Quick and easy acyl fluorides

Tetramethylammonium trifluoromethylthiolate, [N(CH₃)₄]SCF₃, is a mouthful to say, but the inexpensive, bench-stable, and easy-to-use salt has been impressing chemists over the past few years for its versatility in adding SCF3 groups to molecules and as a fluorinating reagent. For example, Franziska Schoenebeck and her group at RWTH Aachen University have shown that [N(CH₃)₄]SCF₃ has untapped potential as a fluorinated surrogate of thiophosgene (SCCl₂), using it to functionalize alcohols and amines. Going further, Schoenebeck’s group has now used the trifluoromethylthiolate salt to convert aromatic and aliphatic carboxylic acids to acyl fluorides, which themselves are useful reagents (Org. Lett. 2017, DOI: 10.1021/acs.orglett.7b02516). The appeal of using [N(CH₃)₄]SCF₃ to fluorinate carboxylic acids is its ability to replace specialized reagents derived from SF₄. Those reagents often are toxic and corrosive, require additives, and tend to have poor functional-group tolerance and selectivity leading to undesired by-products. The trifluoromethylthiolate salt, first reported years ago but little used until recently, does away with those problems. Schoenebeck says her team has had “quite a lot of interest” from industry and other academic groups about using [N(CH₃)₄]SCF₃, which could lead to efforts by her group to commercialize it.