Radicals in Annulation of Mixed Benzoyl Phosphonium‐Iodonium Ylide and Acetylenes Explored by EPR‐ST Spectroscopy

Annulation of mixed phosponium‐iodonium ylides and compounds with a triple bond is an interesting example of the synthesis of different types of heterocycles in one‐pot, metal‐free systems at ambient temperature to give substituted oxazoles in the reaction with nitriles and phosphorus‐containing λ5‐phosphinolines and substituted furans in the reaction with acetylenes. The iodonium group in the mixed ylides provides the possibility for the radical initiation of the reaction. Herein, we investigated the generation of primary radicals and the formation of phosphorus‐containing products in the photolysis of benzoyl phosphonium‐iodonium ylide alone and in its reaction with acetylenes in DCM by EPR and 31P NMR spectroscopies with the use of two most popular spin traps, PBN and DMPO. The results allowed us to account the crucial difference in the registered radicals in the two systems for the aggregation of the components, with ylide molecules forming a core and acetylene molecules being a shell of the aggregates in DCM, in which the annulation occurs. The peculiarities of the reactions of PBN and DMPO with generated radicals are discussed.