In contrast to the potent amine and thiol nucleophiles at the 5' position of ribose, which readily give the N- and S-cyclonucleosides in good yields, the cyclization reaction from the "natural" 5'-hydroxyl is tedious and has so far been overlooked most probably because of the thermodynamic instability of the O-cyclo-adduct. 
THERM
In contrast to the potent amine and thiol nucleophiles at the 5' position of ribose, which readily give the N- and S-cyclonucleosides in good yields, the cyclization reaction from the "natural" 5'-hydroxyl is tedious and has so far been overlooked most probably because of the thermodynamic instability of the O-cyclo-adduct. 
THERM
In contrast to the potent amine and thiol nucleophiles at the 5' position of ribose, which readily give the N- and S-cyclonucleosides in good yields, the cyclization reaction from the "natural" 5'-hydroxyl is tedious and has so far been overlooked most probably because of the thermodynamic instability of the O-cyclo-adduct. 
THERM
In contrast to the potent amine and thiol nucleophiles at the 5' position of ribose, which readily give the N- and S-cyclonucleosides in good yields, the cyclization reaction from the "natural" 5'-hydroxyl is tedious and has so far been overlooked most probably because of the thermodynamic instability of the O-cyclo-adduct. 
THERM