Configurational Lability at Tetrahedral Phosphorus: syn/anti ‐Isomerization of a P‐Stereogenic Phosphiranium Cation by Intramolecular Epimerization at Phosphorus
Configurational Lability at Tetrahedral Phosphorus: syn/anti ‐Isomerization of a P‐Stereogenic Phosphiranium Cation by Intramolecular Epimerization at Phosphorus
复制标题
四面体磷的构型不稳定性：通过磷分子内差向异构化实现 P-立体磷鎓阳离子的顺/反异构化
DOI：
10.1002/anie.202110753
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Rheingold, Arnold L.
中科院分区：
文献类型：
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作者：
Tipker, Ryan M.;Muldoon, Jake A.;Pham, Daniel H.;Varga, Balazs R.;Hughes, Russell P.;Glueck, David S.;Balaich, Gary J.;Rheingold, Arnold L.
四面体主族化合物通常构型稳定，但手性磷鎓阳离子顺式或反式[Mes*P（Me）CH 2CHPh][OTf]（Mes*= 2，4，6-（t-Bu）3C 6 H2）的P-差向异构化在60 °C的温和条件下在CD 2Cl 2中发生，导致异构化，得到顺式富集的平衡混合物。用过量的[NBu 4][Δ-TRISPHAT]（Δ-TRISPHAT=Δ-P（o-C6 Cl 4 O2）3）进行离子交换，然后在二氧化硅上进行色谱法除去[NBu 4][OTf]，得到顺式和反式-[Mes*P（Me）CH 2CHPh][Δ-TRISPHAT]双[NBu 4][Δ-TRISPHAT]的混合物。NMR谱表明，异构化过程中，在P位发生差向异构化，在C位保留。DFT计算与涉及P-C裂解以产生超共轭稳定的碳正离子、由P孤对电子与相邻β-碳正离子的σ-相互作用促进的锥体反转以及在P处构型反转的环闭合的机制一致。
Tetrahedral main‐group compounds are normally configurationally stable, but P‐epimerization of the chiral phosphiranium cations syn‐ or anti‐[Mes*P(Me)CH2CHPh][OTf] (Mes*=2,4,6‐(t‐Bu)3C6H2) occurred under mild conditions at 60 °C in CD2Cl2, resulting in isomerization to give a syn‐enriched equilibrium mixture. Ion exchange with excess [NBu4][Δ‐TRISPHAT] (Δ‐TRISPHAT=Δ‐P(o‐C6Cl4O2)3) followed by chromatography on silica removed [NBu4][OTf] and gave mixtures of syn‐ and anti‐[Mes*P(Me)CH2CHPh][Δ‐TRISPHAT]⋅x[NBu4][Δ‐TRISPHAT]. NMR spectroscopy showed that isomerization proceeded with epimerization at P and retention at C. DFT calculations are consistent with a mechanism involving P‐C cleavage to yield a hyperconjugation‐stabilized carbocation, pyramidal inversion promoted by σ‐interaction of the P lone pair with the neighboring β‐carbocation, and ring closure with inversion of configuration at P.