Divergent regioselectivity in photoredox-catalyzed hydrofunctionalization reactions of unsaturated amides and thioamides

A direct method to construct 2-oxazolines and 2-thiazolines from corresponding allylic amides and thioamides is reported

Reversing the Regioselectivity of Halofunctionalization Reactions through Cooperative Photoredox and Copper Catalysis

Halofunctionalization of alkenes is a classical method for olefin difunctionalization. It gives rise to adducts which are found in many natural products and biologically active molecules, and offers a synthetic handle for further manipulation. Classically, this reaction is performed with an electrophilic halogen source and leads to regioselective formation of the halofunctionalized adducts. Herein, we demonstrate a reversal of the native regioselectivity for alkene halofunctionalization through the use of an acridinium photooxidant in conjunction with a copper cocatalyst

Discovery and characterization of an acridine radical photoreductant

Photoinduced electron transfer (PET) is a phenomenon whereby the absorption of light by a chemical species provides an energetic driving force for an electron-transfer reaction1-4. This mechanism is relevant in many areas of chemistry, including the study of natural and artificial photosynthesis, photovoltaics and photosensitive materials. In recent years, research in the area of photoredox catalysis has enabled the use of PET for the catalytic generation of both neutral and charged organic free-radical species. These technologies have enabled previously inaccessible chemical transformations and have been widely used in both academic and industrial settings. Such reactions are often catalysed by visible-light-absorbing organic molecules or transition-metal complexes of ruthenium, iridium, chromium or copper5,6. Although various closed-shell organic molecules have been shown to behave as competent electron-transfer catalysts in photoredox reactions, there are only limited reports of PET reactions involving neutral organic radicals as excited-state donors or acceptors. This is unsurprising because the lifetimes of doublet excited states of neutral organic radicals are typically several orders of magnitude shorter than the singlet lifetimes of known transition-metal photoredox catalysts7-11. Here we document the discovery, characterization and reactivity of a neutral acridine radical with a maximum excited-state oxidation potential of -3.36 volts versus a saturated calomel electrode, which is similarly reducing to elemental lithium, making this radical one of the most potent chemical reductants reported12. Spectroscopic, computational and chemical studies indicate that the formation of a twisted intramolecular charge-transfer species enables the population of higher-energy doublet excited states, leading to the observed potent photoreducing behaviour. We demonstrate that this catalytically generated PET catalyst facilitates several chemical reactions that typically require alkali metal reductants and can be used in other organic transformations that require dissolving metal reductants

IMPACT OF ATHERMIC PROPERTIES OF THE ELECTROMAGNETIC MICROWAVE RADIATION ON THE PROCESS OF ANAEROBIC DIGESTION OF DAIRY WASTEWATER

Celem badań było określenie wpływu elektromagnetycznego promieniowania mikrofalowego na aktywność mikroorganizmów prowadzących proces fermentacji metanowej ścieków mleczarskich. Substratem wykorzystywanym w badaniach były modelowe ścieki mleczarskie, spreparowane na bazie odtłuszczonego mleka w proszku. Osad beztlenowy, na potrzeby przeprowadzenia badań, pobierany był z reaktora beztlenowego pracującego w warunkach mezofilowych, a następnie ogrzewano go za pomocą promieniowania mikrofalowego (wariant 1) lub ogrzewania konwencjonalnego w szafie termostatycznej (wariant 2). Badania podzielone były na dwa etapy, których kryterium podziału była temperatura procesu. Etap pierwszy przewidywał określenie wpływu promieniowania mikrofalowego w temperaturze 38 °C, natomiast etap drugi w temperaturze 58 °C. Wyniki badań wykazują, że wykorzystanie mikrofalowego pola elektromagnetycznego może wpływać na wzrost ilości produkowanego biogazu. Ponadto obróbka osadu, przy pomocy elektromagnetycznego pola mikrofalowego, intensyfikuje usuwanie związków organicznych w procesie fermentacji metanowej.The aim of this study was to determine the effect of electromagnetic microwave radiation on the activity of micro-organisms for the process of anaerobic digestion of dairy sewage. The substrate used in the study was a model dairy wastewater crafted based on skimmed milk powder. The sludge was necessary for the anaerobic testing were taken from the anaerobic reactor operated at mesophilic conditions, then it was heated by microwave irradiation (Option 1) or heating in a conventional thermostatic cabinet (Option 2). The study was divided into two stages, where the criterion of division was the temperature of the process. A first step provided to determine the effect of microwave irradiation at 38 °C, and the second step at 58 °C. The studies show that the use of microwave electromagnetic field may affect an increase of the biogas produced. Furthermore, sludge treatment using electromagnetic microwave field enhances the removal of organic compounds in the methane fermentation process

Self-Consistent Synthesis of the Squalene Synthase Inhibitor Zaragozic Acid C via Controlled Oligomerization

Despite the prevalence of repeating subunits in chiral natural products, stereocontrolled oligomerization is a largely unexplored strategy for construction of carbon skeletal frameworks. This report describes the use of silyl glyoxylates as dipolar glycolic acid synthons in a controlled oligomerization reaction for the efficient construction of the squalene synthase inhibitor zaragozic acid C. This new methodology allows rapid, stereocontrolled formation of the carbon skeleton with a desirable protecting group scheme while minimizing functional group repair and oxidation state manipulations

Silyl Glyoxylates. Conception and Realization of Flexible Conjunctive Reagents for Multicomponent Coupling

This Perspective describes the discovery and development of silyl glyoxylates, a new family of conjunctive reagents for use in multicomponent coupling reactions. The selection of the nucleophilic and electrophilic components determines whether the silyl glyoxylate reagent will function as a synthetic equivalent to the dipolar glycolic acid synthon, the glyoxylate anion synthon, or the α-keto ester homoenolate synthon. The ability to select for any of these reaction modes has translated to excellent structural diversity in the derived three- and four-component coupling adducts. Preliminary findings on the development of catalytic reactions using these reagents are detailed, as are the design and discovery of new reactions directed toward particular functional group arrays embedded within bioactive natural products