Fluorinated liquid crystals--properties and applications

Preparation of fluoroalkoxy or fluorophenoxy substituted N-heterocycles from heterocyclic N-oxides and polyfluoroalcohols

A novel and efficient approach to introduce fluorine-containing groups into N-heterocycles was reported.

Electrophilic trifluoromethylselenolation of terminal alkynes with Se-(trifluoromethyl) 4-methylbenzenesulfonoselenoate

Herein the nucleophilic addition of Se-(trifluoromethyl) 4-methylbenzenesulfonoselenoate, a stable and easy-to-handle reagent, to alkynes is described. This reaction provides trifluoromethylselenylated vinyl sulfones with good results and the method was extended also to higher fluorinated homologs. The obtained compounds are valuable building blocks for further syntheses of fluoroalkylselenolated molecules.

Exploring the Reactivity of Trifluoromethyl Tolueneselenosulfonate with Alkynes under Copper Catalysis

The direct fluoroalkylselenolation of terminal alkynes is reported herein involving shelf stable electrophilic reagents TsSeR_F . The use of these reagents allows for the first time performing the reaction under catalytic conditions (copper/ligand). Moreover, the presence of oxygen directing groups allows the selective addition of the reagents to alkynes, therefore yielding a new family of vinyl sulfones.

Transition-Metal-Free Catalytic Hydrodefluorination of Polyfluoroarenes by Concerted Nucleophilic Aromatic Substitution with a Hydrosilicate

A transition-metal-free catalytic hydrodefluorination (HDF) reaction of polyfluoroarenes is described. The reaction involves direct hydride transfer from a hydrosilicate as the key intermediate, which is generated from a hydrosilane and a fluoride salt. The eliminated fluoride regenerates the hydrosilicate to complete the catalytic cycle. Dispersion-corrected DFT calculations indicated that the HDF reaction proceeds through a concerted nucleophilic aromatic substitution (CS_N Ar) process.

Perfluoroalkylation of Aryl-N,N-dimethyl Hydrazones Using Hypervalent Iodine(III) Reagents or Perfluoroalkyl Iodides

Radical trifluoromethylation of aryl N,N-dimethyl hydrazones using TBAI as an initiator and Togni's reagent as a trifluoromethyl radical source is described. Cascades proceed via electron-catalysis; this approach is generally more applicable to hydrazone perfluoroalkylation using perfluoroalkyl iodides as the radical precursors in combination with a base under visible-light initiation.

Electrophilic Triflyl-arylation and Triflyl-pyridylation by Unsymmetrical Aryl/Pyridyl-λ3-iodonium Salts: Synthesis of Aryl and Pyridyl Triflones

Unsymmetrical diaryl-λ³-iodonium salts containing aryl triflone (Ar-SO₂CF₃) were designed and synthesized. X-ray crystal structure analysis of the salt indicated a T-shaped geometry at the iodine atom. The salts were found to be powerful electrophilic reagents for triflyl-arylation of C-, N-, and O-centered nucleophiles under mild conditions. Electrophilic transfer of pyridine triflone (Py-SO₂CF₃) to nucleophiles was also realized by the use of corresponding triflylpyridyl-aryl-λ³-iodonium salts. Selection of auxiliaries (dummy ligands) of unsymmetrical diaryl-λ³-iodonium salts is crucial for this transformation.

Engineered Fluorine Metabolism and Fluoropolymer Production in Living Cells

Fluorine has become an important element for the design of synthetic molecules for use in medicine, agriculture, and materials. Despite the many advantages provided by fluorine for tuning key molecular properties, it is rarely found in natural metabolism. We seek to expand the molecular space available for discovery through the development of new biosynthetic strategies that cross synthetic with natural compounds. Towards this goal, we engineered a microbial host for organofluorine metabolism and show that we can achieve the production of the fluorinated diketide 2-fluoro-3-hydroxybutyrate at approximately 50 % yield. This fluorinated diketide can be used as a monomer in vivo to produce fluorinated poly(hydroxyalkanoate) (PHA) bioplastics with fluorine substitutions ranging from around 5-15 %. This system provides a platform to produce mm flux through the key fluoromalonyl coenzyme A (CoA) building block, thereby offering the potential to generate a broad range of fluorinated small-molecule targets in living cells.

Hydrogen Bond Directed Photocatalytic Hydrodefluorination: Overcoming Electronic Control

The photocatalytic C-F functionalization of highly fluorinated arenes is a powerful method for accessing functionalized multifluorinated arenes. The decisive step in the determining regioselectivity in fluorine functionalization is fluoride fragmentation from the radical anion of the multifluorinated arene. To date, the availability of regioisomers has been dictated by the innate electronics of the fluorinated arene, limiting the synthetic utility of the chemistry. This study investigates the remarkable ability of a strategically located hydrogen bond to transcend the normal regioselectivity of the C-F functionalization event. A significant rate acceleration is additionally observed for hydrodefluorination of fluorines that can undergo intramolecular hydrogen bonds that form 5-8-membered cycles with moderately acidic N-H's. The hydrogen bond is expected to facilitate the fragmentation not only by bending the C-F bond of the radical anion out of planarity but also by increasing the exothermicity of the fluoride extrusion step through protonation of the naked fluoride. Finally, the synthetic utility of the method is demonstrated in an expedited synthesis of the trifluorinated α-phenyl acetic acid derivative required for the commercial synthesis of Januvia, an antidiabetic drug. This represents the first synthesis of a commercially important multifluorinated arene via a defluorination strategy and is significantly shorter than the current strategy.

