Synergistic effect of palladium and copper catalysts: catalytic cyclizative dimerization of ortho-(1-alkynyl)benzamides leading to axially chiral 1,3-butadienes.

Two is better than one: In the presence of Pd(OAc)(2) and Cu(OAc)(2), o-(1-alkynyl)benzamides 1 were converted into bis-iminobenzoisofurans with an axially chiral 1,3-diene 2 unit. The coexistence of both Pd and Cu catalysts was found to be essential for both the cyclizative dimerization process and for the observed unusual cyclization mode.