Abstract
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 SN2 reaction as a key step instead of the hitherto considered carbene pathway.
Highlights
Organophosphorus zwitterions are one of the most important but elusive intermediates for carbon–carbon bond formation in synthetic chemistry and biology
Dicarbonyl compounds, in which a carbene intermediate has been proposed to be formed from Kukhtin–Ramirez adduct without definitive evidence[10,11,12]
The mechanistic studies disclosed a rational pathway for forming βoxo-phosphorus ylide, which is different from hitherto considered carbene pathway, as supported both experimentally and theoretically
Summary
Organophosphorus zwitterions are one of the most important but elusive intermediates for carbon–carbon bond formation in synthetic chemistry and biology. We report isolation and crystallographic characterization of phosha-Michael adduct (1-phosphonium-5-oxabetaine) and β-oxo-phosphorus ylide embedded in a conjugated macrocyclic orifice on fullerene C60. The reaction of 1 with the smallest alkyl phosphine (PMe3) was examined in odichlorobenzene-d4 (ODCB-d4) at room temperature.
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