Thioamide derivatives of cannabinoids. A study of the influence of the thioamide function on regiochemistry in the synthesis of thioamide cannabinoids from 2,4-dihydroxybenzothioamides

Several thiocarbamoyl derivatives of cannabinoids were obtained in the collidine-catalysed condensation of 2,4-dihydroxybenzothioamides with citral and citronellal. The thioamide function was found to change the regioselective preferences of the reaction as compared with the known cannabinoid syntheses from hydroxyacetophenones. The experimental results and theoretical (FMO theory) considerations made it possible to advance the reaction mechanism. Convenient methods were developed for the synthesis of the starting 2,4-dihydroxybenzothioamides from resorcinol and isothiocyanates in the presence of the boron trifluoride/acetic acid 1:2 complex or aluminum chloride in nitromethane.