Direct Light-Enabled Access to α-Boryl Radicals: Application in the Stereodivergent Synthesis of Allyl Boronic Esters**

Operationally simple strategies to assemble boron containing organic frameworks are highly enabling in organic synthesis. While conventional retrosynthetic logic has engendered many platforms focusing on the direct formation of C−B bonds, α-boryl radicals have recently reemerged as versatile open-shell alternatives to access organoborons via adjacent C−C bond formation. Direct light-enabled α-activation is currently contingent on photo- or transition metal-catalysis activation to efficiently generate radical species. Here, we disclose a facile activation of α-halo boronic esters using only visible light and a simple Lewis base to enable homolytic scission. Intermolecular addition to styrenes facilitates the rapid construction of highly versatile E-allylic boronic esters. The simplicity of activation permits the strategic merger of this construct with selective energy transfer catalysis to enable the complimentary stereodivergent synthesis of Z-allylic boronic esters.     

Adaptation of the Barton Reaction to Carborane Chemistry: The Synthesis and Reactivity of 2-Hydroxyimino-1-hydroxymethylnona-B-methyl-1,12-dicarba-closo-dodecaborane(12)

Just one of the ten methyl groups of deca-B-methyl-1,12-dicarba-closo-dodecarborane(12) ( 1 ) is selectively functionalized in a reaction sequence in which photolysis of a nitrite of 1 is the key step. Reduction of the resulting aldoxime with LiAlH₄ generates, by way of the first Beckmann rearrangement of a boron-substituted oxime, the methylamino alcohol 2 .     

Versatile Visible-Light-Driven Synthesis of Asymmetrical Phosphines and Phosphonium Salts

Asymmetrically substituted tertiary phosphines and quaternary phosphonium salts are used extensively in applications throughout industry and academia. Despite their significance, classical methods to synthesize such compounds often demand either harsh reaction conditions, prefunctionalization of starting materials, highly sensitive organometallic reagents, or expensive transition-metal catalysts. Mild, practical methods thus remain elusive, despite being of great current interest. Herein, we describe a visible-light-driven method to form these products from secondary and primary phosphines. Using an inexpensive organic photocatalyst and blue-light irradiation, arylphosphines can be both alkylated and arylated using commercially available organohalides. In addition, the same organocatalyst can be used to transform white phosphorus (P₄) directly into symmetrical aryl phosphines and phosphonium salts in a single reaction step, which has previously only been possible using precious metal catalysis.     

含有1,2-二硫(硒、碲)碳硼烷的16和18电子体系CptRh化合物的合成及表征

有机半夹心结构过渡金属配位化学的研究是现代化学研究中十分活跃的一个领域[1,2].用一个6电子有机环戊二烯配体屏蔽过渡金属原子的一边,形成半夹心结构,而另一边与硫族元素配体结合形成各种结构的有机金属化合物[3～5].碳硼烷(H2C2B10H10)是由12个簇顶原子组成的球型化合物,其中2个碳原子上的氢具有一定的酸性,可与BuLi作用,形成Li2C2B10H10.元素硫(硒、碲)可定量地插入到Li-C键中,形成Li2E2C2B10H10(E=S,Se,Te,如图1).     

Remarkably Efficient and Direct Route to Quinolines and Benzoazepines from the Condensation of Benzoxazinediones with Phosphonium Carbanion Salts

Treatment of 2H‐3,1‐benzoxazine‐2,4(1H)‐dione (1a) with vinyltriphenylphosphonium bromide (2a) gives substituted benzoazepine 8a (48% yield) and indolizinone 12 (27% yield), whereas substituted quinolinone 15 and benzoazepine 8b were isolated from the reaction of N‐methylisatoic anhydride (1b) and 2a. Furthermore, a series of quinoline derivatives was synthesized from the reactions of 1a and 1b with allyl‐(2b), alkyl‐(2c), (2d), and cyanomethyl‐(3) triphenylphosphonium salts.     

Synthesis and Chemical Constitution of Diphenoxyphosphoryl Derivatives and Phosphonium Salts as Coupling Reagents for Peptide Segment Condensation

The reactions of diphenoxyphosphoryl chloride ((PhO) 2 P(O)Cl) and different chlorophosphonium salts ([R 3 PCl]X, R = (CH 3 ) 2 N, pyrrolidine, X = PF 6 m , BF 4 m ), respectively, with 7-aza-1-hydroxybenzotriazole (HOAt), 1-hydroxybenzotriazole (HOBt), hydroximinomalonitrile (HOxDCO), and ethyl hydroximinocyanoacetate (HOxO) are described. The structures of the new compounds, which are useful coupling reagents for epimerization-free peptide segment condensation, are discussed on the basis of their 1 H, 13 C, 31 P NMR, and IR spectra. The reactions of (PhO) 2 P(O)Cl lead to mixtures of O - and N -phosphorylated isomers of varying ratios. Contrary, reactions of chlorophosphonium salts yield exclusively one isomer.     

