Unusual influence of substituents on ring-opening metathesis reactions.

The ring-opening cross-metathesis of oxabicyclo[3.2.1]octene derivatives provides a convenient method for preparing differentially substituted 4-pyrones. The major competing reaction is the ring-opening metathesis polymerization of the bridged olefin. Studies on this reaction have shown that substituents on the bicyclic alkene can have a dramatic influence on the competing reactions. [reaction: see text]