"On water" synthesis of spiro-indoles via Schiff bases

A fast, efficient, and clean "on water" synthesis of new Schiff bases and their conversion to spiro compounds under microwave irradiation, as well as in water, is reported. Indol-2,3-diones were reacted separately with various heterocyclic and aromatic amines in water at room temperature to obtain corresponding Schiff bases in high purity and yield. These were then converted into corresponding spiro compounds using mercaptoacetic acid under microwave irradiation in neat conditions as well as in water on refluxing. Hence, a green synthetic protocol is developed to synthesize new molecules with improved profile under ecofriendly conditions, in which no wastes or side-products are formed.