Iron(0)‐mediated stereoselective (3+2)‐cycloaddition of thiochalcones via a diradical intermediate

Reactions of α,β‐unsaturated aromatic thioketones 1 (thiochalcones) with Fe 3 (CO) 12 leading to η 4 ‐1‐thia‐1,3‐diene iron tricarbonyl complexes 2 , [FeFe] hydrogenase mimics 3 , and the thiopyrane adduct 4 are described. Obtained products have been characterized by X‐ray crystallography and by computational methods. Completely regio‐ and diastereoselective formation of the five‐membered ring system in products 3 , containing four stereogenic centers, can be explained by an unprecedented, stepwise (3+2)‐cycloaddition of two thiochalcone molecules mediated by Fe 3 (CO) 12 . Quantum chemical calculations aimed at elucidation of the reaction mechanism, suggest that the formal (3+2)‐cycloaddition proceeds via sequential intramolecular radical transfer events upon homolytic cleavage of one carbon‐sulfur bond leading to a diradical intermediate.Making the rounds : A series of new cyclopentenes was obtained from thiochalcones via a Fe 0 ‐mediated formal (3+2)‐cycloaddition. Reactions occurred diastereoselectively and the postulated reaction mechanism was elucidated by a combined experimental and theoretical approach. imag