A synthesis of ψ-cytidine

A practical, seven-step synthesis of 5-(β-d-ribofuranosyl)cytosine (1, ψ-cytidine) was achieved. ψ-Uridine was converted into the 2′,3′-isopropylidene acetal 2 in 85% yield. Tosylation of 2 to the 5′-sulfonate 3, followed by deacetonation, afforded 5′-O-tosyl-ψ-uridine (6) in good yield. Treatment of 6 with 1,1′-carbonyldiimidazole afforded the 2′,3′-cyclic carbonate 10, which was converted into 4,5′-anhydro-2′,3′-O-carbonyl-ψ-uridine (11) by treatment with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in N,N-dimethylformamide. 4,5′-Anhydro-ψ-uridine (7) was obtained in quantitative yield from 11 by decarbonylation in aqueous pyridine. Ammonolysis of 7 afforded ψ-cytidine (1) in good yield.