Organocatalytic Oxidative Cyclization of Amidoximes for the Synthesis of 1,2,4-Oxadiazolines

Abstract

Organocatalytic synthesis of bi- and tricyclic fused 1,2,4-oxadiazolines is reported. The reaction proceeds through oxidative cyclization of the corresponding amidoxime using 2,4,6-tris(4-fluorophenyl)pyrylium tetrafluoroborate (T(p-F)PPT) as the organocatalyst, and molecular oxygen as the green oxidant. During the transformation, T(p-F)PPT acts as both the electrophilic catalyst and photocatalyst, and the reaction is promoted by irradiation with visible light. The method introduced herein offers a straightforward route to the preparation of 1,2,4-oxadiazolines with different functionalities, and is highly atom economical.