Synthesis of 1,2,4-Oxadiazolines through Deoxygenative Cyclization of <i>N</i>-Vinyl-α,β-Unsaturated Nitrones with <i>in Situ</i> Generated Nitrile Oxides from Hydroxamoyl Chlorides
Cai‐Mei Nong, Si-Ning Lv, Wei‐Min Shi, Cui Liang, Gui‐Fa Su, Dong‐Liang Mo
Abstract
A variety of 1,2,4-oxadiazoline derivatives were synthesized in moderate to good yields through a deoxygenative cyclization cascade reaction of N-vinyl-α,β-unsaturated nitrones and hydroxamoyl chlorides. Mechanistic studies revealed that the reaction underwent double additions of nitrile oxides to N-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 i-PrOH solvent through [3 + 3] cycloaddition and selective [3,3]-rearrangement. Moreover, the prepared 1,2,4-oxadiazolines were easily converted to polysubstituted pyrroles under thermal conditions.