Ru(II)-Catalyzed Chemo- and Regioselective Cyclotrimerization of Three Unsymmetrical Alkynes through Boron Temporary Tether. One-Pot Four-Component Coupling via Cyclotrimerization/Suzuki−Miyaura Coupling
The Ru(II)-catalyzed [2+2+2] cyclotrimerization of alkynylboronates, propargyl alcohol, and terminal alkynes proceeded chemo- and regioselectively to give rise to arylboronates, which were subjected to Suzuki-Miyaura cross-coupling with aryliodides to afford highly substituted biaryls in 53-76% yields.
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.
One-pot sequential four-component coupling via Cp*RuCl-catalyzed cyclotrimerization and Suzuki–Miyaura coupling
The catalytic intermolecular cyclotrimerization of alkynylboronates, propargyl alcohols, and terminal alkynes was accomplished by means of the ruthenium catalysis and the temporary tethering approach with the C-B-0 linkage to give rise to highly substituted arylboronates with excellent selectivity. The resultant arylboronates were further converted to highly substituted biaryls via the Suzuki-Miyaura coupling with various aryl iodides using Pd-2(dba)(3)/PCy3 as a catalyst precursor in aqueous toluene. As a consequence, the four-component coupling approach to highly substituted biaryls was successfully established by combining these two operations into a sequential one-pot process. (c) 2005 Elsevier Ltd. All rights reserved.