Enantioselective Synthesis of Cyclic Enol Ethers and All-Carbon Quaternary Stereogenic Centers Through Catalytic Asymmetric Ring-Closing Metathesis

详细信息    查看全文

• 作者：Ai-Lan Lee ; Steven J. Malcolmson ; Alessandra Puglisi ; Richard R. Schrock ; and Amir H. Hoveyda
• 刊名：Journal of the American Chemical Society
• 出版年：2006
• 出版时间：April 19, 2006
• 年：2006
• 卷：128
• 期：15
• 页码：5153 - 5157
• 全文大小：145K
• 年卷期：v.128,no.15(April 19, 2006)
• ISSN：1520-5126

文摘

The first examples of catalytic asymmetric ring-closing metathesis (ARCM) reactions of enolethers are reported. To identify the most effective catalysts, various chiral Mo- and Ru-based catalystswere screened. Although chiral Ru catalysts (those that do not bear a phosphine ligand) promote ARCMin some cases, such transformations proceed in <10% ee. In contrast, Mo-based alkylidenes give rise toefficient ARCM and deliver the desired products in the optically enriched form. Thus, Mo-catalyzedenantioselective transformations allow access to various five- and six-membered cyclic enol ethers in upto 94% ee from readily available achiral starting materials. The first examples of catalytic ARCM that leadto the formation of all-carbon quaternary stereogenic centers are also disclosed. Mechanistic models thatoffer a plausible rationale for the identity of major enantiomers as well as the observed levels ofenantioselectivity are provided. Representative examples demonstrate that the enol ether moiety and theunreacted alkene of the ARCM products can be discriminated with excellent site selectivity (>98%).