Ammonium Chloride → 1-[1,3]Dioxolan-2-yl-6,6,6-trifluoro-hexan-3-one

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Reaction Steps

4,4,4-Trifluorobutyric acid chloride (6.4 g from above) in CH2Cl2 (80 ml) was treated with O,N-dimethylhydroxylamine hydrochloride (60.0 mmol, 5.85 g). The mixture was cooled to 0° C., then treated with pyridine (160.0 mmol, 12.9 ml), then allowed to warm to room temperature overnight. The mixture was diluted with CH2Cl2 (200 ml), then washed with brine(2×50 ml). Solvent was removed from the volatile product by simple distillation at atmospheric pressure to provide 20 g of 4,4,4-trifluoro-N-methoxy-N-methyl butyramide, which may be used without further purification. 1H NMR (CDCl3) δ 3.70 (3H, s), 3.19 (3H, s), 2.78-2.65 (2H, m), 2.57-2.40 (2H, m). Mg (92.0 mmol, 2.2 g) in THF (80 ml), under an argon atmosphere, was treated with 2-(2-bromoethyl)-[1,3]dioxolane (80 mmol, 9.4 ml), while keeping the internal temperature below 35° C. with the aid of an ice bath. After the addition was complete, the mixture was stirred for 2 h at room temperature, then cooled to −78° C. Crude 4,4,4-trifluoro-N-methoxy-N-methyl butyramide (20 g, prepared above) in THF (40 ml) was cooled to −78° C., then the freshly prepared Grignard reagent was transferred via cannula into the amide solution at −78° C. The resulting mixture was allowed to warm to room temperature, held at room temperature overnight, then poured into saturated aqueous ammonium chloride (200 ml). The mixture was extracted with ethyl acetate (3×75 ml). The combined organics were washed with brine (2×75 ml) and concentrated under reduced pressure to provide crude 1-[1,3]dioxolan-2-yl-6,6,6-trifluoro-hexan-3-one (18 g) 1H NMR (CDCl3) δ 4.91 (1H, t, J=4.1), 3.97-3.82 (4H, m), 2.70 (2H, t, J=7.3), 2.57 (2H, t, J=7.2), 2.49-2.34 (2H, m), 2.01 (2H, dt, J=7.3, 4.1).

Provenance & Evidence