Photoredox-Catalyzed Stereoselective Radical Reactions to Synthesize Nucleoside Analogues with a C2′-Stereogenic All-Carbon Quaternary Center

The design of novel nucleoside analogues
bearing a C2′ all-carbon
quaternary center is described. The construction of this all-carbon
stereogenic center involves the use of photoredox catalysis to initiate
an intramolecular attack of a silyl-tethered vinyl functionality on
a tertiary radical. Density functional theory calculations were performed
to explore the origin of the high syn diastereoselectivity
obtained through the preferred 5-exo-trig cyclization mode. The intramolecular
vinyl addition also enables the preparation of the complementary configuration
of the C2′ all-carbon stereocenter when performed after lactonization.