To a solution of sodium borohydride (0.32 g) in dry tetrahydrofuran (40 ml) was added dropwise boron trifluoride-etherate (1.81 g) at 10°-20° C. under nitrogen gas, and the resultant mixture was stirred for 1 hour. After addition of 1,5-octadiene (1.21 g) and stirring for 1 hour, a solution of (3S,4S)-4-(1-methylethenyl)-3-(1-(R)-benzyloxycarbonyloxyethyl)-1-di(p-anisyl)methyl-2-azetidinone (2.63 g) in dry tetrahydrofuran (10 ml) was dropwise added thereto at 20°-25° C. over a period of 1 hour, followed by stirring for 3 hours. The reaction mixture was quenched with water (7 ml) at 10°-30° C. for 1 hour. After addition of 4% sodium bicarbonate solution (5.3 ml), the mixture was heated at 40°-45° C., treated with 35% hydrogen peroxide solution (5.3 ml) at 40°-45° C. and cooled down to room temperature. Sodium sulfite (0.2 g) and toluene (6 ml) were added to the mixture, followed by stirring. The organic layer was separated and the aqueous layer was extracted with toluene (12 ml). The combined extracts were washed with brine and dried over anhydrous sodium sulfate. Filtration and concentration of the filtrate in vacuo gave an oily residue, which was purified by silica gel chromatography to yield (3S,4R) 4-(1-(S)-hydroxymethylethyl)-3-(1-(R)-benzyloxycarbonyloxyethyl)-1-di(p-anisyl)methyl-2-azetidinone (1.88 g) and the corresponding 4-(1-(R)-hydroxymethylethyl) compound (0.51 g).
