Cycloaddition of CO2 and CS2 to a cyclic phosphazene

Structural changes in a 1,2?5-azaphosphole/nitrilimine cycloaddition

“…They show a reactivity considerably higher than that of acyclic, six-membered, or larger ring phosphazenes. The difference is best demonstrated by a variety of cycloaddition reactions of 1 and related compounds [1] and becomes visible in particular by the high stability of the cycloadducts of 1. The difference can be explained by geometrical considerations [2]: The fivemembered ring necessitates a relatively small endocyclic angle at phosphorus (98.5Њ for 1, Table 1 , the molecular structure is known from an Xray investigation, and the structural changes connected to the cycloaddition have been discussed [2].…”