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Investigating the Ritter Type Reaction of α‐Methylene‐β‐hydroxy Esters in Acidic Medium: Evidence for the Intermediacy of an Allylic Cation
Author(s) -
Sá Marcus M.,
Ferreira Misael,
Caramori Giovanni F.,
Zaramello Laize,
Bortoluzzi Adailton J.,
Faggion Deonildo,
Domingos Josiel B.
Publication year - 2013
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201300035
Subject(s) - chemistry , allylic rearrangement , methylene , kinetic isotope effect , carbenium ion , carbocation , transition state , ritter reaction , medicinal chemistry , hammett equation , computational chemistry , acetamide , nucleophile , reaction mechanism , photochemistry , acetonitrile , stepwise reaction , stereochemistry , reaction rate constant , organic chemistry , kinetics , ion , deuterium , order of reaction , catalysis , physics , quantum mechanics
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.