Stereoconservative Negishi arylation and alkynylation as an efficient approach to enantiopure 2,2'-diarylated 1,1'-binaphthyls

Negishi arylation and alkynylation of easily synthesized chiral 2,2'-diodo-1,1'-binaphthyl rapidly proceeds in refluxing THF utilizing controlled microwave irradiation, affording enantiopure 2,2'-diarylated 1,1'-binaphthyls in good to excellent yields.     

A high-throughput platform for low-volume high-temperature/pressure sealed vessel solvent extractions

A high-throughput platform for performing parallel solvent extractions in sealed HPLC/GC vials inside a microwave reactor is described. The system consist of a strongly microwave-absorbing silicon carbide plate with 20 cylindrical wells of appropriate dimensions to be fitted with standard HPLC/GC autosampler vials serving as extraction vessels. Due to the possibility of heating up to four heating platforms simultaneously (80 vials), efficient parallel analytical-scale solvent extractions can be performed using volumes of 0.5-1.5 mL at a maximum temperature/pressure limit of 200°C/20 bar. Since the extraction and subsequent analysis by either gas chromatography or liquid chromatography coupled with mass detection (GC-MS or LC-MS) is performed directly from the autosampler vial, errors caused by sample transfer can be minimized. The platform was evaluated for the extraction and quantification of caffeine from commercial coffee powders assessing different solvent types, extraction temperatures and times. For example, 141±11 μg caffeine (5 mg coffee powder) were extracted during a single extraction cycle using methanol as extraction solvent, whereas only 90±11 were obtained performing the extraction in methylene chloride, applying the same reaction conditions (90°C, 10 min). In multiple extraction experiments a total of ~150 μg caffeine was extracted from 5 mg commercial coffee powder. In addition to the quantitative caffeine determination, a comparative qualitative analysis of the liquid phase coffee extracts and the headspace volatiles was performed, placing special emphasis on headspace analysis using solid-phase microextraction (SPME) techniques. The miniaturized parallel extraction technique introduced herein allows solvent extractions to be performed at significantly expanded temperature/pressure limits and shortened extraction times, using standard HPLC autosampler vials as reaction vessels. Remarkable differences regarding peak pattern and main peaks were observed when low-temperature extraction (60°C) and high-temperature extraction (160°C) are compared prior to headspace-SPME-GC-MS performed in the same HPLC/GC vials.     

Continuous‐Flow Synthesis of CdSe Quantum Dots: A Size‐Tunable and Scalable Approach

In recent years, continuous‐flow/microreactor processing for the preparation of colloidal nanocrystals has received considerable attention. The intrinsic advantages of microfluidic reactors have opened new opportunities for the size‐controlled synthesis of nanocrystals either in the laboratory or on a large scale. Herein, an experimentally simple protocol for the size‐tunable continuous‐flow synthesis of rather monodisperse CdSe quantum dots (QDs) is presented. CdSe QDs are manufactured by using cadmium oleate as cadmium source, selenium dioxide as selenium precursor, and 1‐octadecene as solvent. Exploiting selenium dioxide as selenium source and 1‐octadecene as solvent allows execution of the complete process in open air without any requirement for air‐free manipulations using a glove box or Schlenk line. Continuous‐flow processing is performed with a stainless steel coil of 1.0 mm inner diameter pumping the combined precursor solution through the reactor by applying a standard HPLC pump. The effect of different reaction parameters, such as temperature, residence time, and flow rate, on the properties of the resulting CdSe QDs was investigated. A temperature increase from 240 to 260 °C or an extension of the residence time from 2 to 20 min affords larger nanocrystals (range 3–6 nm) whereas the size distribution does not change significantly. Longer reaction times and higher temperatures result in QDs with lower quantum yields (range 11–28 %). The quality of the synthesized CdSe QDs was confirmed by UV/Vis and photoluminescence spectroscopy, small‐angle X‐ray scattering, and high‐resolution transmission electron microscopy. Finally, the potential of this protocol for large‐scale manufacturing was evaluated and by operating the continuous‐flow process for 87 min it was possible to produce 167 mg of CdSe QDs (with a mean diameter of 4 nm) with a quantum yield of 28 %.     

Shifting Chemical Equilibria in Flow—Efficient Decarbonylation Driven by Annular Flow Regimes

To efficiently drive chemical reactions, it is often necessary to influence an equilibrium by removing one or more components from the reaction space. Such manipulation is straightforward in open systems, for example, by distillation of a volatile product from the reaction mixture. Herein we describe a unique high‐temperature/high‐pressure gas/liquid continuous‐flow process for the rhodium‐catalyzed decarbonylation of aldehydes. The carbon monoxide released during the reaction is carried with a stream of an inert gas through the center of the tubing, whereas the liquid feed travels as an annular film along the wall of the channel. As a consequence, carbon monoxide is effectively vaporized from the liquid phase into the gas phase and stripped from the reaction mixture, thus driving the equilibrium to the product and preventing poisoning of the catalyst. This approach enables the catalytic decarbonylation of a variety of aldehydes with unprecedented efficiency with a standard coil‐based flow device.     

Batch‐ and Continuous‐Flow Aerobic Oxidation of 14‐Hydroxy Opioids to 1,3‐Oxazolidines—A Concise Synthesis of Noroxymorphone

14‐Hydroxymorphinone is converted to noroxymorphone, the immediate precursor of important opioid antagonists, such as naltrexone and naloxone, in a three‐step reaction sequence. The initial oxidation of the N‐methyl group in 14‐hydroxymorphinone with in situ generated colloidal palladium(0) as the catalyst and molecular oxygen as the terminal oxidant constitutes the key transformation in this new route. This oxidation results in the formation of an unexpected oxazolidine ring structure. Subsequent hydrolysis of the oxazolidine under reduced pressure followed by hydrogenation in a packed‐bed flow reactor using palladium(0) as the catalyst provides noroxymorphone in high purity and good overall yield. To overcome challenges associated with gas–liquid reactions with molecular oxygen, the key oxidation reaction was translated to a continuous‐flow process.     

Synthesis and structure elucidation of 3,4‐dihydroxy‐2‐quinolin‐2‐ylpyrido[3,2,1‐jk]carbazol‐6‐ones

3,4‐Dihydroxy‐2‐quinolin‐2‐ylpyrido[3,2,1‐jk]carbazol‐6‐ones 6 were obtained by cyclocondensation of carbazole 1 with malonates 2 in the presence of quinoline. The assignment of the structures of 6 was performed by NMR experiments such as 1D ¹H, ¹³C and DEPT, as well as 2D COSY, HSQC, HMBC and 1,1‐ADEQUATE spectra.     

A generalization of 2-Baer groups

A group in which all cyclic subgroups are 2-subnormal is called a 2-Baer group. The topic of this paper are generalized 2-Baer groups, i.e., groups in which the non-2-subnormal cyclic subgroups generate a proper subgroup of the group. If this subgroup is non-trivial, the group is called a generalized T₂-group. In particular, we provide structure results for such groups, investigate their nilpotency class, and construct examples of finite p-groups which are generalized T₂-groups.