Silver‐Catalyzed Stereoselective trans Addition of 4‐Hydroxycoumarins to Haloalkynes and Late‐Stage Nitration

Silver-Catalyzed Radical Umpolung Cross-Coupling of Silyl Enol Ethers with Activated Methylene Compounds: Access to Diverse Tricarbonyl Derivatives

A silver-catalyzed protocol for the intermolecular radical umpolung cross-coupling protocol of silyl enol ethers with activated methylene compounds is disclosed. The protocol exhibits excellent functional group tolerance, enabling the expedient preparation of a variety of tricarbonyl compounds. Preliminary mechanistic investigations suggest that the reaction proceeds through a process involving free radicals in which silver oxide has a dual role, acting as both a catalyst and a base.

Silver-catalyzed direct selanylation of indoles: synthesis and mechanistic insights

Herein we describe the Ag(i)-catalyzed direct selanylation of indoles with diorganoyl diselenides. The reaction gave 3-selanylindoles with high regioselectivity and also allowed direct access to 2-selanylindoles when the C3 position of the indole ring was blocked via a process similar to Plancher rearrangement. Experimental analyses and density functional theory calculations were carried out in order to picture the reaction mechanism. Among the pathways considered (via concerted metalation-deprotonation, Ag(iii), radical, and electrophilic aromatic substitution), our findings support a classic electrophilic aromatic substitution via Lewis adducts between Ag(i) and diorganoyl diselenides. The results also afforded new insights into the interactions between Ag(i) and diorganoyl diselenides.

Synthetic Diversity from a Versatile and Radical Nitrating Reagent

We leverage the slow liberation of nitrogen dioxide from a newly discovered, inexpensive succinimide-derived reagent to allow for the C-H diversification of alkenes and alkynes. Beyond furnishing a library of aryl β-nitroalkenes, this reagent provides unparalleled access to β-nitrohydrins and β-nitroethers. Detailed mechanistic studies strongly suggest that a mesolytic N-N bond fragmentation liberates a nitryl radical. Using in situ photo-sensitized, electron paramagnetic resonance spectroscopy, we observed direct evidence of a nitryl radical in solution by nitrone spin-trapping. To further exhibit versatility of N-nitrosuccinimide under photoredox conditions, the late-stage diversification of an extensive number of C-H partners to prepare isoxazolines and isoxazoles is presented. This approach allows for the formation of an in situ nitrile oxide from a ketone partner, the presence of which is detected by the formation of the corresponding furoxan when conducted in the absence of a dipolarophile. This 1,3-dipolar cycloaddition with nitrile oxides and alkenes or alkynes proceeds in a single-operational step using a mild, regioselective, and general protocol with broad chemoselectivity.