Trimethyl borate → HCID 69416314, compound

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Reaction Steps

A solution of 5.2 g of 3,4-difluoro-6-propylfluorene (example 1) in 50 ml of dry THF is cooled to −70° C. and 15 ml of n-BuLi (1.6 m solution in hexane) are added dropwise under a protective gas atmosphere in such a way that the internal temperature is always below −70° C. Subsequently, the mixture is stirred at this temperature for a further 2 h and then 2.7 g of trimethyl borate dissolved in 10 ml of THF are added at the same temperature. The reaction mixture is allowed to come to −10° C., quenched with water and acidified with hydrochloric acid. After extraction with MTBE, the combined organic phases are washed with saturated NaCl solution and dried over sodium sulfate. The crude boronic acid obtained after the removal of the solvent is dissolved in 100 ml of MTBE, heated to boiling, admixed rapidly with 7.5 ml of 35 percent aqueous hydrogen peroxide solution and stirred under reflux for a further 2.5 h. After cooling, the phases are separated, the aqueous phase is extracted once more with MTBE and the combined organic phases are washed successively with water, saturated sodium sulfite solution and saturated NaCl solution. After drying over sodium sulfate and removal of the solvent under reduced pressure, the crude product is purified by column chromatography on silica gel using 9:1 (v/v) heptane/ethyl acetate as the eluent. The resulting 3,4-difluoro-6-propylfluoren-2-ol is heated to boiling with 2.4 g of 1-bromobutane and 5.4 g of potassium carbonate in 120 ml of MEK for 6 h. After cooling, the reaction mixture is added to ice/water and extracted with MTBE, and the organic phases are washed with water and saturated NaCl solution and dried over sodium sulfate. After the solvents have been removed under reduced pressure, the colorless crude product is purified chromatographically on silica gel with 2:8 (v/v) dichloromethane/heptane as the eluent and recrystallized from heptane. 2.7 g of 2-butyloxy-3,4-difluoro-6-propylfluorene are obtained.

Provenance & Evidence