Fluorination based on addition of molecular fluorine to conjugated enones

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Introduction of fluorine atoms in specific site of molecules is very important task from both chemical and pharmaceutical points of view. Though molecular fluorine is the most economical as the electrophilic fluorinating reagent, it is normally regarded as being too reactive for site-specific fluorination. We studied efficient fluorination of organic molecules based on addition of molecular fluorine to conjugated enones. We found that 4-methoxy- or 4-chloro- 2-pyrones are selectively fluorinated at the 3- or 5-position by molecular fluorine at a low temperature. We also found that fluorination of α-hydroxymethylene carbonyl compounds affords a-fluoro carbonyl compounds in high yields. By this fluorination method, 3-fluoro-2-quinolones are also synthesized. 3-Fluoro-2-quinolones are alternatively synthesized cyclization of α-fluoroacetoasetanilides obtained by fluorination of acetoasetanilides with molecular fluorine. Reaction of diketene with molecular fluorine followed by treatment of the resulting fluoride with anilines produced γ-fluoroacetoasetanilides, which on cyclization afforded 4-fluoromethyl- 2-quinolones.