Preparation and Application of Iron‐substituted (Z)‐Enals: Synthesis of 5‐Substituted α,β‐Butenolides

A reaction sequence furnishing cyclic β‐[η⁵‐C₅H₅(CO)₂Fe]‐substituted enals 5 starting from β‐keto esters 1 is described. Organolithiums were found to react smoothly with the iron‐substituted enals yielding α,β‐butenolides 6 by an intramolecular cyclocarbonylation of the lithiumalkoxide initially formed. The influence of e.g. the reaction temperature and the solvent on the reaction cascade is discussed. A reaction mechanism is proposed.