In order to perform selective fluorination using molecular fluorine, mechanistic studies using ab initio MO calculation were carried out. As a result, it was confirmed that both fluorine addition to ethylene and fluorine substitution of methane are electrophilic reactions. These studies suggested that bicyclo [2.2.1] hept-2-ene derivatives would be suitable fluorinating substrates because they have tertiary hydrogens with somewhat lower p-character than sp³ and a more activated double bond. As expected, addition of molecular fluorine to the bicyclo [2.2.1] hept-2-ene derivatives having electronegative substituents on the ethano bridge was found to give exo, exo-difluoro adducts selectively. The difluoro adducts derived from 2-azabicyclo [2.2. 1] kept-5-en-3-one or 7-oxabicyclo [2.2. 1] hept-2-ene derivatives were converted to the difluorinated carbocyclic nucleosides or ribofuranosides. Novel α-fluorination of alkyl phenyl sulfoxides by molecular fluorine was also developed and applied to the synthesis of cis-2-fluorocyclopropane-1-carboxylic acid and fluorine substituted 1-aminocyclopropane-l-carboxylic acid derivatives.