A bimetallic catalyst and dual role catalyst:: Synthesis of N-(alkoxycarbonyl)indoles from 2-(alkynyl)phenylisocyanates

3-Allyl-N-(alkoxycarbonyl)indoles are synthesized via the reaction of 2-(alkynyl)phenylisocyanates and allyl carbonates in the presence of Pd(PPh3)(4) (1 mol %) and CuCl (4 mol %) bimetallic catalyst. It is most probable that Pd-0 acts as a catalyst for the formation of a pi-allylpalladium alkoxide intermediate and Cu-I behaves as a Lewis acid to activate the isocyanate, and the cyclization step proceeds with a cooperative catalytic activity of Pd and Cu. On the other hand, N-(alkoxycarbonyl)indoles are produced via the reaction of 2-(alkynyl)phenylisocyanates and alcohols under a catalytic amount of Na2PdCl4 (5 mol %) or PtCl2 (5 mol %). Pd-II or Pt-II catalyst exhibits dual roles; it acts as a Lewis acid to accelerate the addition of alcohols to isocyanates and as a typical transition-metal catalyst to activate the alkyne for the subsequent cyclization.