Piperidine hydrogen fluoride

Chloromethoxy-1,2,2 2-tetrafluoroethane is converted by triethylammonium fluoride or piperidine hydrogen fluoride to fluoromethoxy 1 2,2,2-tetra-fluoroethane in greater than 60% yield Piperidine hydrogen fluoride or butyl-ammonium fluoride can convert methoxy-l-chloro-2,2,2-trifluoroethane to methoxy-1,2,2,2-tetrafluoroethane in 80% yield [79]... 

Although controlled substitution with molecular fluorine is difficult to attain, noteworthy is the recent success in perfluorinating both saturated and unsaturated heterocycles by electrolysis in anhydrous hydrogen fluoride. Cf. T. C. Simmons and F. W. Hoffmann, J. Am. Chem. Soc. 79, 3429 (1957), for the preparation of undecafluoropiperidine (from piperidine). The latter compound can be converted into pentafluoropyridine by passing it over an iron contact at 600° [R. E. Banks, A. E. Ginsberg, and R. N. Haszeldine, J. Chem. Soc. p. 1740 (1961)]. 

The active fluorinating agent of the mixture is 2, while 3 alone docs not fluorinate alcohols however, 3 is converted into 2 by addition of the hydrogen fluoride which is liberated by reaction of 2 with an alcohol and thus is also consumed during the reaction. The use of dibutylamine and piperidine instead of diethylamine has also been described by Ishikawa. but there is no difference in the reactivity of the products as fluorinating reagents. 

Cleavage and neutralization reagents trifluoroacetic acid (TFA), liquid hydrogen fluoride (HF) , A,A-diisopropylethylamine (DIEA), and piperidine (Fluka, Buchs, Switzerland or SDS, Peypin, France). 

The strong leaving group character of the 9-fluorenylmethyl (Fm) group, which derives from the aromaticity effect of a base-induced proton abstraction to form the dibenzocyclo-pentadienyl anion, is exploited in the 5-(9-fluorenylmethyl) groupf to obtain a cysteine derivative fully stable even to hydrogen fluoride, but cleavable under relatively weak basic conditions such as piperidine (10-50%) or DBU (2%) in DMF (Scheme 13) [154,155] qijjg S-protection is thus compatible with the Boc/Bzl chemistry and fully or-... 

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