Electrochemically-promoted synthesis of benzo[b]thiophene-1,1-dioxides via strained quaternary spirocyclization

Cycloaddition and Skeleton Rearrangement of Heterocyclic Ketene Aminals (HKAs) with 1-Diazonaphthalen-2(1H)-ones for the Synthesis of Functionalized 1,2,3-Triazoles

We developed a protocol for the synthesis of highly functionalized 5,6-dihydro-imidazo[1,2-c][1,2,3]triazole derivatives 4-5 (DHITs) from 1-diazonaphthalen-2(1H)-one derivatives with heterocyclic ketene aminals (HKAs). This strategy involved cycloaddition and skeletal rearrangement entailing the heating of a mixture of substrates 1 with HKAs 2-3 and THF without any catalyst. As a result, a series of DHITs 4-5 were produced by cleaving one bond (1 C═N bond) and forming three bonds (1 N-N and 2 C-N bonds) in a single step. This protocol achieved the dual functionalization of diazo building blocks involving both the aromatic nitrogen alkylation reaction to form an ArC-N bond without any metal catalyst and the intermolecular cycloaddition of the N═N bond. These strategies can be used to synthesize functionalized DHITs for combinatorial and parallel syntheses via one-pot reactions without any catalyst.

Electrochemical stereoselective synthesis of polysubstituted 1,4-dicarbonyl Z-alkenes via three-component coupling of sulfoxonium ylides and alkynes with water

The first straightforward strategy for the synthesis of 1,4-dicarbonyl Z-alkenes has been developed via an electrochemical cross-coupling reaction of sulfoxonium ylides and alkynes with water. The metal-free protocol showed an easy-to-handle nature, good functional group tolerance, and high Z-stereoselectivity, which is rare in previous cases. The proposed reaction mechanism was convincingly established by carrying out a series of control experiments, cyclic voltammetry experiments, and density functional theory (DFT) studies.

Tf2O/2-Chloropyridine-Triggered Synthesis of Benzo[b]thiophene 1,1-Dioxides from Sulfonium α-Acyl Sulfonylmethylides

Triflic anhydride and 2-chloropyridine-comediated tandem activation, intramolecular aromatic electrophilic addition, and 1,2-sulfonyl shift via spirocyclic intermediates of sulfonium α-acyl sulfonylmethylides realize the efficient synthesis of 2-alkyl/arylthiobenzo[b]thiophene 1,1-dioxides. The deactivated sulfonyl group determines the site-selectivity of the electrophilic addition via the ipso-attack, while the following S-migration controls the regioselectivity. Some of 2-methylthiobenzo[b]thiophene 1,1-dioxides show fluorescence properties in the solid state and in their solutions.

Electrochemical cascade migratory versus ortho-cyclization of 2-alkynylbenzenesulfonamides

Efficient control over several possible reaction pathways of free radicals is the chemical basis of their highly selective transformations. Among various competing reaction pathways, sulfonimidyl radicals generated from the electrolysis of 2-alkynylbenzenesulfonamides undergo cascade migratory or ortho-cyclization cyclization selectively. It is found that the incorporation of an extra 2-methyl substituent biases the selective migration of the acyl- over vinyl-linker of the key spirocyclic cation intermediate and thus serves as an enabling handle to achieve the synthetically interesting yet under-investigated cascade migratory cyclization of spirocyclic cations.

Electrochemical chemoselective hydrogenation of 1,4-enediones with HFIP as the hydrogen donor: scalable access to 1,4-diketones

A straightforward electrochemical protocol for efficient hydrogenation of unsaturated CC bonds has been reported in an undivided cell. A series of versatile 1,4-diketones are smoothly generated under metal-free and external-reductant-free electrolytic conditions. Moreover, the tolerance of various functional groups and decagram-scale experiments have shown the practicability and potential applications of this methodology. Moreover, a range of heterocyclic compounds were easily prepared through follow-up procedures of 1,4-diketones.

SO42- ions as a nucleophilic reagent: straightforward electrochemical access to organosulfates

An electrooxidation direct difunctionalization of alkynes with sulfonyl hydrazides has been developed for the construction of sulfonyl alkenyl sulfates in the absence of metal catalysts and a stoichiometric amount of oxidants. Notably, it is the first example to verify that SO42- ions can act as a nucleophilic reagent for the preparation of organosulfates.

Access to Saturated Oxygen Heterocycles and Lactones via Electrochemical Sulfonylative Oxycyclization of Alkenes with Sulfonyl Hydrazides

A facile electrochemical sulfonylative cycloetherification of linear unsaturated alcohols with sulfonyl hydrazides under mild conditions has been accomplished. This catalyst- and oxidant-free protocol proceeds via electro-oxidation, followed by radical addition, as well as an intramolecular oxygen nucleophilic process. This methodology is compatible with a broad substrate scope and good functional group compatibility, which provides a valuable and convenient synthetic tool for the synthesis of saturated five-, six-, seven-, and eight-membered ring oxygen heterocycles. Furthermore, sulfonylative cycloesterification of linear unsaturated acids toward the lactone products has also been established under this electrochemical system. In addition, control experiments indicated that the N-H bonds of the sulfonyl hydrazide molecule are non-essential.