10-oxatricyclodecadienone epoxides have been prepared in high yields by a stereospecific nucleophilic epoxidation of the corresponding 10-oxatricyclo[5.2.1.02,6]deca-4,8-dien-3-ones. These polycyclic epoxides could efficiently be converted into cyclopentadienoneepoxides using Flash Vacuum Thermolysis. The synthetic potential of the last named epoxides in the field of natural product synthesis is illustrated