Incompatibility-Driven Self-Organization in Polycatenar Liquid Crystals Bearing Both Hydrocarbon and Fluorocarbon Chains

The synthesis and liquid crystal properties are reported for tri- and tetra-catenar mesogens in which both hydrocarbon and semiperfluorocarbon chains have been incorporated. In the tricatenar mesogens, the lamellar spacing in the smectic C phase of the all-hydrocarbon mesogen almost doubles when the isolated hydrocarbon chain is replaced by a semiperfluorinated chain on account of the localized segregation in different sublayers between the two chain types. In the tetracatenar materials, the replacement of at least one hydrocarbon chain by semiperfluorocarbon chains is sufficient to promote columnar phase formation, but when the molecule has two hydrocarbon chains at one end and two semiperfluorocarbon chains at the other, the requirement for localized phase segregation leads to the formation of a rectangular phase with very large lattice parameters. The juxtaposition of terminal chains of different nature within the same molecular structure thus leads to a reduction in mesophase symmetry and the emergence of more complex supramolecular organization.

α-Perfluoroalkyl-β-alkynylation of alkenes via radical alkynyl migration

Transition metal-free radical α-perfluoroalkylation with concomitant β-alkynylation of unactivated alkenes is presented.

Transition metal-free radical α-perfluoroalkylation with concomitant β-alkynylation of unactivated alkenes is presented. These cascades proceed via electron-catalysis and comprise a radical 1,4- or 1,5-alkynyl migration from tertiary propargylic alcoholates to secondary or tertiary C-radicals as the key step. Alkynyl migration leads to a ketyl radical anion that sustains the chain as a single electron transfer reducing reagent.

Polyfluoroalkylated 2-ethoxymethylene- 3-oxo esters: synthesis and chemical properties overview

The review focuses on the synthesis and chemical properties of polyfluoroalkylated 2-ethoxymethylene-3-oxo esters. The scope and peculiarities of their use as organic reagents in reactions with various N-, C-, O-, mono- and dinucleophiles are discussed in detail. The high reactivity of such derivatives is employed in the construction of enaminoketone, arene and heterocycle frameworks. Particular attention is paid to applications of these building blocks as chemicals for fine organic synthesis, bioactive compounds and metal complexes synthesis.

Broadband mid-infrared polarization rotator based on optically addressable LCs

This work proposes a mid-infrared polarization rotator that incorporates a twisted nematic liquid crystal (TNLC) cell with a photo-controllable alignment layer. The TNLC device with a sufficient phase retardation can act as an achromic polarization rotation device over a wide wavelengths range and thus can rotate the polarization of a mid-IR laser beam. The photo-alignment technique enables TNLCs with arbitrary twisting angles to be generated by the use of visible polarized addressing light to control the directors of the photo-alignment layer. Therefore, arbitrary rotation angles of the polarization axis of a linearly polarized mid-IR laser beam can be realized. Moreover, the rewritable property and reliability of this polarization rotator are experimentally verified. The flexibility of polarization control for broadband mid-IR opens up a large range of potential mid-IR applications.

Transition from nematic to gyroid-type cubic soft self-assembly by side-chain engineering of π-conjugated sticky rods

A sequence of liquid crystalline phases, involving cybotactic nematics, a lamellar phase, bicontinuous cubics and triangular honeycombs, was observed for oligo(phenylene ethynylene) based X-shaped bolapolyphiles with two long lateral alkyl chains and sticky ends provided by glycerol groups. In the cubic phase with Ia3[combining macron]d lattice - which is tailored by alkyl chain engineering - the aromatic cores are organized on the gyroid minimal surface in 3D curved layers of almost parallel aligned π-conjugated rods. It is shown that this type of cubic phase is a general mode of soft self-assembly of X-shaped bolapolyphiles at the cross-over from the (long or short range) lamellar to the triangular honeycomb-like organization. Cubic phase formation is found only in a narrow range with respect to temperature and chain-length for the non-fluorinated compounds and in much wider ranges for related core-fluorinated molecules.

Electrophilic Trifluoromethylselenolation of Boronic Acids

Trifluoromethylselenylated compounds are emergent compounds with interesting physicochemical properties that still suffer from a lack of efficient synthetic methods. We recently developed an efficient one-pot strategy to generate in situ CF₃SeCl and use it in various reactions. Herein, we continue our study of the reactivity scope of this preformed reagent. Cross-coupling reactions with aromatic and heteroaromatic boronic acids have been investigated. The expected products have been obtained, using a stoichiometric amount of copper, with moderate yields.