Asymmetric Fluorination of Enolates with Nonracemic N-Fluoro-2,10-Camphorsultams

Abstract

The asymmetric "electrophilic" fluorination of tertiary enolates by nonracemic N-fluoro-2,10-camphorsultams 3 affords quaternary α-fluoro carbonyl compounds in modest yield and ee. The highest asymmetric induction was observed for the fluorination of the sodium enolate of 2-methyl-1-tetralone (8a) by (-)-N-fluoro-2,10-(3,3-dichlorocamphorsultam) (3b) to give (S)-(+)-2-fluoro-2-methyl-1-tetralone (9a) in 70% ee. The absolute configuration was established by X-ray crystallography of the corresponding diastereomeric β-hydroxy sulfoximine prepared from (±)-9a and the Johnson reagent. The asymmetric induction exhibited by 3 is opposite to that of the closely related enolate hydroxylation reagents nonracemic (camphorylsulfonyl)oxaziridines 4. The N-fluoro sultams 3 were prepared by fluorination (10% F2/N2) of the corresponding sultams 5.