Department of Chemistry, Stanford University, Stanford, California 94305, USA.
J Am Chem Soc. 2010 Jul 7;132(26):9206-18. doi: 10.1021/ja103663h.
Complementary methods for the transition-metal-catalyzed enyne cycloisomerizations of cyclic olefins have been developed. By using distinct ruthenium and palladium catalysts, decalins and 7,6-bicycles can be obtained with dichotomous stereochemical outcomes. The change in mechanism that accompanies the change in metal affords trans-fused 1,4-dienes with ruthenium and their cis-fused diastereomers under palladium catalysis. In the reactions under ruthenium catalysis, a coordinating group is required and acts to direct the metal to the same side of the carbocycle, resulting in the observed trans diastereoselectivity. Subtle changes in the carbocyclic substrate led to the discovery of a heretofore-unobserved mechanistic pathway, providing bicyclic cycloisomerization products under palladium catalysis and tricyclic products under ruthenium catalysis in N,N-dimethylacetamide (DMA). The differential effect of DMA supports a mechanism in which the coordination requirements of the two paths differ, allowing for the reaction to be shuttled through the metallacycle pathway (generating tricyclic products) when DMA is used as a solvent.
已经开发出了用于过渡金属催化的环烯烃烯炔环异构化的补充方法。通过使用不同的钌和钯催化剂，可以获得具有二分立体化学结果的 decalins 和 7,6-双环。伴随金属变化的机制变化在钯催化下提供顺式稠合的非对映异构体和反式稠合的 1,4-二烯。在钌催化的反应中，需要一个配位基团，它的作用是将金属引导到碳环的同一侧，从而导致观察到的反式非对映选择性。碳环底物的细微变化导致发现了一种迄今未观察到的机制途径，在 N,N-二甲基乙酰胺 (DMA) 中提供了双环环异构化产物和在钌催化下的三环产物。DMA 的差异效应支持了两种途径的配位要求不同的机制，允许反应在使用 DMA 作为溶剂时通过金属环化途径（生成三环产物）进行穿梭。
