Fig. 1. (A) Representative THF-containing natural products and pharmaceuticals. (B) Direct oxygen transfer for oxygenation of organic molecules at the anode. (C) This work: electrosynthesis of THFs from styrenes with H2O as oxygen source.

Fig. 2. (A) Adsorption energies and (B) work function of styrene on graphite, Fe2O3, Co3O4 and NiO. (C) Electrosynthesis of 1b from 1a with H2O over different anode materials. (D) Transformations of 1b with H2O for 4 h under different current densities. (E) Time-dependent transformations of 1a with H2O. (F) Cycle-dependent performance of converting 1a into 1b (2 mA cm-2, 4h). All yields are 1H NMR yields (2,3,5-trichloropyridine as an internal standard).

Fig. 3. (A) CV curves of 1a on GC electrode with successive scans (10 cycles). 0.1 mmol 1a in 0.5 mol L-1 H2SO4/CH3CN (1:2 v/v, 3 mL, pH = 0.56, nH2SO4 = 0.5 mmol). (B) CV curves of GC in 0.1 mol L-1 n-Bu4NBF4 in CH3CN at a scan rate of 100 mV s-1 with and without 1a and/or H2O. (C) HR-MS of 1b obtained using H218O as oxygen source. (D,E) HR-MS data of key reaction intermediates trapped by DMPO during the electrosynthesis of 1b from 1a with H2O. (F) A proposed reaction mechanism.

Fig. 4. Substrate scope. aReaction conditions: undivided cell, CP as both anode and cathode, substrates (0.1 mmol), 0.5 mol L-1 H2SO4/CH3CN (1:2 v/v, 3 mL, pH = 0.56, nH2SO4 = 0.5 mmol), current density 2.0 mA cm-2, room temperature, in air. b Current density 3.0 mA cm-2, Ratios of stereoisomers (cis/trans) were determined by 1H NMR analysis. All yields are isolated yields. N.D. = not detected.

Fig. 5. (A) Gram-scale synthesis. (B) Schematic illustration. (C) voltage-time curves of the scale-up electrosynthesis of 1b from 1a with H2O in an undivided cell under constant current density at 2.0 mA cm-2 for 24 h.