Lithium diisopropylamide-mediated enolization: catalysis by hemilabile ligands.
Structural, kinetic, and computational studies reveal the mechanistic complexities of a lithium diisopropylamide (LDA)-mediated ester enolization. Hemilabile amino ether MeOCH2CH2NMe2, binding as an eta1 (ether-bound) ligand in the reactant and as an eta2 (chelating) ligand in the transition structure, accelerates the enolization 10,000-fold compared with n-BuOMe. At the onset of the reaction, a dimer-based enolization prevails. As the reaction proceeds, significantly less reactive LDA-enolate mixed dimers appear and divert the reaction through monomer- and mixed dimer-based pathways. The mechanistic and computational investigations lead to a proof-of-principle ligand-catalyzed enolization in which an ancillary ligand allows the catalytic ligand to re-enter the catalytic cycle.
Ramirez
Antonio
A
Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA.
Sun
Xiufeng
X
Collum
David B
DB
D002384:Catalysis; D019281:Dimerization; D007700:Kinetics; D008024:Ligands; D011437:Propylamines / Q000737:chemistry*
D008024:Ligands; D011437:Propylamines; C007442:diisopropylamine