HFIP-Promoted Synthesis of Substituted Tetrahydrofurans by Reaction of Epoxides with Electron-Rich Alkenes

In the present work, the employment of fluorinated alcohols, specifically 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), as solvent and promoter of the catalyst-free synthesis of substituted tetrahydrofuranes through the addition of electron-rich alkenes to epoxydes is described. The unique properties of this fluorinated alcohol, which is very different from their non-fluorinated analogs, allows carrying out this new straightforward protocol under smooth reaction conditions affording the corresponding adducts in moderate yields in the majority of cases. Remarkably, this methodology has allowed the synthesis of new tetrahydrofuran-based spiro compounds as well as tetrahydrofurobenzofuran derivatives. The scope and limitations of the process are also discussed. Mechanistic studies were also performed pointing towards a purely ionic or a SN2-type process depending on the nucleophilicity of the alkene employed.

On the Ability of Nickel Complexes Derived from Tripodal Aminopyridine Ligands to Catalyze Arene Hydroxylations

The development of catalysts for the selective hydroxylation of aromatic C–H bonds is an essential challenge in current chemical research. The accomplishment of this goal requires the discovery of powerful metal-based oxidizing species capable of hydroxylating inert aromatic bonds in a selective manner, avoiding the generation of non-selective oxygen-centered radicals. Herein we show an investigation on the ability of nickel(ii) complexes supported by tripodal tetradentate aminopyridine ligands to catalyze the direct hydroxylation of benzene to phenol with H2O2 as oxidant. We have found that modifications on the ligand structure of the nickel complex do not translate into different reactivity, which differs from previous findings for nickel-based arene hydroxylations. Besides, several nickel(ii) salts have been found to be effective in the oxidation of aromatic C–H bonds. The use of fluorinated alcohols as solvent has been found to result in an increase in phenol yield; however, showing no more than two turn-overs per nickel. These findings raise questions on the nature of the oxidizing species responsible for the arene hydroxylation reaction.

Similar Behavior of Rheological Properties and the Evaluation of the Melting Temperatures of Fluorinated Aliphatic Alcohols

On the basis of experimental data obtained for the viscosity, density, and refractive index of fluorinated alcohols and proceeding from the similarity laws, the structural features of molecules of the researched liquids are determined. A comparison of molecular refraction values determined for fluorinated and non-fluorinated alcohols made it possible to reveal a modification of the structure of fluorinated alcohol molecules. Namely, this is a probable minor change in the arrangement of fluorine atoms in the alcohol molecule, at which the structure of a molecule remains similar to the structure of molecules of aliphatic alcohols. A similarity in the behavior of the rheological properties of 2,2,3,3-tetrafluoropropan-1-ol and 1H,1H-pentafluoropropan-1-ol, on the one hand, and propan-1-ol, on the other hand, as well as 1H,1H,7H-dodecafluoroheptan-1-ol and 1H,1H-tridecafluoroheptan-1-ol, on the one hand, and heptan-1-ol, on the other hand, is found. A method for estimating the melting temperatures of halogenated molecular liquids, which is based on the similarity of the rheological properties of those liquids, is proposed. The melting temperatures for 1H,1H-pentafluoropropan-1-ol, Tm = (244.5 ± 1.0) K, and 1H,1H-tridecafluoroheptan-1-ol, Tm = (255.0 ± 1.0) K, which are not available in the literature, are evaluated.