Selective rhodium-catalyzed insertion of carbon monoxide into the nitrogen-oxygen bond of isoxazolidines. New reduction, migration, and rearrangement reactions catalyzed by iridium complexes

Reaction of isoxazolidines with carbon monoxide in benzene, catalyzed by the dimer of chloro(1,5-cyclooctadiene)rhodium, results in the formation of tetrahydro-1,3-oxazin-2-ones as the major or only product, often in fine yields. A novel conversion of 3-arylisoxazolidines to tetrahydro-1,3-oxazines occurs using an iridium catalyst (i.e. IrCl3 . 3H(2)O,Ir(CO)(3)Cl) and carbon monoxide. This remarkable reaction was shown to proceed by an intermolecular hydrogen transfer process. In some cases, an isomeric tetrahydro-1,3-oxazine, resulting from methyl migration from nitrogen to the carbon atom arising from carbon monoxide insertion, was isolated as a byproduct in the reaction. Isoxazolidines containing an alkyl group at the 3-position undergo a novel iridium-catalyzed rearrangement and ring expansion reaction. This transformation also occurred, albeit in lower yield, by treatment of 3-alkylisoxazolidines with hydrochloric acid in p-xylene.