Potassium Phosphate, Tribasic → Ethyl 7-(4-(tert-butoxycarbonyl)-2-nitrophenoxy)-6,8-dicyclopropylchroman-4-carboxylate

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Reaction Steps

To a stirred solution of ethyl 8-bromo-7-(4-(tert-butoxycarbonyl)-2-nitrophenoxy)-6-chlorochroman-4-carboxylate (Example 38, Step B; 0.56 g, 1.0 mmol) in xylenes (6 mL) was added successively water (0.3 mL), potassium phosphate (1.27 g, 6.0 mmol), tricyclohexylphosphine (0.11 g, 0.40 mmol), and cyclopropylboronic acid (0.34 g, 4.0 mmol). The resulting mixture was stirred and a balloon of nitrogen with a three-way purge valve was attached, and the flask was evacuated and refilled five times with nitrogen. Palladium(II) acetate (0.045 g, 0.20 mmol) was added, and again the flask was evacuated and refilled five times with nitrogen. The mixture was stirred in an oil bath set to 140° C. under the nitrogen balloon for 2 hours. The mixture was cooled to ambient temperature, and diluted with ethyl acetate (25 mL) and water (15 mL). The organic layer was dried over sodium sulfate and concentrated. The residue was purified by chromatography on silica gel, eluting with 90/10 hexanes/ethyl acetate, to afford ethyl 7-(4-(tert-butoxycarbonyl)-2-nitrophenoxy)-6,8-dicyclopropylchroman-4-carboxylate as a light yellow glass (0.24 g, 46%).

Provenance & Evidence