Generation and reactions of thiocarbonyl S-(2,2,2-trifluoroethanides). Synthesis of trifluoromethylated 1,3-dithiolanes, thiiranes and alkenes

Abstract

The ‘in situ’ generated 1,1,1-trifluorodiazoethane reacts with thioketones as C=S dipolarophiles in a two-phase system (DCM/H$_2$O) at room temperature to yield trifluoromethylated 2,5-dihydro-1,3,4-thiadiazoles. Whereas stable crystalline products were obtained with cyclobutanethiones, the reaction with aromatic and heteroaromatic thioketones occured with spontaneous elimination of nitrogen. The formation of sterically crowded 4,4,5,5-tetrahetaryl-1,3-dithiolanes indicates that thiocarbonyl S-methanides are formed immediately and entered formal [3+2]-cycloaddition as diradical species with the starting thioketone. A protocol for the preparation of 3,3,3-trifluoropropene derivatives starting from corresponding thioketones and 1,1,1-trifluorodiazoethane is also presented.