The reaction of terminal alkenylarenes having either o-(dimethylamino) or o-[(dimethylamino)methyl] substituents with PdCl2(MeCN)(2) in MeOH in the presence of NaOAc and PPh(3) has been studied. This reaction affords allylic phosphonium compounds for those substrates having more than six carbon atoms between the alkene function and the tertiary amine nitrogen atom, In those cases where the alkene is closer to the NMe(2) unit, this reaction leads, via allylic metalation, to intramolecular cyclization that involves generation of a new C-N bond and results in the formation of cationic 5-, 6-, or 7-membered heterocyclic ammonium compounds. For example, C6H4(CH2CH=CH2)-1-(CHMeNMe(2))-2 can be converted to the endo-cyclization product [C6H4{CH=CHCH(2)NMe(2)CH(Me)}-1,2]Cl in 86% yield with this Pd(II)-based system. The cyclization reaction is highly selective and occurs either at the terminal, less substituted olefinic carbon atom (C-gamma), affording ende-cyclization, or at the allylic C-alpha carbon atom, resulting in the formation of exo-cyclic products. The cyclization reaction is thought to proceed via a palladium-assisted C-H activation route : in most cases it was possible to isolate and characterize an eta(3)-allylpalladium complex as a key intermediate and then allow it to react further with PPh(3) to afford a cyclized end product. The X-ray crystal structures of a palladium-allyl complex, i.e., 2i(syn), and a quinolinium derivative, 3a, are described. Crystal data for 2i(syn) : monoclinic, space group P2(1)/c, with a = 8.902(1), b = 20.587(1), and c = 9.702(1) Angstrom, beta = 95.52(1)degrees, Z = 4, R = 0.038. Crystal data for 3a : monoclinic, space group P2(1)/n with a = 13.032(1), b = 6.544(1), and c 13.415(1) Angstrom, beta = 114.72(1)degrees, Z = 4, R = 0.042,