Department of Chemistry, University of Rochester, Rochester, New York 14627, USA.
J Am Chem Soc. 2012 Apr 11;134(14):6296-308. doi: 10.1021/ja211970p. Epub 2012 Apr 3.
Highly functionalized cyclopentenones can be generated by a chemoselective copper(II)-mediated Nazarov/Wagner-Meerwein rearrangement sequence of divinyl ketones. A detailed investigation of this sequence is described including a study of substrate scope and limitations. After the initial 4π electrocyclization, this reaction proceeds via two different sequential [1,2]-shifts, with selectivity that depends upon either migratory ability or the steric bulkiness of the substituents at C1 and C5. This methodology allows the creation of vicinal stereogenic centers, including adjacent quaternary centers. This sequence can also be achieved by using a catalytic amount of copper(II) in combination with NaBAr(4)(f), a weak Lewis acid. During the study of the scope of the reaction, a partial or complete E/Z isomerization of the enone moiety was observed in some cases prior to the cyclization, which resulted in a mixture of diastereomeric products. Use of a Cu(II)-bisoxazoline complex prevented the isomerization, allowing high diastereoselectivity to be obtained in all substrate types. In addition, the reaction sequence was studied by DFT computations at the UB3LYP/6-31G(d,p) level, which are consistent with the proposed sequences observed, including E/Z isomerizations and chemoselective Wagner-Meerwein shifts.
高度官能化的环戊烯酮可以通过二乙烯基酮的选择性铜(II)介导的 Nazarov/Wagner-Meerwein 重排序列来生成。详细描述了该序列的研究，包括底物范围和限制的研究。在初始的 4π 电环化后，该反应通过两个不同的顺序[1,2]-迁移进行，其选择性取决于 C1 和 C5 处取代基的迁移能力或空间位阻。该方法允许创建毗邻立体中心，包括相邻的季碳原子。通过使用催化量的铜(II)与弱路易斯酸 NaBAr(4)(f)的组合，也可以实现该序列。在研究反应范围的过程中，在一些情况下，在环化之前观察到烯酮部分的部分或完全 E/Z 异构化，导致非对映异构体产物的混合物。使用 Cu(II)-双恶唑啉配合物可以防止异构化，从而在所有底物类型中获得高非对映选择性。此外，通过 UB3LYP/6-31G(d,p)水平的 DFT 计算研究了反应序列，这与观察到的提议序列一致，包括 E/Z 异构化和选择性 Wagner-Meerwein 迁移。
