Building a small polypropionate library. Synthesis of all possible stereotetrads (building blocks for polyketide synthesis) from furan

The all diastereomeric stereotetrads (polypropionate fragments) were synthesized in a stereodivergent fashion, starting from the Dials-Alder adducts of furan with acrylic acid and (-)-2-camphanoxyacrylonitrile, respectively. The key intermediates of these sequences were the oxanorbornenic sulfones 7, (-)-53 and (+)-54. Regio- and stereocontrolled alkylative ring opening of these intermediates afforded the cyclohexenyl sulfones 14, (+)-55 and (-)-58 which were transformed into the desired stereotetrads 30, 31, 40, 41, (+)-62, (+)-63, (-)-66, and (+)-69.