Studies towards the total synthesis of solanoeclepin A: synthesis of the 7-oxabicyclo[2.2.1]heptane moiety and attempted seven-membered ring formation

Abstract

This paper details studies towards the total synthesis of solanoeclepin A (1), the most active natural hatching agent of potato cyst nematodes. The first goal was the preparation of the tetracyclic left-handed substructure 2 in enantiopure form. The 7-oxabicyclo[2.2.1]heptane moiety was obtained via a diastereoselective intramolecular Diels–Alder strategy by using (R)-phenylglycinol as a chiral auxiliary as pioneered by Mukaiyama. A chromium-mediated nickel-catalysed coupling of aldehyde 5 with vinyl triflate 6 gave α,β-unsaturated lactone 18 as a single stereoisomer. The seven-membered ring was expected to arise from a McMurry coupling of dialdehyde 4. Surprisingly, oxidation of diol 24 did not lead to the desired dialdehyde 4, but to the eight-membered ring lactone 25.