Carbon Disulfide → Lithium Hexamethyldisilazide

Participants

Reaction Steps

A solution of lithium hexamethyldisilazide was prepared by the addition of n-butyllithium in hexane (4.21 ml of a 1.6M solution) to 2.13 ml of hexamethyldisilazane in 10 ml of dry tetrahydrofuran at 0° C. while stirring under nitrogen. The solution was added via a cannula to a solution of 1.08 g of 4-nitrobenzyl 2-(4(R)-ethylthio-3(S)-[1'(R)-dimethyl-{2-methylprop-2-yl}silyloxyethyl]-2-azetidinon-1-yl)acetate in 10 ml of dry tetrahydrofuran at -78° C., with stirring under nitrogen. After 5 minutes, 0.35 ml of carbon disulphide was added by syringe and after a further 90 minutes phosgene in toluene (3.56 ml of a 12.5% solution) was added by syringe. The mixture was stirred for 90 minutes and poured into 50 ml of diethyl ether and 10 ml of 2M acetic acid. The organic layer was separated, washed with water, 12% sodium chloride solution, dried over magnesium sulphate and evaporated to give an orange oil. Chromatography over silica gel using diethyl ether/hexane mixtures as eluent gave 0.485 g of the title compound in purified form.

Provenance & Evidence