フッ素による反応の活性化と制御
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概要
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Fluorine has remarkable electronic effects and leaving-group ability as fluoride ion. Paying particular attention to the use of these properties in organic synthesis, we discuss the preparation of gemdifluoroolefins and their synthetic applications. <I>gem</I>-Difluoroolefins with a wide 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 <I>gem</I>-difluorovinylboranes 4, and (ii) a variety of their direct functionalizations <I>via gem</I>-difluorovinylcoppers 5. This methodology provides a useful synthetic route to unsymmetrically disubstituted difluoroolefins <I>via</I> the introduction of <I>difluorovinylidene</I> unit (CF<SUB>2</SUB>=C). The obtained difluoroolefins readily undergo addition-elimination, cycloaddition-elimination, and cationic cyclization-elimination processes leading to new synthetic reactions. Regiocontrolled syntheses of fluorinated heterocycles, hetero Diels-Alder reactions, fluorine directed Nazarov cyclizations, Friedel-Crafts cyclizations, and tandem cyclizations in their combination are achieved to construct highly functionalized and/or fused ring systems. Throughout these reactions, fluorine substituent functions as an activator of the substrates and a controller over the reaction pathways.
- 社団法人 有機合成化学協会の論文
- 1996-08-01