Catalytic Asymmetric Amination of N-Nonsubstituted alpha-Alkoxycarbonyl Amides: Concise Enantioselective Synthesis of Mycestericin F and G

In an attempt to explore the synthetic utility of a ternary asymmetric catalyst comprising La(NO3)(3)center dot 6H(2)O, amide-based ligand (R)-L1, and D-valine tert-butyl ester H-D-Val-OtBu, we investigated a catalytic, asymmetric amination of functionalized N-nonsubstituted alpha-alkoxycarbonyl amides using di-tert-butyl azodicarboxylate as an electrophilic aminating reagent. A highly functionalized, cyclic N-nonsubstituted alpha-alkoxycarbonyl amide delivered the desired amination product in up to 96% enantiometric excess, with the requisite functionalities of the polar heads of sphingosines with the appropriate stereochemical arrangement. The rapid asymmetric assembly of these functional groups allowed a concise enantioselective synthetic route to sphingosines to be established with a broad flexibility towards derivative synthesis. These studies have culminated in an efficient catalytic enantioselective total synthesis of immunosuppressive fungal metabolites mycestericin F (3a) and G (3b).