The cis-isomer of 4-allyl-1-(1-benzyloxycarbonyl-1-triphenylphosphoranylidenemethyl)-3-(2-hydroxy-2-propyl)azetidin-2-one (10 ) (0.188 g) was dissolved in ethyl acetate (14 ml). An excess of trifluoroacetic acid (0.37 g) was added and the mixture cooled to -78° C. Ozone was passed into the reaction mixture until it was pale blue in colour. Argon was then bubbled through the solution until all the excess ozone had been removed. A solution of triphenylphosphine (0.085 g) in ethyl acetate was added and argon bubbled through the mixture for a further ten minutes. The reaction flask was then transferred to an ice bath and a saturated aqueous solution of sodium bicarbonate (20 ml) was added and the mixture stirred vigourously under argon for thirty minutes. The ethyl acetate layer was separated, washed with brine and dried.
