Acetyl Hypofluorite, a New Moderating Carrier of Elemental Flourine and Its Use in Fluorination of 1,3-Dicarbonyl Derivatives

Elemental fluorine and most of the fluoroxy reagents do not react efficiently or cleanly with 1,3-dicarbonyl derivatives or with their corresponding metal enolates even at -75 °C. It has been found that a suspension of sodium acetate in CFC1₃ or in CFCl₃-AcOH, when treated with elemental fluorine, forms a new electrophilic fluorinating reagent, CH₃COOF (1), which reacts with substrates without further isolation or purification. This reagent is milder than F₂, CF₃OF, or CF₃COOF and reacts successfully where the other reagents fail. When 1 reacts with 1,3-dicarbonyl compounds, the main product is the 1,3-dioxo-2-fluoro derivative in reasonable yields. When, however, the corresponding sodium enolates were treated with 1, the yields of the monofluoro derivatives were considerably higher. In the case of 1,3-dicarbonyl derivatives with low enol content, only the sodium enolates react with 1 to produce good to very good yields of the corresponding 2-monofluoro derivatives. Thus 1 can be considered as a moderating carrier of the highly reactive F₂.