A diastereoselective synthesis of 1,2-diamino-1,2-di-tert-butylethane has been developed by addition of tert-butyl magnesium chloride to a chiral bis-imine derived from glyoxal and (S)-methylbenzylamine. Addition of the bis-imine to the Grignard reagent in hexane at 50 °C gave only one diastereomer detectable by 1H and 13C NMR. Hydrogenolysis of the phenylethyl groups led to the expected free diamine 3 in good yields. The absolute configuration (R,R) of the carbons bearing the tert-butyl groups has been confirmed by X-ray spectroscopy.