Acetic Anhydride → Lithium Hexamethyldisilazide

Participants

Reaction Conditions

Reaction Steps

A solution of lithium hexamethyldisilazide was prepared by the addition of n-butyllithium in hexane (2.79 ml of a 1.6M solution) to 0.982 ml of hexamethyldisilazane in 8 ml of dry tetrahydrofuran at -10° C., while stirring under argon. The solution was cooled to -78° C. and added by cannula to a solution of 0.98 g of 4-nitrobenzyl 2-(4(R)-allylthio-3(S)-[1(R)-{dimethyl-{2-methylprop-2-yl}silyloxy}ethyl]azetidin-2-on-1-yl)acetate in 8 ml of dry tetrahydrofuran at 78° C., with stirring under argon. After 5 minutes, 0.357 ml of carbon disulphide was added by syringe, followed by 0.748 ml of acetic anhydride. The mixture was allowed to warm to room temperature, and 30 ml of dichloromethane were added, followed by 30 ml of water. The organic layer was separated, and the aqueous layer was extracted with further dichloromethane. The combined organic extracts were washed with 1M HCl, with water, and with a 12% sodium chloride solution, and were then dried over magnesium sulphate and evaporated to give 1.38 g of an orange oil. 1.21 g of this crude product was chromatographed on silica gel using ethyl acetate/hexane mixtures as eluant to give 0.800 g of the title compound in purified form.

Provenance & Evidence