Anomalous Fluorescence Quenching in Fluorous Solvent-Added Media

Due to the inherent high electronegativity of fluorine, perfluorocarbons have the potential to exhibit unusual characteristics. Fluorous solvents, in this context, may afford an anomalous solubilizing behavior compared to their hydrocarbon analogues. Addition of perfluorodecalin (PFD) to n-hexane results in unusual fluorescence quenching of polycyclic aromatic hydrocarbons (PAHs) by the quencher nitromethane. As more viscous PFD is added to less viscous n-hexane, the dynamic viscosity (η) of the media increases. The bimolecular quenching rate constants (kq) of the PAHs, instead of decreasing, increase as PFD is added to n-hexane until an equimolar mixture composition is obtained; kq exhibits an expected decrease only in the PFD-rich region of the mixture. The expected decrease in kq in the hydrocarbon analogue decalin added to n-hexane is observed across all compositions. It is proposed that highly electronegative fluorines on PFD stabilize the partial positive charge (δ+) that develops on excited PAHs during electron/charge transfer to the quencher nitromethane, facilitating quenching in the process. In the PFD-rich region, however, increased η starts to dominate the quenching, resulting in the expected decrease in kq. A monotonic decrease in kq is observed in the PFD-added n-hexane system for fluoranthene quenching by triethylamine (TEA) as TEA acts as the electron/charge donor and a partial negative charge (δ-) develops on excited fluoranthene during the quenching process. No such stabilization by PFD is observed when nitrobenzene is employed as the quencher. This is attributed to the significantly higher quenching (KS > 104 M-1) of PAH fluorescence by nitrobenzene due to the presence of aromatic π-π interactions between PAH and nitrobenzene, further facilitated by the higher electron affinity of nitrobenzene as compared to nitromethane. The role of fluorous media in facilitating electron/charge transfer processes is clearly established.

B(C6F5)3/Chiral Phosphoric Acid Promoted Asymmetric C-3 gem-Difluoroalkylation of Quinoxalin-2-ones with Difluoroenoxysilanes

The asymmetric Mannich-type reaction of quinoxalin-2-ones with difluoroenoxysilanes has been developed for the synthesis of chiral gem-difluoroalkylated quinoxalin-2-ones. The reaction worked in the presence of chiral phosphoric acid CPA 1 and B(C6F5)3 in THF at room temperature. The reaction exhibited a good substrate scope furnishing the products in good yields (up to 97%) with up to 96% ee.

Catalytic Asymmetric Difluoroalkylation Using In Situ Generated Difluoroenol Species as the Privileged Synthon

A robust and practical difluoroalkylation synthon, α,α-difluoroenol species, which generated in situ from trifluoromethyl diazo compounds and water in the presence of dirhodium complex, is disclosed. As compared to the presynthesized difluoroenoxysilane and in situ formed difluoroenolate under basic conditions, this difluoroenol intermediate displayed versatile reactivity, resulting in dramatically improved enantioselectivity under mild conditions. As demonstrated in catalytic asymmetric aldol reaction and Mannich reactions with ketones or imines in the presence of chiral organocatalysts, quinine-derived urea, and chiral phosphoric acid (CPA), respectively, this relay catalysis strategy provides an effective platform for applying asymmetric fluorination chemistry. Moreover, this method features a novel 1,2-difunctionalization process via installation of a carbonyl motif and an alkyl group on two vicinal carbons, which is a complementary protocol to the metal carbene gem-difunctionalization reaction.

