Dehydrogenative Lactonization of Diols in Aqueous Media Catalyzed by a Water-Soluble Iridium Complex Bearing a Functional Bipyridine Ligand

A new catalytic system for the dehydrogenative lactonization of a variety of benzylic and aliphatic diols in aqueous media was developed. By using a water-soluble, dicationic iridium catalyst bearing 6,6-dihydroxy-2,2-bipyridine as a functional ligand, highly atom economical and environmentally benign synthesis of various lactones was achieved in good to excellent yields. Recovery and reuse of the catalyst were also accomplished by a simple phase separation and the recovered catalyst maintained its high activity at least until the fifth run.