NUCLEOSIDES .6. A NOVEL AND CONVENIENT SYNTHESIS OF PURINE S-CYCLONUCLEOSIDES VIA MITSUNOBU REACTION

Two representative S-cyclonucleosides, 8,5'-anhydro-2', 3'-O-isopropyl idene-8-mercaptoadenosine (3) and aisopropyldisiloxane-1,3-diyl)-8-mer captoguanosine (8), were prepared in good yields by dropwise addition of one equivalent each of triphenylphosphine and DEAD in DMF into a mi xture of 2',3'-O-isopropylidene-8-mercaptoadenosine (2) or iso-propyld isiloxane-1,3-diyl)-8-mercaptoguanosine (7), respectively, in DMF. Tre atment of compound 2 with two equivalents each of triphenylphosphine a nd DEAD in DMF afforded -mercaptopurin-6-yl]triphenylphospha-lambda5-a zene (4) in 87% yield.