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À propos de : Electrophilic Fluorinating Reagent Mediated Synthesis ofFluorinated α-Keto Ethers, Benzil, and6,6‘-Dialkoxy-2,2‘-bipyridines        

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  • Electrophilic Fluorinating Reagent Mediated Synthesis ofFluorinated α-Keto Ethers, Benzil, and6,6‘-Dialkoxy-2,2‘-bipyridines
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  • Interactions of various fluorinated and nonfluorinated alcohols with trans-stilbene in the presenceof electrophilic reagents were studied. Under neat conditions, reactions of trans-stilbene (1) withfluorinated alcohols, RfOH (Rf = CF3CH2-, CFH2CH2-, CF3CF2CH2-, CF2H(CF2)3CH2-, (CF3)2CH-,(CF3)3C- (2a−f) in the presence of an electrophilic reagent, 1-(chloromethyl)-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor) or N,N-difluoro-2,2‘-bipyridinium bis(tetrafluoroborate) (MEC-31), gave α-keto ethers (3a−f) and benzil (4) in good to moderate yields. α-Ketoether and benzil formation was very much dependent on the reaction time, the degree of fluorinationof the alcohols, and whether a solvent such as CH3CN, DMF or DMA was utilized. In solution,α-keto ethers and benzil did not form. Interestingly, under neat conditions, nonfluorinated alcohols,ROH (R = CH3-, CH3CH2-, CH3CH2CH2-, CH3CH2CH2CH2-, CH3CH2CH2CH2CH2CH2-) (5g−k) didnot react with trans-stilbene in the presence of MEC-31 but gave 6,6‘-dialkoxy-2,2‘-bipyridines (6g−k), regioselectively, in excellent isolated yields. On the other hand, fluorinated alcohols did notreact with MEC-31. Reaction of MEC-31 with an excess of diethylene glycol (7) gave the bipyridinederivative (8) in 88% isolated yield. Reaction of 8 either with diethylaminosulfur trifluoride (DAST)or bis(2-methoxyethyl)aminosulfur trifluoride (Deoxofluor) readily produced the correspondingdifluoro derivative (9) in 85% isolated yield. All new compounds have been characterized byspectroscopic and elemental analysis.
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