On the Reaction of Isatin with Cyanomethylene(triphenyl)-phosphorane. A Nucleophilic Attack of Alkyl Phosphites on the Carbon–Carbon Double Bond of (E)-Oxindolylideneacetonitrile

The reaction of cyanomethylene(triphenyl)phosphorane (2) with isatin (1) in dry benzene at room temperature for 1 h led to the formation of (1,2-dihydro-2-oxo-3H-indol-3-yl)acetonitrile as a mixture of E- and Z-stereo isomers 3 and 4. Trialkyl phosphites 7 reacted with (E)-nitrile 3 in dry benzene at 70°C for about 10 h to give the phosphonates 8 as two isomers together with the unexpected spiro products of isomers 9. When the (E)-nitrile 3 was allowed to react with dialkyl phosphites (11) without solvents at 100°C for about 30 h, a mixture of the phosphonate derivatives 8 and one isomer of the dimeric structure 9 were obtained. The reaction mechanisms are considered and the structural assignments of the new compounds are based on chemical and spectroscopic evidence.