title: Exploiting the Imidazolium Effect in Base-free Ammonium Enolate Generation: Synthetic and Mechanistic Studies.
abstract: N-Acyl imidazoles and catalytic isothiourea hydrochloride salts function as ammonium enolate precursors in the absence of base. Enantioselective Michael addition-cyclization reactions using different α,β-unsaturated Michael acceptors have been performed to form dihydropyranones and dihydropyridinones with high stereoselectivity. Detailed mechanistic studies using RPKA have revealed the importance of the "imidazolium" effect in ammonium enolate formation and have highlighted key differences with traditional base-mediated processes.
authors.affiliation: EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK.
authors.forename: Claire M
authors.initials: CM
authors.lastname: Young
authors.affiliation: EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Stark
authors.affiliation: EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: West
authors.affiliation: EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK.
authors.forename: James E
authors.initials: JE
authors.lastname: Taylor
authors.affiliation: EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK. ads10@st-andrews.ac.uk.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Smith
keywords: Michael addition; N-acyl imidazoles; imidazolium effect; isothiourea catalysis; mechanistic study