Electrochemistry and electrosynthetic methods are a part of the repertoire of the organic synthesis toolbox. In general, only electrons are employed as reagents or the reagents are electrochemically regenerated. Consequently, waste can be avoided, and limited resources can be used in a careful and economic manner. Because alternative reaction pathways are employed by electrosynthetic methods, scarce and toxic elements can be replaced or are not required at all. When changing feed stocks and natural resources begin to play a more crucial role, electrosynthetic methodologies will not only be of ecological interest but also of economic significance. The contributions within this Thematic Series demonstrate the broad use of electrosynthesis and represent a snapshot of this current and vividly developing field.
Graphical Abstract
Figure 1: Common types of electrochemically induced cyclization reactions.
Scheme 1: Principle of indirect electrolysis.
Scheme 2: Anodic intramolecular cyclization of olefines in methanol.
Scheme 3: Anodic cyclization of olefines in CH2Cl2/DMSO.
Scheme 4: Intramolecular coupling of 1,6-dienes in CH2Cl2/DMSO.
Scheme 5: Cyclization of bromopropargyloxy ester 12.
Scheme 6: Proposed mechanism for the radical cyclization of bromopropargyloxy ester 12.
Scheme 7: Preparation of pyrrolidines and tetrahydrofurans via Kolbe-type electrolysis of unsaturated carboxy...
Scheme 8: Anodic cyclization of chalcone oximes 19.
Scheme 9: Generation of N-acyliminium (23) and alkoxycarbenium species (24) from amides and ethers with and w...
Scheme 10: Anodic cyclization of dipeptide 25.
Scheme 11: Anodic cyclization of a dipeptide using an electroauxiliary.
Scheme 12: Anodic cyclization of hydroxyamino compound 29.
Scheme 13: Cyclization of unsaturated thioacetals using the ArS(ArSSAr)+ mediator.
Scheme 14: Cyclization of biaryl 35 to carbazol 36 as key-step of the synthesis of glycozoline (37).
Scheme 15: Electrosynthesis of 39 as part of the total synthesis of alkaloids 40 and 41.
Scheme 16: Wacker-type cyclization of alkenyl phenols 42.
Scheme 17: Cathodic synthesis of indol derivatives.
Scheme 18: Fluoride mediated anodic cyclization of α-(phenylthio)acetamides.
Scheme 19: Synthesis of 2-substituted benzoxazoles from Schiff bases.
Scheme 20: Synthesis of euglobal model compounds via electrochemically induced Diels–Alder cycloaddition.
Scheme 21: Cycloaddition of anodically generated N-acyliminium species 58 with olefins and alkynes.
Scheme 22: Electrochemical aziridination of olefins.
Scheme 23: Proposed mechanism for the aziridination reaction.
Scheme 24: Electrochemical synthesis of benzofuran and indole derivatives.
Scheme 25: Anodic anellation of catechol derivatives 66 with different 1,3-dicarbonyl compounds.
Scheme 26: Electrosynthesis of 1,2-fused indoles from catechol and ketene N,O-acetals.
Scheme 27: Reaction of N-acyliminium pools with olefins having a nucleophilic substituent.
Scheme 28: Synthesis of thiochromans using the cation-pool method.
Scheme 29: Electrochemical synthesis and diversity-oriented modification of 73.
Graphical Abstract
Scheme 1: Application of anodic oxidation to the generation of new carbon-carbon bonds [11].
Scheme 2: The influence of the amino protecting group on the “kinetic” and “thermodynamic” anodic methoxylati...
Scheme 3: Example of the application of the cation pool method [17].
Scheme 4: A thiophenyl electroauxiliary allows for regioselective anodic oxidation [32].
Scheme 5: A diastereoselective cation carbohydroxylation reaction and postulated intermediate 18 [18].
Scheme 6: A radical addition and electron transfer reaction of N-acyliminium ions generated electrosynthetica...
Scheme 7: Catalytic indirect anodic fluorodesulfurization reaction [37].
Figure 1: Schematic of a cation flow system and also shown is the electrochemical microflow reactor reported ...
Figure 2: Example of a parallel laminar flow set-up. Figure redrawn from reference [38].
Figure 3: A catch and release cation pool method [42].
Scheme 8: Micromixing effects on yield 92% vs 36% and ratio of alkylation products [43].
Figure 4: Schematic illustration of the anodic substitution reaction system using acoustic emulsification. Fi...
Scheme 9: Electrooxidation to prepare a chiral oxidation mediator and application to the kinetic resolution o...
Scheme 10: Electrooxidation reactions on 4-membered ring systems [68].
Figure 5: Example of a chiral auxiliary Shono-oxidation intermediate [69].
Scheme 11: An electrochemical multicomponent reaction where a carbon felt anode and platinum cathode were util...
Scheme 12: Preparation of dienes using the Shono oxidation [23].
Scheme 13: Combination of an electroauxiliary mediated anodic oxidation and RCM to afford spirocyclic compound...
