The coupling reaction of a D-ribofuranosyl fluoride with indoles in the presence of boron trifluoride gives the corresponding C-nucleosides in a stereoselective manner depending upon reaction temperatures and solvents: the β-anomer is preferred under such conditions as–15 to–40° C in nitroethane while the α-anomer is preferred at–78° C in propiononitrile.
![1H-Pyrrolo[2,3-b]pyridine, 1-[(1,1-dimethylethyl)dimethylsilyl]- Structure](https://image.chemsrc.com/caspic/105/183001-71-0.png)