Organophosphorus Compounds, 112 . Lewis Acid Mediated Spirocyclotrimerization of Kinetically Stabilized Phosphaalkynes – Key Step for the Selective Generation and Trapping of Triphospha Dewar Benzenes

In the presence of Lewis acidic derivatives of group 13 elements, phosphaalkynes 7 undergo spirocyclotrimerization with incorporation of the corresponding Lewis acids to form 10a–f . Scope and limitations of this novel cyclooligomerization process are examined. Starting from the spirocyclotrimer 10a reaction with the Lewis base dimethyl sulfoxide, we have in hand for the first time a method for the selective generation of two isomeric triphospha Dewar benzene derivatives ( 18, 19 ). Both can be trapped efficiently by further reaction with the phosphaalkyne to furnish the two novel phosphaalkyne cyclotetramers 20 and 21 , both still possessing a phosphorus–carbon double bond. In the case of 21 , further functionalization of the phosphaalkene unit is possible by [3 + 2] cycloaddition with a nitrile oxide (→ 23 ).