Enantioselective fluorinating agents, (R)- and (S)-,N-fluoro-3-tert-butyl-7-nitro-3,4-dihydro-2H-benzo[e][1,2]thiazine 1,1-dioxides (BNBT-F, 2) are readily prepared in 3 steps from racemic 3-tert-butyl-7-nitro-3,4-dihydro-2H-benzo[e][1,2]thiazine 1,1-dioxides (5) via optical resolution and fluorination. These agents make accessible both enantiomers of optically active quaternary alpha-fluoro carbonyl compounds in modest to high enantioselectivities. X-ray crystallographic analysis of chiral 2 reveals a unique structure wherein the nitrogen atom is highly pyramidalized and fluorine occupies an axial position.
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Shibata et al. (2000) studied this question.