title: 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.
authors.affiliation: Institut de Chimie Moléculaire de Reims, Université de Reims Champagne-Ardenne- CNRS, UFR Sciences, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Harakat
authors.forename: Fabien
authors.initials: F
authors.lastname: Massicot
authors.forename: Jean
authors.initials: J
authors.lastname: Nonnenmacher
authors.forename: Fabienne
authors.initials: F
authors.lastname: Grellepois
authors.forename: Charles
authors.initials: C
authors.lastname: Portella