Systematic Analysis of the Intramolecular Competition Associate with the Ring Closing Metathesis of Ene-Diene Systems of Differing Chain Length with a Pair of Ruthenium Catalysts
The (alkylidene) ruthenium complexes 1 and 2b were examined as catalysts for the ring-closing metathesis of the homologous series of ene-dienes 16 to ascertain the extent to which a divergence in product distribution would be observed. In each case, the levels of cyclic alkene and conjugated diene were determined (see Table 1). Double bond geometric assignments were made on the basis of vinyl proton 1H-NMR chemical shifts and coupling constants. MM3 Calculations were undertaken to gauge the levels of steric strain in end products of varying ring size. The global ensemble of facts, including key control experiments, demonstrate the striking differences between 1 and 2b. Finally, the steric energies are seen not to correlate with the product distributions, most probably due to the distinctive reactivity patterns of the metathesis reagents.