Application, Reactivity and Synthesis of Isoxazole Derivatives

Mechanochemical Conditions for Intramolecular N-O Couplings via Rhodium Nitrenoids Generated from N-Acyl Sulfonimidamides

Starting from N-acyl sulfonimidamides, mechanochemically generated rhodium nitrenoids undergo intramolecular N-O couplings to provide unprecedented 1,3,2,4-oxathiadiazole 3-oxides in good to excellent yields. The cyclization proceeds efficiently with a catalyst loading of only 0.5 mol % in the presence of phenyliodine(III) diacetate (PIDA) as oxidant. Neither an inert atmosphere nor additional heating is required in this solvent-free procedure. Under heat or blue light, the newly formed five-membered heterocycles function as nitrene precursors reacting with sulfoxides as exemplified by the imidation of dimethyl sulfoxide.

Palladium-Catalyzed Carbohalogenation of Olefins with Alkynyl Oxime Ethers: Rapid Access to Chlorine-Containing Isoxazoles

A palladium-catalyzed carbohalogenation of olefins with alkynyl oxime ethers has been described, which provides efficient and practical access to various chlorine-containing isoxazoles. This method exhibits excellent regioselectivity, good functional group compatibility, and mild reaction conditions. The mechanistic studies suggest that the reaction proceeds via a stabilized π-benzyl palladium intermediate, which is essential for the formation of C(sp3)-Cl bonds.

Unveiling the regioselective synthesis of antiviral 5-isoxazol-5-yl-2´-deoxyuridines from the perspective of a molecular electron density theory

The regioselective synthesis of a potent antiviral sugar nucleoside isoxazole analogue in the [3+2] cycloaddition (32CA) reaction of acetonitrile- -N-oxide (ANO) and acetyl-protected 5-ethynyl-2?-deoxyuridine (EDU) has been studied at the MPWB1K/6-311G(d,p) level within perspective of the molecular electron density theory (MEDT). From an electron localization function (ELF) analysis, ANO is classified as a zwitterionic species devoid of any pseudoradical or carbenoid centre. The ortho regioisomer is energetically preferred over the meta one by the activation enthalpy of 21.7?24.3 kJ mol-1, suggesting complete regioselectivity in agreement with the experiment. The activation enthalpy increases from 53.9 kJ mol-1 in the gas phase to 71.5 kJ mol-1 in water, suggesting more facile reaction in low polar solvents. The minimal global electron density transfer (GEDT) at the TSs suggests non-polar character and the formation of new covalent bonds has not been started at the located TSs, showing non-covalent intermolecular interactions from an atoms-in- -molecules (AIM) study and in the independent gradient model (IGM) isosurfaces. The AIM analysis shows more accumulation of electron density at the C?C interacting region relative to the C?O one, and earlier C?C bond formation is predicted from a bonding evolution theory (BET) study.