A Convenient General Access to Methyl 2-Chloro-2-cyclopropylidenacetates, Reactive Michael Acceptors and Cycloaddends
作者:Thomas Liese、Stephan Teichmann、Armin de Meijere
DOI:10.1055/s-1988-27456
日期:——
The reaction of 1-chloro-1-(trichlorovinyl)cyclopropanes 1 with potassium hydroxide/methanol or sodium methoxide/methanol yields trimethyl 2-chloro-2-cyclopropylidenorthoacetates 7, which can be quantitatively converted to the corresponding esters 8 by acid treatment. The methyl 2-chloro-2-cyclopropylidenacetates 8 are highly reactive Michael acceptors, which readily undergo 1,4-addition with soft nucleophiles such as thiophenolate, secondary amines, azide, cyanide, and lithium dimethylcuprate. The reactivity, however, is influenced by substituents on the cyclopropane ring, the unsubstituted compound 8j reacting 86 times faster with thiophenolate than the tetramethyl derivative 8a, which in turn is 2.5 times as reactive as methyl 3,3-dimethylacrylate 16. Compound 8j is a reasonably reactive cycloaddend in both [2+2]- and [2+4]-cycloadditions.
1-chloro-1-(三氯乙烯基)环丙烷 1 与氢氧化钾/甲醇或甲氧基钠/甲醇反应,生成三甲基 2-氯-2-环丙烯基正乙酸酯 7,通过酸处理可以定量转化为相应的酯 8。这些甲基 2-氯-2-环丙烯基乙酸酯 8 是高度反应性的迈克尔受体,能与软亲核试剂如噻吩酯、二级胺、叠氮、氰化物和二甲基铜锂发生 1,4-加成。然而,反应性受到环丙烷环上取代基的影响,无取代基的化合物 8j 与噻吩酯的反应速率比四甲基衍生物 8a 快 86 倍,而后者的反应性又是甲基 3,3-二甲基丙烯酸酯 16 的 2.5 倍。化合物 8j 是在 [2+2] 和 [2+4] 环加成中均具有相当反应性的环加成体。