Electrochemical C(sp3)-H Lactonization of 2-Alkylbenzoic Acids toward Phthalides

Electrochemical Oxidation of Benzyl Alcohols via Hydrogen Atom Transfer Mediated by 2,2,2-Trifluoroethanol

We report a novel electrochemical oxidation of benzyl alcohols. We found that trifluoroethanol plays a role as a hydrogen atom transfer (HAT) mediator, enabling the oxidation of electron-deficient substrates that are difficult to directly oxidize on electrode surfaces. Density functional theory calculations, cyclic voltammetry measurements, and constant potential electrolysis studies supported the proposed HAT mechanism. Moreover, the obtained carbonyl compounds could be functionalized in an electrochemical one-pot manner, further highlighting their synthetic utility.

Electrochemical Benzylic C─H Sulfation beyond the O-Sulfonation Limitation

Direct C─H sulfation represents a valuable transformation for the synthesis of organosulfates. However, it has been challenging to achieve owing to the presence of multiple C─H bonds with comparable strengths and steric environments. Current methods for producing organosulfates primarily rely on O-sulfonation, which limits their applicability to hydroxyl-containing compounds. Herein, we report a practical and cost-efficient method for the electrochemical sulfation of benzylic C─H bonds. This reaction avoids the need for strong oxidants, demonstrating broad substrate scope, excellent chemoselectivity, and site selectivity. The orthogonal reactivity of this protocol is particularly evident in the transformation of alcohol substrates.

Temperature-Dependent Photoreactivity of 2-Azidomethylbenzophenone: Insights into the Triplet Imine Biradical Pathway

Photoenols, formed through photoinduced intramolecular H atom abstraction in o-alkyl-substituted arylketones, typically have limited utility as reactive intermediates owing to fast reversion to the starting material. Herein, we introduced an azido group on the o-alkyl substituent to render the photoreaction irreversible. Irradiation of 2-azidomethylbenzophenone (1) in methanol yielded 2-(hydroxy(phenyl)methyl)benzonitrile (2). Laser flash photolysis of 1 revealed the formation of biradical 3Br1 followed by intersystem crossing to photoenols Z-3 (τ ∼ 3.3 μs) and E-3 (τ > 45 μs), both of which reverted to 1. Alternatively, 3Br1 could lose N2 to form 3Br2 (not detected), which decays to 2. In cryogenic argon matrices, irradiation of 1 yielded nitrene 31N and 2 but no photoenols, likely because Z-3 regenerated 1. Both ESR spectroscopy and absorption analysis in methyltetrahydrofuran (80 K) confirmed 31N formation. Upon prolonged irradiation, the absorbance of 31N decreased, whereas that of 3 remained unchanged and that of 2 increased. Thus, TK of 1 is proposed to form 3Br1 via H atom abstraction, with subsequent intersystem crossing to 3 competing with the loss of N2 to generate 3Br2. DFT calculations revealed a small energy gap (∼2 kcal/mol) between the triplet and singlet configurations of Br2, supporting a mechanism in which 3Br2 intersystem crosses to yield 2.

Electrochemical Synthesis of Spirolactones from α-Tetralone Derivatives with Methanol as a C1 Source

Spirolactones are widely found in pharmaceuticals and bioactive natural products. However, efficient and environmentally friendly approaches to accessing spirolactones are still highly desirable. Herein, a novel electrochemical synthesis of spirolactones from α-tetralone derivatives with methanol as a C1 source is described. This electrochemical reaction exhibits a high efficiency and good functional group tolerance.

Electrochemical Benzylic C(sp3)-H Imidation Enabled by Benzoic Acid Derived Radicals

We developed an electrochemical approach for benzylic C(sp3)-H imidation by virtue of the in situ generated oxygen-centered radicals (OCRs). The electrochemical imidation provides a complementary approach to giving distinct imide products compared with previous acyloxylation products. This protocol exhibits good site selectivity and broad substrate generality. Moreover, the utility of the OCR-mediated protocol was extended to the electrochemical oxidation of silane, and its robustness was also highlighted by the imidation of complex substrates, which would otherwise be inaccessible for previous approaches. A plausible reaction mechanism was proposed to rationalize the experimental observations.

Electrochemical Lactonization Enabled by Unusual Shono-Type Oxidation from Functionalized Benzoic Acids

A novel method for electrochemical lactonization via C(sp3)-H functionalization was developed. This metal- and oxidant-free strategy enabled the efficient synthesis of various lactones. Gram-scale reaction and derivatization of the lactone product demonstrated the synthetic utility of this methodology. Mechanistic studies using control experiments and CV curves elucidated the proposed intramolecular HAT and the oxidative cyclization pathway. An unusual Shono-type oxidation was realized through this electrochemical approach, proceeding without a traditional nucleophilic addition process.

Chlorobenzene-driven palladium-catalysed lactonisation of benzoic acids

Herein, we developed a palladium-catalysed C-H cyclisation of benzoic acids in chlorobenzene without additional oxidants. The key to the success of these reactions is the use of chlorobenzene, which serves a dual role as a solvent and an oxidant, thus providing a simple and efficient method for synthesising phthalides.