- Expanding the Toolbox of Heterogeneous Asymmetric Organocatalysts: Bifunctional Cyclopropenimine Superbases for Enantioselective Catalysis in Batch and Continuous Flow
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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.
- Leonardi, Costanza,Brandolese, Arianna,Preti, Lorenzo,Bortolini, Olga,Polo, Eleonora,Dambruoso, Paolo,Ragno, Daniele,Di Carmine, Graziano,Massi, Alessandro
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p. 5473 - 5485
(2021/10/14)
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- Structure-activity relationship studies of cyclopropenimines as enantioselective Bronsted base catalysts
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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.
- Bandar, Jeffrey S.,Barthelme, Alexandre,Mazori, Alon Y.,Lambert, Tristan H.
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p. 1537 - 1547
(2015/02/05)
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- Chiral octahedral complexes of cobalt(III) as "organic catalysts in disguise" for the asymmetric addition of a glycine schiff base ester to activated olefins
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Stereochemically inert and positively charged chiral complexes of cobalt(III) prepared from Schiff bases derived from chiral diamines and salicylaldehydes were shown to be efficient catalysts of the benchmark asymmetric phase-transfer Michael addition of nine activated olefins to O'Donnell's substrate. The reaction products had enantiomeric purities of up to 96%. DFT calculations were invoked to rationalize the stereochemistry of the addition.
- Maleev, Victor I.,North, Michael,Larionov, Vladimir A.,Fedyanin, Ivan V.,Savel'Yeva, Tatyana F.,Moscalenko, Margarita A.,Smolyakov, Alexander F.,Belokon, Yuri N.
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supporting information
p. 1803 - 1810
(2014/06/09)
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- CYCLOPROPENIMINE CATALYST COMPOSITIONS AND PROCESSES
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The present invention provides, inter alia, a cyclopropenimine Br?nsted base catalyst and a cyclopropenimine scaffold for use as a Br?nsted base catalyst. This cyclopropenimine has the structure (100). Methods for making such a cyclopropenimine are also provided. Further provided are processes for carrying out an organic synthetic reaction and processes for catalyzing a proton transfer reaction enantioselectively using such a cyclopropenimine Br?nsted base catalyst.
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Paragraph 0208; 0221
(2013/05/09)
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- Enantioselective Bronsted base catalysis with chiral cyclopropenimines
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Cyclopropenimines are shown to be a highly effective new class of enantioselective Bronsted 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 P1-tBu phosphazene base. An X-ray crystal structure of the protonated catalyst is shown along with a proposed mechanistic and stereochemical rationale.
- Bandar, Jeffrey S.,Lambert, Tristan H.
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supporting information; experimental part
p. 5552 - 5555
(2012/05/20)
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- Preparation of chiral amino esters by asymmetric phase-transfer catalyzed alkylations of schiff bases in a ball mill
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The asymmetric alkylation of Schiff bases under basic conditions in a ball mill was performed. The starting Schiff bases of glycine were prepared beforehand by milling protected glycine hydrochloride and benzophenone imine, in the absence of solvent. The Schiff base was then reacted with a halogenated derivative in a ball mill in the presence of KOH. By adding a chiral ammonium salt derived from cinchonidine, the reaction proceeded asymmetrically under phase-transfer catalysis conditions, giving excellent yields and enantiomeric excesses up to 75 %. Because an equimolar amount of starting material was used, purification was greatly simplified. Copyright
- Nun, Pierrick,Perez, Violaine,Calmes, Monique,Martinez, Jean,Lamaty, Frederic
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p. 3773 - 3779
(2012/04/23)
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- Co-catalyst enhancement of enantioselective PTC Michael additions involving glycine imines
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In this Letter we demonstrate that the use of 2,4,6-trimethylphenol (mesitol) as a co-catalyst facilitates highly enantioselective addition of benzophenone glycine imine tert-butyl ester to a range of Michael acceptors.
- Lygo, Barry,Beynon, Christopher,Lumley, Christopher,McLeod, Michael C.,Wade, Charles E.
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experimental part
p. 3363 - 3365
(2009/08/17)
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- Synthesis of (ε-13C-,ε-15N)-enriched L-lysine - Establishing schemes for the preparation of all possible 13C and 15N isotopomers of L-lysine, L-ornithine, and L-proline
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In this paper we describe a simple synthetic strategy that, with the right rational adaptation, gives direct access to any 13C/15N isotopomer of L-glutamate, L-ornithine, L-proline, L-lysine, and L-α, amino adipic acid. This strategy also allows access to nonproteinogenic amino acids like L-citrulline in high yields and optical purity. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Siebum, Arjan H. G.,Tsang, Robert K. F.,Van Der Steen, Rob,Raap, Jan,Lugtenburg, Johan
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p. 4391 - 4396
(2007/10/03)
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- Synthesis of chiral azacrown ethers derived from α-D-glucose and their catalytic properties on the asymmetric Michael addition
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Three types of chiral azacrown ethers have been synthesized from (+)(4,6-O-benzylidene)-O-methyl-α-D-glucopyranoside and their catalytic properties for the asymmetric Michael addition have been investigated; enantioselectivity switching which is dependent on the azacrown ether catalysts has been achieved.
- Itoh, Toshiyuki,Shirakami, Shohei
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- Enantioselective solution- and solid-phase synthesis of glutamic acid derivatives via Michael addition reactions
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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
- O'Donnell, Martin J.,Delgado, Francisca,Dominguez, Esteban,De Blas, Jesus,Scott, William L.
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p. 821 - 828
(2007/10/03)
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- Highly enantioselective Michael reactions catalyzed by a chiral quaternary ammonium salt. Illustration by asymmetric syntheses of (S)-ornithine and chiral 2-cyclohexenones.
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[formula: see text] The use of the chiral quaternary ammonium salts 1a and 1b makes possible enantioselective Michael reactions which have been applied to the asymmetric syntheses of (S)-ornithine (2) and the chiral 2-cyclohexenone 6.
- Zhang,Corey
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p. 1097 - 1100
(2007/10/03)
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