Two Routes of Heterocyclization in the Reaction Between Benzoyl Phosphonium–Iodonium Ylide and Terminal Alkynes

ABSTRACT Currently the interest to the synthesis of phosphacycles increases due to the possibility of their application as functional materials for organic electronics, imaging, and analysis in biological systems. λ 5 ‐Phosphinolines with six‐membered phosphacycles can be easily synthesized in the reaction between mixed phosphonium–iodonium ylides and alkynes. In addition to λ 5 ‐phosphinolines substituted furan derivatives are formed for some carbonyl mixed ylide‒terminal alkyne compositions. Herein, a mechanistic study of the reaction between benzoyl phosphonium–iodonium ylide with a series of terminal alkynes is presented. The study combines in situ 31 P NMR spectroscopy, ESI‐MS of intermediate products, and computational chemistry. Furan derivatives are formed in a radical pair generated as a result of SET to ylide from alkynes with the ionization potentials lower than a critical value. CIDNP effect is registered in this case by 31 P NMR spectroscopy. λ 5 ‐Phosphinolines are formed in two parallel reactions: the minority in the radical pair and the majority in multistep reaction with participation of intermediate radicals giving dimers in the recombination reaction and subsequent transformations of these dimers.