Alkynyl transmetalation triggered by a nucleophilic attack

Abstract

We report an interesting alkynyl transmetalation process in the cyclization of π-Au, σ-M acetylides (M = Pd, Ni, Pt) bearing a N-propiolic formamidine moiety. The cyclization was triggered by nucleophilic attack and afforded 5-membered heterodinuclear M/Au vinylidene species through a 5-exo-dig mode followed by ring-opening and recyclization to give their 6-membered endo-isomers at an elevated temperature. This suggests that the regiochemistry (5-exo vs. 6-endo) observed in the cyclization is kinetically and thermodynamically controlled. The mechanism of the domino cyclization/ring-opening/recyclization reaction is analyzed by DFT calculations.