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

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.