Polar Effects in Free-Radical Reactions. The Paradox of Reduction of Alkyl Iodides and Reductive Alkylation of Alkenes by Strong Oxidants (t-BuOOH, Pb(OAc)₄)

Abstract

Alkanes are directly iodinated by perfluoroalkyl iodides by a free-radical chain process initiated by t-BuOOH in acetic acid solution. The initially formed iodoalkanes are reduced back to alkanes by excess t-BuOOH; the rate constant for hydrogen abstraction from t-BuOOH by a primary alkyl radical has been roughly evaluated to be ∼104 M-1 s-1. Two new procedures for the reductive alkylation of alkenes by t-BuOOH and Pb(OAc)4 are reported. The importance of the polar effects and the rate constants of the key elementary steps involved in these processes is discussed.

Metal‐Free, Selective Alkane Functionalizations

“…29). [44,144] Polar effects, i.e., the polarization in the transition structures for the hydrogen abstractions of type TS3 (Scheme 1) are largely responsible for the observed selectivities. [147] The 38:28 selectivity of the iodination of adamantane with n-C 4 F 9 I/t-BuOOH is 17 : 1, [144] which is, however, slightly lower than for the BrCCl 3 /t-BuOOt-Bu bromination (27 : 1) [140] where Cl 3 C is the abstracting radical.…”

“…[43] It may be concluded that radical chemistry still is the preparatively most useful approach for alkane functiuonalizations. As the selectivities of radical reactions (™radical∫ path, TS3, Scheme 1) often are traced back to polar effects (especially with electrophilic radicals), [44] one may argue that the same is true for electrophilic alkane activations where the selectivities are also controlled by charge (electron) transfer. In other words, alkane activations with different electron-deficient reagents fit into the same mechanistic regime.…”

Electrochemical Study of Lead Species in Acetate Media:In Situ Formation of Alkyl and Lead Species on CarbonPaste Electrode

“…± Pb(II) is oxidized and as there is an excess of acetate ions in the solution at pH 6.65, the product resulting from this oxidation, Pb(IV), can form the Pb(Ac) 4 species [6]. ± The second hypothesis is complex, as it considers two simultaneous oxidation processes [1,6].…”

“…± The second hypothesis is complex, as it considers two simultaneous oxidation processes [1,6]. The ®rst one would be that acetate ion undergoes oxidation to form the alkyl radicals (Eqs.…”

“…In these studies, it was concluded that the methyl radicals have a short life span and are stabilized when adsorbed on the surface of the electrode [5]. On the other hand, Minisci et al [6] presented a new methodology to form alkyl radicals from Pb(Ac) 4 . The synthesis path suggested by these scientists is: PbAc 4 3 PbAc 3 CH 3 CO 2 1e À 4 PbAc 3 3 PbAc 2 2 CH 3 CO 2 1e À 5…”