KCS

Hypervalent iodine compounds, which enable to transfer electrophilic groups such as trifluoromethyl, aryl, amine, halogen and other groups to substrates have been studied in abundance.¹ However, synthesis and reactivity of imidazolium sulfuranes containing hypervalent sulfur with bromine, chloride or cyanide group was reported recently by the Alcarazo group.² The cyanide group was further transferred to other molecules by C-H bond activation. With the importance of hypervalent sulfurane, we have been exploring imidazolium difluorosulfuranes containing hypervalent sulfur with fluorine. By oxidation of N-heterocyclic carbene (NHC) thioureas with xenon difluoride, we successfully synthesized the imidazolium diflurosulfuranes and it is the first example of stabilization of highly reactive sulfur difluoride. It was characterized by NMR spectroscopy and X-ray crystallography. Their fluorine atom transfer reactivity includes fluorination of carboxylic acid to afford corresponding carbonyl fluoride. Although it was found that fluorination capability of the difluoro(imidazolium)sulfuranes is very limited unlike other deoxyfluorinating sulfur-based reagents, synthetic methods and structural characterization of NHC-SF₂ will be added to another important example of carbenes’ unique reactivity. Furthermore, synthesis of thiourea dimers by trimethylsilyl trifluoromethanesulfonate will be presented. Reference (1) Merritt, E.; Olofsson, B. Angew. Chem., Int. Ed. 2009, 48, 9052−9070. (2) Talavera, G.; Peña, J.; Alcarazo, M. J. Am. Chem. Soc. 2015, 137, 8704−8707.