Selectivity Aspects in Cross Metathesis Reactions

When certain catalysts that display a low apparent metathesis activity on terminal olefins are employed on mixtures of terminal and internal olefins, they lead to a selective formation of cross metathesis products. Critical experimentation using deuterated 1-pentene reveals that terminal olefins prefer to scramble "head-to-tail". A study of the macrocyclics distribution produced at various conversions during 1,5-cycloocta-diene polymerization suggests that these are being formed exclusively via an intramolecular transalkylidenation. The significance of the two sets of results is discussed in terms of two basic mechanistic schemes.