Reactions of anions with electrophiles

Aldol condensation with aldehydes and ketones gives hydroxy compounds (265 — 267) which usually spontaneously lose water (by a reverse Michael addition) to give unsaturated compounds (268). 

The following exemplify reactions of the aldol type. 3-Hydroxythiophene with benzaldehyde forms (269). Anions derived from oxindole (270 Z = NH) and indoxyl (271) react with isatin (272) to give isoindigo (273) and indirubin (274). 

---