FLUORINE AS ACTIVATOR AND CONTROLLER IN O RGANIC-SYNTHESIS

Fluorine has remarkable electronic effects and leaving-group ability a s fluoride, ion. Paying particular attention to the use of these prope rties in organic synthesis, we discuss the preparation of gem-difluoro olefins and their synthetic applications, gem-Difluoroolefins with a w ide range of substituents are synthesized from commercially available 2,2,2-trifluoroethyl p-toluenesulfonate (1), wherein the two processes are included: (i) a boron-mediated alkylation leading to gem-difluoro vinylboranes 4, and (ii) a variety of their direct functionalizations via gem-difluorovinylcoppers 5. This methodology provides a useful syn thetic route to unsymmetrically disubstituted difluoroolefins via the introduction of difluorovinylidene unit (CF2=C). The obtained difluoro olefins readily undergo addition-elimination, cycloaddition-eliminatio n, and cationic cyclization-elimination processes leading to new synth etic reactions. Regiocontrolled syntheses of fluorinated heterocycles, hetero Diels-Alder reactions, fluorine -directed Nazarov cyclizations , Friedel-Crafts cyclizations, and tandem cyclizations in their combin a tion are achieved to construct highly functionalized and/or fused ri ng systems. Throughout these reactions, fluorine substituent functions as an activator of the substrates and a controller over the reaction pathways.