoxy derivatives on catalysis can react equally well with aldehydes and ketones in an inter- and intramolecular manner to give monocyclic, bicyclic and bridged bicyclic trioxane derivatives. The chemistry of the trioxane ring is demonstrated by its use as a new protecting group and as an intermediate in synthesis for preparing cis-1,2-diols.