Citric Acid → (4R,9aR)-6-Formyl-4-methyl-3,4,9,9a-tetrahydro-1 H-2,4a,5-triaza-fluorene-2-carboxylic acid tert-butyl ester

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Reaction Steps

A solution of 2.0 g (5.43 mmol) (4R,9aR)-6-bromo-4-methyl-3,4,9,9a-tetrahydro-1H-2,4a,5-triaza-fluorene-2-carboxylic acid tert-butyl ester (example 5, intermediate c) in 15 mL tetrahydrofuran was cooled to −75 deg C. and treated with 4.40 mL (0.65 mmol) tert-butyllithium (1.5 M solution in n-pentane). After 30 min., 0.60 mL (0.63 g, 8.15 mmol) N,N-dimethylformamide was added dropwise. After 2.5 h the reaction mixture was poured on 10% aqueous citric acid solution and extracted three times with ethyl acetate. The combined organic layers were washed with brine, dried over magnesium sulfate, filtered and evaporated. The remaining residue was purified by flash column chromatography on silica gel (0.032–0.063 mm) with ethyl acetate:n-hexane (1:3) as eluant to give the desired compound as a yellow oil (40.1%).

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