Cyclizations versus rearrangements in the reactions of some epoxyolefins with Lewis acids

Treatment of various substituted epoxyolefins A with BF3. OEt2 and other re agents that could be expected to induce carbocyclization to give cyclohexan es was investigated. It turned out that the general reaction of these syste ms was the epoxide to ketone rearrangement, while the carbocyclization was only a rare event. Only substrates carrying the allylsilane grouping underw ent carbocyclization and in addition the protecting groups and the stereoch emistry of the system had a decisive influence on whether ring closure or r earrangement were to take place.