Search

Thermal reactions of hitherto α3pyridylNphenylnitrone 1 with monosubstituted electronrich and electronneutral dipolarophiles are regio, and stereoselective exoselective, controlled by LUMO dipole HOMO dipolarophile interaction, and furnish syn5substituted33pyridylisoxazolidines 5 in high yields. With electron deficient dipolarophiles such as acrylonitrile there is observed a loss of regioselectivity as well as stereoselectivity and the regioselectivity is reversed in reactions with methyl vinyl ketone and methyl acrylate, due to intervention of HOMOdipole LUMOdipolarophile interaction, affording 4substituted33pyridylisoxazolidines 7 as major products. Reactions of nitrone 1 with disubstituted dipolarophiles such as methyl methacrylate and ethyl coronate furnish methyl syn5methy3pyridyl1phenylisoxazolidine5carboxylate 8 and ethyl anti5methy3pyridyl1phenylisoxazolidine4carboxylate 10, respectively, in high yields. Reaction with NPhenylmaleimide affords novel isoxazolidinopyrrolidinediones bearing a 3pyridyl moiety 11, 12. A mechanistic rationalization of the obtained results in terms of electronic, steric and secondary interactions is proffered.