Reactions of indole related compounds. III. (E) and (Z)-2-oxoindolin-3-ethylidenes.

The reaction of 2-indolinone (I) with acetaldehyde was carried out in the presence of dimethylaniline and afforded the epimeric mixture of 2-oxoindolin-3-ethylidenes in good yield. The epimeric 2-oxoindolin-3-ethylidenes were successfully separated to give pale yellow needles (II), mp 173-174°(15%) and bright yellow needles (III), mp 147-148.5°(38%). The configurations of II and III were assigned Z and E respectively on the basis of their 1H- and 13C-NMR spectral data.