Michael Forrest E, Duncan Andrew P, Sweeney Zachary K, Bergman Robert G
Department of Chemistry and Center for New Directions in Organic Synthesis, University of California at Berkeley, Berkeley, California 94720, USA.
J Am Chem Soc. 2003 Jun 18;125(24):7184-5. doi: 10.1021/ja0348389.
The zirconium-mediated stereoinversion of allenes has been investigated by studying the stereochemical behavior of metallacycles derived from [2 + 2] cycloaddition of enantioenriched allenes with chiral and achiral imidozirconocene complexes. Relative rates of metallacycle racemization were measured by circular dichroism, and intermediates in the selective stereoinversion of diphenylallene with a chiral imidozirconium complex were observed by NMR spectroscopy. Metallacycles derived from dialkylallenes are proposed to racemize via reversible beta-hydride elimination. Stereoinversion of diarylallene-derived metallacycles proceeds much more slowly and is thought to proceed through an eta4-azatrimethylenemethane transition state.
通过研究对映体富集的丙二烯与手性和非手性亚胺锆茂配合物进行[2 + 2]环加成反应生成的金属环化物的立体化学行为，对锆介导的丙二烯立体反转进行了研究。通过圆二色性测量金属环化物消旋化的相对速率，并通过核磁共振光谱观察二苯基丙二烯与手性亚胺锆配合物选择性立体反转过程中的中间体。由二烷基丙二烯生成的金属环化物被认为是通过可逆的β-氢消除进行消旋化。由二芳基丙二烯生成的金属环化物的立体反转进行得要慢得多，并且被认为是通过η4-氮杂三亚甲基甲烷过渡态进行的。
