N. S. Zefirov

Photochemical Synthesis of Phosphinolines from Phosphonium−Iodonium Ylides

We describe three different series of experiments which were undertaken to test our hypothesis that during irradiation of phosphonium-iodonium ylides (1a, 1b) an electrophilic carbene is generated. By opposing the assumed intermediate to monosubstituted alkynes, we observed in the case of electron-rich substituents at the triple bond a domination of a 1,3-dipolar cycloaddition of the intermediate with the triple bond to yield furans. In the case of electron poorer substituents, the formation of phosphinolines prevails. A second series of experiments was carried out with mixed ylides in which one phenyl ring at the triarylphosphonium group was replaced by a thienyl group. In this case, we observe only an intramolecular reaction with the thienyl ring to yield the phosphinolines 21-23. In a third test, we replaced in the mixed ylides 1a, 1b the COR group by a CN substituent. This modification leads to phosphinolines only and avoids a 1,3-dipolar cycloaddition.

Hetaryl-Substituted Phosphonium-Iodonium Ylides in Synthesis of Heterocycles

A series of hitherto unknown hetaryl-substituted (in phosphonium part) phosphonium-iodonium ylides were synthesized. The reaction of these mixed phosphonium-iodonium ylides with acetylenes opens a way to new furyl annelated phosphinolines or unusually substituted phosphininofurans.

Photocyclization of a mixed phosphonium-iodonium ylide with phenylacetylene: A formal kinetic approach to the mechanistic study

The recently discovered photoheterocyclization of a mixture of mixed phosphonium-iodonium ylides and acetylene compounds to give λ5-phosphinoline, a new phosphorus-containing heterocycle, occurs with self-acceleration and an induction period at relatively high concentrations of the reactants. The reaction was found to be catalyzed by the acid formed during photolysis. We developed a spectrophotometric method to study the kinetics of photocyclization between phenylacetylene and a phosphonium-iodonium ylide in the presence of trifluoroacetic acid and studied how the yield of target λ5-phosphinoline and kinetic parameters of the reaction, such as the induction period and maximum rate of product formation, depend on the initial concentrations of the starting compounds and catalyst. It was shown that the addition of the acid has no effect on the critical character of the dependence of the reaction on the concentration of the starting compound: the reaction proceeds only at an ylide concentration of >0.02 mol/L in a microheterogeneous suspension and the self-accelerating character of λ5-phosphinoline formation is preserved. The optimum reagent ratios maximizing the yield of the target product were determined. The acid was found to play a dual role: it catalyzes the reaction only at concentrations not higher than the initial ylide concentration. At higher acid concentrations, no formation of λ5-phosphinoline was observed.