Dioxazole and dioxetane intermediates in the thermal rearrangement of endo-peroxides obtained by dye-sensitized photo-oxygenation of 2-alkoxyoxazoles

Abstract

Singlet oxygen reacts with 2-alkoxyoxazoles (2c,d) leading to endo-peroxides (1c,d), which easily rearrange into dioxazoles (3c,d) and dioxetanes (4c,d). Both give carbamates (5c,d)via imino anhydrides (7c,d). When the reaction is carried out in alcohols at –60 °C only the dioxetanes (4c,d) are obtained. These compounds, which are the first examples of a bicyclic system of this type, at higher temperatures add methanol to give 2,5-dihydro-oxazoles (9c,d) and already at –60 °C react with diethyl sulphide to give the imines (10c,d).