Organocatalyzed synthesis of (-)-4-epi-fagomine and the corresponding pipecolic acids

Abstract

The enantioselective synthesis of 4-epi-fagomine was accomplished starting from dioxanone and Cbz-protected benyzlamine, in 4 steps, with 18% overall yield. The key feature of this synthetic approach is the tactical combination of reactions: organocatalyzed aldolization/reductive amination, which allows for a quick formation of heterocyclic rings with defined absolute configuration of all stereogenic centers. Two hydroxypipecolic acids and a reduced fagomine analogue were also synthesized.