Metathesis Ring-Chain Equilibrium in Cyclobutene and 1-Methylcyclobutene Systems

Abstract

Ring-opening metathesis polymerization (ROMP) of cyclic oligomers of butadiene (c,c-l,5-cyclooctadiene - COD -, t,t,t-l,5,9-cyclododecatriene — CDT -), acyclic diene metathesis of 1,5-hexadiene and the intramolecular metathesis degradation of 1,4-polybutadiene (1,4-BR) were studied intensely using several stable tungsten and molybdenum carbene complexes as well as classical metathesis catalyst. Focus of our interest was the determination of the spectrum of cyclic oligomers. In contrast to earlier literature data our results show the strongly preferred formation of all trans cyclic trimers and give evidence that the product spectrum obtained is thermodynamically controlled. As consequence a way was opened for determination of hitherto not available thermodynamic data as well as for the synthesis of valuable organic products. As example the intramolecular metathetic degradation of 1,4-polyisoprene, leading to the preferred, all trans cyclic isoprene trimers is described.