Recent Advances in Microwave-Assisted Copper-Catalyzed Cross-Coupling Reactions

Cross-coupling reactions furnishing carbon–carbon (C–C) and carbon–heteroatom (C–X) bond is one of the most challenging tasks in organic syntheses. The early developed reaction protocols by Ullmann, Ullman–Goldberg, Cadiot–Chodkiewicz, Castro–Stephens, and Corey–House, utilizing elemental copper or its salts as catalyst have, for decades, attracted and inspired scientists. However, these reactions were suffering from the range of functional groups tolerated as well as severely restricted by the harsh reaction conditions often required high temperatures (150–200 °C) for extended reaction time. Enormous efforts have been paid to develop and achieve more sustainable reaction conditions by applying the microwave irradiation. The use of controlled microwave heating dramatically reduces the time required and therefore resulting in increase in the yield as well as the efficiency of the reaction. This review is mainly focuses on the recent advances and applications of copper catalyzed cross-coupling generation of carbon–carbon and carbon–heteroatom bond under microwave technology.

Ultrasound-assisted Strecker synthesis of novel 2-(hetero)aryl-2-(arylamino)acetonitrile derivatives

This work describes an efficient, simple, and ecofriendly sonochemical procedure for the preparation of new α-(arylamino)acetonitrile derivatives C-substituted with phenothiazine or ferrocene units. The synthetic protocol is based on the Strecker reaction of a (hetero)aryl aldimine substrate with trimethylsilyl cyanide (TMSCN) in poly(ethylene glycol) (PEG) solution. The advantages of the sonochemical versus the conventional α-(arylamino)acetonitrile synthesis are the significantly shorter reaction time (30 min instead of 72 hours), the higher purity and the easier separation of the product that precipitated from the reaction mixture in crystalline form as depicted by scanning electron microscopy (SEM) analysis. The single crystal X-ray diffraction analysis disclosed the arrangement of the α-(arylamino)acetonitrile molecules in the aggregated crystalline state as a racemic mixture. The mutagenic/antimutagenic potential for three representative derivatives containing phenothiazinyl, ferrocenyl, and phenyl units, respectively, was evaluated by the Ames Salmonella/microsome test using S. typhimurium TA98 and TA100 strains with and without metabolic activation. The preliminary screening results pointed out that the C-(hetero)aryl-α-(arylamino)acetonitrile derivatives can be considered genotoxically safe and possibly antimutagenic.

On the Apparent Redox Reactivity of "Oxygen-Enriched Water"

Molecular oxygen-enriched water (OxEW) is advocated in popular media as useful for various health issues, presumably due to involvement of a purported antioxidant activity and to such notions as "active oxygen." To our knowledge, there are no explicit reports in the scientific literature where such redox reactivity would be described and explained. Reported here are data showing that a commercial preparation of OxEW does display a measurable, albeit very small, antioxidant activity as monitored by reaction with a standard reagent, DPPH. Moreover, OxEW also displays an apparent pro-oxidant reactivity, against caffeic acid. This does not correlate with any UV-vis-detectable contents of chemical substances in the water, nor can it be explained by typical chemical impurities (e.g., hydrogen peroxide or molecular hydrogen) that would arise upon enrichment with molecular oxygen of pure water by the two most common procedures: purging with gaseous O₂ or electrolysis. Instead, this apparent redox reactivity is revealed to be due to differences in pH and in chemical content - and the differences in turn are most likely due to the trace amounts of inorganic ions/elements in the OxEW; importantly, electrolysis, which is often employed as a means to generate O₂ in OxEW preparation, is also found to enhance the redox effect of OxEW-like preparations. Thus, in line with expectations, the herein-reported data show that there are no long-lived reactive oxygen species, no activated oxygen, and no extra reducing agents in OxEW - but that an apparent weak redox reactivity can still be measured and assigned to simple side effects of the electrolysis procedure presumably performed in order to enrich the sample in oxygen.

Novel Thiazolo[5,4-b]phenothiazine Derivatives: Synthesis, Structural Characterization, and In Vitro Evaluation of Antiproliferative Activity against Human Leukaemia

The molecular frame of the reported series of new polyheterocyclic compounds was intended to combine the potent phenothiazine and benzothiazole pharmacophoric units. The synthetic strategy applied was based on oxidative cyclization of N-(phenothiazin-3-yl)-thioamides and it was validated by the preparation of new 2-alkyl- and 2-aryl-thiazolo[5,4-b]phenothiazine derivatives. Optical properties of the series were experimentally emphasized by UV-Vis absorption/emission spectroscopy and structural features were theoretically modelled using density functional theory (DFT). In vitro activity as antileukemic agents of thiazolo[5,4-b]phenothiazine and N-(phenothiazine-3-yl)-thioamides were comparatively evaluated using cultivated HL-60 human promyelocytic and THP-1 human monocytic leukaemia cell lines. Some representatives proved selectivity against tumour cell lines, cytotoxicity, apoptosis induction, and cellular metabolism impairment capacity. 2-Naphthyl-thiazolo[5,4-b]phenothiazine was identified as the most effective of the series by displaying against THP-1 cell lines a cytotoxicity close to cytarabine antineoplastic agent.

Accessing N-Stereogenicity through a Double Aza-Michael Reaction: Mechanistic Insights

Further development of the chemistry and applications of chiral compounds that possess configurationally stable stereogenic nitrogen atoms is hampered by the lack of efficient strategies to access such compounds in an enantiomerically pure form. Esters of propiolic acid and chiral alcohols were evaluated as cheap and readily available Michael acceptors in a diastereoselective synthesis of N-stereogenic compounds by means of a double aza-Michael conjugate addition. Diastereomeric ratios of up to 74:26 and high yields were achieved with (-)-menthyl propiolate as a substrate. Furthermore, a detailed mechanistic investigation was undertaken to shed some light on the course of this domino transformation. Kinetic studies revealed that the protic-solvent additive acts as a Brønsted acid and activates the ester toward the initial attack of the tetrahydrodiazocine partner. Conversely, acidic conditions proved unfavorable during the final cyclization step that provides the product.

Tuning the coordination properties of phenothiazine by regioselective introduction of diphenylphosphanyl groups

New phenothiazinyl-phosphines and their palladium and platinum complexes have been synthesized and characterized and their biological properties have been discussed.