Chapter 25, Problem 14P

The example of a silyl–Hilbert–Johnson nucleosidation reaction in Section 25.3 is presumed to involve an intermediate ribosyl cation that is stabilized by intramolecular interactions involving the C2 benzoyl group. This intermediate blocks attack by the heterocyclic base from the $\alpha$ face of the ribose ring but allows attack on the $\beta$ face, as required for formation of the desired product. Propose a struc-ture for the ribosyl cation intermediate that explains the stereoselective bonding of the base