Computational Insights into the Mechanism of Lewis Acid-Catalyzed Alkene-Aldehyde Coupling.

The Lewis acid-catalyzed coupling of alkenes and aldehydes presents a modern, versatile synthetic alternative to classical carbonyl addition chemistry, offering exceptional regio- and stereoselectivity. In this work, we present a comprehensive computational investigation into the reaction mechanism of this transformation. Our findings confirm the occurrence of an enantioselective trans-annular [1,5]-hydride shift step and demonstrate that the enantioselectivity of the reaction arises predominantly from steric clashes between functional groups in the cyclization step. Combining computational and experimental results, we establish that the Lewis acid catalyst facilitates the initial C-O coupling step between the alkene and the activated aldehyde. Investigations into systems with longer alkyl chains reveal that while they follow a similar mechanistic pathway, cyclization becomes kinetically hindered, preventing the reaction from proceeding. These insights illuminate the factors governing reaction outcomes and limitations, paving the way for future developments in this area.