A facile conversion of the phenylthio group to acetoxy by copper reagents for a practical synthesis of 4-acetoxyazetidin-2-one derivatives from (R)-butane-1,3-diol

(3S,4R,1′R)-4-Acetoxy-3-(1′-tert-butyldimethylsilyloxyethyl)-azetidin-2-one 8, an important intermediate for the synthesis of penem and carbapenem antibiotics, was synthesized from (R)-butane-1,3-diol 1, using chlorosulphonyl isocyanate for the formation of β-lactam ring in which a significant solvent effect on the ratio of diastereoisomers 6a and 6b was observed; copper(II) acetate rather than the poisonous mercury(II) acetate was used to convert the phenylthio group of compound 6a to acetoxy.