Dienes from ring opening cross metathesis

Apart from cross-metathesis, ROMP, and RCM, there are other less common metathesis reactions. These are acyclic diene metathesis polymerization (ADMET), ring-opening cross-metathesis (ROCM), ring-rearrangement metathesis (RRM), and ethenolysis. A general ADMET reaction is shown by reaction 7.3.1.7. ADMET reactions are generally performed on a,well-defined and strictly linear polymers with unsaturated polyethylene backbones. Ethenolysis is the cross-metathesis of ethylene with an internal olefin. 

Olefin metathesis is a reaction that is over fifty years old and has been developed over this time period from a process nm at high temperatures with ill-defined catalysts by unknown mechanisms to a process that can be conducted imder nuld conditions with designed catalysts by mechanisms that occur by established steps. Olefin metathesis, and the related alk3me metathesis, fully cleaves carbon-carbon double and triple bonds and reforms these bonds to generate new alkenes and alkynes. The reaction is often under equilibrium control, but certain classes of reactions can be conducted in a selective fashion that is controlled by relative rates or thermod)mamic preferences. This reaction can open strained rings to form polymers or small dienes. It can close small rings and macrocycles by a reaction that is driven by the expulsion of ethylene that makes the reaction favored entropically or by running in an open system under non-equilibrium conditions. It can also be run as a "cross metathesis" to form imsymmetrical alkenes when the steric or electronic properties of the two alkenes properly match. 

Later, the detailed study on the reaction mechanism was shown by Lippstreu and Staub, who described that the reaction would proceed via route 2, and mthenacy-clobutene 4 generated from the alkyne part of ene-yne 2 and ruthenium carbene complex 3 do not exist as local minimum in the catalytic cycle [6]. Using ruthenium carbene complexes [Ru]-IV and (Ru]-I, various carbo- and heterocycles could be synthesized from the corresponding ene-ynes [5]. Furthermore, diene-yne metathesis, cross ene-yne metathesis, and ring-opening ene-yne metathesis have been developed (Scheme 6.2). 

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