Chloride → t-Butyl 2-[(3R,4R)-3-Phenylacetamido-4-[(RS)-tetrahydrofuran-3-ylcarbonylmethylthio]azetidin-2-on-1-yl]-2-tri-n-butylphosphoranylideneacetate

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t-Butyl (RS)-2-hydroxy-2-[(3R,4R)-3-phenylacetamido-4-[(RS)-tetrahydrofuran-3-ylcarbonylmethylthio]azetidin-2-on-1-yl]acetate (2.719 g) in THF (20 ml) was treated with thionyl chloride (1.01 g, 0.615 ml) and 2,6-lutidine (0.913 g, 0.989 ml) as described in Example 1 (d). Following work-up the crude chloride in dioxan (30 ml) was then treated with n-butyl-phosphine (2.53 g, 3.11 ml). After purification by flash chromatography with 50, 70% ethyl acetate/hexane then ethyl acetate the title compound was obtained as a pale yellow foam (1.496 g, 40%); νmax (CH2Cl2) 3420, 1762, 1717 (shoulder), 1681 and 1625 cm-1. [Mass spectrum: +ve ion (3NOBA, Na+), MH+ (663), MNa+ (685)].

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