Harnessing the Reactivity of Nitroarene Radical Anions to Create Quinoline N-Oxides by Electrochemical Reductive Cyclization

Electrochemical reduction of 2-allyl-substituted nitroarenes using a simple, undivided electrochemical cell with non-precious electrodes to generate nitroarene radical anions was developed. The nitroarene radical anion intermediates participate in 1,5-hydrogen atom transfer reactions to construct quinoline N-oxides bearing aryl-, heteroaryl-, alkenyl-, benzyl-, sulfonyl-, or carboxyl groups.

Direct Aromatic Nitrosation Using 2-Methoxyethyl Nitrite as a NO Cation Source

This work presents an acid-free method for aromatic nitrosation using 2-methoxyethyl nitrite (MOE-ONO). While originally developed as a NOx radical source in our group, we demonstrate the utility of MOE-ONO as a NO cation source for aromatic electrophilic nitrosation. This method successfully nitrosates phenols, naphthols, and other pronucleophiles, completely suppressing undesired nitration by NOx radicals. Notably, it enables nitrosation of acid-sensitive substrates, which has been difficult to achieve with existing protocols.

I2-catalyzed synthesis of 3-aminopyrrole with homopropargylic amines and nitrosoarenes

The synthesis of 3-aminopyrrole using the amination reagent nitrosoarenes and homopropargylic amines catalyzed by I2 through cyclization and amination has been developed. This protocol features excellent functional group tolerance and mild reaction conditions, yielding 3-aminopyrroles in moderate to good yields without a metal catalyst. This method realizes the construction and amination of the 3-aminopyrroles in which nitrosoarenes serve as the amine source and oxidant.

Metal-Free, Hindered, Regioselective Access to Multifunctional Groups Diarylamines via SN Ar Substitution of P-Nitroso Aromatic Methyl Ether by Arylamines

Multifunctional groups diarylamines, an innovative product, efficiently produced from arylamines and p-nitrosoanisole derivatives by intermolecular SN Ar under weak acid conditions. This SN Ar proceeds under mild reaction conditions, and more significantly, the substrates involved do not necessarily require strong electron-withdrawing groups. Moreover, this SN Ar is characterized by resistance to space crowding, tolerance to halogen and nitroso functional groups, and high regioselectivity. Mechanistic observations suggest that the SN Ar is the result of the transfer of the positive charge center of the protonated nitroso group to the p-methoxy group.

Continuous Flow Synthesis of Nitrosoarenes via Photochemical Rearrangement of Aryl Imines

Nitrosoarenes are versatile organic building blocks; however, their intrinsic instability and limited synthetic accessibility have so far restricted their widespread use. Herein, we present a new continuous flow route toward these entities that is based on a direct photochemical rearrangement process using o-nitrophenylimines as starting materials. Due to the underlying redox mechanism, a new amide group accompanies the formation of the nitroso group. Crucial to the success of this approach is the use of trifluoroethanol as a solvent and high-power light-emitting diodes (365 nm) as light sources that provide uniform irradiation and high efficiency of the resulting continuous flow method. The process is fast and robust, with high functional group tolerance and high throughput. The formation of the nitroso moiety is supported by full spectroscopic analysis, including X-ray crystallography. The scalability of this flow approach allows access to gram quantities of nitroso species for which we highlight a small set of derivatization reactions underlining their synthetic utility.

Unlocking mild-condition benzene ring contraction using nonheme diiron N-oxygenase

Benzene ring contractions are useful yet rare reactions that offer a convenient synthetic route to various valuable chemicals. However, the traditional methods of benzene contraction rely on noble-metal catalysts under extreme conditions with poor efficiency and uncontrollable selectivity. Mild-condition contractions of the benzene ring are rarely reported. This study presents a one-step, one-pot benzene ring contraction reaction mediated by an engineered nonheme diiron N-oxygenase. Using various aniline substrates as amine sources, the enzyme causes the phloroglucinol-benzene-ring contraction to afford a series of 4-cyclopentene-1,3-dione structures. A reaction detail study reveals that the nonheme diiron N-oxygenase first oxidizes the aromatic amine to a nitroso intermediate, which then attacks the phloroglucinol anion and causes benzene ring contraction. Besides, we have identified two potent antitumor compounds from the ring-contracted products.

Nitrosoarenes Implement Cascade Cyclization of 1-Allenyl-2-alkynylbenzenes through Diradical Mechanism

This work reports cascade cyclization between 1-allenyl-2-alkynylbenzenes and nitrosoarenes. When these two components reacted alone under N₂, N,O-functionalized indane-fused isoxazolidines 3 were obtained selectively. DFT calculations verify that this reaction sequence involves unprecedented nitrone/alkyne cycloadditions, followed by diradical rearrangement.

Azodioxy compounds as precursors for C-radicals and their application in thermal styrene difunctionalization

An atom-economic thermal α,β-difunctionalization of various styrenes with readily prepared azodioxy compounds is reported. Mechanistic studies reveal that the starting azodioxy compounds can thermally be cleaved to the corresponding C-nitroso compounds, which under these thermal conditions further homolyze to generate reactive C-radicals along with the persistent NO radical. In the presence of a styrene, C-radical addition with subsequent nitrosylation followed by tautomerization is occurring, resulting in an overall styrene β-alkylation-α-oximation reaction.

Iron-catalyzed one-pot cyclization and amination of 2-alkynylthioanisoles using nitrosobenzenes as the amine source

A direct strategy for the synthesis of 3-phenylaminobenzothiophene via iron-catalyzed cyclization of 2-alkynylthioanisoles and nitrosoarenes is presented in this work.

Three decades of unveiling the complex chemistry of C-nitroso species with computational chemistry

This review revisits the complex reactivity of C-nitroso derivatives through the synergistic combination of computational and synthetic organic chemistry, with an emphasis on the rationalization of mechanisms and selectivities. 

Photo-Mediated Intermolecular Coupling of Alkenes with Ketones via Acyloxy Nitroso Compounds

An atom-economic intermolecular radical addition reaction of acyloxy nitroso compounds to electron-deficient alkenes mediated by visible light is reported. The starting nitroso derivatives are readily prepared by oxidation of the corresponding oximes prepared from ketones and the overall transformation represents an oxidative coupling of a ketone with a Michael acceptor. The cascade proceeds smoothly under mild conditions, providing a series of valuable functionalized oximes in moderate to good yields. Mechanistic studies suggest that these cascades proceed via addition/coupling processes that are controlled by the persistent radical effect (PRE) with NO acting as the persistent species.

Catalyst-free generation of acyl radicals induced by visible light in water to construct C–N bonds

A new route to produce acyl radicals by the cleavage of C_sp2–C_sp2 bonds of α-diketones irradiated by visible light was developed and hydroxylamides or amides were selectively synthesized in water.