The Role of the Counterion and of Silicon Chelation in the Selective Mono(trifluoromethylation) of Tartaric Acid Derived 1,4‐Diketones

Abstract

The addition of trifluoromethyl(trimethyl)silane (TFMTMS) to tartaric acid derived aromatic 1,4-diketones was reported to be highly stereoselective but also chemoselective towards a monoaddition product. This chemoselectivity remained unexplained. Complementary experiments and monitoring of the reaction by electrospray ionization mass spectrometry (ESI-MS) show that: i) the countercation (tetrabutylammonium (TBA(+)) or Cs(+)) associated to the initiator and the charged intermediates in the chain reaction plays a crucial role and ii) in the case of a tetrabutylammonium salt initiator, the second addition on the preformed monoadduct does occur but the resulting bis(trifluoromethyl)carbinolate is unable to evolve through the chain-transfer process and it exhibits an intramolecular Si-O interaction.

TEFDDOLs (α,α,α′,α′-Tetrakis(perfluoroaryl/alkyl)-2,2′-dimethyl-1,3-dioxolane-4,5-dimethanols): Highly Fluorinated Chiral H-Bond Donors and Brønsted Acids with Distinct H-Bonding Patterns and Supramolecular Architectures

“…When the acid chloride 7 was treated with increasing amounts of Ruppert’s reagent 6 and tetramethyl­ammonium fluoride at −50 °C in DME, significant conversion was observed beginning from ca. 4 equiv of reagent and fluoride used.…”

cis-Dihydroxylated α-Trifluoromethylated N,O-Acetal from l-Tartaric Acid: Synthesis of Tetrasubstituted Stereocenter via Diastereoselective Pictet-Spengler Cyclization of N-Acyliminium Ions

“…A few years ago, in the course of our studies, a control experiment highlighted that trifluoromethyltrimethylsilane in the presence of fluoride ion can undergo nucleophilic trifluoromethylation of bis-Weinreb amide derived from l -tartaric acid to give the corresponding mono-trifluoromethylated silylated hemiaminal. , As this functional group can be easily transformed into trifluoromethyl ketones, we studied this reaction on bis-Weinreb tartramide 1 , protected with an acetonide group, in order to gain access to the corresponding mono-trifluoromethyl ketone. Our investigations are summarized in Table .…”