5-Thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylicacid,7-(1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)-3-methyl-4-(methylthio)-8-oxo-,1,1-dimethylethyl ester, [6R-(6a,7b)]- (9CI)