Sodium hydride → (E)-3-(2'-tert-butoxycarbonyl-ethenyl)-4,6-dichloro-1H-indole-2-carboxylic acid isopropyl ester

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Reaction Steps

Sodium hydride (1 g; 95%) was added in two 0.5 g portions to a solution of (tert-butoxycarbonylmethyl)-triphenylphosphonium bromide (8.4 g) in isopropanol (100 ml). After the evolution of hydrogen ceased ethyl-3-formyl-4,6-dichloro-indole-2-carboxylate (5 g) was added and the reaction mixture was refluxed for 2 h. (tert-Butoxycarbonylmethylene)-triphenylphosphorane (1 g) was added and the reflux was continued for 8 h. An other amount of (tert-butoxycarbonylmethylene)-triphenylphosphorane (3.5 g) was added and the reaction mixture was refluxed for additional 3 h. After cooling to r.t. the solution was poured into water and extracted with ethyl acetate. The organic extracts were dried and evaporated under reduced pressure. The residue was purified by flash chromatography using cyclohexane/ethyl acetate 3:1 as eluant to give the title compound (2.2 g) as a white solid.

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