F makes the break: The carbon–fluorine single bond is quite strong, thus making aliphatic CF bond scission unusually challenging. A new methodology utilizing YbI3 leads to the conversion of a CF bond into a CI bond, and is compatible with various functional groups. The reaction is exceptionally selective towards alkyl fluorides and proceeds under mild conditions.
Sm(HMDS)(2) in n-hexane mediates fast cleavage of primary, secondary and tertiary alkyl fluorides in good to excellent yields. In n-hexane Sm(HMDS)(2) exhibits uniquely enhanced reductive ability towards the C-F bond compared to when using THF as solvent.
A facile iodination protocol of unactivated alkyl fluorides using catalytic amounts of YbI3(THF)3 in the presence of iodotrimethylsilane as a stoichiometric fluoride trapping agent is presented. (1)H NMR spectroscopy demonstrates a two-step catalytic cycle where TMSI regenerates active YbI3(THF)3. Finally, the catalytic reaction is extended into a one-pot procedure to demonstrate a potential application of the method. Overall, the findings present a distinct strategy for C-F bond transformations in the presence of catalytic YbI3(THF)3.
A procedure for chemoselectively manipulating the strong aliphatic C-F bond with direct transformation into a C-N bond under mild conditions is reported. The activation and subsequent substitution of primary alkyl fluorides is mediated by La[N(SiMe3)2]3, and results in high to excellent yields of tertiary amines. The methodology displays high selectivity towards the C(sp(3))-F bond, and a variety of secondary amines are applicable as nucleophiles. Mechanistic investigations reveal a reaction that is first order with respect to [La[N(SiMe3)2]3], [R(1)R(2)NH], and [alkyl fluoride], and a 6-membered cyclic transition state is proposed. In addition, (1)H NMR spectroscopy shows that La[N(SiMe3)2]3 is the active species involved in the substitution and that protonolysis of the amine, yielding La[NR(1)R(2)]3, lowers the reactivity.
Aliphatic 1,2-aminofluorides undergo extremely fast substitution reactions under the influence of lanthanum tris(hexamethyldisilazide). The substitution proceeds via an in situ generated aziridinium ion intermediate, which subsequently undergoes ring opening by addition of a nucleophile, yielding various β-substituted amines.
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