Radical "On Water" Addition to the C═N Bond of Hydrazones: A Synthesis of Isoindolinone Derivatives

Radical Reactions in Organic Synthesis: Exploring in-, on-, and with-Water Methods

Radical reactions in water or aqueous media are important for organic synthesis, realizing high-yielding processes under non-toxic and environmentally friendly conditions. This overview includes (i) a general introduction to organic chemistry in water and aqueous media, (ii) synthetic approaches in, on, and with water as well as in heterogeneous phases, (iii) reactions of carbon-centered radicals with water (or deuterium oxide) activated through coordination with various Lewis acids, (iv) photocatalysis in water and aqueous media, and (v) synthetic applications bioinspired by naturally occurring processes. A wide range of chemical processes and synthetic strategies under different experimental conditions have been reviewed that lead to important functional group translocation and transformation reactions, leading to the preparation of complex molecules. These results reveal how water as a solvent/medium/reagent in radical chemistry has matured over the last two decades, with further discoveries anticipated in the near future.

2-Methoxyethyl Nitrite as a Reagent for Chemoselective On-Water Nitration

An on-water approach has been developed that allows a nitration of tyrosines and phenols under mild conditions. We envisioned that the assembly of tyrosine/tyrosyl radical couples with interfacial water molecules would realize a biomimetic stacking hydrogen atom transfer (HAT) transition state to facilitate the electron-transfer process. The optimal organic nitrite, 2-methoxyethyl nitrite, resulted in rapid coupling of the tyrosyl radicals with •NO 2 at the oil-water interface to afford the nitrated phenols. Many characteristics found in our on-water strategy are distinct from other complementary systems that include radical nitration. These enticing roles of water in the reaction process introduce new avenues to explore in the design of synthetic organic chemistry systems.

Synthesis of Polysubstituted Isoindolinones via Radical Cyclization of 1,3-Dicarbonyl Ugi-4CR Adducts Using Tetrabutylammonium Persulfate and TEMPO

The development of an efficient method for the synthesis of polysubstituted isoindolinones from 1,3-dicarbonyl Ugi-4CR adducts, employing an aromatic radical cyclization process promoted by tetrabutylammonium persulfate and 2,2,6,6-tetramethyl-1-piperidine 1-oxyl (TEMPO), is described. The protocol allowed the construction of a library of isoindolinones bearing a congested carbon in good to excellent yields under mild conditions and in short reaction times.

Synthesis of Polysubstituted Pyrroles via Silver-Catalyzed Oxidative Radical Addition of Cyclopropanols to Imines

A silver-catalyzed formal [3 + 2] cycloaddition reaction, with cyclopropanols as a C3 subunit and imines as a two-atom subunit, is developed. The reaction takes place under mild conditions and produces a broad array of polysubstituted pyrroles in medium to high yields. It represents the first example of oxidative radical addition to imines, thus offering a new choice for the direct C-H functionalization of imines.

Modular Synthesis of Alkylarylazo Compounds via Iron(III)-Catalyzed Olefin Hydroamination

A novel Fe-catalyzed olefin hydroamination with aryldiazo sulfones for accessing alkylarylazo compounds has been successfully developed. Aryldiazo sulfones are used as radical acceptors, and N-N double bonds will be regenerated when an arene sulfonyl group leaves. The reaction features mild reaction conditions and a broad substrate scope, allowing access to many azo compounds that would be difficult or perhaps impossible to access using other methods.