Primary radicals can be generated by photoinduced electron transfer (PET) from a suitable donor to different alkyl halides and dihalides. We report the reactivity of these radicals toward different carbanions like enolate anions of cyclohexenone (1), acetophenone (2), 2-acetylnaphthalene (3) and the anion of nitromethane (4).
Once the primary radicals are formed, two main pathways can be possible, the unimolecular cyclization to give the cyclopropane derivative and the halogen, pathway (a) in Scheme 1, or the coupling with the nucleophile ensuing SRN1 processes, pathway (b).1
Our results suggest that there is a competition between both pathways; the efficiency of the SRN1 reaction against pathway (a) (assumed as a termination step in a SRN1 process) depends on the nature of the halogen at carbon 3 from the radical center, and on the nucleophile employed. The rate constant for pathway (a) can be determined relative to the addition of anion 2 to the radical intermediate, whose rate constant has been established.2
References
1- Rossi, R.A., Pierini A.B., Peñéñory, A.B. Chem. Rev., 2003, 103, 71-167.
2-Argüello, J. E.; Peñéñory, A. B.; Rossi, R. A. J. Org. Chem. 2000, 65, 7175-82.
