- Cooperative catalysis by carbenes and Lewis acids in a highly stereoselective route to γ-lactams
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Enzymes are a continuing source of inspiration for the design of new chemical reactions that proceed with efficiency, high selectivity and minimal waste. In many biochemical processes, different catalytic species, such as Lewis acids and bases, are involved in precisely orchestrated interactions to activate reactants simultaneously or sequentially. This type of 'cooperative catalysis', in which two or more catalytic cycles operate concurrently to achieve one overall transformation, has great potential in enhancing known reactivity and driving the development of new chemical reactions with high value. In this disclosure, a cooperative N-heterocyclic carbene/Lewis acid catalytic system promotes the addition of homoenolate equivalents to hydrazones, generating highly substituted γ-lactams in moderate to good yields and with high levels of diastereo- and enantioselectivity.
- Raup, Dustin E. A.,Cardinal-David, Benoit,Holte, Dane,Scheidt, Karl A.
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scheme or table
p. 766 - 771
(2010/11/18)
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- Stereoselective Michael addition of glycine anions to chiral fischer alkenylcarbene complexes. Asymmetric synthesis of β-substituted glutamic acids
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The reaction of lithium enolates of achiral N-protected glycine esters with chiral alkoxyalkenylcarbene complexes of chromium provided the corresponding Michael adducts with either high anti or syn selectivity depending on the nature of the nitrogen protecting group, and high diastereofacial selectivity when carbene complexes containing the (-)-8- phenylmenthyloxy group were employed. subsequent oxidation of the metal- carbene moiety followed by deprotection of the amine group and hydrolysis of both carboxylic esters afforded enantiomerically enriched 3-substituted glutamic acids of natural as well as unnatural stereochemistry. Alternatively, when the deprotection step was performed previously to the oxidation, cyclic aminocarbene complexes were formed, which finally led to optically active 3-substituted pyroglutamic acids.
- Ezquerra, Jesus,Pedregal, Concepcion,Merino, Isabel,Florez, Josefa,Barluenga, Jose,Garcia-Granda, Santiago,Llorca, Maria-Amparo
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p. 6554 - 6565
(2007/10/03)
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- Selective Inhibition of γ-Aminobutyric Acid Aminotransferase by (3R,4R),(3S,4S)- and (3R,4S),(3S,4R)-4-Amino-5-fluoro-3-phenylpentanoic Acids
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(3R,4R),(2S,4S)- and (3R,4S),(3S,4R)-4-amino-5-fluoro-3-phenylpentanoic acid (1a and 1b) were synthesized and studied as selective inactivators of γ-aminobutyric acid (GABA) aminotransferase.Neither compound caused time-dependent inactivation of the enzym
- Silverman, Richard B.,Nanavati, Shrenik M.
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p. 931 - 936
(2007/10/02)
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