The stereoselective formation of quaternary carbon centers is one of the most challenging tasks in organic chemistry and can only be achieved using methods which employ some form of carbon ± carbon bond forming reaction. [1] One of the most straightforward methods for the formation of carbon ± carbon bonds is the alkylation of an enolate with an alkyl halide and, fluoride ions were 1 to 2 mm. The protonation constant of fluoride in water is: log K HF/F 3.15. NMR Measurements: 1 H NMR spectra were recorded on a Bruker AM500 spectrometer at 500 MHz. Binding constants were obtained by NMR titrations of L with fluoride from 25 measurements in D 2 O at pD 5.0 AE 0.1. Initial concentrations were [L] 0 2 mm and titrations were performed using aliquots from a 20 mm stock solution of NaF. A solution of the sodium salt of [2,2,3,3-D 4 ]-3-(trimethylsilyl)propionic acid (TPS) in D 2 O in a capillary tube was used as an external reference. The pD value was adjusted with a concentrated solution of TsOH and NaOD in D 2 O. All spectra were recorded at room temperature. The association constants K s were calculated by fitting f to d obs (consisting of several independent NMR signals) with a 1:1 association model using Sigma Plot software. Equations (1) and (2) were used, where L is the ligand and A À is the anion, and the error limit in K is less than 10 %:
The Job×s plot was performed by examining different concentration ratios of L and NaF in D 2 O at pD 5.0 AE 0.1, while maintaining the total concentration of the ligand plus NaF at 10 mm. The pD value was adjusted with a concentrated solution of TsOH and NaOD in D 2 O. NMR measurements were recorded at room temperature.