Intramolecular dimer formation reveals anomalous solvation within fluorous solvent perfluorodecalin

Due to the unusual properties of fluorine, a fluorous solvent obtained by replacing hydrogen atoms with fluorine atoms in a hydrocarbon solvent may afford unusual solute solvation and aggregation. A fluorescent dipyrenyl probe, 1,3-bis(1-pyrenyl)propane (BPP), was utilized to explore intramolecular aggregation within perfluorodecalin (PFD), a prototypical fluorous solvent. Steady-state fluorescence emission and excitation along with excited-state emission intensity decay of BPP were acquired in the temperature range of 293.15 to 333.15 K in fluorous solvent PFD and n-hexane-added PFD. The probe BPP is known to form an intramolecular excimer in common hydrocarbon solvents, which is characterized by a broad structureless low-energy emission band; the formation of intramolecular excimers exclusively in the excited state was confirmed via excitation scans along with the intensity decay of the monomer and excimer, respectively. While intramolecular dimerization of BPP does occur in PFD, emission wavelength-dependent excitation spectra and fits of the intensity decay data reveal that intramolecular aggregation takes place in the ground state as well. This ground-state heterogeneity is reduced as the temperature is increased. In the presence of as small as 0.1 mole fraction of n-hexane, the ground-state aggregation vanishes, and intramolecular dimerization again takes place exclusively in the excited state. The data hint at the poor solvation of BPP in PFD to be responsible for intramolecular ground-state aggregation. In PFD-rich (PFD + n-hexane) mixtures, probe pyrene (Py) was found to be preferentially solvated by n-hexane, further corroborating the above-mentioned proposition. Clear differences in solute solvation within a fluorous solvent as compared to hydrocarbon solvents leading to unexpected solubilization and aggregation in fluorous media are amply demonstrated.

Decarboxylative Amination: Diazirines as Single and Double Electrophilic Nitrogen Transfer Reagents

The ubiquity of nitrogen-containing small molecules in medicine necessitates the continued search for improved methods for C-N bond formation. Electrophilic amination often requires a disparate toolkit of reagents whose selection depends on the specific structure and functionality of the substrate to be aminated. Further, many of these reagents are challenging to handle, engage in undesired side reactions, and function only within a narrow scope. Here we report the use of diazirines as practical reagents for the decarboxylative amination of simple and complex redox-active esters. The diaziridines thus produced are readily diversifiable to amines, hydrazines, and nitrogen-containing heterocycles in one step. The reaction has also been applied in fluorous phase synthesis with a perfluorinated diazirine.

Current Contributions of Organofluorine Compounds to the Agrochemical Industry

Currently, more than 1,200 agrochemicals are listed and many of these are regularly used by farmers to generate the food supply to support the expanding global population. However, resistance to pesticides is an ever more frequently occurring phenomenon, and thus, a continuous supply of novel agrochemicals with high efficiency, selectivity, and low toxicity is required. Moreover, the demand for a more sustainable society, by reducing the risk chemicals pose to human health and by minimizing their environmental footprint, renders the development of novel agrochemicals an ever more challenging undertaking. In the last two decades, fluoro-chemicals have been associated with significant advances in the agrochemical development process. We herein analyze the contribution that organofluorine compounds make to the agrochemical industry. Our database covers 424 fluoro-agrochemicals and is subdivided into several categories including chemotypes, mode of action, heterocycles, and chirality. This in-depth analysis reveals the unique relationship between fluorine and agrochemicals.

Fast and Low-Cost Purification Strategy for Oligosaccharide Synthesis Based on a Hop-On/Off Carrier

A feasible and convenient strategy for oligosaccharide synthesis, which realizes reaction in solution while product purification occurs only by solid-liquid filtration, has been developed. By using a hop-on/off carrier (polytetrafluoroethylene particle), rapid synthesis of tumor-associated antigen Globo-H hexasaccharide has been successfully achieved within 5 steps in 48% overall yield without any intermediate purification by column chromatography. Also, global deprotection, including the cleavage of the tag, proceeded simultaneously only by one-step hydrogenolysis.

