Organocatalytic asymmetric synthesis of quaternary α-isoxazole–α-alkynyl amino acid derivatives

Abstract

An enantioselective addition of 5-amino-isoxazoles with β,γ-alkynyl-α-ketimino esters catalyzed by a chiral phosphoric acid has been developed. This procedure allowed the formation of quaternary α-isoxazole-α-alkynyl amino acid derivatives with high...

Accessing unnatural α-amino acids with tetrasubstituted stereogenic centersviacatalytic enantioselective reactions of ketimine-type α-iminoesters/α-iminoamides

“…123 Zhang and co-workers used 5-aminoisoxazoles as nucleophiles in aza-FC reaction of alkynyl-substituted ketimines 47a catalyzed by CPA 161e to afford a-isoxazole-substituted ATAAs 184 (Scheme 75, bottom). 124 All reactions proceeded to afford good yields, diastereoselectivities, and enantioselectivities, and were broadly substrate-tolerant. In addition, ATAAs 182 and 184 were successfully chemically modified.…”

Aromatic C–H bond functionalization through organocatalyzed asymmetric intermolecular aza-Friedel–Crafts reaction: a recent update

“…The chiral phosphoric acid P22 was used as catalyst to introduce the aza-ester quaternary sterocenter in the molecular entities 87 with appreciable chemical yields and excellent enantioselectivities. One example was presented with a 5-aminoisothiazole motif that gave the product with much decreased yield (70%) and enantioselectivity (36% ee) ( Scheme 20b ) [ 49 ].…”

Chiral spirocyclic phosphoric acid-catalyzed enantioselective synthesis of heterotriarylmethanes bearing an amino acid moiety

“…21 b As a result, the synthesis of enantioenriched compounds with isoxazole moieties has garnered attention from chemical researchers. Recently, asymmetric synthesis of compounds bearing isoxazole was synthesized via organocatalytic asymmetric 1,6-addition of pyrazol-5-ones to 3-methyl-4-nitro-5-alkenylisoxazoles 27 and enantioselective addition of 5-amino-isoxazoles with β,γ-alkynyl-α-ketimino esters in high yields and enantioselectivities. 28 …”