Background: Thiocyanation of various compounds such as imidazopyridines, indoles, phenols, anilines, carbonyl compounds, enamines and etc is of great importance in organic synthesis because thiocyano compounds has the ability to be easily converted to other organosulfur compound groups such as sulfides, sulfonic acids, tunitriles, thiocarbamates and nitrilescarbamothioate, in addition, aryl thiocyano compounds are important intermediates in the production of dyes and medicines precursors. Thiocyanation of organic compounds is traditionally done by treatment of organic compounds with SCN+ synthon generated by reaction of a suitable oxidant with a thiocyanate mineral salts such as KSCN, NaSCN and NH4SCN. In this line, different powerful oxidizing agents such as H2O2, tert-butyl hydroperoxide (TBHP), Br2, Cl2, I2, NBS, NCS, NIS, HIO4, I2O5, H2IO6, o-iodoxybenzoicacid, tricholoroisocyanuric acid, DDQ, FeCl3, K2S2O8, CAN, SelectfluorTM , oxone and etc have been applied.
Aim: To the best of our knowledge, no method for thiocyanation of compounds using dimethyl sulfoxide as oxidant has been reported so far. Dimethyl sulfoxide is a stable, non-toxic, cheap and widely available chemical in laboratories and industry. Compared with many used oxidants, it is very mild and can tolerate many functional groups. These advantages convinced us to investigate a new method for thiocyanation of organic compounds using DMSO.
Methodology: To a mixture of an indole, phenol or aniline substrate (1.0 mmol), NH4SCN (1.5 mmol), and H2SO4 (1.5 mmol) in DMF (1 mL), was added DMSO (3.0 mmol for indoles and 1.5 mmol for other substrates). The mixture was stirred magnetically at 60 oC for anilines and 80 oC for other substrates until the starting organic substrate was completely consumed (5-15 min). Next, the reaction was stopped and after dilution with water (1 mL), the mixture was extracted with EtOAc (4×1 mL). The crude product was purified by chromatography on silica gel using a suitable mixtur