Synthesis of an Isolable Diphosphaisobenzene and a Stable Cyclic Allene with Six Ring Atoms

Highly selectively as a single isomer, the diphosphaisobenzene 2 is furnished from the reaction of the phosphatriafulvene 1 with a phosphaalkyne. In addition to NMR and IR spectroscopy, the formation of the six-membered ring allene 3 (X-ray structure analysis), which is stable at room temperature, by chemo-, regio-, and diastereoselective cycloaddition (CA) of trimethylbenzonitrile oxide to the P−C double bond provided proof of its structure.