Photochemical Synthesis of Phosphinolines from Phosphonium−Iodonium Ylides

Abstract

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.

Furyl‐Substituted Mixed Phosphonium–Iodonium Ylides in the Synthesis of Annelated P‐Containing Heterocyclic Compounds

“…The structures of the phosphonium salts and mixed ylides were confirmed using NMR and IR spectroscopy, elemental analysis, and HRMS. 2 2-furyl 8e, 86 14e, 88 -CO-Ph 5-methyl-2-furyl 9c, 69 15c, 95 -COOMe 5-methyl-2-furyl 9d, 62 15d, 82 -CO-Ph 3-furyl…”

“…[2] Taking into account this analogy, we expected the formation of different products for 2-furyl-substituted ylides 14 compared to their 3-furyl-substituted counterparts 16.…”

“…Indeed, the heterocyclization reactions of different stabilized phosphonium-iodonium ylides with a variety of alkynes under pho- tochemical conditions give phosphinolines as the principal products. [2] The proposed mechanism of the heterocyclization involves cationic intermediates A and B. Intermediate B undergoes electrophilic aromatic substitution to give the final phosphinoline (i.e., 2).…”

“…Intermediate B undergoes electrophilic aromatic substitution to give the final phosphinoline (i.e., 2). [2] Taking into account the ease of electrophilic substitution for five-membered heterocyclic systems such as furan and thiophene, we studied mono-heterosubstituted phosphonium-iodonium ylides 3a and 3b in photochemical reactions with alkynes and obtained the corresponding phosphininofurans or phosphininothiophenes with structures 4a and 4b, respectively (Scheme 2). [3] Scheme 2.…”

Iodonium ylides in organic synthesis

“…Zefirov, Matveeva, and co-workers have demonstrated the utility of mixed phosphoniumiodonium ylides as reagents for the synthesis of various heterocyclic systems such as: substituted oxazoles, 92,111 phosphonium-substituted furans, 46 substituted phosphinolines, 46,91,93,94 and annelated phosphorus-containing heterocycles. [112][113][114][115] All these cycloadditions proceed under photochemical conditions.…”