Pentafluorocyclopropanation of (Hetero)arenes Using Sulfonium Salts: Applications in Late-Stage Functionalization

The evaluation of the pentafluorocyclopropyl group as a chemotype in crop protection and medicinal chemistry has been hampered in the past by the lack of suitable methodologies that enable the practical incorporation of this moiety into advanced synthetic intermediates. Herein, we report the gram-scale synthesis of an unprecedented sulfonium salt, 5-(pentafluorocyclopropyl)dibenzothiophenium triflate, and its use as a versatile reagent for the photoinduced C−H pentafluorocyclopropylation of a broad series of non-previously functionalized (hetero)arenes through a radical mediated mechanism. The scope and potential benefits of the protocol developed are further demonstrated by the late-stage introduction of the pentafluorocyclopropyl unit into biologically relevant molecules and widely used pharmaceuticals.     

Four‐Component Synthesis of Phosphonium Salts: Application Toward an Alternative Approach to Cross‐Coupling for the Synthesis of Bis‐Heteroarenes

A series of stable phosphonium salts have been synthesized via a novel four‐component reaction of an arene nucleophile, 2‐heteroatom substituted aryl aldehyde, and phosphine in presence of an acid. The phosphonium salts thus obtained were utilized for the synthesis of a variety of bis‐heteroarenes, providing an efficient alternative method to the classical cross‐coupling strategies.     

From Salts to Ionic Liquids by Systematic Structural Modifications: A Rational Approach Towards the Efficient Modular Synthesis of Enantiopure Imidazolium Salts

This paper reports a simple and robust modular synthetic strategy that leads to a large variety of configurationally and structurally diverse imidazole‐based chiral ionic liquids (CILs) by lipase‐catalyzed resolution. The intimate microscopic interactions of the supramolecular ionic network of these imidazolium chiral salts at the molecular level are investigated both spectroscopically (NMR, FT‐IR‐ATR) and theoretically, and a topological analysis of the experimental electron densities obtained by X‐ray dif fr action of single crystals is performed. Our results support the key role played by the relative configuration of the ‐OR group on the hydrogen‐bonding pattern and its strong influence on the final physical properties of the imidazolium salt. We also obtained a reasonable correlation between the observed melting point and the non‐covalent interactions. The spectroscopic data and the topological analysis reflect the key role played by hydrogen bonds between the OH and imidazolium C2H groups in both cation–anion and cation–cation interactions, with the presence of an OH group leading to an additional inter‐cation interaction. This interaction significantly affects the properties of stereoisomeric salts. Even more interestingly, we also studied the effect of the chirality by comparing enantiopure CILs with their racemic mixtures and found that, with the exception of trans‐Cy6‐OH‐Im‐Bn‐Br, the melting points of the racemic mixtures are higher than those of the corresponding enantiomerically pure forms. For stereoisomeric examples, we have successfully explained the differences in melting temperatures in light of the corresponding structural data. Chirality should therefore be taken into account as a highly attractive design vector in the preparation of ILs with specifically desired properties.     

Keteniminium Salts as Key Intermediates for the Efficient Synthesis of 3-Amino-Indoles and -Benzofurans

Herein, we describe a high yielding approach towards the synthesis of 3-amino-indoles and -benzofurans through 6π-electrocyclization. This was made possible by taking advantage of the high reactivity of keteniminium salts, formed in-situ by treating with triflic anhydride and 2-fluoropyridine amides bearing at the α-position either an aniline or a phenoxy moiety. These mild conditions, on top of furnishing rapidly the 3-aminobenzoheteroles, allow the tolerance of various functional groups. Control experiments were carried out to highlight that the keteniminium is, indeed, in most cases, the reactive intermediate and conformational preferences of such species were investigated through a DFT study.     

Copper(I) Photocatalyzed Bromonitroalkylation of Olefins: Evidence for Highly Efficient Inner-Sphere Pathways

We report the visible light-mediated copper-catalyzed vicinal difunctionalization of olefins utilizing bromonitroalkanes as ATRA reagents. This protocol is characterized by high yields and fast reaction times under environmentally benign reaction conditions with exceptional scope, allowing the rapid functionalization of both activated and unactivated olefins. Moreover, late-stage functionnalization of biologically active molecules and upscaling to gram quantities is demonstrated, which offers manifold possibilities for further transformations, e.g. access to nitro- and aminocyclopropanes. Besides the synthetic utility of the title transformation, this study undergirds the exclusive role of copper in photoredox catalysis showing its ability to stabilize and interact with radical intermediates in its coordination sphere. EPR studies suggest that such interactions can even outperform a highly favorable cyclization of transient to persistent radicals contrasting iridium-based photocatalysts.     

