Direct Catalytic Asymmetric Mannich-Type Reaction en Route to α-Hydroxy-β-amino Acid Derivatives

Copper-Catalyzed Direct Asymmetric Aldol Reaction of Glycine Schiff Bases to Access syn-β-Hydroxy-α-amino Esters

This study reported a copper-catalyzed direct asymmetric aldol reaction between aldehydes and glycine Schiff bases with methyl, allyl, and tert-butyl esters. Additionally, this reaction afforded high yields of syn-β-hydroxy-α-amino esters with excellent enantio- and diastereoselectivities (93-99% ee, up to >99:1 dr). The aldol reaction accepted aromatic, linear aliphatic, and α-substituted aliphatic aldehydes.

High anti Diastereoselectivity in a Tandem Oxyhomologation-Coupling Protocol for the Preparation of Amides and Peptides Incorporating α-Hydroxy β-Amino Acids

The one-pot MAC (Masked Acyl Cyanide) reaction is used to perform the tandem oxyhomologation reaction of N,N-dibenzyl-l-phenylalaninal and coupling with nitrogen nucleophiles to provide a wide selection of amide and peptide derivatives of (2S,3S)-allophenylnorstatin in generally good yields and with high anti selectivity, often with dr >98:2. The procedure works equally well with other selected N,N-dibenzyl α-amino aldehydes, and is used to achieve a very short synthesis of (2S,3S,S)-epibestatin.

Development of Catalytic Enantioselective Mannich Reactions Using Esters

Catalytic enantioselective Mannich reactions of simple nonactivated esters proceeded using a chiral potassium strong base catalyst prepared from a chiral bisoxazoline and potassium hexamethyldisilazide. Alkyl acetates, alkyl propionates, and an alkyl butyrate were employed as the simple esters, and the desired reactions proceeded smoothly to afford Mannich products in good to high yields with high enantioselectivities. One of the products was successfully employed in the asymmetric total synthesis of Maraviroc.

Boron-Catalyzed α-Functionalizations of Carboxylic Acids

Catalytic, chemoselective, and asymmetric α-functionalizations of carboxylic acids promise up-grading simple feedstock materials to value-added functional molecules, as well as late-stage structural diversifications of multifunctional molecules, such as drugs and their leads. In this personal account, we describe boron-catalyzed α-functionalizations of carboxylic acids developed in our group (five reaction types). The reversible boron carboxylate formation is key to the acidification of the α-protons and enolization using mild organic bases, allowing for chemoselective and asymmetric bond formations of carboxylic acids. The ligand effects on reactivity and stereoselectivity, substrate scopes, and mechanistic insights are summarized.

Amide bond formation: beyond the dilemma between activation and racemisation

The development of methods for amide bond formation without recourse to typical condensation reagents has become an emerging research area and has been actively explored in the past quarter century. Inspired by the structure of vitamin B12, we have developed a metal-templated macrolactamisation that generates a new wave towards classical macrolactam synthesis. Further, distinct from the extensively used methods with condensation reagents or catalysts based on catalyst/reagent control our metal-catalysed methods based on substrate control can effectively address long-standing challenges such as racemisation in the field of peptide chemistry. In addition, the substrate-controlled strategy demonstrates the feasibility of "remote" peptide bond-forming reaction catalysed by a metal-ligand complex. Moreover, an originally designed hydrosilane/aminosilane system can avoid not only racemisation but also unnecessary waste production. This feature article documents our discovery and application of our original approaches in amide bond formation.

Chiral Metal Salts as Ligands for Catalytic Asymmetric Mannich Reactions with Simple Amides

Catalytic asymmetric Mannich reactions of imines with weakly acidic simple amides were developed using a chiral potassium hexamethyldisilazide (KHMDS)-bis(oxazoline) potassium salt (K-Box) catalyst system. The desired reactions proceeded to afford the target compounds in high yields with high diastereo- and enantioselectivities. It was suggested that a K enolate interacted with K-Box to form a chiral K enolate that reacted with imines efficiently. In this system, K-Box (potassium salt of Box) worked as a chiral ligand of the active potassium species.

Organocatalytic Enantioselective Mukaiyama-Mannich Reaction of Isatin-Derived Ketimines for the Synthesis of Oxindolyl-β3, 3 -Amino Acid Esters

Mukaiyama-Mannich reactions of ester enolate equivalents with aldimines have been elegantly used for the asymmetric synthesis of β-amino acids; nevertheless, the corresponding asymmetric reaction employing ketimines are unexplored. Herein, the first organocatalytic enantioselective Mukaiyama-Mannich reaction employing isatin-derived ketimines with unsubstituted silyl ketene acetals is disclosed towards the scalable synthesis of 2-oxoindolinyl-β^3, 3 -amino acid esters at room temperature with excellent enantioselectivities (ee >99.5 %). Ultra-low catalyst loadings (as low as 250 ppm) could be used for the quantitative product formation with high enantiopurity. The synthetic utility of this protocol has been showcased in the short formal synthesis of pharmaceutically demanded (+)-AG-041R, a potent gastrin/CCK-B receptor antagonist.

Reversal of Diastereoselectivity in a Masked Acyl Cyanide (MAC) Reaction: Synthesis of Protected erythro-β-Hydroxyaspartate Derivatives

Using Garner's aldehyde as a substrate, one-pot MAC hydroxyhomologation reactions proceeded in good yields and with anti selectivity for the first time (dr up to 9:1). The products were used to prepare a panel of protected derivatives of erythro-β-hydroxyaspartic acid and erythro-β-hydroxyasparagine as single enantiomers in a few steps.

Efficient synthesis of α-alkyl-β-amino amides by transaminase-mediated dynamic kinetic resolutions

A transaminase-catalyzed dynamic kinetic resolution is described for the stereoselective synthesis of a series of α-alkyl-β-amino amides.

Copper-catalyzed enantioselective Mannich reaction between N-acylpyrazoles and isatin-derived ketimines

A copper-catalyzed enantioselective Mannich reaction between N-acylpyrazoles and isatin-derived ketimines is developed.

A AgOAc/quinine-derived aminophosphine complex as an efficient catalyst for diastereo- and enantioselective 1,3-dipolar cycloaddition of α,β-unsaturated 7-azaindoline amides and azomethine ylides

The Dixon’s catalyst system is effective for the asymmetric 1,3-dipolar cycloaddition.