Ligand‐Assisted Palladium(II)/(IV) Oxidation for sp3 C?H Fluorination

The direct functionalization of inert sp³ C H bonds is limited to a few bond types. Although the activation of sp³ C H bonds can be accomplished under mild conditions using palladium catalysts, the subsequent functionalization is not trivial due to the high energy required to convert palladium(II) to palladium(IV). We have systematically studied the palladium oxidation using computation‐guided experiments for reactions involving strong chelation control. We find that a mild external ligand could significantly accelerate the oxidation of palladium(II) to palladium(IV) for strong bidentate directing groups. The acceleration is believed to be a result of ligand stabilization of both the palladium(II) and palladium(IV) intermediates.

     

Copper‐Nitrene Triggered Annulation of α‐Acyl Cinnamides: Access to Isoxazol‐3(2H)‐ones

A facile and efficient one‐pot synthesis of isoxazol‐3(2H)‐ones has been developed starting from α‐acyl cinnamides and tosyliminophenyliodinane catalyzed by copper(II) acetate [Cu(OAc)₂] under very mild conditions involving a tandem aza‐Michael addition and intramolecular cyclization sequence.

     

Design and Synthesis of 2‐Methyl‐7‐aminobenzoxazole as Auxiliary in the Palladium(II)‐Catalyzed Arylation of a beta‐Positioned C(sp3)?H Bond

A palladium(II)‐catalyzed direct arylation of methylene C(sp³) H bonds by 2‐methyl‐7‐aminobenzoxazole as an effective auxiliary is reported. This process exhibited high beta‐site selectivity, broad substrate scope, and compatibility with different functional groups with moderate to high yields up to 89%.

     

Systematics of salt precipitation in complexes of polyethylene oxide and alkali metal iodides

Conductivity measurements in PEO₃₀MI polymer electrolytes with M=Li, Na, K, Rb, or Cs over the temperature range from about 65 to 200 °C show an increasing tendency for salt precipitation with increasing cation size. The salt precipitation in these complexes upon heating is revealed by the decrease of the dc conductivity starting at a critical temperature T_c. Whereas LiI and NaI complexes do not show precipitation effects, T_c monotonically decreases from about 140 to 65 °C when changing the salt component from KI via RbI to CsI. For the PEO-RbI system, precipitation is further investigated by nuclear magnetic resonance (NMR) and tracer diffusion experiments. NMR analysis unambiguously demonstrates the onset of RbI salt precipitation and the increase of the precipitate fraction with increasing temperature. In diffusion experiments on PEO₃₀RbI with the radiotracers and , the precipitation effect is manifested by anomalous features in the penetration profiles, however, without noticeable changes in their depth range. Combining the resulting tracer diffusion coefficients with the dc conductivity data enables us to assess crucial parameters characterizing ionic transport in PEO₃₀RbI.     

Catalytic Use of a Soluble Organoindium(III) Species for Allylation and Crotylation of Ketones with Boronates

The unprecedented use of a soluble organoindium species, indium(III) hexamethyldisilazide [In(III)(hmds)₃], for catalytic carbon carbon bond formations between ketones and boronates, is reported. Various functionalized tertiary homoallyl alcohols were generated easily in high yields. Remarkably, free hydroxy and primary amine functionalities proved to be tolerated. A rate acceleration and markedly improved diastereoselectivities were observed in the presence of methanol. Based on preliminary NMR experiments and the α‐selectivity with an α‐substituted boronate, we assume the in situ generation of reactive allylindium(III) species through catalytic boron‐to‐indium transmetalation.     

An Expeditious Copper‐Catalyzed Access to 3‐Aminoquinolinones, 3‐Aminocoumarins and Anilines using Sodium Azide

An efficient copper‐catalyzed in situ C(sp²) NH₂ bond formation to provide a range of 3‐aminoquinolin‐2(1H)‐ones and 3‐aminocoumarins from 3‐bromoquinolinones and 3‐bromocoumarins, respectively, has been achieved. The reaction conditions involve the use of copper powder as the catalyst, eco‐friendly ethanol as the solvent in the presence of pipecolinic acid as the ligand and ascorbic acid as the additive. The efficiency of this practical method was demonstrated in the synthesis of various anilines.     

Selective Green Coupling of Alkynyltins and Allylic Halides to Trienynes via a Tandem Double Stille Reaction

The palladium‐catalyzed reaction of alkynyltin compounds with allylic chlorides leads to a 2:2 coupling to give trienynes by regio‐ and stereoselective formation of three new C C bonds. The reaction can be applied to different alkynyl and allylic fragments, providing a wide range of trienynes with different substitution patterns in very good yields. They can be prepared in a green way using recyclable polymeric tin alkynyls.     

Continuous‐Flow C?H Borylation of Arene Derivatives

A new continuous‐flow system for C H borylation has been developed. An insoluble catalyst prepared from chloro(1,5‐cyclooctadien)iridium(I) dimer and 2,2′‐bipyridine‐4,4′‐dicarboxylic acid in the presence of bis(pinacolato)diboron exhibited high reactivity under continuous‐flow processing without the loss of expensive iridium metal.     

Polymer Cocktail: A Multitask Supported Ionic Liquid‐Like Species to Facilitate Multiple and Consecutive C?C Coupling Reactions

Polymer‐supported ionic liquid‐like species (SILLPs) with different functionalities have been combined to obtain new catalytic systems (polymer cocktail) with improved properties towards their application for C C coupling reactions. The SILLPs have been synthesized in a simple way and combined to play different functions in the reaction medium. Those roles involve simultaneously (or consecutively) their actuation as supported reagents, precatalysts and scavengers of undesired reaction side‐products. The system has been tested by employing three different C C coupling reactions for 8 consecutive cycles. Moreover, different aryl bromides and iodides have proved to be efficiently transformed by the catalytic cocktail. Finally, the Heck reaction has been conducted in continuous‐flow conditions using a packed bed of this polymer cocktail and employing supercritical carbon dioxide (scCO₂) as a solvent, which cannot be carried out with the use of soluble bases as this would lead to the clogging of the reactor. Finally, the SILLPs cocktail enables one to combine different reaction steps and purification in a single vessel, which represents a significant improvement in terms of process intensification and green chemistry. This is particularly true in the case of the use of scCO₂ as this allows the direct production of crude materials not contaminated either by salts or by solvents.     

Aerobic Oxidative Coupling of o‐Xylene: Discovery of 2‐Fluoropyridine as a Ligand to Support Selective Pd‐Catalyzed C?H Functionalization

An improved method for the direct oxidative coupling of o‐xylene could provide streamlined access to an important monomer used in polyimide resins. The use of 2‐fluoropyridine as a ligand has been found to enable unprecedented levels of chemo‐ and regioselectivity in this palladium‐catalyzed aerobic oxidative coupling reaction. Preliminary insights have been obtained into the origin of the effectiveness of 2‐fluoropyridine as a ligand.