title: Reaction of ketones with lithium hexamethyldisilazide: competitive enolizations and 1,2-additions.
abstract: Reaction of 2-methylcyclohexanone with lithium hexamethyldisilazide (LiHMDS, TMS(2)NLi) displays highly solvent-dependent chemoselectivity. LiHMDS in THF/toluene effect enolization. Rate studies using in situ IR spectroscopy are consistent with a THF concentration-dependent monomer-based pathway. LiHMDS in pyrrolidine/toluene affords exclusively 1,2-addition of the pyrrolidine fragment to form an alpha-amino alkoxide-LiHMDS mixed dimer shown to be a pair of conformers by using (6)Li, (15)N, and (13)C NMR spectroscopies. Rate studies are consistent with a monomer-based transition structure [(TMS(2)NLi)(ketone)(pyrrolidine)(3)](). The partitioning between enolization and 1,2-addition is kinetically controlled.
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: Anthony
authors.initials: A
authors.lastname: Condo
authors.forename: Ivan
authors.initials: I
authors.lastname: Keresztes
authors.forename: David B
authors.initials: DB
authors.lastname: Collum
mesh_terms: D000475:Alkenes / Q000138:chemical synthesis / Q000737:chemistry; D003512:Cyclohexanones / Q000737:chemistry; D007659:Ketones / Q000737:chemistry*; D007700:Kinetics; D018020:Lithium Compounds / Q000737:chemistry*; D008958:Models, Molecular; D011759:Pyrrolidines / Q000737:chemistry; D012821:Silanes / Q000737:chemistry*
chemical_list: D000475:Alkenes; D003512:Cyclohexanones; D007659:Ketones; D018020:Lithium Compounds; D011759:Pyrrolidines; D012821:Silanes; C442341:lithium hexamethyldisilazide