New catalytic methods for the synthesis of selectively substituted aromatics through palladacycles

Joint palladium and norbornene catalysis for selective aromatic functionalization via palladacycles is reported. Both alkylation and arylation of aromatics are considered after a brief outlook on the mechanism. These are multistep reactions that proceed in ordered sequences and are chemio-, regio-, and stereoselective. The study of the single steps with isolation of the organometallic species involved has allowed us to detect subtle steric and electronic effects which have been exploited to achieve catalytic reactions. Recent developments of aromatic alkylation and arylation are reported, in particular, condensed heterocyclic ring formation involving dialkylated arylpalladium complexes or both symmetrically and unsymmetrically substituted biphenylylpalladium complexes.