Coupling of Unprotected 2-Deoxy-D-ribose at C-3 as a New Route to 2,3-Dideoxy-3-phthalimido-D-pentoses

Direct condensation of 2‐deoxy‐D‐ribose (2) with phthalimides using P4O10/H2O/Bu3N reagent in chloroform at 40°C results in a coupling at C‐3 of the carbohydrate moiety to give an isomeric mixture of 2,3‐dideoxy‐3‐phthalimido‐D‐pentoses 3–5. Acetylation of 3b–5b using acetic anhydride in dry pyridine gives the corresponding acetylated derivatives 6–8. After treating the mixture of 3b, 4b, and 5b with triphenylmethyl chloride in pyridine, pure threo‐pyranose derivative 3b and pure tritylated erythro‐furanose derivative 9 are obtained by fractional precipitation.