Ultrasound-assisted synthesis of 2,2′-(2-oxoindoline-3,3-diyl)bis(1H-indene-1,3(2H)-dione) derivatives

A simple and efficient procedure for the synthesis of 2,2′-(2-oxoindoline-3,3-diyl)bis(1H-indene-1,3(2H)-dione) derivatives, 2,2′-(2-oxo-1,2-dihydroacenaphthylene-1,1-diyl)bis(1H-indene-1,3(2H)-dione) and 2,2′-(1,3-dioxo-2,3-dihydro-1H-indene-2,2-diyl)bis(1H-indene-1,3(2H)-dione) by the reaction of 1,3-indandione and isatins or acenaphthylene-1,2-dione or ninhydrine in ethanol under ultrasonic irradiation in the presence of p-TSA is reported. The advantages of this method are the use of an inexpensive and readily available catalyst, easy work-up, good yields, and the use of ethanol as a solvent that is considered to be relatively environmentally benign.