Enantioselective Rhodium-Catalyzed [2 + 2 + 2] Cycloadditions of Terminal Alkynes and Alkenyl Isocyanates: Mechanistic Insights Lead to a Unified Model that Rationalizes Product Selectivity
作者:Derek M. Dalton、Kevin M. Oberg、Robert T. Yu、Ernest E. Lee、Stéphane Perreault、Mark Emil Oinen、Melissa L. Pease、Guillaume Malik、Tomislav Rovis
DOI:10.1021/ja905065j
日期:2009.11.4
describes the development and scope of the asymmetric rhodium-catalyzed [2 + 2 + 2] cycloaddition of terminal alkynes and alkenyl isocyanates leading to the formation of indolizidine and quinolizidine scaffolds. The use of phosphoramidite ligands proved crucial for avoiding competitive terminal alkyne dimerization. Both aliphatic and aromatic terminal alkynes participate well, with product selectivity a function
Perfluorinated Taddol phosphoramidite as an L,Z-ligand on Rh(i) and Co(−i): evidence for bidentate coordination via metal–C6F5 interaction
作者:Derek M. Dalton、Anthony K. Rappé、Tomislav Rovis
DOI:10.1039/c3sc50271f
日期:——
Perfluorinated Taddol-based phosphoramidite, CKphos, is a highly selective ligand for formation of vinylogous amide cycloadducts in the Rh(I) catalyzed [2 + 2 + 2] cycloaddition of alkenyl isocyanates and alkynes. CKphos overrides substrate bias of product selectivity in the cycloaddition, providing indolizidinones in excellent yields and enantioselectivities. The excellent selectivities are attributed to a shortened RhâP bond and coordination of one C6F5 to rhodium via a Z-type interaction, making the phosphoramidite a bidentate L,Z-ligand on rhodium. Evidence for the shortened RhâP and C6F5 coordination is provided by X-ray, NMR and DFT computational analyses. Additionally, an anionic cobalt complex with CKphos was synthesized and two CoâC6F5 interactions are seen. The Rh(C2H4)Cl·CKphos catalyst in the [2 + 2 + 2] cycloaddition of alkenyl isocyanates and alkynes represents a rare example of metalâC6F5 Z-type interaction affecting selectivity in transition metal catalysis.
Total Synthesis of Indolizidine Alkaloid (−)-209D: Overriding Substrate Bias in the Asymmetric Rhodium-Catalyzed [2+2+2] Cycloaddition
作者:Robert T. Yu、Ernest E. Lee、Guillaume Malik、Tomislav Rovis
DOI:10.1002/anie.200805455
日期:2009.3.16
an efficient [2+2+2] cycloaddition between terminal alkyl alkynes and alkenyl isocyanates (see scheme). The cycloaddition proceeds through a CO migration pathway, and facilitates a rapid four‐step asymmetric synthesis of indolizidine (−)‐209D.
对!你让我问好:在铑上使用手性联苯基亚磷酰胺配体提供了末端烷基炔烃和烯基异氰酸酯之间有效的 [2+2+2] 环加成(参见方案)。环加成通过 CO 迁移途径进行,并促进吲哚里西啶 (-)-209D 的快速四步不对称合成。