C. to room temperature over 8 to 24 h, in particular 10 to 14 h.To obtain the diastereomers of the diamine (I) with the relative configuration syn,anti or anti,syn, the diastereomer product mixture of the imine reduction process which has not been carried out stereoselectively can be subjected, for example,to a fractional crystallization, also of its salts, or a chromatographic separation.The imin