A Direct Route to 3‐( D ‐Ribofuranosyl)pyridine Nucleosides

A route for synthesizing C‐nucleosides with 2,6‐substituted pyridines as heterocyclic aglycones is described. Condensation of appropriately substituted lithiated pyridines with ribono‐1,4‐lactone derivatives yields hemiacetal 4a–g (Table 1), which can be reduced by Et3SiH and BF3·Et2O to the corresponding C‐nucleoside (see Scheme 1 for 4d → β‐D‐5). Conditions are presented that optimize the amount of the 2,6‐dichloropyridine‐derived β‐D‐anomer β‐D‐5 formed (Table 3). Aminolysis of β‐D‐5 yields the diaminonucleoside 14 (Scheme 3).