Exploitation of an unprecedented silica-promoted acetylene–allene rearrangement for the preparation of C,C-diacetylenic phosphaalkenes

C,C-Diacetylenic phosphaalkenes have been obtained from a 1-chloro-3-ethynyl-1,2-allene which becomes accessible from a silica-promoted rearrangement of a 3-chloropenta-1,4-diyne; oxidative acetylene homo-coupling of the phosphadiethynyl-ethene is described for the first time and affords a dimeric, cross-conjugated product which features a largely decreased HOMO-LUMO gap compared to all-carbon-based reference compounds.