Electrochemical C-H Sulfonylation of Hydrazones

Electrochemical Oxidative Sulfonylation-Azidation of Alkenes

A novel electrochemical oxidative sulfonylation-azidation of alkenes is accomplished by using sulfonyl hydrazide and trimethylsilyl azide (TMSN3) for the one-pot and green synthesis of β-azidoarylsulfone, which involves the direct construction of new C-S and C-N bonds. Notably, neither exogenous oxidants/additives nor metal catalysts are required for this method. In addition, this electrochemical strategy features mild conditions and wide substrate scope and has been proved to be a radical pathway by mechanistic studies.

Electrochemical and photochemical reaction of isatins: a decade update

This review presents the latest progress in photochemical and electrochemical reactions involving isatins. Isatin and its functionalized scaffolds e.g., oxindoles, spirooxindoles, and quinolines are privileged heterocycles as they are largely present in several agrochemical, natural products, and pharmaceuticals. Thus, the functionalization of isatins using sustainable approaches, i.e., electro- and photochemical methods is of recent research interest worldwide. In this review, we have discussed most of the important reactions of isatins based on types of bond formation involved under electro- and photochemical conditions over the last decade. The reaction mechanism for each reaction has been discussed in detail to offer an inclusive guide to readers. Lastly, a summary of current challenges and the future outlook toward the development of effective electrochemical and photochemical methods for the reaction of isatins is also presented.

Photo-induced phosphorylation/cyclization of N-homoallyl and N-allyl aldehyde hydrazones to access phosphorylated tetrahydropyridazines and dihydropyrazoles

A photocatalytic radical carbophosphorylation/cyclization of N-homoallyl aldehyde hydrazones with phosphine oxides was developed under metal-free conditions, achieving phosphorylated tetrahydropyridazines in yields up to 95%. Phosphorylated dihydropyrazoles were also constructed, by reacting N-allyl aldehyde hydrazones with phosphine oxides under the same conditions.

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.

Supporting Electrolyte-Free Electrochemical Oxidative C-H Sulfonylation and Thiocyanation of Fused Pyrimidin-4-Ones in an All-Green Electrolytic System

An electrooxidative C-H functionalization is a widely accepted route to obtain sulfur-containing arenes and heteroarenes. However, this process often involves using non-recyclable supporting electrolytes, (co)solvents like hexafluoroisopropanol, additives like acid, or catalysts. The use of additional reagents can increase costs and waste, reducing atom efficiency. Moreover, unlike other nitrogen-containing heterocycles, there have only been sporadic reports of electrochemical C-H functionalization in fused pyrimidin-4-ones, and an electrolyte-free process has yet to be developed. This work demonstrates that such anodic coupling reactions can be performed in an all-green electrolytic system without using such additional electrolytes or HFIP, maintaining a high atom economy. This C-H functionalization strategy utilizes inexpensive sodium sulfinates and ammonium thiocyanate as sulfonylating and thiocyanating agents in an undivided cell at a constant current, using a mixture of CH3 CN/H2 O as solvent at room temperature. Thus, fused pyrimidin-4-ones can be selectively converted into C3-sulfonylated and -thiocyanated derivatives in moderate to good yields.

Photocatalytic Carbosulfonylation/Cyclization of N-Homoallyl and N-Allyl Aldehyde Hydrazones toward Sulfonylated Tetrahydropyridazines and Dihydropyrazoles

N'-Benzylidene-N-homoallylacetohydrazides were designed and synthesized as novel skeletons for the construction of functionalized tetrahydropyridazines. A series of aryl- and alkylsulfonylated tetrahydropyridazines were obtained in yields of up to 94% employing sulfonyl chlorides as the sulfonyl radical sources under visible-light irradiation. Besides, sulfonylated dihydropyrazoles were also produced from N-allyl-N'-benzylideneacetohydrazides. Mechanistic investigations indicated that both energy transfer and single electron transfer processes were involved in accomplishing the radical 6/5-endo-trig cyclization to the C═N bond.