Rhodium-Catalyzed Inter molecular [2+2+2] Cross-Trimerization of Aryl Ethynyl Ethers and Carbonyl Compounds To Produce Dienyl Esters

摘要

Transition-metal-catalyzed [2+2+2] cycloaddition reactions of alkynes and C_(sp)-heteroatom multiple bonds, such as nitriles and heterocumulenes, are valuable methods for the synthesis of substituted heterocycles in a highly atom economical manner. However, the analogous transition-metal-catalyzed [2+2+2] cycloaddition of alkynes and C_(sp~2)-heteroatom multiple bonds, such as ketones and aldehydes, have been reported in a limited number of examples. The pioneering example of such a catalysis was the nickel(O)/ monophosphine complex catalyzed cycloaddition of diynes and aldehydes. After this initial report, the [Cp*Ru(cod)Cl]-catalyzed cycloaddition of diynes and electron-deficient ketones, the nickel(0)/imidazolylidene complex catalyzed cycloaddition of diynes and electron-rich aldehydes and ketones, and the neutral rhodium(I) complex catalyzed cycloaddition of diynals were reported. However, a catalyst that can be used for both electron-deficient and electron-rich carbonyl compounds has not been developed. Our research group discovered that a cationic rhodium(I)/H8-binap complex is able to catalyze the [2+2+2] cycloaddition of diynes and both electron-deficient and electron-rich carbonyl compounds at room temperature.Unfortunately, these examples are strictly limited to partially or completely intramolecular reactions between tethered diynes and carbonyl compounds. The development of the transition-metal-catalyzed completely intermolecular [2+2+2] cycloaddition of two untethered alkynes and a carbonyl compound is one of the most challenging targets (Scheme 1).