C([Li:5])CCC.[CH3:6][Si:7]([CH3:14])([CH3:13])[NH:8][Si:9]([CH3:12])([CH3:11])[CH3:10].C(SC1N(CC(OCC2C=CC([N+]([O-])=O)=CC=2)=O)C(=O)C1)C=C.C(OC(=O)C)(=O)C>CCCCCC.C1COCC1.C(Cl)(Cl)Cl.O.C(=S)=S>[CH3:6][Si:7]([CH3:14])([CH3:13])[N-:8][Si:9]([CH3:12])([CH3:11])[CH3:10].[Li+:5]
A solution of lithium hexamethyldisilazide was prepared by the addition of 8.66 ml of a 1.6M solution of n-butyllithium in hexane to 2.96 ml of hexamethyldisilazane in 30 ml of dry THF at -10° with stirring under argon. The solution was cooled to -78° and added by cannula to 2.07 g of 4-nitrobenzyl 2-(4-allylthioazetidin-2-on-1-yl)acetate in 15 ml of dry THF at -78°, with stirring, under argon. After 5 minutes 1.11 ml of carbon disulphide were added by syringe. 2.33 ml of acetic anhydride were then added. The solution was allowed to warm to room temperature and evaporated to give an orange oil. The oil was mixed with water (40 ml) and chloroform (40 ml), the organic layer separated and the aqueous layer extracted with additional chloroform (2×40 ml). The combined organic phase was dried (MgSO4) and evaporated to give an orange oil, which was used without further purification as the starting material for Example 16b.
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