212121-62-5Relevant articles and documents
Modified guanidines as chiral superbases: Application to asymmetric Michael reaction of glycine imine with acrylate or its related compounds
Ishikawa,Araki,Kumamoto,Seki,Fukuda,Isobe
, p. 245 - 246 (2001)
Modified guanidines efficiently catalysed the asymmetric Michael reaction of a prochiral glycine derivative with acrylate or its related compounds either in solution or without a solvent under simple and mild conditions (> 95% ee).
Enantioselective solution- and solid-phase synthesis of glutamic acid derivatives via Michael addition reactions
O'Donnell, Martin J.,Delgado, Francisca,Dominguez, Esteban,De Blas, Jesus,Scott, William L.
, p. 821 - 828 (2001)
The enantioselective conjugate addition of Schiif base ester derivatives to Michael acceptors either in solution (56-89% e.e.) or on solid-phase (34-82% e.e.) gave optically active unnatural α-amino acid derivatives. The reaction was conducted in the pres
Expanding the Toolbox of Heterogeneous Asymmetric Organocatalysts: Bifunctional Cyclopropenimine Superbases for Enantioselective Catalysis in Batch and Continuous Flow
Leonardi, Costanza,Brandolese, Arianna,Preti, Lorenzo,Bortolini, Olga,Polo, Eleonora,Dambruoso, Paolo,Ragno, Daniele,Di Carmine, Graziano,Massi, Alessandro
, p. 5473 - 5485 (2021)
A strategy for the immobilization of chiral 2,3-bisaminocyclopropenium salt (pre-catalyst) onto polystyrene and silica supports is presented together with a suitable procedure for the conversion into the corresponding cyclopropenimine superbase catalysts.
Structure-activity relationship studies of cyclopropenimines as enantioselective Bronsted base catalysts
Bandar, Jeffrey S.,Barthelme, Alexandre,Mazori, Alon Y.,Lambert, Tristan H.
, p. 1537 - 1547 (2015/02/05)
We recently demonstrated that chiral cyclopropenimines are viable Bronsted base catalysts in enantioselective Michael and Mannich reactions. Herein, we describe a series of structure-activity relationship studies that provide an enhanced understanding of the effectiveness of certain cyclopropenimines as enantioselective Bronsted base catalysts. These studies underscore the crucial importance of dicyclohexylamino substituents in mediating both reaction rate and enantioselectivity. In addition, an unusual catalyst CH...O interaction, which provides both ground state and transition state organization, is discussed. Cyclopropenimine stability studies have led to the identification of new catalysts with greatly improved stability. Finally, additional demonstrations of substrate scope and current limitations are provided herein.
Transition state analysis of enantioselective br?nsted base catalysis by chiral cyclopropenimines
Bandar, Jeffrey S.,Sauer, Gregory S.,Wulff, William D.,Lambert, Tristan H.,Vetticatt, Mathew J.
, p. 10700 - 10707 (2014/08/18)
Experimental 13C 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.
