Complete and Remarkable Reversal of Chemoselectivity in [4 + 2] Cycloadditions Involving Electron-Poor Indoles as Dienophiles. Diels−Alder versus Hetero-Diels−Alder Processes
作者:Antony Chrétien、Isabelle Chataigner、Nathalie L'Hélia、Serge R. Piettre
DOI:10.1021/jo034719b
日期:2003.10.1
and 12 are now isolated in high yields, the result of two consecutive [4 + 2] processes on, first, the indole 2,3 C=C bond and, second, the 3-carbonyl unit. The possibility of using two different dienes in a tandem, sequential process is demonstrated by the preparation of tetracycle 13. Interactions between the carbonyl dienophile and Danishefsky diene yield exclusively yet another type of product, namely
吲哚-3-羧醛1a或吲哚-3-乙二醛酸酯1b与2,3-二甲基丁二烯在热活化下的反应仅导致由吲哚2,3-碳-碳双键的参与而产生的Diels-Alder环加合物。氯化锌和高压(16 kbar)的同时使用会引起初级环加合物进一步反应,现在双环加合物11和12的收率很高,这是两个连续[4 + 2]过程的结果,首先是吲哚2,3 C = C键,其次是3-羰基单元。四环化合物13的制备证明了在串联的顺序过程中使用两种不同的二烯的可能性。羰基双亲烯与Danishefsky二烯之间的相互作用仅产生另一种类型的产物,即由顺序的[4 + 2]杂环加成,甲硅烷基烯醇醚的水解以及甲醇的损失产生的γ-二氢吡喃酮。Mukaiyama型加合物16的分离表明,至少在氯化锌催化下,可能涉及逐步机理。N,N-二取代的吲哚-3-乙二酰胺经过预期的,通常的Diels-Alder工艺,以2,3 C = C键作为亲二烯体,无论采用哪种