Danheiser成環反應
Danheiser成環反應（Danheiser annulation），又稱Danheiser TMS-環戊烯成環反應（Danheiser TMS-Cyclopentene annulation）[1][2][3][4][5][6]
α,β-不飽和酮與三烴基矽基（如三甲基矽基、三異丙基矽基）丙二烯在路易斯酸存在下發生反應，生成三烴基矽基環戊烯。
α,β-不飽和醛太活潑，反應會生成大量副產物；而α,β-不飽和酯則太不活潑，反應速度慢，產率低；環狀和開鏈的酮都可以用作反應底物。這個反應是同面反應，具有高度立體選擇性。
反應機理
路易斯酸四氯化鈦首先活化α,β-不飽和酮的羰基，得到烯丙位碳正離子中間體，然後被三烴基矽基丙二烯進攻得到乙烯基碳正離子中間體A；臨近的矽原子可以穩定乙烯基碳正離子（中間體B），或者可以發生1,2-重排反應得到中間體C；接下來鈦烯醇化物進攻中間體C的碳正離子就可以得到環戊烯。有時中間體A也會生成副產物D–F。
參見
參考資料
- ^ "TMS-Cyclopentene Annulation: A Regiocontrolled Approach to the Synthesis of Five-Membered Rings", R. L. Danheiser, D. J. Carini, and A. Basak, J. Am. Chem. Soc. 1981, 103, 1604.
- ^ "Scope and Stereochemical Course of the (Trimethylsilyl)cyclopentene Annulation", R. L. Danheiser, D. J. Carini, D. M. Fink, and A. Basak, Tetrahedron 1983, 39, 935.
- ^ "The Reaction of Allenysilanes with α,β-Unsaturated Acylsilanes: New Annulation Approaches to Five and Six-Membered Carbocyclic Compounds", R. L. Danheiser and D. M. Fink, Tetrahedron Lett. 1985, 26, 2513.
- ^ "A General [3+2] Annulation: cis-4-Exo-isopropenyl-1,9-dimethyl-8-(trimethylsilyl)bicyclo-[4.3.0]non-8-en-2-one", R. L. Danheiser, D. M. Fink, and Y. -M. Tsai, Organic Syntheses 1988, 66, 8.
- ^ "Organic Syntheses Based on Name Reactions", By Alfred Hassner and C. Stumer, Elsevier, p. 78, 2002
- ^ "Name Reactions: A Collection of Detailed Reaction Mechanisms", By Jie Jack Li, Springer, p. 102, 2003