New Catalytic Asymmetric Formation of Oxygen Heterocycles Bearing Nucleoside Bases at the Anomeric Carbon.

Pyrimidine nucleosides are an important class of compounds with versatile applications across many fields, including biology and medicinal chemistry. Synthesis of nucleoside analogs in optically pure form via traditional glycosylation has always been a challenge, especially for unnatural carbohydrate motifs which do not have C2 substitution to dictate the stereochemical outcome of the newly formed glyosidic bond. Herein, we report an asymmetric Pd-catalyzed synthesis of nucleoside analogs enabled by the development of a series of chiral ligands. A variety of 5-substituted pyrimidine nucleobases, ranging from 5- to 12-membered ring nucleoside analogs, are generated in excellent yield (up to 96%) as well as diastereo- (>20:1) and enantioselectivity (up to 99.5% ee). These nucleoside analogs bearing an iodide functional group handle allow for rapid transformation to a variety of other interesting pyrimidine nucleoside structures.