 For example, electronwithdrawing groups like esters, nitriles or sulfones must be in conjugation with the carbon-carbon π-system (see Michael addition) or a directing group like an alcohol or amine must be nearby to direct the reaction.These reactions can be catalyzed by a variety of transition metals such as iron, copper, zirconium, nickel, cobalt and others.Illustrative is the Fe-catalyzed reaction of methylphenylacetylene with phenylmagnesium bromide, which generates a vinyl magnesium intermediate.