Scheme 14: Total synthesis of (+)-myrtine (66) using an electrochemical approach [78].
Scheme 15: Total synthesis of (−)-A58365A (70) and (±)-A58365B (71) [79].
Scheme 16: Anodic oxidation used in the preparation of the poison frog alkaloid 195C [80].
Scheme 17: Preparation of iminosugars using an electrochemical approach [81].
Scheme 18: The electrosynthetic preparation of α-L-fucosidase inhibitors [84,85].
Scheme 19: Enantioselective synthesis of the anaesthetic ropivacaine 85 [71].
Scheme 20: The preparation of synthetically challenging aza-nucleosides employing an electrochemical step [88].
Scheme 21: Synthesis of a bridged tricyclic diproline analogue 93 that induces α-helix conformation into linea...
Scheme 22: Synthesis of (i) a peptidomimetic and (ii) a functionalised peptide from silyl electroauxiliary pre...
Scheme 23: Examples of Phe7–Phe8 mimics prepared using an electrochemical approach [93].
Scheme 24: Preparation of arginine mimics employing an electrooxidation step [96].
Scheme 25: Preparation of chiral cyclic amino acids [20].
Scheme 26: Two-step preparation of Nazlinine 117 using Shono flow electrochemistry [101].
Graphical Abstract
Figure 1: Two synthetic approaches toward the peripherally functionalized dendronized polystyrenes (blue dott...
Figure 2: Preparation of the dendrimer having peripheral bromo groups and their conversion to diarylamino gro...
Figure 3: Preparation of dendronized polystyrenes having peripheral diarylamino groups.
Figure 4: MALDI–TOF MS analysis of the dendronized polystyrene with peripheral bromo groups.
Figure 5: Cyclic voltammograms of dendronized polystyrene 9 (black line), model compound 10 (blue line), and ...
Graphical Abstract
Scheme 1: Anodic fluorination of sulfides having an electron-withdrawing group.
Scheme 2: Anodic fluorination of dithioacetals.
Figure 1: Dependency of fluorinated product selectivity on a series of fluoride salts (a) Et3N·nHF (n = 3–5) ...
Scheme 3: Plausible reaction mechanism for anodic fluorination of 1b, 1d, and 1f.
Scheme 4: Mechanism for suppression of the elimination of HF (deprotonation) and preferable desulfurization o...
Graphical Abstract
Scheme 1: Synthesis of glycoconjugates from different cholesteryl donors.
Figure 1: Cyclic voltammograms registered in 0.2 M tetrabutylammonium tetrafluoroborate (TBABF4) in dichlorom...
Scheme 2: Electrochemical reaction of 3α,5α-cyclocholestan-6β-yl ethers 6a–h with 1,2:3,4-di-O-isopropylidene...
Scheme 3: Plausible mechanism of isomerization.
Graphical Abstract
Scheme 1: Cobalt-catalysed 1,4-hydrovinylation.
Scheme 2: Electrochemical selenoalkoxylation of 2.
Scheme 3: Electrochemical iodoalkoxylation of 2.
Graphical Abstract
Figure 1: Expected coupling products from one-electron oxidation (left) and one-electron reduction (right) of...
Scheme 1: Chemical conversion of (±)-2 into E-5 and E-8.
Graphical Abstract
Scheme 1: Synthesis of halohydrins and epoxides through β-haloalkoxysulfonium ions generated by the reaction ...
Scheme 2: Proposed reaction mechanisms for the syntheses of bromohydrin 5a-Br and epoxide 6a.
Scheme 3: Mechanistic study using 18O-DMSO.
Graphical Abstract
Scheme 1: Electrochemical recycling of a chemical oxidant.
Figure 1: a) Electrolysis setup with a “suitcase” photovoltaic device. b) Electrolysis with a very simple, co...
Scheme 2: Examples of solar-driven direct electrochemical oxidations.
Scheme 3: Overoxidation of dithioketal.
Scheme 4: Examples of solar-driven, indirect electrochemical oxidations.
Scheme 5: Solar-driven synthesis of C-glycosides.
Scheme 6: Solar-driven oxidative condensation.
Scheme 7: Solar-driven oxidative cyclization with a second nucleophile.
Graphical Abstract
Scheme 1: Structural features of 8-substituted menthylamines 1.
Scheme 2: Synthetic strategies to menthylamines.
Scheme 3: Stereoselective synthesis of 8-substituted (1R,3R,4S)-menthylamines.
Scheme 4: Influence of the cathode system onto the stereoselectivity of the reduction of (1R,4S)-menthone oxi...
Scheme 5: Preparation of 8-substituted (1R)-menthones 6 and the corresponding oximes 7.
Scheme 6: Influence of cathode material on the preparation of (1R,3R,4S)-menthylamine 8a.
Scheme 7: Protection of the oxime functionality in 7c due to the sterically demanding diphenyl moiety in 8-po...
Scheme 8: Separation of the diastereomeric 8-substituted menthylamines by crystallization of their hydrochlor...
