Alkyl fluorides dissolving metals

Alkyl fluorides are hard to reduce by any means, but may be reduced by dissolving metal reagents such as potassium in toluene in the presence of a crown ether119. 

ABSTRACT. Toluene radical anion, generated by dissolving potasssium metal in toluene by the assistance of dicyclohexano-18-crown-6, has been proved to be especially effective for reductive removal of fluorine atom from unactivated alkyl fluorides that resist common reduction conditions. Stereochemical and mechanistic aspects of the present method is discussed. In connection with the preparation of substrates the effect of dipolar aprotic solvents on the nucleophilic fluorination with potassium fluoride/dicyclohexano-18-crown-6 system was also examined, and sulfolane or N,N-dimethylformamide was shown to be a solvent of choice. 

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