The Liebeskind–Srogl C?C Cross‐Coupling Reaction

New kid on the block : The cross‐coupling of thioorganic compounds with boronic acids under neutral conditions in the presence of catalytic palladium(0) and a stoichiometric amount of a copper(I) oxygenate has emerged as a very useful method for the construction of C C bonds (see scheme). This intriguing and mechanistically unprecedented base‐free coupling has distinct advantages, in particular when traditional Pd⁰‐catalyzed cross‐coupling is not possible.

     

Microwave-assisted high-throughput derivatization techniques utilizing silicon carbide microtiter platforms

Parallel microwave-assisted gas chromatography (GC) derivatization protocols utilizing a silicon carbide (SiC)-based microtiter plate platform fitted with screw-capped GC vials were developed. For three selected standard derivatization protocols such as acetylation (exemplified for morphine), pentafluoropropionylation (for 6-monoacetylmorphine) and trimethylsilylation (for Δ⁹-tetrahydrocannabinol) complete derivatization was achieved within 5 min at 100 °C in a dedicated multimode microwave instrument using online temperature monitoring. Microwave irradiation leads to rapid and homogeneous heating of the strongly microwave-absorbing SiC plate, with minimal deviations in the temperature recorded at different positions of the plate. The current platform allows the simultaneous derivatization of 80 reaction mixtures under strictly controlled temperature conditions. Similar results can also be obtained using a standard hotplate as heating source, although heating to the target temperature of 100 °C is slightly slower. The results demonstrate that parallel microwave derivatization procedures can significantly reduce the overall analysis time and increase sample throughput for GC–MS-based analytical methods.     

A unified mechanistic view on the Morita-Baylis-Hillman reaction: computational and experimental investigations

The thermodynamic properties and reaction mechanism of the Morita-Baylis-Hillman (MBH) reaction have been investigated through experimental and computational techniques. The impossibility to accelerate this synthetically valuable transformation by increasing the reaction temperature has been rationalized by variable-temperature experiments and MP2 theoretical calculations of the reaction thermodynamics. An increase in temperature results in a switching of the equilibrium to the reactants occurring at even moderate temperature levels. The complex reaction mechanism for the MBH reaction has been investigated through an in-depth analysis of the suggested alternative pathways, using the M06-2X computational method. The results provided by this theoretical approach are in agreement with all the experimental/kinetic evidence such as reaction order, acceleration by protic species (methanol, phenol), and autocatalysis. In particular, the existing controversy about the character of the key proton transfer in the MBH reaction (Aggarwal versus McQuade pathways) has been resolved. Depending on the specific reaction conditions both suggested pathways are competing mechanisms, and depending on the amount of protic species and the reaction progress (early or late stage) either of the two mechanisms will be favored.     

Direct arylation of benzene with aryl bromides using high-temperature/high-pressure process windows: expanding the scope of C-H activation chemistry

A detailed investigation on the direct arylation of benzene with aryl bromides by using first-row transition metals under high-temperature/high-pressure (high-T/p) conditions is described. By employing a parallel reactor platform for rapid reaction screening and discovery at elevated temperatures, various metal/ligand/base combinations were evaluated for their ability to enable biaryl formation through C-H activation. The combination of cobalt(III) acetylacetonate and lithium bis(trimethylsilyl)amide was subjected to further process intensification at 200?°C (15?bar), allowing a significant reduction of the catalyst/base loading and a dramatic increase in catalytic efficiency (turnover frequency) by a factor of 1000 compared to traditional protocols. The high-throughput screening additionally identified novel nickel- and copper-based metal/ligand combinations that favored an amination pathway competing with C-H activation, with the addition of ligands, such as 1,10-phenanthroline, having a profound influence on the selectivity. In addition to metal-based catalysts, high-T/p process windows were also successfully applied to transition-metal-free systems, utilizing 1,10-phenanthroline as organocatalyst.     

Continuous‐Flow Synthesis of ZIF‐8 Biocomposites with Tunable Particle Size

Zeolitic imidazolate framework (ZIF) biocomposites show the capacity to protect and deliver biotherapeutics. To date, the progress in this research area is based on laboratory batch methods. Now, the first continuous flow synthetic method is presented for the encapsulation of a model protein (bovine serum albumin, BSA) and a clinical therapeutic (α1‐antitrypsin, AAT) in ZIF‐8. The in situ kinetics of nucleation, growth, and crystallization of BSA@ZIF‐8 were studied by small‐angle X‐ray scattering. By controlling the injection time of ethanol, the particle growth could be quenched by ethanol‐induced crystallization from amorphous particles to ZIF‐8 crystals. The particle size of the biocomposite was tuned in the 40–100 nm range by varying residence time prior to introduction of ethanol. As a proof‐of‐concept, this procedure was used for the encapsulation of AAT in ZIF‐8. Upon release of the biotherapeutic from the composite, the trypsin inhibitor function of AAT was preserved.     

Finite groups with trivial Frattini subgroup

All groups considered are finite. A group has a trivial Frattini subgroup if and only if every nontrivial normal subgroup has a proper supplement.The property is normal subgroup closed, but neither subgroup nor quotient closed. It is subgroup closed if and only if the group is elementary, i.e. all Sylow subgroups are elementary abelian. If G is solvable, then G and all its quotients have trivial Frattini subgroup if and only if every normal subgroup of G has a complement. For a nilpotent group, every nontrivial normal subgroup has a supplement if and only if the group is elementary abelian. Consequently, the center of a group in which every normal subgroup has a supplement is an elementary abelian direct factor.     

Microwave-assisted synthesis of colloidal inorganic nanocrystals

Colloidal inorganic nanocrystals stand out as an important class of advanced nanomaterials owing to the flexibility with which their physical-chemical properties can be controlled through size, shape, and compositional engineering in the synthesis stage and the versatility with which they can be implemented into technological applications in fields as diverse as optoelectronics, energy conversion/production, catalysis, and biomedicine. The use of microwave irradiation as a non-classical energy source has become increasingly popular in the preparation of nanocrystals (which generally involves complex and time-consuming processing of molecular precursors in the presence of solvents, ligands and/or surfactants at elevated temperatures). Similar to its now widespread use in organic chemistry, the efficiency of "microwave flash heating" in dramatically reducing overall processing times is one of the main advantages associated with this technique. This Review illustrates microwave-assisted methods that have been developed to synthesize colloidal inorganic nanocrystals and critically evaluates the specific roles that microwave irradiation may play in the formation of these nanomaterials.     

Microwave-assisted nickel(II) acetylacetonate-catalyzed arylation of aldehydes with arylboronic acids

Applying sealed vessel microwave heating at 180 °C in toluene the arylation of aromatic and aliphatic aldehydes with arylboronic acids using 1-2 mol % of Ni(acac)₂ as a catalyst can be performed efficiently within 10-30 min providing the desired diarylmethanols or benzyl alcohols in good yields.