Cp*RuCl-catalyzed formal intermolecular cyclotrimerization of three unsymmetrical alkynes through a Boron temporary tether: Regioselective four-component coupling synthesis of phthalides

Highly substituted phthalides are efficiently synthesized by sequential Cp*RuCl-catalyzed cyclotrimerization of alkynylboronates, propargyl alcohols, and terminal alkynes and palladium(II) catalyzed carbonylation of the resultant arylboronates. The perfect regioselectivity of the ruthenium-catalyzed formal intermolecular cyclotrimerization is discussed on the basis of the density functional calculations of a boraruthenacycle intermediate.