Facile Access to 3,5-Dihalogenated Pyrazoles by Sydnone Cycloaddition and their Versatile Functionalization by Pd-Catalyzed Cross-Coupling Processes
作者:Thierry Delaunay、Mazen Es-Sayed、Jean-Pierre Vors、Nuno Monteiro、Geneviève Balme
DOI:10.1002/ejoc.201100119
日期:2011.7
The 1,3-dipolar cycloaddition of diversely N-substituted 4-iodosydnones with 3-halopropiolates produces easily separable mixtures of dihalogenated pyrazolylcarboxylic esters at a preparative scale level, with the 3,5-dihalogenopyrazole regioisomers always predominating. Further decarboxylation of the major isomers provided the corresponding 3,5-dihalogenopyrazoles with a free C-4 position. These were
不同 N-取代的 4-碘代炔酮与 3-卤代丙炔酸酯的 1,3-偶极环加成在制备规模水平上产生易于分离的二卤化吡唑基羧酸酯混合物,其中 3,5-二卤代吡唑区域异构体始终占主导地位。主要异构体的进一步脱羧提供相应的具有游离 C-4 位的 3,5-二卤代吡唑。这些被发现是通过位点选择性 Pd 催化交叉偶联反应制备不对称 1,3,5-三取代吡唑衍生物的有价值的支架。值得注意的是,在吡唑核的 C-5 和 C-3 位置灵活且选择性地引入不同的(杂)芳基、乙烯基或烷基取代基可以通过与各种硼化合物的顺序 Suzuki 型反应来实现。此外,