ヒドロシランの活性化を利用した芳香族トリフルオロメチル基の選択的変換

抄録

Organofluorines are of great importance in broad research fields including pharmaceutical sciences and materials chemistry. Despite the significance, it is not always easy to synthesize organofluorines due to limited synthetic methods. We recently developed a new approach for the preparation of organofluorines via single C-F transformations of benzotrifluorides triggered by hydride abstraction of the ortho-hydrosilyl group. Indeed, we found that single C-F allylation took place by the treatment of a mixture between benzotrifluorides having a diphenylsilyl group and allyltrimethylsilane with triphenylmethylium tetrafluoroborate in dichloromethane and 1,1,1,3,3,3-hexafluoro-2-propanol(HFIP)to provide difluoromethylenes bearing a fluorodiphenylsilyl group. The resulting fluorosilyl group successfully served in the C-Si transformations such as Hiyama cross-coupling. Then, we succeeded in the C-F thiolation of o-(hydrosilyl)benzotrifluorides catalyzed by Yb(OTf)₃ using trityl sulfides as an all-in-one reagent for generating a trityl cation and thiolate anions. Treatment of benzotrifluorides having a diphenylsilyl group with trityl chloride afforded diverse difluorobenzyl chlorides without Lewis acid catalysis. We also found that the hydride reduction of fluorosilyl group proceeded smoothly using lithium alminum hydride leaving the difluoromethylene group untouched. The resulting hydrosilyl group served in the further C-F transformations to furnish various highly functionalized benzyl fluorides. These C-F transformations allowed us to synthesize a wide range of novel organofluorines which are difficult to prepare by conventional methods.