Formation of tetracyclic oxazolidinones from cycloadducts of benzylidene ketones with 4-phenyl-4,5-dihydro-3H-1,2,4-triazole-3,5-dione (PTAD) by base-promoted backbone participation and rearrangement

Abstract

Alcoholysis and aminolysis of urazoles 4a–j prepared by the reactions of benzylidene ketones with 4-phenyl-4,5-dihydro-3H-1,2,4-triazole-3,5-dione (PTAD) afforded tricyclic oxazolidinone derivatives 5a–o in moderate yields (16–77%). The structure of compound 5b was confirmed by a single-crystal X-ray analysis. The reaction proceeded via opening of the urazole ring by initial Michael addition of nucleophiles (solvents) to the enone substructure, followed by participation of the carbonyl group and final skeletal rearrangements.