title: Transition state analysis of enantioselective Brønsted base catalysis by chiral cyclopropenimines.
abstract: Experimental (13)C kinetic isotope effects have been used to interrogate the rate-limiting step of the Michael addition of glycinate imines to benzyl acrylate catalyzed by a chiral 2,3-bis(dicyclohexylamino) cyclopropenimine catalyst. The reaction is found to proceed via rate-limiting carbon-carbon bond formation. The origins of enantioselectivity and a key noncovalent CH···O interaction responsible for transition state organization are identified on the basis of density functional theory calculations and probed using experimental labeling studies. The resulting high-resolution experimental picture of the enantioselectivity-determining transition state is expected to guide new catalyst design and reaction development.
authors.affiliation: Department of Chemistry, Columbia University , 3000 Broadway, New York, New York 10027, United States.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Bandar
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Sauer
authors.forename: William D
authors.initials: WD
authors.lastname: Wulff
authors.forename: Tristan H
authors.initials: TH
authors.lastname: Lambert
authors.forename: Mathew J
authors.initials: MJ
authors.lastname: Vetticatt
mesh_terms: D000179:Acrylates / Q000737:chemistry*; D002247:Carbon Isotopes / Q000032:analysis; D002384:Catalysis; D003521:Cyclopropanes / Q000737:chemistry*; D005998:Glycine / Q000031:analogs & derivatives*; D007097:Imines / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D011789:Quantum Theory; D013237:Stereoisomerism
chemical_list: D000179:Acrylates; D002247:Carbon Isotopes; D003521:Cyclopropanes; D007097:Imines; C021985:cyclopropene; C036658:acrylic acid; D005998:Glycine