2-​Azetidinone, 4-​[4-​[[(1,​1-​dimethylethyl)​dimethylsilyl]​oxy]​phenyl]​-​1-​(4-​fluorophenyl)​-​3-​[(3S)​-​3-​(4-​fluorophenyl)​-​3-​hydroxypropyl]​-​, (3R,​4S)​-