Reaction of ketones with lithium hexamethyldisilazide: competitive enolizations and 1,2-additions.
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.
Zhao
Pinjing
P
Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA.
Condo
Anthony
A
Keresztes
Ivan
I
Collum
David B
DB
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*
D000475:Alkenes; D003512:Cyclohexanones; D007659:Ketones; D018020:Lithium Compounds; D011759:Pyrrolidines; D012821:Silanes; C442341:lithium hexamethyldisilazide