Lewis-Acid-Promoted Ligand-Controlled Regiodivergent Cycloaddition of Pd-Oxyallyl with 1,3-Dienes: Reaction Development and Origins of Selectivities

For nearly 30 years, considerable research effort has been focused on the development of methods for catalytic (3 + 2) cycloaddition reactions of palladium-oxyallyl species with alkenes. However, because C-O bond formation is kinetically favored, the (3 + 2) cycloadditions achieved to date have involved C-O reductive elimination. We herein report a method of lithium triflate-promoted (3 + 2) cycloaddition reactions of palladium-oxyallyl species with 1,3-dienes that proceed via a pathway terminated with C-C bond formation to give a five-membered carbocycle. Coordination of the lithium ion with the alkoxide moiety disrupts the C-O reductive elimination and forms a metal-enolate tethered pi-allyl-Pd. The pi-allyl-Pd moiety then accepts intramolecular allylic attack from the enolate moiety to form carbocyclic products. Furthermore, by tuning the steric properties of the palladium ligand, we could also accomplish the competing (4 + 3) cycloadditions, and thus this method provides regiodivergent access to both cyclopentanones and cycloheptanones. The reaction mechanism was investigated by DFT calculation and the origins of the regioselectivities of the cycloaddition were rationalized.

Automated summary

This study presents a novel method for the (3+2) cycloaddition reactions of palladium-oxyallyl species with 1,3-dienes, leading to the formation of five-membered carbocycles with C-C bond formation. The research also achieved regiodivergent access to cyclopentanones and cycloheptanones by tuning the steric properties of the palladium ligand. The reaction mechanism was investigated using DFT calculation, providing insights into the regioselectivities of the cycloaddition.