Investigation on the reactivity of α-azidochalcones with carboxylic acids: Formation of α-amido-1,3-diketones and highly substituted 2-(trifluoromethyl)oxazoles

Lewis acid-mediated transformations of 5-acyl-N-fluoroalkyl-1,2,3-triazoles to cyclopentenones, indenones, or oxazoles

We present a transition metal-free approach to 2-N-substituted indenones, cyclopentenones, and 4-carbonyl oxazoles, based on the reaction of 5-acylated N-fluoroalkyl substituted 1,2,3-triazoles (prepared by a three-component click reaction of copper acetylides, fluoroalkyl azides, and acyl chlorides) with Lewis acids aluminium trichloride or boron trifluoride etherate, proceeding via the generation and cyclization of vinyl cations.

Copper Loading-Controlled Selective Synthesis of 2,5-Bis(trifluoromethyl) and Monotrifluoromethyl-Substituted Oxazoles

A general domino annulation reaction of sulfonylmethyl isocyanide with trifluoroacetic anhydride in the presence of copper chloride as an additive is developed. The reaction affords 2,5-bis(trifluoromethyl)oxazoles in modest to good yields under mild conditions. A wide variety of sulfonylmethyl isocyanide and perfluorocarboxylic anhydride substrates are amenable to this transformation. Under a higher copper salt loading conditions, the reaction led to the formation of monotrifluoromethyl-substituted oxazole product.

Synthesis of 2-Fluoroalkylated Oxazoles from β-Monosubstituted Enamines via Fluoroacyloxylation and Cyclization Mediated by Fluoroalkyl-Containing Hypervalent Iodine(III) Species Generated In Situ

A metal-free synthesis of a series of fluoroalkyl-containing oxazoles from β-monosubstituted enamines was developed. This fluoroacyloxylation/cyclization cascade process was mediated by fluoroalkyl-containing hypervalent iodine(III) species formed in situ from the reaction of phenyliodine(III) diacetate (PIDA) and RCF₂CO₂H (R = H, Cl, Br, F, CF₃, CH₃, Ph, SAr, OAr).

One-pot synthesis of 4-substituted 2-fluoroalkyloxazoles from NH-1,2,3-triazoles and fluoroalkylated acid anhydrides

An efficient one-pot method for the synthesis of 2-fluoroalkyloxazoles from 4-substituted NH-1,2,3-triazoles, fluorinated anhydrides and triethylamine was developed.

Access to highly substituted oxazoles by the reaction of α-azidochalcone with potassium thiocyanate

The reactivity of α-azidochalcones has been explored for the preparation of highly substituted oxazoles via a 2H-azirine intermediate. The azidochalcones, when treated with potassium thiocyanate in the presence of potassium persulfate, lead to 2,4,5-trisubstituted oxazoles in good yields. Incidentally, 2-aminothiazoles are the products when ferric nitrate is employed instead of persulfate in the above reaction.

BF3·OEt2-TFAA Mediated Tetra-Functionalization of Amino Acids - Synthesis of Di- and Tri-Substituted 2-Trifluoromethyl Oxazoles in One Pot

A highly efficient, TFAA-BF₃·OEt₂ mediated multicomponent coupling of amino acid, TFAA, and aromatics provides a broad library of 2-trifluoromethyl equipped 2,5-disubstituted/2,4,5-trisubstituted oxazoles or N-(trifluoroacetyl)-β-aminoalkyl ketones. This amino acid tetra-functionalization approach involves amidation (C-N), anhydride (C-O), Friedel-Crafts acylation (C-C), and Robinson-Gabriel annulation (C-O) followed by dehydrative aromatization. This reaction takes place under operationally simple, mild, and metal-free conditions using readily available amino acids and aromatic compounds.

Copper-Catalyzed Three-Component Domino Cyclization for the Synthesis of 4-Aryl-5-(arythio)-2-(trifluoromethyl)oxazoles

A copper-catalyzed oxidative cyclization of oxime, arylthiol, and trifluoroacetic anhydride for the construction of trisubstituted oxazoles has been developed. This transformation combines N-O bond cleavage, C-H functionalization, and intramolecular annulation, providing a practical protocol for the introduction of a trifluoromethyl (-CF₃) group at oxazole rings.

Facile access to 2-acyloxy-, aryloxy- and alkenyloxy-2H-azirinesviaan SN2′–SN2′ cascade in 2-halo-2H-azirines

A convenient method of synthesis of 2-oxygen-substituted 2H-azirinesviathe unusual S_N2′–S_N2′ cascade halogen substitution in 2-halo-2H-azirines is developed.

Divergent reactivity of α-azidochalcones with metal β-diketonates: tunable synthesis of substituted pyrroles and indoles

A divergent reactivity of α-azidochalcones with metal β-diketonates for the synthesis of substituted pyrroles and indoles is described.