HETERODIENE SYNTHESES-XXIV CHANGES IN THE REACTIVITY OF 2-OXOINDOLIN-3-YLIDENE DERIVATIVES WITH ETHYLVINYLETHER INDUCED BY ELECTRON-WITHDRAWING GROUPS. THE IMPORTANCE OF THE LUMO COEFFICIENTS

Article abstract of DOI:10.1016/S0040-4020(01)98944-6

Ethylvinylether reacts in acetonitrile with 1-acetyl-2-oxoindolin-3-ylidene derivatives β,β-disubstituted with electron-withdrawing substituents.When the β-substituents act by inductive effect alone, a regiospecific β-attack occured giving rise, through a 1,4-cycloaddition, to 2,3-dihydropyran<2,3-b>indoles.As a by product Michael adduct can be obtained.When the β-substituent act by conjugative effect also, a regiospecific α-attack occured giving rise to spiro-dihydropyrane or-cyclobutane-2-oxoindolines depending on the nature of the substituents.In a less polar solvent, the latter ones are formed together with the adduct arising from the regioisomeric β attack.The overall reactivity can be rationalized in terms of LUMO coefficients of the heterodiene and of different stabilization offered by the solvent to the various reaction pathways.