Process for preparing 1, 4-diphenylazetidinone derivatives

Cyclization catalysts employed in the process for preparing 1, 4-diphenylazetidinone derivatives from -substituted amino amides which are protected in a suitable way in the presence of silylating agents have as cation, phosphonium ions and as anion that of the general formulae below, where the symbols, substituents and indices have the following meaning, Z = C=O, C=S, S=O, SO2 or C=NR20 K = O, S, NR21 or CR22R23 L = NR24 or CR25R26 N = 0 or 1 M = O, C=O, NR27 or CR28R29 Q = O, S, NR30, CR31R32, C=O, C=S, S=O, SO2 or C=NR34 R = CR35 or N T = CR36 or N U = CR37 or N V = CR38 or N and the radicals listed R16 to R19 may be for example aryl or (C1-C15)alkyl, aryl(C1-C10)alkylene, and the radicals R20 to R32 and R34 to R38 may additionally also be H or heteroary; R39 and R40 are, for example, (C1-C6)alkyl. The anion may also be R41O-, R42COO- or Cl-, Br- or I-(combined with Ag2O).