Organophosphorus zwitterions are one of the most important but elusive intermediates for carbon–carbon bond formation in synthetic chemistry and biology. However, a lack of isolated examples due to their lability has hampered in-depth understanding of structures and their reaction mechanisms. In this study, we crystallographically reveal the solid-state structure of a phosha-Michael adduct engaged in a cage-opened C₆₀ skeleton, which is formed as a kinetic product. This compound exhibits dark brown colour in solution with an intense absorption band that extends to 1000 nm, reflecting intramolecular charge transfer transitions. From the 1,2-dicarbonyl moiety on the conjugated orifice, β-oxo-phosphorus ylide is formed as a thermodynamic product. The reaction mechanism that has long been disputed is examined by experimental and theoretical studies, showing a pathway which includes an S_N2 reaction as a key step instead of the hitherto considered carbene pathway.

有机磷两性离子是合成化学和生物学中碳-碳键形成最重要但难以捉摸的中间体之一。然而，由于它们的不稳定性而缺乏孤立的例子阻碍了对结构及其反应机制的深入理解。_{在这项研究中，我们通过晶体学揭示了参与开笼 C 60}的 phosha-Michael 加合物的固态结构骨架，它是作为动力学产物形成的。该化合物在溶液中呈深棕色，具有延伸至 1000 nm 的强吸收带，反映了分子内电荷转移跃迁。从共轭孔上的 1,2-二羰基部分，β-氧-磷叶立德形成为热力学产物。长期存在争议的反应机制通过实验和理论研究进行了检验，显示了一条包括 S _N 2 反应作为关键步骤的途径，而不是迄今认为的卡宾途径。