Pyridine → Methyl (S)-4,4-difluoro-2-isocyanatopentanoate

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Under argon, 2.0 g of methyl (S)-2-amino-4,4-difluoropentanoate hydrochloride (9.8 mmol) were dissolved in 80 ml of dichloromethane, admixed with 3.2 ml of pyridine (4 eq.) and cooled to approx. 5° C. (ice bath). After 10 min, 6.7 ml (1.3 eq.) of a 20% phosgene solution in toluene were slowly added dropwise. The resulting suspension was stirred with ice bath cooling for 3 h and then concentrated under reduced pressure. The residue thus obtained was taken up in toluene and filtered. After the solvent had been removed under reduced pressure, methyl (S)-4,4-difluoro-2-isocyanatopentanoate was obtained as a brown oil which was used in the subsequent reaction without further purification. Yield: 1.1 g (58% of theory).

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