Investigating the Ritter Type Reaction of α‐Methylene‐β‐hydroxy Esters in Acidic Medium: Evidence for the Intermediacy of an Allylic Cation

The acid‐mediated solvolytic transformation of α‐methylene‐β‐hydroxy esters in acetonitrile was investigated. The reaction was shown to involve nucleophilic attack either at the terminal methylene or at the benzylic carbon. Kinetic and theoretical studies were performed to elucidate the possible pathways involved in the formation of the acetamide products, i.e., through an addition‐elimination mechanism, a concerted process (S N 2 and S N 2′), or involving an allylic cation (S N 1 and S N 1′). The results of the kinetic analysis, including the isotope effect, Hammett plot, and Eyring plot, are in agreement with a proton transfer equilibrium prior to the formation of a benzylic carbenium ion intermediate, which is consistent with a unimolecular stepwise mechanism. Theoretical examination at the DFT level of theory corroborated these findings, with the lowest activation energy being associated with the S N 1′‐type mechanism.