Expanding the Scope of Hypervalent Iodine Reagents for Perfluoroalkylation: From Trifluoromethyl to Functionalized Perfluoroethyl

A series of new hypervalent iodine reagents based on the 1,3‐dihydro‐3,3‐dimethyl‐1,2‐benziodoxole and 1,2‐benziodoxol‐3‐(1H)‐one scaffolds, which contain a functionalized tetrafluoroethyl group, have been prepared, characterized, and used in synthetic applications. Their corresponding electrophilic fluoroalkylation reactions with various sulfur, oxygen, phosphorus, and carbon‐centered nucleophiles afford products that feature a tetrafluoroethylene unit, which connects two functional moieties. A related λ³‐iodane that contains a fluorophore was shown to react with a cysteine derivative under mild conditions to give a thiol‐tagged product that is stable in the presence of excess thiol. Therefore, these new reagents show a significant potential for applications in chemical biology as tools for fast, irreversible, and selective thiol bioconjugation.     

Base‐Stabilized Phosphinidene Boranes by Silylium‐Ion Abstraction

We report the preparation of N‐heterocyclic carbene (NHC)‐stabilized compounds containing P=B double bonds. The reaction of the highly functionalized phosphinoborane Mes*(SiMe₃)P?B(Cl)Cp* with Lewis bases allows access to base‐stabilized phosphinidene boranes Mes*P=B(L)Cp* (L=4‐dimethylaminopyridine (DMAP), NHC) by Me₃SiCl elimination. The formation of these species is shown to proceed through transient borylphosphide anions generated by Me₃Si abstraction.     

Structure of Amido Pyridinium Betaines: Persistent Intermolecular C−H⋅⋅⋅N Hydrogen Bonding in Solution

A hydrogen bond of the type C?H???X (X=O or N) is known to influence the structure and function of chemical and biological systems in solution. C?H???O hydrogen bonding in solution has been extensively studied, both experimentally and computationally, whereas the equivalent thermodynamic parameters have not been enumerated experimentally for C?H???N hydrogen bonds. This is, in part, due to the lack of systems that exhibit persistent C?H???N hydrogen bonds in solution. Herein, a class of molecule based on a biologically active norharman motif that exhibits unsupported intermolecular C?H???N hydrogen bonds in solution has been described. A pairwise interaction leads to dimerisation to give bond strengths of about 7 kJ mol^?1 per hydrogen bond, which is similar to chemically and biologically relevant C?H???O hydrogen bonding. The experimental data is supported by computational work, which provides additional insight into the hydrogen bonding by consideration of electrostatic and orbital interactions and allowed a comparison between calculated and extrapolated NMR chemical shifts.     

Tunable and Specific Formation of C@NiCoP Peapods with Enhanced HER Activity and Lithium Storage Performance

The superior properties of nanomaterials with a special structure can provide prospects for highly efficient water splitting and lithium storage. Herein, we fabricated a series of peapodlike C@Ni_2?xCo_xP (x≤1) nanocomposites by an anion‐exchange pathway. The experimental results indicated that the HER activity of C@Ni_2?xCo_xP catalyst is strongly related to the Co/Ni ratio, and the C@NiCoP got the highest HER activity with low onset potential of ～45 mV, small Tafel slope of ～43 mV dec^?1, large exchange current density of 0.21 mA cm^?2, and high long‐term durability (60 h) in 0.5 m H₂SO₄ solutions. Equally importantly, as an anode electrode for lithium batteries, this peapodlike C@NiCoP nanocomposite gives excellent charge–discharge properties (e.g., specific capacity of 670 mAh g^?1 at 0.2 A g^?1 after 350 cycles, and a reversible capacity of 405 mAh g^?1 at a high current rate of 10 A g^?1). The outstanding performance of C@NiCoP in HER and LIBs could be attributed to the synergistic effect of the rational design of peapodlike nanostructures and the introduction of Co element.     

