Switchable radical carbonylation by polarity-regulation

Carbonylation reactions involving CO as readily available C1 synthons have become one of the most important tools for construction of carbonyl compounds from feedstock chemicals in modern chemical synthesis. Whereas numerous catalytic methods for carbonylation reactions proceeding via ionic or radical pathways have been reported, an inherent limitation to these methods is the need to control switchable single and double carbonylative formation of value-added products from the same and simple starting materials. Here we describe a new strategy that exploits simple visible-light-driven photoredox catalysis to regulate the polarity of coupling partners to drive switchable radical carbonylation reactions. Controlled trap of various alkyl radicals by single or double CO thereby proceed smoothly with excellent selectivity in the presence of various amine nucleophiles at room temperature, generating valuable amides and α-ketoamides in a versatile and controlled fashion. Combined experimental and DFT computational studies suggest that trap of the initially formed acyl radical by the second molecule of CO to form α-ketoacyl radical is a facile but reversible process; and photoredox-catalyzed SET oxidation of natural nucleophilic amines into relatively electrophilic nitrogen radical cations is responsible for switchable coupling with such two radical intermediates.

Nitrogen radical-triggered trifunctionalizing ipso-spirocyclization of unactivated alkenes with vinyl azides towards new spiroaminal frameworks

Radical-mediated spirocyclization is a powerful and efficient tool to forge complex spirocyclic frameworks. Radical-mediated non-dearomative double-cyclization of linear precursors for the concomitant construction of both rings is more challenging but highly attractive. Herein, we report the first example of non-dearomative trifunctionalizing ipso-spirocyclization of unactivated alkenes through photoredox-catalyzed, nitrogen radical-triggered cyclization-trapping-translocation-cyclization cascade, providing a single-step modular access to architecturally new and fascinating spiroaminal frameworks through simultaneous formation of one C−C bond and two geminal C−N bonds. The developed protocol utilizes not only internal or terminal olefinic oxime esters but also olefinic amides as nitrogen radical precursors, and features broad substrate scope, varied functional group compatibility, easy scalability, and potential for product derivatization and late-stage functionalization of biologically active molecule. Importantly, the mechanistic studies including DFT calculations indicate that such photocatalytic trifunctionalizing ipso-spirocyclization undergoes a radical relay cascade of intramolecular 5-exo-trig cyclization, intermolecular radical trapping, 1,5-hydrogen atom transfer, and sequential 5-endo-trig cyclization, which would open up a new reaction mode of alkenes.

Detoxification of Cyanide Wastewater by Cyanotrophic Organisms: the case of Phanerochaete chrysosporium

Cyanide, a carbon-nitrogen radical, is a major building block in many industries including pharmaceuticals, petrochemical and gold processing. In the gold extraction industry, cyanide has been the universal lixiviant for over a century due to better understood process chemistry, among others. Industries that discharge cyanide-laden effluents are mandated to keep concentrations below 0.2 mg/L to prevent death by cyanide-intoxification, which occurs when cyanide binds to key iron-containing enzymes and prevent them from supplying oxygen-containing blood to the tissues. Techniques used to attenuate cyanide in wastewater can broadly be grouped into chemical, physical and biological methods. In recent times, attention has been placed on biotechnological methods, which make use of cyanotrophic microorganisms to clean up cyanide-contaminated environments. This paper reports on studies set out to assess the ability of Phanerochaete chrysosporium to degrade cyanide under different conditions including changes in cyanide concentration, culture mass, time, closed system and open system. At the end of 24-hour contact in an open agitated system with initial pH of 11.5, a control experiment using 100 mg/L cyanide revealed a natural attenuation of 15% with pH decreasing to 9.88, while the best myco-detoxification of 85% was achieved by contacting 100 mg/L cyanide with 0.5 g culture mass, translating into degradation capacity of 17.2 mg/g (milligram of cyanide per gram of culture) with pH reducing to 8.4 in 24 hours. The degradation could be based on a number of mechanisms including hydrolysis to HCN, oxidation to cyanyl radical and cyanate due to natural attenuation through atmospheric contact, and secretion of organic acid, oxidative enzymes, and hydrogen peroxide by the fungus. Keywords: Cyanotrophic Organism, Myco-Detoxification, Cyanide-Laden Effluents, pH