Mandelic Acid: An Efficient Organo-catalyst for the Synthesis of 3-substituted-3- Hydroxy-indolin-2-ones and Related Derivatives in Aqueous Ethanol at Room Temperature

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Author(s): Gurpreet Kaur, Rajat Kumar, Shivam Saroch, Vivek Kumar Gupta, Bubun Banerjee*

Journal Name: Current Organocatalysis

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Background: Indoles and various indolyl derivates are very common in naturally occurring biological active compounds. Many methods are being developed for the synthesis of various bioactive indole derivatives.

Objective: Synthesis of biologically promising structurally diverse indole derivatives under mild and environmentally benign conditions.

Methods: Synthesis of 3-hydroxy-3-(5-(trifluoromethoxy)-1H-indol-3-yl)indolin-2-one was achieved by the reaction of equimolar mixture of isatin and 3-(trifluoromethoxy)-1H-indol using 20 mol% of mandelic acid as catalyst in aqueous ethanol at room temperature. Under the same optimized reaction conditions, synthesis of 3-(3-hydroxy-2-oxoindolin-3- yl)chroman-2,4-diones was accomplished via the reactions of substituted isatins and 4-hydroxycoumarin. On the other hand, 2-hydroxy-2-(indol-3-yl)-indene-1,3-diones and 10-hydroxy-10-(5-methoxy-1H-indol-3-yl)phenanthren-9(10H)-one were synthesized from the reactions of indoles and ninhydrin or 9,10-phenanthrenequinone respectively using the same 20 mol% of mandelic acid as an efficient organo-catalyst in aqueous ethanol at room temperature.

Results: Mild, safe and clean reaction profiles, energy efficiency, high atom-economy, use of naturally occurring nontoxic organo-catalyst, easy isolation procedure by avoiding column chromatographic purification and gram scale production are some the major advantages of this developed protocol.

Conclusion: A simple, straightforward and eco-friendly protocol has been developed for the efficient synthesis of biologically promising novel 3-hydroxy-3-(5-(trifluoromethoxy)-1H-indol-3-yl)indolin-2-one, 3-(3-hydroxy-2- oxoindolin-3-yl)chroman-2,4-diones, 2-hydroxy-2-(indol-3-yl)-indene-1,3-diones and 10-hydroxy-10-(5-methoxy-1Hindol-3-yl)phenanthren-9(10H)-one using a catalytic amount of mandelic acid in aqueous ethanol at room temperature.

Keywords: Indole, isatin, mandelic acid, organocatalysis, sustainable synthesis.

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(E-pub Ahead of Print)
DOI: 10.2174/2213337207999200713145440
Price: $95

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