Palladium-Mediated Intramolecular C-N bond Formation between Tertiary amines and Alkenes

Abstract

The reaction of terminal alkenylarenes having either o-(dimethylamino) or 0-[(d imethylamino)methyl] substituents with PdC12(MeCN)2 in MeOH in the presence of NaOAc and PPh3 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 NMe2 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, C~H~(CHZCH=CH~)- l-(CHMeNMe2)-2 can be converted to the endo-cyclization product [CsH@H=CHCH2NMe2CH(Me))-l,2]Cl in 86% yield with this Pd(I1)-based system. The cyclization reaction is highly selective and occurs either at the terminal, less substituted olefinic carbon atom (Cy)a,f fording endo-cyclization, or at the allylic C, 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 ~$allylpalladium complex as a key intermediate and then allow it to react further with PPh3 to afford a cyclized end product. The X-ray crystal structures of a palladium-allyl complex, i.e., 2i,,, and a quinolinium derivative, 3a, aredescribed. Crystal data for 2iS,,,: monoclinic, space group P2,/c, with a = 8.902(1), b = 20.587(1), and c = 9.702(1) A, /3 = 95.52(1)', Z = 4, R = 0.038. Crystal data for 3a: monoclinic, space group P21/n with a = 13.032(1), b = 6.544(1), and c = 13.415(1) A, fi = 114.72(1)O, Z = 4, R = 0.042.