Selectfluor → 3'-Fluoro-6'-(3-chloro-benzyloxy)-3,4,5,6-tetrahydro-2h-[1,2']bipyrazinyl-4-carboxylic acid tert-butyl ester

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Reaction Steps

A solution of 6′-(3-chloro-benzyloxy)-2,3,5,6-tetrahydro-[1,2′]bipyrazinyl-4-carboxylic acid tert-butyl ester (1-1b) (600 mg, 1.49 mmol) in acetonitrile (12.4 ml) at 0° C. under a nitrogen atmosphere was treated with Selectfluor™ ([1-(chloromethyl)-4-fluoro-1,4-diazoniabicyclo[2.2.2]-octane bis(tetrafluoroborate)]) (526 mg, 1.49 mmol). The resulting mixture was allowed to warm to room temperature and stirred for 16 h. The reaction mixture was partitioned between CH2Cl2 and water. The organic phase was washed twice with water, twice with saturated aqueous NaHCO3 solution and twice with brine, dried over MgSO4 (anhydrous), filtered and concentrated in vacuo. The residue was purified by flash chromatography (CHCl2-EtOAc 99:1 to 95:5). Three compounds were obtained in the following elution order: difluorinated material (160 mg, 25%), Intermediate I-3i (32 mg, 5%) and Intermediate I-3i′ (141 mg, 22%). The structures of the two monofluorinated products were assigned by nuclear Overhauser effect (nOe) experiments.

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