Synthesis of Di- and Tridentate Ligands Containing Two Aziridine Rings

Optically pure N,N- and N,N,N-ligands containing two aziridine rings have been prepared by a three-step sequence. Reactionof optically pure 1,2-aminoalcohols, e.g. (S)-valinol, with 0.5 molar equivalents of dialdehydes, e.g. 1,1’-ferrocene- and 2,6-pyridinedicarboxaldehyde, gave the corresponding diimines, which underwent reduction or addition of organometallic reagents to give 1,2-aminoalcohols with high diastereoselectivities. The aziridine ring was then constructed from the 1,2-aminoalcohol moiety. The new ligands feature two aziridine rings which are connected by a spacer, e.g. ferrocene, or a pyridine ring providing an additional basic center, so that they can act as di- and tridentate ligands towards organometallic species and catalysts, which are active in enantioselective transformations, e.g. Pd-catalyzed allylic alkylation.