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

An efficient and straightforward synthetic method for constructing trifluoromethyl 2H-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.