Regioselective cyclizations of 2-(prop-2-yn-1-yloxy)anilines using palladium and platinum catalysts

Transition-metal-catalyzed intramolecular reactions involving a C-C multiple bonds have been recognized as useful processes to obtain heterocyclic systems.1 Among them the palladium-catalyzed reactions were exploited by us to achieve nitrogenated rings2 and in this contest the hydroamination reactions involving the C-N bond formation continue to gain our interests. The present work is regarding the reactivity of 2-(prop-2-yn-1-yloxy)anilines as a useful scaffold to obtain nitrogenated systems. The use of different transition metal-catalysts results in a complete regioselectivity depending on the metal catalyst used: in the presence of Pd(PPh3)4 6-exo-dig cyclization was observed, while with PtCl2 the 7-endo-dig cyclization occurred. Moreover the 5-membered ring formation was obtained under the same Pd-catalysis conditions, working on the allenyl derivatives arising from the alkyne pendant under basic conditions.