A General and Efficient Synthesis of Pyridin-2-yl <i>C</i>-Ribonucleosides Bearing Diverse Alkyl, Aryl, Amino, and Carbamoyl Groups in Position 6

An efficient and practical methodology of preparation of 6-substituted pyridin-2-yl C-ribonucleosides was developed. A one-pot two-step addition of 2-lithio-6-bromopyridine to TBS-protected ribonolactone followed by acetylation gave 1β-(6-bromopyridin-2-yl)-1-O-acetyl-2,3,5-tri-O-(tert-butyldimethylsilyl)-d-ribofuranose in high yield. Its reduction with Et3SiH and BF3·Et2O afforded the desired TBS-protected 6-bromopyridine C-ribonucleoside as pure β-anomer in good overall yield of 63%. This intermediate was then subjected to a series of palladium catalyzed cross-coupling reactions, aminations and aminocarbonylations to give a series of protected 1β-(6-alkyl-, 6-aryl-, 6-amino-, and 6-carbamoylpyridin-2-yl)-C-ribonucleosides. Deprotection of silylated nucleosides by Et3N·3HF gave a series of title free C-ribonucleosides (12 examples).