Activation of Saturated Fluorocarbons to Synthesize Spirobiindanes, Monofluoroalkenes, and Indane Derivatives.

ABSTRACT: Fluorinated organic compounds are produced in abundance by the pharmaceutical and agrochemical industry, making such compounds attractive as building blocks for further functionalization. Unfortunately, activation of C(sp3)-F bond in saturated fluorocarbons, especially for aliphatic gem-difluoroalkanes, remains challenging. Here we describe the selective activation of inert C(sp3)-F bonds catalyzed by B(C6F5)3. In hexafluoro-2-propanol (HFIP), chemically robust aliphatic gem-difluorides are converted in high yields to the corresponding substituted 2,2',3,3'-tetrahydro-1,1'-spirobiindenes via a B(C6F5)3-catalyzed intramolecular cascade Friedel-Crafts cyclization, not requiring a silicon-based trapping reagent. However, in the absence of a hydrogen-bonding donor solvent such as HFIP, the aliphatic gem-difluorides preferentially engage in a defluorination/elimination process that provides monofluorinated alkenes in good yields. Furthermore, a series of substituted 1-alkyl-2,3-dihydro-1H-indenes was obtained in high yield from the B(C6F5)3-catalyzed defluorinative cyclization of aliphatic secondary monofluorides in HFIP. The protocol could inspire development of a new class of main-group Lewis acid-catalyzed C(sp3)-F bond activation in general unactivated fluorocarbons.

SUBMITTER: Wang J 

PROVIDER: S-EPMC6612000 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature