Theoretical investigation on the palladium-catalyzed selective formation of spirocyclenes from dienallenes

Abstract The mechanisms of Pd(TFA)2-catalyzed cascade reactions of dienallenes and alkyne have been investigated by density functional theory (DFT) calculations. The computational results indicate that spiro[4.4]nonene rather than spiro[3.4]octene is the product in DCE solvent, due to the lower free-energy barrier for CO insertion from vinylpalladium intermediate than the competing olefin insertion, which is consistent with the experimental fact. The origin of regioselectivity in this reaction could be attributed to the electronic effect through performing the NPA charge calculation. In contrast, the participant solvent coordination could decrease the olefin insertion transition state effectively, and lead to the formation of product spiro[3.4]octene in CH3CN solvent.