Oxidative Radical Arylation of Anilines with Arylhydrazines and Dioxygen from Air

Substituted 2-aminobiphenyls have been prepared from arylhydrazine hydrochlorides and anilines in biphasic radical arylation reactions with dioxygen from air as a most simple and readily available oxidant. Under optimized conditions, the free amino functionality of the aniline leads to high <i>ortho</i>:<i>meta</i> regioselectivities, now even for anilines bearing a donor substituent in the <i>para</i> position. Finally, the mild and metal-free new access to aminobiphenyls was shown to be applicable on a gram scale

Base-Induced Radical Carboamination of Nonactivated Alkenes with Aryldiazonium Salts

A new transition-metal-free version of the Meerwein arylation has been developed. The key feature of this carboamination-type reaction is the slow base-controlled generation of aryl radicals from aryldiazonium tetrafluoroborates, so that a sufficient quantity of diazonium ions remains to enable efficient trapping of the alkyl radical adduct resulting from aryl radical addition to the alkene. Under strongly basic conditions, diazoanhydrides are likely to take over the role of the nitrogen-centered radical scavengers

Regioselective Radical Arylation of Anilines with Arylhydrazines

Substituted 2-aminobiphenyls have been prepared from arylhydrazines and anilines via radical arylation reactions under simple oxidative conditions. The strong directing effect of the free and unprotonated amino functionality leads to high regioselectivities, and anilines have been shown to be significantly better aryl radical acceptors than nitrobenzenes or phenyl ethers. The methodology is also applicable to phenols, which react best as phenolates under strongly basic conditions. Finally, radical arylation reactions of anilines and anilinium salts under various conditions have for the first time demonstrated that regioselectivity can also be controlled through the rearomatization step and that the addition of an aryl radical to a substituted benzene might even be reversible

Synthesis of Spirocyclohexadienones through Radical Cascade Reactions Featuring 3‑Fold Carbon–Carbon Bond Formation

The radical 5-<i>exo</i> cyclization starting from 2-allyl­oxyphenyl­diazonium ions can be employed for the diastereoselective synthesis of <i>ortho</i>-spirocyclo­hexadienones through a consecutive addition to alkynes. The spirocyclic systems are formed in a radical [2 + 2 + 1] cycloaddition comprising three carbon–carbon formations, of which the final one is an <i>ipso</i> attack onto the aromatic system at the original position of the diazonium-derived aryl radical

Strongly Directing Substituents in the Radical Arylation of Substituted Benzenes

Although general interest in radical arylation reactions has grown rapidly in recent years, poor regioselectivities and the need to use a large excess of the radical-accepting arene have hindered their application to substituted benzenes. We now describe experimental and computational investigations into the substituent effects that lead to regioselective addition based on the recent discovery of anilines as outstanding substrates for radical arylations

Hydrogen Peroxide Promoted Mizoroki–Heck Reactions of Phenyldiazenes with Acrylates, Acrylamides, and Styrenes

Mizoroki–Heck reactions, which are well-known for aryldiazonium salts and which have recently been described for arylhydrazines, have now been extended to phenyldiazenes. In situ generation of phenyldiazenes from azocarboxylates allowed clean and selective reactions with styrenes, acrylates, and acrylamides using palladium­(II) acetate in the presence of silver­(I) acetate or hydrogen peroxide as oxidant. Hydrogen peroxide was thereby shown to be a cheap and broadly applicable alternative for the established palladium–silver­(I) system

Nucleophilic Substitutions and Radical Reactions of Phenylazocarboxylates

<i>tert</i>-Butyl phenylazocarboxylates are versatile building blocks for synthetic organic chemistry. Nucleophilic substitutions of the benzene ring proceed with aromatic amines and alcohols under mild conditions. The attack of aliphatic amines may be directed to the aromatic core as well as to the carbonyl unit leading to azocarboxamides. The benzene ring can further be modified through radical reactions, in which the <i>tert</i>-butyloxycarbonylazo group enables the generation of aryl radicals at either elevated temperatures or under acidic conditions. Radical reactions include oxygenation, halogenation, carbohalogenation, carbohydroxylation, and aryl–aryl coupling

Nitrogen Oxides and Nitric Acid Enable the Sustainable Hydroxylation and Nitrohydroxylation of Benzenes under Visible Light Irradiation

A new type of waste recycling strategy is described in which nitrogen oxides or nitric acid are directly employed in photocatalyzed hydroxylations and nitrohydroxylations of benzenes. Through these transformations, otherwise costly denitrification can be combined with the synthesis of valuable compounds for various applications

Visible-Light-Mediated Radical Arylations Using a Fluorescein-Derived Diazonium Salt: Reactions Proceeding via an Intramolecular Forth and Back Electron Transfer

Functionalizations of arenes and alkenes via additive-free radical reactions using highly photosensitive, fluorescein-derived diazonium salts are described. The particular properties of the diazonium salts enable unique Meerwein-type carbohydroxylations of non-activated alkenes, which can be rationalized by a reaction mechanism involving forth and back electron transfer from and to the xanthene subunit of the fluorescein moiety

Denitrification Combined with Diazotization of Anilines and the Synthesis of 4′-Chlorobiphenyl-2,5-diamine and 1‑Chloro-4-iodobenzene

The diazotization of anilines in aqueous solution has been found to be highly useful as a key reaction step to achieve the denitrification of low-concentrated nitrogen dioxide in air. The diazonium salt from the wet scrubberalthough obtained in highly diluted aqueous solutionwas shown to be directly applicable in a radical Gomberg-Bachmann aryl–aryl coupling and a Sandmeyer iodination reaction