Fluorinated analogs of polyhedral hydrocarbons have been predicted to localize an electron within their cages upon reduction. Here, we report the synthesis and characterization of perfluorocubane, a stable polyhedral fluorocarbon. The key to the successful synthesis was the efficient introduction of multiple fluorine atoms to cubane by liquid-phase reaction with fluorine gas. The solid-state structure of perfluorocubane was confirmed using x-ray crystallography, and its electron-accepting character was corroborated electrochemically and spectroscopically. The radical anion of perfluorocubane was examined by matrix-isolation electron spin resonance spectroscopy, which revealed that the unpaired electron accepted by perfluorocubane is located predominantly inside the cage. Description A fluorinated cube The synthesis of a cube-shaped hydrocarbon nearly 60 years ago was a major event in chemistry, both because of the compound’s beautiful, high symmetry and its distinctly unnatural bonding geometry. Sugiyama et al. have now synthesized and structurally characterized a cubane derivative in which the hydrogen atoms at each vertex are replaced by fluorines (see the Perspective by Krafft and Riess). Consistent with theoretical predictions, low-temperature electron spin resonance spectroscopy suggests that the molecule centrally internalizes an electron upon reduction. —JSY A perfluorinated carbon cube internalizes an electron upon reduction.

Electron in a cube: Synthesis and characterization of perfluorocubane as an electron acceptor

Two new reaction processes involving the in situ oxidative photochemical conversion of CHCl3 to COCl2 allowed selective syntheses of N-substituted ureas and isocyanates from amines. (I) A CHCl3 solution containing an amine and an organic base under O2 bubbling provided the urea derivative under exposure to UV light generated from a low-pressure mercury lamp at 20–40 °C. (II) A two-step reaction involving the oxidative photodecomposition of CHCl3 at lower temperatures and subsequent sequential injections of an amine and organic base into the sample solution provided the isocyanate in high yield. The reaction processes of (I) and (II) capitalize on the solution conditions of [COCl2] < [amine] and [COCl2] > [amine], respectively, to result in 1:2 and 1:1 reactions. In general, isocyanates, especially aromatic and haloalkyl ones, readily undergo hydrolysis in the presence of an organic base. However, with the advantage of synthesizing the isocyanates in CHCl3 solvent, direct addition of monoalcohols and diols to the as-prepared sample solution containing the diisocyanate allowed the one-pot syntheses of biscarbamates and polyurethanes, respectively. The reactions developed in this study are simple, safe, and inexpensive methods of synthesizing N-substituted ureas and isocyanates, and derivatives of isocyanates such as carbamates and polyurethanes. The present new methods can replace current synthetic methods using COCl2 in both academia and industry.

Photo-on-Demand Phosgenation Reactions with Chloroform for Selective Syntheses of N-Substituted Ureas and Isocyanates

Chloroform (CHCl3) upon bubbling with O2 containing ∼2% Cl2 underwent oxidative photochemical conversion to phosgene (COCl2) when exposed to a white LED light. Cl2 may serve as a visible light-responsive radical initiator in the radical chain reactions of CHCl3 and O2. This photochemical reaction allowed both in situ and stepwise one-pot phosgenation reactions, which are simple and safe methods, without expensive apparatus. It can be applied to a variety of conventional organic syntheses using phosgene and phosgene oligomers. Chloroform under bubbling with O2 containing ∼2% Cl2 underwent oxidative photochemical conversion to phosgene under exposure to a white LED light. This photochemical reaction allowed in situ synthesis of chloroformate and one-pot syntheses of carbonate esters and isocyanates. 

Photo-on-Demand Conversion of Chloroform to Phosgene Triggered by Cl2 upon Irradiation with Visible Light: Syntheses of Chloroformates, Carbonate Esters, and Isocyanates

Flow Photo-On-Demand Phosgenation Reactions with Chloroform

Amino acid N-carboxyanhydrides (NCAs) are conventionally synthesized from α-amino acids and phosgene. The present study reports in situ photo-on-demand phosgenation reactions of amino acids with CHCl3 for synthesizing NCAs. A series of NCAs were obtained on a gram scale upon photo-irradiation of a mixture solution of CHCl3 and CH3CN containing an amino acid at 60–70 °C under O2 bubbling. This method presents a safe and convenient reaction controlled by light without special apparatuses and reagents.

Photo-On-Demand Synthesis of α-Amino Acid N-Carboxyanhydrides with Chloroform

Carbonate esters are utilized as solvents and reagents for C1 building blocks in organic synthesis. This study reports a novel photo-on-demand in situ synthesis of carbonate esters with CHCl3 solutions containing a mixture of an aromatic or haloalkyl alcohol having relatively high acidity, and an organic base. We found that the acid-base interaction of the alcohol and base in the CHCl3 solution plays a key role in enabling the photochemical reaction. This reaction allows practical syntheses of diphenyl carbonate derivatives, haloalkyl carbonates, and polycarbonates, which are important chemicals and materials in industry.

Yuka Hashimoto

Papers

Photo-on-Demand Base-Catalyzed Phosgenation Reactions with Chloroform: Synthesis of Arylcarbonate and Halocarbonate Esters.