Pd‐PEPPSI‐IHeptCl: A General‐Purpose,Highly Reactive Catalyst for the Selective Coupling of Secondary Alkyl Organozincs

Dichloro[1,3‐bis(2,6‐di‐4‐heptylphenyl)imidazol‐2‐ylidene](3‐chloropyridyl)palladium(II) (Pd‐PEPPSI‐IHept^Cl), a new, very bulky yet flexible Pd–N‐heterocyclic carbene (NHC) complex has been evaluated in the cross‐coupling of secondary alkylzinc reactants with a wide variety of oxidative addition partners in high yields and excellent selectivity. The desired, direct reductive elimination branched products were obtained with no sign of migratory insertion across electron‐rich and electron‐poor aromatics and all forms of heteroaromatics (five and six membered). Impressively, there is no impact of substituents at the site of reductive elimination (i.e., ortho or even di‐ortho), which has not yet been demonstrated by another catalyst system to date.     

Toward Fluorescence‐Based High‐Throughput Screening for Enantiomeric Excess in Amines and Amino Acid Derivatives

A highly accurate and reliable screening method for enantiomeric excess of amine derivatives in the presence of water is reported. The fluorescence‐based screening system has been realized by self‐assembly of chiral diol‐type dyes (BINOL, VANOL and VAPOL), 2‐formylphenylboronic acid, and chiral amines forming iminoboronate esters. The structure and chirality of the amine analytes determine the stability of the diastereomeric iminoboronate esters, which in turn display differential fluorescence. The fluorescence signal reflects the enantiomeric purity of the chiral amines and was utilized in high‐throughput arrays. The arrays were able to recognize enantiomeric excess of amines, amino esters, and amino alcohols. In addition to qualitative analysis, quantitative experiments were successfully performed. Studies of the role of additives such as water or citrate were carried out to gain insight into the stability of the iminoboronate esters. It is shown that the above additives destabilize less stable esters while the stable esters remain unchanged. Thus, the presence of water and citrate leads to increased difference between the diastereomeric iminoboronates and contributes to the enantiodiscrimination of the chiral amines.     

Bis‐clickable Mesoporous Silica Nanoparticles: Straightforward Preparation of Light‐Actuated Nanomachines for Controlled Drug Delivery with Active Targeting

Bis(clickable) mesoporous silica nanospheres (ca. 100 nm) were obtained by the co‐condensation of TEOS with variable amounts (2–5 % each) of two clickable organosilanes in the presence of CTAB. Such nanoparticles could be easily functionalized with two independent functions using the copper‐catalyzed alkyne‐azide cycloaddition (CuAAC) reaction to transform them into nanomachines bearing cancer cell targeting ligands with the ability to deliver drugs on‐demand. The active targeting was made possible after anchoring folic acid by CuAAC click reaction, whereas the controlled delivery was performed by clicked azobenzene fragments. Indeed, the azobenzene groups are able to obstruct the pores of the nanoparticles in the dark whereas upon irradiation in the UV or in the blue range, their trans‐to‐cis photoisomerization provokes disorder in the pores, enabling the delivery of the cargo molecules. The on‐command delivery was proven in solution by dye release experiments, and in vitro by doxorubicin delivery. The added value of the folic acid ligand was clearly evidenced by the difference of cell killing induced by doxorubicin‐loaded nanoparticles under blue irradiation, depending on whether the particles featured the clicked folic acid ligand or not.     

Eosin Y (EY) Photoredox‐Catalyzed Sulfonylation of Alkenes: Scope and Mechanism

Alkyl‐ and aryl vinyl sulfones were obtained by eosin Y (EY)‐mediated visible‐light photooxidation of sulfinate salts and the reaction of the resulting S‐centered radicals with alkenes. Optimized reaction conditions, the sulfinate and alkene scope, and X‐ray structural analyses of several reaction products are provided. A detailed spectroscopic study explains the reaction mechanism, which proceeds through the EY radical cation as key intermediate oxidizing the sulfinate salts.     

Stereoselective Ketone Rearrangements with Hypervalent Iodine Reagents

The first stereoselective version of an iodine(III)‐mediated rearrangement of arylketones in the presence of orthoesters is described. The reaction products, α‐arylated esters, are very useful intermediates in the synthesis of bioactive compounds such as ibuprofen. With chiral lactic acid‐based iodine(III) reagents product selectivities of up to 73 % ee have been achieved.