A new approach to enantiopure β-endo-substituted azabicyclic proline analogues by base induced epimerization of a formyl derivative

Abstract

The β-epimer of methyl (1S,2R,4R)-N-benzoyl-2-formyl-7-azabicyclo[2.2.1]heptane-1- carboxylate, (1S, 2S, 4R)-7, has been obtained by treatment of the exo-formyl derivative with triethylamine in methanol. The development of this epimerization procedure has further increased the already wide possibilities offered by our methodology and solves the problem of access to the endo derivatives that would result from the Diels–Alder reaction of Danishefsky’s diene and the C-4 unsaturated E-oxazolones, whose preparation frequently proves to be problematic.