Synthesis of a BODIPY-based pH Sensor

Example 117

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BODIPY pH-sensor 163. To a solution of aldehyde 159 (0.336 g, 1 mmol) in CH₂Cl₂ (50 mL) 2,4-dimethylpyrrole (0.25 mL, 2.4 mmol) was added, followed by TFA (0.09 mL, 1.2 mmol). The reaction was stirred for 16 h, diluted with CHCl₃ (200 mL) and washed successively with 1% Me₄NOH (2×50 mL), water (50 mL), brine (50 mL), filtered through paper filter, evaporated and co-evaporated with toluene (2×30 mL). The residue was dissolved in toluene (25 mL), stirred with chloranil (0.295 g, 1.2 mmol) for 2 h, then DIEA (1.74 mmol, 10 mmol) was added, followed by Et₂OBF₃ (1.0 mL, 8 mmol). The mixture was stirred for 4 h, evaporated, and the residue was purified on a silica gel column (3×45 cm bed, packed with 5% MeOH and 1% AcOH in CHCl₃), eluant: 5% MeOH and 1% AcOH in CHCl₃. The fractions containing the compound were evaporated, and chromatographed again on the second silica gel column (4×50 cm bed, packed in EtOAc/hexanes (1:1), eluant: EtOAc/hexanes (1:1) to get compound 163 (0.180 g, 32%) as an orange oil.