An enantioconvergent route to carbocyclic nucleosides (–)-aristeromycin and (–)-neplanocin a via the asymmetric Diels–Alder reaction

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Abstract
The asymmetric Diels–Alder reaction of (SS)-menthyl-3-(2-pyridylsulphinyl)acrylate (4) with cyclopentadiene gave almost a pure single diastereoisomeric cycloadduct. The cycloadduct was then converted into the central intermediate (+)-(3) which was involved in the synthesis of both (–)-aristeromycin and (–)-neplanocin A. Similarly, the Diels–Alder adduct of (RS)-menthyl-3-(2-pyridylsulphinyl)acrytate (6) with cyclopentadiene was transformed into the lactone (3) with the same absolute configuration. Namely, an enantioconvergent synthesis of (3) starting from each of the diastereoisomeric sulphoxides (4) and (6) has been achieved.