Formal Asymmetric (4+1) Annulation Reaction between Sulfur Ylides and 1,3-Dienes

A highly enantioselective synthesis of functionalized cyclopentanoids by a formal asymmetric (4+1) annulation strategy was developed. The methodology consists of a stereoselective cyclopropanation reaction between chiral sulfur ylides and 1,3‐dienes followed by a, in situ, stereospecific MgI2‐catalyzed rearrangement of vinylcyclopropanes. This method is distinguished by a remarkable compatibility with functional groups and a high stereocontrol. 2 plus 1 makes 5? A direct access to cyclopentenes has been achieved through the reaction of 1,3‐dienes and sulfur ylides under mild conditions. The one‐pot procedure involves a cyclopropanation followed by a magnesium iodide mediated vinylcyclopropane–cyclopentene rearrangement (see scheme).