Timelotem can be prepared by cyclization of the acyl diamine (I) with phosphorus oxychloride at 80-130 C, yielding the ring isomers (II) and (III). At higher reaction temperatures (II) is formed almost exclusively. It can be separated into its enantiomers. Subsequent reaction with methylamine -either of the crude mixture of (II) and (III) or of the pure racemic or enantiomeric (II)- affords anellation te yield title compound.