title: Lithium hexamethyldisilazide/triethylamine-mediated ketone enolization: remarkable rate accelerations stemming from a dimer-based mechanism.
abstract: Mechanistic studies of the enolization of 2-methylcyclohexanone mediated by lithium hexamethyldisilazide (LiHMDS; TMS2NLi) in toluene and toluene/triethylamine (Et3N) mixtures are described. Structural studies of LiHMDS/ketone mixtures in toluene reveal cyclic dimer (TMS2NLi)2(ketone). Rate studies using in situ IR spectroscopy show the enolization proceeds via a dimer-based transition structure, [(TMS2NLi)2(ketone)]. NMR spectroscopic studies of LiHMDS/ketone mixtures in the presence of relatively unhindered trialkylamines such as Me2NEt reveal the quantitative formation of cyclic dimers of general structure (TMS2NLi)2(Et3N)(ketone). Rate studies trace a >3000-fold rate acceleration to a dimer-based transition structure, [(TMS2NLi)2(Et3N)(ketone)].
authors.affiliation: Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA.
authors.forename: Pinjing
authors.initials: P
authors.lastname: Zhao
authors.forename: David B
authors.initials: DB
authors.lastname: Collum
mesh_terms: D019281:Dimerization; D005021:Ethylamines / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D018020:Lithium Compounds / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*
chemical_list: D005021:Ethylamines; D007659:Ketones; D018020:Lithium Compounds; D012821:Silanes; C442341:lithium hexamethyldisilazide; C016162:triethylamine