| Abstrakt: |
2,6-Di-t-butyl-4-nitrophenol reacted with O2-methyluridine, N3-methyluridine or 4-triazolyl-1-(ß-d-ribofuranosyl)-2(1H)-pyrimidinone in the presence of diethyl azodicarboxylate and triphenylphosphine selectively at the 5'-position to give the corresponding 4-(nucleosid-5'-yl-aci-nitro)-2,6-di-t-butylcyclohexa-2,5-dienone (aci-nitro ester of nucleoside) in 39–72% yields along with varied amounts of 5'-deoxy-5'-[N,N'-bis(ethoxycarbonyl)hydrazino]nucleosides. By comparison of the reactions of pyrimidine nucleosides having free 2'- and 3'-hydroxyl groups with those of their 2',3'-O-isopropylidene derivatives, the ratio of aci-nitxo ester to 5'-deoxy-5'-hydrazinonucleoside was affected by the protecting groups as well as the time required for the addition of diethyl azodicarboxylate to a solution of other reactants. Similarly, N1,N6,2'3'-O-tetrabenzoyladenosine afforded the expected aci-nitro ester in 83% yield. The aci-nitro esters prepared were successfully reacted with stabilized phosphoranes such as (ethoxycarbonylmethylene)triphenylphosphorane or (acetylmethylene)triphenylphosphorane giving 1-[(E)-ß-d-ribo-hept-5-enofuranosyl]- or 1-[(E)-ß-d-ribo-oct-5-enofuranosyl]-pyrimidines and -purines. When the two stage reactions were carried out by one-pot procedure without isolation of aci-nitro esters, overall yields of alkenofuranosylpyrimidines were markedly improved. |
