Triisopropyl borate → 5-Acetyl-2-methyl-indole-1-carboxylic acid tert-butyl ester

Participants

Reaction Conditions

Reaction Steps

To a solution of 5-(2-methyl-[1,3]dioxolan-2-yl)-indole-1-carboxylic acid tert-butyl ester [4.96 g, 16.35 mmol, Intermediate (19)] in anhydrous tetrahydrofuran (20 mL) is added triisopropyl borate (4.61 g, 24.51 mmol) and cooled to 0° C. under N2. To it is added LDA (1.8M in heptane/tetrahydrofuran/ethylbenzene, 14 mL) drop wise at 0° C. over 40 minutes periods. After another 35 minutes, the reaction is quenched by the addition of aqueous 2N hydrochloric acid at 0° C. The white solid precipitated is slowly acidified with 3N hydrochloric acid till pH=3. The mixture became solution which is extracted twice with ethyl acetate (100 mL). The combined ethyl acetate phases are dried over sodium sulfate and filtered. The solid crude is triturated with acetonitrile and water to obtain 5-acetyl-2-methyl-indole-1-carboxylic acid tert-butyl ester (4.76 g, 96%, Intermediate (20)] as light yellow solid; 1H NMR (CDCl3): δ 8.30 (2.67, 3H), 8.18 (1H, d), 7.90 (1H, d), 6.78 (1H, s), 2.61 (3H, s), 1.62 (9H, s); LC/MS: ESI+ 304 (M+H)

Provenance & Evidence