Distinct advantage of the in situ generation of quaternary ammonium fluorides under phase-transfer conditions toward catalytic asymmetric synthesis.

[structure in text] Quaternary ammonium fluorides were found to be efficiently generated in situ from the corresponding ammonium hydrogensulfates by treatment with commercially available potassium fluoride dihydrate (KF.2H(2)O) in THF and directly used as a fluoride source for the generation of carbon nucleophiles from organosilicon compounds. This method can be successfully applied to the preparation of structurally well-defined, C(2)-symmetric chiral quaternary ammonium fluorides of type 1 (X = F), thereby allowing catalytic enantioselective Mukaiyama-type aldol reactions under mild conditions.