Ethanol → (RS)-[3-(tert-butyl-diphenyl-silanyloxy)-5-ethoxy-2-fluoro-phenyl]-(4-cyano-phenylamino)-acetic acid ethyl ester

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To a solution of 49 g (RS)-[3-(tert-butyl-diphenyl-silanyloxy)-2-fluoro-5-hydroxy-phenyl]-(4-cyano-phenylamino)-acetic acid ethyl ester described in example 3.3 in 900 ml THF 24.86 g triphenylphosphine, 5.53 ml EtOH and 21.82 g di-tert-butyl azodicarboxylate were added sequentially. The solution was stirred for 4 hrs at room temperature and then evaporated. The crude product was purified by chromatography on silica gel (cyclohexane/EtOAc) to yield 27.6 g (RS)-[3-(tert-butyl-diphenyl-silanyloxy)-5-ethoxy-2-fluoro-phenyl]-(4-cyano-phenylamino)-acetic acid ethyl ester as slightly yellow, amorphous solid.

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