Bicarbonate Salts as Cost-Effective Bases for the Synthesis of Ketenes and Their Synthetic Equivalents Applied to the Asymmetric Synthesis of β-Lactams
We report the use of bicarbonate salts as viable alternatives to more expensive bases for the in situ generation of ketenes and their synthetic equivalents. We have successfully applied this to the catalytic, asymmetric synthesis of β-lactams.
Bifunctional Asymmetric Catalysis: A Tandem Nucleophile/Lewis Acid Promoted Synthesis of β-Lactams
(matrix presented) We describe a superior procedure for the catalytic, asymmetric synthesis of β-lactams using a bifunctional catalyst system consisting of a chiral nucleophile and an achiral Lewis acid.
France, Stefan,Wack, Harald,Hafez, Ahmed M.,Taggi, Andrew E.,Witsil, Daniel R.,Lectka, Thomas
Column asymmetric catalysis for beta-lactam synthesis.
[structure] A catalytic asymmetric reaction process was designed involving the use of solid-phase reagents and catalysts that constitute the packing of a series of "reaction columns". This process was applied to the catalytic asymmetric synthesis of beta-
Molecular mechanics calculations as predictors of enantioselectivity for chiral nucleophile catalyzed reactions
We present molecular mechanics (MM) calculations as models of activated complexes for the β-lactam forming [2+2] cycloaddition between imino ester 4 and the zwitterionic intermediates derived from ketenes and various chiral nucleophilic catalysts. Our met
Taggi, Andrew E.,Hafez, Ahmed M.,Dudding, Travis,Lectka, Thomas
Development of a new dimeric cyclophane ligand: Application to enhanced diastereo- and enantioselectivity in the catalytic synthesis of β-lactams
We detail the synthesis of a new C2-symmetric bis(cyclophane) ligand system that can be thought of as electronically analogous to binol, but which possesses the added third dimension of cyclophane chirality. The ligand synthesis involves a spontaneous (but unexpected) atropisomerization to the desired product. We have employed this ligand to form a metal complex that is an effective cocatalyst for the highly enantio- and diastereoselective catalytic asymmetric synthesis of a β-lactam.
Wack, Harald,France, Stefan,Hafez, Ahmed M.,Drury III, William J.,Weatherwax, Anthony,Lectka, Thomas
Bifunctional Lewis acid-nucleophile-based asymmetric catalysis: Mechanistic evidence for imine activation working in tandem with chiral enolate formation in the synthesis of β-lactams
We report a mechanistically based study of bifunctional catalyst systems in which chiral nucleophiles work in conjunction with Lewis acids to produce β-lactams in high chemical yield, diastereoselectivity, and enantioselectivity. Chiral cinchona alkaloid
France, Stefan,Shah, Meha H.,Weatherwax, Anthony,Wack, Harald,Roth, Justine P.,Lectka, Thomas
p. 1206 - 1215
(2007/10/03)
Catalytic, Asymmetric α-Chlorination of Acid Halides
We present a full account of a tandem catalytic, asymmetric chlorination/esterification process that produces highly optically enriched α-chloroesters from inexpensive, commercially available acid halides using cinchona alkaloid derivatives as catalysts and polychlorinated quinones as halogenating agents. We have performed kinetics and control experiments to investigate the reaction mechanism and establish conditions under which the reactions can be best performed. We have developed NaH and NaHCO3 shuttle base systems as the easiest and most cost-effective ways of conducting the reactions, rendering the methodology economically competitive with known chiral halogenation procedures. We have also demonstrated the utility of our reactions by converting the products to synthetically useful derivatives.
France, Stefan,Wack, Harald,Taggi, Andrew E.,Hafez, Ahmed M.,Wagerle, Ty R.,Shah, Meha H.,Dusich, Crystal L.,Lectka, Thomas
p. 4245 - 4255
(2007/10/03)
The development of the first catalyzed reaction of ketenes and imines: Catalytic, asymmetric synthesis of β-lactams
We report practical methodology for the catalytic, asymmetric synthesis of β-lactams resulting from the development of a catalyzed reaction of ketenes (or their derived zwitterionic enolates) and imines. The products of these asymmetric reactions can serve as precursors to a number of enzyme inhibitors and drug candidates as well as valuable synthetic intermediates. We present a detailed study of the mechanism of the β-lactam forming reaction with proton sponge as the stoichiometric base, including kinetics and isotopic labeling studies. Stereochemical models based on molecular mechanics (MM) calculations are also presented to account for the observed stereoregular sense of induction in our reactions and to provide a guidepost for the design of other catalyst systems.
Taggi, Andrew E.,Hafez, Ahmed M.,Wack, Harald,Young, Brandon,Ferraris, Dana,Lectka, Thomas
p. 6626 - 6635
(2007/10/03)
Asymmetric catalysis on sequentially-linked columns
We report a catalytic asymmetric reaction process that involves the use of solid-phase reagents and catalysts that constitute the packing of a series of "reaction columns". This process was applied to the catalytic asymmetric synthesis of β-lactams, to yi
Hafez,Taggi,Dudding,Lectka
p. 10853 - 10859
(2007/10/03)
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