The acylation of 3-amino-2,2-dimethyl-5-phenylpentanoic acid (I) with benzoyl chloride (II) in pyridine gives the corresponding amide (III), which is finally converted into the target anhydride by reaction with bromo-tris-pyrrolidino-phosphonium hexafluorophosphate (PyBroP) and triethylamine in dichloromethane.