Diisopropylamine → (3S,4R)-1-(t-butyl dimethylsilyl)-3-(1-oxoethyl)-4-[2,2,2-tri(methylthio)ethyl]azetidin-2-one

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n-Butyllithium (2.43 ml of 2.4 m solution, 5.84 mmol) is added by syringe to a solution of diisopropylamine (591 mg, 5.84 mmol) in 25 ml of freshly distilled tetrahydrofuran at -78° C. The resulting solution is stirred at -78° C. for 15 minutes prior to the addition of a solution of (4R)-1-(t-butyldimethylsilyl)-4-[2,2,2-tri(methylthio) ethyl]azetidin-2-one (1.00 g, 2,85 mmol) in tetrahydrofuran (5 ml). This solution is stirred at -78° C. for 15 minutes, then added via a Teflon tube to a mixture of N-acetylimidazole (642 mg. 5.84 mmol) in 25 ml of THF at -78° C. The resulting yellow reaction mixture is stirred at -78° C. for 10 minutes, then quenched by addition of saturated aqueous ammonium chloride solution. The mixture is diluted with ether (200 ml) and washed with 2.5 N hydrochloric acid solution (50 ml), water (50 ml) and brine (50 ml) and dried over magnesium sulfate. Removal of solvents in vacuo gives a yellow oil which is chromatographed on silica gel (30% ether in petroleum ether) to yield (3S, 4R)-1-(t-butyldimethylsilyl)-3-(1-oxoethyl)-4-[2,2,2-tri(methylthio)ethyl]azetidin-2-one. n.m.r. (CDCl3) δ 4.42(m,l), δ 4.32(d,l) δ 2.35(m,2), δ 2.32(s,3), δ 2.2(s,9), δ 0.98(s,9), δ 0.3(2s,6).

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