A Synthetic and Mechanistic Investigation of the Chromium Tricarbonyl-Mediated Masamune–Bergman Cyclization. Direct Observation of a Ground-State Triplet<i>p</i>-Benzyne Biradical
作者:Kai E. O. Ylijoki、Séverine Lavy、Angelika Fretzen、E. Peter Kündig、Théo Berclaz、Gérald Bernardinelli、Céline Besnard
DOI:10.1021/om300427j
日期:2012.8.13
bond formation from an η6-enediyne complex is the lowest-energy path, forming a metal-bound p-benzyne biradical. NMR spectroscopy suggests that enediyne alkene coordination occurs in preference to alkyne coordination, forming a THF-stabilized olefin intermediate; subsequent alkyne coordination leads to cyclization. While biradical quenching occurs rapidly and primarily via the singlet biradical, the
报道了一种新的室温下三羰基铬介导的苯二炔环芳香化反应。发生反应以在存在环状和非环状烯二炔[CR(CO)3(η 6 -萘)]和两个配位溶剂和氢原子源,提供铬-芳烃在合理产率和良好的diastereocontrol络合物。反应的机理已通过DFT计算和光谱方法进行了探讨。这些研究表明由该η直接C1-C6键形成6 -enediyne络合物具有最低能量的路径,形成金属结合的p-双苄基。NMR光谱表明,烯炔炔的配位优先于炔配位,形成了THF稳定的烯烃中间体。随后的炔烃配位导致环化。虽然双自由基淬灭迅速且主要通过单线态双自由基发生,但三重态双自由基可通过EPR光谱检测到,表明系统间交叉为三重态基态。