title: Enantioselective Brønsted base catalysis with chiral cyclopropenimines.
abstract: Cyclopropenimines are shown to be a highly effective new class of enantioselective Brønsted base catalysts. A chiral 2,3-bis(dialkylamino)cyclopropenimine catalyzes the rapid Michael reaction of a glycine imine substrate with high levels of enantioselectivity. A preparative scale reaction to deliver 25 g of product is demonstrated, and a trivial large scale synthesis of the optimal catalyst is shown. In addition, the basicity of a 2,3-bis(dialkylamino)cyclopropenimine is measured for the first time and shown to be approximately equivalent to the P(1)-tBu phosphazene base. An X-ray crystal structure of the protonated catalyst is shown along with a proposed mechanistic and stereochemical rationale.
authors.affiliation: Department of Chemistry, Columbia University, New York, New York 10027, United States.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Bandar
authors.forename: Tristan H
authors.initials: TH
authors.lastname: Lambert