PALLADIUM-MEDIATED INTRAMOLECULAR C-N BOND FORMATION BETWEEN TERTIARY-AMINES AND ALKENES

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 a ffords allylic phosphonium compounds for those substrates having more than six carbon atoms between the alkene function and the tertiary ami ne nitrogen atom, In those cases where the alkene is closer to the NMe (2) unit, this reaction leads, via allylic metalation, to intramolecul ar cyclization that involves generation of a new C-N bond and results in the formation of cationic 5-, 6-, or 7-membered heterocyclic ammoni um compounds. For example, C6H4(CH2CH=CH2)-1-(CHMeNMe(2))-2 can be con verted 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 reac tion is highly selective and occurs either at the terminal, less subst ituted 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-a llyl complex, i.e., 2i(syn), and a quinolinium derivative, 3a, are des cribed. Crystal data for 2i(syn): monoclinic, space group P2(1)/c, wit h 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 g roup P2(1)/n with a = 13.032(1), b = 6.544(1), and c 13.415(1) Angstro m, beta = 114.72(1)degrees, Z = 4, R = 0.042,