Synthesis of Nucleosides and Related Compounds. Part XX. 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.

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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.