Acid-catalysed solvolyses of cyclopentadienoneepoxides lead to epoxide ring opening and take place regioselectively at C-4. The stereochemical outcome of the epoxide ring opening depends on the substitution pattern and the nature of the substituents. Trans opening is preferred in most cases. Participation of the substituents in the transition state, however, leads to cis opened products. Selective
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