Model synthesis of six-membered carbocyclic spironucleosides

Model study focusing on the synthesis of carbocyclic spironucleosides is presented. Hydantoin base was built on the easily accessible ketone precursors by Bucherer–Bergs reaction. On saturated substrates the reaction proceeded smoothly. On α,β-unsaturated ketones, however, the Bucherer–Bergs reaction competed with Michael addition of cyanide ion. We showed that the equilibrium of the reaction could be significantly shifted depending on the applied reaction conditions. Significant diastereoselectivity was observed for tandem Michael addition/Bucherer–Bergs reaction.