Treatment of both the E and 2 isomers of alkoxyallylic sulfones 20a and 20b with TiC14 results in the formation of 4+ 3 cycloadducts by intramolecular cycloaddition. The distribution of diastereomers is different from each isomer of educt. This suggests that cycloaddition occurs faster than any isomerization process of the intermediate allylic cations. Both the E and 2 isomers of 20c lead to the same 4+ 3 cycloadduct with essentially complete ...
