Synthesis of Cr(III) Salen Complexes as Supramolecular Catalytic Systems for Ring‐Opening Reactions of Epoxides

Abstract The synthesis of two conformationally restricted Cr(III) salen complexes, 2 and 3, is described. Together, they constitute a supramolecular hydrogen‐bonding catalytic system for the recently reported asymmetric ring‐opening reactions of epoxides by a dynamic supramolecular catalyst. The synthesis involves state‐of‐the art transformations in frontline synthetic chemistry applied to heterocyclic chemistry. Hence, palladium‐catalyzed reactions were employed, including carbonylative annelation and Suzuki cross‐coupling reactions, for the formation of one of the heterocyclic rings (quinolone) and the functionalization of the formed rings. For the construction of the second heterocyclic ring (isoquinolone), a Curtius rearrangement was employed. The corresponding salen ligands were then prepared by Schiff‐base reactions, yielding the final complexes after metal insertion. For reference purposes the less conformationally restricted Cr(III) complexes 4 and 5 were also synthesized.