Synthesis of 1,2,4-Oxadiazolines through Deoxygenative Cyclization of -Vinyl-α,β-Unsaturated Nitrones with Generated Nitrile Oxides from Hydroxamoyl Chlorides.

A variety of 1,2,4-oxadiazoline derivatives were synthesized in moderate to good yields through a deoxygenative cyclization cascade reaction of -vinyl-α,β-unsaturated nitrones and hydroxamoyl chlorides. Mechanistic studies revealed that the reaction underwent double additions of nitrile oxides to -vinyl-α,β-unsaturated nitrones, sequential elimination, and intramolecular cyclization to afford 1,2,4-oxadiazolines. Alternatively, 1,2,5-oxadiazolines were also obtained as major products in PrOH solvent through [3 + 3] cycloaddition and selective [3,3]-rearrangement.