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 were 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 intermediate arylboronate was isolated and unambiguously
characterized by X-ray crystallography. The perfect regioselectivity of the ruthenium-catalyzed formal
intermolecular cyclotrimerization was discussed on the basis of the density functional calculations of a
boraruthenacycle intermediate