Choline Chloride/Glycerol Promoted Synthesis of 3,3-Disubstituted Indol- 2-ones

Abstract

Objective:: 3,3-Disubstituted indol-2-one derivatives have wider applications in pharmaceuticals and they are key intermediates for the synthesis of many kinds of drug candidates. The development of an efficient and practical method to prepare this class of compound is highly desirable from both environmental and economical points of views. Methods:: In order to establish an effective synthetic method for preparing 3,3-disubstituted indol- 2-one derivatives, the bis-condensation reaction of isatin and 1H-indene-1,3(2H)-dione was selected as a model reaction. A variety of natural deep eutectic solvents (NADESs) were prepared and used for this reaction. The generality and limitation of the established method were also investigated. Results:: It was found that model reaction can be carried out in natural deep eutectic solvent (NADES) based on choline chloride (ChCl) at 80°C under microwave irradiation. This protocol with a broad substrate applicability afforded various 2,2'-(2-oxoindoline-3,3-diyl)bis(1H-indene- 1,3(2H)-dione) derivatives in high yields. Conclusion:: A simple and efficient procedure has been developed for synthesis of 2,2'-(2-oxoindoline- 3,3-diyl)bis(1H-indene-1,3(2H)-dione), spiro[indoline-3,7'-pyrano[5,6-c:5,6-c']dichromene]- 2,6',8'-trione, and spiro[indoline-3,9'-xanthene]trione via bis-condensation between isatin with 1,3- indandione, 4-hydroxycoumarin or 1,3-cyclohexanedione in natural deep eutectic solvent (NADES) based on choline chloride (ChCl) and glycerol (Gl) under microwave irradiation. The salient features of this protocol are avoidance of any additive/catalyst and toxic organic solvent, clean reaction profiles, non-chromatographic purification procedure, and high to excellent yield. Furthermore, the use of NADES as green reaction medium reduces burden on environment and makes the present method environmentally sustainable.