Photoinduced Difunctionalization of Diazenes Enabled by N-N Radical Coupling

Visible light-mediated dearomative spirocyclization/imination of nonactivated arenes through energy transfer catalysis

Aromatic compounds serve as key feedstocks in the chemical industry, typically undergoing functionalization or full reduction. However, partial reduction via dearomative sequences remains underexplored despite its potential to rapidly generate complex three-dimensional scaffolds and the existing dearomative strategies often require metal-mediated multistep processes or suffer from limited applicability. Herein, a photocatalytic radical cascade approach enabling dearomative difunctionalization through selective spirocyclization/imination of nonactivated arenes is reported. The method employs bifunctional oxime esters and carbonates to introduce multiple functional groups in a single step, forming spirocyclic motifs and iminyl functionalities via N-O bond cleavage, hydrogen-atom transfer, radical addition, spirocyclization, and radical-radical cross-coupling. The reaction constructs up to four bonds (C-O, C-C, C-N) from simple starting materials. Its broad applicability is demonstrated on various substrates, including pharmaceuticals, and it is compatible with scale-up under flow conditions, offering a streamlined approach to synthesizing highly decorated three-dimensional frameworks.

Synthesis of Sulfenamides via Photoredox N-S Coupling of Dialkyl Azodicarboxylates and Thiols

We herein report a photoredox N-S coupling reaction between dialkyl azodicarboxylates and thiols to access sulfenamide scaffolds. This reaction proceeds under mild, green, and operationally simple conditions, offering a broad scope of sulfenamides with high yields and excellent atom efficiency. Mechanistic investigations revealed this reaction followed a photoinitiated radical pathway in which iodide plays a crucial role as both a radical initiator and a single-electron reductant.

Recent Developments and Challenges in the Enzymatic Formation of Nitrogen-Nitrogen Bonds

The biological formation of nitrogen-nitrogen (N-N) bonds represents intriguing reactions that have attracted much attention in the past decade. This interest has led to an increasing number of N-N bond-containing natural products (NPs) and related enzymes that catalyze their formation (referred to in this review as NNzymes) being elucidated and studied in greater detail. While more detailed information on the biosynthesis of N-N bond-containing NPs, which has only become available in recent years, provides an unprecedented source of biosynthetic enzymes, their potential for biocatalytic applications has been minimally explored. With this review, we aim not only to provide a comprehensive overview of both characterized NNzymes and hypothetical biocatalysts with putative N-N bond forming activity, but also to highlight the potential of NNzymes from a biocatalytic perspective. We also present and compare conventional synthetic approaches to linear and cyclic hydrazines, hydrazides, diazo- and nitroso-groups, triazenes, and triazoles to allow comparison with enzymatic routes via NNzymes to these N-N bond-containing functional groups. Moreover, the biosynthetic pathways as well as the diversity and reaction mechanisms of NNzymes are presented according to the direct functional groups currently accessible to these enzymes.

Nitrogen-Nitrogen Radical Coupling-Enabled Precise Difunctionalization of Carbon-Nitrogen Double Bonds

In this study, we have developed a metal-free, photoinduced energy transfer strategy for the efficient difunctionalization of carbon-nitrogen double bonds (C═N). Utilizing oxime ester-based bifunctional reagents, we have achieved direct radical difunctionalization of C═N bonds through nitrogen-nitrogen radical coupling, with over 35 examples and yields up to 96%. This method exhibits broad substrate scope, being compatible with a variety of carboxylic acids and biologically active molecules, thus offering a novel approach for the difunctionalization of heteroatom-containing unsaturated bonds in synthetic chemistry.

Oxidative N-N Bond Formation Versus the Curtius Rearrangement

The oxidative formation of N-N bonds from primary amides has been recently reported and then retracted in the journal Nature Communications by Kathiravan, Nicholls, and co-authors, utilizing a hypervalent iodane reagent. Unfortunately, the authors failed to recognize the Curtius reaction taking place under the described reaction conditions. Thus, the claimed N-N coupling products were not formed. Instead, the Curtius rearrangement urea coupling products were obtained. We demonstrate this herein by means of NMR and x-ray analysis, as well as with the support of an alternative synthetic route.

Synthesis of 2H-imidazoles via copper-catalyzed homo/cross-coupling of oxime acetates

A facile and practical protocol to construct 2H-imidazoles by applying an oxime acetate block as the sole component via oxidative homo/cross-coupling catalyzed by Cu(I) was developed. This strategy provides a straightforward method to produce a series of substituted 2H-imidazoles in moderate to excellent yields. The transformation process is straightforward to operate and is considered as a readily available catalytic system exhibiting good substrate compatibility, eliminating the necessity for pre-functionalization of azides or the use of additives.

Photochemical α-amination of carbonyl groups with iodinanes

We report on a photochemical reaction of silyl enol ethers with iminoiodinanes. This aza Rubottom reaction provides a direct access towards α-amino carbonyl compounds under catalyst free reaction conditions with light as the sole source of energy. Control experiments suggest the participation of triplet nitrene intermediates.

Improving reproducibility through condition-based sensitivity assessments: application, advancement and prospect

The fluctuating reproducibility of scientific reports presents a well-recognised issue, frequently stemming from insufficient standardisation, transparency and a lack of information in scientific publications. Consequently, the incorporation of newly developed synthetic methods into practical applications often occurs at a slow rate. In recent years, various efforts have been made to analyse the sensitivity of chemical methodologies and the variation in quantitative outcome observed across different laboratory environments. For today's chemists, determining the key factors that really matter for a reaction's outcome from all the different aspects of chemical methodology can be a challenging task. In response, we provide a detailed examination and customised recommendations surrounding the sensitivity screen, offering a comprehensive assessment of various strategies and exploring their diverse applications by research groups to improve the practicality of their methodologies.

Photocatalyzed Amination of Alkyl Halides to Access Primary Amines

We demonstrate that oxime ester derivatives can be used as both a halogen atom transfer (XAT) agent and an imine source under photocatalytic conditions, allowing the radical amination of alkyl halides, resulting in the formation of a broad scope of imines. Hydrolysis of the latter gives direct access to the corresponding primary amines. Mechanistically, the reaction is believed to proceed through the formation of aryl radical intermediates, which are responsible for the activation of alkyl halides via XAT.