Ammonium Chloride → (3S,4R)-4-[(1,5-Diethylpyrazol-3-yl)carbonylmethyl]-3-[(R)-1-tert-butyldimethylsilyloxyethyl]azetidin-2-one

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Reaction Steps

3-Acetyl-1,5-diethylpyrazole (1.65 g) in dry tetrahydrofuran (THF) (50 ml) under an argon atmosphere was cooled in an acetone/solid carbon dioxide bath and then treated with a 1M solution of lithium bis(trimethylsilyl)amide (19.8 ml). The mixture was stirred for 45 minutes and then (3R,4R)-4-acetoxy-3-[(R)-1-tert-butyldimethylsilyloxyethyl]azetidinone (2.84 g) in dry THF (10 ml), added by syringe over ca. 1 minute. The mixture was stirred in the cold for 5 h. Saturated aqueous ammonium chloride was then added, followed by ethyl acetate. The layers were separated and the aqueous layer was re-extracted with ethyl acetate. The combined ethyl acetate layers were washed with saturated brine. dried and evaporated. Chromatography on silica gel, eluting with ethyl acetate/hexane mixtures gave the title compound (1.82 g); νmax (CH2Cl2) 3412, 2957, 2885, 2857, 1761, 1677, 1473, and 1376 cm-1 ; δ (CDCl3) 0.078 (6H, s), 0.88 (9H, s), 1.21 (3H,d, J 6.3 Hz), 1.29 (3H, t, J 7.6 Hz), 1.45 (3H, t, J 7.3 Hz), 2.63 (2H, q, J 7.3 Hz), 2.90 (1H, dd, J 1.6 & 4.9 Hz), 3.15 (1H, dd, J 10.0 & 17.0 Hz), 3.50 (1H, dd, J 3.6 & 17.0 Hz), 4.06-4.25 (4H, m), 6.09 (1H, s), 6.56 (1H, s). (Found m/z 393.2445. C20H35N3O3Si requires m/z 393.2448).

Provenance & Evidence