Synthesis of Isoxazoles via One-Pot Oxidation/Cyclization Sequence from Propargylamines

Access to Isoxazoles via Photo-oxygenation of Furan Tethered α-Azidoketones

Photocatalyst-free visible light-enabled direct oxygenation of furan-tethered α-azidoketones was studied. The reaction yielded various products depending on the substituents, with isoxazoles forming as the major products. The findings suggest that singlet oxygen was generated during the reaction and reacted with α-azidoketones in a [4 + 2] fashion to yield endoperoxides, which rearranged in multiple ways to generate isoxazoles. Some of the synthesized isoxazoles were evaluated as α-glucosidase inhibitors, and three of them 5bi, 5bj, and 5bl exhibited good activity with IC50 values of 454.57 ± 29.34, 147.84 ± 2.28, and 272.58 ± 42.06 μM, respectively, when compared with the standard drug acarbose (IC50 = 1224.33 ± 126.72 μM).

Synthesis of 3,5-disubstituted isoxazoles by domino reductive Nef reaction/cyclization of β-nitroenones

β-Nitroenones can be efficiently converted into 3,5-disubstituted isoxazoles by using tin(II)chloride dihydrate and ethyl acetate as a reducing agent and solvent, respectively. Products are obtained in good yields and several functional groups are tolerated thanks to the mild reaction conditions.

Lewis acid-promoted direct synthesis of isoxazole derivatives

Isoxazole derivatives were synthesized via a one-pot method utilizing 2-methylquinoline derivatives as template substrates, sodium nitrite as a nitrogen-oxygen source, and solely using aluminum trichloride as the additive. This approach circumvents the need for costly or highly toxic transition metals and presents a novel pathway for the synthesis of isoxazole derivatives.

Tunable Key [3 + 2] and [2 + 1] Cycloaddition of Enaminones and α-Diazo Compounds for the Synthesis of Isomeric Isoxazoles: Metal-Controlled Selectivity

The three-component reactions of enaminones, α-diazo esters/ketones, and t-butyl nitrite (TBN) for the switchable synthesis of isomeric isoxazoles have been realized. The catalysis with Cu(II) salt provides 3,4-disubsituted isoxazoles via [3 + 2] cycloaddition. On the other hand, the catalysis of Ag(I) with identical substrates leads to isomeric isoxazoles with reversed C3 and C4 substitution based on a key [2 + 1] cycloaddition.

Catalytic Methylene Insertion between Amines and Terminal Alkynes via C-N Bond Cleavage of N,N-Dimethylacetamide: A Unique Route to Propargylic Amines

A copper-based system allows for the methylene insertion between an amine and a milder nucleophile, including a terminal alkyne counterpart, via C-N bond cleavage of N,N-dimethylacetamide. The method gives an expedient access to propargylic amines in good to excellent yields. A wide-ranging substrate scope and late-stage functionalization of complex molecules make the protocol practically valuable.