The metal-initiated cyclooligomerization of phospha-alkynes and its consequences [1]

1,3-Diphosphacyclobutadienes 4 are almost certainly intermediates in the co nversion by hexachloroethane of phosphaalkyne dimer complexes 3 to the tetr aphosphacubanes 5. We, now describe trapping reactions of 4, generated in t he same way, with phosphaalkyne 1 (-->9), ynamines 10 (-->13), and electron -poor alkynes 11 (-->14). The cyclooligomerization of 1 initiated by t-Bu-N =VCl3. DME (15) leads to the azatetraphosphaquadricyclanes 20 while the rea ction with the stronger Lewis acid t-Bu-N=VCl3 (21) furnishes the 1,3,5-tri phosphabenzenes 23 in high selectivity.