Some Observations Concerning the Thermally Induced Oxy‐Ene Reaction

Several examples of thermally induced intramolecular oxy‐ene reactions leading to six‐ or five‐membered rings are reported. The yields vary from poor to good, depending on the thermal lability of the substrate. Considering the high temperatures required to effect these transformations (several hours at ca . 250°), the observed diastereoselectivities favoring the trans ‐1,2‐substituted cycloalkane derivatives are excellent. In the case of product 26 , these substituents were shown to prefer a trans ‐diaxial orientation both in the solid state (X‐ray evidence) and in solution, presumably to avoid the allylic strain prevailing in the diequatorial conformer.