5-(tert-butyl-dimethyl-silanyloxy)-1H-indole-2-carboxylic acid ethyl ester → 1-(2-tert-butoxycarbonylamino-ethyl)-5-(tert-butyl-dimethyl-silanyloxy)-1H-indole-2-carboxylic acid ethyl ester

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Reaction Steps

The solution of 7.0 g (21.9 mmol) 5-(tert-butyl-dimethyl-silanyloxy)-1H-indole-2-carboxylic acid ethyl ester in 60 mL N,N-dimethylformamide was cooled down to 0° C. and 2.7 g (24.1 mmol) potassium tert-butoxide was added. After 30 min., 5.4 g (24.2 mmol) 2,2-dioxo-[1,2,3]oxathiazolidine-3-carboxylic acid tert-butyl ester (prepared according to WO 02/072584) was added and the cooling bath was removed. After 1.5 hours, 10% aqueous ammonium chloride solution was added and the two-phase mixture was extracted twice with ethyl acetate. The combined organic layers were washed with water and brine, dried over magnesium sulfate, filtered and evaporated. The thus obtained crude product (brown oil; 12.0 g, 100%) was used without further purification for the next step.

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