Sodium Carbonate → (R)-4,6-Dimethyl-3,4-dihydro-1H-2,4a,5-triaza-fluorene-2-carboxylic Acid Tert-butyl Ester

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To a solution of 0.20 g (0.55 mmol) (R)-6-bromo-4-methyl-3,4-dihydro-1H-2,4a,5-triaza-fluorene-2-carboxylic acid tert-butyl ester (Example 5, intermediate a) in 10 ml 1,2-dimethoxyethane was added 63 mg (55 μmol) tetrakis(triphenylphosphine)palladium. After 30 min, 5 ml saturated aqueous sodium carbonate solution and 0.09 ml (0.65 mmol) of a 1M trimethylboroxine solution in THF were added and the resulting suspension was heated to reflux for 5 h. The reaction mixture was cooled to room temperature, poured into 20 ml 1M aqueous sodium hydroxide solution and extracted three times with ethyl acetate. The combined organic layers were washed with brine, dried over magnesium sulfate, filtered and evaporated. The residue was purified by flash column chromatography on silica gel (0.032–0.063 mm) with ethyl acetate:n-hexane (1:1) as eluant to yield the desired product as a yellow solid (71.1%).

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