Synthesis of Carbocyclic Nucleosides from 2-Azabicyclo[2.2.1]hept-5-en-3-ones : Sodium Borohydride-Mediated Carbon : Nitrogen Bond Cleavage of Five- and Six-Membered Lactams

Abstract

Various carbocyclic ribofuranosyl nucleosides were stereoselectively synthesized through a small number of steps from 2-azabicyclo[2.2.1]hept-5-en-3-ones by the use of sodium borohydride-mediated C-N bond cleavage as a key step. Ready availability of a novel synthetic precursor, (±)-4β-hydroxymethyl-1β-ureidocyclopentane-2α, 3α-diol [(±)-carbocyclic ribofuranosylurea], provides not only facile routes to carbocyclic robofuranosylpyrimidines, but also another route to the corresponding cyclopentylamine, (±)-1β-amino-4β-hydroxymethylcyclopentane-2α, 3α-diol [(±)-carbocyclic ribofuranosylamine], which is useful for the synthesis of the corresponding purine nucleosides.