Synthesis of α,α′‐Disubstituted Linear Ethers by an Intermolecular Nicholas Reaction – Application to the Synthesis of (+)‐cis/(–)‐trans‐Lauthisan and (+)‐cis/(+)‐trans‐Obtusan

A new and efficient methodology to prepare α,α′‐disubstituted linear ethers through an intermolecular Nicholas reaction (interNR) is described. cis ‐2,8‐Disubstituted oxocanes, cis ‐2,9‐disubstituted oxonanes, their trans isomers, and their parent unsaturated precursors were prepared from the corresponding Co 2 (CO) 6 –cycloalkynic ethers. Key steps in such syntheses were the ether linkage formation by interNR, RCM of the suitable acyclic dienyl ether, and montmorillonite K‐10 induced isomerization of the complexed cycloalkyne. By taking advantage of the developed methodology a short synthesis of (+)‐ cis ‐ and (–)‐ trans ‐lauthisan and (+)‐ cis ‐ and (+)‐ trans ‐obtusan are described. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)