Asymmetric Total Syntheses of (-)-Hedycoropyrans A and B

The first and asymmetric total synthesis of (‒)-hedycoropyrans A (1) was accomplished in 18 steps with 5.4% overall yield. The key features of our strategy include 1) construction of the unusual trans-2-aryl-6-alkyl tetrahydropyran core via Achmatowicz rearrangement, Zn-mediated reductive deoxygenation and Heck-Matsuda coupling reaction, and 2) installation of 3,4-anti-dihydroxy from the corresponding 3,4-syn-dihydroxy THP through chemo- and regioselective IBX oxidation and Evans-Saksena reduction. In addition, C2 epimerization of (-)-hedycoropyan A (1) under the acidic condition furnished (‒)-Hedycoropyan B (2) with 71% yield. This finding might suggest the biogenetic origin of hedycoropyran B.