Department of Medicinal Natural Products, West China School of Pharmacy, Sichuan University, Chengdu, 610041, P. R. China.
Chemistry. 2011 Oct 4;17(41):11553-8. doi: 10.1002/chem.201101630. Epub 2011 Sep 2.
Intermolecular cycloadditions of conjugated dienes and nitrene precursors usually produce aziridines. A generally useful method was lacking to directly provide the [4+1] cycloadducts, 3-pyrrolines. We have realized this transformation by using an uniquely active catalyst, copper(II) 1,1,1,5,5,5-hexafluoroacetylacetonate ([Cu(hfacac)(2)]). The method is applicable to a wide array of dienes with good yields. When 1,4-disubstituted dienes are used as substrates, good-to-excellent cis or trans selectivity can be obtained. Interestingly, the cis or trans preference depends on the nature of the substituents, rather than diene geometry. Mechanistic studies reveal that the [4+1] cycloaddition proceeds through diene aziridination and subsequent ring expansion. Among common copper catalysts, only [Cu(hfacac)(2)] can efficiently catalyze both steps, which explains the unique efficiency of the catalyst.
共轭二烯与氮烯前体的分子间环加成通常生成氮丙啶。目前缺乏一种通用的方法来直接提供[4+1]环加成产物 3-吡咯啉。我们使用一种独特活性的催化剂，即铜（II）1,1,1,5,5,5-六氟乙酰丙酮酸盐([Cu(hfacac)(2)])，实现了这一转化。该方法适用于具有良好收率的各种二烯底物。当使用 1,4-二取代二烯作为底物时，可以获得良好至优异的顺式或反式选择性。有趣的是，顺式或反式选择性取决于取代基的性质，而不是二烯的几何形状。机理研究表明，[4+1]环加成通过二烯氮丙啶化和随后的环扩张进行。在常见的铜催化剂中，只有[Cu(hfacac)(2)]能够有效地催化这两个步骤，这解释了催化剂的独特效率。
