A convenient preparation of enantiomerically pure (+)-(1R,2R)-and (-)-(1S,2S)-1,2-diamino-1,2-diphenylethanes

A gram-scale preparation of (1S,2S)- and (1R,2R)-1,2-diamino-1,2-diphenylethanes, (1S,2S)-1 and (IR,2R)-1, is reported via (+/-)-iso-amarine 4. Strategically, the activation of (+/-)-iso-amarine 4 for hydrolysis to the required diamines and enantiomeric resolution is achieved simultaneously by formation of two separable diastereoisomeric N-acylamidines 5 and 6 derived from direct DCC-mediated coupling of (+/-)-iso-amarine 4 with (R)-acetylmandelic acid. iso-Amarine 4 is conveniently obtained from amarine 3, and a one-pot synthesis of the latter is reported from benzaldehyde and hexamethyldisilazane as catalysed by benzoic acid.