1324009-01-9Relevant academic research and scientific papers
Facile access to 3,5-dihalogenated pyrazoles by sydnone cycloaddition and their versatile functionalization by Pd-catalyzed cross-coupling processes
Delaunay, Thierry,Es-Sayed, Mazen,Vors, Jean-Pierre,Monteiro, Nuno,Balme, Genevieve
, p. 3837 - 3848 (2011/09/12)
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 found to be valuable scaffolds for the elaboration of unsymmetrically 1,3,5-trisubstituted pyrazole derivatives by site-selective Pd-catalyzed cross-coupling reactions. Notably, the flexible and site-selective introduction of different (hetero)aryl, vinyl, or alkyl substituents at the C-5 and C-3 positions of the pyrazole core could be achieved through sequential Suzuki-type reactions with various boron compounds. Copyright
