Sulfuranes As Group-Transfer Reagents

Hypervalent aryl iodine compounds are popular reagents for their ability to transfer trifluoromethyl, alkynyl, cyano, and other electrophilic groups to a variety of nucleophilic organic molecules under mild reaction conditions. With that chemistry in mind, Garazi Talavera, Javier Peña, and Manuel Alcarazo of the Max Planck Institute for Coal Research, in Mülheim, Germany, found it surprising that no one seems to have extended the group-transfer concept to noniodine species. The team envisioned that imidazolium sulfuranes, which have a similar electronic structure to hypervalent iodine species, might be viable alternatives. The researchers designed the new sulfur-based reagents and have now shown that they are useful for cyanation and alkynylation reactions (J. Am. Chem. Soc. 2015, DOI: 10.1021/jacs.5b05287). They first halogenated known cyclic thioureas to make hypervalent sulfuranes. Treating the sulfuranes with trimethylsilyl cyanide or silver propiolate led to the desired imidazolium sulfurane cyanates and alkynes, respectively. The team then used the cyano version with amines to make cyanamides and for direct C–H cyanation of aromatics and used the alkynyl version for the alkynylation of thiols, amides, and ketoesters.