Cross-metathesis is a powerful method for the rapid synthesis of simple and complex olefinic building blocks, and an excellent model has been developed by Grubbs to predict the outcome of cross-metathesis reactions, based upon reactant olefin type (i.e., propensity of the olefin towards homodimerization, and reactivity of those homodimers towards further metathesis) and catalyst used.1 Both first- and second-generation catalysts can be used in CM, with the latter exhibiting excellent reactivity in effecting the metathesis of sterically demanding or highly deactivated olefin substrates.2 Some examples of these more difficult metatheses employing second-generation catalysts are illustrated below.3 - See more at: http://www.sigmaaldrich.com/chemistry/chemical-synthesis/technology-spotlights/metathesis.html#sthash.ez6Uocsp.dpuf