Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704 Poznań, Poland.
J Org Chem. 2020 Mar 20;85(6):4312-4323. doi: 10.1021/acs.joc.9b03506. Epub 2020 Feb 26.
Boranephosphonate diesters react with heteroaromatic and certain tertiary amines in the presence of an oxidant (I) to afford the boron-modified phosphodiester analogues containing a P-B-N structural motif. Our multinuclear P and B NMR spectroscopy studies lend support for a two-step mechanism involving generation of a λ-boranephosphonate intermediate that immediately coordinates an amine in the solvent cage, leading to -pyridinium or -ammonium boranephosphonate betaine derivatives. We found that the type of the solvent used (e.g., dichloromethane vs acetonitrile) significantly affected the course of the reaction, resulting in either formation of boron-modified derivatives or loss of the boron group with a subsequent oxidation of the phosphorus atom. In aprotic, electron-donating, polar solvents., e.g., acetonitrile (ACN) and tetrahydrofuran (THF), a λ-boranephosphonate intermediate can also coordinate solvent molecules forming P-B-ACN or P-B-THF complexes that may influence the type of the products formed.
硼酸膦二酯与杂芳族和某些叔胺在氧化剂 (I) 的存在下反应，生成含有 P-B-N 结构基序的硼修饰的磷酸二酯类似物。我们的多核 P 和 B NMR 光谱研究支持涉及生成 λ-硼酸膦中间体的两步机制，该中间体立即在溶剂笼中与胺配位，导致形成 -吡啶鎓或 -铵硼酸膦甜菜碱衍生物。我们发现所使用的溶剂类型（例如二氯甲烷与乙腈）对反应过程有显著影响，导致形成硼修饰的衍生物或硼基团的损失，随后磷原子被氧化。在非质子、供电子、极性溶剂中，例如乙腈 (ACN) 和四氢呋喃 (THF)，λ-硼酸膦中间体也可以与溶剂分子配位，形成 P-B-ACN 或 P-B-THF 配合物，这可能会影响形成的产物类型。
