PdCl2(HNMe2)2-Catalyzed Highly Selective Cross [2+2+2] Cyclization of Alkynoates and Alkenes under Molecular Oxygen

In the course of our study on palladium-catalyzed aerobic oxidation synthesis, We found that the PdCl2/O-2/DMF system consistently experienced DMF hydrolysis to afford PdCl2(HNMe2)(2), which is the real active catalyst for the aerobic oxidation. Although in situ DMF hydrolysis has been widely used in generating supramolecular assembly architectures, as far as we know, it is the first successful example to utilize PdCl2(HNMe2)(2) in synthetic reactions. The highly selective cross [2 + 2+2] cyclization of alkynoates and different alkenes with electron-withdrawing groups could be smoothly catalyzed by PdCl2(HNMe2)(2)/O-2/DMF to afford the corresponding functionalized pentasubstituted benzenes in good to excellent yields (70-97%). The extension of alkyne surrogates for cross [2 + 2 + 2] cyclization from special alkenes with leaving groups to simple alkenes under molecular oxygen led to a paradigm shift in arene synthesis.