Synthesis of 4-Oxoisoxazoline N-Oxides via Pd-Catalyzed Cyclization of Propargylic Alcohols with tert-Butyl Nitrite

A cyclization of propargylic alcohols with tert -butyl nitrite at room temperature in air was achieved using Pd(OAc) 2 as catalyst. The first reported 4-oxoisoxazoline N -oxides could be directly accessed from a range of multisubstituted propargylic alcohols in moderate to excellent yields under mild conditions. Density functional theory calculations indicated that the reaction proceeds through a palladium-catalyzed NO 2 addition that efficiently generates a ketoxime radical, which eventually produces 4-oxoisoxazoline N -oxide.