Developing Catalytic Enantioselective Fluorination

Abstract

The background that led to the development ofthe first catalytic and enantioselective carbon-fluorine bond-forming reaction is presented. Two different approaches, i.e. the use of nucleophilic and electrophilic fluorinating agents, respectively, have been pursued. Well-defined RU(II) 16-electron systems of the type [RuF(PP)₂]+ (where PP is a chelating diphosphine), as well as analogous complexes containing tetradentate PNNP ligands, were found to catalyze the halogen exchange reaction of activated alkyl chlorides, bromides, and iodides in the presence of TIF as the fluorine source. Isolable crystalline [TiCl₂ (TADDOLato)] complexes are efficient catalysts in the enantioselective fluorination of 2-substituted 1,3-dicarbonyl compounds with Selectfluor^® (also called F-TEDA; 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis{tetrafluoroborate}). Levels of enantioselectivity up to 90% ee were obtained.