Synthesis of a Dihydropyranonucleoside Using an Oxidative Glycosylation Reaction­ Mediated by Hypervalent Iodine

Abstract As a part of our ongoing studies of structure–activity relationships regarding cyclohexenyl nucleosides, we were prompted to synthesize a dihydropyranonucleoside as a potential anti-HIV agent. The synthesis of a glycal moiety started from but-2-enediol, which was converted into a di-PMB derivative in several steps. The introduction of an allyl group followed by ring-closing metathesis gave a dihydropyran derivative. After isomerization of the double bond catalyzed by Wilkinson’s catalyst, the resulting glycal, 2,3-bis[(4-methoxybenzyloxy)methyl]-3,4-dihydro-2 H -pyran, was subjected to an oxidative glycosylation reaction mediated by hypervalent iodine. Treatment of 2,3-bis[(4-methoxybenzyloxy)methyl]-3,4-dihydro-2 H -pyran with (PhSe) 2 /PhI(OAc) 2 /TMSOTf (cat.) gave the desired pyranyluracils as a mixture of anomers that were converted into the final target, dihydropyranocytidine, after several manipulations and separation of the anomers.