Synthesis of Nucleosides and Their Related Compounds. XII. : Menthyl 2,4-Dioxo-1,3-oxazine-5-carboxylates : New Dienophiles for the Asymmetric Diels-Alder Reaction Directed towards Synthesis of Carbocyclic C-Nucleosides

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2,4-Dioxo-1,3-oxazine-5-carboxylic acid esters prepared by thermal reaction of 4-oxo-1,3-dioxin-5-carboxylates with isocyanates were found to react with cyclopentadiene either in the presence or absence of suitable Lewis acid catalysts under quite mild conditions. Thus, reaction of methyl 3-substituted 2,4-dioxo-1,3-oxazine-5-carboxylates with cyclopentadiene either at room temperature or in the presence of a catalytic amount of titanium tetrachloride at -15℃ gave the corresponding adducts in almost quantitative yield. The 5-phenyl derivative was converted to a carbocyclic C-uncleoside precursor through reductive retrograde aldol reaction (RRA reaction) as a key step. This titanium tetrachloride-catalyzed Diels-Alder reaction, when applied to l-8-phenylmenthyl 2,4-dioxo-1,3-oxazine-5-carboxylate, afforded the corresponding adduct in high diastereomeric excess (95% for the major endo adduct).
公益社団法人日本薬学会の論文
1989-04-25