Synthesis of a Chiral Alkyl-BIAN

Until recently only Ar-BIAN ligands in which the aryl group contained electrondonating or moderately electronwithdrawing groups were known. We have recently expanded the available range of derivatives to ligands where the aryl group bears strongly electronwithdrawing substituents,1 two different aryl groups are present,2 and even to Alkyl-BIAN compounds.3,4 The latest had never been isolated before because an isomerization reaction occurred leading to their decomposition. We identified the cause of the decomposition in the ring strain of the five-membered ring of the acenaphthene moiety, which is partly released upon isomerization of the C=N double bond. The problem could be solved by employing ring-strained amines, best cyclopropylamine, for which this isomerization is thermodinamically unfavorable.3,4 Here we report the first synthesis of a chiral cyclopropylamine derived from enantiomerically pure -pinene.