Unexpected Facile Formation of an Achaetolide Dimer

Ring‐closing metathesis (RCM)‐based approaches to achaetolide usually lead to smooth ring closures. In contrast, lactonization gave none of the expected monolactone, but instead a diolide was obtained as the predominant product. This result not only illustrates that the current method is a facile “one‐pot” route to dilactones, but it also demonstrates an unnoticed advantage of RCM over lactonization for the formation of the given ring system. Expect the unexpected: In contrast to the smooth ring closures in all ring‐closing metathesis (RCM)‐based approaches to achaetolide, lactonization led to no monolactone, in spite of the high‐dilution conditions, but gave a diolide as the predominant product. This method is a facile one‐pot route to dilactones and also reveals a so far unnoticed advantage of RCM over lactonization in the construction of the given ring system. R=methoxymethyl.