Cycloaddition of acyclic nitrones with phenyl isocyanate: Synthesis and ring-opening reactions of 1,2,4-oxadiazolidin-5-ones

Abstract

The cycloaddition of nitrones with unsubstituted or electron-donating substituents on the C-phenyl 1a,c,f with phenyl isocyanate proceeds smoothly for a short time with high yields to give the corresponding 1,2,4-oxadiazolidinone 2, and 1b,d,e with electron-withdrawing substituents gave the corresponding oxadiazolidinone in moderate yields after prolonged heating. Oxadiazolidinones 2a,c,f undergo diethylamine-induced fragmentation for a short time to give the corresponding Schiff bases, and oxadiazolidinones 2b,d,e remain unchanged in these conditions. Prolonged heating of 2d,e in the presence of diethylamine led to complex mixtures. In the case of 2b the corresponding amidine was the main product of the reaction.