Diphosphaenones: beyond the phosphorus analogue of enones

Phosphaenones, like their carbon analogue enones (C[double bond, length as m-dash]C-C[double bond, length as m-dash]O), are promising building blocks for synthetic chemistry and materials science. However, in contrast to the α- and β-phosphaenones, structurally and spectroscopically well-defined diphosphaenones (DPEs) are rare. In this study, we disclose the isolation and spectroscopic characterization of N-heterocyclic vinyl (NHV) substituted acyclic DPEs 3a,b [NHV-P[double bond, length as m-dash]P-C(O)-NHV]. X-ray diffraction methods allowed determination of the structures, which show a central planar trans P[double bond, length as m-dash]P-C[double bond, length as m-dash]O configuration. Compound 3a behaves like classical enones and shows 1,4-addition across the P[double bond, length as m-dash]P-C[double bond, length as m-dash]O unit, which proceeds in a stepwise manner. In contrast, 3a exhibits also 1,2-addition across the P[double bond, length as m-dash]P but not the C[double bond, length as m-dash]O double bond, which differentiates it from enones.