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.magnified image

Green Protocols in Heterocycle Syntheses via 1,3-Dipolar Cycloadditions

“…The design of a new synthetic path of 1,2,4-oxadiazolines, especially greener methods, is highly desirable because many of these methods suffer from one or more drawbacks. Soni et al (2018) have very recently presented a greener method for the synthesis of 1,2,4-oxadiazolines via an intramolecular oxidative cyclisations of amidoximes in the presence of an organocatalyst and molecular oxygen. The authors optimized the reaction conditions to give 3-phenyl- 5,6,7,7a-tetrahydropyrrolo[1,2-d][1,2,4]oxadiazole from phenyl(pyrrolidin- 1-yl)methanone oxime, which was used as a model substrate.…”

Recent Advances on Metal-Free, Visible-Light- Induced Catalysis for Assembling Nitrogen- and Oxygen-Based Heterocyclic Scaffolds

“…1,2,4-Oxadiazole derivatives besides exhibiting biological activities have also found application in light-emitting diodes (OLEDs) [76]. Due to the importance of this group, Cho and co-workers developed oxidative cyclization of amidoximes under visible-light conditions [77]. Described protocol involves the intramolecular oxidative cyclization of amidoximes 166 in the presence of the triphenylpyrylium 8c catalyst and molecular oxygen as the oxidant, promoted by compact fluorescent lamp (Scheme 23a).…”

Recent Advances in the Synthesis of Specialized Heterocyclic Molecules by 1, 3-Dipolar Cycloaddition Reaction: A Study Based on Greener Protocols

“…This reaction has many applications. Chakraborty et al 76 have also successfully reported the synthesis of spiro isoxazolidine derivatives under microwave-induced 1,3-dipolar cycloaddition reactions of α-chloro nitrone in atom efficient reactions with excellent yields (Scheme-43).…”