The quest for unligated oxaphosphiranes with phosphorus in different coordination numbers.

After more than 160 years of oxirane (epoxide) chemistry, the first derivative of a phosphorus analogue, namely oxaphosphirane, has been synthesized. Reactions with borane sulfane, a peroxy compound and elemental sulfur, as well as tetra-chloro- ortho -benzoquinone (TOB) reveal a significant destabilization upon increasing the coordination number at phosphorus from σ 3 to σ 4 , thus somehow supporting previous reports on such fleeting species. Theoretical studies provide insight into ring strain energy, ring/ring interconversion and the oxidation pathways.