Trifluorothioacetic acid

Tetramethyldiphosphine adds photochemically to vinyl and vinylidene fluoride to give the bisphosphines Me2P-CH2-CXF-PMe2 (X H or F), and tetrakis(trifluoromethyl)diphosphine similarly adds thermally (at 50 Q or photochemically to the same olefins and to tetrafluoroethylene. Free-radical additions of trifluorothioacetic acid to the olefins CHF CF2, CHarCFa, and CH2 CHF (see p. 138) have been described only one-way addition was observed. Bis(trifluoromethyl) disulphide adds to fluoro-olefins with u.v. Irradiation in Pyrex or silica apparatus in the vapour phase to yield a variety of 1 1 and telomeric adducts. The products are consistent with the following mechanism ... 

Trifluorothioacetic acid undergoes free-radical and nucleophilic addition to olefins and ketones respectively, paralleling in many ways the well-known reactions of thioacetic acid. Novel uses of thiolesters in synthesis... 

Thus other trifluoroacetylation reagents have been investigated. iS -Ethyl trifluorothioacetate [Ethanethioic acid, trifluoro-, S-ethyl ester]6 has none of the above disadvantages. It does require, however, weakly basic conditions (pH 8-9) and an aqueous medium. Phenyl... 

Wolfrom and Conigliaro4 found that S-ethyl trifluorothioacetate selectively acylates the amino group of 2-amino-2-desoxy-D-glucose (methanolic sodium methoxide, 24 hours, room temperature, 73% yield). They used this protective group in the synthesis of purine nucleosides. The group was removed by means of methanolic ammonia. (Note that purine nucleosides are unstable to acid.)... 

---