Indole-4-carboxylic acid, Mannich reaction

Mannich Reaction on a Resin-Bound Indole Scaffold (89) (Fig. 18).50 Commercially available indole 5- or 6-carboxylic acid supported on Rink amide resin is suspended in HOAc/l,4-dioxane (1 4). A secondary amine (1.5 equiv.) and formaldehyde (1.5 equiv.) are added. The suspension is shaken for 1.5 h at RT. The resin is then filtered, washed with appropriate solvents, and dried under vacuum to obtain (90). 

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