High Cytotoxic Activity of Phosphonium Salts and Their Complementary Selectivity towards HeLa and K562 Cancer Cells: Identification of Tri-n-butyl-n-hexadecylphosphonium bromide as a Highly Potent Anti-HeLa Phosphonium Salt

Quaternary ammonium and phosphonium salts have been screened for their toxic effect on HeLa and K562 cancer cell lines, as well as on normal HUVEC cells. Tri-n-butyl-n-hexadecylphosphonium bromide, the first phosphonium salt with a halogen anion tested against HeLa cells, was 12 times more potent (IC₅₀ <5 μm after 24 and 48 h) than the clinically used reference compound cisplatin and 17 times more potent than tri-n-hexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide, which, to the best of our knowledge, is the first phosphonium salt to be evaluated in HeLa cells. However, it was inactive against K562 cells (24 and 48 h). According to a caspase-3/7 assay, its toxicity has not been connected with the induction of apoptosis. In contrast, triphenylalkylphosphonium iodides with shorter C_1–5 alkyl chains were inactive against HeLa cells but very active against K562 cells (IC₅₀=6–10 μm after 48 h). Phosphonium cations with halide counterions proved to be more potent than those with (CF₃SO₂)₂N⁻ as the anion, as in the anticancer agent NSC 747251, or other anions in molecules with similar alkyl chain lengths. On the other hand, a series of ammonium salts containing a short methylthiomethyl or methoxymethyl side chain revealed low cytotoxicity (IC₅₀ >500 μm after 24 and 48 h) against both HeLa and K562 cancer cell lines as well as normal HUVEC cells, showing that the nontoxic N⁺CH₂YMe (Y=S, O) structural motif in ammonium salts could be suitable for further optimization and development, especially in transfection experiments.     

Phosphonium Salts as Pseudohalides: Regioselective Nickel‐Catalyzed Cross‐Coupling of Complex Pyridines and Diazines

Heterobiaryls are important pharmacophores that are challenging to prepare by traditional cross‐coupling methods. An alternative approach is presented where pyridines and diazines are converted into heteroaryl phosphonium salts and coupled with aryl boronic acids. Nickel catalysts are unique for selective heteroaryl transfer, and the reaction has a broad substrate scope that includes complex pharmaceuticals. Phosphonium ions also display orthogonal reactivity in cross‐couplings compared to halides, enabling chemoselective palladium‐ and nickel‐catalyzed coupling sequences.     

Efficient One-Pot Synthesis of Substituted Pyrido[2,3-d]pyrimidines from Vinamidinium and Chloropropeniminium Salts

A novel and efficient one-pot preparation of 6-substituted pyrido-[2,3-d]pyrimidines by cyclocondensation of 6-amino-1,3-dimethyluracil with symmetrical vinamidinium salts under basic conditions has been developed. Regioselectivity was observed with an unsymmetrical chloropropeniminium salt.     

Molecular Engineering of Corrole Radicals by Polycyclic Aromatic Fusion: Towards Open-Shell Near-Infrared Materials for Efficient Photothermal Therapy

Open-shell radicals are promising near-infrared (NIR) photothermal agents (PTAs) owing to their easily accessible narrow band gaps, but their stabilization and functionalization remain challenging. Herein, highly stable π-extended nickel corrole radicals with [4n+1] π systems are synthesized and used to prepare NIR-absorbing PTAs for efficient phototheranostics. The light-harvesting ability of corrole radicals gradually improves as the number of fused benzene rings on β-pyrrolic locations increases radially, with naphthalene- and anthracene-fused radicals and their one-electron oxidized [4n] π cations exhibiting panchromatic visible-to-NIR absorption. The extremely low doublet excited states of corrole radicals promote heat generation via nonradiative decay. By encapsulating naphthocorrole radicals with amphiphilic polymer, water-soluble nanoparticles Na-NPs are produced, which exhibit outstanding photostability and high photothermal conversion efficiency of 71.8 %. In vivo anti-tumor therapy results indicate that Na-NPs enable photoacoustic imaging of tumors and act as biocompatible PTAs for tumor ablation when triggered by 808 nm laser light. The “aromatic-ring fusion” strategy for energy-gap tuning of corrole radicals opens a new platform for developing robust NIR-absorbing photothermal materials.     

