Selective Substitution of Aliphatic Remote Tertiary Hydrogens by Fluorine

Substitution of saturated hydrogens is a very desirable but difficult task. Elemental fluorine under suitable conditions, including a polar solvent and low temperatures, acts as an electrophile strong enough to react with saturated tertiary CH bonds of various aliphatic compounds. The regioselectivity and the readiness of the hydrogen substitution by fluorine are functions of the p-orbital contribution to the bond, in agreement with the electrophilic nature of the reaction. Apart from branched paraffins, oxygen- as well as nitrogen-containing aliphatic molecules can participate in the reaction, and various protecting groups and their effectiveness were examined. The role of the electron-withdrawing group on the selectivity was also evaluated.