Anodic thiocyanation of mono- and disubstituted aromatic compounds

A low-cost electrochemical thio- and selenocyanation strategy for electron-rich arenes under catalyst- and oxidant-free conditions

“…(Scheme 1a) Despite their efficiencies, these approaches suffered from many drawbacks and limitations: harsh oxidizing experimental procedures, the use of stoichiometric oxidants and the bad impact of heavy-metal wastes. Recently photocatalysis 13,14 and electrolysis [15][16][17] have been proved to be eco-friendly alternative methods for oxidative aromatic thiocyanation (Scheme 1b and c). Nevertheless, the costly photocatalyst or supporting electrolyte is required and the substrate scope is still narrow in these approaches.…”

A Two‐step Anodic Thiocyanation of Alkenes in Formic Acid

“…Presumably, such a modified procedure avoids an initial protonation of alkenes and consequent follow‐up reactions that can take place prior to their reaction with (SCN) 2 . Also it should be commented that the yields of obtained products are poor to moderate probably due to the weak elecrophilicity of (SCN) 2 (or [SCN] + ), as was previously evident in the case of anodic thiocayanation of aromatic derivatives by this weak electron‐donating group . It is noteworthy that the formation of a single major α‐thiocyanate‐β‐formate product in all cases described in Scheme is indicative of an isomer‐selective process because the alternative isothiocyanation isomers were not detected at all or only in minute amounts ( vide infra ).…”

“…Scheme describes a mechanistic framework involving an initial electrogeneration of thiocyanogen by anodic oxidation of thiocyanate anion that undergoes hydrogen bonding by the solvent formic acid, and – as a consequence – polarization of the S−S bond. Previously it was found that acidic conditions are essential for promoting this reaction. Then a concerted (or non‐concerted) electrophilic attack by the electron‐deficient sulfur moiety of the polarized cyanogen on the alkene could take place, possibly to generate a cyano‐sulphonium ion (or an ‘open′ carbocation) intermediate.…”

“…The two‐step electrochemical thiocyanation of alkenes in formic acid has been found to be highly selective towards formation of α‐thiocyano‐β‐formato adducts as the major products, but in moderate yields at best. Apparently the weak electrophilic nature of [SCN] + or (SCN) 2 that was demonstrated before could be accounted for this observation. The reaction is isomer ‐selective because only small (or trace) amounts of the isothiocyanato isomer were observed.…”

A Brief on Thiocyanation of N-Activated Arenes and N-Bearing Heteroaromatic Compounds

“…Generation of this dimer is a symbol of electrophilic (polar) mechanism. The electrochemical thiocyanation also defined by thiocyanogen formation 65 . Karade 42 reported that PhI(OAc) 2 (DIB) undergoes a ligandexchange by the initial nucleophilic attack of thiocyanate ion which will form an intermediate 67 Radical mechanism of thiocyanation The redox potential of oxone and indole were estimated to be +0.325 v and -1.050 v, yet NH 4 SCN exhibited no redox potential.…”