Allylsilanes in "Tin-free" Oximation, Alkenylation, and Allylation of Alkyl Halides

Tin‐free oximation, vinylation, and allylation of alkyl halides have been developed by using allylsilanes as di‐tin surrogates. Initiation of the radical process with a peroxide provides the silyl radical, which can a halogen from the corresponding alkyl halide. The resulting carbon‐centered radical then adds to various acceptors, including a sulfonyloxime, a vinylsulfone, and an allylsulfone, leading to formation of the desired products along with the corresponding allylsulfone resulting from the reaction of the PhSO2 radical with the allylsilane precursor. Better results were generally obtained with methallylsilane 1 b than with 1 a. This observation was rationalized by invoking the higher nucleophilicity of 1 b and the faster β‐fragmentation of the corresponding β‐silyl radical intermediate. Calculation of the energy barrier for the β‐fragmentation of a series of β‐silyl radicals at the DFT level supported this hypothesis. Finally, a second version of these oximation and vinylation reactions, based on the utilization of 3‐tris(trimethylsilyl)silylthiopropene, was devised, affording the desired oximes and olefins in reasonable yields. This strategy allowed the title reaction to be performed under milder conditions (AIBN, benzene, 80 °C), as a result of the easier β‐fragmentation of the CS bond as compared with the CSi bond. The supersilyl radical is generated through addition of a sulfonyl radical species onto readily available allylsilanes. This silyl radical is then used as a radical chain carrier in oximation, alkenylation, and allylation of alkyl halides (see scheme). This silicon group efficiently replaces tributyltin, which is generally used for such group transfer processes.