New N,N-diamine ligands derived from (-)-menthol and their application in the asymmetric transfer hydrogenation

Natural (-)-menthol was applied to construction of mono-N-tosylated-1,2-diamine derivatives. The O-tosylation and elimination of the tosylate of the menthol intermediate led to trans-p-menth-2-ene. The unsaturated menth-2-ene was next transformed into a mixture of N-tosylaziridines, which upon reaction with sodium azide gave four isomeric azides. The reduction of the formed tosylazides on Pd/C gave new chiral mono-N-tosylated-1,2-diamines, which were used as ligands in the asymmetric transfer hydrogenation protocol on aromatic ketones and endocyclic imine.