New Polyfluorinated Cyanine Dyes for Selective NIR Staining of Mitochondria

In this communication, the synthesis of three unknown polyfluorinated cyanine dyes and their application as selective markers for mitochondria are presented. By incorporating fluorous side chains into cyanine dyes, their remarkable photophysical properties were enhanced. To investigate their biological application, several different cell lines were incubated with the synthesized cyanine dyes. It was discovered that the presented dyes can be utilized for selective near-infrared-light (NIR) staining of mitochondria, with very low cytotoxicity determined by MTT assay. This is the first time that polyfluorinated cyanine fluorophores are presented as selective markers for mitochondria. Due to the versatile applications of polyfluorinated fluorophores in bioimaging and materials science, it is expected that the presented fluorophores will be stimulating for the scientific community.

Asymmetric Conjugate Additions of Carbonyl Compounds to Nitroalkenes under Solvent-Free Conditions Using Fluorous Diaminomethylenemalononitrile Organocatalyst

The novel fluorous organocatalyst bearing a diaminomethylenemalononitrile motif is prepared. The fluorous organocatalyst efficiently promotes asymmetric conjugate additions of ketones to nitroalkenes and results in high yields of these addition products with excellent enantioselectivities under solvent-free conditions.

Brominated CF3-allyl alcohols as multicentered electrophiles in TfOH promoted reactions with arenes

Reactions of (di-)bromo-substituted CF₃-allyl alcohols with/without arenes with TfOH lead to CF₃-alkenes or CF₃-indenes.

Synthesis of trifluoromethyl-containing vicinal diamines by asymmetric decarboxylative mannich addition reactions

Herein is reported a study of asymmetric decarboxylative Mannich addition reactions between (Ss)-N-t-butylsulfinyl-3,3,3-trifluoroacetaldimine and Schiff bases derived from various aldehydes and lithium 2,2-diphenylglycinate. These reactions proceed with excellent diastereoselectivities and good chemical yields, providing a practical method for preparation of trifluoromethyl-containing vicinal diamines. The procedures can be conducted under convenient conditions, rendering this approach of high synthetic value.

Gold trifluoromethyl complexes

This Perspective reviews the synthesis, structure, reactivity and applications of gold trifluoromethyl complexes. The recently reported reactions of gold(iii) trifluoromethyl complexes with potential application in synthesis are discussed.

Ni-catalyzed asymmetric decarboxylative Mannich reaction for the synthesis of β-trifluoromethyl-β-amino ketones

A Ni-catalyzed asymmetric decarboxylative Mannich reaction between (S_s)-N-t-butylsulfinyl-3,3,3-trifluoro-acetaldimine and β-keto-acids was reported, affording β-trifluoromethyl-β-amino ketones with excellent yields and diastereoselectivities.

Rhodamine F: a novel class of fluorous ponytailed dyes for bioconjugation

Incorporation of fluorous ponytails such as polyfluorinated alkyl residues (CH2)m(CF2)nCF3 leads to a novel class of bright rhodamine-based fluorescence dyes. These dyes combine the excellent photophysical properties of the frequently used rhodamine dyes with the unique features of "light" fluorous molecules. One of those features is the possibility to separate substances utilizing fluorous solid-phase extraction (F-SPE), which is based on the specific intermolecular interaction between fluorous compounds. Thus, molecules, which are labeled with these new dyes, are not only accessible to fluorescence experiments, but can also be easily purified (via so-called FluoroFlash columns) prior to use. The dyes were bound to a cell penetrating peptoid (polycationic oligo(N-substituted) glycine) on solid supports. These conjugates were purified with F-SPE before their photophysical and biological properties were investigated.

Enantioselective synthesis of α,α-difluoro-β-lactams using amino alcohol ligands

A practical and highly enantioselective Reformatsky reaction of ethyl bromodifluoroacetate with imines using a cheap and commercially available amino alcohol ligand is described.

Perfluoroalkanesulfonamide organocatalysts for asymmetric conjugate additions of branched aldehydes to vinyl sulfones

Asymmetric conjugate additions of branched aldehydes to vinyl sulfones promoted by sulfonamide organocatalyst 6 or 7 have been developed, allowing facile synthesis of the corresponding adducts with all-carbon quaternary stereocenters in excellent yields with up to 95% ee.