To a solution of (3S, 4R)-3-[(R)-1-t-butyldimethylsilyloxyethyl]-1-[1-hydroxy-1-(p-nitrobenzyloxycarbonyl)methyl]-4-[(R)-1-methyl-2-(p-nitrobenzyloxycarbonylamino)ethylthio(thiocarbonyl)]thioazetidin-2-one (12.6 g, 16.1 mmole) in tetrahydrofuran (150 ml) were added at -15° C., in turn, 2,6-lutidine (2.00 g, 18.7 mmole) and thionyl chloride (2.11 g, 17.7 mmole), and the mixture was stirred at the same temperature for 15 minutes. 2,6-Lutidine (3.45 g, 32.2 mmole) and triphenylphosphine (12.6 g, 48.1 mmole) were then added and the mixture was stirred at 65° C. under a nitrogen stream for a further 35 hours. After completion of the reaction, the reaction mixture was diluted with ethyl acetate; washed with water and dried. The solvent was distilled off under reduced pressure and the residue was purified by column chromatography (250 g of silica gel); eluted with a 15-20% v/v solution of ethyl acetate in benzene; giving the desired compound (10.9 g; 66%) in the form of a yellow oil.
