Exploring the Border between Concerted and Two-Step Pathways of 1,3-Dipolar Cycloadditions of Organic Azides to Cyclic Ketene N,X-Acetals. - Synthesis and15N-NMR Spectra of Zwitterions and Spirocyclic Cycloadducts
作者:Helmut Quast、Manfred Ach、Jürgen Balthasar、Thomas Hergenröther、Dieter Regnat、Jens Lehmann、Klaus Banert
DOI:10.1002/hlca.200590126
日期:2005.6
Cyclic ketene N,X-acetals 1 are electron-rich dipolarophiles that undergo 1,3-dipolar cycloaddition reactions with organic azides 2 ranging from alkyl to strongly electron-deficient azides, e.g., picryl azide (2L; R1=2,4,6-(NO2)3C6H2) and sulfonyl azides 2M–O (R1=XSO2; cf. Scheme 1). Reactions of the latter with the most-nucleophilic ketene N,N-acetals 1A provided the first examples for two-step H
环烯酮N,X-乙缩醛1是富含电子的双亲亲子,与有机叠氮化物2发生1,3-偶极环加成反应,有机叠氮化物2的烷基化程度强至电子缺乏性叠氮化物,例如吡啶甲基叠氮化物(2L ; R 1 = 2,4, 6-(NO 2)3 C 6 H 2)和磺酰叠氮化物2M – O(R 1 = XSO 2;参见方案1)。后者与亲核性最强的乙烯酮N,N-缩醛1A的反应提供了一种用于两步骤HOMO(亲偶极)-LUMO(1,3-偶极子)的第一实施例-controlled 1,3-偶极环加成经由中间两性离子3。为了为探索这种类型的协同步骤和两步式1,3-偶极环加成之间的边界奠定基础,我们首先描述了2到1的协同环加成的范围和局限性,并描述了两性离子3。烷基叠氮化物2A – C仅添加到由1 H-四唑(参见1A)和1 H-咪唑(参见1B,C)衍生的乙烯酮N,N-缩醛中),而几乎所有的芳基叠氮化物都使用烯酮N,X-乙缩醛(X = NR,O,S)生成环加合物4,但1