One-pot anodic thiocyanation and isothiocyanation of alkenes

The one-pot anodic thiocyanation and isothiocyanation of alkenes in both acidic two-phase (water-dichloromethane) and homogeneous one-phase (water-acetonitrile) media has been studied. Optimisation experiments on tetramethylethylene as a model alkene involved the use of different acids, anodes, current densities, charge consumption and electrolysis methods. In the two-phase medium mainly two addition products (in moderate yields) of SCN/NCS (major) and two SCN/SCN groups were formed. Other alkyl substituted alkenes also yielded similar addition products but those involving two SCN groups became the major ones. In addition, also allylic thiocyanato and isothiocyanato substitution products were observed, but in lower yields. Activated alkenes such as, styrene, indene and butylvinyl ether did not yield addition products, whereas 1,1-diphenylethylene and 2,3-dimethylfuran gave substitution products exclusively. Under homogeneous one-phase aqueous-acetonitrile medium the formation of SCN/OH adducts became prominent in all cases, including those of styrene and indene. Also they all afforded the corresponding SCN/SCN and SCN/NCS addition products. However 1,1-diphenylethylene gave a sole vinylic substitution product whereas 2,3-dimethylfuran did not react.