Cyclization of Diols Using Ferrocenium Cations & Other Iron-Based Catalysts

Our research involves the study and improvement of iron-based catalysts. The Bauer group has recently found that the ferrocenium cation, along with other iron-based compounds, are catalytically active in the cyclization of various diols to obtain five-membered tetrahydrofuran derivatives. My research involved comparing the effect of 2 different counter-anions of the ferrocenium cation along with 2 other iron-based catalysts that were previously synthesized in the Bauer lab for their catalytic activity in the title reaction. Cyclization test reactions were performed by reacting three different types of diols with each of four different iron catalysts. The three diols used were 4-methyl-1-phenyl-1,4-pentanediol (I), 4-butyl-1-phenyl-1,4-octanediol (II) and 1,4,4-phenyl-1,4-butanediol (III). The four catalysts used were ferrocenium hexafluorophosphate (IV), ferrocenium tetrafluoroborate (V), [FeCl3(NNN)] (VI) (where NNN is a tridentate, nitrogen-based ligand) and [Fe(PA)2(OTf)2] (VII) (where PA is a picoyl acid derivative).\nIn each reaction, one of the three diols and one of the four catalysts were combined and heated at 45 °C using CH2Cl2 as a solvent. Reactions were stirred for 72 hours and catalysts were added at 10% catalytic load. The complexes were analyzed using 1H NMR and analyzed to see if cyclization occurred. Cyclization was observed for each of the diols with use of these catalysts. This research assists with increasing the efficiency of iron-based catalyst systems in the title reaction, which saves time, energy and resources for potential industrial applications.