Unequivocal S_RN1 Route of Vinyl Halides with a Multitude of Competing Pathways:  Reactivity and Structure of the Vinyl Radical Intermediate

Abstract

Unambiguous examples of the vinylic S(RN)1 reaction initiated by a single-electron transfer from an electron-donor anion (Y(-)) to a suitable VyX substrate, and proceeding through a vinyl radical (Vy(*)()) intermediate, are described. Competition by alternative substitution routes is extensive, but through a systematic modification of the structure of the substrate, unequivocal examples of the vinylic S(RN)1 route are documented. The geometry of the Vy(*)() and kinetic parameters for H-abstraction and coupling with Y(-) are reported.

Synthesis of cyclohexadienylstannanes – Novel example of vinylic SRN1 mechanism: A theoretical and experimental study

“…Nevertheless, under irradiation in the same time period, the substitution products 1-trimethylstannyl-4-methyl-1,3-cyclohexadiene (3b) and 1-trimethylstannyl-6-methyl-1,3-cyclohexadiene (3c) were obtained in 44% and 46% yields, respectively (entries 3 and 5). It should be mentioned that both photostimulated reactions were largely inhibited by addition of p-dinitrobenzene (p-DNB) (10%), a well-known radical anion trap and inhibitor of the S RN 1 propagation cycle (entries 4 and 6) [3,10]. These results clearly indicate that these substrates also react with 1 by the S RN 1 mechanism.…”

“…It should be mentioned that not only the substrate structure but also the nature of the anion are essential factors for the prevalence of an S RN 1 vinylic route over ionic pathways and it is necessary an appropriate combination of both [3][4][5][6]. Thus, only vinyl systems supporting, at least, a phenyl group afforded the substitution product by S RN 1.…”

“…(1)) [10]. Stimulation by UV light or by Fe 2+ has been recently applied in vinylic S RN 1 reactions [3][4][5]. It should be noted that the coupling with the nucleophile (Eq.…”

Strategies in Synthetic Radical Organic Chemistry. Recent Advances on Cyclization and SRN1 Reactions

“…Nucleophilic addition to a rearranged radical from a 1,3-hydrogen shift is possible when the vinyl halides have γ-hydrogen [142]. For discussion of a different mechanism on vinylic substitutions, see [143].…”

“…67) [148a]. It is known that some vinyl radicals intermediates are configurationally unstable radicals, and from an (E)-or (Z)-isomer, the S RN 1 products yield a mixture of (E)-and (Z)-isomers [143]. The reaction of 74a and 74b with Me 3 Snions affords only one isomer with the same configuration of the starting vinyl chlorides, which indicates a slower inversion of these vinyl radical intermediates than the coupling reaction.…”