The phosphorus based radical precursors N-ethylpiperidine hypophosphite (EPHP) and diethylphosphine oxide (DEPO) are efficient reagents for carrying out the formation of seven- and eight-membered rings. Esters and amides were successfully converted into the corresponding eight-membered lactones and seven- and eight-membered lactams in good to excellent yields.
Lang, S., Corr, M., Muir, N., Khan, T., Schonebeck, F., Murphy, J., Payne, A., & Williams, A. (2005). First organophosphorus radical-mediated cyclisations to afford medium-sized rings: eight-membered lactones and seven- and eight-membered lactams . Tetrahedron Letters, 46(23), 4027-4030. https://doi.org/10.1016/j.tetlet.2005.04.032