More particular conditions are pyridine and methanesulfonyl chloride at 0??? C. [0060] Intramolecular nucleophilic displacement of the 6???-mesylate, or other such leaving groups, by the 3 ???-hydroxyl moiety is catalyzed by a base like triethylamine or Hunig's base, but more particularly fluoride ion (such as tetrabutylammonium fluoride).