Modular synthesis of fluorinated 2 H -thiophenes via [4 + 1] cyclization of enaminothiones.

An efficient and straightforward synthetic method for constructing trifluoromethyl 2 H -thiophenes through [4 + 1] cycloaddition of enaminothiones with trifluoromethyl N -tosylhydrazones has been disclosed. The cycloaddition platforms were found to be compatible with a broad substrate scope and to show high regio- and stereo-selectivities under very mild reaction conditions such as room temperature, neutral media and low loading of catalyst.