Synthesis of 3- Benzylidene, 5-Substituted 3-Benzylidene, 3- Hetarylmethylene and 5-Substituted Hetarylmethylene Derivatives of Indolin- 2-ones

A wide variety of titled compounds, several of which have neuro-protecting properties has been prepared in yields ranging between 70 to 90%. The compounds were identified by 1 HNMR, 13 C NMR, 1D and 2D NOE analysis, and HRMS. An investigation of the effect of certain 5-substitutuents on the E to Z ratios in DMSO-d6 was carried out. The 5- nitro and 5-acetyl substituents were not isomerized, whereas the 5-fluoro, 5-chloro and 5-bromo underwent significant isomerization. In the former cases resonance interaction of the lone pair electrons of NH group of the indolin-2-one with the 5-nitro or 5-acetyl of the indolin-2-one prevents rotation of the benzylidene C=C bond whereas in the case of the latter 5-halo substituent, the lone pair electrons on the NH group interacts with the benzylidene C=C bond giving rise to anionic C-C - bond in which rotation about this bond can occur.