Phosphonium Salts as Chiral Phase‐Transfer Catalysts: Asymmetric Michael and Mannich Reactions of 3‐Aryloxindoles

It′s a PTC : A highly efficient reaction of 3‐aryloxindoles in an asymmetric Michael addition was achieved by using a quaternary tetraalkylphosphonium salt as a chiral phase‐transfer catalyst (PTC). The products were obtained in quantitative yields high ee values. The reaction of 3‐aryloxindoles in an asymmetric Mannich reaction using the same catalyst also proved to be feasible.

     

Phosphonium Salts of 1,8‐Bis(diphenylphosphino)naphthalene: Molecular Structures and NMR‐spectroscopic Studies

A representative series of diphosphine monophosphonium salts [1‐Ph₂P(C₁₀H₆)‐8‐PRPh₂]⁺X^– ( 2 b : R = H, X = CF₃SO₃; 4 : R = Me, X = CF₃SO₃; 5 : R = C₆H₅CH₂ = Bn, X = Br) has been prepared by treatment of 1,8‐bis(diphenylphosphino)naphthalene (dppn, 1 ) with stoichiometric amounts of HSO₃CF₃ or CH₃SO₃CF₃ in CH₂Cl₂ at +20 °C and with C₆H₅CH₂Br in toluene at +80 °C. Their X‐ray crystal structures show that there is no evidence for dative P → P⁺ interactions. Instead, steric repulsion deflects the substituent groups to opposite faces of the naphthalene plane [splay angles: +11.4° ( 2 b ), +13.6° ( 4 ); +16.7° ( 5 )]. In solution 2 b , 4 , and 5 were dynamic according to ³¹P, ¹³C, and ¹H NMR spectroscopy. The fluxionality of 2 b involves rapid intramolecular proton exchange between the two phosphorus atoms, which slows down at low temperature, whereas the dynamic behaviour of 4 and 5 is interpreted in terms of hindered rotation of the bulky RPh₂P⁺ groups (R = Me or Bn) about the P–C(naphthyl) bond. Treatment of 1,8‐bis(diphenylphosphoryl)naphthalene (dppnO₂, 6 ) with HSO₃CF₃ gave the protonated bis(phosphine oxide), as the triflate salt, dppnO₂H⁺ CF₃SO₃^– ( 7 ). The X‐ray structure analysis of 7 revealed a highly strained molecule (P1…P2 365.5 pm) in which the P=O bonds point to the same face of the naphthalene plane to accommodate the proton. All isolated compounds were characterised by a combination of ³¹P, ¹H, and ¹³C NMR spectroscopy, IR spectroscopy ( 7 ), mass spectrometry and elemental analysis.     

Aryldiazonium Salts as Nitrogen‐Based Lewis Acids: Facile Synthesis of Tuneable Azophosphonium Salts

Inspired by the commercially available azoimidazolium dyes (e.g., Basic Red 51) that can be obtained from aryldiazonium salts and N‐heterocyclic carbenes, we developed the synthesis of a unique set of arylazophosphonium salts. A range of colours were obtained by applying readily tuneable phosphine donor ligands and para‐substituted aryldiazonium salts as nitrogen‐based Lewis acids. With cyclic voltammetry, a general procedure was designed to establish whether the reaction between a Lewis acid and a Lewis base occurs by single‐electron transfer or electron‐pair transfer.     

Efficient Synthesis and Properties of Single‐Crystalline [SnTe4]4− Salts

Single‐crystalline K⁺, Rb⁺, and Cs⁺ salts of the ortho‐tellurostannate anion have been prepared by a very efficient fusing/extraction/evaporation method. The resulting compounds with the general composition [A₄(H₂O)_n][SnTe₄] can be transferred into mixed H₂O/en solvates by solving the hydrates in 1,2‐diaminoethane (en) and ensuing layering by toluene. A mixed Rb⁺/Ba²⁺ salt results from a partial cation exchange of the Rb⁺ hydrate phase in solution. All hydrates react to polytellurides when exposed to air and represent useful starting materials for the synthesis of transition metal complexes with [SnTe₄]^4? groups as binary main group elemental ligands. [K₄(H₂O)_0.5][SnTe₄] ( 1 ), [Rb₄(H₂O)₂][SnTe₄] ( 2 ), [Cs₄(H₂O)₂][SnTe₄] ( 3 ), [K₄(H₂O)(en)][SnTe₄] ( 4 ), [Rb₄(H₂O)_0.67(en)_0.33][SnTe₄] ( 5 ), [Cs₄(H₂O)_0.5(en)_0.5][SnTe₄] ( 6 ), and [Rb₂Ba(H₂O)₁₁][SnTe₄] ( 7 ) were characterized by means of X‐ray diffractometry and optical absorption spectroscopy.