Partial reduction of alkynes with Lindlar’s catalyst to give cis alkenes
Description: Catalytic hydrogenation of alkynes with Lindlar’s catalyst and hydrogen gas provides cis-alkenes (Z-alkenes)
Notes: Lindlar’s catalyst is a “poisoned” palladium catalyst that will reduce alkynes to alkene but not alkenes to alkanes. It is a useful counterpart to Na/NH3 which gives trans alkenes. It can also be written “Lindlar”, Pd/quinoline/PbO2
Notes: Note that the cis alkene is always formed. Furthermore note example 4 – there is no reaction of Lindlar’s catalyst with alkenes.
Mechanism: For the purposes of Org 1/Org 2, the mechanism of this reaction is not that important. The role of lead (Pb) is to moderate the reactivity of palladium, while it is thought that quinoline helps to inhibit polymerization.