A Synthesis of (+)‐Oblongolide

The absolute configuration of natural oblongolide is reassigned as (3aS,5aR,7S,9aS,9bS)‐3a,5a,6,7,8,9,9a,9b‐octahydro‐7,9b‐dimethylnaphtho[1,2‐c]furan‐1(3H)‐one 2 by a 7‐stage synthesis of its enantiomer 1 from (+)‐citronellol involving a regioselective reduction and an intramolecular Diels‐Alder reaction (IMDA) as the key steps. (+)‐Citronellol was converted into methyl (2E,4E,10E)‐(S)‐(+)‐11‐ tert ‐butoxycarbonyl‐7‐methyl‐undeca‐2,4,10‐trienoate 7 by sequential Lemieux‐Johnson oxidation, Wittig reaction, pyridinium chlorochromate oxidation, and Wadsworth‐Emmons‐Homer alkenation. A regioselective reduction of the methoxycarbonyl group in 7 afforded tert ‐butyl (2.E,8E,10E)‐(S)‐(+)‐2,6‐dimethyl‐12‐hydroxy‐dodeca‐2,8,10‐trienoate 8 from which (+)‐oblongolide was readily obtained via an IMDA reaction.