Synthesis of l-cyclopentenyl nucleosides using ring-closing metathesis and palladium-mediated allylic alkylation methodologies

The enantiomeric synthesis of l-cyclopentenyl nucleosides is described. The key intermediate (+)-cyclopentenyl alcohol () was prepared from methyl-α-d-galactopyranoside using a ring closing metathesis reaction. Transformation of the allylic alcohol into the allylic acetate () or carbonate (), allows their coupling with purine and pyrimidine bases under Pd(0)-catalyzed Tsuji–Trost allylic alkylationʹs to yield . The Pd catalyzed reaction was found to require the use of AlEt3.