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Efficient and Sustainable Electrosynthesis of N-Sulfonyl Iminophosphoranes by the Dehydrogenative P-N Coupling Reaction

Iminophosphoranes are commonly used reagents in organic synthesis and are, therefore, of great interest. An efficient and sustainable iodide-mediated electrochemical synthesis of N-sulfonyl iminophosphoranes from readily available phosphines and sulfonamides is reported. This method features low amounts of supporting electrolytes, inexpensive electrode materials, a simple galvanostatic setup, and high conversion rates. The broad applicability could be demonstrated by synthesizing 20 examples in yields up to 90%, having diverse functional groups including chiral moieties and biologically relevant species. Furthermore, electrolysis was performed on a 20 g scale and could be run in repetitive mode by recycling the electrolyte, which illustrates the suitability for large-scale production. A reaction mechanism involving electrochemical mediation by the iodide-based supporting electrolyte is proposed, completely agreeing with all of the results.

SN2 Reaction at the Amide Nitrogen Center Enables Hydrazide Synthesis

Nucleophilic substitutions are fundamentally important transformations in synthetic organic chemistry. Despite the substantial advances in bimolecular nucleophilic substitutions (SN2) at saturated carbon centers, analogous SN2 reaction at the amide nitrogen atom remains extremely limited. Here we report an SN2 substitution method at the amide nitrogen atom with amine nucleophiles for nitrogen-nitrogen (N-N) bond formation that leads to a novel strategy toward biologically and medicinally important hydrazide derivatives. We found the use of sulfonate-leaving groups at the amide nitrogen atom played a pivotal role in the reaction. This new N-N coupling reaction allows the use of O-tosyl hydroxamates as electrophiles and readily available amines, including acyclic aliphatic amines and saturated N-heterocycles as nucleophiles. The reaction features mild conditions, broad substrate scope (>80 examples), excellent functional group tolerability, and scalability. The method is applicable to late-stage modification of various approved drug molecules, thus enabling complex hydrazide scaffold synthesis.

An Electrochemical Oxo-amination of 2H-Indazoles: Synthesis of Symmetrical and Unsymmetrical Indazolylindazolones

We have established a supporting-electrolyte free electrochemical method for the synthesis of indazolylindazolones through oxygen reduction reaction (eORR) induced 1,3-oxo-amination of 2H-indazoles where 2H-indazole is used as both aminating agent as well as the precursor of indazolone. Moreover, we have merged indazolone and indazole to get unsymmetrical indazolylindazolones through direct electrochemical cross-dehydrogenative coupling (CDC). This exogenous metal-, oxidant- and catalyst-free protocol delivered a number of multi-functionalized products with high tolerance of diverse functional groups.

Dehydrogenative Electrochemical Synthesis of N-Aryl-3,4-Dihydroquinolin-2-ones by Iodine(III)-Mediated Coupling Reaction

Electrochemically generated hypervalent iodine(III) species are powerful reagents for oxidative C-N coupling reactions, providing access to valuable N-heterocycles. A new electrocatalytic hypervalent iodine(III)-mediated in-cell synthesis of 1H-N-aryl-3,4-dihydroquinolin-2-ones by dehydrogenative C-N bond formation is presented. Catalytic amounts of the redox mediator, a low supporting electrolyte concentration and recycling of the solvent used make this method a sustainable alternative to electrochemical ex-cell or conventional approaches. Furthermore, inexpensive, readily available electrode materials and a simple galvanostatic set-up are applied. The broad functional group tolerance could be demonstrated by synthesizing 23 examples in yields up to 96 %, with one reaction being performed on a 10-fold higher scale. Based on the obtained results a sound reaction mechanism could be proposed.

Rh(III)-Catalyzed C-H Functionalization/Annulation of 1-Arylindazolones: Divergent Synthesis of Fused Indazolones and Allyl Indazolones

Rh(III)-catalyzed C-H/N-H annulation and C-H allylation of phenylindazolones have been realized by employing 5-methylene-1,3-dioxan-2-one and 4-vinyl-1,3-dioxolan-2-one as scalable cross-coupling partners, delivering functionalized indazolone fused heterocycles and branched and linear allyl indazolones respectively in moderate to high yield. These divergent synthesis protocols showcase mild conditions, broad substrate scope, and high functional-group compatibility. In addition, scale-up synthesis and preliminary mechanistic exploratory were also accomplished.

Electrochemically Driven Selective Removal of the S═N Bond-Directing Group Using Cyclohexanone Oxime as the Mediator

An inexpensive electrochemical induction system was used for the efficient reductive defunctionalization of sulfoximines through a radical pathway. This practical and robust strategy could be used for the removal of the S═N bond-directing group from various sulfoximines. The practicability of this method was demonstrated by its mild conditions, simple operation, one-pot procedure, gram-scale synthesis, and the undivided cell. Furthermore, preliminary mechanistic studies suggested that the reaction might proceed via a homocoupling reaction and a denitrification procedure.

Emerging trends in the sustainable synthesis of N-N bond bearing organic scaffolds

N-N bond bearing organic frameworks such as azos, hydrazines, indazoles, triazoles and their structural moieties have piqued the interest of organic chemists due to the intrinsic nitrogen electronegativity. Recent methodologies with atom efficacy and a greener approach have overcome the synthetic obstacles of N-N bond construction from N-H. As a result, a wide range of amine oxidation methods have been reported early on. This review's vision emphasizes the emerging methods of N-N bond formation, particularly photo, electro, organo and transition metal free chemical methods.