5,5′-Bistriazoles as axially chiral, multidentate ligands: synthesis, configurational stability and catalytic application of their scandium(III) complexes

The design and development of 5,5′-bistriazoles featuring aminomethyl substituents is discussed. An efficient synthetic procedure for the selective preparation of 4,4′-bis(aminomethyl)-5,5′-bistriazoles from commercially available propargylamine derivatives and benzyl azide has been optimized. The first experimental determination of the configurational stability of 5,5′-bistriazoles is disclosed on the basis of rotational energy barriers and half-life times. Fast racemization was observed for a bistriazole possessing solely axial chirality whereas a more heavily substituted bistriazole involving axial and central chirality proved to be configurationally stable. A successful catalytic application has been implemented by using a N,N-dimethylpropargylamine-derived 5,5′-bistriazole as a multidentate ligand controlling the product selectivity (single vs. double addition) in scandium(III)-catalyzed nucleophilic additions of indoles to isatin electrophiles.