Graphical Abstract
Scheme 1: Polymer constitutions of the electropolymerized films.
Figure 1: Cyclic voltammograms in 0.1 M NBu4PF6/MeCN (A) and vis–NIR spectra (B) of electropolymerized films ...
Figure 2: A: Raman spectra of electrodeposited films of the homopolymer P3T and PEDOT, PEDOT/P3T-blend, a sim...
Figure 3: A: Modification of the copolymer films P(EDOT-N3-co-3T) with 1-hexyne and alkyne sulfonate with [Cu...
Figure 4: Cyclic voltammograms of films deposited under potentiostatic control on gold-coated glass substrate...
Figure 5: Water contact angle (CA) of the films of P(EDOT-N3-co-3T) (left), P(EDOT-clickHex-co-3T)-1:1 (middl...
Graphical Abstract
Figure 1: a, b) Cyclic voltammograms of 0.1 M EDOT in [EMMIM]Tf2N at 100 mV s−1. 10 cycles are shown: a) Pt(1...
Figure 2: Cyclic voltammograms of PEDOT on Pt(111) (black line), Pt(100) (red line), Pt(110) (blue line) in [...
Figure 3: a) Cyclic voltammograms of PEDOT on Pt(111) in [EMMIM]Tf2N. The total charge densities used for the...
Figure 4: Chronoamperometry of PEDOT films synthesized on platinum single crystals in [EMMIM]Tf2N. The total ...
Figure 5: AFM images of PEDOT thin films synthesized on a) Pt(111), b) Pt(100) and c) Pt(110) with a charge d...
Figure 6: In situ FTIR spectra of a PEDOT thin film synthesized with a charge density of 0.6 mC cm−2 on Pt(11...
Figure 7: a) In situ FTIR spectra of a PEDOT thin film synthesized with a charge density of 0.6 mC cm−2 on Pt...
Graphical Abstract
Figure 1: Preferential sites of cholesterol electrooxidation.
Scheme 1: Functionalization of the cholesterol side chain.
Scheme 2: Oxidation of cholestane-3β,5α,6β-triol triacetate (3) with the Gif system.
Scheme 3: Electrochemical oxidation of cholesteryl acetate (1a) with dioxygen and iron–picolinate complexes.
Scheme 4: Electrochemical chlorination of cholesterol catalyzed by FeCl3.
Scheme 5: Electrochemical chlorination of Δ5-steroids.
Scheme 6: Electrochemical bromination of Δ5-steroids in different solvents.
Scheme 7: Direct electrochemical acetoxylation of cholesterol at the allylic position.
Scheme 8: Direct anodic oxidation of cholesterol in dichloromethane.
Scheme 9: A plausible mechanism of the electrochemical oxidation of cholesterol in dichloromethane.
Scheme 10: The electrochemical formation of glycosides and glycoconjugates.
Scheme 11: Efficient electrochemical oxidation of cholesterol to cholesta-4,6-dien-3-one (24).
Graphical Abstract
Scheme 1: Direct electrochemical degradation of lignin into low molecular weight phenolic compounds.
Figure 1: Crude product composition after electrochemical treatment of lignin at Ni-based electrodes by gasch...
Figure 2: Influence of the current density onto the yield of 1 using Ni or Stellite 21 anodes.
Figure 3: Influence of the current density on the yield of 1 using different geometries of anodic materials.
Figure 4: Influence of the reaction temperature onto anodic degradation of lignin using stainless steel elect...
Figure 5: Influence of the applied current onto the yield of 1 by electrochemical degradation of lignin using...
Figure 6: Amount of vanillin (1) removed by adsorption in a batch process at different strongly basic anion e...
Figure 7: Different attractive interactions between ion exchange resin and the vanillate anion.
Figure 8: Recovery of vanillin (1) by adsorption from lignin containing reaction solutions after electrochemi...
Figure 9: Adsorption of vanillin (1) on anion exchange resins and size exclusion of lignin particles by appli...
Graphical Abstract
Scheme 1: Proposed mechanisms via pathways (I) to (III) for the cathodic hydrodimerization of olefins with el...
Scheme 2: Cathodic reduction of nitroalkene 1 to hydrodimer 2 and oxime 5.
Scheme 3: Preparation of the 1-aryl-2-nitroalkenes 1, 4, 8–15.
Scheme 4: Reduction potentials (Ep,c in Volt) of nitroolefins. Conditions: amalgamated gold wire, v = 0.1 V/s...
Figure 1: (a) CV of 15; v = 0.1 V/s, (b) CV of 15; v = 10 V/s.
Scheme 5: Hydrodimerization of nitroalkene 14 and 15.
Scheme 6: (a) Intramolecular hydrocoupling of dinitrodiene 16 and (b) hydrodimerization of 1-nitrocyclohexene...
Scheme 7: Possible stereoisomers and their mirror images for the hydrodimers 2 and 18–23; R and S are the con...
Figure 2: 1H NMR spectrum of 18b (without aromatic H); below experimental spectrum, above: simulated signals ...