3,5-Diphenyl-2-phosphafuran: Synthesis, Structure, and Thermally Reversible [4 + 2] Cycloaddition Chemistry

Abstract

Treatment of trans-chalcone with dibenzo-7-phospha­norborna­diene EtOPA (A = C14H10, anthracene), a source of ethoxy­phosphinidene, followed by formal elimination of ethanol yields 3,5-diphenyl-2-phosphafuran (DPF) in 43% yield. We show that the phosphadiene moiety of DPF is a potent diene in the Diels–Alder reaction and reacts with dienophiles dimethyl acetylenedicarboxylate (DPF·DMAD, 68%), norbornene (DPF·norbornene, 73%), and ethylene (DPF·C2H4, 80%) under ambient conditions. Mild heating of DPF·C2H4 results in the corresponding retro-Diels–Alder reaction, establishing DPF as a molecule that is able to reversibly bind ethylene.

Intramolecular Activation of Enones by Electrophilic Phosphinidene Complexes to Construct 2-Phosphafurans

“…Cummins and co-workers described a noncomplexed 4a through the Diels–Alder reaction of 3,5-diphenyl-2-phosphafuran 5a with ethylene . The observations described above and previous results of 2-phosphafuran , suggest that 3a was converted into 5a , accompanied by the elimination of ethylene. Subsequently, the [4+2] cycloaddition between in situ -generated 5a and ethylene provides 4a .…”

“…4a was structurally characterized by X-ray crystallography, and its molecular structure is shown in Scheme . Cummins and co-workers described a noncomplexed 4a through the Diels–Alder reaction of 3,5-diphenyl-2-phosphafuran 5a with ethylene . The observations described above and previous results of 2-phosphafuran , suggest that 3a was converted into 5a , accompanied by the elimination of ethylene.…”

Acetylene and Ethylene: Universal C2 Molecular Units in Cycloaddition Reactions

“…Reaction of 3,5-diphenyl-2-phosphafuran with ethylene. 151 Ethylne can also enter the hetero-Diels-Alder reaction with acyclic heteroatom-containing electron-deficient dienes. [4+2] Cycloaddition between 1,2-diaza-1,3-butadienes and ethylene was reported.…”

Dimerization and Cycloaddition Reactions of Transient Tri-tert-butylphosphacyclobutadiene Generated by Lewis Acid Induced Isomerization of Tri-tert-butylphosphatetrahedrane

“…This [4 + 2] cycloadduct exhibits a resonance centered at 8.3 ppm in the 31 P NMR spectrum. Note that examples of phosphorus-containing heterocycles that undergo [4 + 2] cycloaddition to ethylene under mild conditions are exceedingly rare . After triphenylborane was removed and a pentane solution of the crude reaction mixture was filtered through a plug of silica, compound 6 was isolated as a colorless oil in 74% yield.…”

“…Note that examples of phosphoruscontaining heterocycles that undergo [4 + 2] cycloaddition to ethylene under mild conditions are exceedingly rare. 34 After triphenylborane was removed and a pentane solution of the crude reaction mixture was filtered through a plug of silica, compound 6 was isolated as a colorless oil in 74% yield. The product is contaminated with a small amount of 4 and trace amounts of unidentified impurities.…”